JP2006300784A - Saw pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a size, and to reduce a cost, in an SAW pressure sensor for sensing pressure by frequency fluctuation of an SAW element. <P>SOLUTION: This SAW pressure sensor is provided with: a piezoelectric substrate 10 with the SAW element 11 formed on a one-side main face; a case member 1 opened in a ceiling part and having a through hole 3 formed in the central part of an inner bottom part; a bonding member 4 for joining the piezoelectric substrate 10 to the case member 1 to surround the through-hole 3; and a lid body 20 for sealing the ceiling part of the case member 1. An antenna 15 performing transmission and reception with an external sensing device is formed on the piezoelectric substrate 10 in a form of a strip line. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a SAW pressure sensor that uses a SAW element to detect pressure based on frequency fluctuations.

  In recent years, surface acoustic wave (SAW) devices have been widely used in the communication field and have excellent characteristics such as high performance, small size, and mass productivity. Therefore, in addition to being used as filters in communication devices such as mobile phones, pressure sensors It has been used as.

FIG. 5A shows a sectional view of the SAW pressure sensor disclosed in Japanese Patent Laid-Open No. 60-20134. The case 51 is a case having one end opened, and a step 52 and a through hole 53 are provided on the inner surface of the case. The surface wave substrate 54 is composed of a piezoelectric ceramic such as PZT, a single crystal such as LiNbO ₃ , or a glass substrate on which a piezoelectric thin film such as ZnO is formed. As shown in FIG. 5B, comb-shaped electrodes 55 and 56 are arranged on the surface wave substrate 54 at a predetermined interval, and the amplifier 7 is interposed between one of the comb-shaped electrodes 55 and 56. Is inserted and the other electrode is grounded. The surface wave substrate 54 is fixed on the step 52 in the case 51, forms a sealed space 58 with the case 51, and after the pressure in the sealed space 58 is set to a constant value through the through hole 53, the sealing member 59 is formed. Is attached. A lid 60 having a large number of holes is attached to the open end of the case 51.

  Next, FIG. 6 shows a sectional view of the SAW pressure sensor disclosed in Japanese Patent Laid-Open No. 61-80024. This SAW pressure sensor includes a base 73 composed of a thick part 71 and a thin diaphragm part 72, and a comb-shaped electrode 74 is formed on the diaphragm part 72. The base 73 has a concave substrate formed by etching or the like, and the diaphragm portion 72 and the thick portion 73 are integrated.

  In the SAW pressure sensor described above, when pressure is applied to the piezoelectric substrate, the distance between the electrode fingers of the comb-shaped electrode changes due to the bending of the piezoelectric substrate, and the oscillation frequency changes accordingly, and the pressure is detected by the amount of frequency change. It is a mechanism that does.

Further, as shown in FIG. 7, the SAW pressure sensor receives a drive signal transmitted from an antenna 82 of an external sensing device 81 by an antenna 84 connected to the SAW pressure sensor 83 to drive the SAW element. Then, the frequency change detected by the SAW element is transmitted again to the sensing device 81 via the antenna 84. Therefore, the SAW pressure sensor does not require an external power source for operation, and has an advantage that signals can be transmitted and received wirelessly.
Japanese Patent Laid-Open No. 60-20134 Japanese Patent Application Laid-Open No. 61-80024

  By the way, in the SAW pressure sensor, since the sensor and the antenna are provided separately, there is a problem that the device on the sensor side becomes large. In addition, since the antenna needs to be packaged in a case or the like, there is a problem that the cost becomes high for mass production. In order to solve the above problems, an object of the present invention is to reduce the size and cost of a SAW pressure sensor using a SAW element.

  In order to solve the above-mentioned problems, the invention according to claim 1 of the SAW pressure sensor according to the present invention includes a piezoelectric substrate having a comb-shaped electrode formed on one main surface, and a ceiling portion that is open and penetrates through the center of the inner bottom portion. In a SAW pressure sensor comprising: a case member in which a hole is formed; an adhesive member for joining the piezoelectric substrate and the case member so as to surround the through hole; and a lid for sealing the case member; An antenna that performs transmission and reception with an external sensing device is formed on the piezoelectric substrate by a strip line.

