JP2008076075A - Absolute pressure sensor - Google Patents

Abstract

An absolute pressure sensor capable of easily measuring an absolute pressure with high accuracy and high resolution is provided.
A first concave portion is formed on one main surface, a first concave portion and a second thick portion on the other main surface, a second concave portion having a terminal portion, and a through hole penetrating both main surfaces. The first diaphragm, the second diaphragm having a third recessed portion formed on one main surface thereof, a pair of vibration beams extending in parallel, base ends connected to both ends of the vibration beam, and A double tuning fork type piezoelectric vibration element comprising a drive electrode formed on the surface of the vibration beam, and both base ends of the double tuning fork type piezoelectric vibration element are respectively the first and second flesh of the first diaphragm. The absolute pressure sensor is configured to be coupled to the thick portion and coupled so that the second recessed portion of the first diaphragm and the recessed portion of the second diaphragm face each other, and the inside of the recessed portion is evacuated.
[Selection] Figure 1

Description

  The present invention relates to a pressure sensor, and in particular, a space inside formed by a concave portion of an upper diaphragm and a concave portion of a lower base is evacuated, and an applied pressure is changed using a frequency change of a double tuning fork type piezoelectric vibration element. The absolute pressure sensor to measure.

  A pressure sensor using a phenomenon in which a frequency changes when stress is applied to a piezoelectric vibration element has been known (Non-Patent Document 1). Patent Document 1 discloses a pressure sensor in which a stress sensitive element, a swinging arm supported by a hinge at the end of a support, and a bellows are fixed to a base and the whole is housed in a container. The principle is that the pressure is transmitted to the swing arm through the bellows, is transmitted to the stress sensitive element via the hinge, the pressure is converted into a frequency change by the stress sensitive element, and the pressure is measured via the electronic circuit.

  Patent Document 2 discloses a pressure sensor as shown in FIG. 5A is a schematic plan perspective view of the pressure sensor 40, and FIG. 5B is a schematic cross-sectional view taken along QQ. The pressure sensor 40 includes an upper diaphragm 41, a lower diaphragm 42 facing the diaphragm 41, and a piezoelectric vibration element 46. The upper diaphragm 41 is circular, and a circular recess 43a is formed at the center of the lower surface in the drawing. The lower diaphragm 42 is also circular, and two support poles 44 for force transmission are provided at the center of the upper surface in the figure, and two mounting portions 45a and 45b are provided orthogonal to the two support poles 44 for force transmission, A circular recess 43b is formed around these. The recessed portions 43a and 43b are formed so as to face each other vertically. A double tuning fork type piezoelectric vibrating element with good stress sensitivity is used as the piezoelectric vibrating element 46, and both base ends of the double tuning fork type piezoelectric vibrating element 46 are mounted on the mounting portions 45a and 45b and fixed with an adhesive.

  When the stress is applied to the double tuning fork type piezoelectric vibration element 46, the relationship between the stress and the frequency change is shown in the cross-sectional views (a), (b), (c) of FIG. This is explained using the difference-frequency characteristic. If the pressure applied to the lower diaphragm 42 is P1, and the pressure applied to the double tuning fork type piezoelectric vibration element 46 is P2, the state of FIG. 6A is a state where the pressure P1 and the pressure P2 are equal. The resonance frequency of the piezoelectric vibration element 46 is f0. FIG. 6B shows a state in which the pressure P1 applied to the lower diaphragm 42 is larger than P2, and an extension stress is applied to the double tuning fork type piezoelectric vibration element 46, and the resonance frequency becomes higher than f0 as shown by a straight line in FIG. On the other hand, when the pressure P2 applied to the double tuning fork type piezoelectric vibration element 46 becomes larger than the pressure P1 applied to the lower diaphragm 42, compressive stress is applied to the double tuning fork type piezoelectric vibration element 46, and the frequency becomes lower than f0. That is, it is disclosed that the pressure difference (P1-P2) and the frequency change amount are in a very good proportional relationship and show linearity as shown in FIG.

