JP6581849B2 - Micro mechanical equipment - Google Patents

Description

  The present invention relates to a micro mechanical device having a fine movable part.

  2. Description of the Related Art In recent years, MEMS (Micro Electro Mechanical System) using a micro mechanical device that performs a function by mechanical operation in switches and sensors has been regarded as important. MEMS have already been used as pressure sensors and acceleration sensors, and have become important components together with LSIs. The MEMS has a three-dimensional structure including a fine movable structure by fine processing using a thin film formation technique, a photolithography technique, and various etching techniques.

  For example, in a capacitive pressure sensor, as shown in FIGS. 5A and 5B, a thin diaphragm 501 that is displaced by pressure is disposed on a substrate 502 so as to be spaced apart and supported by a support portion 503. There is a gap between the substrate 502 and the diaphragm 501, and electrodes (not shown) are arranged facing each of the portions facing the gap to form a capacitor. The pressure of the medium to be measured is applied to the surface opposite to the surface forming the capacity of the diaphragm 501, and the portion corresponding to the gap of the diaphragm 501 is deformed by this pressure application. Corresponding to this change, the distance between the electrodes changes, and in response to this change, the capacitance between the electrodes changes to provide a sensor output. If the air gap is a vacuum, this pressure sensor can measure absolute pressure.

  Such a micro mechanical device has a problem called a pull-in phenomenon as described below. Generally, when a voltage is applied between two electrodes facing each other at a certain distance as in a capacitance sensor, an attractive force that is inversely proportional to the square of the distance is generated. For this reason, when the diaphragm 501 deformed by the application of pressure approaches a distance very close to the substrate 502, the distance is extremely short, and an attractive force due to voltage is applied, so that the diaphragm 501 is strongly attracted and reaches the bottom (pull-in). .

  Here, since the electrodes are short-circuited as soon as they reach the bottom, the attractive force due to the voltage acts, and the diaphragm 501 is detached from the substrate 502. However, immediately after the separation, the attractive force due to the voltage is applied again, so that it is strongly attracted and settles again. These separation and bottoming are repeated when the distance between the electrodes is extremely small.

  In the case of a capacitance type pressure sensor, it is necessary to apply a voltage in order to measure the capacitance, a pull-in phenomenon occurs due to the influence of the attractive force accompanying this, and as a result, the above-described bottoming and separation are repeated. The sensor output becomes unstable regardless of the pressure received by the diaphragm from the measured medium. This pull-in phenomenon is conspicuous in a MEMS sensor that is small and has a small distance between the electrodes, and further has a smooth surface of the contact portion on the substrate and the electrodes.

  Further, in the above-described micro mechanical device, there is a case where these parts are joined by contact with the substrate of the movable part such as the bottoming described above, and the movable part cannot be restored by repulsion due to elastic force (Patent Document 1). , 2, 3, 4, 5). This phenomenon is called sticking or sticking, and is a problem in micro mechanical devices.

  For example, pressure sensors that measure pressures lower than atmospheric pressure, such as the above-mentioned diaphragm vacuum gauge, are exposed to the atmosphere during transport / installation and maintenance, so excessive pressure exceeding the measurement range is often applied. Occurs. When an excessive pressure is applied in this way, the received diaphragm 501 bends greatly beyond the actual use range as shown in FIG. 5C, and a part of the diaphragm 501 contacts (bottoms) the substrate 502. End up.

  Although the above-mentioned bottoming state varies depending on the thickness of the diaphragm 501, the size of the deformation region, and the design parameters such as the material of the diaphragm 501, sticking occurs due to the bottoming especially when the deformed portion of the diaphragm is thin. . In particular, in order to suppress the pull-in phenomenon described above, sticking occurs remarkably when an electrode is not formed at the contact location. This is presumably because, in the region where the electrode is not formed for preventing the pull-in phenomenon, the materials constituting the diaphragm 501 and the substrate 502 are in direct contact with each other at the bottom.

