JP2007225344A - Pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-precision pressure sensor of static capacitance type excellent in linearity of pressure-capacitance performance. <P>SOLUTION: The pressure sensor 1 is provided with a capacitor constituted of the first electrode 7 formed on the bottom surface of diaphragm 4 of the upper substrate, the second electrode 9 formed on the top surface of the lower substrate and coated with the dielectric film 10 in the vacuum chamber 18 demarcated by airtightly joining the upper substrate 2 of AT cut crystal plate and the lower substrate 3 of glass material. The pressure is measured by the static capacitance varying by the static capacitance caused by contacting the first electrode and the dielectric film by the external pressure. By providing the second electrode in the area provided with the recess 12 on the top surface of the lower substrate, the contact area between the first electrode and the dielectric film is linearly increased regarding the pressure, consequently the linearity of the pressure-capacitance performance is improved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pressure sensor that measures pressure using a change in capacitance corresponding to the amount of diaphragm deflection caused by pressure, and more particularly to a capacitive pressure sensor called a touch mode type.

  Conventionally, a capacitance type pressure sensor is known in which a diaphragm deformed by an applied pressure and a fixed electrode are arranged to face each other with a narrow gap, and the pressure is measured from a change in capacitance between the diaphragm and the electrode. Yes. In particular, the capacitive pressure sensor of the touch mode type exhibits excellent linearity and high pressure resistance in the output characteristics of the capacitance with respect to the applied pressure, so that it can be used for various applications such as automobile tire air pressure sensors. Use is proposed.

  Generally, a touch mode type pressure sensor is formed by forming a diaphragm on a silicon substrate and doping it with impurities such as boron to form a movable electrode, and forming a fixed electrode on the glass substrate on the glass substrate, and a dielectric film thereon And the gap between the diaphragm and the dielectric film is sealed in a vacuum (see, for example, Patent Documents 1 and 2). In addition, by forming a diaphragm on the quartz substrate, the thickness can be controlled with high precision, and the pressure that eliminates the poor detection accuracy and poor repeatability of elastic deformation in silicon diaphragms. Sensors are known (see, for example, Patent Document 3).

  FIG. 12 shows a change in capacitance with applied pressure in a conventional touch mode type pressure sensor. In the non-contact area A before the diaphragm contacts the dielectric film, the capacitance hardly changes. In the initial contact region B where the diaphragm starts to contact the dielectric film at the pressure P0, the capacitance increases rapidly. Thereafter, in the region C between the pressures P1 and P2, the capacitance changes approximately linearly with respect to the pressure. When the pressure P2 is exceeded, the capacitance saturates and does not increase any further. In general, the linear region C is used as a measurable pressure range. The linearity of the output characteristics is related to the shape of the diaphragm, and it is said that the thickness of the diaphragm and the width of the gap need to be optimized (see, for example, Non-Patent Document 1).

  Various pressure sensors that improve the linearity of output characteristics by the planar shape of the electrodes are known. For example, in order to widen the linear region of the capacitance with respect to the pressure and widen the measurement range, the electrode formed on the glass substrate has a shape in which the longitudinal dimension gradually increases from the center in the width direction to the width direction, and the diaphragm There is a pressure sensor in which the rate of increase of the area in contact with the electrode is constant with respect to the pressure increase (see, for example, Patent Document 4). Further, there is a pressure sensor (see, for example, Patent Document 5) that provides a notch portion at a portion facing the initial contact region of the electrode diaphragm, reduces stray capacitance that does not contribute to measurement, and realizes high sensitivity with low capacitance. is there. Further, there is known a pressure sensor (see, for example, Patent Document 6) in which a divided region is provided in an electrode facing the diaphragm so that the electrode area of the capacitor can be changed to adjust the sensor output.

  Furthermore, a recess is formed on the surface of the base made of a conductive metal material so that the gap with the diaphragm is reduced outward from the center, and an electrode portion and an insulating layer are formed on the recess. As a result, when the diaphragm bends, the gap between the electrode and the electrode section will change stably at a constant rate of change, so that the capacitance will also change stably and stably, and the electrode contact area will be devised. However, pressure sensors that can eliminate the saturation region and widen the dynamic range have been developed (see, for example, Patent Document 7).

