JP2001253073A - Droplet ejection head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid drop ejecting head wherein variation of each of parameters of a thickness, a length of a short side and a gap of a diaphragm that may cause variation of a displacement position of the diaphragm is reduced in order to obtain a stable liquid drop ejection characteristic by suppressing variation of the ejection characteristic among channels in an electrostatic type ink jet head, thereby reducing the variation of the liquid ejection characteristic. SOLUTION: A width (A) of a pressure generating chamber 6 in a short side direction of the diaphragm formed on a liquid chamber substrate 1 is shorter than a length (C) of a short side of a displaceable region of the diaphragm 2 that forms a wall of the pressure generating chamber and doubles as a first electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a droplet discharge head,
In particular, the present invention relates to an electrostatic liquid droplet ejection head.

[0002]

2. Description of the Related Art An ink jet head used in an ink jet recording apparatus used as an image recording apparatus (image forming apparatus) such as a printer, a facsimile, a copying apparatus, a plotter, etc. has a nozzle for ejecting ink droplets and a pressure generating passage communicating with the nozzle. A chamber (also referred to as a liquid chamber, a discharge chamber, a pressure chamber, a pressurized liquid chamber, an ink flow path, etc.); and an energy generating means (actuator) for generating energy for pressurizing the ink in the pressure generating chamber. Then, by driving the actuator, the ink in the liquid chamber is pressurized to eject ink droplets from the nozzles.

As a conventional ink jet head, as described in, for example, Japanese Patent Application Laid-Open No. 2-289351, a diaphragm forming a part of a liquid chamber made of Si, and a diaphragm facing the diaphragm are disposed. A separate electrode outside the liquid chamber, and deforming the vibration plate by an electrostatic force generated by applying an electric field between the vibration plate and the electrode, and changing the pressure / volume inside the liquid chamber to cause ink to flow from the nozzles. An electrostatic type in which droplets are ejected has been proposed.

In such an electrostatic ink jet head, as a method for forming a liquid chamber at a high density by a simple process, anisotropic wet etching of single crystal Si, which has been established in the field of micromachining,
In particular, a Si substrate having a crystal plane orientation (110) capable of forming a vertical wall is used as the liquid chamber substrate.

A conventional electrostatic ink jet head using a silicon substrate having a crystal plane orientation of (110) as a liquid chamber substrate has a pressure generating chamber 102 having a depth D and a first substrate 101, as shown in FIG. A concave portion forming a diaphragm 103 serving also as a first electrode serving as a wall surface of the pressure generating chamber 102 is formed by etching, and a second substrate 1 is formed below the first substrate 101.
04, and the electrode substrate 104 has a concave portion 1 having a depth E.
The second electrode 107 having a width B is formed on the bottom surface of the concave portion 105 so as to face the diaphragm 103 via the gap 106.
Is provided. Note that the second electrode 107 is covered with an insulating film 108.

As can be seen from FIG. 1, in the conventional ink jet head, the width B of the second electrode 107 is larger than the width A (hereinafter simply referred to as “width”) of the pressure generating chamber 102 in the width direction of the diaphragm. And thus also the pressure generating chamber 1
Recesses (grooves) formed in the second substrate 104 beyond the width A of 02
The width C (same as the width of the gap 106) of 105 is large.
As a result, the entire diaphragm 103 forming the wall surface of the pressure generating chamber 102 is a displaceable area, and its short side length is equal to the width A of the pressure generating chamber 102.

[0007]

Incidentally, in the electrostatic ink jet head, the displacement amount δ of the diaphragm is structurally a function of the diaphragm thickness, the shorter side length of the diaphragm, and the gap. Therefore, in order to obtain a stable droplet ejection characteristic by suppressing variation in ejection characteristics between channels,
It is important to reduce variations in the parameters of these diaphragms.

In the above-described conventional ink jet head, both ends of the diaphragm are fixed to the first substrate forming the pressure generating chamber, and the short side length of the diaphragm is equal to the width A of the pressure generating chamber. Matches. Since the pressure generating chamber is also a part of the ink flow path, the height (depth) D cannot be reduced so much. Therefore, for example, a concave portion of the second substrate provided with the second electrode is formed in the pressure generating chamber. Deep trench etching must be performed as compared with the case of forming.

