JP2012229926A - Elastic wave sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve sensing accuracy of an elastic wave sensor.SOLUTION: A reference part constituted by an elastic boundary wave element for generating a boundary wave that an elastic wave excited by a second IDT electrode 5 propagates a boundary between a piezoelectric substrate 2 and a dielectric film 7 prevents a detection target substance, etc., from sticking on the second IDT electrode 5 constituting the reference part when contacting a substance (expiration, suspension, etc.) with possibility of including the detection target substance to an elastic wave sensor 1. Thereby, since a characteristic change by the deposits is suppressed, sensing accuracy of the reference part constituted by the second IDT electrode 5 can be improved. Consequently, sensing accuracy of the elastic wave sensor 1 is improved.

Description

  The present invention relates to an elastic wave sensor including a reaction unit that reacts with a specific substance.

  A conventional elastic wave sensor will be described with reference to FIG. FIG. 4 is a schematic cross-sectional view of a conventional acoustic wave sensor.

  In FIG. 4, a conventional acoustic wave sensor 101 determines the frequency of an acoustic wave excited by the piezoelectric substrate 102, the first IDT electrode 103 formed on the piezoelectric substrate 102, and the first IDT electrode 103. And a reaction unit that is formed on the piezoelectric substrate 102 so as to cover the first IDT electrode 103 and reacts with a detection target substance that may be included in exhalation or the like 104. The conventional acoustic wave sensor 101 includes a second IDT electrode 105 formed on the piezoelectric substrate 102 and a second determination unit that determines the frequency of the acoustic wave excited by the second IDT electrode 105 ( (Not shown). When the ambient temperature or the like of the elastic wave sensor 101 changes, the elastic constant and volume of the piezoelectric substrate 102 change, and as a result, the resonance frequency of the elastic wave excited by the first IDT electrode 103 changes. That is, the second IDT electrode 105 and the second determination unit function as a reference unit. Furthermore, the conventional acoustic wave sensor 101 compares the frequency determined by the first determination unit with the frequency determined by the second determination unit, and detects a detection target substance (not shown) based on the comparison result. Prepared).

  As described above, the conventional elastic wave sensor 101 has the frequency that the detection unit has determined by the first determination unit even if the frequency of the elastic wave excited by the first IDT electrode 103 changes due to a change in ambient temperature or the like. Since the frequency determined by the second determination unit is compared and the determination result of the first determination unit is corrected, the accuracy of sensing of the elastic wave sensor 101 can be improved.

  Note that Patent Documents 1 and 2 are known as prior art documents related to this application.

JP 2009-290914 A JP 2009-002677 A

  However, since the first IDT electrode 103 and the second IDT electrode 105 exist on the same substrate, the conventional elastic wave sensor 101 may contain a substance (exhaled breath, test liquid, etc.) that may contain a detection target substance. ) Are attached to the second IDT electrode 105 constituting the reference portion, and the resonance frequency of the elastic wave excited by the second IDT electrode 105 is changed by the attached substance. As a result, there is a problem in that the accuracy of sensing of the reference portion configured by the second IDT electrode 105 is deteriorated, and thereby the accuracy of sensing of the elastic wave sensor 101 is deteriorated.

  Therefore, an object of the present invention is to improve the accuracy of sensing of an elastic wave sensor.

  In order to achieve the above object, an elastic wave sensor of the present invention has characteristics of a piezoelectric substrate, a first IDT electrode formed on the piezoelectric substrate, and an elastic wave excited by the first IDT electrode. A first determination unit for determining, a reaction unit formed on the piezoelectric substrate so as to cover the first IDT electrode and reacting with a detection target substance or a binding substance that binds to the detection target substance; A second IDT electrode formed on the first IDT electrode, a dielectric film provided on the second IDT electrode, and a second determination unit for determining the characteristics of the elastic wave excited by the second IDT electrode And a detection unit that compares the characteristic determined by the first determination unit and the characteristic determined by the second determination unit, and detects a detection target substance or a binding substance that binds to the detection target substance based on the comparison result. Elastic wave excited by the second IDT electrode It is obtained by characterized in that it constitutes a reference portion in the boundary acoustic wave device comprising a boundary wave propagating through the boundary between the piezoelectric substrate and the dielectric film.