  In addition, a projecting portion toward the diaphragm is formed on the insulating layer covering the fixed electrode to increase the distance between the fixed electrode and the portion in contact with the insulating layer of the diaphragm, or a notch in the central portion of the fixed electrode A pressure sensor has been proposed in which the opposed area of the fixed electrode facing the diaphragm is reduced, the capacitance with respect to the measurement start pressure is lowered, and the amount of change within the measurement range is increased (for example, (See Patent Document 8).

  In addition, although it is not a touch mode type, a fixed electrode is provided on the surface of a fixed substrate that is bonded and integrated with a semiconductor substrate having a diaphragm, and the capacitance generated between the diaphragm and the fixed electrode that is displaced by external pressure is changed. A capacitance-type pressure sensor that outputs a signal based thereon is known (for example, see Patent Document 9). This pressure sensor is provided with a second chamber by forming a recess in the surface of the fixed substrate, in which air that has received pressure due to the displacement of the diaphragm escapes, and thus the viscosity of the air applied to the diaphragm and the damping effect are reduced. The effect is eliminated and accurate pressure measurement is possible.

Toshigai Yamamoto, “Touch Mode Capacitive Pressure Sensor”, Fujikura Technical Report, October 2001, No. 101, p. 71-74 Japanese National Patent Publication No. 10-509241 Japanese Patent Laid-Open No. 2002-214058 International Publication WO2005 / 003711 Pamphlet JP 2002-195903 A JP 2002-221460 A JP 2002-221461 A Japanese Patent Laying-Open No. 2005-83801 JP 2005-233877 A Japanese Patent Laid-Open No. 10-332511

  However, the above-described conventional touch mode type capacitive pressure sensor has the following problems. When the capacitance C between the movable electrode on the diaphragm side and the fixed electrode on the glass substrate side is d, the dielectric film thickness is d, the dielectric constant is ε, and the contact area between the movable electrode and the dielectric film is S. , C = ε · S / d is conventionally known. In general, the film thickness d of the dielectric film is constant, but the contact area S is proportional to the square of the distance (radius) from the center of the diaphragm bent downward to the outer edge of the contact surface. Therefore, in the pressure sensor of Patent Document 1 or the like, the change in the capacitance in the region C of FIG. 12 is not a complete straight line, but rather changes to draw an upwardly convex parabola, so that high measurement accuracy can be ensured. Have difficulty.

  Further, as described in Patent Document 5 and the like, when the fixed electrode has various irregular shapes, it is difficult to accurately align the bending position of the diaphragm and the electrode position. For this reason, the measurement accuracy may vary, and the yield may be reduced.

  In the pressure sensor described in Patent Document 7, since the base itself is a fixed electrode, it is difficult to ensure electrical insulation from the diaphragm, and thus a complicated structure may be required. Further, the measurement pressure range can be expanded by eliminating the saturation region on the high pressure side, but the measurement pressure range on the low pressure side cannot be expanded. On the low pressure side, the thickness of the insulating layer in the initial contact state is thick, so there is a possibility that the measurement sensitivity is rather lowered. Similarly, since the pressure sensor described in Patent Document 8 reduces the capacitance change on the low pressure side, it is difficult to widen the measurement pressure range on the low pressure side.

  In addition, when the linearity of the pressure-capacitance characteristics is insufficient, it is necessary to devise extra measures such as adding a compensation circuit to the output of the pressure sensor to improve this. . Even in such a case, since the necessary correction amount varies depending on the pressure, a difference occurs in the resolution of the sensor, and it is difficult to stably perform highly accurate pressure measurement.

  Therefore, the present invention has been made in view of the above-described conventional problems, and the object of the present invention is to influence the sensitivity and withstand voltage of the touch mode type capacitive pressure sensor with a relatively simple configuration. It is to improve the linearity of the pressure-capacitance characteristic without giving, and to enable high measurement accuracy stably. In particular, an object of the present invention is to improve the linearity of the pressure-capacitance characteristic on the low pressure side, and to set a wider measurable pressure range.

  According to the present invention, in order to achieve the above object, an insulating material having an upper substrate made of an insulating material having a diaphragm and a first electrode formed on the lower surface thereof, an insulating material having a second electrode and a dielectric film laminated thereon. A lower substrate, wherein the upper substrate and the lower substrate define a chamber sealed in a vacuum therebetween, and the dielectric film and the first electrode are opposed to each other with a slight gap in the chamber The lower substrate has a concave portion on the upper surface thereof, and the second electrode is formed in the region of the upper surface including the concave portion, and the diaphragm receives pressure from the outside. In order to measure the pressure by detecting the capacitance between the first electrode and the second electrode that are in contact with the dielectric film by bending, the contact area between the dielectric film and the first electrode is linear with respect to the pressure. The pressure sensor provided with the concave portion. Service is provided.