Here, generally, the variation in the etching width shows a substantially monotonous increase with the etching depth. Therefore, it is difficult to suppress a variation in the width (liquid chamber width) A of the pressure generating chamber having a high height D formed on the first substrate.

The pressure generating chamber is formed by anisotropic etching of a silicon substrate. In order to form vertical partition walls by this etching, a silicon substrate having a crystal plane orientation of (110) is used. In addition, the pattern is
Accurate alignment is required, and if the alignment is shifted, the deviation of the finished dimension from the mask pattern becomes large. However, it is extremely difficult to accurately specify the crystal axis at the photolithography stage, and the width A of the pressure generating chamber is difficult.
There is a limit in suppressing the variation in

Since the variation in the width A of the pressure generating chamber becomes the variation in the short side length of the diaphragm, there is a problem that the variation in the injection characteristics becomes large and the stable injection characteristics cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a droplet discharge head with less variation in droplet ejection characteristics.

[0013]

In order to solve the above-mentioned problems, in a droplet discharge head according to the present invention, the shorter side length of the deformable region of the diaphragm is larger than the width of the pressure generating chamber in the transverse direction of the diaphragm. Is also short.

Here, the length of the short side of the deformable region of the diaphragm can be defined by the concave portion formed in the second substrate provided with the second electrode. Further, the short side length of the deformable region of the diaphragm can be defined by the spacer member that defines the gap length between the diaphragm and the second electrode. Further, the length of the short side of the displaceable region of the diaphragm can be defined by the width of the concave portion provided on the substrate on which the pressure generating chamber and the diaphragm are formed.

In these droplet discharge heads, the pressure generating chamber is preferably formed by anisotropic etching of a silicon substrate. Further, it is preferable that the length of the pressure generating chamber in the transverse direction of the diaphragm is 0.7 μm or more longer than the short side length of the displaceable region of the diaphragm.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an explanatory perspective view showing an external appearance of an ink-jet head which is a droplet discharge head according to a first embodiment of the present invention, FIG. 2 is a cross-sectional explanatory view of the head in the longitudinal direction of the diaphragm, and FIG. FIG. 4 is an enlarged sectional plan view of a main part of the head, and FIG.

The ink jet head includes a liquid chamber substrate 1 as a first substrate, and a diaphragm 2 provided on the liquid chamber substrate 1.
And an electrode substrate 3 which is a second substrate provided below the vibration plate 2 and a nozzle plate 4 provided above the liquid chamber substrate 1. It has a common liquid chamber 8 for supplying ink to the generation chamber 6 and the pressure generation chamber 6 via the fluid resistance part 7, and the like.

The liquid chamber substrate 1 has a through hole for forming the pressure generating chamber 6, a through hole for forming the common liquid chamber 8, and the like. The lower surface of the liquid chamber substrate 1 forms a part of the wall surface of the pressure generating chamber 6, and the vibration plate 2 also serving as the first electrode is joined thereto. Here, the diaphragm 2 itself also serves as the first electrode, but the first electrode may be formed on the surface of the diaphragm 2 on the electrode substrate 3 side.

Here, the liquid chamber substrate 1 is formed by anisotropically etching a p-type or n-type dosed silicon single crystal substrate having a crystal plane orientation (110) with a strong alkaline etching solution such as a KOH aqueous solution. A desired fine liquid chamber pattern such as the pressure generating chamber 6 having the above is formed. Here, the silicon substrate above the SOI substrate is used as the liquid chamber substrate 1, the silicon oxide film 9 is used as an etching stop layer, and the lower silicon substrate is used as the diaphragm 2.

The vibration plate 2 is formed using a silicon substrate of an SOI substrate which is dosed to p-type or n-type as described above, but the CV is formed on a Si substrate or a ceramic substrate.
It may be a Si epitaxial layer / polycrystalline film formed by a thin film forming process such as D or sputtering, or a metal thin film, a ceramic thin film, or the like. Liquid chamber substrate 1
Not only silicon and ceramics, but also resin or SUS can be used if they can be micro-processed and have rigidity as a liquid chamber.
Such a metal can be used as a part of the liquid chamber member.

