JP5217163B2 - Pressure sensor - Google Patents

Description

  The present invention relates to an improvement in a pressure sensor used to measure the pressure of a fluid, and in particular, a thin-walled portion (diaphragm) is bent so as to bend and deform quickly at a low pressure stage while gradually bending at a high pressure state. It is related with the pressure sensor which improved the linearity of the pressure sensitivity characteristic by comprising.

2. Description of the Related Art Conventionally, a tire pressure monitoring system that detects an air pressure of a tire equipped in a vehicle such as an automobile by a pressure sensor and issues a warning when an abnormality occurs is known.
As an air pressure sensor that is mounted in rubber tires of automobiles and the like and measures air pressure, Japanese Patent Laid-Open No. 2001-174357 discloses a ceramic diaphragm and a ceramic base joined to each other, and a static in a gap formed between the two. A technique for converting a capacitance change into a pressure is disclosed. However, an air pressure sensor using ceramics as a detection piece has a problem in terms of detection accuracy and is desired to be improved.
As an air pressure sensor not having such a problem, a touch mode capacitive pressure sensor using a detection piece made of silicon (Si) as shown in FIG. This pressure sensor has a configuration in which a detection piece 110 made of silicon is assembled on a bottom plate 100 formed by sequentially laminating a lower electrode film 102, a dielectric thin film 103, and an electrode film 104 on a glass plate 101 as a base. ing. This pressure sensor utilizes a change in capacitance that occurs when the thin portion (diaphragm) 110a of the detection piece 110 is deformed by pressure and directly contacts the dielectric thin film 103 for pressure detection. This type of air pressure sensor is disclosed in, for example, IEEJ Transactions 2003 Vol. No. 1233-E “Touch Mode Capacitive Pressure Sensor for Tire Pressure Monitoring System”.
In the air pressure sensor using the detection piece made of silicon, not only the thickness of the diaphragm 110a of the silicon wafer needs to be thinned by etching to about 3 μm, but also between the diaphragm 110a and the dielectric thin film 103. It is necessary to set the gap to a minimum dimension of about 3 μm. However, when etching silicon, it is difficult to accurately control the thickness, and it is difficult to ensure high accuracy at such a minute dimension level. As a result, manufacturing variation increases.
In addition, the silicon material has a problem in the reproducibility of the elastic deformation due to the physical properties of its crystal structure.
With respect to this problem, as disclosed in Japanese Utility Model Laid-Open No. 63-175833, a pressure sensor using a detection piece made of silicon is used by using a quartz crystal having physical properties more stable than silicon as the detection piece of the pressure sensor. It is possible to eliminate the poor reproducibility in elastic deformation, which was a drawback of the above.

However, in order to obtain sensitive sensor sensitivity, the above conventional pressure sensors all have the entire diaphragm configured in a uniform parallel plate shape. In particular, in the touch mode type pressure sensor, the diaphragm suddenly greatly deforms and deforms at a specific pressure value and comes into contact with the upper surface of the base, so that when the pressure continues to increase, the movable range remaining on the diaphragm is small. As a result, there is a problem that the pressure range in which sensor characteristics with excellent linearity can be obtained is limited to a narrow range (low pressure range).
7 (a) and 7 (b) are cross-sectional views for explaining the operation of a touch mode type pressure sensor having a uniform diaphragm thickness. This pressure sensor is formed on a base 101 made of an insulating material. The detection piece 110 is assembled on the bottom plate 100 in which the electrode film 102 and the dielectric film 103 are sequentially laminated. An upper electrode 111 is formed on the lower surface of the diaphragm 110a of the detection piece 110, and the upper electrode 111 is disposed opposite to the dielectric film 103 with a predetermined minute gap.
FIG. 7A shows a measurement start state in which the diaphragm 110a is deformed downward and the lower surface of the center part contacts the upper surface of the bottom plate. This is a state in which the waist of the diaphragm 110a starts to be broken. Since the amount of bending beyond this is substantially determined only by the rigidity of the joint structure between the diaphragm 110a and the base 101, the diaphragm is in a state where it is difficult to bend toward the bottom plate beyond the state of (a). Therefore, even when a slightly higher pressure is applied in the state (a), the diaphragm is greatly deformed and shifts to the state (b). However, since the state of (b) is already near the limit of the range in which the diaphragm can bend, the amount of deformation of the diaphragm 110a is extremely limited due to the influence of the rigidity of the joint between the detection piece and the bottom plate. It becomes a range. For this reason, the conventional pressure sensor shown in the figure has a very narrow measurable pressure range.
Therefore, when applying such a pressure sensor with a narrow measurable pressure range to an automobile tire, it is necessary to prepare a pressure sensor with optimum sensitivity for each tire having a different standard air pressure. Therefore, it is necessary to manufacture a pressure sensor, which causes an increase in cost.
JP 2001-174357 A Japanese Utility Model Publication No. 63-175833 Japanese Patent Laid-Open No. 06-021740 IEEJ Transactions 2003, Vol. 123-E “Touch Mode Capacitive Pressure Sensor for Tire Pressure Monitoring System”

