JP2007225546A - Elastic surface wave sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an elastic surface wave sensor which ensures detection/measurement precision by suppressing the corrosion or deterioration of an IDT electrode or the like caused by a chemical substance to be detected/measured, has high reliability and can be miniaturized or set to a high frequency system. <P>SOLUTION: The elastic surface wave sensor 10 is constituted so that a response film 7 having to be brought into contact with the chemical substance to be detected/measured is provided on the under main surface of a quartz substrate 1 isolated from the exciting and detecting IDT electrodes 4 and 5 provided on the upper main surface of the quartz substrate 1 through the quartz substrate 1. By this constitution, since the chemical substance to be detected/measured can be detected or measured without being brought into contact with the exciting and detection IDT electrodes 4 and 5, the corrosion or deterioration of the exiting and detecting IDT electrodes 4 and 5 caused by the chemical substance to be detected/measured can be prevented. Accordingly, the elastic surface wave sensor 10 of high reliability can be provided without causing the corrosion or deterioration of the exciting and detecting IDT electrodes 4 and 5. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave sensor using a surface acoustic wave (SAW) as a transducer for detecting a specific chemical substance and / or measuring a physical property thereof.

  In recent years, surface acoustic wave elements (SAW elements) have been used as transducers to detect chemical or physical changes in sensitive membranes that recognize chemical substances to be detected and measured in technical fields such as biotechnology and medicine. Such surface acoustic wave sensors (SAW sensors) have been developed and their use has been expanded (see, for example, Patent Documents 1 to 4).

  As the surface acoustic wave used for such a surface acoustic wave device such as a surface acoustic wave sensor, a leaky surface acoustic wave called Rayleigh wave or Leaky wave is mainly used. A Rayleigh wave is a surface wave that propagates on the surface of an elastic body, and propagates without propagation loss theoretically without radiating the energy into the piezoelectric substrate. As a piezoelectric substrate for a surface acoustic wave device using a Rayleigh wave, an ST cut crystal having a phase velocity of 3150 [m / sec] can be mentioned.

There are three types of volume waves (bulk waves) of “slow transverse waves”, “fast transverse waves”, and “longitudinal waves” in the piezoelectric substrate, but the Rayleigh wave has a slower phase velocity than “slow transverse waves”. It propagates with.
The leaky surface acoustic wave is a surface acoustic wave that propagates while radiating energy in the depth direction of the elastic body, and can be used at a special cutting angle and propagation direction. For example, an LST cut crystal having a phase velocity of 3900 [m / sec] is known. This leaky surface acoustic wave propagates at a phase velocity between a “slow transverse wave” and a “fast transverse wave”.

In recent years, the theory of leaky surface acoustic waves has been developed, and most of the displacements on the substrate surface are composed of longitudinal wave components, and while radiating two transverse wave components inside the piezoelectric substrate as bulk waves, A quasi-longitudinal-type surface acoustic wave propagating at a high phase velocity between “longitudinal waves” has been discovered one after another.
In addition, the use of quasi-longitudinal wave type surface acoustic waves using a quartz substrate with a predetermined cut-out angle has been reported even for quartz substrates that have been conventionally considered not to be suitable materials for high-frequency surface acoustic wave devices. (See, for example, Non-Patent Document 1).

  A conventional example of the basic configuration of a surface acoustic wave sensor using such surface acoustic waves will be described with reference to FIG. The surface acoustic wave sensor 110 is a so-called resonance type (one-port resonator type), and includes an IDT (interdigital transducer) electrode 104 formed substantially at the center of the upper main surface of the piezoelectric substrate 101 made of quartz or the like, and an IDT electrode 104. It has a sensitive film 107 formed substantially at the center and a pair of reflectors 106a and 106b formed on both sides of the IDT electrode 104 with a lattice structure. The sensitive film 107 is disposed on the SAW propagation surface between the electrode fingers of the cross finger electrodes 102 a and 102 b constituting the IDT electrode 104. In such a surface acoustic wave sensor 110, when a predetermined high-frequency signal voltage is applied between the interdigitated electrodes 102a and 102b, a surface acoustic wave having the same frequency as the input signal is excited on the surface of the piezoelectric substrate 101. The surface acoustic wave propagates to the left and right sides of the IDT electrode 104, is reflected by the reflectors 106a and 106b arranged on the left and right, and returns toward the IDT electrode 104. As a result, a standing wave is generated between the reflectors 106a and 106b. To do. When the sensitive film 107 absorbs a chemical substance to be detected / measured and its weight increases, the propagation speed of the surface acoustic wave changes and the frequency changes. By measuring the amount of frequency change, the target chemical substance can be detected or measured with high accuracy (see, for example, Patent Document 1).