As the electrode substrate 3, an n-type or p-type single crystal silicon substrate is used, and an oxide layer (SiO ₂ layer) 3a is formed on the single crystal silicon substrate by a thermal oxidation method or the like. A concave portion (groove portion) 11 is formed in 3a, and the second electrode 13 facing the diaphragm 2 along the bottom surface of the concave portion 11 is formed.
And a gap 14 is provided between the diaphragm 2 and the second electrode 13.
Is formed, and the diaphragm 2 and the second electrode 13 constitute an actuator. As shown in FIG. 2, the second electrode 13 is an electrode pad 13a extending outward from the liquid chamber substrate 1 and connected to connection means such as an FPC cable connected to an external drive circuit.

The electrode protection film 15 made of an oxide insulating film such as a SiO ₂ film and a nitride insulating film such as a Si ₃ N ₄ film is formed on the surface of the second electrode 13. An insulating film may be formed on the surface of the plate 2 on the second electrode 13 side. In addition, other than a silicon substrate, an insulating substrate such as a glass substrate or a ceramic substrate can be used as the electrode substrate 3.

The electrode 13 is formed by a reactive sputtering method,
Titanium, tungsten, which can be formed by a VD method or the like;
A metal such as tartan and a refractory metal such as a nitride or compound thereof, preferably titanium nitride, or silicon containing P-type or N-type impurity atoms can be used.

Here, the width A of the pressure generating chamber 6 formed by the liquid chamber substrate 1 is defined by the distance between the liquid chamber spacing walls 6a. Also,
Since the vibration plate 2 is bonded to the electrode substrate 3, the short side length of the displaceable region of the vibration plate 2 is the width C of the concave portion (groove portion) 11 where the second electrode 13 is provided (this is the distance C between the concave space 11a). And the length of the space to be the gap 14 in the transverse direction of the diaphragm.) Therefore, by making the width C of the concave portion 11 of the electrode substrate 3 smaller than the width A of the pressure generating chamber 6, the short side length C of the deformable region of the diaphragm 2 in the transverse direction of the diaphragm of the pressure generating chamber 6 is increased. Shorter than width A (C <
A).

The liquid chamber substrate 1 having the vibration plate 2 and the electrode substrate 3 can be joined by processes such as anodic joining, direct joining, and eutectic joining.

The nozzle plate 4 is made of a silicon substrate and has a groove serving as the nozzle 5, a groove serving as the fluid resistance portion 7, and an ink supply hole 18 for supplying ink to the common liquid chamber 8 from outside.
Is formed. The nozzle plate 4 may be made of a metal plate such as Ni or SUS, ceramics, glass, resin, or the like.

In the ink jet head thus configured, by applying a drive waveform between the diaphragm 2 and the second electrode 13, an electrostatic force (electrostatic force) is applied between the diaphragm 2 and the second electrode 13. A suction force is generated, and the diaphragm 2 is deformed and displaced toward the second electrode 13 by the electrostatic force. As a result, the internal volume of the pressure generating chamber 6 is expanded and the internal pressure is reduced, so that the pressure generating chamber 6 is moved from the common liquid chamber 8 through the fluid resistance portion 7.
Is filled with ink.

Next, when the application of the voltage between the diaphragm 2 and the second electrode 13 is stopped, the electrostatic force stops working, and the diaphragm 2 is restored by its own elasticity. With this operation, the internal pressure of the pressure generating chamber 6 increases, and ink droplets are ejected from the nozzles 5. When a voltage is applied to the electrodes again, the diaphragm is drawn back to the electrodes by the electrostatic attraction force. The vibration plate 2 is connected to the second electrode 13 (actually, the insulating protective film 15).
The contact driving method is a method of displacing until it contacts the surface)
A method in which the diaphragm 2 is displaced to a position where the diaphragm 2 is not brought into contact with the second electrode 13 is referred to as a non-contact drive method, and can be driven by either method.

