GB2338580A

GB2338580A - Electrode substrate for a display system

Info

Publication number: GB2338580A
Application number: GB9913913A
Authority: GB
Inventors: Nobuyuki Itoh; Hisashi Akiyama; Masahiko Tomikawa; Tetsuya Igarashi
Original assignee: UK Secretary of State for Defence; Sharp Corp
Current assignee: UK Secretary of State for Defence; Sharp Corp
Priority date: 1998-06-15
Filing date: 1999-06-15
Publication date: 1999-12-22
Anticipated expiration: 2019-06-15
Also published as: GB9913913D0; GB2338580B; JP2000075807A; JP4511652B2

Abstract

An electrode substrate is fabricated by forming parallel electrodes containing two portions of different etching characteristics which are aligned and in contact. If, during manufacture, one portion is mis-formed, resulting in a break, the other portion allows the current to proceed along the electrode as a whole. The short-circuiting (42) of one end every other electrode (22-2, 22-4, 22-6, 22-8) and also short-circuiting (41) one end of every other electrode (22-1, 22-3, 22-5, 22-7), followed by the application of a voltage between both short-circuits results in any leakage portion (S) between electrodes being burnt off.

Description

2338580 ELECTRODE SUBSTRATE FOR USE IN A DISPLAY DEVICE AND FABRICATION

METHOD THEREOF The present invention relates to an electrode substrate for use in a display device such as a liquid crystal display device, and more particularly to an electrode substrate having an electrode structure for applying a voltage to a display medium. The present invention also relates to a method for fabricating such an electrode substrate.

A simple matrix method as one of matrix methods are used in many display devices such as liquid crystal and EL (electro luminescence) display devices. According to the simple matrix method, for example, a plurality of transparent electrodes 101 in the form of stripes of equal length as shown in Fig. 14 are arranged on a transparent substrate so that the ends of the transparent electrodes 101 are aligned with each other. Two pieces of substrates are disposed to face each other so that the transparent electrodes 101 on the two substrates cross each other at right angles, thereby providing a matrix structure. In the simple matrix method, an electric field is applied to any dots in the matrix by selectively applying signals to the i transparent electrodes 101 on the substrates.

By the way, as the transparent electrode 101, a transparent electrode material typified by ITO (indium tin bxide) is widely used. The formation of an electrode with the use of such an electrode material is usually carried out as follows. First, the electrode material is deposited in a predetermined film thickness on a substrate such as glass by evaporation, and then a photoresist is formed to cover the electrode material. In a state in which necessary portions of the electrode material are protected by the photoresist patterned in the form of stripes, etching is performed to remove unnecessary portions, thereby patterning a layer of the electrode material in a predetermined design.

When forming the electrodes in the above-mentioned manner, the following problems arise quite often. For instance, if a portion which is not etched or a portion which is not sufficiently etched exists in a section to be etched between adjacent electrodes, a short-circuit section is produced at such a portion between the electrodes and a leakage current flows through the short-circuit section. If an electrode section of the electrode material layer intended to be protected by the photoresist is etched, the formed electrode is broken off. Such leakage and break are critical 3 problems as they prevent selective application of signals to the electrodes. It is considered that the causes of leakage and break are an alien substance which is mixed in depositing ITO, and faults such as a dirt on a photomask used in exposing the photoresist. However, in the aspects of the fabrication techniques and cost, it is extremely difficult to eliminate these causes completely.

Hence, according to a prior art, the presence of leakage and the position of leakage are detected by inspecting whether there is continuity between each pair of adjacent electrodes with probes, and then unnecessary ITO remaining at the detected leakage position is burnt off with a laser, etc.

Since these processes are completely mechanized, it is not technically difficult to execute the processes. However, a precise positioning mechanism is required to bring the probes into contact with the electrodes accurately and position the laser on the detected portion. Thus, an expensive device and a long processing time are required for the inspection and repair, resulting in an increase in the fabrication cost.

Fig. 15 shows a state in which parts of the transparent electrodes 101 are cut off because of a - 4 failure to obtain a normal electrode structure shown in Fig. 14. This state results from contacting the transparent electrode section, which is intended to be protected, with an etchant due to a resist defect in the process of patterning electrodes to produce a conventional electrode structure. When inspecting the electrode substrate having such an electrode structure with the probes, continuity between separate probes 102 and 103 in contact with a single transparent electrode 101 is inspected for every transparent electrode 101 so as to find whether the transparent electrode 101 is broken or not, thereby determining whether the electrode substrate is a satisfactory product or defective product.

In the conventional electrode structure, as shown in Fig. 16, a leakage is inspected by continuity between probes 103 and 104 in contact with two adjacent transparent electrodes 101. This inspection is the same as the above-mentioned inspection of break, and determines whether the electrode substrate is a satisfactory product or defective product by,inspecting every line to f ind whether there is a leakage or not. In actual, the above-mentioned inspections of break and leakage are executed concurrently by the probes 102 to 104. If the presence of leakage is confirmed as a - 5 result of the inspection, a leakage position on the electrode substrate is specified, and the leakage is eliminated by repairing the leakage position with a laser'.

There is no problem if the electrode substrate is a product having no break. on the other hand, if the electrode substrate is a defective product including a break, the substrate must be abandoned as a defective product because the break is not repaired like the leakage. Not only the break inspection with the probes, but also the leakage inspection can be performed relatively easily when the number of lines (the number of electrodes) is small and the line pitch is large. However, when the number of lines are.increased and the line pitch becomes smaller, it is difficult to perform the inspections. Thus, there is a possibility that the results of inspection contain errors. If break and leakage are detected at the final stage of inspecting a displayed image after the electrode substrate containing the break and leakage is incorporated into a display device due to faulty inspections of break and leakage, the display device can not be shipped as a product. Thus, when the inspections of break and leakage are not carried out accurately, the yield of the display device is lowered and the fabrication cost is increased.

In order to solve such problems, Japanese laidopen patent application No. (Tokukaisho) 62-143025 discloses a prior art of easily inspecting a leakage between the electrodes by drawing one end of every other electrode of electrodes arranged in stripe in a direction and the other ends of the remaining electrodes in the opposite direction, short- circuiting the ends of the electrodes drawn in either direction respectively, and applying a voltage across the ends. In this method, when it is confirmed has a leakage between electrodes, the is repaired with a laser in the same conventional repairing method. However that a substrate leakage position manner as in the with the electrode structure of this prior art, even if the presence or absence of leakage between electrodes is easily inspected, it is not easy to specify the position.

In the above-mentioned inspection method with the probes, since every single electrode is inspected, it is possible to accurately determine the coordinates of the leakage position from the relationship between the resistance (sheet resistance) per unit area of the electrode, the dimensions of electrode (width, length, etc.) and the value of the detected current. However, i - 7 with the above-mentioned prior art of short-circuiting the ends of the electrodes in advance, although the presence or absence of a leakage between electrodes is found more quickly than the inspection method using the probes, it is difficult to sufficiently repair the leakage like the inspection method using the probes because it is difficult to specify the leakage position. Thus, it can be said that the abovementioned prior art is insufficient for practical use.

In addition, with the inspection method using the probes, although it is possible to inspect a break, it is impossible to repair the broken section. Therefore, a substrate having a break must be abandoned as a defective product, resulting in a further increase in the fabrication cost. Furthermore, needless to say, the above-mentioned prior art does not provide an effective measure to solve the break. Such a problem becomes more serious as the size and definition of the display device are increased.

By the way, as the transparent electrode 101, transparent electrode materials typified by an ITO (indium tin oxide) electrode have been widely used. Such a transparent electrode material has a high electric resistance as a conductor. It is usually used in a film thickness of around 1000 A, and the sheet 8 - resistance is 200 O/D for the film thickness of around 1000 Even when a thick film of 5000 A is used, the sheet resistance is around 5 Q/M If the f ilm is thicker than 5000 A, the transparent electrode material can not be actually used because it colors or is difficult to be formed into a film or patterned.

With the transparent electrode with such a high electric resistance, there are many problems in order to meet recent or future demands for a large-scale display device, a large-display capacity and a highspeed video signal transmission. The most important factors are attenuation of signal level and distortion due to the electric resistance. Since the level of a signal input to an end of the electrode is attenuated by the electrode resistance, it is difficult to ensure a signal waveform sufficient for driving at the other end of the electrode of the display device. As a result, the display characteristics on the display screen become uneven.

As a method for achieving any electrode resistance of not more than 10/E], there is a method of reducing the resistance of a display electrode by providing a low-resistant conductor electrode made of a metal in parallel and contact with transparent electrode 101.

As means for solving such problems, (1) Japanese z 9 laid-open patent application No. (Tokukaihei) 1-280724 and (2) Japanese laid-open patent application No.

2-63019 disclose a method of widening the aperture of the transparent electrode by reducing the contact section between the metal electrode and transparent electrode.

According to prior art (1), as illustrated in Fig. 20(a), a metal electrode 106 is formed over a transparent substrate 105 and one side of the upper surface of each of transparent electrodes 101 formed in stripes on the transparent substrate 105. Moreover, with prior art (1), as shown in Fig. 20 (a), an insulating film 107 is formed so as to cover portions between transparent electrodes 101 on the transparent substrate 105 and the upper surfaces of the transparent electrodes 101, and metal electrodes 106 are formed on the insulating film 107 so that they are in contact with the upper surfaces of the transparent electrodes 101 at one side.