  The present invention has been made in view of the above, and the linearity of the pressure sensitivity characteristic can be obtained by configuring the diaphragm so that it bends and deforms quickly when the pressure to be measured is small, while gradually deforming when the pressure is high. An object of the present invention is to provide a pressure sensor that can be measured with high sensitivity from a low pressure to a high pressure with a single type of pressure sensor.

In order to solve the above problems, the present invention provides a base and a diaphragm that is displaced according to a change in pressure and that faces the base so that the direction of displacement intersects the surface of the base. A touch mode capacitive pressure sensor that integrally surrounds the outer periphery of the diaphragm and that is fixed to the base, wherein the diaphragm and the base are in contact with each other, and the diaphragm has a cross-section A first portion in which the thickness of the base on one end side of the frame is thicker than the thickness of the base on the other end side of the frame and extends from the root on the one end side toward the other end side And a second portion that extends from the first portion toward the other end side and is thinner than the first portion.
The present invention is characterized in that the first portion changes so as to decrease in thickness as it extends from the base on the one end side toward the other end side.
The present invention is characterized in that the thickness of the first portion gradually decreases as it extends from the base on the one end side toward the other end side.
The present invention is characterized in that the first portion has at least one step portion.
The present invention is characterized in that the second portion has a uniform thickness.
The present invention is characterized in that the diaphragm has a flat surface on the side facing the surface of the base.
The present invention is characterized in that an airtight space is provided between the diaphragm and the base.

The present invention is characterized in that the frame is thicker than a base of the first portion.
The present invention is characterized in that the stepped portion is formed by adding a metal layer on a base material of a diaphragm.
The present invention is characterized in that it is formed by adding a metal layer on a base material of a diaphragm.
The present invention is characterized in that the base and the diaphragm are made of a piezoelectric crystal material.
In the present invention, the diaphragm comprises a quartz plate, and the normal to the principal surface of the quartz plate forms an angle other than 0 ° with respect to the quartz crystal axis Z. The diaphragm is formed by wet etching the quartz plate. It is obtained by processing thinly.
The present invention is characterized in that the piezoelectric crystal material constituting the diaphragm has a thickness-slip mode.
The present invention is a piezoelectric crystal material constituting the diaphragm, you being a AT-cut quartz plate.