Here, in an electrostatic ink jet head that ejects ink droplets by causing the solid vibration plate to bend and vibrate, the thickness of the vibration plate is t, the short side length of the fixed end of the vibration plate is a,
When the effective electrostatic gap is h and the voltage applied to the gap (between the diaphragm and the electrode) is V, the displacement of the diaphragm (vibration displacement)
Is proportional to the fourth power of the short side length a and the square of the applied voltage V,
It is known that it is inversely proportional to the square of the effective gap h and the cube of the diaphragm thickness t. Therefore, reducing the variation in the short side length of the diaphragm 2 leads to a reduction in the variation in the droplet discharge characteristics.

When the height D of the pressure generating chamber 6 is reduced, the fluid resistance increases and the discharge efficiency decreases. Therefore, the height D of the pressure generating chamber 6 is preferably set to 100 μm or more. In the case where the pressure generating chamber 6 is formed in the liquid chamber substrate 1 by anisotropic etching, it is necessary to perform the etching to a depth of 100 μm or more. However, as described above, generally, the variation in the etching width shows a substantially monotonically increasing relationship with the etching depth, and in particular, 100 μm
It becomes difficult to suppress the variation in the width A of the pressure generating chamber 6 in the deep trench etching that exceeds the depth.

When forming the pressure generating chamber 6 by anisotropic etching of the silicon substrate, it is necessary to accurately align the pattern with respect to the crystal axis in order to form vertical partition walls (wall surfaces). If this misalignment occurs, the deviation of the finished dimension from the mask pattern becomes large.
However, it is extremely difficult to specify the crystal axis accurately at the photolithography stage, and from this point, the width A of the pressure generating chamber 6 is also considered.
It is difficult to suppress the variation of. for that reason,
It was difficult to suppress the variation in the width A of the pressure generating chamber 6 within ± 1 μm in the mass production process.

Therefore, in this ink jet head,
The width A of the pressure generating chamber 6 formed by the liquid chamber substrate 1 is
By making the width C longer (A <C) than the width C of the recess 11 of the electrode substrate 3, the length of the short side of the deformable area of the diaphragm 2 is reduced.
Is defined by the width C.

The depth E of the concave portion 11 formed in the electrode substrate 3 is extremely shallow, about 1 μm, and it is not necessary to use anisotropic etching, so that the amount of side etching can be controlled substantially constant. Therefore, the width C of the recess 11
Can be reduced to a level not exceeding ± 0.1 μm. As a result, the variation in the short side length of the displaceable region of the diaphragm 2 becomes extremely small, and a head with little variation in the ejection characteristics can be obtained.

Next, the manufacturing process of the ink jet head according to the present invention will be described with reference to FIGS.
First, as shown in FIG. 5A, a silicon oxide film 61 serving as an oxide layer 3a of the electrode substrate 3 is formed on the surface of a silicon substrate 60 serving as the electrode substrate 3 by using thermal oxidation. Next, as shown in FIG. 2B, the silicon oxide film 61 is etched by about 1 μm using wet etching to form a concave portion (groove) 11. Next, as shown in FIG. 4C, a second electrode 13 is formed by forming a TiN film on the entire surface and then patterning, and then a silicon oxide film is formed on the entire surface and then patterned to form an insulating protective film. (Electrode protection layer) 15 is formed, and FIG.

Thereafter, as shown in FIG. 4D, the SOI substrate 1 serving as the liquid chamber substrate 1 on which the silicon layer 65 serving as the diaphragm 2 and the oxide film layer 67 serving as the etching stop layer are formed.
A silicon substrate 66 serving as a substrate is bonded onto a silicon oxide film 61 of a silicon substrate 60 serving as an electrode substrate 2 by a silicon-oxide film direct bonding.

Then, as shown in FIG. 6A, the silicon substrate 66 is polished to a thickness of about 100 μm, and then, as shown in FIG. 6B, a silicon nitride film is formed on the entire surface. The pressure generating chamber 6, the fluid resistance part 7, and the common liquid chamber 8
The pattern 71 corresponding to the above is formed to form the pattern 71.

