JP2011058944A - Pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure sensor hardly damaged if an excess pressure is applied and easily assembled. <P>SOLUTION: Both ends of a crystal oscillator 30 are bonded to the outer circumferential edge of a recess 23a in a diaphragm 23. A second spacer 22b, a first spacer 22a and a base body 21 are provided so as to surround the crystal oscillator 30 in the described order on the lower side of a surface of the diaphragm 23 on which the recess 23a is formed. The Young's modulus of an adhesive for bonding the first spacer 22a and the base body 21 is lower than that of the adhesive for bonding the diaphragm 23 and the second spacer 22b. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a pressure sensor that senses pressure based on a change in the frequency of a piezoelectric vibrator.

  TPMS (Tire Pressure Monitoring System) that measures the internal pressure of automobile tires and issues an alarm when the pressure falls below a set air pressure has been put into practical use. As a TPMS sensor, a sensor using quartz has been proposed. For example, when a double tuning fork type quartz vibrator is used as a stress sensitive element (piezoelectric vibrator), it is axially (perpendicular to the thickness direction). Sensitivity is improved by applying tensile stress for stretching. For this reason, the sensor package (container) has been devised such as thinning a stress converting portion and a diaphragm for converting to a tensile stress that extends in the axial direction.

  As shown in FIG. 9, this type of pressure sensor includes a diaphragm 11 having a concave portion 11 a that forms a lid portion and a central portion that is recessed in a circular shape, and both ends bonded to the outer peripheral edge of the concave portion 11 a of the diaphragm 11. A rectangular crystal resonator 13 fixed through an agent 12 and a container (housing) 14 that hermetically seals the crystal resonator 13 by bonding to the diaphragm 11 through an adhesive 12. Things are known. In such a configuration, as shown in FIG. 10, when pressure is applied to the diaphragm 11 from the outside, the diaphragm 11 is recessed and the outer edge of the recess 11a is expanded outward. Along with this, the crystal resonator 13 is pulled in the longitudinal direction and is bent (receives tensile stress), whereby the frequency (frequency) of the crystal resonator 13 is changed and pressure can be sensed.

  In the pressure sensor, a small amount of adhesive 12 is applied only to a portion where the crystal resonator 13 and the diaphragm 11 are bonded together, and the crystal resonator 13 has a double-supported beam structure. In this case, since the amount of the adhesive used for the pressure sensor is reduced, the leakage of vibration energy from the crystal resonator 13 to the diaphragm 11 is small, and the sensitivity of the pressure sensor is good, but the crystal resonator 13 and the diaphragm 11 Since stress concentrates on the bonded portion, the crystal resonator 13 may be damaged when a large pressure is applied.

  The container 14 is formed by forming a cavity of the container 14 by processing (for example, etching or the like) from one side of the wafer, for example, in order to reduce manufacturing costs and manufacturing processes. For this reason, the container 14 is an integral type in which the bottom surface portion and the side wall portion are integrated, and in order to bond the container 14 and the diaphragm 11 together, the thin diaphragm 11 is fixed to the container 14 and the container 14 is fixed at the same time. In order to make the inside airtight, there is a problem that it is difficult to assemble the pressure sensor because the airtightness must be kept while performing positioning accurately.

  On the other hand, in Patent Document 1, in order to improve the airtightness of the pressure sensor and simplify the manufacturing process of the pressure sensor, the container is divided into a side wall portion and a bottom surface portion, and the bottom surface portion, the side wall portion, and the diaphragm are formed. The pressure sensors stacked with adhesives in this order are listed. However, there is no description of a structure that prevents damage to the pressure sensor when excessive pressure is applied to the pressure sensor.

JP 2008-128724 A

  The present invention has been made under such circumstances, and an object thereof is to provide a pressure sensor that is not easily damaged.

The pressure sensor according to the present invention is:
A diaphragm configured to bend by pressure from the outside;
A piezoelectric vibrator fixed to the diaphragm so as to face the diaphragm through a gap;
A base body facing the opposite side of the diaphragm with respect to the piezoelectric vibrator;
A plurality of surrounding members provided so as to be interposed between the diaphragm and the base body so as to surround the piezoelectric vibrator;
An adhesive layer for bonding between the surrounding members and between the surrounding member and the base body,
A container is constituted by the diaphragm, the enclosing member, and the base body.