The present invention is not a uniform thickness across the wall thickness over the entire surface of the thin portion, or increasing the inclined, is configured to increase stepwise, the invention also refers to the thin portion of the detection piece The range of the predetermined width from one end is a uniform thickness region, and the range from the uniform thickness region to the other end of the thin portion is a thickened region thicker than the uniform thickness region, so there is a thickness difference in the thin portion as a diaphragm. A thin, uniform thickness area functions at low pressure measurement, and a thick increase area functions at high pressure measurement, improving the linearity of pressure sensor sensitivity in total. Can do.
In the present invention, first, the thickness of the thickened portion is tapered, and the thickness of the thinned portion gradually increases linearly, so that the thickness becomes a continuous inclined structure. And the linearity of the pressure sensor sensitivity can be improved. Further, since the thickened region has a stepped configuration having at least one step portion, the strength of the waist of the thin portion can be maintained during high pressure measurement, and the linearity of the pressure sensor sensitivity can be improved.
In the present invention, since the detection piece has a configuration in which the thick annular portion is integrated with the outer peripheral edge of the thin portion, the strength of the detection piece can be increased and the durability can be improved.
In the present invention, the thin part of the detection piece has a flat surface on one side and an inclined surface or a stepped shape on the other surface. A space can be formed, and the performance of the pressure sensor can be stabilized.
In the present invention, the detection piece and the base are made of the same type of piezoelectric crystal material, and the crystal axis of the detection piece and the crystal axis of the base are made to coincide with each other. And the influence of thermal distortion can be avoided.

In the present invention, the base has a recessed portion and an outer frame surrounding the outer periphery of the recessed portion. In this case, the detection piece can be mounted using the outer frame as a spacer.
In the present invention, since the detection piece is made of a quartz material, the secular change is small and the reproducibility by mechanical deformation is high (the hysteresis is small). In addition, it is easy to strictly manage the thickness of the thin portion as a diaphragm, and a diaphragm having a uniform plate thickness with no difference in thickness of the thin portion can be obtained for each piece.
In the present invention, the radiation to the main surface of the detection piece made of quartz forms an angle other than 0 ° with respect to the crystal axis Z, and the crystal plate has a thin portion processed thinly by wet etching. The material of the detection piece for realizing the etching can be specified. Thereby, when wet etching is performed, the inclined surface can be easily formed in the thin portion.
In the present invention, since the quartz plate constituting the detection piece has a thick sliding mode, the thickness management becomes easy.
In the present invention, since the quartz plate constituting the detection piece is an AT cut quartz plate, the same effects as described above can be obtained.
In the present invention, since the pressure sensor is a touch mode capacitive pressure sensor, it can be used in an environment where a strong pressure is applied.
In the present invention, since the step portion can be formed by adding a metal layer on the thin-walled base material, the manufacturing is easy.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.
FIG. 1 is a longitudinal sectional view showing a configuration of a touch mode capacitive pressure sensor according to an embodiment of the present invention, and (a), (b) and (c) show a change state of a diaphragm.
This touch mode capacitive pressure sensor (hereinafter referred to as a pressure sensor) 1 includes a bottom plate 2, a detection piece 10 assembled on the bottom plate 2, and a small gap between the upper surface of the bottom plate 2 and the lower surface of the detection piece 10. It is schematically composed of a joining member 20 that joins the two with the airtight space S interposed.
The bottom plate 2 includes a base 3 made of an insulating material such as quartz, glass, or ceramic, and a lower electrode film 4 and a dielectric film 5 that are sequentially formed on the base 3.
The detection piece 10 is made of, for example, a quartz plate, and has a thin portion (diaphragm) 11 facing the dielectric film 5 on the lower electrode film 4 and a thick annular portion that integrally surrounds the outer periphery of the thin portion 11. 12.
An upper electrode film 13 is formed on the lower surface of the thin portion 11 so as to face the lower electrode film 4.
The pressure sensor 1 is used by being fixedly arranged in a state where it is assembled to a transponder at an appropriate position in a tire of a vehicle such as an automobile. The transponder includes an antenna coil, operates a pressure sensor with a current induced in the antenna coil by electromagnetic waves output from the vehicle-side antenna, and outputs measured pressure information to the vehicle side as electromagnetic waves. The air pressure in the tire is applied to the thin portion 11 of the pressure sensor 1, and when the pressure exceeding the pressure in the airtight space S set to the atmospheric pressure is applied, the thin portion 11 is bent and deformed.
That is, when the external pressure exceeds the pressure in the airtight space S, the upper electrode film 13 and the dielectric film 5 when the thin portion 1 is bent downward and the lower surface of the upper electrode film 13 is in contact with the dielectric film 5. It is possible to sense the external pressure by detecting the change in the contact area with the capacitance value.
When this pressure sensor 1 is incorporated in a tire, it is mainly used for monitoring a decrease state of air pressure in the tire. In order to detect in real time that the air pressure has fallen below the allowable value and promptly display a warning to the driver or the like, the linearity of the pressure sensitivity characteristic is important.
The joining member 20 also serves as an adhesive means and a spacer, and forms an airtight space S for obtaining a reference pressure between the lower surface of the thin portion 11 and the upper surface of the bottom plate 2.