  In the case of a pressure sensor, if sticking occurs, the diaphragm will not return even if the pressure is removed, and an output will appear as if pressure is being applied, leading to a measurement error. In particular, a micro mechanical device manufactured from a very flat substrate having a surface roughness (Rz) of 0.1 to several nm is a big problem.

  In order to prevent the sticking described above, a fine structure such as a protrusion is formed on at least one surface of the bottom so as to reduce the contact area and suppress the contact force. Specifically, fine protrusions are formed on a semiconductor such as silicon or a base material such as quartz constituting a micro mechanical device using a well-known semiconductor device manufacturing technique. For example, a projection having a size of several μm is formed by patterning using a known lithography technique and etching technique. Other techniques include a method of reducing the attractive force generated by forming a surface coating that stabilizes the surface, and a method of roughening the surface by sandblasting to form protrusions.

Japanese National Patent Publication No. 10-512675 Japanese Patent Laid-Open No. 11-340477 JP 2000-040830 A JP 2000-196106 A JP 2002-299640 A

  Although the above-described sticking countermeasure that reduces the contact area by the protrusion is effective to some extent, particularly in the case of a pressure sensor, a large stress is applied when an excessive pressure is applied, so that a small protrusion leads to the destruction of the diaphragm or the substrate. On the other hand, if the protrusion is enlarged to prevent this, the contact area is increased, and the effect of the countermeasure itself cannot be obtained. As described above, in order to prevent sticking by the protrusion, the size of the contact surface in the protrusion portion must be strictly managed, and the management becomes complicated.

  In addition, in the case of crystal materials such as sapphire and high insulating properties such as alumina ceramics that are used to provide corrosion resistance, pressure resistance, and heat resistance in accordance with the environment used, such as silicon and glass In comparison, sticking is more likely to occur. In particular, when the diaphragm has a thin structure, a protrusion having a size of about several μm is not an effective measure.

  For this reason, it is necessary to form minute irregularities of sub-μm size, but materials such as sapphire and alumina ceramics have high mechanical strength, high corrosion resistance, and chemical resistance, but silicon, glass, etc. It is harder to process than the above materials, and it is extremely difficult to perform fine processing with a size of sub-μm or less.

  There is also a technology to prevent sticking with a surface coating that stabilizes the surface. In this case, organic materials are often used for the surface coating, and the space between the diaphragm and the substrate is often used in high-temperature environments. Cannot be used in a vacuum configuration.

  As described above, conventionally, there has been a problem that it is not easy to prevent sticking in a micro mechanical device using a highly insulating base material such as sapphire used in various environments.

  The present invention has been made to solve the above-described problems, so that sticking in a micromechanical device using a highly insulating base material used in various environments can be more easily prevented. The purpose is to do.

  The micromechanical device according to the present invention includes a substrate made of an insulator, an insulating material supported on the substrate by a support unit and spaced apart from the substrate in the movable region, and is displaceable in the direction of the substrate in the movable region. A movable part made of a body, a substrate facing in the movable region and a convex part formed on one surface of the movable part, an electrode formed on each surface of the substrate facing the movable region and the movable part, and a convex part are formed At least one of an electrode non-formed portion provided with an electrode provided on at least one surface of the substrate and the movable portion facing each other in the region, and an electrode non-formed portion provided on at least one surface of the substrate and the movable portion. An antistatic layer formed on one side and connected to the formed electrode, and the antistatic layer is made of a material having a surface resistance of an antistatic level.

In the micro mechanical device, the antistatic layer may have a surface resistance of 10 ⁹ to 10 ¹⁴ Ω / □.

  In the above-described micro mechanical device, the time constant obtained by multiplying the resistance formed for the electrode connected to the antistatic layer by the capacitance formed between the electrode connected to the antistatic layer and the substrate facing the movable region and the movable It is preferable that the surface resistance of the antistatic layer is set to be in a range that is larger than the oscillation cycle of the alternating voltage applied to the two electrodes formed on the respective surfaces of the part during operation.