In addition to this, for example, in an SHW (Shear Horizon) mode SAW device, an electrical short circuit and an electrical release are provided between the excitation IDT electrode and the reception IDT electrode on the SAW propagation surface made of a piezoelectric material, respectively, Surface acoustic wave biosensors that detect physical properties such as pH and conductivity are known from changes in SAW propagation speed that occur between electrical short-circuiting and electrical opening when the same liquid is loaded on a sample cell with a fixed surface. (For example, refer to Patent Document 2).
Further, an excitation IDT electrode and a reception IDT electrode and a gas adsorber disposed between the excitation and reception IDTs are formed on the piezoelectric substrate of the surface acoustic wave device, respectively, and a gas absorber (sensitive film). A surface acoustic wave sensor (gas sensor) that detects a change in SAW propagation velocity due to heat generated by increasing the mass by adsorbing a specific gas as a change in output frequency is known (see, for example, Patent Document 3). .
Further, the other surface of the non-piezoelectric substrate such as an acrylic plate having a sensitive film provided on one surface is bonded to the other main surface of the piezoelectric substrate provided with the IDT electrode on one main surface, whereby the IDT 2. Description of the Related Art A surface acoustic wave sensor (gas sensor) that detects or measures a gas by utilizing the fact that a surface acoustic wave excited by an electrode leaks to a non-piezoelectric substrate as a bulk wave is known (see, for example, Patent Document 4). ).

JP 2005-315646 A JP-A-6-133759 JP-A-8-68781 JP 7-318542 A 1999 IEEE ULTRASONS SYMPOSIUM 321-324 "Study of Propagation of Quasi-longitudinal Leakyu Surface Acoustic-Right Propagating Propagating Propagating

  However, in the conventional surface acoustic wave sensor described above, the IDT electrode and the sensitive film are provided on the same main surface of the piezoelectric substrate. For this reason, by increasing the surface acoustic wave propagation path and increasing the sensitive film in order to increase detection and measurement accuracy, the size of the surface acoustic wave sensor is increased. It was difficult to satisfy the requirements at the same time. In addition, when the non-measurement object has a corrosive property, the IDT electrode and the electrode constituting the sensor circuit may be corroded to adversely affect the detection / measurement accuracy. In order to avoid this, an IDT electrode or the like may be used. If measures were taken to protect, there was a problem of increasing costs. Furthermore, in a surface acoustic wave sensor using a leaky surface acoustic wave in which a non-piezoelectric substrate is bonded to a piezoelectric substrate, there is reflection of the surface acoustic wave caused by impedance mismatch at the interface between the piezoelectric and non-piezoelectric substrates. There is a problem that accurate detection and measurement cannot be performed because bulk waves cannot be efficiently leaked to the substrate. In addition, there is a problem that the bonding process causes an increase in cost.

  The present invention has been made in view of the above problems, and its object is to ensure detection and measurement accuracy by suppressing corrosion and deterioration of IDT electrodes and the like caused by chemical substances to be detected and measured, and to have high reliability. It is an object of the present invention to provide a surface acoustic wave sensor that can be reduced in size and frequency.

  In order to solve the above problems, in the present invention, a quartz substrate, an IDT electrode that excites a pseudo-longitudinal wave type surface acoustic wave formed on the principal surface of the quartz substrate, and the opposite of the principal surface on which the IDT electrode is formed. The main purpose is that a sensitive film for recognizing a substance to be detected or measured is formed on the main surface on the side.

