JP2007093213A - Pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure sensor joined integrally with an SAW chip and a base block while forming an air-tight space therebetween without using a spacer of a separate member, in the pressure sensor using the SAW chip as a pressure detecting element, and provided with the base block junction-integrated with the SAW chip via the air-tight space. <P>SOLUTION: The base block has diaphragm structure provided with a recessed part 3 in an upper face opposed to an IDT electrode, in the frequency variable type pressure sensor 1 provided with the SAW chip 10 provided with a piezoelectric substrate 11 and the IDT electrode 12 formed in an under face of the piezoelectric substrate, the base block 2 comprising an insulating material junction-integrated with the SAW chip under the condition where the air-tight space S is interposed with respect to the IDT electrode 12 in the SAW chip under face, and an extraction electrode 13 for bringing the IDT electrode of the SAW chip into continuity with an outside. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an improvement of a frequency change type pressure sensor using a SAW chip as a pressure detection element.

A surface acoustic wave element (SAW chip) has a configuration in which an IDT (interdigital transducer) electrode made up of comb-like electrode fingers is arranged on a piezoelectric substrate such as a crystal. For example, by applying a high-frequency electric field to an IDT electrode Filter characteristics are obtained by exciting a surface acoustic wave and converting the surface acoustic wave into a high-frequency electric field by a piezoelectric action.
Recently, a frequency change type pressure sensor using a SAW chip as a pressure detection element has been proposed and implemented (Patent Documents 1 to 3). This is to detect the change in the resonance frequency as a pressure change by utilizing the characteristic that the resonance frequency changes by changing the IDT electrode interval and the propagation speed of the surface acoustic wave due to the distortion of the piezoelectric substrate due to the pressure. Is.
This type of pressure sensor is suitable for detecting minute pressure changes with high accuracy. For example, this type of pressure sensor is used in a tire pressure monitoring system that detects the air pressure of a tire equipped in a vehicle such as an automobile and issues a warning when an abnormality occurs. Can be applied. This type of pressure sensor is installed in a rubber tire and measures air pressure and air pressure change.
5A and 5B are a front sectional view and a perspective view showing the configuration of a pressure sensor using a conventional SAW device. The pressure sensor 100 is mounted on a base 101 made of an insulating material such as glass. The SAW device 103 is joined and integrated through the spacer 102. The SAW device 103 has a configuration in which an IDT electrode 105 and an extraction electrode 106 are formed on a piezoelectric substrate 104 such as quartz. An airtight space (cavity) 107 is formed between the IDT electrode 105 on the lower surface of the SAW device and the upper surface of the base.
Since the pressure sensor 100 is housed in a casing (not shown) and the IDT electrode 105 formed on the surface of the SAW device 103 is exposed to the outside air through a pressure receiving port provided in the casing, the IDT electrode 105 is quickly contaminated. It becomes easy to corrode. Therefore, the deterioration of characteristics such as frequency fluctuation and deterioration of oscillation intensity becomes remarkable.
In order to cope with such a problem, as shown in FIGS. 6A and 6B, the SAW device 103 is placed on the base 101 so that the surface on which the IDT electrode 105 is formed faces the upper surface of the base 101. A type fixed via a spacer 102 has also been proposed. In this pressure sensor, since the IDT electrode 105 is sealed in the airtight space 107, the pressure sensor is not exposed to the outside air, and durability can be maintained.
However, in any of the above types, since it is necessary to use the spacer 102 as a separate substrate in order to form the hermetic space 107 for assuring free vibration of the piezoelectric substrate 104, the multilayer substrate structure must be used. This is a cause of cost increase.
JP 2005-181292 A JP-A-2005-181303 JP 2005-208031 A

  The present invention has been made in view of the above, and in a pressure sensor using a SAW chip as a pressure detection element and having a base bonded and integrated with the SAW chip through an airtight space, the cause of cost increase It is an object of the present invention to provide a pressure sensor in which an airtight space is formed between a SAW chip and a base without using a spacer which is a separate member.