“Stacked” of “a plurality of surrounding members stacked on each other” is not limited to the case of stacking in the thickness direction of the surrounding members, but also includes the case of overlapping in the radial direction of the surrounding members (see FIG. 8).
Examples of the adhesive layer include low melting point glass, resin adhesive, and inorganic adhesive. Furthermore, the adhesive layer is preferably an epoxy resin, for example.

  The present invention divides a container for storing a piezoelectric vibrator into a diaphragm, a plurality of surrounding members stacked on each other, and a base body, and an adhesive layer is provided between the surrounding members and between the surrounding member and the base body. ing. For this reason, even if an excessive pressure is applied to the pressure sensor, each adhesive layer absorbs the pressure. For example, excessive pressure is not concentrated on a part of the pressure sensor, and the pressure sensor is not easily damaged. Become.

It is a vertical side view of the pressure sensor which concerns on embodiment of this invention. It is explanatory drawing which shows the surface and back surface of the crystal oscillator used for the said pressure sensor. It is a schematic diagram which shows the inside of the said pressure sensor. It is a schematic diagram explaining the manufacturing process of the said pressure sensor. It is a schematic diagram explaining the manufacturing process of the said pressure sensor. It is a schematic diagram explaining the manufacturing process of the said pressure sensor. It is a schematic diagram explaining the manufacturing process of the said pressure sensor. It is the longitudinal cross-sectional view and cross-sectional view of the pressure sensor which concerns on other embodiment. It is a longitudinal cross-sectional view of the conventional pressure sensor. It is the figure which showed typically a mode that the pressure was applied from the exterior to the conventional pressure sensor.

  An embodiment of a pressure sensor according to the present invention will be described. As shown in FIG. 1, the pressure sensor includes a base body 21 for constituting the container 20, a spacer 22 that is a surrounding member, and a diaphragm 23 that are stacked in this order from the lower side to the upper side. Is an airtight space, and a crystal resonator 30 that is a piezoelectric vibrator is provided in the airtight space. The base body 21, the spacer 22, and the diaphragm 23 are manufactured using, for example, quartz, but a glass plate, a silicon substrate, or the like may be used.

  A circular recess 23 a that faces the surface side of the crystal unit 30 is formed on the lower surface of the diaphragm 23 that forms the lid of the container 20. The diameter of the recess 23 a is formed to be shorter than the length of the crystal unit 30 in the longitudinal direction. By forming the concave portion 23a, the thickness of the central portion of the diaphragm 23 is set to 1.4 mm, and the thickness is reduced, so that greater flexibility can be obtained. Further, the upper surface of the diaphragm 23 faces a measurement atmosphere such as an internal space of a tire provided in the vehicle, and the diaphragm 23 is deformed according to the pressure of the measurement atmosphere. That is, when the pressure of the measurement atmosphere becomes larger than the pressure in the container 23, the diaphragm 23 bends to the inside of the container.

  Both ends of the crystal resonator 30 are bonded and fixed to the outer peripheral edge portion of the concave portion 23a of the diaphragm 23 by using an adhesive 24a, and are supported by the diaphragm 23 as a double-supported beam structure. Accordingly, when the diaphragm 23 is bent by the pressure, the central portion thereof is bent and the outer peripheral edge portion of the concave portion 23a is spread outward, whereby a tensile stress acts in the length direction of the crystal resonator 30 and the crystal resonator 30 is Bend. As a bonding structure of the diaphragm 23 and the crystal unit 30, for example, direct bonding between crystals, anodic bonding, diffusion bonding using a metal thin film, bonding using a resin adhesive, or the like is used. FIG. 1 shows an example using the resin adhesive 24a.

  The crystal unit 30 is composed of, for example, an AT-cut strip-shaped crystal piece 31, and for exciting the crystal piece 31 on the front and back surfaces of the crystal piece 31 as shown in FIGS. Excitation electrodes 32a and 32b are formed. In addition, an extraction electrode 33a is formed which is drawn from the excitation electrode 32a toward the peripheral edge on one side in the length direction of the crystal piece 31, and from the excitation electrode 32b toward the peripheral edge on the other side in the length direction of the crystal piece 31. An extracted extraction electrode 33b is formed. The layout of the electrodes on the front and back surfaces of the crystal piece 31 is formed to be point-symmetric with respect to each other.