  In the micro mechanical device, the antistatic layer may be made of a semiconductor. The antistatic layer may be composed of at least one of titanium oxide, indium oxide, zinc oxide, tin oxide, ruthenium oxide, and zirconia oxide. The antistatic layer may be made of any one of AlN, TiN, TiC, and SiN. The antistatic layer may be formed by introducing a metal into a region where the antistatic layer is disposed. In this case, the metal may be at least one of titanium, niobium, tantalum, nickel, iron, chromium, and manganese. The antistatic layer may be composed of a metal oxide layer having a thickness on the order of atomic layers. The metal oxide layer may be made of at least one of molybdenum oxide and tungsten oxide.

  In the micro mechanical device, the insulator may be either sapphire or alumina ceramics.

  As described above, according to the present invention, it is possible to obtain an excellent effect that sticking in a micromechanical device using a highly insulating base material used in various environments can be more easily prevented.

FIG. 1A is a cross-sectional view illustrating a configuration example of a micromechanical device according to an embodiment of the present invention. FIG. 1B is a cross-sectional view showing a partial configuration example of the micromechanical device according to the embodiment of the present invention. FIG. 2 is a cross-sectional view showing a partial configuration example of another micromechanical device according to the embodiment of the present invention. FIG. 3 is a cross-sectional view showing a partial configuration example of another micro mechanical device according to the embodiment of the present invention. FIG. 4 is an explanatory diagram for explaining an operating state of the micromechanical device according to the embodiment of the present invention. FIG. 5A is a cross-sectional perspective view showing a partial configuration of the pressure sensor. FIG. 5B is a cross-sectional perspective view showing a partial configuration of the pressure sensor. FIG. 5C is a cross-sectional perspective view showing a partial configuration of the pressure sensor.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1A and 1B. FIG. 1A is a cross-sectional view illustrating a configuration example of a micromechanical device according to an embodiment of the present invention. FIG. 1B is a cross-sectional view showing a partial configuration example of the micromechanical device according to the embodiment of the present invention. FIG. 1B shows an enlarged part of FIG. 1A.

  A substrate 101 made of an insulator, and an insulator supported on the substrate 101 by the support unit 102 and spaced apart from the substrate 101 in the movable region 121 and displaceable in the direction of the substrate 101 in the movable region 121. The movable part 103 is provided. The movable portion 103 is fixed to the support portion 102 by a fixed portion around the movable region 121. For example, the support part 102 is formed integrally with the substrate 101. Note that the support portion 102 may be formed integrally with the movable portion 103 on the movable portion 103 side.

  In addition, the micro mechanical device includes a substrate 101 facing in the movable region 121 and a convex portion 104 formed on the surface 101 a of the movable portion 103 on the substrate 101 side. The convex portion 104 is, for example, a column that is circular in plan view, and has a diameter of 1 to several tens of μm. In this example, a plurality of convex portions 104 are provided, and the interval between adjacent convex portions 104 is, for example, about 0.5 mm.

  A convex portion may be formed on the surface 103 a on the movable portion 103 side of the substrate 101 and the movable portion 103 facing each other in the movable region 121. Electrodes 105 and 106 are formed on the surfaces of the substrate 101 and the movable portion 103 facing each other in the movable region 121.

  This micro mechanical device is, for example, a pressure sensor in which the movable portion 103 is a diaphragm. For example, the substrate 101 and the movable part 103 are made of sapphire. When the movable portion 103 that has received the pressure is displaced in the direction of the substrate 101, the distance between the electrode 105 and the electrode 106 in the movable region 121 changes, and the capacitance changes. The pressure received by the movable portion 103 due to this change in capacitance is measured. If the electrode formation region is vacuum, it can be used as a pressure sensor capable of measuring absolute pressure.

  In addition, this micro mechanical device includes an electrode non-formed portion 107a and an electrode non-formed portion 107b in which no electrode is formed on both surfaces of the substrate 101 and the movable portion 103 facing each other in the region where the convex portion 104 is formed. . The electrode non-formed part 107a and the electrode non-formed part 107b are, for example, circular in the same area in plan view, and the center of the electrode non-formed part 107a and the electrode non-formed part 107b is the same position in plan view. .