  With the above configuration, when a substance (exhaled breath, test liquid, etc.) that may contain a detection target substance is brought into contact with the acoustic wave sensor, the detection target substance or the like adheres to the second IDT electrode that constitutes the reference unit. To prevent. Thereby, since the characteristic change by this deposit | attachment is suppressed, the accuracy of sensing of the reference part comprised with a 2nd IDT electrode can be improved. As a result, the sensing accuracy of the elastic wave sensor is improved.

1 is a schematic top view of an elastic wave sensor according to Embodiment 1 of the present invention. Sectional schematic diagram of an elastic wave sensor according to Embodiment 1 of the present invention. Sectional schematic diagram of an elastic wave sensor according to Embodiment 2 of the present invention. Cross-sectional schematic diagram of a conventional elastic wave sensor

(Embodiment 1)
Hereinafter, the elastic wave sensor according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic top view of the acoustic wave sensor according to the first embodiment, and FIG. 2 is a schematic sectional view taken along the line AB of the acoustic wave sensor according to the first embodiment.

1 and 2, an elastic wave sensor 1 includes a piezoelectric substrate 2 and a first that is formed on the piezoelectric substrate 2 and excites an elastic wave having a wavelength λ ₁ such as an SH (Shear-Horizon) wave or a Rayleigh wave. An IDT (InterDigital Transducer) electrode 3, a first determination unit 6 that determines the frequency of the elastic wave excited by the first IDT electrode 3, and the first IDT electrode 3 so as to cover the piezoelectric substrate 2 And a reaction unit 4 that reacts with a detection target substance that may be contained in exhaled air or a binding substance that binds to the detection target substance. The elastic wave sensor 1, the dielectric having a second IDT electrode 5 for exciting an acoustic wave of a wavelength lambda ₂ are formed on the piezoelectric substrate 2, the thickness of the wavelength lambda ₂ or more to cover the second IDT electrode A body membrane 7 and a second determination unit 8 that determines the frequency of the elastic wave excited by the second IDT electrode 5 are provided. When the ambient temperature or the like of the elastic wave sensor 1 changes, the elastic constant and volume of the piezoelectric substrate 2 change, and as a result, the resonance frequency of the elastic wave excited by the first IDT electrode 3 changes. That is, the second IDT electrode 5 and the second determination unit 8 function as a reference unit. Furthermore, the acoustic wave sensor 1 compares the frequency determined by the first determination unit 6 with the frequency determined by the second determination unit 8, and based on the comparison result, binds to the detection target substance or the detection target substance. A detection unit 9 for detecting a substance is provided. Even if the frequency of the elastic wave excited by the first IDT electrode 3 is changed by the detection unit 9 due to the ambient temperature change or the like, the detection unit 9 determines the frequency determined by the first determination unit. Is compared with the frequency determined by the second determination unit, and the determination result of the first determination unit is corrected, so that the accuracy of sensing of the elastic wave sensor 1 can be improved.

  Further, the reference portion is configured by an elastic boundary wave element in which the elastic wave excited by the second IDT electrode 5 is a boundary wave that propagates through the boundary between the piezoelectric substrate 2 and the dielectric film 7. With this configuration, when a substance (exhaled breath, test liquid, etc.) that may contain a detection target substance is brought into contact with the acoustic wave sensor 1, the detection target substance or the like adheres to the second IDT electrode 5 constituting the reference unit. To prevent. Thereby, since the resonant frequency change by this deposit | attachment is suppressed, the accuracy of sensing of the reference part comprised by the 2nd IDT electrode 5 can be improved. As a result, the accuracy of sensing by the elastic wave sensor 1 is improved.