  The spacer 22 serving as the enclosing member constitutes a side wall portion of the container 20 and is composed of two layers of a first spacer 22a and a second spacer 22b in this example. The first spacer 22a is bonded to the surface of the base body 21 which is a flat bottom plate using an adhesive 24b. The second spacer 22b is joined to the upper surface of the first spacer 22a using an adhesive 24b. The spacers 22 a and 22 b are formed in a ring shape as shown in FIG. 3, and a space 25 surrounded by the spacers 22 is formed larger than the crystal resonator 30. The spacer 22 has a role for securing a space for housing the crystal unit 30 in the container 20, and the height of the storage space for the crystal unit 30 can be changed by adjusting the thickness of the spacer 22. .

  A diaphragm 23 is provided on the upper surface of the second spacer 22b, and the upper surface of the second spacer 22b and the lower surface of the diaphragm 23 are bonded together. Examples of the bonding method include bonding using low melting glass, direct bonding between crystals, anodic bonding, diffusion bonding using a metal thin film, bonding using a resin adhesive, and the like. FIG. 1 shows an example in which low melting point glass is used as the adhesive 24c.

  Further, as the adhesive 24b used for joining the spacers 22a and 22b or joining the spacer 22a and the base body 21, for example, low melting glass, resin adhesive, inorganic adhesive, or the like is used. In the case where the adhesive 24b is bonded by the diaphragm 23, the spacer 22, and the adhesive 24a, it is preferable that the elastic force is larger than that of the adhesive 24a (the Young's modulus is small) from the viewpoint of dispersing the stress applied to the diaphragm 23. . The adhesives 24a and 24b correspond to the adhesive layers in the claims.

  As shown in FIG. 3, the lower surface of the diaphragm 23 is provided with two conductive paths 34a and 34b extending from the periphery of the diaphragm 23 toward the periphery of the recess 23a. The conductive paths 34a and 34b are formed of a metal film that is a laminated film of, for example, Cr and Au. The conductive path 34a is connected to the extraction electrode 33a by silver paste, and is further connected to the excitation electrode 32a via the extraction electrode 33a. The conductive path 34b is connected to the extraction electrode 33b by the silver paste 35, and further connected to the excitation electrode 32b via the extraction electrode 33b. The other ends of the conductive paths 34a and 34b are electrically connected to a detection unit (not shown) provided outside the pressure sensor. Therefore, the quartz vibrator 30 is bent by the pressure sensor from the outside, and the change in the vibration frequency of the quartz vibrator 30 is detected by the external detector through the electrodes.

  Next, an example of the manufacturing method of the pressure sensor according to the present invention will be described. First, a wafer 41 for the diaphragm 23, a wafer 42 for the crystal oscillator 30, a wafer 43 for the first spacer 22a, a wafer 44 for the second spacer 22b, and a wafer 45 for the base body 21 are prepared. The material of these wafers is, for example, a Z-cut quartz plate. In addition to the quartz plate, a glass plate or a silicon substrate may be used. Then, by performing mask formation and wet etching process on each wafer by a photolithography process, the outer shape of a plurality of diaphragms 23 is produced on the wafer 41 as shown in FIG. As shown in FIGS. 4C and 5A, a plurality of first spacers 22a and a first spacer 22a are formed on the wafers 43 and 44, respectively. The outer shape of the two spacers 22b is produced, and the outer shapes of the plurality of base bodies 21 are produced on the wafer 45 as shown in FIG.

  Subsequently, a conductive path is formed on the lower surface of the diaphragm 23 shown in FIG. 6A, and a lid of the container 20 is formed as shown in FIG. 6B. In addition, excitation electrodes 32 a and 32 b and extraction electrodes 33 a and 33 b are formed on the front and back surfaces of the crystal unit 30. Then, as shown in FIG. 6 (c), both ends of the upper surface of the crystal unit 30 are attached to the outer peripheral edge of the recess 23a of the diaphragm 23 using an adhesive 24a such as a low melting glass paste at a temperature of 400 ° C. to 500 ° C. Bonding is performed in the air. Next, as shown in FIG. 6D, in order to establish electrical continuity between the excitation electrodes 32a and 32b and the conductive paths 34a and 34b, a silver paste 35 is applied, and the solvent and binder in the silver paste 35 are blown off. For this reason, firing is performed at a temperature of 400 ° C. to 500 ° C. in an atmosphere containing oxygen.