In addition, the micro mechanical device includes an antistatic layer 108 on the electrode non-formed portion 107 a of the substrate 101. The antistatic layer 108 is connected to the electrode 105 on the side where the antistatic layer 108 is formed. The antistatic layer 108 is made of a material having a surface resistance of an antistatic level. For example, the surface resistance of the antistatic layer 108 may be 10 ⁹ to 10 ¹⁴ Ω / □. Such materials include semiconductors such as silicon and silicon carbide. Further, the antistatic layer 108 may be made of a metal oxide such as titanium oxide, indium oxide, zinc oxide, tin oxide, ruthenium oxide, zirconia oxide or the like.

  Further, the antistatic layer 108 may be made of a carbide or nitride such as AlN, TiN, TiC, or SiN. Further, the antistatic layer 108 may be formed by introducing a metal into a region where the antistatic layer 108 is disposed. By introducing a metal into the metal addition region, the antistatic level can be achieved. Such metals include titanium, niobium, tantalum, nickel, iron, chromium, manganese and the like. For example, after the metal is deposited and heated for thermal diffusion, excess metal may be removed by etching. Another method is to introduce these ions into the substrate by ion implantation.

  The antistatic layer 108 may be composed of a metal oxide layer having a thickness on the order of atomic layers. For example, the antistatic layer 108 may be formed from a metal oxide layer having a thickness on the order of an atomic layer made of molybdenum oxide, tungsten oxide, or the like. Molybdenum oxide or tungsten oxide has a lower vapor pressure than sapphire. If the metal oxide is evaporated (sublimated) by heating this material together with the substrate 101 made of sapphire to about 900 ° C. in the same furnace, the metal oxide having a thickness on the order of the atomic layer is formed on the surface of the substrate 101. A layer can be formed.

  According to the above-described embodiment, when the movable part 103 that has received pressure is greatly bent beyond the actual use range, a part of the surface 103a of the movable part 103 settles on the upper surface of the convex part 104 of the substrate 101. In this state, since the antistatic layer 108 is formed at the contacted position and is not charged, sticking does not occur. Of course, the electrode 105 and the electrode 106 are not connected at the place of contact by bottoming, so that the phenomenon of repeating bottoming and separation does not occur.

  Here, the background to the present invention will be described. First, as described above, if electrodes are formed on the entire surface of the surface 101a of the substrate 101 and the surface 103a of the movable portion 103 facing each other in the movable region 121, they come into contact with each other at the time of bottoming, which causes a problem. In order to solve this problem, an electrode is not arranged at the contact location. However, the surface 101a of the substrate 101 and the surface 103a of the movable portion 103 are in direct contact with each other at a location where no electrode is formed.

  As described above, when contact between the substrate 101 having a large insulation resistance and the movable portion 103 is repeatedly generated, contact charging occurs and static electricity is generated on the surface. Such static electricity is accumulated every time contact is repeated because the insulation resistance of the substrate 101 and the movable portion 103 is large and the contact atmosphere does not escape in a vacuum. This occurs more frequently in absolute pressure gauges where the atmosphere in contact is a vacuum. As a result, it is considered that an electrostatic attractive force is generated between the substrate 101 and the movable portion 103 to cause sticking.

  In order to suppress the occurrence of such contact charging, it is an effective measure to reduce the contact area itself. For this reason, the convex part 104 is formed and the contact area at the time of bottoming is made small. However, in the case of an insulating material such as sapphire, as is well known, the convex portion 104 having a pattern of about several μm can be easily formed, but fine processing at the nm level is extremely difficult. Therefore, the dimension of the convex part 104 which can be easily realized is a unit of several μm.

  However, the convex portion 104 having a size of about several μm is not an effective measure against the above-described sticking caused by static electricity.

  On the other hand, an antistatic layer 108 made of a material having a small resistance value is provided at a location that contacts the bottom. Since it contacts the antistatic layer 108 at the bottom of the bottom, the charge is neutralized on the antistatic layer 108 and electrostatic attraction does not work, and sticking can be prevented.