  The piezoelectric substrate 2 is made of a piezoelectric single crystal substrate, for example, a quartz crystal, lithium niobate-based, lithium tantalate-based, or potassium niobate-based substrate.

The 1st IDT electrode 3 and the 2nd IDT electrode 5 are comprised by arrange | positioning so that the electrode finger of two comb-shaped electrodes may each mesh. The electrode finger pitch of the first IDT electrode 3 (= 1/2 of λ ₁ ) and the electrode finger pitch of the second IDT electrode 5 (= 1/2 of λ ₂ ) may be different or the same. . However, if the electrode structures such as the electrode finger pitch, the number of electrode fingers, the crossing width, and the film thickness of the first IDT electrode 3 and the second IDT electrode 5 are the same, the degree of influence from the ambient temperature of both IDT electrodes And the sensing accuracy of the elastic wave sensor 1 is improved. The film thickness of the first IDT electrode 3 and the second IDT electrode 5 is about 0.01λ to 0.12λ, where λ ₁ = λ ₂ = λ. For example, aluminum, copper, silver, gold, It is a structure in which a single metal made of titanium, tungsten, platinum, molybdenum, or chromium, an alloy containing these as a main component, or a stack of these metals. In particular, it is desirable to use gold which is resistant to corrosion and has a large mass as a material for the IDT electrodes 3 and 5.

  The reaction section 4 may be provided in contact with the first IDT electrode 3, but a piezoelectric film (not shown) or a dielectric film (not shown) provided on the first IDT electrode 3. ). That is, the reaction part 4 should just be provided in the range in which the displacement of the surface acoustic wave excited by the 1st IDT electrode 3 exists. The reaction unit 4 is made of an organic material film such as an appropriate artificial cell film that reacts with a detection target substance or a binding substance that binds to the detection target substance, a single metal such as nickel, copper, gold, cobalt, or zinc, or an alloy. It can be composed of a metal film. Moreover, this reaction part 4 does not need to be a film | membrane form, For example, the reaction particle which consists of a particulate liposome may be sufficient.

  The first determination unit 6 determines the frequency of the elastic wave excited by the first IDT electrode 3, but other characteristics such as the velocity, amplitude, and wavelength of the elastic wave excited by the first IDT electrode 3 are determined. You may judge. Similarly, the second determination unit 8 determines the frequency of the elastic wave excited by the second IDT electrode 5, but other than the velocity, amplitude, wavelength, etc. of the elastic wave excited by the second IDT electrode 5. The characteristics may be determined.

  The detection unit 9 compares the elastic wave characteristic determined by the first determination unit 6 with the elastic wave characteristic determined by the second determination unit 8, and based on the comparison result, the detection target substance or the detection target substance A binding substance that binds to is detected. For example, the detection unit 9 calculates the ambient temperature of the elastic wave sensor 1 based on the frequency of the elastic wave determined by the second determination unit 8 during the comparison, and based on the calculation result, the first The determination unit 6 corrects the frequency of the elastic wave, and detects the presence or absence of the detection target substance based on the corrected frequency. The detection unit 9 may detect the presence or absence of a detection target substance or a binding substance that binds to the detection target substance, or may detect the concentration of these substances.

  The first determination unit 6, the second determination unit 8, and the detection unit 9 may exist in the same semiconductor package or may exist in different semiconductor packages.