On the other hand, according to prior art (2), metal electrodes 106 are formed in stripes on the transparent substrate 105, instead of the transparent electrodes 101. In this structure, the insulating film 107 is formed so as to cover portions between the metal electrodes 106 on the transparent substrate 105 and the upper surfaces of the metal electrodes 106, and transparent electrodes 101 are formed so that they are in contact with the upper surfaces of the metal electrodes 106 and cover the portions between the metal electrodes 106.

In both of the structures shown in Figs. 20(a) 20(b), an electrode surface formed on the transparent substrate 105, i.e., a substrate surface from which an electric field is applied to the liquid crystal or the light emitting layer of the EL display device, has a difference in level at a portion where the metal electrodes 106 and transparent electrodes 101 are in contact with each other. It is impossible to prevent such a difference in level from viciously affecting the alignment of liquid crystal in the liquid crystal display device. on the other hand, in the EL display device, the difference in level causes abnormal discharge. moreover, in these structures, since the insulating film 107 is used, a great number of processes including the process of forming a throughhole in the insulating film 107 for ensuring connection between the transparent electrodes 101 and metal electrodes 106 are required to achieve the respective structures. Consequently, the production yields of these devices are lowered, and thus it is difficult to reduce the production cost.

Moreover, in the structure of Fig. 20(a), the ortion of the transparent electrode 101 covered with the metal electrode 106 is small. Therefore, when this electrode substrate is incorporated into a display device, the display device can ensure a relatively large aperture ratio. However, in the structure shown in Fig. 20 (b), the portion of the transparent electrode 101 covered with the metal electrode 106 is large, and the aperture ratio is smaller compared with the structure shown in Fig. 20(a).

Objects of the present invention are to provide an electrode substrate for use in a display device, which prevents a break defect and leakage from being caused when etching display-use electrodes, and a method for fabricating an electrode substrate for use in a display device, capable of preventing a break defect from being caused during the etching and repairing a leakage portion between electrodes with a simple method. Further objects of the present invention are to provide a structure capable of improving the flatness of the electrode substrate and the aperture ratio and of reducing the number of fabrication processes, and to provide a fabrication method thereof.

1 - 12 According to the present invention, it is possible to provide an electrode substrate for use in a display -device. which includes thereon a plurality of electrodes in stripes and is characterized in that the electrode is composed of at least two electrode sections which are juxtaposed parallel and in contact with each other, the electrode sections being made of conductors of different etching characteristics, wherein, in a state in which one end of every other electrode is short-circuited and the other ends of the remaining electrodes are short-circuited, when a voltage is applied across both of the short-circuited ends, a leakage portion formed between the electrodes is cut off.

In the above-mentioned structure, the conductors constituting at least two electrode sections forming the electrode show different etching characteristics. Therefore, for example, when forming one electrode section on another electrode section, even if the electrode section formed by etching is broken off due to a defect in the resist pattern, the under layer electrode section which was already formed can never be corroded at the same position by etching. Consequently, it is possible to prevent the different electrode sections from being broken off at the same - 13 position, thereby providing a structure in which the entire electrodes are connected by either of the electrode sections. Moreover, in a state in which one end of every other electrode is short-circuited and the other ends of the remaining electrodes are shortcircuited, when a voltage is applied across both ends, a leakage portion formed between adjacent electrodes is cut off. At this time, a large current f lows in the leakage portion which is usually very narrow, and therefore the leakage portion is burnt off. It is thus possible to provide an electrode structure which can hardly be broken off, and the effect of easily repairing a leakage portion without detecting the leakage portion and without using a laser, etc.

In the electrode substrate, it is more preferred that the conductors are made of materials which are not etched by the same etchant. For instance, when the electrode is composed of two electrode sections, the conductor forming one of the electrode sections is etched by an etchant, but the conductor f orming the other electrode section is not etched by the etchant. It is therefore possible to easily provide the conductors with etch selectivity. Thus, this structure can surely prevent the electrodes from being broken off.

14 Alternatively, in the electrode substrate, it is more preferred that the conductors are made of materials whose etch rates by the same etchant are at least five times different from each other. For instance, when the electrode is made of two layers of electrode sections, an etch rate (r,) of the conductor forming the under layer electrode section is much lower than an etch rate (r,) of the conductor forming the upper layer electrode section. More specifically, the etch rates are set so as to satisfy r, s r,/5. Under such a condition, when etching the conductor for forming the upper layer electrode section, even if the formed upper layer electrode section is broken off by etching through a defective portion of the resist pattern, a speed at which the under layer electrode section which was already formed is corroded by the etchant is very low. Therefore, the under layer electrode section can never be broken off at the same position as the upper layer electrode section. Consequently, an etchant is shared for both of the materials, thereby reducing the fabrication cost.

In each of the above-mentioned electrode substrates, it is more preferred that at least one of the electrode sections is formed as a transparent electrode and the other electrode section is formed as - is - a low-resistant conductor electrode. In general, since the leakage portion between electrodes formed due to a -defect in the resist pattern is very narrow, it has a higher resistance compared to the electrodes. Therefore, when the low-resistant conductor electrode and the transparent electrode are juxtaposed, the overall resistance of the electrode composed of the transparent electrode and low- resistant conductor electrode is limited to a very small value. consequently, in general, the heat generated by the Joule effect is highly concentrated in the leakage portion which is very narrow and has a high resistance. Hence, even when a relatively low voltage is applied across both ends of the electrode, a large current capable of burning off the leakage portion can flow in the transparent electrode. As a result, the leakage portion is burnt off, but the transparent electrode is not damaged. It is thus possible to more surely repair the leakage portion.

In each of the above-mentioned electrode substratesi it is more preferred that the low-resistant conductor electrode is buried in the substrate and in contact with the transparent electrode so that only part of the lowresistant conductor electrode is covered with the transparent electrode. In such a 16 structure, since the low-resistant conductor electrode is buried in the substrate, the surface of the electrode substrate can be made flatter compared with a structure in which the low-resistant conductor electrode is formed on the transparent electrode. Furthermore, since only part of the low-resistant conductor electrode is covered with the transparent electrode, the area of a pixel section formed by the transparent electrode, which is covered with the lowresistant conductor electrode having a light blocking property, is reduced. Besides, in this electrode substrate, since an insulating film which is present between the transparent electrode and metal electrode of the above-mentioned conventional structure is not required, the structure is simplified. It is thus possible to easily improve the flatness of the electrode substrate and the aperture ratio with a simple structure.

In each of the above-mentioned electrode substrates, it is more preferred that the electrode is composed of a pair of a f irst electrode and a second electrode of different widths for forming divided pixels, the first electrodes of adjacent electrodes are positioned next to each other, and the second electrodes of adjacent electrodes are positioned next to each other. In the structure where the electrode is composed of the f irst electrode and second electrode, when the ends of the electrodes are drawn alternately in the opposite directions, every other electrode can be easily short-circuited for the application of voltage (see Fig. 13). In such an electrode structure, when a driving circuit is connected to the ends of the electrodes on each side, the loads of the driving circuits are increased. As a result, the heat generated by the consumption of power in driving the electrodes varies. Whereas in the above-mentioned structure where the first electrodes of adjacent electrodes are positioned next to each other and the second electrodes of adjacent electrodes are positioned next to each other (see Fig. 12), the loads of the driving circuits are equal to each other, thereby maintaining a uniform power consumption in driving the electrodes. Thus, this structure can limit the variation in the heat generated from the electrodes, which causes a vicious effect on the display quality.

According to the present invention, it is possible to provide a method for fabricating an electrode substrate for use in a display device, the electrode substrate having thereon a plurality of electrodes in stripes, the method including: the first step of - 18 forming the plurality of electrodes by etching conductors so that at least two electrode sections constituting the electrode are juxtaposed parallel and in contact with each other by causing the conductors constituting the electrode sections to have different etching characteristics; and the second step of shortcircuiting one end of every other electrode and shortcircuiting the other ends of the remaining electrodes, and cutting off a leakage portion formed between adjacent electrodes by applying a voltage across the short-circuited ends.

with this method, in the first step, since the conductors constituting the electrode sections are caused to have different etching characteristics, for example, even if the electrode section formed by etching is broken off due to a defect in the resist pattern when forming one electrode section on another electrode section, the under layer electrode section which was already formed can never be corroded at the same position by etching. It is thus possible to prevent different electrode sections from being broken off at the same position. Hence, a structure in which the entire electrodes are connected by either of the electrode sections can be obtained.

Moreover, in the second step, in a state in which - 19 one end of every other electrode is short-circuited and the other ends of the remaining electrodes are short- -Circuited, when a voltage is applied across both ends, a leakage portion formed between the electrodes is cut off. At this time, a large current flows in the leakage portion which is usually very narrow, and therefore the leakage portion is burnt off. Thus, this method provides an electrode structure which is hardly broken off, and can easily repair the leakage portion without detecting the leakage portion and without using a laser, etc.

In the first step of the above-mentioned fabrication method, it is more preferred that materials which are not etched by the same etchant are used as the conductors. For instance, when the electrode is composed of two electrode sections, the conductor forming one of the electrode sections is etched by an etchant, but the conductor forming the other electrode section is not etched by the etchant. It is therefore possible to easily provide the conductors with etch selectivity. Thus, this method can surely prevent a break of the electrodes.