  The invention described in claim 2 is characterized in that the case member or the piezoelectric substrate is provided with an annular frame so as to surround the through hole.

  The invention described in claim 3 is characterized in that the piezoelectric substrate is thinned around the comb-shaped electrode by etching.

  According to the first aspect of the present invention, in the SAW pressure sensor that detects the pressure by changing the frequency of the SAW element, the antenna is formed on the piezoelectric substrate by the stripline, and the sensor and the antenna are integrated. Miniaturization and cost reduction can be realized.

  According to the second aspect of the present invention, since the frame member is provided so as to surround the through hole in the case member or the piezoelectric substrate, the distance between the fulcrums at the joint portion between the piezoelectric substrate and the case member can be accurately controlled. Thus, variations in sensor sensitivity can be suppressed, and a sensor with good reproducibility can be realized.

  According to the third aspect of the present invention, the thickness of the substrate is reduced without deteriorating the mechanical strength as compared with the flat plate-shaped piezoelectric substrate by making the periphery of the comb-shaped electrode of the piezoelectric substrate thin by etching and making it concave. Can be made thin, so that good sensor sensitivity can be obtained. Further, since the distance between the fulcrums at the joint portion between the piezoelectric substrate and the case member can be accurately controlled, variations in sensor sensitivity can be suppressed, and a sensor with good reproducibility can be realized. Furthermore, since the accuracy is not required when the piezoelectric substrate is mounted on the case, the manufacturing efficiency can be improved.

  Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. FIG. 1A shows a cross-sectional view of a SAW pressure sensor according to the present invention. The case member 1 has an open ceiling, a connection terminal 2 for connection to the outside is provided on the back surface, and a through hole 3 is formed in the center of the inner bottom. The piezoelectric substrate 10 has a SAW element 11 formed on one main surface. A pressure receiving diaphragm is configured by joining the back surface of the surface of the piezoelectric substrate 10 on which the SAW element 11 is formed and the case member 1 so as to surround the through-hole 3 by the adhesive member 4. After mounting the piezoelectric substrate 10 on the case member 1, an opening in the ceiling portion of the case member 1 is sealed with a lid 20 by seam welding to form a sealed space 21 maintained at a constant pressure.

  FIG. 1B shows the surface of the piezoelectric substrate on which the SAW element is formed. The SAW element 11 includes a pair of comb-shaped electrodes 12 and 13 that are interleaved with each other, and reflectors 14 disposed on both sides thereof. And antenna 15. The antenna 15 is configured by short-circuiting the comb electrodes 12 and 13 and forming a strip line along the outer periphery of the piezoelectric substrate so as to surround the SAW element portion.

  A feature of the present invention is that an antenna that receives a drive signal transmitted from an antenna of an external sensing device and transmits a detection result is provided on the same piezoelectric substrate as the SAW element. With such a configuration, the sensor and the antenna can be integrally formed, and downsizing and cost reduction can be realized.

  When the SAW pressure sensor receives pressure from the through hole to the piezoelectric substrate, the piezoelectric substrate is bent by the pressure, and the interval between the electrode fingers of the comb-shaped electrode changes. When the distance between the electrode fingers changes, the resonance frequency changes, and the pressure is detected by the change in the frequency. Therefore, in order to increase the sensor sensitivity, it is desirable to make the thickness t of the piezoelectric substrate as thin as possible so that the mechanical strength does not deteriorate. In addition, if the distance L between the fulcrum between the piezoelectric substrate and the case member or the shape of the joining portion varies, the amount of deflection of the piezoelectric substrate changes, and an error occurs when calculating pressure from the amount of frequency change, resulting in poor reproducibility. Become. Therefore, it is necessary to accurately control the distance L between the fulcrums and the shape of the joint portion.