The characteristic configuration of the pressure sensor 1 of the present invention is that the thickness of the thin portion 11 of the detection piece is not uniform over the entire surface, and the range of the predetermined width from one end of the thin portion 11 is a uniform thickness region 11a. The range from the thick region 11a toward the other end is a thickened region 11b in which the thickness of the thin portion is larger than the uniform thickness region. In this example, the thickened region 11b has a tapered cross-sectional shape in which the thickness gradually increases linearly.
That is, in the thickened region 11b in the pressure sensor 1 of this embodiment, the main surface on the airtight space S side is flat (parallel to the top surface of the bottom plate), and the main surface on the opposite side to the airtight space is tapered and linear. It is an inclined surface. That is, in the range from the terminal end A of the uniform thickness region 11a to the other end B of the thin-walled portion, the plate thickness gradually increases in an inclined manner. That is, in the uniform thickness region 11a, the upper and lower main surfaces are parallel, but in the thickened region 11b, the upper main surface is non-parallel to the lower main surface and extends so as to expand in a tapered shape. ing.
With such a configuration, it is possible to sufficiently maintain the linearity of the pressure sensitivity characteristic up to the limit value of the measurable pressure even in the high pressure measurement. In addition, since linear pressure detection is possible up to a saturation pressure value at which measurement is impossible, tires of different types of air pressure, for example, passenger car tires (air pressure is 2 kg / cm ² ), truck tires ( It is possible to use a pressure sensor having the same structure for an air pressure of 8 kg / cm ² .
In addition, as shown in FIG.2 (b), it is good also as a structure of the thin part 11 provided only with the thickness increase area | region 11b, without providing the uniform thickness area | region 11a. That is, the thickness may be gradually increased from one end edge to the other end edge of the thin portion in an inclined manner or increased in a stepped manner.

Next, the operation of the pressure sensor of the present invention will be described based on FIGS. 1 (a), (b) and (c). First, when the external pressure (in the tire) is equal to the pressure in the airtight space S, the thin portion 11 is not deformed as shown in (a), but when the measured pressure is low, it is shown in (b). As described above, the waist (shape retention force) of the uniform thickness region 11a of the thin portion 11 is quickly lost and bends, and comes into contact with the bottom plate upper surface (dielectric film 5).
On the other hand, the thickened region 11b of the thin wall portion has a sufficient waist and is gradually pressed against the bottom plate side as the measurement pressure increases.
In the present embodiment, since the thickness difference is provided so that the cross-sectional shape of the thickened region 11b is an inclined (tapered) shape, the measurement pressure shows a constant change after the state of FIG. In this case, the operation of the thin wall portion can be controlled more smoothly and quantitatively.
In this embodiment, a lower lead electrode (not shown) extends from the lower electrode film 4 provided on the upper surface of the base 3 toward the outer edge of the base, while an upper electrode formed on the lower surface of the thin portion 11. An upper lead electrode (not shown) is extended from 13 to the outer edge of the detection piece. It is possible to calculate the external pressure based on the change in the capacitance value C between the electrode films 4 and 13 that are energized from both the extraction electrodes and face each other through the airtight space and the dielectric film 5.
That is, the capacitance value C of the capacitor formed between the electrode films 4 and 13 is
C = ε · (S / d) (ε: dielectric constant of dielectric, S: area of electrode, d: distance between electrodes)
It is represented by
That is, when the distance d between the electrode films 4 and 13 is set narrow (wide), the capacitance value C becomes large (small). On the other hand, when the opposing area of the two opposing electrode films is increased (decreased) , the capacitance value C is increased (decreased).