Alternatively, in the first step of the abovementioned fabrication method, it is preferred that materials whose etch rates by the same etchant are five - 20 times different from each other are used as the conductors. For instance, in the case where the -electrode is made of two layers of electrode sections, when etching the conductor for forming the upper layer electrode section, even if the upper layer electrode section formed by etching is broken off due to a defect of the resist pattern, a speed at which the under layer electrode section which was already formed is corroded by the etchant is very low. Therefore, the under layer electrode section can never be broken off at the same position as the upper Consequently, the etchant materials, thereby reducing In the f irst step of fabrication methods, it is of the electrode sections 1 i layer electrode section. is shared for both of the the fabrication cost.

each of the above-mentioned preferred that at least one is formed as a transparent electrode and the other electrode section is formed as a low-resistant conductor electrode. With this arrangement, the overall resistance of the electrode composed of the transparent electrode and low-resistant conductor electrode is limited to a very small value.

consequently, the heat generated by the Joule effect is highly concentrated in a leakage portion which is usually very narrow, formed between adjacent electrodes, and has a high resistance. Hence, even - 21 when a relatively low voltage is applied across both ends of the electrodes, a large current which is capable of burning off the leakage portion can flow in the transparent electrode. As a result, the leakage portion is burnt off, but the transparent electrode is not damaged. It is thus possible to surely prevent a break of the electrodes.

Moreover, in the above-mentioned first step, it is preferred that, after forming the low-resistant conductor electrode so that it is buried in the substrate, the transparent electrode is formed on the substrate so that it covers only part of the lowresistant conductor electrode and is in contact with the low-resistant conductor electrode. In the structure produced by such a first step, since the lowresistant conductor electrode is buried in the substrate, the surface of the electrode substrate can be made flatter compared with a structure in which the low-resistant conductor electrode is formed on the transparent electrode. Furthermore, since only part of the low-resistant conductor electrode is covered with the transparent electrode, the area of a pixel section formed by the transparent electrode, which is covered with the low-resistant conductor electrode having a light blocking property, is reduced. Additionally, in - 22 the first step, since there is no need to perform the process of forming an insulating substrate which is -1resent between the transparent electrode and metal electrode of the above-mentioned conventional substrate structure, the fabrication processes are simplified. It is thus possible to easily improve the flatness of the electrode substrate and the aperture ratio with simple processes.

In the first step of each of the above-mentioned fabrication methods, it is preferred to form the electrodes so that the electrode is composed of a pair of a first electrode and a second electrode of different widths for forming divided pixels, the first electrodes of adjacent electrodes are positioned next to each other, and the second electrodes of adjacent electrodes are positioned next to each other. With such an arrangement of the first electrode and second electrode, when the ends of the electrodes are drawn alternately in the opposite directions and a driving circuit is connected to the ends of the electrodes on each side, the loads of the driving circuits are equal to each other, thereby maintaining a uniform power consumption in driving the electrodes. Thus, these methods can limit the variation in the heat generated from the electrodes, which causes a vicious effect on 23 the display quality.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a plan view showing a structure for detecting a break and repairing a short-circuit section on an electrode substrate according to an embodiment of the present invention; Fig. 2 is a cross sectional view showing a structure of a liquid crystal display device having the above electrode substrate; Fig. 3 is a plan view showing an arrangement of transparent electrodes on the above electrode substrate; Figs. 4(a) to4(c) are cross sectional views showing other arrangements of transparent electrodes on the above electrode substrate; Figs. 5(a) to 5(c) are cross sectional views showing still other arrangements of transparent electrodes on the above electrode substrate; Fig. 6 parts of electrodes are broken Figs.

is a plan view showing a state in which transparent electrodes and auxiliary on the electrode substrate shown in Fig. 1 off; 7(a) and 7(b) are perspective views showing - 24 a mechanism for preventing a break in the electrode structure of this embodiment by presenting a process of fabricating an electrode of a two-layer structure as an example; Fig. 8 is a cross sectional view showing a structure of a reflective-type liquid crystal device having the above electrode substrate; Figs. 9(a) to -9(g) are cross sectional views showing the structures produced in the processes (Example 1 of the present invention) of fabricating the electrode substrate of Fig. 4 (a) or Fig. 5 (a); Figs. 10 (a) to 10 (e) are cross sectional views showing the structures produced in the processes (Example 2 of the present invention) of fabricating the electrode substrate of Fig. 4 (b) or Fig. 5 (b); Figs. 11 (a) to 11 (e) are cross sectional views showing the structures produced in the processes (Example 3 of the present invention) of fabricating the electrode substrate of Fig. 4 (c) or Fig. 5 (c); Fig. 12 is a plan view showing an electrode structure for divided pixels according to Example 4 of the present invention; Fig. 13 is a plan view showing an electrode structure for divided pixels as a comparative example to the electrode structure of Example 4; Fig. 14 is a plan view showing an electrode structure of a conventional electrode substrate; Fig. 15 is a plan view showing a method of inspecting a break in the electrode structure shown in Fig. 14; Fig. 16 is a plan view showing a method of inspecting a leakage in the electrode structure shown in Fig. 14; Fig. 17 is a perspective view showing a schematic structure of a display device having an electrode substrate according to an embodiment of the present invention; Figs. 18 (a) to 18 (9) are views showing part of a cross sectional structure produced in the processes of fabricating the electrode substrate of Fig. 5 (a); Fig. 19(a) is an enlarged cross sectional view of part of an electrode substrate of Example 8 of the present invention, and Fig. 19(b) is a cross sectional view of an electrode substrate obtained by a process as a substitute for the process of Fig. 18(d) for fabricating the electrode substrate of Fig. 19(a); and Figs. 20(a) and 20(b) are cross sectional views showing the structure of other conventional electrode substrates.

- 26 The following descriptions will explain an embodiment of the present invention with reference to -Pigs. 1 to 13 and 17 to 19.

As illustrated in Fig. 17, a display device according to this embodiment includes two pieces of opposing glass substrates 1 and 2 as light transmitting substrates. Note that, it is possible to use substrates made of a resin such as polymethyl methacrylate, instead of the glass substrates 1 and 2, if the substrates have light transmitting and insulating properties.

A plurality of signal electrodes 3 (electrode section) made of, for example, above-mentioned ITO are placed parallel to each other on a surface of the glass substrate 1. On the other hand, a plurality of transparent scanning electrodes 5 (electrode section) made of, for example, ITO are arranged parallel to each other on a surface of the glass substrate 2 so that the scanning electrodes 5 cross the signal electrodes 3 at right angles.

The glass substrates 1 and 2 are fastened together so that they face each other with a predetermined space (cell gap) therebetween. In the case of a liquid crystal display device, a liquid crystal layer is formed in the space formed between the glass substrates, 1 and 2 by injecting liquid crystal. In the case of an EL device, a light emitting layer is formed in the space between the glass substrates 1 and 2.

Subsequently, the following descriptions will explain in great detail an example in which the display device is a liquid crystal display device. As illustrated in Fig. 2, this liquid crystal display element includes two opposing glass substrates 1 and 2. A transparent insulating film 4 made of, for example, silicon oxide (S'02) is placed on a surface of the glass substrate 1 whereon the signal electrodes 3 are placed. on the other hand, a surface of the glass substrate 2 on which the scanning electrodes 5 are placed is covered with a transparent insulating film 6 made of, for example, S'02.

Alignment films 7 and 8 to which a uniaxial alignment treatment such as rubbing has been applied are formed on the insulating films 4 and 6, respectively. As the alignment films 7 and 8, it is possible to use films made of organic polymers such as polyimide, nylon, polyvinyl alcohol (PVA), or films formed by S'02 by oblique deposition.

The glass substrate 1 having the signal electrodes 3, insulating film 4 and alignment film 7 formed in the above-mentioned manner and the glass substrate 2 having 1 - 28 the scanning electrodes 5, insulating film 6 and alignment film 8 are disposed to face each other with a -predetermined space (cell gap) therebetween, and fastened together with a sealing agent 9. The space formed between the glass substrates 1 and 2 is filled with a liquid crystal, thereby forming a liquid crystal layer 10. The liquid crystal is injected from an inlet (not shown) provided in the sealing agent 9, and sealed in the space by sealing the inlet with a sealing agent 11.

Two polarisers 12 and 13 are disposed on the outer surf aces of the glass substrates 1 and 2 so that their polarisation axes cross each other at right angles. Moreover, when the display area is large, spacers 14 for maintaining a uniform cell gap are provided between the alignment films 7 and 8.

Pixel regions (not shown) are formed by square regions where the signal electrodes 3 and scanning electrodes 5 face each other. In a pixel region, when a voltage is applied to the signal electrode 3 and scanning electrode 5, an alignment state of liquid crystal molecules is switched by an electric field produced between the signal electrode 3 and scanning electrode 5, and the display state is switched between bright and dark (and half tone), thereby providing a

29 - display.

Auxiliary electrodes.ach other on the glass auxiliary electrode 15 is each scanning electrode 3. arranged parallel to each 2 so that each auxiliary with a side of each are arranged parallel to substrate 1 so that each in contact with a side of Auxiliary electrodes 16 are other on the glass substrate electrode 16 is in contact scanning electrode 5. The auxiliary electrodes 15 and 16 are made of metal materials, such as Cu and Ta, whose resistances are lower than the resistances of the signal electrodes 3 and scanning electrodes 5, so as to lower the wiring resistances of the signal electrodes 3 and scanning electrodes 5. The auxiliary electrodes 15 and 16 are made of materials having etch selectivity with respect to the signal electrodes 3 and scanning electrodes 5.