Patent Document 3 discloses an electrode structure of a double tuning fork type piezoelectric vibration element. As shown in FIG. 8A, the double tuning fork type piezoelectric vibrating element 50 is a piezoelectric vibrating element configured such that the free ends of two tuning fork type piezoelectric vibrating elements are coupled to each other. The electrodes are arranged so as to bend and vibrate symmetrically with respect to the axis. FIG. 8B shows charges generated on the electrodes at a certain moment, and the electrodes are connected as shown in FIG. That is, by connecting the electrodes as shown in FIG. 8C, symmetrical bending vibration as shown by the broken line in FIG. 8A can be driven.
Japanese Unexamined Patent Publication No. 64-9331 JP 2004-132913 A JP-A-64-39911 Masao Kurihara, 3 others, “Crystal pressure sensor using double tuning fork vibrating element”, Toyo Communication Equipment Technical Report, Toyo Communication Equipment Co., Ltd., 1990, No. 46, p. 1-8

However, in the pressure sensor disclosed in Patent Document 1, the bellows which is a mechanical part cuts out an aluminum block to form a mold, and after nickel plating is applied to the mold, the aluminum mold is melted and removed. Therefore, there is a problem that the bellows is very expensive and the pressure sensor is expensive.
The pressure sensor disclosed in Patent Document 2 is based on the resonance frequency f0 of the double tuning fork type piezoelectric vibration element, and the stress P1 is positive with respect to the stress P2 depending on whether the frequency is higher or lower than the frequency f0. The absolute pressure can be measured by exposing the stress P2 side to a vacuum-sealed space and measuring the stress P1 side as the pressure to be measured. There is a problem that it is necessary and it takes much time to measure the absolute pressure.
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a high-precision, high-resolution, small and lightweight absolute pressure sensor that can easily measure absolute pressure at a low price. .

In order to achieve the above object, the present invention provides a high-performance, high-resolution absolute pressure sensor that is compact and lightweight, so that a base and a deformation region that forms a vacuum chamber between the base and the deformation region A diaphragm made of an elastic material that supports an outer peripheral edge of the diaphragm and has a joining region joined to the upper surface of the base, and a stress-sensitive element supported by an element mounting portion formed on the inner wall of the deformation region of the diaphragm. I did it. Specifically, a diaphragm having a first concave portion on one main surface, a first concave portion having first and second thick portions and a terminal portion on the other main surface, and one main surface A stress sensing element comprising a base formed with a recess, a pair of vibrating beams extending in parallel, a base end connected to both ends of the vibrating beam, and a drive electrode formed on the surface of the vibrating beam; And both base ends of the stress sensitive element are coupled to the first and second thick portions of the diaphragm, respectively, and the second concave portion of the diaphragm and the concave portion of the base are coupled to face each other. Then, an absolute pressure sensor in which the inside of the recessed portion was evacuated was configured.
With this configuration, not only the absolute pressure can be easily measured, but also the stress sensitive element is used, so that there is an effect that an absolute pressure sensor with high accuracy and high resolution, a small size, a light weight and a low price can be realized.

  In the absolute pressure sensor of the present invention, the base material and the diaphragm of the stress sensitive element are made of quartz, and the base is made of a glass material. With this configuration, the stress expansion element and the diaphragm have the same linear expansion coefficient, eliminating the effect on accuracy due to temperature changes, and realizing an absolute pressure sensor with high accuracy, high resolution, small size, light weight, and low cost. it can.

  In the absolute pressure sensor of the present invention, the base material of the stress sensitive element, the diaphragm and the base are both formed of quartz. With this configuration, the stress sensitive element, diaphragm, and base have the same linear expansion coefficient, so the influence on accuracy due to temperature changes is eliminated, and high accuracy, high resolution, small size, light weight, and low price absolute A pressure sensor can be realized.

Further, the absolute pressure sensor of the present invention includes metal films on the diaphragm joining region, the inner wall surface and the upper and lower peripheral edges of the through hole penetrating the joining region, terminal electrodes on both base ends of the stress sensitive element, The metal film of the diaphragm and the metal film at the periphery of the through hole penetrating the bonding region are connected to each other, and the metal films are bonded to each other by thermocompression bonding in a vacuum.
With this configuration, not only the absolute pressure can be easily measured, but also the stress sensitive element is used, so that an absolute pressure sensor with high accuracy and high resolution, small size, light weight and low cost can be realized.

In the absolute pressure sensor of the present invention, the joint region of the diaphragm and the peripheral portion of the through hole and the inner side surface of the base are coupled in vacuum using an adhesive.
If comprised in this way, joining of a diaphragm and a base will be easy, and a highly accurate, high-resolution, small-sized absolute pressure sensor can be implement | achieved at low cost.