  Subsequently, as shown in FIG. 7A, the diaphragm 23 and the second spacer 22b are aligned, and the lower surface of the diaphragm 23 and the upper surface of the second spacer 22b are bonded using an adhesive 24c such as an epoxy resin. For example, the epoxy resin is cured at a temperature of 100 ° C. to 200 ° C. Further, as shown in FIG. 7B, the positions of the second spacer 22b and the first spacer 22a are aligned, and the lower surface of the second spacer 22b and the upper surface of the first spacer 22a are bonded to an adhesive 24b such as an epoxy resin. The epoxy resin is cured at a temperature of 100 ° C. to 200 ° C. Thereby, the side wall part of the container 20 which consists of the 1st spacer 22a and the 2nd spacer 22b will be created.

Next, as shown in FIG. 7C, the lower surface of the first spacer 22a and the upper surface of the base body 21 are bonded to each other using an adhesive 24b, for example, epoxy resin, and the inside of the container is set to a vacuum atmosphere. The epoxy resin is cured at temperature.
After the wafers are bonded together, dicing is performed to divide the body into individual pressure sensor bodies, whereby pressure sensors are manufactured.
In addition, as a method of manufacturing the pressure sensor, the diaphragm 23, the crystal unit 30, the first spacer 22a, the second spacer 22b, and the base body 21 are diced in advance, separated into individual pieces, and the members are bonded together. To produce a pressure sensor.

  Next, the operation of the pressure sensor according to the above-described embodiment will be described. The base body side 21 of the pressure sensor is attached to a tire valve, for example. At this time, the inside of the tire is in a pressurized state (atmosphere above atmospheric pressure), and the diaphragm 23, specifically, the region where the recess 23a is formed bends inward (inner side of the container) according to the pressure. In accordance with the amount of bending, the outer edge of the recess 23a is pushed outward and the crystal resonator 30 is subjected to tensile stress in the longitudinal direction, whereby the crystal resonator 30 is bent. Due to this bending, the resonance frequency of the crystal unit 30 is changed, and the frequency signal is measured by the measurement circuit unit from the conductive paths 34a and 34b via the external conductive path and the oscillation circuit (not shown), thereby detecting the pressure.

  According to the above-described embodiment, the base body 21, the first spacer 22a, and the second spacer 22b are laminated in this order on a part of the container 20, and the adhesive 24b, for example, an epoxy resin is used for joining them. It is made using an adhesive. As the adhesive 24b, an adhesive 24c that joins the diaphragm 23 and the second spacer 22b is used with the same or small Young's modulus. Therefore, even when excessive pressure is applied to the pressure sensor from the outside, the adhesive 24b The adhesive layer made of the agent 24b absorbs part of the pressure. Therefore, it is possible to suppress damage along the deformed portion of the diaphragm 21 and damage to the bonded portion between the crystal unit 30 and the diaphragm 23.

  When the diaphragm 23 and the second spacer 22b are joined without using the adhesive 24c, the diaphragm 23 and the second spacer 22b are directly joined, so that the adhesive 24b is used for the diaphragm 23 or the second spacer 22b. It is preferable that the Young's modulus is the same or smaller than the material of the spacer 22b.

  Further, since the container 20 is prepared by dividing the diaphragm 23, the base body 21, and the spacer 22, the spacer 23 and the spacer 22 are bonded together, and then the spacer 22 is maintained while keeping the inside of the container 20 in a vacuum atmosphere. And the base body 21 can be bonded together. Accordingly, the manufacturing process of the pressure sensor is facilitated, which contributes to the reduction of work time and work cost. Furthermore, since the spacer 22 and the base body 21 can be finally bonded as described above, the range of selection of the adhesive for bonding the diaphragm 23 and the spacer 22 is widened. In addition, the spacer 22 can be processed from both surfaces of the wafer W, and a free shape can be produced. In this embodiment, the pressure sensor uses a container having a circular planar shape, but a container having a square planar shape may be used.