For instance, the electrode substrate having the signal electrodes 3 and auxiliary electrodes 15, and the electrode substrate having the scanning electrodes 5 and auxiliary electrodes 16 are fabricated as follows. The following explanation discusses only the steps of forming the signal electrodes 3 and auxiliary electrodes 15 on the glass substrate 1, but the formation of the scanning electrodes 5 and auxiliary electrodes 16 on the glass substrate 2 can also follow the same steps.

First, ITO is deposited in a thickness of 2000 -on the glass substrate 1 to form a transparent electrode film, and a resist pattern corresponding to an electrode pattern is formed on the transparent electrode film. Next, the transparent electrode film is etched to form the signal electrodes 3. Furthermore, for example, Cu is deposited in a thickness of 2000 A to form a metal layer. Thereafter, the resist pattern is removed to lift off the metal layer on the resist pattern. As a result, parts of the metal layer remaining between the signal electrodes 3 form a metal electrode pattern.

Since the metal electrode pattern is in contact with both of adjacent signal electrodes 3, processing is performed so that the metal electrode pattern is in contact with only one of the adjacent electrodes 3. At this time, a resist pattern is formed on the signal electrodes 3 and metal electrode pattern except a part of the metal electrode pattern which is in contact with the other signal electrode 3, electrode pattern is etched. As a result, auxiliary electrodes 15 are formed.

Referring now to Fig. 3, the following description will explain the structures of the signal electrodes 3

1 and the metal the 31 and scanning electrodes 5. Here, the same transparent electrodes 22 (electrode section) are used as the -signal electrode 3 and scanning electrode 5, and the same metal electrodes 23 (electrode section and lowresistant conductor electrode) are used as the auxiliary electrodes 15 and 16.

As illustrated in Fig. 3, the transparent electrodes 22 have a uniform length, and are arranged parallel to each other so that every other transparent electrode is aligned at an end. More specifically, one end of each of odd-numbered transparent electrodes 22-1 to 22-N (where N = 7) protrudes from one end of each of even-numbered transparent electrodes 222 to 22-M (where M = 8), and the other ends of the even-numbered transparent electrodes 22-2 to 22-M protrude from the other ends of the odd-numbered transparent electrodes 22-1 to 22-N.

As the transparent electrodes 22 and metal electrodes 23, for example, it is possible to employ the structures shown in Figs. 4(a) to 4(c) other than the above-mentioned structures. Incidentally, for the sake of convenience, the same substrates 21 are used as the glass substrates 1 and 2.

First, in the structure shown in Fig. 4(a), the metal electrodes 23 are buried in the substrate 21, and 32 - the transparent electrodes 22 are formed to metal electrodes 23. The metal electrode 6ontact with the transparent electrode 22 at appearing at the surface of the substrate 21.

the structure shown in Fig. 4(b), the metal 23 is formed on the transparent electrode 22.

Meanwhile, in the structure shown in Fig. 4(c), both of the transparent electrode 22 and metal electrode 23 are formed on the substrate 21 so that a part of the transparent electrode 22 covers the upper surface of the metal electrode 23.

In the structures shown in Figs. 4(b) and 4(c), in order to lower the electrode resistance, the transparent electrode 22 and metal electrode 23 are laminated as mentioned above. In these structures, unlike the structures of prior arts (see Figs. 20(a) and 20(b)), the transparent electrode 22 and metal electrode 23 are not in contact with each other through the through-hole provided in the insulating film. it is therefore possible to eliminate the process for ensuring the contact. However, in these structures, since a protruding portion is formed on the substrate because the metal electrode 23 is provided, sufficient flatness of the substrate surface can not be obtained.

Whereas in the structure shown in Fig. 4(a), as cover the 23 is in a surface Next, in electrode 33 also disclosed in Japanese laid-open patent application No. (Tokukaihei) 9-127494, since the metal electrodes -23 do not appear at the transparent electrodes 22, it is possible to improve the flatness of the substrate surface. However, in this structure, since the transparent electrode 22 is formed to cover the metal electrode 23, the aperture ratio of pixel formed by the transparent electrode 22 is lowered by the metal electrode 23 having no light transmitting property. Thus, it is impossible to prevent the display brightness and contrast from being lowered. The same can be said for the structures shown in Figs. 4 (b) and 4(c).

On the other hand, in order to increase the aperture ratio, it is possible to employ the structures shown in Figs. 5 (a) to 5 (c) In the structures of Figs. 5(a) and 5(c), the position of the metal electrode 23 is shifted from that of the structures shown in Figs. 4(a) and 4(c) so that the metal electrode 23 appears through the transparent electrode 22. The structure of Fig. 5 (b) is similar to the structure shown in Fig. 4 (b), but a part of the metal electrode 23 is formed on the substrate 21.

In particular, in the structure shown in Fig. 5(a), the metal electrode 23 is buried in the substrate - 34 21, and the surface of the substrate 21 is flat like the structure in which the metal electrode 23 is not -provided. Moreover, the transparent electrode 22 is formed on the substrate 21 so that its bottom face is in contact with part of the metal electrode 23. Therefore, the electrode resistance is lowered compared with a structure including no metal electrode 23, and the aperture ratio is higher compared with the structure shown in Fig. 4(a) and the structures of prior arts (see Figs. 20(a) and 20(b)).

As described in the prior art section (see Fig. 15), in the structure where only the transparent electrodes 101 are provided without the metal electrodes 23, there is a possibility that a part of the transparent electrode 101 is completely broken off during etching performed in the process of forming the transparent electrode 101. Whereas in the structure where the above-mentioned transparent electrode 22 and the metal electrode 23 made of conductors having etch selectivity are formed as shown in Fig. 6, even when either of the transparent electrode 22 and metal electrode 23 is broken off due to a resist defect, etc. during etching, both of the transparent electrode 22 and metal electrode 23 are rarely broken off. It is thus possible to reduce the break defects to a great degree.

Here, the theory of preventing break defects with -the use of two kinds of conductors will be explained. A first conductor 31 and a second conductor 32 shown in Fig. 7(b) are made of materials having so-called etch selectivity. The first conductor 31 is not etched by an etchant for etching the second conductor 32. Moreover, as shown in Fig. 7 (a), in the case where a broken portion 31a is formed during the etching of the first conductor 31, if the second conductor 32 is formed to cover the broken portion 31a as shown in Fig. 7(b), even when a broken portion 32a is formed in the second conductor 32, the first conductor 31 can never be broken off at the broken portion 32a because the first conductor 31 and second conductor 32 have different etching properties.

Thus, even when both of the first conductor 31 and second conductor 32 are broken off, continuity through the entire electrodes can be ensured by laminating the first conductor 31 and second conductor 32 made of materials having etch selectivity. The first conductor 31 and second conductor 32 are made of substances having etch selectivity. However, even when their etching times differ from each other to a great degree with respect to the same etchant, they are not broken 36 off at the same portion, thereby preventing break defects as described below. Therefore, in such a case, -it is not necessarily that the first conductor 31 and second conductor 32 have etch selectivity.

It is considered that it is sufficient to etch the conductor to a depth equivalent to the thickness of the conductor. However, in actual, the following problem arises. Specifically, in the case where the conductor is etched to a depth equivalent to its thickness (just etching), when forming a large number of transparent electrodes at extremely small line intervals (gm order) like the electrode structures described in the later described examples, it is extremely difficult to perform etching over the entire substrate of a large size without forming a leakage portion. Therefore, so-called over etching in which etching is performed 200 to 300% more than just etching has been widely carried out. Namely, it is common to perform etching over a time two to three times more than a rated etching (just etching).

Hence, in the case where the resist pattern has a defect, after the second conductor 32 is etched by an amount equivalent to the thickness thereof, the first conductor 31 is exposed to the etchant at the defective portion as shown in Fig. 7(b). Thus, when etching the 1 - 37 first conductor 31 and second conductor 32 forming the upper and lower layers with the same etchant, the etch rate of the conductor 31 and the etch rate of the conductor 32 need to be greatly different from each other.

More specifically, when the etch rate of the second conductor 32 as the upper layer needs to be around two to three times faster than the etch rate of the first conductor 31 as the lower layer. It is more preferred that the etch rates of the first conductor 31 and second conductor 32 are five or more times different from each other. Namely, the etch rate (r.,) of the first conductor 31 is set to satisfy r, s r2/5 where r2 is the etch rate of the second conductor 32. with such a difference in the etch rates, even when the first conductor 31 is expo sed to the etchant due to overetching in etching the second conductor 32, the first conductor 31 is not broken off because the etch rate of the first conductor is low.

The following descriptions will explain the inspection of leakage for the above-mentioned electrode structure.

In this embodiment, as illustrated in Fig. 1, one ends of the oddnumbered transparent electrodes 22-1 to 22-7 are short-circuited by a conductive paste 41, while one ends of the even-numbered transparent electrodes 22-2 to 22-8 are short-circuited by a 6onductive paste 42, and a DC voltage is applied across the conductive pastes 41 and 42. Hence, by inspecting continuity between the conductive pastes 41 and 42, the presence or absence of leakage can be easily found. Moreover, in such an inspection method, even when a short-circuit section S is present, if a voltage is applied across both ends of the short-circuit section S which is usually very narrow, a large current flows and the short-circuit section S is burnt off. It is therefore not necessary to detect the position of leakage, and the leakage can be repaired simultaneously with the leakage inspection.