In order to solve the above-mentioned problems, the invention of claim 1 is provided between a SAW chip having a piezoelectric substrate and an interdigital transducer electrode formed on the lower surface of the piezoelectric substrate, and an interdigital transducer electrode on the lower surface of the SAW chip. In a frequency change type pressure sensor comprising: a base integrally joined to the SAW chip with an airtight space interposed therebetween; and an extraction electrode for electrically connecting the interdigital transducer electrode of the SAW chip and the outside. The base has a diaphragm structure having a concave portion on an upper surface facing the interdigital transducer electrode.
Since the concave portion is formed in the portion where the base faces the IDT electrode so as to ensure the airtight space, the pressure sensor can be constructed without using any special spacer.
According to a second aspect of the present invention, in the first aspect, the SAW chip has a diaphragm structure having a recess in a region corresponding to the interdigital transducer electrode on the upper surface of the piezoelectric substrate. And
While the piezoelectric substrate is a thick plate having excellent mechanical strength, a recess is formed on the upper surface of the piezoelectric substrate in order to secure a thin portion for forming the IDT electrode, while ensuring a desired resonance frequency. Mechanical strength can be secured.
A third aspect of the present invention is characterized in that, in the first or second aspect, the extraction electrode is exposed on the upper surface of the SAW chip.
In this configuration, a lead electrode is provided on the upper surface of the pressure sensor to ensure supply of current to the pressure sensor and output of a signal from the pressure sensor.
According to a fourth aspect of the present invention, in the first or second aspect, the extraction electrode is exposed on the bottom surface of the base.
In this configuration, a lead electrode for securing current supply to the pressure sensor and output of a signal from the pressure sensor is provided at the bottom of the pressure sensor.
According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the piezoelectric substrate constituting the SAW chip is made of quartz.

As described above, according to the present invention, in the pressure sensor in which the SAW chip is used as the pressure detection element and the base is joined and integrated through the SAW chip and the airtight space, the base is on the surface facing the IDT electrode. Since an airtight space can be secured by forming a recessed portion, the airtight space is formed between the SAW chip and the base without using a spacer, which is another member that causes an increase in cost, and the two are joined and integrated. An integrated pressure sensor can be provided.
In addition, while making the piezoelectric substrate a thick plate with excellent mechanical strength, a recess is formed on the upper surface of the piezoelectric substrate in order to secure a thin portion for forming the IDT electrode, so a desired resonance frequency is secured. However, mechanical strength can be secured.

Hereinafter, a pressure sensor of the present invention will be described based on an embodiment shown in the accompanying drawings.
1A and 1B are a longitudinal sectional view and an external perspective view of a pressure sensor according to the first embodiment of the present invention.
The frequency change type pressure sensor (hereinafter referred to as a pressure sensor) 1 is used by being fixedly arranged in a state where it is assembled to a transponder (not shown) 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 SAW chip surface of the pressure sensor 1, and when a pressure exceeding the pressure in the airtight space S set to a vacuum is applied, the SAW chip portion where the IDT electrode is formed is bent and deformed.
This pressure sensor 1 is characterized in that a concave portion 3 is formed in the center of the upper surface of the base 2 so that a surface acoustic wave element (SAW chip) 10 is directly joined to the upper surface of the base without using a spacer. It is.
That is, the base 2 is made of an insulating material such as ceramic, glass, crystal, etc., and has a diaphragm structure having a recessed portion 3 formed by etching at the center of the upper surface.
A SAW chip 10 as a pressure detection element includes a piezoelectric substrate 11 such as a quartz substrate, an interdigital transducer electrode (IDT electrode) 12 (and a reflector) formed on the lower surface of the piezoelectric substrate 11, and an IDT electrode 12 electrically connected to the outside. And an extraction electrode 13 for connection. In this example, the lead electrode 13a on the lower surface side of the piezoelectric substrate 11 is connected to the lead electrode 13b that is exposed on the surface side through a through hole (through hole) provided in the piezoelectric substrate. This example is a configuration example in the case where an extraction electrode for ensuring supply of current to the pressure sensor and output of a signal from the pressure sensor is provided on the top of the pressure sensor.
Since the recessed portion 3 of the base 2 is formed in a region corresponding to the region where the IDT electrode 12 of the SAW chip 10 is formed, the flat surface 4 on the top surface of the base 2 and the bottom surface of the SAW chip are joined together. An airtight space S composed of the recessed portions 3 is formed immediately below the electrode formation region.
When pressure is applied to the upper surface of the SAW chip of the pressure sensor 1, the SAW chip is bent and deformed according to the pressure difference from the inside of the airtight space S, and the distance between the electrode fingers of the IDT electrode is changed. Change.
In the present invention, the IDT electrode 12 is sealed in the hermetic space S to prevent contamination and corrosion of the IDT electrode.