  By the way, a material such as a metal is also a material having a small resistance value, but in this case, it is the same as the state in which the electrode is formed, and a connection between the electrode 105 and the electrode 106 may be generated. Become. In contrast, in the above-described embodiment, the antistatic layer 108 is made of a material having a surface resistance of an antistatic level, and this is connected to the electrode 105. Further, the antistatic layer 108 is provided in a region where the convex portion 104 which is a region to be contacted at the time of bottoming is provided, so that the antistatic layer 108 is in contact at the time of bottoming.

  For example, the time constant in the antistatic layer 108 may be made sufficiently larger than the period of the alternating voltage applied between the electrode 105 and the electrode 106 when the micro mechanical device is operated. With this configuration, the charge on the surface of the antistatic layer 108 can be released to the outside through the electrode 105 to which the antistatic layer 108 is connected, so that sticking can be prevented from occurring.

  Incidentally, as shown in FIG. 2, the antistatic layer 108 a may be provided on the electrode non-formed portion 107 a of the substrate 101, and the antistatic layer 108 b may be provided on the electrode non-formed portion 107 b of the movable portion 103. The antistatic layer 108 b is disposed in connection with the electrode 106. In this case, the antistatic layer 108a and the antistatic layer 108b are in contact with each other at the bottom.

  In addition, as shown in FIG. 3, on the movable portion 103 side, an electrode non-formed portion may not be provided, and an electrode 106 may be formed in a region facing the convex portion 104 of the surface 103a. In this case, the electrode 106 and the antistatic layer 108 are in contact with each other at the bottom.

  As described above, the antistatic layer 108 is obtained by multiplying the resistance R formed with respect to the electrode 105 to which the antistatic layer 108 is connected by the capacitance C formed between the antistatic layer 108 and the electrode 105. The surface resistance of the antistatic layer 108 is set so that RC is in a range (RC >> T) that is greater than the oscillation period T of the AC voltage applied during operation between the electrodes 105 and 106 facing each other in the movable region 121. It is good to be.

  The time constant in the above-described antistatic layer 108 will be described more specifically with reference to FIG. FIG. 4 is a cross-sectional view showing a part of the state in which the movable portion 103 of the micromechanical device configured as shown in FIG. Here, it is assumed that the micromechanical device is a pressure sensor in which the movable portion 103 is a diaphragm, and the measurement voltage during operation is an alternating current.

As shown in FIG. 4, it is assumed that the potential of the electrode 106 is 0 and the potential of the electrode 105 is V ₀ sin (2πft) at the moment of bottoming. The electric potential in the antistatic layer 108 on the convex portion 104 in contact with the electrode 106 is naturally zero, but if the resistance between the electrode 105 on the same surface is too small, the antistatic layer 108 also quickly becomes V ₀ sin ( 2πft), and a potential difference is generated between the electrode 106 having a potential of 0 and an electrostatic attractive force due to the voltage is generated, causing the above-described abnormality in the measured voltage.

  On the other hand, when the resistance between the antistatic layer 108 and the electrode 105 is R, and the capacitance between the antistatic layer 108 and the electrode 105 is C, the antistatic layer 108 and the electrode 105 to which an alternating current is applied are: It can be regarded as a simple primary filter (RC circuit). Therefore, if the cutoff frequency 1 / (2πRC) of the RC circuit defined with respect to the AC frequency f applied to the electrode 105 is sufficiently small, the potential on the surface of the antistatic layer 108 can follow the peripheral electrode 105. The potential remains zero and no potential difference is generated between the electrode 106 and the electrode 106. As a result, no electrostatic attractive force is generated, and the above-described abnormality in the measurement voltage can be prevented.

On the other hand, since the diffusion of charging due to static electricity generated by contact is a direct current, if the initially charged charge is Q ₀ , this charge is attenuated as Q ₀ exp (−t / RC). If the time constant RC is sufficiently smaller than the response speed of the pressure sensor, charging-induced sticking does not occur. However, in general, if the surface resistance of the antistatic layer 108 is 10 ⁹ to 10 ¹⁴ Ω / □, charging is not performed. Difficult to remove static electricity quickly. Thus, in order to avoid abnormalities due to sticking and measurement voltage, the resistance between the antistatic layer 108 and the electrode 105 on the same surface should be limited to a cutoff frequency and an upper limit to prevent charging. become.