Like the above-mentioned prior art (Japanese laidopen patent application No. (Tokukaisho) 62-143025), when the inspection of leakage between the electrodes is performed by short-circuiting the ends of the electrodes drawn alternately in the opposite directions at each side and applying a voltage across the shortcircuit ends, the overall resistance of the electrodes becomes higher because the electrodes do not include metal electrodes. Consequently, even when a practical voltage is applied, the leakage position can not be burnt off by a current because a large current does not flow through the leakage position. On the other hand, if a high voltage is applied across the short-circuited &nds, the leakage position between the electrodes is burnt off, but the electrodes used for display are also damaged.

In general, since the short-circuit section S formed between the electrodes due to a defect of resist is very narrow as described above, the resistance is higher compared to the transparent electrode 22 used for display. Therefore, heat generated by the Joule effect is concentrated in the short-circuit portion S. In this embodiment, since the metal electrode 23 is arranged beside the transparent electrode 22, the overall resistance of the electrode including the transparent electrode 22 and metal electrode 23 is limited to an extremely small value. As a result, the concentration of heat generated by the Joule effect in the short-circuit section S is enhanced. It is thus possible to cause such a large current that burns off the short-circuit section S to flow through the transparent electrode by simply setting the DC voltage practical value rather than a high value. the short-circuit section S is burnt off at z Consequently, but the transparent electrode required for display is not damaged 1 22 that is essentiall 1 In general, the resistance of ITO is around 15 Q/C] (sheet resistance) for a thickness of 2000 A, and is extremely large compared with Ta (0.1 0/E1) and Cu (0.05 Q/Cl).- The above-mentioned practical voltage is a voltage within a range (a range between around 30 V) in which the display-use transparent electrode 22 is not damaged. However, in an actual display device, a voltage exceeding this range is sometimes applied to the transparent electrode 22. At this time, since the voltage is applied across the signal electrode 3 and scanning electrode 5 whose loads are increased by the capacitance of the liquid crystal and the wiring resistance as the combined resistance of the transparent electrodes 22 (signal electrode 3 and scanning electrode 5) and metal electrode 23, a large current that damages the transparent electrodes 22 does not flow through the transparent electrodes 22.

In the above-mentioned inspection method, a DC voltage is applied. However, it is also possible to apply an AC voltage.

Moreover, in this embodiment, conductive sheets, etc. can be used instead of the conductive pastes 41 and 42. Although not shown in any drawing, it is also practical to form an electrode pattern for short - 41 circuiting the ends of the odd-numbered transparent electrodes 22-1 to 22- 7 and an electrode pattern for ihort-circuiting the ends of the even- numbered transparent electrodes 22-2 to 22-8 in advance, and separate these electrode pattern portions after the inspection and repair of leakage.

Furthermore, a pair of transparent electrode 22 and metal electrode 23 can have a structure in which all of their ends are aligned (see Fig. 14), instead of a structure in which an end of every other pair of transparent electrode 22 and metal electrode 23 protrudes as shown in Fig. 1. In this structure, although the linear conductive pastes 41 and 42 can not be used, it is possible to use a conductive paste of a shape that short-circuits every other pair of transparent electrode 22 and metal electrode 23.

The electrode structure and leakage inspection method according to this embodiment are all targeted on structures using transparent electrodes, but also applicable to a structure which does not require the transparent electrodes on one of the substrates like a reflective-type display device. Namely, when the electrodes are formed by laminating a plurality of metals having etch selectivity or metals which are considerably different from each other in the etching time, it is possible to prevent break defects. Besides, in the reflective- type display device, the rftetal electrode which also functions as a reflector is formed on one of the substrates. Since this metal electrode can be used as the display-use electrode, the electrode resistance becomes much lower compared with a structure using the transparent electrode. It is thus possible to easily repair the leakage position by a current. Unlike the transparent electrode which transmits light, a reflective metal electrode does not suffer from a problem that the aperture ratio is lowered by the lamination of the metal electrode. Therefore, in a reflective-type liquid crystal display device, electrodes 51, 52 (reflective metal electrodes) to be laminated can have a uniform width as shown in Fig. 8.

Next, the following descriptions will explain in great detail the embodiment of the present invention by presenting examples.

[Example 11

An electrode substrate of this example has the structure shown in Fig. 4(a). In this structure, transparent electrodes 22 are made of ITO, and metal electrodes 23 are made of Ta. ITO is deposited to form a film with a thickness of 2000 A and a width of 100 - 43 gm, while Ta is deposited to form a film with a thickness of 2000 A and a width of 10 gm. Each of the -transparent electrodes 22 and metal electrodes 23 is formed to have a length of 300 mm. Every other electrode protrudes for inspection of leakage, and the length of the protruding portion is 30 mm. Therefore, the length of a display-use portion of the transparent electrode 22 is 270 mm. Moreover, the interval of electrodes, each of which is composed of a pair of transparent electrode 22 and metal electrode 23, is 10 gm.

The processes of fabricating an electrode substrate having such a structure will be explained below.

First, as illustrated in Fig. 9(a), a resist pattern 24 corresponding to the reverse pattern of the metal electrodes 23 is formed on a substrate 21 made of glass or a resin. Then, as shown in Fig. 9 (b), the substrate 21 is etched by an amount of 2000 A so as to portions 21a in the substrate 21. When 21 made of glass is used, the substrate is etched by wet etching using a hydrofluoric acid solution. On the other hand, when the substrate 21 made of a resin is used, the substrate 21 is etched by dry etching using oxygen plasma.

form recessed the substrate 44 Next, as shown in Fig. 9 (c), a metal layer 25 made of Ta with a thickness of 2000 A is formed on the substrate 21 by a method such as sputtering, EB vapor deposition, or plating. Thereafter, the metal layer 25 on the resist pattern 24 is lif ted of f by removing the resist pattern 24 by immersing the substrate 21 in a solution of, for example, acetone, dimethyl sulfoxide, sodium hydroxide As a result, asshown in Fig.

electrodes 23 are formed in the or 9(d), the metal recessed portions 21a Furthermore, as illustrated in Fig. 9(e), a transparent electrode film 26 made of ITO with a thickness of 2000 A is formed by sputtering or EB vapor deposition. Thereafter, as shown in Fig. 9(f), a resist pattern 27 is formed on the transparent electrode film 26 by performing exposure and development after positioning the resist pattern 27 to completely cover the metal layer 25. Then, by etching the transparent electrode film 26 with a solution of hydrogen bromide (HBr), iron(III) chloride (FeC13), etc., the transparent electrodes 22 are formed as shown in Fig. 9(g).

The hydrogen bromide solution is an optimum etchant f or ITO. Besides, Ta is not corroded by most of acids including the hydrogen bromide.

Here, the ends of the transparent electrodes 22 that protruded alternately in the opposite directions -Were short-circuited by conductive pastes 41, 42 as shown- in Fig. 1. At this time, continuity between the electrodes was confirmed, and thus it was found that a leakage occurred between the electrodes. Hence, after applying a voltage of 10 V and 1 Hz across the shortcircuited terminals for five seconds, the abovementioned polyvinyl alcohol (PVA) was applied to the electrode substrate to cover the transparent electrodes 22, and rubbing was performed. Next, two electrode substrates were fastened together so that the respective transparent electrodes 22 cross each other to form a matrix pattern, and a nematic liquid crystal E7 (available from Merck) was introduced between the electrode substrates so as to fabricate a TN liquid crystal display element. Display tests were carried out over the entire screen of the liquid crystal display element. As a result, it was confirmed that there was no break and leakage.

Since Ta is not corroded by most of acids, it is difficult to pattern Ta by etching. It is therefore preferred to obtain the structure shown in Fig. 4(a) by using the lift-off technique like this example. moreover, it is also possible to obtain the structure - 4 shown in Fig. 5 (a) having a high aperture ratio with the use of the stability of Ta in etching. The -processes of fabricating this structure will be explained in Example 5 given later.

[Example 21

An electrode substrate of this example has the structure shown in Fig. 4 (b). In this structure, transparent electrodes 22 are made of ITO, and metal electrodes 23 are made of Cu. ITO is deposited to form a film with a thickness of 2000 A and a width of 100 gm, while Cu is deposited to form a film with a thickness of 2000 A and a width of 10 gm. Each of the transparent electrodes 22 and metal electrodes 23 is formed to have alength 300 mm. The length of each protruding portion that protrudes every other electrode for inspection of leakage is 30 mm. Therefore, the length of a display-use portion of the transparent electrode 22 is 270 mm. Moreover, the interval of electrodes, each of which is composed of a pair of transparent electrode 22 and metal electrode 23, is 10 gm.

6 First, as illustrated in Fig. 10(a), ITO is - 47 deposited in a thickness of 2000 A on a substrate 21 so as to form a transparent electrode film 26, and a -resist pattern 24 corresponding to the electrode pattern is formed thereon. Then, as shown in Fig. 10 (b), the transparent electrode film 26 is etched with a hydrogen bromide solution so as transnarent electrodes 22 to form the Next, as shown in Fig. 10 (c), Cu is deposited in a thickness of 2000 A on the substrate 21 so as to form a metal layer 25. Thereafter, as shown in Fig. 10(d), a resist pattern 27 corresponding to the metal electrodes 23 is formed on the metal layer 25 at regions above the transparent electrodes 22. Then, as shown in Fig. 10(e), the metal electrodes 23 are formed by etching the metal layer 25 with a liquid prepared by mixing a phosphoric acid and an acetic acid.