  As described above, the capacitance C of the capacitor composed of the first electrode and the second electrode with the dielectric film interposed therebetween is set such that the film thickness and the dielectric constant of the dielectric film are d and ε, When the contact area with the dielectric film is S, C = ε · S / d. The contact area S is proportional to the square of the distance (radius) from the center of the dielectric film to the outer edge of the contact surface, but is set more gently and more linearly by reducing the increase by the area of the recess. be able to. Accordingly, it is possible to effectively improve the increase in the electrostatic capacity with respect to the increase in pressure, that is, the linearity of the pressure-capacitance characteristic more effectively than before.

  In addition, since the diaphragm and the first electrode do not require any special configuration and operation, there is no risk of damaging the sensitivity and pressure resistance of the sensor, and high stability and detection accuracy can be obtained. Further, the linearity of the pressure-capacitance characteristic improves the compensation of the signal detected from the pressure sensor even if it is necessary. Therefore, there is no difference in the resolution of the sensor due to the magnitude of pressure, and pressure measurement can be performed stably and accurately over a wide measurement range. In addition, since the volume of the vacuum chamber defined by the lower substrate and the upper substrate increases by the volume of the recess, even if moisture enters the chamber from the outside, the operation of the sensor is not affected. As such, it can be stored in the recess.

  In one embodiment, the concave portion of the lower substrate is formed at the center position of the initial contact region between the first electrode and the dielectric film due to the deflection of the diaphragm. This alleviates the sudden increase in capacitance at the initial contact between the first electrode and the dielectric film with respect to the pressure acting on the diaphragm, and particularly improves the linearity of the pressure-capacitance characteristics on the low pressure side of the pressure sensor. The measurement range on the low pressure side can be expanded.

  In another embodiment, the concave portion of the lower substrate is formed to extend in the radial direction with respect to the center position of the initial contact region between the first electrode and the dielectric film due to the deflection of the diaphragm. Thereby, the linearity of the pressure-capacitance characteristic of the pressure sensor with respect to the pressure applied to the diaphragm can be improved as a whole, and the measurement range can be expanded particularly on the high pressure side.

  In one embodiment, the diaphragm has a constant thickness over the entire contact area between the first electrode and the dielectric film due to the deflection, so that the entire diaphragm can be uniformly bent in the measurement range of the pressure sensor. The operation can be made more stable.

  In another embodiment, the diaphragm includes a flat portion having a constant thickness in an initial contact region between the first electrode and the dielectric film due to the bending, and a slope portion having a thickness gradually increasing from the flat portion. Prepare. As a result, the contact area between the first electrode and the dielectric film is gradually increased with respect to the pressure acting on the diaphragm, and the linearity of the pressure-capacitance characteristic of the pressure sensor is further improved as a whole. Can be enlarged.

  Further, in some embodiments, the upper substrate is formed of an AT cut quartz plate. Quartz can be wet-etched with high precision by its crystal orientation, and the diaphragm can be easily processed to a desired uniform thickness. In particular, the AT-cut quartz plate can process the diaphragm having the flat portion and the inclined portion with high accuracy as described above by using the difference in the etching rate based on the anisotropy of the crystal structure.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
1A, 1B and 2 schematically show the structure of a first preferred embodiment of a pressure sensor according to the present invention. The pressure sensor 1 includes a rectangular upper substrate 2 and a lower substrate 3 that are each made of an insulating material and bonded together. In this embodiment, the upper substrate 2 is formed of quartz such as AT cut, and the lower substrate 3 is formed of glass material such as soda glass or pyrex glass, quartz, and ceramic. In another embodiment, the upper substrate 2 can be made of a glass material such as silicon, pyrex glass, or soda glass. When the upper substrate 2 and the lower substrate 3 are formed of different materials, it is preferable to select them so that their coefficients of thermal expansion are equal or close to each other.