The dielectric film 7 is, for example, a single layer of silicon oxide (SiO ₂ ), diamond (C), silicon (Si), silicon nitride (SiN), aluminum nitride (AlN), or aluminum oxide (Al ₂ O ₃ ). It is a structure or a laminated structure thereof. When a medium having a frequency temperature characteristic opposite to that of the piezoelectric substrate 2 such as silicon oxide is used as the dielectric film 7, the frequency temperature characteristic of the acoustic wave sensor 1 can be improved. In addition, the piezoelectric substrate 2, the second IDT electrode 5, and the dielectric so that the velocity of the bulk wave propagating through the piezoelectric substrate 2 and the dielectric film 7 is faster than the velocity of the elastic wave excited by the second IDT electrode 5. By determining the material of the body film 7 and the film thickness thereof, an elastic wave can be confined at the boundary between the dielectric film 7 and the piezoelectric substrate 2. The velocity of the main acoustic wave in the second IDT electrode 5 is mainly determined by the material of the dielectric film 7 and the material and film thickness of the second IDT electrode 5. For example, silicon oxide, which is a medium having a frequency temperature characteristic opposite to that of the piezoelectric substrate 2, is used as the first dielectric film from the piezoelectric substrate 2 side that covers the second IDT electrode 5, and the second dielectric layer on the dielectric layer. As the body layer, for example, diamond, silicon nitride, aluminum nitride, or aluminum oxide, which is a medium in which the velocity of the slowest bulk wave propagating in the dielectric layer is faster than the velocity of the elastic wave excited by the second IDT electrode 5 is used. If used, both frequency temperature characteristics and confinement of the main wave can be achieved.

The thickness of the dielectric film 7 is preferably not less than the wavelength λ _{2 and not} more than 5λ _{2 when} normalized by the wavelength λ ₂ of the elastic wave excited by the second IDT electrode 5. When the film thickness of the dielectric film 7 is equal to or greater than the wavelength λ ₂ , it is easy to confine the elastic wave excited by the second IDT electrode 5 in the element, and the film thickness of the dielectric film 7 is equal to or less than the wavelength 5λ ₂ . If so, the height of the element can be reduced. Desirably, when the film thickness of the dielectric film 7 is not less than the wavelength 2λ ₂ of the elastic wave, the elastic wave can be almost completely confined in the element.

  In such an acoustic wave sensor 1, the first IDT electrode 3 excites a surface acoustic wave propagating on the surface of the piezoelectric substrate, and the second IDT electrode 5 propagates on the boundary between the piezoelectric substrate 2 and the dielectric film 7. In this configuration, the boundary acoustic wave is excited.

  With this configuration, when a substance (exhaled breath, test liquid, etc.) that may contain a detection target substance is brought into contact with the acoustic wave sensor 1, the detection target substance or the like adheres to the second IDT electrode 5 constituting the reference unit. To prevent. Thereby, since the resonant frequency change by this deposit | attachment is suppressed, the accuracy of sensing of the reference part comprised by the 2nd IDT electrode 5 can be improved. As a result, the accuracy of sensing by the elastic wave sensor 1 is improved.

(Embodiment 2)
Hereinafter, an elastic wave sensor according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a schematic cross-sectional view of the acoustic wave sensor 11 according to the second embodiment. Unless otherwise specified, the configuration is the same as that of the first embodiment.

  The elastic wave sensor 11 according to the second embodiment is characterized in that the second IDT electrode 5 excites a surface acoustic wave and is covered with a cover portion 12 that forms the excitation space 15. The second IDT electrode 5 excites a surface acoustic wave propagating on the surface of the piezoelectric substrate.

  For example, the cover 12 is provided on the side wall 13 so as to surround the second IDT electrode 5 on the piezoelectric substrate 2 and on the side wall 13 so as to cover the second IDT electrode 5. And a lid 14.

  The side wall 13 is an insulator having a height of about 5 to 15 μm surrounding at least a part of the periphery of the second IDT electrode 5, and resin is used because it can be easily processed into a predetermined shape. In particular, by using a photosensitive resin as the side wall 13, the side wall 13 for making a plurality of acoustic wave filter components on the piezoelectric substrate can be accurately formed in a desired shape. As the photosensitive resin, various materials can be used as long as they are photosensitive resin materials such as a photosensitive polyimide resin, a photosensitive epoxy resin, and a photosensitive acrylate resin. A photosensitive polyimide resin is particularly preferable as the side wall 13 because it has a high glass transition point and high reliability in a high temperature environment.