In the absolute pressure sensor of the present invention, the joint region of the diaphragm and the peripheral portion of the through hole and the inner side surface of the base are joined in vacuum using direct joining.
With this configuration, it is possible not only to easily measure absolute absolute pressure, but also to realize an absolute pressure sensor with high accuracy, high resolution, small size, light weight and low cost.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1A and 1B are diagrams showing a configuration of an absolute pressure sensor according to the present invention. FIG. 1A is a schematic plan view, and FIG. 1B is a cross-sectional view taken along the line Q-Q.
The absolute pressure sensor 1 supports a deformation area F that forms an airtight space S (vacuum chamber) between the base 3 and the base 3, an outer peripheral edge of the deformation area F, and is joined to the upper surface of the base. And a double tuning fork type piezoelectric vibration element 5 that is a stress sensitive element supported by an element mounting portion 2A formed on the inner wall of the deformation area of the diaphragm. Is done.

  In the absolute pressure sensor 1 configured as described above, when stress is applied to the diaphragm 2, bending stress is applied to the diaphragm 2, and the double tuning fork type piezoelectric vibration element 5 connected to the diaphragm 2 receives tensile stress or compressive stress. become. When tensile stress is applied to the double tuning fork vibrator 5, the vibration frequency of the double tuning fork type piezoelectric vibration element 5 increases, and conversely, when compression stress is applied, the vibration frequency of the double tuning fork type piezoelectric vibration element 5 decreases. Therefore, the absolute pressure sensor 1 detects the absolute pressure by detecting the vibration frequency of the double tuning fork type piezoelectric vibration element 5.

を求めると、

但し Ｋ：基本波モードによる定数（＝0.0458）で表され、断面２次モーメント

より、（１）式は、次式のように変形することができる。

但し

Here, the characteristics of the double tuning fork type piezoelectric vibration element, that is, the resonance frequency when the external force F is applied will be described.
Resonance frequency when external force F is applied to two vibrating beams

Ask for

Where K: Constant in the fundamental wave mode (= 0.0458)

Therefore, the equation (1) can be modified as the following equation.

However,

の関係は力Ｆが圧縮で共振周波数

が減少し、引張りでは増加する。また応力感度

は振動ビームの

の２乗に比例する。
なお、本実施形態では応力感応素子として双音叉型圧電振動子を用いるようにしているが、これはあくまでも一例であり、引張・圧縮応力に反応する素子、例えば、他のＡＴカット圧電振動素子、ＳＡＷ素子、音叉型圧電振動素子等を用いることもできる。 From the above, when the force F acting on the double tuning fork type piezoelectric vibration element is negative in the compression direction and positive in the tension direction, the force F and the resonance frequency

The relationship is that the force F is compression and the resonance frequency

Decreases and increases with tension. Also stress sensitivity

Of the vibrating beam

Is proportional to the square of.
In this embodiment, a double tuning fork type piezoelectric vibrator is used as the stress sensitive element, but this is only an example, and an element that reacts to tensile / compressive stress, such as another AT-cut piezoelectric vibration element, A SAW element, a tuning fork type piezoelectric vibration element, or the like can also be used.

A specific configuration of the absolute pressure sensor 1 in the present embodiment is as follows.
That is, the absolute pressure sensor 1 has a first concave portion 2a formed on one main surface, and a second concave portion having first and second thick portions 2b and 2c and a terminal portion 2d on the other main surface. A diaphragm 2 having a through hole 2f penetrating the portion 2e and both main surfaces, a base 3 having a concave portion 3a formed on one main surface, a pair of vibration beams (base material) extending in parallel, A base end portion (base material) connected to both ends of the vibration beam, and a double tuning fork type piezoelectric vibration element 5 made of a drive electrode formed on the surface of the vibration beam. The base end portion is coupled to the first and second thick portions 2b and 2c of the diaphragm, respectively, and the second recessed portion 2e of the diaphragm 2 and the recessed portion 3a of the base 3 are coupled to face each other, The insides of these recesses 2e and 3a (airtight space S) are configured as a vacuum.

FIG. 2A is a plan view showing the inside of the absolute pressure sensor 1 with the lower surface of the diaphragm 2 facing upward (the upper surface is FIG. 1A). FIG. 2B is a cross-sectional view taken along Q-Q. The diaphragm 2 is formed by etching both surfaces of a quartz plate, for example, an AT-cut quartz plate, using a photolithography technique and an etching technique.
As shown in FIG. 2B, a first recessed portion 2a is formed on the lower surface of the diaphragm 2 in the drawing, and the first and second thick portions 2b and 2c and a terminal portion are formed on the upper surface of the diaphragm 2 in the drawing. Etching is performed so as to leave 2d, and the second recessed portion 2e is formed.
Further, the through-hole 2f is formed by etching from the upper and lower surfaces of the diaphragm 2. The etching speed of quartz differs depending on the crystal axis direction, and the wall surfaces of the first and second recesses 2a and 2e and the through-hole hole 2f formed by the etching are inclined surfaces.
At this time, by using an AT-cut quartz plate for the diaphragm 2, it is possible to inspect whether the thickness is appropriate from the frequency of thickness-shear vibration.