  The upper substrate 2 has a rectangular diaphragm 4 as shown in FIG. The diaphragm 4 is thinned to a certain thickness as shown in FIG. 2 by, for example, wet etching the upper and lower surfaces of the upper substrate 2 to form the recesses 5 and 6. The diaphragm 4 can be formed thin or thick according to the required pressure sensitivity. In the case of the quartz crystal of this embodiment, the diaphragm 4 can be thinned to a thickness of 10 μm or less, for example. A rectangular first electrode 7 is formed on the lower surface of the diaphragm 4 as shown in FIG. Furthermore, an extraction electrode 8 is drawn out from the first electrode 7 to the outside of the lower surface of the upper substrate 2 beyond the one side of the recess 6 toward the one side.

As shown in FIG. 4A, a rectangular second electrode 9 corresponding to the first electrode 7 of the diaphragm 4 is formed on the upper surface of the lower substrate 3 at a position facing it. A dielectric film 10 having a constant thickness is stacked on the second electrode 9. The dielectric film 10 can be formed, for example, by sputtering a glass material. In addition to glass, for example, an insulating material such as SiO ₂ or ceramics can be used for the dielectric film. Further, an extraction electrode 11 is drawn out from the second electrode 9 to the outside on the upper surface of the lower substrate 3 toward the same side as the extraction electrode 8 of the first electrode 7.

  According to the present embodiment, a plurality of recesses 12 are formed on the upper surface of the lower substrate 3 in the region where the second electrode 9 is to be formed. Each recess 12 has a sector shape extending radially with respect to the center position of the diaphragm 4. The shape, size, and arrangement of the recesses 12 are set such that when the diaphragm 4 is bent by receiving pressure from the outside, the contact area between the dielectric film 10 and the first electrode increases linearly with respect to the pressure. As shown in FIG. 4B, the second electrode 9 and the dielectric film 10 are also formed continuously on the inner surface of each recess 12.

  The first and second electrodes 7 and 9 are formed by depositing and patterning a conductive metal material such as an Al film or an Al alloy, for example, by vapor deposition or sputtering. The extraction electrodes 8 and 11 are formed of, for example, a Cr / Au film or a Cr / Ni / Au film, and are similarly formed by depositing these conductive metal materials by vapor deposition or sputtering and patterning them. .

  Further, the lower substrate 3 is provided with through holes 13 and 14 at positions corresponding to the extraction electrodes 8 of the upper substrate 2 and positions corresponding to the extraction electrodes 11 of the lower substrate. The through holes 13 and 14 are each formed in a tapered shape from the lower surface to the upper surface by etching or machining the lower substrate. As shown in FIG. 1B, external electrodes 15 and 16 are formed on the lower surface of the lower substrate 3 at the peripheral edges of the through holes 13 and 14, respectively.

  As shown in FIG. 3, the lower surface of the upper substrate 2 is formed with a metal bonding portion 17 made of an electrode film having a predetermined width along the entire periphery. The upper substrate 2 and the lower substrate 3 are integrally and airtightly bonded by anodic bonding at the metal bonding portion 17. As a result, a chamber 18 consisting of a narrow gap with a constant thickness is defined between the diaphragm 4 and the lower substrate 3 inside the pressure sensor 1. In another embodiment, metal bonding portions are provided along the entire periphery on the opposing surfaces of the upper substrate and the lower substrate, respectively, and they are bonded together by thermocompression bonding or eutectic bonding in the same manner. can do.

  The through holes 13 and 14 are filled with sealing materials 19 and 20 made of a conductive material, respectively. The sealing material is filled so that the through hole is hermetically sealed in a vacuum atmosphere after the upper substrate 2 and the lower substrate 3 are joined. As a result, the chamber 18 is sealed in a vacuum, and at the same time, the extraction electrodes 8 and 11, that is, the first and second electrodes 7 and 9 and the corresponding external electrodes 15 and 16 are electrically connected to each other by the sealing materials 19 and 20. Connected. As the sealing material, for example, AuSn, AuGe, a solder material, high-temperature solder, or the like can be used. Further, it is advantageous that the inner peripheral surface of each through-hole is previously coated with a metal film because the introduction of the sealing material is facilitated.

  When the pressure sensor 1 is used, if the diaphragm 4 is bent by an external pressure, the first electrode 7 contacts the dielectric film 10 corresponding to the size. The contact area gradually increases in the region where the recess 12 is provided, and changes linearly with respect to the pressure.