  The lid 14 is a top plate having a thickness of about 1 to 10 μm held by being bonded to the upper portion of the side wall 13 via an adhesive layer (not shown). The IDT electrode 5 is accommodated. A metal is preferably used for the lid 14 because it is excellent in mechanical strength and can control the potential of the lid 14 by having conductivity, and further, if copper is used, a single crystal piezoelectric material is used. It is more preferable in that the linear expansion coefficient is substantially equal to the substrate 2. Moreover, as the cover body 14, for example, a photosensitive resin composition sheet may be used. The adhesive layer (not shown) is an adhesive having a thickness of about 1 to 10 μm, and is made of, for example, an epoxy-based, polyphenylene-based, or butadiene-based resin, or a mixed resin thereof.

  The excitation space 15 is a region surrounded by the piezoelectric substrate 2, the side wall 13, and the lid body 14. This excitation space 15 has airtightness, and the second IDT electrode 5 is accommodated therein. The inside of the excitation space 15 may be air at normal atmospheric pressure, but it is more preferable that the second IDT electrode 5 is prevented from being corroded if sealed under reduced pressure.

  When the cover part 12 covering the second IDT electrode 5 is brought into contact with a substance (exhaled breath, test liquid, etc.) that may contain the detection target substance with respect to the acoustic wave sensor 11, a second part constituting the reference part is formed. The detection target substance or the like is prevented from adhering to the IDT electrode 5. Thereby, since the resonant frequency change by this deposit | attachment is suppressed, the accuracy of sensing of the reference part comprised by the 2nd IDT electrode 5 can be improved. As a result, the accuracy of sensing by the elastic wave sensor 11 is improved.

  The elastic wave sensor according to the present invention has an effect of improving the accuracy of sensing, and can be applied to electronic devices such as various medical devices.

DESCRIPTION OF SYMBOLS 1, 11 Elastic wave sensor 2 Piezoelectric substrate 3 1st IDT electrode 4 Reaction part 5 2nd IDT electrode 6 1st determination part 7 Dielectric film 8 2nd determination part 9 Detection part 12 Cover part 13 Side wall 14 Cover Body 15 Excitation space

Claims (2)

A piezoelectric substrate;
A first IDT electrode formed on the piezoelectric substrate;
A first determination unit for determining characteristics of an elastic wave excited by the first IDT electrode;
A reaction portion formed on the piezoelectric substrate so as to cover the first IDT electrode and reacting with a detection target substance or a binding substance that binds to the detection target substance;
A second IDT electrode formed on the piezoelectric substrate;
A dielectric film provided on the second IDT electrode;
A second determination unit for determining characteristics of an elastic wave excited by the second IDT electrode;
Comparing the characteristic determined by the first determination unit with the characteristic determined by the second determination unit, and detecting a detection target substance or a binding substance that binds to the detection target substance based on the comparison result; Prepared,
The elastic wave sensor, wherein the second IDT electrode excites an elastic boundary wave propagating along a boundary between the piezoelectric substrate and the dielectric film. A piezoelectric substrate;
A first IDT electrode formed on the piezoelectric substrate;
A first determination unit for determining characteristics of an elastic wave excited by the first IDT electrode;
A reaction portion formed on the piezoelectric substrate so as to cover the first IDT electrode and reacting with a detection target substance or a binding substance that binds to the detection target substance;
A second IDT electrode formed on the piezoelectric substrate;
A second determination unit for determining characteristics of an elastic wave excited by the second IDT electrode;
Comparing the characteristic determined by the first determination unit and the characteristic determined by the second determination unit, and a detection unit for detecting the detection target substance based on the comparison result,
The elastic wave sensor, wherein the second IDT electrode is covered with a cover part that forms an excitation space of the second IDT electrode.

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