Next, FIGS. 2A and 2B are modified embodiments of FIG. 1, and a lead electrode 13 a on the bottom surface of the piezoelectric substrate is exposed on the base bottom surface side through a through hole provided in the base 2. The connection with the electrode 13b is different from FIG.
This is a configuration example in the case where a lead electrode for securing current supply to the pressure sensor and output of a signal from the pressure sensor is provided at the bottom of the pressure sensor.
Next, FIGS. 3A and 3B are a longitudinal sectional view and an external perspective view of a pressure sensor according to a second embodiment of the present invention.
In the pressure sensor according to the embodiment of FIG. 1 and FIG. 2, the SAW chip 10 using the piezoelectric substrate 11 made of a thin plate is used to increase the sensitivity, so that the pressure sensor can be thinned. Thus, the mechanical strength at the joint with the base 2 may be reduced.
In the pressure sensor 1 according to the present embodiment, the piezoelectric substrate 11 is formed of a thick plate material having sufficient strength, and a recess 20 is formed on the upper surface of the region where the IDT electrode 12 is formed to form a diaphragm structure. The strength of the thin IDT electrode formation region located at the bottom of the recess 20 is kept high while ensuring the desired strength. That is, since the piezoelectric substrate 11 has a structure in which the outer periphery of the thin portion on which the IDT electrode 12 is formed is integrally held by the thick portion, the mechanical strength can be improved.
In this example, the extraction electrode 13a on the lower surface side of the piezoelectric substrate 11 is connected to the extraction electrode 13b exposed on the surface side through a through hole (through hole) provided in the piezoelectric substrate. This example is a configuration example in the case where the lead electrode 13 for ensuring the supply of current to the pressure sensor and the output of a signal from the pressure sensor is provided above the pressure sensor.

Next, FIGS. 4 (a) and 4 (b) are modified embodiments of FIG. 3, in which the lead electrode 13a on the bottom surface of the piezoelectric substrate is pulled out to the bottom surface side of the base through a through hole provided in the base 2. 3 and different.
This is a configuration example in the case where a lead electrode for securing current supply to the pressure sensor and output of a signal from the pressure sensor is provided at the bottom of the pressure sensor.
The above-described pressure sensor of the present invention has been described as a pneumatic sensor that is mounted in a vehicle tire and measures a change in air pressure. However, the present invention is not limited to a tire but is used as a means for measuring various air pressures (gas pressures). be able to.

(A) And (b) is a longitudinal cross-sectional view of the pressure sensor of this invention which concerns on 1st Embodiment, and an external appearance perspective view. (A) And (b) is a longitudinal cross-sectional view of the pressure sensor which concerns on the deformation | transformation embodiment of FIG. 1, and an external appearance perspective view. (A) And (b) is a longitudinal cross-sectional view of the pressure sensor of this invention which concerns on 2nd Embodiment, and an external appearance perspective view. (A) And (b) is a longitudinal cross-sectional view of the pressure sensor which concerns on the deformation | transformation embodiment of FIG. 3, and an external appearance perspective view. (A) And (b) is front sectional drawing which shows the structure of the pressure sensor using the conventional SAW device, and an external appearance perspective view. (A) And (b) is front sectional drawing which shows the structure of the pressure sensor using the SAW device based on another prior art example, and an external appearance perspective view.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Pressure sensor, 2 ... Base, 3 ... Recessed part, 4 ... Flat surface, 10 ... SAW chip, 11 ... Piezoelectric substrate, 12 ... IDT electrode, 13, 13a, 13b ... Extraction electrode, 20 ... Recessed part.

Claims (5)

A SAW chip having a piezoelectric substrate and an interdigital transducer electrode formed on the lower surface of the piezoelectric substrate and an interdigital transducer electrode on the lower surface of the SAW chip are joined and integrated with the SAW chip with an airtight space interposed therebetween. In a frequency change type pressure sensor comprising: a base made into a base; and an extraction electrode for electrically connecting the interdigital transducer electrode of the SAW chip and the outside.
The pressure sensor according to claim 1, wherein the base has a diaphragm structure having a concave portion on an upper surface facing the interdigital transducer electrode.   2. The pressure sensor according to claim 1, wherein the SAW chip has a diaphragm structure having a recess in an area corresponding to the interdigital transducer electrode on the upper surface of the piezoelectric substrate.   The pressure sensor according to claim 1, wherein the extraction electrode is exposed on the upper surface of the SAW chip.   The pressure sensor according to claim 1, wherein the extraction electrode is disposed so as to be exposed on a lower surface of the base.   The pressure sensor according to any one of claims 1 to 4, wherein the piezoelectric substrate constituting the SAW chip is made of crystal.

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