  FIG. 5 shows a relationship between the pressure in the pressure sensor 1 of the present embodiment and the capacitance of the capacitor formed by the first electrode 7 and the second electrode 9 by a solid line 21. In the figure, for comparison, the relationship between the pressure and the capacitance in a conventional pressure sensor having no recess on the upper surface of the lower substrate on which the second electrode is formed is shown by a broken line 22.

  In FIG. 12, the pressure P0 is a pressure when the first electrode 7 starts to contact the dielectric film 10, and the pressure P1 is from the initial contact state, as in FIG. It is the pressure that starts the linear relationship. In this embodiment, the linear relationship ends at the pressure P3 higher than the pressure P2 of the prior art, and the saturation region D starts. From this figure, in the initial contact region B between the pressures P0 P1, this embodiment is not much different from the prior art, but in the region C between the pressures P1 P3 having a linear relationship, the present embodiment is more dependent on the prior art. It can be seen that it is larger than the region between the pressures P1 and P2. As described above, according to the present embodiment, the increase in the electrostatic capacity with respect to the increase in the pressure applied to the diaphragm, that is, the linearity of the pressure-capacitance characteristic is effectively and better improved than before. Furthermore, since the linearity range expands to the high pressure side, the measurable range of the pressure sensor can be expanded to the high pressure side than before.

  FIG. 6 shows the lower substrate 3 used in the second embodiment of the pressure sensor according to the present invention. The second embodiment differs from the first embodiment in that an additional recess 23 is provided on the upper surface of the lower substrate 3. The concave portion 23 is formed at the center of the concave portion 12 in the radial direction in FIG. 4A, that is, substantially at the center position of the diaphragm 4. The shape and dimensions of the recess 23 are set so as to avoid a sudden increase in the contact area in the initial contact between the first electrode 7 and the dielectric film 10 when the diaphragm 4 is bent by an external pressure.

  By this recess 23, the pressure sensor of the second embodiment can mitigate a rapid increase in capacitance due to a significant decrease in the contact area in the initial contact between the first electrode 7 and the dielectric film 10. Therefore, as indicated by the solid line 24 in FIG. 5, the capacitance in the initial contact region B, particularly the capacitance at the pressure P1, can be reduced as compared with the prior art. As a result, the initial contact region B can be adjusted to a straight line continuous with the region C, and the pressure range that can be measured with high accuracy can be expanded to the low pressure side.

  FIGS. 7A, 7B and 8 schematically show the structure of a third embodiment of the pressure sensor according to the present invention. As in the first embodiment, the pressure sensor 31 includes a rectangular upper substrate 32 and a lower substrate 33 each made of an insulating material. In this embodiment, the upper substrate 32 is formed of an AT-cut quartz plate, and the lower substrate 33 is formed of a glass material such as soda glass or pyrex glass, quartz, or ceramic.

  The upper substrate 32 has a rectangular diaphragm 34 as shown in FIG. As shown in FIG. 8, the diaphragm 34 includes a rectangular flat portion 34 a having a constant thickness and a rectangular inclined portion 34 b whose thickness gradually increases from the flat portion. The lower surface of the diaphragm 34 is flat as a whole, whereas the upper surface is formed such that the inclined portion 34b gradually becomes shallower from the flat portion 34a with a certain inclination. The diaphragm 34 having such a cross-sectional shape uses the etching rate difference based on the anisotropy of the crystal structure of the AT-cut quartz plate to form the recesses 35 and 36 on the upper and lower surfaces of the upper substrate 32 by wet etching. Therefore, it is possible to process with relatively easy and sufficient control. A rectangular first electrode 37 is formed on the lower surface of the diaphragm 34 as shown in FIG. Further, an extraction electrode 38 is drawn out from the first electrode 37 to the outside of the lower surface of the upper substrate 32 beyond the one side of the recess 36 toward the one side.

As shown in FIG. 10, a rectangular second electrode 39 corresponding to the first electrode 37 of the diaphragm 34 is formed on the upper surface of the lower substrate 33 at a position facing it. A dielectric film 40 having a constant thickness is stacked on the second electrode 39. The dielectric film 40 is formed by sputtering an insulating material such as a glass material, SiO ₂ or ceramics. Further, on the upper surface of the lower substrate 3, an extraction electrode 41 is drawn out from the second electrode 39 toward the same side as the extraction electrode 38 of the first electrode 37.