When the pressure sensor 1 having the above-described configuration is arranged in the atmosphere, the airtight space S is set to an atmospheric pressure similar to the atmospheric pressure. When the external air pressure is the same as the air pressure in the airtight space S, as shown in FIG. 1A, the air pressure in the airtight space is balanced with the outside air, so that the thin portion 11 is not deformed. On the other hand, when the external air pressure becomes higher than the air pressure in the airtight space, the thin portion 11 is deformed and approaches (contacts) the dielectric film 5 as shown in FIGS. Figure 1 (b) (c), depending on the amount of external pressure, shows a state in which the contact area S varies with the thin portion 11 and the dielectric film 5, the contact area shown in FIG. 1 (b) When the capacitance values C1 and C2 at the time of S1 and the contact area S2 shown in FIG. 1C (S1 <S2) are compared,
When the contact area is S1, C1 = ε · (S1 / d),
When the contact area is S2, C2 = ε · (S2 / d).
Thus, when the external pressure becomes larger than the pressure (atmospheric pressure) of the airtight space S, the thin portion is deformed and the upper electrode film 13 comes into contact with the dielectric film 5. It is possible to sense pressure by detecting a change in the contact area with the body membrane 5 as a capacitance value.
Next, FIG. 2 (a) is a cross-sectional view showing another embodiment of the pressure sensor of the present invention. This pressure sensor 1 is a diagram in that the detection piece 10 does not have the thick annular portion 12. This is different from the first embodiment. This embodiment is effective in reducing the thickness of the pressure sensor because the maximum thickness of the detection piece 10 can be reduced.
FIG. 2B is a modification of FIG. 2A, in which the base 3 has a recessed portion 3a and an outer frame 3b surrounding the outer periphery of the recessed portion, and on the inner bottom surface of the recessed portion 3a. The lower electrode film 4 and the dielectric film 5 are stacked. A minute gap is formed between the thin portion 11 and the dielectric film 5 by supporting the bottom surface of the detection piece 10 by the upper surface of the outer frame 3b of the base. Unlike the detection piece of FIG. 2A , the detection piece 10 does not have a uniform thickness region, and the entire thin portion is a thickened region 11b.

Next, FIGS. 3A and 3B are cross-sectional views of a pressure sensor according to another embodiment of the present invention. The pressure sensor 1 includes a thickened region 11b of at least one stepped portion. 15 and has a structure in which the thickness gradually increases stepwise.
In the above configuration, the external although pressure (the tire) is not the thin portion 11 as in the case of equal to the pressure in the airtight space S shown in FIG. 3 (a) variations in the pressure measured high state As shown in FIG. 3 (b), the waist (shape retention force) of the uniform thickness region 11a of the thin wall portion 11 quickly disappears and bends, and comes into contact with the bottom plate upper surface (dielectric film 5).
On the other hand, the thickened region 11b of the thin-walled portion is thicker than the uniform-thickness region 11a and has a sufficient waist, so that it is gradually pushed toward the bottom plate as the measurement pressure increases.
In the present embodiment, since the cross-sectional shape of the thickened region 11b is set to be thicker and uniform than the uniform thickness region 11a, the measurement pressure changes constantly after the state of FIG. In this case, the operation of the thin wall portion can be controlled more smoothly and quantitatively. Therefore, highly accurate pressure measurement with few errors is possible.
Further, the pressure sensor of FIG. 4 has a stepped shape in which the thickened region 11b has a plurality of stepped portions 15a and 15b, and the thickness of the stepped portion 15b is set to be thicker than that of the stepped portion 15a. Therefore, as the measurement pressure increases after the stage in which the uniform thickness region 11a is in contact with the upper surface of the bottom plate, the operation of the thin portion can be controlled more smoothly and quantitatively.
When manufacturing the thin portion 11 having the step portions 15, 15 a and 15 b as shown in FIGS. 3 and 4, the thickness is increased by forming a metal film on the main surface of the thin portion having a uniform thickness. The region 11b may be formed.