  The effects described above are in the order of the configuration described using FIG. 3> the configuration described using FIG. 2> the configuration described using FIGS. 1A and 1B. The structure described with reference to FIG. 3 in which the antistatic layer and the electrode are in contact with each other at the bottom is most effective for the antistatic layer because the charge due to contact charging is most likely to escape. On the other hand, the structure described with reference to FIGS. 1A and 1B in which one side is an insulator at the time of bottoming is less effective by the antistatic layer.

  The electrode non-formed part may be provided on both surfaces of the substrate and the movable part facing each other in the region where the convex part is formed, or may be provided on either one. When the electrode non-formed part is provided on both, the antistatic layer may be formed on each of the electrode non-formed parts provided on both surfaces of the substrate and the movable part, and provided on either one of them. May be. Further, when the electrode non-formed part is provided on either the substrate or the movable part facing each other in the region where the convex part is formed, the antistatic layer is formed on any one of the electrode non-formed parts. Just do it.

  As described above, according to the present invention, since the antistatic layer is provided at the position where the convex portion where the substrate and the displaced movable portion come into contact is formed, the high insulation used in various environments. Sticking in a micro mechanical device using a porous substrate can be more easily prevented.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious.

  DESCRIPTION OF SYMBOLS 101 ... Board | substrate, 101a ... surface, 102 ... Support part, 103 ... Movable part, 103a ... surface, 104 ... Convex part, 105 ... Electrode, 106 ... Electrode, 107a, 107b ... Electrode non-formation part, 108 ... Antistatic layer, 121 ... A movable region.

Claims (10)

A substrate made of an insulator;
A movable portion made of an insulator supported by a support portion on the substrate and disposed apart from the substrate in a movable region, and displaceable in the direction of the substrate in the movable region;
A convex portion formed on one surface of the substrate and the movable portion facing each other in the movable region;
Electrodes formed on the surfaces of the substrate and the movable part facing each other in the movable region;
An electrode non-formed part where the electrode provided on at least one surface of the substrate and the movable part facing each other in the region where the convex part is formed; and
An antistatic layer formed on at least one of the electrode-unformed part provided on at least one surface of the substrate and the movable part, and connected to the electrode on the formed side;
The antistatic layer is made of a material having a surface resistance of an antistatic level ,
The substrate and the movable part that face each other in the movable region have a time constant obtained by multiplying a resistance formed with respect to the electrode to which the antistatic layer is connected by a capacitance formed between the electrode to which the antistatic layer is connected. The surface resistance of the antistatic layer is set so as to be in a range larger than the oscillation period of the alternating voltage applied to the two electrodes formed on the respective surfaces during operation. . The micromechanical device according to claim 1,
The surface resistance of the antistatic layer is 10 ⁹ to 10 ¹⁴ Ω / □. The micro mechanical device according to claim 1 or 2 ,
The antistatic layer is made of a semiconductor. The micro mechanical device according to claim 1 or 2 ,
The antistatic layer is composed of at least one of titanium oxide, indium oxide, zinc oxide, tin oxide, ruthenium oxide, and zirconia oxide. The micro mechanical device according to claim 1 or 2 ,
The antistatic layer is made of any one of AlN, TiN, TiC, and SiN. The micro mechanical device according to claim 1 or 2 ,
The antistatic layer is formed by introducing a metal into a region where the antistatic layer is disposed. The micro mechanical device according to claim 6 ,
The metal is at least one of titanium, niobium, tantalum, nickel, iron, chromium, and manganese. The micro mechanical device according to claim 1 or 2 ,
The antistatic layer is composed of a metal oxide layer having a thickness on the order of an atomic layer. The micromechanical device according to claim 8 ,
The metal oxide layer is composed of at least one of molybdenum oxide and tungsten oxide. In the micro mechanical device according to any one of claims 1 to 9 ,
The insulator is one of sapphire and alumina ceramics.