The hydrogen bromide solution is an optimum etchant for ITO, while the liquid prepared by mixing a phosphoric acid and an acetic acid is a suitable etchant for Cu. Besides, ITO can not be etched with the liquid prepared by mixing a phosphoric acid and an acetic acid. Therefore, even if the resist pattern 27 has a defect in etching the metal layer 25 (Cu) shown in Fig. 10(d), the transparent electrode 22 is not broken off because the transparent electrode 22 is not 48 etched through the defective portion.

Here, the ends of the transparent electrodes 22 -that protruded alternately in the opposite directions were -short- circuited by conductive pastes 41, 42 as shown in Fig. 1. At this time, continuity between the electrodes was confirmed, and thus it was found that a leakage occurred between the electrodes. Hence, after applying a voltage of 10 V and 1 Hz across the shortcircuited terminals for five seconds, the abovementioned PVA was applied to the electrode substrate to cover the transparent electrodes 22, and rubbing was performed. Next, two electrode substrates were fastened together so that the respective transparent electrodes 22 cross each other to form a matrix pattern, and a nematic liquid crystal E7 was introduced between the electrode substrates so as to fabricate a TN liquid crystal display element. Display tests were carried out over the entire screen of the liquid crystal display element. As a result, it was confirmed that there was no break and leakage.

In this example, the electrode substrate having the structure shown in Fig. 4(b) was explained. However, it is possible to form an electrode substrate having the structure shown in Fig. 5(b) with a high aperture ratio by the above-mentioned fabrication 49 processes.

[Example 31

An electrode substrate of this example has the structure shown in Fig. 4 (c). In this structure, transparent electrodes 22 are made of ITO, and metal electrodes 23 are made of Cu. ITO is deposited to form a film with a thickness of 2000 A and a width of 100 gm, while Cu is deposited to form a film with a thickness of 2000 A and a width of 10 gm. Each of the transparent electrodes 22 and metal electrodes 23 is formed to have a length of 300 mm. The length of each protruding portion that protrudes every other electrode for inspection of a leakage is 30 mm. Therefore, the length of a display-use portion of the transparent electrode 22 is 270 mm. Moreover, the interval of electrodes, each of which is composed of a pair of transparent electrode 22 and metal electrode 23, is 10 11m.

First, as illustrated in Fig. 11(a), Cu is deposited in a thickness of 2000 A on a substrate 21 so as to form a metal layer 25, and a resist pattern 27 corresponding to the metal electrodes 23 is formed -1 1 - so thereon. Then, as shown in Fig. 11(b), the metal layer 25 is etched with a liquid prepared by mixing a -phosphoric acid and an acetic acid so as to form the metal- electrodes 23. Furthermore, as illustrated in Fig. 11(c), a transparent electrode film 26 is formed by depositing ITO with a thickness of 2000 A on the substrate 21. Thereafter, a resist pattern 24 corresponding to the electrode pattern is formed on the transparent electrode film 26 as shown in Fig. 11 (d). Then, by etching the transparent electrode film 26 with a hydrogen bromide solution, the transparent electrodes 22 are formed as shown in Fig. 11(e).

The hydrogen bromide solution is an optimum etchant for ITO, and also has the etching effect for Cu. However, there is a difference in the etch rate between ITO and Cu with respect to the hydrogen bromide solution. For instance, with a 47% hydrogen bromide solution at 40 OC, the etch rate of ITO is about 1000 A/min., while the etch rate of Cu is 150 A/min. Therefore, in a period in which ITO is etched by 2000 A, Cu is etched by only 300 A. Thus, even when the metal electrodes 23 as the under layer are over-etched during the etching of the transparent electrode film 26 due to a defect of the resist pattern 24, the metal electrodes 23 are not broken off.

Here, the ends of the transparent electrodes 22 that protruded alternately in the opposite directions Were short-circuited by conductive pastes 41, 42 as shown. in Fig. 'I. At this time, continuity between the electrodes was confirmed, and thus it was found that a leakage occurred between the electrodes. Hence, after applying a voltage of 10 V and 1 Hz across the shortcircuited terminals for five seconds, the abovementioned PVA was applied to the electrode substrate to cover the transparent electrodes 22, and rubbing was performed. Next, two electrode substrates were fastened together so that the respective transparent electrodes 22 cross each other to form a matrix pattern, and a nematic liquid crystal E7 was introduced between the electrode substrates so as to fabricate a TN liquid crystal display element. Display tests were carried out over the entire screen of the liquid crystal display element. As a result, it was confirmed that there was no break and leakage.

In this example, the electrode substrate having the structure shown in Fig. 4(c) was explained. However, it is possible to form an electrode substrate having the structure shown in Fig. 5(c) with a high aperture ratio by the above-mentioned fabrication processes.

[Comparative Example 11 In this comparative example, an electrode jubstrate was fabricated in the same manner as in Example 3, except that the transparent electrode film 26 (ITO) was etched with an iron(III) chloride solution instead of the hydrogen bromide solution. Like the hydrogen bromide solution, the iron(III) chloride solution is an optimum etchant for ITO, and also has the etching effect for Cu. For example, with a 302k iron(III) chloride solution at 50 OC, the etch rate of ITO is about 1000 A/min., while the etch rate of Cu is about 5000 A/min. Therefore, in a period in which ITO is etched by 2000 A, Cu is etched by 10000 A. Thus, if there is a defect in the resist pattern 24 during the etching of the transparent electrode film 26, the metal layer 25 is broken off.

moreover, the above-mentioned PVA was applied to the electrode substrate to cover the transparent electrodes 22, and rubbing was performed. Next, two electrode substrates were fastened together so that the respective transparent electrodes 22 cross each other to form a matrix pattern, and a nematic liquid crystal E7 was introduced between the electrode substrates so as to fabricate a TN liquid crystal display element. Display tests were carried out over the entire screen 1 - 53 of the liquid crystal display element. was confirmed that there was a break.

[Example 41

As illustrated in Fig. 12, an electrode substrate of this example includes a transparent electrode 22 (pixel dividing electrode) composed of a pair of two dividing electrodes 22a, 22b of different widths for area grey-scale display so that a pixel divided into two parts is formed. In the event where this embodiment is applied to such a pixel dividing electrode, usually, as shown in Fig. 13, a wide dividing electrode 22a (first electrode) and a narrow dividing electrode 22b (second electrode) are alternately arranged so that the dividing electrodes 22a protrude in the same direction, and the dividing electrodes 22b protrude in the same direction.

However, in such a structure, since the dividing electrodes 22a and 22b of different widths are driven by individual driving circuits (not shown), respectively, the loads of the driving circuits differ f rom each other to a great degree. As a result, heat generated by the consumption of power in driving the electrodes varies. on the other hand, as shown in Fig. 12, by exchanging the positions of the dividing electrodes 22a, 22b of every other transparent As a result, it - 54 electrode 22, the loads of both driving circuits become equal to each other, thereby maintaining a uniform power consumption in driving the electrodes.

-Note that, in Figs. 12 and 13, the illustration of the metal electrodes 23 is omitted.

Here, two pieces of electrode substrates having the electrode structure shown in Fig. 12 were fabricated in the same manner as in Example 1. These electrode substrates were fastened together so that the respective transparent electrodes 22 cross each other to form a matrix pattern, and a nematic liquid crystal E7 was introduced between the electrode substrates so as to provide a TN liquid crystal display element. Display tests were carried out over the entire screen of the liquid crystal display element. As a result, it was confirmed that there was no break and leakage. In addition, there was no difference in the power consumption between the driving of one of the driving circuits and the driving of the other driving circuit. Moreover, there was no variation in the heat generated by electrodes driven by the respective driving circuits.

[Comparative Example 21 As a second comparative substrates which were the same example, electrode as the electrode substrates of Examples 1 to 4, except that the transparent electrodes 22 made of ITO were provided but -the metal electrodes 23 were not provided, were fabricated. In these electrode substrates, like Examples 1 to 4, the ends of the transparent electrodes 22 that protruded alternately in the opposite directions were short-circuited by conductive pastes 41, 42. At this time, continuity between the electrodes was confirmed, and thus it was found that a leakage occurred between the electrodes. Hence, after applying a voltage of 10 V and 1 Hz across the shortcircuited terminals for five seconds, PVA was applied to the electrode substrate to cover the transparent electrodes 22, and rubbing was performed. Next, the two electrode substrates were fastened together so that the respective transparent electrodes 22 cross each other to form a matrix pattern, and a nematic liquid crystal E7 was introduced between the electrode substrates so as to fabricate a TN liquid crystal display element. Display tests were carried out over the entire screen of the liquid crystal display element. As a result, it was confirmed that there was break and leakage. Again, four types of the electrode substrates which were the same as the above electrode substrates were fabricated. Three types of electrode substrates were prepared by performing a repairing treatment to each electrode substrate by applying -Voltages of 20 V, +50 V, and 80 V, respectively, across the ends which were short-circuited by the conductive pastes 41 and 42. With the use of these electrode substrates, liquid crystal display elements were fabricated in the same manner as in Examples 1 to 4.

Display tests were carried out over the entire screen of these liquid crystal display elements. As a result, like the case when the applied voltage was 10 V, a break and a leakage were confirmed. Moreover, when the applied voltage was 100 V, it was confirmed that part of transparent electrodes 22 is partially burnt off.

Thus, in the electrode substrate having no metal electrodes 23, since the electrode resistance is high, the short-circuit section formed between adjacent transparent electrodes 22 can not be burnt off by a current. moreover, when a higher voltage was applied to burn off the short-circuit section, the display-use transparent electrodes 22 were damaged.