  3A and 3B are diagrams showing the configuration of the base 3, wherein FIG. 3A is a plan view and FIG. 3B is a cross-sectional view taken along the line QQ. A recess 3a is formed on one surface of the base 3 by using a photolithography technique and an etching technique. FIG. 3 shows an example in which a glass material is used, but when a quartz plate is used, the wall surface of the recessed portion becomes a slope.

2 (a), 2 (b), 3 (a), and 3 (b), the metal film 4a is formed on the peripheral edge of the surface of the diaphragm 2 where the recessed portion 2e is provided, and the through hole 2f of the diaphragm 2 is formed. A metal film 4b is attached to the inner wall surface and the upper and lower peripheral edges thereof using a technique such as vacuum deposition. Further, the metal film 3b is attached to the upper surface of the base 3, that is, the peripheral edge of the surface provided with the recessed portion 3a, and the metal film 3c is attached to the metal film 4b in the vicinity of the through hole 2f slightly inside. .
As shown in FIG. 2, both base end portions of the double tuning fork type piezoelectric vibration element 5 are placed on the thick portions 2 b and 2 c of the diaphragm 2, and a terminal electrode of one base end portion of the double tuning fork type piezoelectric vibration element 5 is placed. And the metal film 4a attached to the terminal portion 2d of the diaphragm 2 are connected by a bonding wire 6, and the terminal electrode at the other base end of the double tuning fork type piezoelectric vibration element 5 and the metal film 4b at the periphery of the through hole 2f. Are connected to each other by a ding wire 6. Then, the diaphragm 2 metal films 4 a and 4 b shown in FIG. 2 and the metal films 3 b and 3 c on the upper surface of the base 3 are bonded by thermocompression bonding in a vacuum. With this configuration, the space formed by the opposing recessed portions 2e and 3a is evacuated and the electrode films 4a and 4b are insulated from each other, so that the driving electrode of the double tuning fork type piezoelectric vibration element 5 is used. It becomes.

FIG. 4A is a perspective view showing a configuration of a double tuning fork type piezoelectric vibration element (stress sensitive element) 10 used in the absolute pressure sensor 1 of the present invention. The double tuning fork type piezoelectric vibrating element 10 includes a pair of vibrating beams (base materials) 10a and 10b extending in parallel, base end portions (base materials) 10c and 10d connected to both ends of the vibrating beams 10a and 10b, and vibrations. It consists of drive electrodes 13a-18b and terminal electrodes 11, 12 formed on the surface of the beam. Further, sectional views of the drive electrodes 13a to 18b viewed from B, C, and D in FIG. 4A are shown in FIGS. 4B, 4C, and 4D.
The connection method of each drive electrode is performed as described above. That is, the vibrating beams 10a and 10b vibrate symmetrically with respect to the center line 10P of the double tuning fork type piezoelectric vibrating element 10, so that + charge is applied to the driving electrodes 13a, 15a and 17b at a certain moment, and the driving electrodes 13b and 15b. , 17a-charges are generated. Further, negative charges are generated on the side drive electrodes 14a, 16a, and 18b, and positive charges are generated on the drive electrodes 14b, 16b, and 18a. Accordingly, the drive electrodes that generate the electric charges having the same sign are wired so as to be connected, the electrode 13 a is connected to the terminal electrode 12, and the electrode 13 b is connected to the terminal electrode 11. In FIG. 4A, the terminal electrodes 11 and 12 are provided on the base end portion 10c. However, the terminal electrodes may be provided separately on both base end portions 10c and 10d. In the embodiment of the absolute pressure sensor shown in FIGS. 1 and 2, the latter is used.

  The example in which the base material of the double tuning fork type piezoelectric vibration element 5 and the diaphragm 2 are both formed of quartz and the base 3 is made of a glass material has been described, but this constitutes the double tuning fork type piezoelectric vibration element 5. By making the linear expansion coefficient of the base material to be fixed and the diaphragm 2 on which the double tuning fork type piezoelectric vibration element 5 is placed and fixed the same, the influence of distortion on the double tuning fork type piezoelectric vibration element 5 due to temperature change is eliminated. Because it can. Furthermore, if quartz, for example, an AT-cut quartz plate is used as the material of the base 3, the linear expansion coefficients of the diaphragm 2 and the base 3 become the same, and the distortion of the diaphragm 2 and the base 3 due to temperature change is removed. As a result, the measurement accuracy of the absolute pressure sensor is improved.