At this time, it is necessary to accurately align the pattern 71 with the concave portion 11.
6, and the diaphragm 2 cannot be aligned with ordinary visible light. Therefore, for this alignment, infrared light having a wavelength corresponding to or greater than the band gap of silicon is used. Further, at this time, the width A of the pressure generating chamber 6 in the short direction of the diaphragm is larger than the width C of the concave portion 11 in the short direction of the diaphragm, and here, is increased by 1 μm.

Thereafter, as shown in FIG.
The silicon substrate 66 is etched using
Anisotropic etching is performed until the etching stop layer 67 is removed using a hydrofluoric acid-based etchant, and the silicon nitride film pattern 71 is further etched using a phosphoric acid-based etchant.
Is removed. Next, as shown in FIG. 3D, the nozzle plate 4 is bonded onto the silicon substrate 66 which is the liquid chamber substrate 1.

In this manufacturing process, as described above, the alignment of the pattern of the pressure generating chamber 6 with the concave portion 11 is performed as follows.
Infrared light is used. For this reason, the resolution of the image is lower than in the case of using visible light, and the positioning accuracy is reduced.
If there is a displacement here, the partition 6 between the pressure generating chambers 6
a is located inside the recess 11, the diaphragm 2
Becomes narrower, and the width of the diaphragm 2 becomes substantially shorter.

Therefore, it is necessary to ensure that the pressure generating chamber spacing wall 6a is positioned outside the concave portion 11 at the time of positioning. By using a normal image processing technique or the like, if there is an alignment margin of about の of the wavelength, alignment can be performed. Therefore, by setting the difference between the width C and the width A to 0.7 μm or more, it is possible to ensure that the partition wall 6a is positioned outside the concave portion 11.

Next, a second embodiment of the ink jet head according to the present invention will be described with reference to FIG. In this ink jet head, the electrode substrate 23 is formed of a glass substrate. Since the electrode substrate 2 has an insulating property, the concave portion 11 can be formed directly on the electrode substrate 23.

Next, a third embodiment of the ink jet head according to the present invention will be described with reference to FIG. In this inkjet head, a high-concentration P ⁺ diffusion layer or a high-concentration boron diffusion layer is formed in a region where a vibration plate is formed on a silicon substrate, and the high-concentration P ⁺ diffusion layer or the boron diffusion layer is used as an etch stop layer. By performing anisotropic etching, a liquid chamber substrate 31 having a vibration plate 32 formed of an impurity diffusion layer is formed.

Next, a fourth embodiment of the ink jet head according to the present invention will be described with reference to FIG. This ink jet head forms a liquid chamber substrate 42 in which a concave portion 44 for forming the gap 14 between the second electrode 13 and the diaphragm 42 is formed together with a concave portion for forming the pressure generating chamber 6 from both sides of the silicon substrate. An electrode substrate 43 having a flat surface on which the second electrode 13 is formed is joined to the liquid chamber substrate 41. Therefore, in this head, the displaceable length of the diaphragm 32 in the lateral direction is defined by the concave portion 33 of the liquid chamber substrate 31.

Next, a fifth embodiment of the ink jet head according to the present invention will be described with reference to FIG. The ink jet head includes a pressure generating chamber 6 and a diaphragm 32.
And a spacer member 51 for forming the gap 14 between the diaphragm 42 and the second electrode 13 is provided between the liquid chamber substrate 31 having the second electrode 13 and the flat electrode substrate 43 provided with the second electrode 13. is there. Therefore, in this head, the width of the spacer member 51 defines the short side length of the displaceable region of the diaphragm 32.

In each of the above-described embodiments, an example is described in which the invention is applied to an edge shooter type ink jet head in which the direction of displacement of the diaphragm and the direction of ink droplet ejection are orthogonal, but the direction of displacement of the diaphragm and the direction of ink droplet ejection are described. Can be applied to a side shooter type ink jet head having the same value. Further, the present invention can be applied not only to the ink jet head but also to a droplet discharge head for discharging a liquid such as a liquid resist.

[0046]

As described above, according to the droplet discharge head of the present invention, the length of the short side of the deformable region of the diaphragm is shorter than the width of the pressure generating chamber in the width direction of the diaphragm. Therefore, variation in deformation of the diaphragm is reduced, and variation in droplet discharge characteristics is reduced.