According to this configuration, the sensitive film that needs to be in contact with the chemical substance to be detected / measured is separated from the IDT electrode provided on one main surface of the quartz substrate via the quartz substrate. It is provided on the other main surface. As a result, detection or measurement can be performed without touching the IDT electrode with a chemical substance, and therefore corrosion and deterioration of the IDT electrode due to the chemical substance can be prevented without providing a protective film or the like. Therefore, it is possible to provide a highly reliable surface acoustic wave sensor that has high accuracy and does not cause corrosion or deterioration of the IDT electrode without increasing the cost associated with the formation of the protective film.
Further, since the chemical substance is detected or measured using a quasi-longitudinal wave type surface acoustic wave having a relatively high phase velocity, the electrode width and the electrode interval of the IDT electrode are compared with those using Rayleigh waves or leaky surface acoustic waves. It is possible to easily realize a high frequency without reducing the size, and a highly accurate surface acoustic wave sensor can be realized. Even when there is a restriction on the thickness of the IDT normalized electrode film thickness, it is possible to provide a margin for each electrode film thickness of the IDT electrode as compared with the case where Rayleigh waves or leaky surface acoustic waves are used. As a result, an increase in electrical resistance loss can be suppressed and a reduction in Q value can be prevented, and a decrease in manufacturing yield due to miniaturization of IDT electrodes can be prevented, thereby making it easier to manufacture a surface acoustic wave sensor.
In addition, since the electrode film thickness can be increased, the pad portion to be bonded can be increased, and electrode peeling during wire bonding can be prevented.
Further, since the bulk wave leaks to the lower main surface without bonding the substrates, the manufacturing cost can be reduced.
Furthermore, since the IDT electrode and the sensitive film are provided so as to be vertically arranged on another main surface of the quartz substrate, the plane area of the sensitive film can be increased without increasing the plane size. Thereby, since the amount of the chemical substance to be detected or measured can be increased in the sensitive film, the detection / measurement accuracy can be improved without increasing the size of the surface acoustic wave sensor.

  In the present invention, the IDT electrode may be composed of one IDT electrode having a pair of cross finger electrodes.

  Such a so-called 1-port resonator type surface acoustic wave sensor can omit one IDT compared to a so-called transversal type surface acoustic wave sensor provided with two IDT electrodes for excitation and reception. The surface acoustic wave sensor can be downsized and the manufacturing cost can be reduced. Also, compared to conventional 1-port resonator type surface acoustic wave sensors using Rayleigh waves or SH mode surface waves, no sensitive film is provided on the IDT electrode, improving detection and measurement accuracy. Can be made.

  In the present invention, it is preferable to include a pair of reflectors arranged so as to sandwich the IDT electrode along the propagation direction of the pseudo longitudinal wave type surface acoustic wave in plan view.

  According to this configuration, reflection is performed on reflectors located on both sides in a plan view of the IDT electrode along the propagation direction of the pseudo-longitudinal surface acoustic wave excited by applying a predetermined high-frequency signal voltage to the IDT electrode. Then, returning toward the IDT electrode, a quasi-longitudinal surface acoustic wave standing wave is generated between the reflectors. Due to the surface wave confinement effect by such a reflector, the loss can be reduced, the Q value can be increased, and the Cl value can be decreased, whereby a more excellent resonance characteristic can be obtained. Therefore, the sensitivity of the surface acoustic wave sensor is improved, and highly accurate detection / measurement is possible.

  In the present invention, at least the IDT electrode on the quartz substrate may be covered with the storage container, and at least a part of the sensitive film may be exposed to the atmosphere.

  According to this configuration, the IDT electrode and the surface of the quartz substrate, which is the propagation surface of the surface acoustic wave, are protected from scattering and exposure of the chemical substance to be detected / measured. Contamination can be suppressed. As a result, it is possible to provide a surface acoustic wave sensor that can be applied to a corrosive chemical substance and has excellent detection and measurement accuracy and high reliability.

  In the present invention, an IDT electrode and a circuit unit including means for driving and controlling the IDT electrode to detect or measure a substance to be detected or measured and record the result are sealed in a storage container. It is good also as a structure accommodated in the state.