  Next, another embodiment of the pressure sensor according to the present invention will be described. The same components as those in the above-described embodiment are denoted by the same reference numerals, and different portions will be mainly described. In this example, as shown in FIG. 8, instead of stacking the spacers, the first spacer 122 a and the second spacer 122 b having a size that can fit in the through hole of the first spacer 122 a Provided on the surface, the inner wall surface of the first spacer 122a and the side wall surface of the second spacer 122b are joined by an adhesive 24b. The through hole of the second spacer 122b is formed larger than the crystal unit 30. Further, as described above, the lower surface of the spacer 122 and the upper surface of the base body 21 are joined by the adhesive 24b. In this embodiment, since the layer of the adhesive 24b that joins the spacers 122a and 122b and the layer of the adhesive 24b that joins the spacer 122 and the base body 21 are connected to each other, compared to the above-described embodiment. Pressure is easily distributed in the sensor. Furthermore, since the spacer itself becomes large, it becomes easy to take airtightness inside the pressure sensor.

  One feature of the present invention is a structure in which a plurality of surrounding members (in the embodiment, spacers) are stacked. However, “stacking the surrounding members” means that the surrounding members are stacked as in the embodiment of FIG. In addition to a configuration in which the layers are stacked in the thickness direction, a configuration in which the layers are stacked in the radial direction (when the diaphragm 23 is the upper surface and the base body 21 is the lower surface) is included as in the example of FIG.

Next, an evaluation test of the pressure sensor according to the present invention will be described.
Test Method The stress distribution when a pressure of 600 kPa was externally applied to the pressure sensor was measured using a three-dimensional FEM (Finite Element Method) simulator 3GA.

A conventional pressure sensor shown in FIG. 9 was used as a sample comparative example. This pressure sensor has an outer diameter of 14 mm, and the diaphragm, spacer, and base body are each set to a thickness of 0.33 mm. Further, the crystal resonator is set to have a width of 1.6 mm, a length of 8.0 mm, and a thickness of 170 μm. The adhesive for bonding the diaphragm and the container was a low melting point glass paste having a Young's modulus of 7.9 GPa, and the thickness of the adhesive was set to 50 μm after bonding.
In the example, the pressure sensor according to the present invention shown in FIG. 1 was used. The adhesive used for joining the first spacer and the second spacer and the first spacer and the base body was an epoxy resin having a Young's modulus of 1.55 GPa, and other conditions were the same as in the comparative example.

Results and Discussion In the comparative example, the stress applied to the center portion of the crystal resonator was 33.36 MPa, and the stress applied to the bonded portion of the crystal resonator and the diaphragm was 18.85 MPa. In the example, the stress applied to the central portion of the crystal resonator was 32.01 MPa, and the stress applied to the bonded portion of the crystal resonator and the diaphragm was 25.76 MPa. Therefore, in the embodiment, the stress applied to the central portion of the crystal resonator is reduced by 1.25 MPa, and the stress applied to the bonded portion of the crystal resonator is increased by 6.91 MPa. That is, in the embodiment, since the spacers and the spacer and the base body are bonded with an adhesive, a part of the pressure applied to the diaphragm is transmitted to the adhesive, and one of the stresses applied to the crystal resonator. It can be considered that the department has been relaxed. In addition, an epoxy resin was used for bonding between the spacers and between the spacer and the base body. However, if the Young's modulus is smaller than the adhesive that bonds the diaphragm and the first spacer, it seems to have a stress relieving effect. Therefore, it is not limited to an epoxy resin.

20 Container 21 Base body 22, 22a, 22b Spacer 23 Diaphragm 24a, 24b, 24c Adhesive 30 Crystal resonator 31 Crystal piece 32a, 32b Excitation electrode 34a, 34b Conductive path

Claims (3)

A diaphragm configured to bend by pressure from the outside;
A piezoelectric vibrator fixed to the diaphragm so as to face the diaphragm through a gap;
A base body facing the opposite side of the diaphragm with respect to the piezoelectric vibrator;
A plurality of surrounding members provided so as to be interposed between the diaphragm and the base body so as to surround the piezoelectric vibrator;
An adhesive layer for bonding between the surrounding members and between the surrounding member and the base body,
A pressure sensor, wherein a container is constituted by the diaphragm, the enclosing member, and a base body.   The pressure sensor according to claim 1, wherein the adhesive layer is made of low-melting glass, resin adhesive, or inorganic adhesive.   3. The pressure sensor according to claim 1, wherein a Young's modulus of the adhesive layer is equal to or smaller than a Young's modulus of a joint portion between the diaphragm and the surrounding member.

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