  In the present embodiment, a rectangular recess 42 is formed in a region where the second electrode 39 is formed on the upper surface of the lower substrate 3, and is disposed at substantially the center position of the flat portion 34 a of the diaphragm 34. The shape and dimensions of the recess 42 are set so as to avoid a sudden increase in the contact area in the initial contact between the first electrode 37 and the dielectric film 40 when the flat portion 34a of the diaphragm 34 is bent by an external pressure. By this recess 42, the pressure sensor of the third embodiment can mitigate a rapid increase in capacitance due to a significant decrease in the contact area in the initial contact between the first electrode 37 and the dielectric film 40.

  Further, the lower substrate 33 is provided with through holes 43 and 44 at positions corresponding to the extraction electrode 41 of the lower substrate and positions corresponding to the extraction electrode 38 of the upper substrate 32, respectively. The through holes 43 and 44 are formed in a tapered shape from the lower surface to the upper surface, respectively, by etching or machining the lower substrate. As shown in FIG. 7B, external electrodes 45 and 46 are formed on the lower surface of the lower substrate 3 at the opening peripheral edges of the through holes 43 and 44, respectively.

  Further, as shown in FIG. 9, a metal bonding portion 47 made of an electrode film having a predetermined width is formed on the lower surface of the upper substrate 32 along the entire periphery. Similar to the first embodiment, the upper substrate 32 and the lower substrate 33 are integrally and airtightly bonded by anodic bonding at the metal bonding portion 47. As a result, a chamber 48 having a narrow gap with a constant thickness is defined in the pressure sensor 31 between the diaphragm 34 and the lower substrate 33. The upper substrate and the lower substrate are similarly integrally and air-tightly joined by providing metal joint portions along their entire circumferences on their opposing surfaces, and thermocompression bonding or eutectic bonding. You can also. After joining the upper substrate 32 and the lower substrate 33, the through holes 43 and 44 are filled with sealing materials 49 and 50 made of a conductive material in a vacuum atmosphere, respectively, and hermetically sealed. As a result, the chamber 48 is sealed in vacuum, and at the same time, the extraction electrodes 38 and 41, that is, the first and second electrodes 37 and 39 and the corresponding external electrodes 45 and 46 are electrically connected to each other by the sealing materials 49 and 50, respectively. Connected.

  In the pressure sensor 31 of this embodiment, since the diaphragm 34 has the inclined portion 34b, the increase in the contact area after the initial contact between the first electrode 37 and the dielectric film 40 can be moderated. When an external pressure is applied to the diaphragm 34, the thin flat portion 34 a first bends downward and comes into contact with the dielectric film 40. When the external pressure increases, the inclined portion 34 b starts to bend gradually and comes into contact with the dielectric film 40. Since the inclined portion 34b increases in rigidity as it moves away from the flat portion 34a, the bending with respect to the pressure is gentle, and therefore, the dielectric film 40 and the contact area also gradually increase with respect to the pressure.

  FIG. 11 shows the relationship between the pressure in the pressure sensor 31 of the third embodiment and the capacitance of the capacitor formed by the first electrode 37 and the second electrode 39 by a solid line. In the figure, for comparison, the relationship between the pressure and the capacitance in the pressure sensor of the prior art is shown by a broken line. Further, an imaginary line shows a case where the diaphragm has a flat portion and an inclined portion but does not have a concave portion on the upper surface of the lower substrate on which the second electrode is formed.

  5, the pressure P0 is the pressure when the first electrode 37 starts to contact the dielectric film 40, and the pressure P1 is the pressure at which the linear relationship starts from the initial contact state. . When the diaphragm has a flat portion and an inclined portion as in the present embodiment, the linear relationship ends at the pressure P3 higher than the pressure P2 of the prior art, the saturation region D starts, and the pressure P1 having the linear relationship is reached. The region C between P3 is larger than the region between the pressures P1 and P2. However, even in that case, since the contact area at the initial contact between the first electrode and the dielectric film increases rapidly, the contact initial region B between the pressures P0 and P1 is not much different from the prior art.