  According to this configuration, the IDT electrode and the circuit unit used for driving / control / recording of detection / measurement are housed in a sealed state in the housing container, and at least a part of the sensitive film is exposed to the outside. As a result, it is possible to detect and measure the substance to be detected and measured in a state where the parts other than the sensitive film are completely blocked from the substance to be detected and measured. Therefore, it is possible to perform the detection or measurement operation by introducing the surface acoustic wave sensor into the liquid or gas atmosphere of the chemical substance to be detected / measured having corrosive properties.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1A is an explanatory view for explaining the structure of an embodiment of a surface acoustic wave sensor according to the present invention. FIG. 1A is a perspective view, and FIG. It is AA sectional view.

  The surface acoustic wave sensor 10 has a rectangular thin plate-shaped quartz crystal substrate 1. On the upper main surface of the quartz substrate 1, an excitation IDT electrode 4 composed of a pair of cross finger electrodes 2a and 2b and a reception IDT electrode 5 composed of a pair of cross finger electrodes 3a and 3b are formed. Yes. A sensitive film 7 is formed on the other main surface side of the quartz substrate 1.

In FIG. 1 (b), t is the thickness of the quartz substrate 1, P is the pitch of the input and output interdigitated electrodes 2a, 3a, 2b, 3b, and λ is the excitation and receiving IDT electrodes 4, 5 Each wavelength, h, indicates the thickness of each of the excitation and reception IDT electrodes 4 and 5.
The quartz substrate 1 is cut out in a range of Euler angles (0 °, 100 ° to 150 °, 0 °). Further, the thickness t of the quartz substrate 1 is adjusted so that spurious is sufficiently suppressed. For example, when a surface acoustic wave sensor is configured, abnormal oscillation and frequency jump (frequency shift) do not occur. Yes.

The excitation IDT electrode 4 is formed such that the interdigital electrodes 2a and 2b having a comb-like shape intersect with each other with a predetermined interval so as not to touch each other. Similarly, the receiving IDT electrode 5 is formed so that the input-side cross finger electrode 3a and the output-side cross finger electrode 3b having a comb-like shape intersect with each other with a predetermined interval so as not to touch each other. Yes. The excitation IDT electrode 4 and the reception IDT electrode 5 are provided side by side with a predetermined interval at the approximate center on the upper main surface of the quartz substrate. Each of the interdigitated electrodes 2a, 2b, 3a, 3b is a known conductive material such as gold, aluminum, or an aluminum alloy, and is formed using a conventionally known electrode patterning method such as photolithography, vapor deposition, or sputtering. Is done.
Further, the excitation IDT electrode 4 excites a quasi-longitudinal wave type surface acoustic wave propagating parallel to the + X axis in FIG. 1B on the surface of the quartz substrate 1, and the IDT normalized electrode thickness h / For example, λ is set to 0.02 or more. Here, the IDT normalized electrode thickness h / λ is obtained by normalizing the thickness h of the excitation IDT electrode 4 with the IDT electrode wavelength λ.

  The sensitive film 7 is formed so as to be laminated on the main surface of the quartz substrate 1 opposite to the main surface on which the excitation and reception IDT electrodes 4 and 5 are formed. In addition, the sensitive film | membrane 7 can use conventionally well-known various things, such as a gas adsorbent, an enzyme, microorganisms, an antibody, DNA, according to the property and the property, etc. of the chemical substance to be detected and measured, It is formed and used in various conventionally known forms such as a membrane and a cell on which they are fixed.

  In such a so-called transversal type surface acoustic wave sensor 10, when a predetermined high-frequency signal voltage is applied between the interdigital electrodes 2 a and 2 b of the excitation IDT electrode 4, a pseudo-vertical surface is formed on the upper main surface of the quartz substrate 1. As the wave-type leaky surface acoustic wave propagates, the bulk wave leaks in the direction of the main surface on the lower side of the quartz substrate 1, is reflected on the lower main surface, and returns toward the upper main surface. That is, a stationary wave is generated in the thickness direction of the quartz substrate 1, and vibration is also generated on the lower main surface side. When the sensitive film 7 formed on the lower main surface of the quartz substrate 1 absorbs the chemical substance to be detected and its weight increases, the propagation speed of the pseudo longitudinal wave type surface acoustic wave changes. By measuring the propagation delay output from the reception IDT electrode 5 with the changed propagation speed, the target chemical substance can be detected or its physical properties such as its concentration and pH can be measured.