Here, by defining the short side length of the deformable region of the diaphragm with the concave portion formed on the second substrate on which the second electrode is provided, a head having a simple structure and little variation in the droplet discharge characteristics is constituted. can do. Also, by defining the short side length of the deformable area of the diaphragm with a spacer member that defines the gap length between the diaphragm and the second electrode, a head having a simple structure and less variation in droplet discharge characteristics can be obtained. Can be configured. Furthermore, by defining the short side length of the displaceable area of the diaphragm by the width of the concave portion provided on the substrate forming the pressure generating chamber and the diaphragm, a head having a simple structure and a small variation in droplet discharge characteristics is configured. can do.

In these droplet discharge heads, by forming the pressure generating chamber by anisotropic etching of the silicon substrate, a substrate having a diaphragm can be formed in a simple process. In addition, by making the length of the pressure generating chamber in the transverse direction of the diaphragm 0.7 μm or more longer than the short side length of the displaceable region of the diaphragm, the short side length of the substrate on which the pressure generating chamber is formed and the diaphragm is reduced. Alignment with the regulating member is facilitated.

[Brief description of the drawings]

FIG. 1 is an external perspective explanatory view of an inkjet head according to a first embodiment of the present invention.

FIG. 2 is an explanatory cross-sectional view of the head in the longitudinal direction of the diaphragm.

FIG. 3 is an enlarged sectional explanatory view of a main part of the head in the transverse direction of the diaphragm.

FIG. 4 is an enlarged plan view of a main part of the head.

FIG. 5 is an explanatory view illustrating a manufacturing process of the head.

FIG. 6 is an explanatory view illustrating a manufacturing process of the head.

FIG. 7 is an enlarged sectional explanatory view of a main part of an inkjet head according to a second embodiment of the present invention.

FIG. 8 is an enlarged sectional explanatory view of a main part of an inkjet head according to a third embodiment of the present invention.

FIG. 9 is an enlarged sectional explanatory view of a main part of an inkjet head according to a fourth embodiment of the present invention.

FIG. 10 is an enlarged sectional explanatory view of a main part of an inkjet head according to a fifth embodiment of the present invention.

FIG. 11 is an enlarged sectional explanatory view of a main part of a conventional inkjet head in a lateral direction of a diaphragm.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Liquid chamber substrate, 2 ... Vibration plate, 3 ... Electrode substrate, 4 ... Nozzle plate, 5 ... Nozzle, 6 ... Pressure generation chamber, 11 ... Depression, 13 ...
Second electrode, 14 gap, 51 spacer member.

Claims (6)

[Claims] 1. A nozzle for discharging droplets, a pressure generating chamber to which the nozzle communicates, a diaphragm forming a wall surface of the pressure generating chamber, providing a first electrode, or serving as a first electrode,
A second electrode opposed to the vibration plate, wherein in the droplet discharge head that discharges droplets from the nozzles by deforming the vibration plate by electrostatic force, the short side length of the deformable region of the vibration plate is A droplet discharge head, wherein the width of the pressure generating chamber in the transverse direction of the diaphragm is shorter. 2. The droplet discharge head according to claim 1, wherein a short side length of a deformable region of the diaphragm is defined by a concave portion formed in a second substrate provided with the second electrode. Droplet discharge head. 3. The droplet discharge head according to claim 1, wherein a short side length of a deformable region of the diaphragm is defined by a spacer member that defines a gap length between the diaphragm and the second electrode. A droplet discharge head characterized in that: 4. The droplet discharge head according to claim 1, wherein a width of a concave portion provided in a substrate forming the pressure generating chamber and the diaphragm defines a short side length of a displaceable region of the diaphragm. A droplet discharge head. 5. The droplet discharge head according to claim 1, wherein the pressure generating chamber is formed by anisotropic etching of a silicon substrate. 6. The droplet discharge head according to claim 1, wherein a length of the pressure generating chamber in a width direction of the diaphragm is smaller than a length of a shorter side of a displaceable region of the diaphragm by 0. 7
A droplet discharge head having a length of at least μm.