  On the other hand, in the pressure sensor of the present embodiment, the concave portion 42 avoids a rapid increase in the contact area at the initial contact between the first electrode 37 and the dielectric film 40 in the flat portion 34a, and the electrostatic capacitance rapidly increases. Can be mitigated. Therefore, as shown by a solid line in FIG. 11, the electrostatic capacity in the initial contact region B, particularly the electrostatic capacity at the pressure P1, can be reduced as compared with the prior art. As a result, the contact initial region B can be adjusted to a linear shape continuous to the region C, and the pressure range that can be measured with high accuracy can be expanded to the low pressure side. In addition, since excellent linearity is obtained on the high pressure side in the region C, the measurable range of the pressure sensor can be expanded to both the low pressure side and the high pressure side, as in the case of the second embodiment.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention can be implemented by adding various modifications and changes to the above embodiments. For example, the shape of each of the recesses is not limited to the above embodiment, and can be variously changed. In the third embodiment, the upper surface of the lower substrate can be provided with a recess not only in the region corresponding to the flat portion of the diaphragm but also in the region corresponding to the inclined portion. Further, in each of the above embodiments, the external electrode is drawn out through the through hole provided in the lower substrate, but the same through hole can be provided in the upper substrate and the external electrode can be drawn out on the upper surface thereof.

(A) is a plan view showing a first embodiment of a pressure sensor according to the present invention, and (B) is a bottom view thereof. Sectional drawing in the II-II line of FIG. The bottom view which shows the upper side board | substrate of 1st Example. (A) The figure is a top view which shows the lower board | substrate of 1st Example, (B) The figure is the elements on larger scale of the IVB-IVB line. The diagram which shows the relationship between the pressure in 1st and 2nd Example, and an electrostatic capacitance. The top view which shows the lower board | substrate of 2nd Example of this invention. (A) is a plan view showing a third embodiment of the present invention, and (B) is a bottom view thereof. Sectional drawing in the VIII-VIII line of FIG. The bottom view which shows the upper side board | substrate of 3rd Example. The top view which shows the lower board | substrate of 3rd Example. The diagram which shows the relationship between the pressure and electrostatic capacitance in 3rd Example. The diagram which shows the relationship between the pressure and the electrostatic capacitance in the conventional electrostatic capacitance type pressure sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,31 ... Pressure sensor, 2,32 ... Upper board | substrate, 3,33 ... Lower board | substrate, 4,34 ... Diaphragm, 5, 6, 35, 36 ... Recessed part, 7, 37 ... 1st electrode, 8, 11 , 38, 41 ... take-out electrode, 9, 39 ... second electrode, 10, 40 ... dielectric film, 12, 23, 42 ... recess, 13, 14, 43, 44 ... through hole, 15, 16, 45, 46 ... external electrode, 17, 47 ... metal joint, 18, 48 ... chamber, 19, 20, 49, 50 ... sealing material, 21, 24 ... solid line, 22 ... imaginary line.

Claims (6)

An upper substrate of an insulating material having a diaphragm and a first electrode formed on a lower surface thereof; and a lower substrate of an insulating material having a second electrode and a dielectric film laminated thereon;
The lower substrate and the upper substrate define a chamber sealed in a vacuum therebetween, and the dielectric film and the first electrode are disposed to face each other with a slight gap in the chamber. , United and airtight,
The lower substrate has a recess on the upper surface, and the second electrode is formed in a region of the upper surface including the recess,
In order to detect the capacitance between the first electrode and the second electrode contacting the dielectric film by bending the diaphragm under pressure from the outside, and to measure the pressure, the dielectric film The pressure sensor is characterized in that the recess is provided so that a contact area between the first electrode and the first electrode increases linearly with respect to the pressure.   2. The pressure sensor according to claim 1, wherein the concave portion is formed at a center position of an initial contact region between the first electrode and the dielectric film due to bending of the diaphragm.   The said recessed part is formed so that it may extend in a radial direction with respect to the center position of the initial contact area | region of the said 1st electrode and said dielectric film by the bending of the said diaphragm. Pressure sensor.   4. The pressure sensor according to claim 1, wherein the diaphragm has a constant thickness over the entire contact area between the first electrode and the dielectric film due to the bending thereof. 5.   The diaphragm includes a flat portion having a constant thickness in an initial contact region between the first electrode and the dielectric film due to the bending, and an inclined portion having a thickness gradually increasing from the flat portion. The pressure sensor according to any one of claims 1 to 3, wherein The pressure sensor according to any one of claims 1 to 5, wherein the upper substrate is formed of an AT-cut quartz plate.

Images