Next, when the same kind of piezoelectric crystal material is selected as the material constituting the detection piece 10 and the base 3, the detection piece is in a state where the crystal axis of the detection piece and the crystal axis of the base are aligned. It is preferable to superimpose the base on the surface. By configuring in this way, the thermal expansion characteristics of the detection piece and the base coincide with each other, and there is an advantage of eliminating the adverse effects due to thermal distortion. Therefore, durability can be improved and performance can be stabilized.
Next, it is preferable to use a quartz material as a material constituting the detection piece 10. That is, the following advantages can be obtained by using quartz instead of the conventionally used silicon as the material of the detection piece 10. That is, quartz is a material that is physically stable compared to silicon, has little secular change, and has high reproducibility due to mechanical deformation (less hysteresis). Further, according to quartz, it is easy to strictly manage the thickness of the thin portion as a diaphragm, and a diaphragm having a uniform plate thickness without any difference in thickness of the thin portion can be obtained for each piece. That is, in order to process the thin portion 11 to the target thickness, first, after forming the thin portion 11 by etching the quartz plate, an electrode is attached to the thin portion 11 and energized to measure the natural frequency of the thin portion. To compare with the target frequency (target wall thickness). If the target frequency does not match, fine etching is performed until the target frequency is reached. As a result, it is possible to obtain a thin portion having a uniform thickness without a difference in thickness of the thin portion for each piece.
Note that a technique for measuring the natural frequency in order to finely adjust the thickness of the thin portion 10a of the piezoelectric material such as quartz is disclosed in, for example, Japanese Patent Laid-Open No. 06-021740. It is well known as a processing technology for thin plate piezoelectric vibrators, and this technology can be applied as it is.
As a quartz material to be used, a material having a thick sliding mode, for example, an AT cut quartz plate is preferable.

Next, when manufacturing a detection piece having a thin portion as shown in the above embodiments, a method by wet etching is preferable. Manufacture is also possible by dry etching methods such as gas etching, but wet etching is effective in consideration of productivity. In this case, it is preferable to use a material having anisotropy with respect to the etching rate by wet etching. As the material having such anisotropy, it is preferable to use a quartz material, particularly an AT-cut quartz plate. That is, quartz is a material that is stable with respect to temperature changes, but has anisotropy with respect to the etching rate by wet etching, so that the uniform thickness region 11a as shown in FIGS. The thin part 11 provided with the thickened region 11b can be easily manufactured.
In particular, when the angle θ formed between the normal line of the crystal plate surface and the Z axis of the crystal crystal is θ ≠ 0 °, there is an advantage that an inclined surface can be easily formed on the etched surface due to anisotropy. Yes, a desired inclined surface can be obtained.
That is, when the detection piece 10 is formed of a quartz plate, it is preferable that the ray with respect to the main surface of the detection piece forms an angle other than 0 ° with respect to the quartz crystal axis Z.
Furthermore, when the detection piece is made of a material having a thick sliding mode such as an AT-cut quartz plate, it is possible to monitor the thickness in terms of frequency in addition to the advantage due to anisotropy. Therefore, the thin portion can be processed with high accuracy.
Further, when the thickened region 11b whose thickness is gradually increased by etching is formed, as shown in FIG. 1, only the center portion of the upper surface of the detection piece is etched to form a recessed portion, and the lower surface is kept flat. And it is preferable to assemble | attach so that a flat lower surface may be made to oppose the upper surface of the baseplate 2. As shown in FIG. By doing so, the gap of the airtight space S is made uniform, so that the measurement accuracy can be improved.
When processing the detection piece having the structure shown in FIGS. 1, 2, and 3 by gas etching, the etching time of each part is varied by shifting the position of the mask covering the etching surface. There is a need to do.