The metal films 4a and 4b are respectively opposed to the upper peripheral edge of the diaphragm 2 shown in FIG. 2, the inner wall surface of the through hole 2f, and the upper and lower peripheral edges thereof, and the upper peripheral edge of the base 3 and the through hole 2f. Although it has been described that the metal films 3b and 3c are formed at the positions using a technique such as vacuum deposition, a metal such as gold (Au) or indium can be used as the metal film. In addition, the diaphragm 2 and the base 3 are joined by joining the opposite recessed portions 2e and 3a using an anodic joining apparatus which is a well-known direct joining or a kind of direct joining, and facing the through hole 2f part. The space formed by the recessed portions 2e and 3a can be evacuated by joining a part of the three.
Further, the diaphragm 2 and the through-hole 2f can be joined to the base 3 by curing the adhesive in a vacuum, and the opposing concave portions 2e and 3a can be evacuated. Moreover, joining of the said diaphragm 2 and the base 3 can be performed using low melting glass.

  A terminal electrode that facilitates connection to the outside may be formed at the end of the diaphragm 2 and the base 3. The terminal electrode can be formed by metallizing the end portions of the diaphragm 2 and the base 3 as used in a ceramic package.

It is the schematic which showed the structure of the absolute pressure sensor which concerns on this invention, (a) is a top view, (b) is sectional drawing. (A) is the top view which turned the diaphragm upside down, (b) is sectional drawing. (A) is a top view of the base 3, (b) is sectional drawing. (A) is a perspective view of a double tuning fork type piezoelectric vibration element, (b)-(d) is a sectional view in BD. It is a figure which shows the structure of the conventional pressure sensor, (a) is a top view, (b) is sectional drawing. In the state where pressures P2 and P1 are applied from above and below the double tuning fork type piezoelectric vibration element, (a) shows a state when P1 = P2, and (b) shows a state when P1> P2. The figure which showed the state in case of P1 <P. The relationship figure of a pressure difference and frequency variation. (A) is a figure which shows the vibration mode of a double tuning fork type piezoelectric vibration element, (b) is the figure which showed the electric charge which generate | occur | produces on an electrode at a certain moment, (c) is the connection figure of each electrode.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Absolute pressure sensor, 2 Diaphragm, 2a, 2e, 3a Recessed part, 2b, 2c Thick part, 2d Terminal part, 2f Through hole, 3 Base, 3b, 3c, 4a, 4b Electrode film, 5 Double tuning fork type piezoelectric Vibration element, 6 bonding wire, 10 double tuning fork type piezoelectric vibration element, 10a, 10b vibration beam, 10c, 10 base end, 10P center line, 11, 12 terminal electrode, 13a-18b drive electrode,

Claims (6)

  A diaphragm made of an elastic material having a base and a deformation region that forms a vacuum chamber between the base, a support region that supports an outer peripheral edge of the deformation region and is joined to the upper surface of the base; and An absolute pressure sensor comprising: a stress sensitive element supported by an element mounting portion formed on an inner wall of a deformation area of the diaphragm.   2. The absolute pressure sensor according to claim 1, wherein the base material of the stress sensitive element and the diaphragm are formed of quartz, and the base is formed of a glass material.   The absolute pressure sensor according to claim 1, wherein the base material of the stress sensitive element, the diaphragm and the base are both formed of quartz. A metal film is provided on each of the bonding area of the diaphragm and the inner wall surface and upper and lower peripheral edges of the through hole that penetrates the bonding area,
The terminal electrodes at both base ends of the stress sensitive element and the metal film of the diaphragm and the metal film at the periphery of the through hole penetrating the bonding region are connected to each other, and the metal films are vacuum-bonded to each other. The absolute pressure sensor according to any one of claims 1 to 3, wherein the absolute pressure sensor is bonded by thermocompression bonding.   The bonding region of the diaphragm and the peripheral portion of the through hole and the inner side surface of the base are bonded in an adhesive using a vacuum in any one of claims 1 to 3. Absolute pressure sensor.   The absolute region according to any one of claims 1 to 4, wherein the joining region of the diaphragm and the peripheral portion of the through hole and the inner side surface of the base are joined in vacuum using direct joining. Pressure sensor.

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