[Example 51

An electrode substrate of this example has the structure shown in Fig. 5 (a) In this structure, the 57 transparent electrodes 22 are made of ITO, and the metal electrodes 23 are made of Ta. ITO is deposited -to form a film with a thickness of 2000 A, a width of 105 gm and a line pitch of 120 gm (an interval of adjacent transparent electrodes 22 is 15 gm), while Ta is deposited to form a film with a thickness of 5000 A and a width of 20 gm. Each of the transparent electrodes 22 and metal electrodes 23 is formed to have a length of 300 mm. Every other electrode protrudes for inspection of leakage, and the length of the protruding portion is 30 mm. Therefore, the length of a display-use portion of the transparent electrode 22 is 270 mm. Moreover, the metal electrode 23 is in contact with the transparent electrode 22 in a width of 10 gm.

First, as illustrated in Figs. 18(a) to 18(e), the metal electrodes 23 are buried in the substrate 21, and a transparent conductive film 26 is formed on the substrate 21 by the same processes as those shown in Figs. 9 (a) to 9 (e) of Example 1. Moreover, unlike Example 1, in the process shown in Fig. 18(f), after positioning the resist pattern 27 so that it covers 58 part of the metal layer 25, the resist pattern 27 is formed on the transparent electrode film 26 by -performing exposure and development. Then, as shown in Fig. -18(g), by etching the transparent electrode film 26 with an aqueous 47% hydrogen bromide solution, the transparent electrodes 22 are formed.

The hydrogen bromide solution is a very suitable etchant for ITO. Besides, Ta is not corroded by most of acids including the hydrogen bromide. Therefore, when etching the transparent electrode film 26 in the process of Fig. 18(g), the metal electrodes 23 are not etched with the aqueous hydrogen bromide solution.

Here, the ends of the transparent electrodes 22 that protruded alternately in the opposite directions were short-circuited by conductive pastes 41, 42 as shown in Fig. 1. At this time, continuity between the electrodes was confirmed, and thus it was found that a leakage occurred between the electrodes. Hence, after applying a voltage of 10 V and 1 Hz across the shortcircuited terminals for five seconds, the abovementioned PVA was applied to the electrode substrate to cover the transparent electrodes 22, and rubbing was performed. Next, two electrode substrates were fastened together so that the respective transparent electrodes 22 cross each other to form a matrix 1 - 59 pattern, and the nematic liquid crystal E7 was introduced between the electrode substrates so as to -fabricate a TN liquid crystal display element. Display tests, were carried out over the entire screen of the liquid crystal display element. As a result, it was confirmed that there was no break and leakage.

Incidentally, in later-described Examples 6 to 12, similar TN liquid crystal display elements were fabricated and display tests were carried out over the entire screen thereof. As a result, it was confirmed that there was no break and leakage.

[Example 61

Like the electrode substrate of Example 5, an electrode substrate of this example has the structure shown in Fig. 5 (a), but the fabrication process thereof differs from that of the electrode substrate of Example 5. More specifically, when etching the transparent electrode film 26 in the process of Fig. 18 (g), a 30'-. iron(III) chloride solution at 50 OC is used as the etchant. The transparent electrode film 26 is etched with such an iron(III) chloride solution at an etch rate of about 1000 A/min.

Like the hydrogen bromide solution, the iron(III) chloride solution is a very suitable etchant for ITO. Moreover, Ta is not corroded by the iron(III) chloride - 60 solution. Therefore, when etching the transparent electrode film 26 in the process of Fig. 18 (g), the Tdetal electrodes 23 are not etched with the iron(III) chloride solution.

[Example 71

Like the electrode substrate of Example 5, an electrode substrate of this example has the structure shown in Fig. 5 (a), but the metal electrode 23 is made of Cu instead of Ta. ITO is deposited to form a film with a thickness of 2000 A and a width of 110 gm, while Cu is deposited to form a film with a thickness of 5000 A and a width of 10 gm. ITO is deposited at a line pitch of 120 gm (an interval of adjacent transparent electrodes 22 is 10 gm). Moreover, the metal electrode 23 is in contact with the transparent electrode 22 in a width of 5 gm.

When fabricating an electrode substrate having such a structure, the metal layer 25 is formed by depositing Cu with a thickness of 5000 A in the process of Fig. 18 (c), and the metal electrodes 23 are formed (Fig. 18(dH by lifting off the metal layer 25 on the resist pattern 24. Then, by etching the transparent electrode film 26 made of ITO with an aqueous 470k hydrogen bromide solution in the process of Fig. 18(g), the transparent electrodes 22 are formed.

Cu which forms the metal layer 25 has a lower resistance than other metals such as Ta, and can reduce -the electrode resistance in a narrow width. Thus, Cu has the advantage of improving the aperture ratio. Besides, the hydrogen bromide solution at 40 OC etches ITO at an etch rate of about 1000 A/min., but etches Cu at an etch rate of only about 150 A/min. As a result, even if the metal electrode 23 located under the etching portion of the transparent electrode film 26 is over-etched, the metal layer 25 does not disappear.

[Comparative Example 31 In this comparative example, an electrode substrate was fabricated in the same manner as in Example 7, except that the transparent electrode film 26 (ITO) was etched with an iron(III) chloride solution instead of the hydrogen bromide solution. Like the hydrogen bromide solution, the iron(III) chloride solution is an optimum etchant for ITO, and also has the etching effect for Cu. For example, with a 3056 iron(III) chloride solution at 50 OC, the etch rate of ITO is about 1000 A/min., while the etch rate of Cu is about 5000 A/min. Therefore, in a period in which ITO is etched by 2000 A, Cu is etched by 10000 A. Thus, the metal electrode 23 of this electrode substrate disappeared, and the substrate structure shown in Fig.

62 5(a) was not obtained.

[Example 81

In the electrode structure of this example, as shown in Fig. 19 (a), the metal electrode 23 has a three-layer structure composed of a first layer 23a, second layer 23b and third layer 23c, and a width of 10 Am. Each of the first and third layers 23a, 23c are made of Ta with a thickness of 1000 A. The second layer 23b held between the first and third layers 23a, 23c is made of Cu with a thickness of 5000 A. Like the electrode substrate of Example 7, the width of the transparent electrode 22, the line pitch of the transparent electrode 22, and the contact width of the metal electrode 23 and transparent electrode 22 are 110 gm, 120 gm, and 5 gm, respectively.

When fabricating an electrode substrate having such a structure, the first film 25a made of Ta, the second film made of Cu, the third film 25c made of Ta are sequentially deposited as shown in Fig. 19(b) instead of forming the metal in the process of Fig. 18(c) layer 25 by a single metal Then, in the process of Fig. 18 (e), normal ITO is deposited to form a film with a thickness of 2000 A as the transparent electrode film 26. Next, in the process of Fig. 18 (g), the ITO is etched with an aqueous 47% hydrogen bromide solution.

As described above, the hydrogen bromide solution at 40 OC etches ITO at an etch rate of about 1000 A/min., but does not etch Ta at all. Meanwhile, although Cu is etched with the same hydrogen bromide solution only at a speed of about 150 A/min., it is etched to some extent. Therefore, in the electrode structure of Example 7 where the metal layer 25 is made of only Cu, there is a possibility that the metal layer 25 is separated from a recessed portion 21a and the yield of the electrode substrate is lowered. However, a structure in which the second layer 23b made of Cu is sandwiched between the f irst and third layers 23a, 23c made of Ta is adopted for the metal electrode 23, since the second layer 23b does not make direct contact with the hydrogen bromide solution, it is possible to easily obtain the electrode structure shown in Fig. 19 (a) [Example 91

Like the electrode substrate of Example 8, the electrode substrate of this example has the structure shown in Fig. 19 (a), but the fabrication processes thereof differ from those of the electrode substrate of Example 8. More specifically, when etching the transparent electrode film 26 in the process of Fig. 18(g), a 30% iron(III) chloride solution at 50 OC is used as the etchant.

Like Comparative Example 3, although the iron(III) -chloride solution etches Cu quickly, since the second -layer 23b (Cu) shown in Fig. 19(a) is held between the first and third layers 23a, 23c (Ta) which are not etched by iron(III) chloride, the second layer 23b does not disappear even after the etching process using the iron(III) chloride solution. It is thus possible to easily obtain a desired electrode structure.

(Example 101

An electrode substrate of this example has the structure shown in Fig. 5(a). Like the electrode substrate of Example 7, the width of the transparent electrode 22, the line pitch of the transparent electrode 22, and the contact width of the metal electrode 23 and transparent electrode 22 are 120 pm, 110 pm, and 5 pm, respectively.

When fabricating this electrode substrate, the metal layer 25 made of Cu is formed with a width of 10 pm and a thickness of 5000 A in the process of Fig. 18 (d). Then, in the process of Fig. 18(e), the transparent electrode film 26 made of amorphous ITO (IDIXO available from Idemitsu Kosan co., Ltd.) is formed with a thickness of 2000 A. Moreover, in the process of Fig. 18(g), the transparent electrode film 26 is etched with an aqueous oxalic acid solution.

IDIXO is etched at an etch rate of 200 A/min. by a 5% oxalic acid solution at 25 OC. However, Cu is not -etched at all by the same oxalic acid solution. It is therefore possible to easily obtain a desired electrode structure.