Next, FIGS. 5A and 5B show the conventional touch mode type pressure sensor using a detection piece made of silicon having a thin portion with a uniform thickness and the detection piece made of an AT cut crystal in FIG. It is a figure which compares the pressure-capacitance characteristic of the touch mode type pressure sensor of this invention shown. All of the pressure sensors are the same in that they are saturated when the capacitance reaches 80 pF. However, the pressure sensor of the present invention has excellent linearity of pressure sensitivity in the process until reaching the saturation state, and the higher pressure side. It has the potential to measure pressure up to. The pressure sensor of the conventional example reaches a state close to saturation when the measured pressure reaches 5 kg / cm ² , whereas the pressure sensor of the present invention maintains linearity until it reaches 10 kg / cm ^2. Yes.
Therefore, in the present invention, the same pressure sensor can be shared by tires having different air pressures. That is, it is not necessary to manufacture and apply different pressure sensors for tires having different air pressures.
The pressure sensor of the present invention can be applied to general pressure measurement of fluids in addition to measuring a pressure change of a gas in a closed space such as a tire.

(A) (b) And (c) is a longitudinal cross-sectional view which shows the structure of the touch mode capacitive pressure sensor which concerns on one Embodiment of this invention. (A) is sectional drawing which shows other embodiment of the pressure sensor of this invention, (b) is explanatory drawing of the deformation | transformation embodiment. (A) and (b) are sectional drawings of a pressure sensor concerning other embodiments of the present invention. Sectional drawing of the pressure sensor which concerns on other embodiment of this invention. (A) and (b) are the figures which compare the pressure-capacitance characteristic of the conventional touch mode type pressure sensor and the touch mode type pressure sensor of this invention. Explanatory drawing of a prior art example. (A) (b) is sectional drawing explaining operation | movement of the touch mode type pressure sensor of the type with the uniform thickness of a diaphragm.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pressure sensor, 2 Bottom plate, 3 Bases, 4 Lower electrode film, 5 Dielectric film, 10 Detection piece, 11 Thin part (diaphragm), 11a Uniform thickness area, 11b Thickening area, 12 Thick annular part, 13 Upper part Electrode film, 15, 15a, 15b Stepped portion, S airtight space, 20 bonding member

Claims (13)

The base,
A diaphragm that is displaced in accordance with a change in pressure and that faces the base so that the direction of displacement intersects the surface of the base;
A frame that integrally surrounds the outer periphery of the diaphragm and is fixed to the base;
With
A touch mode capacitive pressure sensor in which the diaphragm and the base come into contact;
The diaphragm has a cross-sectional shape in which the base at one end of the frame is thicker than the base at the other end of the frame, and extends from the base at the one end toward the other end. And a second part extending from the first part toward the other end and having a thickness smaller than that of the first part. .   2. The pressure sensor according to claim 1, wherein the first portion is configured to change in thickness so as to extend from the base on the one end side toward the other end side. .   3. The pressure sensor according to claim 2, wherein the first portion gradually decreases in thickness as it extends from the base on the one end side toward the other end side.   The pressure sensor according to claim 2, wherein the first portion has at least one step portion.   The pressure sensor according to claim 1, wherein the second portion has a uniform thickness.   The pressure sensor according to any one of claims 1 to 5, wherein the diaphragm has a flat surface on a side facing the surface of the base.   The pressure sensor according to any one of claims 1 to 6, wherein a space between the diaphragm and the base is an airtight space.   The pressure sensor according to any one of claims 1 to 7, wherein the frame is thicker than a base of the first portion. The pressure sensor according to claim 4 , wherein the stepped portion is formed by adding a metal layer on the base material of the diaphragm.   The pressure sensor according to claim 1, wherein the base and the diaphragm are made of a piezoelectric crystal material.   The diaphragm is made of a quartz plate, and the normal to the principal surface of the quartz plate forms an angle other than 0 ° with respect to the quartz crystal axis Z, and the diaphragm is thinly processed by wet etching. The pressure sensor according to claim 10, obtained by:   The pressure sensor according to claim 10 or 11, wherein the piezoelectric crystal material constituting the diaphragm has a thickness-slip mode.   The pressure sensor according to claim 11 or 12, wherein the piezoelectric crystal material constituting the diaphragm is an AT-cut quartz plate.

Images