  The effects of the above embodiment will be described below.

  (1) The surface acoustic wave sensor 10 having the above-described configuration is configured to detect or measure a chemical substance using a pseudo longitudinal wave type surface acoustic wave having a relatively fast phase velocity. Thereby, compared with the case where Rayleigh waves or leaky surface acoustic waves are used, the electrode widths and electrode intervals of the cross finger electrodes 2a and 2b and the cross finger electrodes 3a and 3b of the excitation and reception IDT electrodes 4 and 5 are made smaller. It is possible to easily realize high frequency without doing so. Further, even when the IDT electrode standardized electrode film thickness h / λ is limited, each electrode of the IDT electrodes 4 and 5 for excitation and reception is compared with the case where Rayleigh waves or leaky surface acoustic waves are used. Since a margin can be provided for the film thickness h, an increase in electrical resistance loss can be suppressed, and a decrease in the Q value can be prevented. Further, since the electrode film thickness can be increased, the pad portion to be bonded can be increased, and for example, electrode peeling during wire bonding can be prevented. Therefore, it is possible to provide the surface acoustic wave sensor 10 that has high frequency, high detection or measurement accuracy, and high reliability.

  (2) In the surface acoustic wave sensor 10 having the above-described configuration, the sensitive film 7 that needs to be brought into contact with a chemical substance to be detected or measured is provided with an excitation and reception IDT electrode provided on the upper main surface of the quartz substrate 1. 4 and 5 are provided on the lower main surface of the quartz substrate 1 which is separated by the quartz substrate 1. As a result, detection or measurement can be performed without bringing chemical substances into contact with the excitation and reception IDT electrodes 4 and 5, so that the excitation and reception IDT electrodes 4 are not particularly provided with a protective film or the like. , 5 can be prevented from corrosion and deterioration by chemical substances. In addition, by using the quasi-longitudinal wave type surface acoustic wave, the lower main surface can be vibrated without bonding the substrates, and the manufacturing cost can be reduced. Accordingly, a highly reliable surface acoustic wave sensor 10 having high accuracy and not causing corrosion or deterioration of the excitation and reception IDT electrodes 4 and 5 is provided without increasing the cost associated with the formation of the protective film. can do.

  (3) Further, the surface acoustic wave sensor 10 having the above configuration increases the planar size because the excitation and reception IDT electrodes 4 and 5 and the sensitive film 7 are provided on another main surface of the quartz substrate 1. The plane area of the sensitive film 7 can be increased without any problem. Thereby, since the amount of the chemical substance to be detected / measured to the sensitive film 7 can be increased, the accuracy of detection or measurement can be improved without increasing the size of the surface acoustic wave sensor 10. .

  The present invention is not limited to the above-described embodiment, and the following modified examples can also be implemented.

(Modification 1) In the above embodiment, the so-called transversal type surface acoustic wave sensor 10 having the excitation and reception IDT electrodes 4 and 5 has been described. However, the present invention is not limited to this. It is also possible to provide a so-called resonator type surface acoustic wave sensor to be generated.
FIG. 2 is an explanatory view for explaining the configuration of a resonator type surface acoustic wave sensor using a quasi-longitudinal wave type surface acoustic wave according to the present invention. FIG. 2 (a) is a perspective view, and FIG. It is the BB sectional view taken on the line of Fig.2 (a). Note that, among the configurations of the surface acoustic wave sensor according to this modification, the description of the same configurations as those of the first embodiment described above will be omitted.

In FIG. 2, the surface acoustic wave sensor 20 includes an IDT electrode formed by intersecting the crossed finger electrodes 12a and 12b at a predetermined center so as not to touch each other at the approximate center of the upper main surface of the quartz substrate 11. 14 is provided. Also, reflectors 16a and 16b having a lattice structure are disposed on the left and right sides of the IDT electrode 14, respectively. These interdigital electrodes 12a and 12b and reflectors 16a and 16b are made of a known conductive material and are simultaneously formed by using a conventionally known electrode patterning method.
A sensitive film 17 is formed on the main surface of the quartz substrate 11 opposite to the main surface on which the IDT electrode 14 is formed.