[Example ill

In this example, a liquid crystal display device shown in Fig. 2 was fabricated with the use of electrode substrates formed in Examples 5 and 6. The liquid crystal display device is a ferroelectric liquid crystal display device including a liquid crystal layer 10 formed by ferroelectric liquid crystal.

In the electrode substrates, a light transmitting section of the transparent electrode 22 which does not overlap the metal electrode 23 has a width of 95 gm. Therefore, in the liquid crystal display device, an aperture ratio of 62.67% was obtained. Moreover, in this liquid crystal display device, there were no attenuation and distortion of signals due to the electrode resistance and alignment defects due to the difference in level of the substrate surface, thereby achieving bright and high contrast (a contrast ratio of not less than 200) characteristics.

[Comparative Example 41 In this comparative example, the electrode - 66 substrates of Example 11 were fabricated according to the structure of prior art (see Fig. 21(a)), and a -liquid crystal display device (ferroelectric liquid crystal display device) shown in Fig. 2 was fabricated. In this liquid crystal display device, there were no attenuation and distortion of signals due to the electrode resistance, and bright and high contrast (a contrast ratio of not less than 200) characteristics were obtained.

However, in this liquid crystal display device, alignment defects due to the difference in level of the substrate surface occurred, and the unifomity of display was deteriorated.

[Example 121

Like Example 11, in this example, a liquid crystal display device (ferroelectric liquid crystal display device) shown in Fig. 2 was fabricated with the use of electrode substrates formed in Examples 7 to 11.

In the electrode substrates, a light transmitting section of the transparent electrode 22 which does not overlap the metal electrode 23 has a width of 105 gm. Therefore, in this liquid crystal display device, an aperture ratio of 76.56-1k was obtained. Moreover, in this liquid crystal display devices, there were no attenuation and distortion of signals due to the W 67 electrode resistance and alignment defects due to the difference in level of the substrate surface, thereby dchieving bright and high contrast (a contrast ratio of not less than 250) characteristics.

[Comparative Example 51 In this comparative example, the electrode substrates of Example 12 were fabricated according to the structure of prior art (see Fig. 21(a)), and a liquid crystal display device (ferroelectric liquid crystal display device) shown in Fig. 2 was fabricated. In this liquid crystal display device, there were no attenuation and distortion of signals due to the electrode resistance, and bright and high contrast (a contrast ratio of not less than 250) characteristics were obtained.

Examples 1 to 12 of the present invention were explained above. However, the present invention is not necessarily limited to Examples 1 to 12.

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Claims

CLAIMS:

1. An electrode substrate for use in a display device, having thereon a plurality of electrodes in stripes, said electrode including at least two electrode sections which are juxtaposed parallel and in contact with each other, said electrode sections being made of conductors of different etching characteristics, wherein in a state in which one end of every other electrode is short-circuited and the other.ends of remaining electrodes are short-circuited, when a voltage is applied across both of the short-circuited ends, a leakage portion formed between the electrodes is cut off.

2. The electrode substrate for use in a display device as set forth in claim 1, wherein said conductors are made of materials which are not etched by same etchant.

3. The electrode substrate for use in a display device as set forth in claim 2, wherein said conductor which forms one of said electrode sections is made of indium tin oxide and said conductor which forms the other electrode section is - 69 made of tantalum, and said etchant is a hydrogen bromide solution.

4. The electrode substrate for use in a display device as set forth in claim 1, wherein said conductors are made of materials whose etch rates by same etchant are at least five times different from each other.

5. The electrode substrate for use in a display device as set forth in claim 4, wherein said conductor which forms one of said electrode sections is made of indium tin oxide and said conductor which forms the other electrode section is made of copper, and said etchant is a hydrogen bromide solution.

6. The electrode substrate for use in a display device as set forth in claim 1, 2 or 4, wherein at least one of said electrode sections is a transparent electrode, and the other electrode section is a low-resistant conductor electrode.

7. The electrode substrate for use in a display device as set forth in claim 6, 1 - 70 wherein said low-resistant conductor electrode is buried in said substrate and in contact with said -transparent electrode so that only part of said lowresistant conductor electrode is covered with said transparent electrode.

8. The electrode substrate for use in a display device as set forth in claim 7, wherein said transparent electrode is made of indium tin oxide and said low-resistant conductor electrode is made of tantalum, and said etchant is a hydrogen bromide solution.

9. The electrode substrate for use in a display device as set forth in claim 7, wherein said transparent electrode is made of indium tin oxide and said low-resistant conductor electrode is made of tantalum, and said etchant is an iron(III) chloride solution.

10. The electrode substrate for use in a display device as set forth in claim 7, wherein said transparent electrode is made of indium tin oxide and said low-resistant conductor electrode is made of copper, and said etchant is a hydrogen bromide solution.

11. The electrode substrate for use in a display device as set forth in claim 7, wherein said transparent electrode is made of amorphous indium tin oxide and said low-resistant conductor electrode is made of copper, and said etchant is an oxalic acid solution.

12. The electrode substrate for use in a display device as set forth in claim 7, wherein said low-resistant conductor electrode is formed by first to third layers so that the second layer is held between said first and third layers, said first and third layers being made of a metal material which is hard to be etched by an etchant for forming the transparent electrode.

13. The electrode substrate for use in a display device as set forth in claim 12, wherein the metal material which forms said first and third layers is tantalum and the metal material which forms said second layer is copper, and said etchant is a hydrogen bromide solution.

14. The electrode substrate for use in a display device as set forth in claim 12, wherein the metal material which forms said first and third layers is tantalum and the metal material which forms said second layer is copper, and said etchant is an iron(III) chloride solution.

15. The electrode substrate for use in a display device as set forth in any one of claims 1 to 14, wherein said electrode is composed of a pair of a first electrode and a second electrode of different widths for forming divided pixels, and the first electrodes of adjacent electrodes are positioned next to each other and the second electrodes of adjacent electrodes are positioned next to each other.

16. A display device comprising an electrode substrate as set forth in any one of claims 1 to 15.

17. The display device as set forth in claim 16, wherein said display device is a liquid crystal display device.

18. The display device as set forth in claim 16, wherein said display device is an EL display - 73 device.

19. A method for fabricating an electrode substrate for use in a display device, said electrode substrate having thereon a plurality of electrodes in stripes, said method comprising: the first step of forming said plurality of electrodes by etching conductors so that at least two electrode sections constituting said electrode are juxtaposed parallel and in contact with each other by causing etching characteristics of the conductors forming said electrode sections to differ from each other; and the second step of short-circuiting one end of every other electrode and short-circuiting the other ends of remaining electrodes, and cutting off a leakage portion formed between adjacent electrodes by applying a voltage across the short-circuited ends.

20. The method as set forth in claim 19, wherein, in the first step, materials which are not etched by same etchant are used as said conductors.

21. The method as set forth in claim 20, wherein, in the f irst step, said conductor which - 74 forms one of said electrode sections is made of indium tin oxide and said conductor which forms the other i!lectrode section is made of tantalum, and a hydrogen bromide solution is used as said etchant.

22. The method as set forth in claim 19, wherein, in the f irst step, materials whose etch rates by same etchant are at least five times different from each other are used as said conductors.

23. The method as set forth in claim 22, wherein, in the first step, said conductor which forms one of said electrode sections is made of indium tin oxide and said conductor which forms the other electrode section is made of copper, and a hydrogen bromide solution is used as said etchant.

24. The method as set forth in claim 19, 20 or 22, wherein, in the f irst step, at least one of said electrode sections is formed as a transparent electrode, and the other electrode section is formed as a low-resistant conductor electrode.

25. The method as set forth in claim 24, - 75 wherein, in the first step, after forming said low-resistant conductor electrode so that it is buried -in said substrate, said transparent electrode is formed on said substrate so that it covers only part of said low-resistant conductor electrode and is in contact with said low-resistant conductor electrode.

26. The method as set forth in claim 25, wherein, in the first step, said transparent electrode is made of indium tin oxide and said lowresistant conductor electrode is made of tantalum, and a hydrogen bromide solution is used as said etchant.

27. The method as set forth in claim 25, wherein, in the first step, said transparent electrode is made of indium tin oxide and said low- resistant conductor electrode is made of tantalum, and an iron(III) chloride solution is used as said etchant.

28. The method as set forth in claim 25, wherein, in the first step, said transparent electrode is made of indium tin oxide and said low- resistant conductor electrode is made of copper, and a hydrogen bromide solution is used as said etchant.

76

29. The method as set forth in claim 25, wherein, in the first step, said transparent 6lectrode is made of amorphous indium tin oxide and said low-resistant conductor electrode is made of copper, and an oxalic acid solution is used as said etchant.

30. The method as set forth in claim 25, wherein, said low-resistant conductor electrode is formed by laminating a first layer, a second layer and a third layer in this order, said first and third layers being made of a metal material which is hard to be etched by an etchant for forming the transparent electrode.

31. The method as set forth in claim 30, wherein the metal material which forms said first and third layers is tantalum and the metal material which forms said second layer is copper, and said etchant is a hydrogen bromide solution.

32. The method as set forth in claim 30, wherein the metal material which forms said first and third layers is tantalum and the metal material which forms said second layer is copper, and said 1 1 - 77 etchant is an iron(III) chloride solution.

33. The method as set forth in any one of claims 19 to 32, wherein, in the first step, said electrodes are formed so that each electrode is composed of a pair of a first electrode and a second electrode of different widths for forming divided pixels, the first electrodes of adjacent electrodes are positioned next to each other, and the second electrodes of adjacent electrodes are positioned next to each other.