In order to accurately control the distance L between the fulcrums and the shape of the joining portion, for example, a base electrode such as Au or solder is previously formed on the piezoelectric substrate or the case member before mounting the piezoelectric substrate, and the base electrode is bonded with an adhesive member. It is desirable to join. Further, as shown in FIG. 2, a frame body 5 may be provided so as to surround the through hole 3, and the upper surface of the frame body 5 and the piezoelectric substrate 10 may be joined by the adhesive member 4. Since the mounting position of the piezoelectric substrate can be fixed by providing the frame, the distance L between the fulcrums can be accurately controlled. The frame body may be provided on the piezoelectric substrate side.

  Furthermore, as shown in FIG. 3, the periphery of the SAW element 11 is made into a thin portion 16 by etching the piezoelectric substrate 10, and the thick portion 17 on the outer periphery of the thin portion 16 and the case member 1 are joined by the adhesive member 4. You may do it. With such a structure, the thickness of the substrate around the SAW element can be reduced without impairing the mechanical strength as compared with the flat plate-shaped piezoelectric substrate of FIG. Can do. Further, since the distance L between the fulcrums and the shape of the joint portion can be accurately controlled, variations in sensor sensitivity can be suppressed, and a sensor with good reproducibility can be realized. Furthermore, since the accuracy is not required when the piezoelectric substrate is mounted on the case member, the manufacturing efficiency can be improved.

  Further, as shown in FIG. 4, the SAW element 32 is formed on the concave side of the piezoelectric substrate 31 dug by etching, and the mounting substrate 30 and the piezoelectric substrate 31 are disposed so that the SAW element 32 and the mounting substrate 30 face each other. May be joined by the adhesive member 33. With such a structure, the piezoelectric substrate can be used as a part of the case, and the number of parts can be reduced, which can contribute to size reduction and cost reduction. The shape of the piezoelectric substrate may be a flat plate shape.

  As the material of the above-described piezoelectric substrate, a glass substrate on which a piezoelectric thin film such as quartz, lithium tantalate, lithium niobate, lithium tetraborate, langasite, or ZnO is formed is applied. In addition, as a material for forming the IDT, reflector and antenna constituting the SAW element portion, Al or an alloy containing Al as a main component, which has a small electric resistance and is easy to form an electrode, is desirable, but Cu, Ti, Cr, Au, Ag, and alloys containing them as main components may be used. In the above description, the one-terminal-pair SAW resonator is used as the SAW element, but a two-terminal-pair SAW resonator or other structures may be used.

A sectional view of the SAW pressure sensor according to the present invention is shown in (a), and a plan view of the piezoelectric substrate is shown in (b). The modification of the SAW pressure sensor which concerns on this invention is shown. 6 shows another modification of the SAW pressure sensor according to the present invention. 6 shows another modification of the SAW pressure sensor according to the present invention. 1 shows a conventional SAW pressure sensor using a flat plate-like piezoelectric substrate. A conventional SAW pressure sensor using a concave piezoelectric substrate is shown. It is a figure explaining transmission and reception of a SAW pressure sensor and a sensing device.

Explanation of symbols

1: Case member 2: Connection terminal 3: Through hole 4: Adhesive member 5: Frame body 10: Piezoelectric substrate 11: SAW element 12: Comb electrode 13: Comb electrode 14: Reflector 15: Antenna 16: Thin portion 17: Thick portion 20: Lid 21: Sealed space 30: Mounting substrate 31: Piezoelectric substrate 32: SAW element 33: Adhesive member

Claims (3)

  A piezoelectric substrate having a comb-like electrode formed on one main surface, a case member having a ceiling opening and a through hole formed in the center of the inner bottom, and the piezoelectric substrate and the case member so as to surround the through hole. In a SAW pressure sensor including an adhesive member to be joined and a lid for sealing the ceiling of the case member, an antenna for transmitting and receiving with an external sensing device is formed on the piezoelectric substrate by a strip line. SAW pressure sensor characterized by   The SAW pressure sensor according to claim 1, wherein the case member or the piezoelectric substrate is provided with an annular frame so as to surround the through hole. The SAW pressure sensor according to claim 1, wherein the piezoelectric substrate is thinned around the comb-shaped electrode by etching.

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