In such a 1-port resonator type surface acoustic wave sensor 20, when a predetermined high-frequency signal voltage is applied between the cross finger electrode 12 a and the output-side cross finger electrode 12 b, it is input to the surface of the upper main surface of the quartz substrate 11. A pseudo longitudinal wave type surface acoustic wave having the same frequency as the signal is excited. Accordingly, the bulk wave leaks in the direction of the lower main surface of the quartz substrate 11, is reflected by the lower main surface, and returns toward the upper main surface. As a result, a settled wave is also generated in the thickness direction of the quartz substrate 11, and vibration is also generated on the lower main surface side. Such a quasi-longitudinal wave type surface acoustic wave propagates to the left and right sides of the IDT electrode 14 in plan view, is reflected by the left and right reflectors 16a and 16b, and returns toward the IDT electrode 14. As a result, a quasi-longitudinal wave surface acoustic wave standing wave is generated between the reflectors 16a and 16b. Thus, by confining the surface wave between the reflectors 16a and 16b, the loss can be reduced, the Q value can be increased, and the CI value can be decreased, so that more excellent resonance characteristics can be obtained. Moreover, the influence of the reflected wave by the end surface of the quartz substrate 11 of the surface acoustic wave sensor 20 can be effectively eliminated.
When the sensitive film 17 absorbs a chemical substance to be detected / measured and its weight increases, the propagation speed of the pseudo-longitudinal wave type surface acoustic wave changes, and the frequency change that occurs is caused by the IDT electrode 14. By measuring, the target chemical substance can be detected or its physical properties can be measured. Further, since one IDT can be omitted as compared with the transversal surface acoustic wave sensor 10 provided with the two IDT electrodes 4 and 5 for excitation and reception, the surface acoustic wave sensor 20 can be downsized and manufactured. Can be reduced.

(Modification 2) The surface acoustic wave sensor 10 described in the above embodiment has a part of the surface acoustic wave sensor 10 accommodated in a package container, thereby expanding the application range of chemical substances to be detected and measured, and maintaining detection and measurement accuracy. Reliability can be improved.
FIG. 3 is a schematic cross-sectional view illustrating a schematic configuration of a package container-accommodating type surface acoustic wave sensor.

The surface acoustic wave sensor 30 in FIG. 3 includes a quartz crystal substrate 21 in which an IDT electrode 24 is formed on an upper main surface and a sensitive film 27 is formed on a lower main surface, and a package container 50 in which a recess is formed. . A package container 50 made of a material resistant to a chemical substance to be detected / measured is bonded to the upper main surface side of the crystal substrate 21 so that the IDT electrode 24 is accommodated in the recess of the package container 50, and crystal The sensitive film 27 formed on the lower main surface of the substrate 21 is exposed to the outside. Further, a through hole 59 is provided in a part of the package container 50. The through-hole 59 is used, for example, when connecting an oscillation circuit for applying a high frequency signal voltage to the IDT electrode 24 or cleaning the IDT electrode 24.
According to this configuration, the IDT electrode 24 for exciting the quasi-longitudinal wave type leaky surface acoustic wave is provided on the upper main surface of the quartz substrate 21 by the package container 50 and is protected from scattering and exposure of the chemical substance to be detected and measured. Therefore, corrosion and deterioration of the IDT electrode 24 and contamination of the surface of the quartz substrate 21 can be suppressed. Accordingly, it is possible to provide the surface acoustic wave sensor 30 that can be applied to detection and measurement of a corrosive chemical substance, has excellent detection and measurement accuracy, and has high reliability.

  (Modification 3) The surface acoustic wave sensor described in the above embodiment can be used for detection and measurement of chemical substances under specific conditions by containing a part of the surface acoustic wave sensor sealed in a package container. It becomes. FIG. 4 is a schematic sectional view conceptually illustrating an example of a locally sealed package type surface acoustic wave sensor.

The surface acoustic wave sensor 40 is a quartz substrate 31 provided with an IDT electrode 34 and a sensitive film 37 on both main surfaces, and a sensor circuit that controls driving / control of the surface acoustic wave sensor 40 and recording of detection / measurement results. An oscillation circuit 80, a memory 90, and a package container 70 having a sealable cavity are included. In the cavity of the package container 70, the IDT electrode 34 on the quartz substrate 31, the oscillation circuit 80, and the memory 90 are housed, and the inside of the cavity is sealed in a sealed state, and the sensitive film 37 is placed outside the package container 70. Exposed. The oscillation circuit 80 and the memory 90 are electrically connected to the IDT electrode 34 by a circuit wiring (not shown) to constitute a circuit.
When a predetermined high frequency signal voltage is applied to the IDT electrode 34 by the oscillation circuit 80, a bulk wave leaks in the thickness direction of the quartz substrate 31 along with the pseudo longitudinal leaky surface acoustic wave excited on the surface of the quartz substrate 31. A resident wave is generated in the thickness direction of the quartz substrate 31, and vibration is also generated on the lower main surface. The frequency change caused by the sensitive film 37 absorbing the chemical substance to be detected of the settled wave is measured by the IDT electrode 34, and the target chemical substance is detected or its physical characteristics are measured. This measurement result is stored in the memory 90 as data.

  According to this configuration, in the surface acoustic wave sensor 40, the sensitive film 37 is exposed to the outside, and the IDT electrode 34, the transmission circuit 80, and the memory 90 are housed in a sealed state in the cavity of the package container 70. As a result, it is possible to detect and measure the substance to be detected and measured in a state where the parts other than the sensitive film are completely blocked from the substance to be detected and measured. Therefore, for example, the surface acoustic wave sensor 40 can be put into a liquid or gas atmosphere of a chemical substance to be detected and measured to perform detection or measurement work.

(A) is a perspective view which shows the structure of the surface acoustic wave sensor of embodiment, (b) is the sectional view on the AA line of (a). The perspective view which shows the modification of a surface acoustic wave sensor, (b) is the BB sectional drawing of (a). Explanatory drawing of the longitudinal cross-section which shows schematic structure of the modification of a surface acoustic wave sensor. Explanatory drawing of the longitudinal cross-section which shows typically schematic structure of the modification of a surface acoustic wave sensor. The perspective view which shows schematic structure of the prior art example of a surface acoustic wave sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 11, 21, 31 ... Quartz substrate, 2a, 2b, 12a, 12b ... Interstitial electrode, 4 ... IDT electrode for excitation, 5 ... IDT electrode for reception, 14, 24, 34 ... IDT electrode, 7, 17, 27, 37 ... sensitive film, 50, 70 ... package container as storage container, 80 ... oscillation circuit as drive unit or control unit, 90 ... memory as recording unit.

Claims (5)

A quartz substrate,
An IDT electrode for exciting a quasi-longitudinal wave type surface acoustic wave formed on the main surface of the quartz substrate;
A surface acoustic wave sensor characterized in that a sensitive film for recognizing a substance to be detected or measured is formed on a main surface opposite to the main surface on which the IDT electrode is formed. The surface acoustic wave sensor according to claim 1,
2. The surface acoustic wave sensor according to claim 1, wherein the IDT electrode comprises one IDT electrode having a pair of cross finger electrodes. The surface acoustic wave sensor according to claim 1,
A surface acoustic wave sensor comprising: a pair of reflectors disposed so as to sandwich the IDT electrode along a propagation direction of the pseudo longitudinal wave type surface acoustic wave in plan view. The surface acoustic wave sensor according to any one of claims 1 to 3,
A surface acoustic wave sensor, wherein at least the IDT electrode on the quartz substrate is covered with a storage container, and at least a part of the sensitive film is exposed to the atmosphere. The surface acoustic wave sensor according to claim 4,
The IDT electrode and a circuit unit having means for driving and controlling the IDT electrode to detect or measure the substance to be detected or measured and record the result are sealed in the storage container. A surface acoustic wave sensor characterized by being housed in a heated state.

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