WO2010146923A1 - Elastic surface wave sensor - Google Patents

Abstract

Provided is an elastic surface wave sensor wherein a metal membrane is used, thereby permitting the detection sensitivity to be improved. An elastic surface wave sensor (10) is equipped with (a) a piezoelectric substrate (12), (b) IDT electrodes (13) formed on the piezoelectric substrate (12), and (c) a coated membrane (17) formed in such a way as to cover the IDT electrodes (13). The coated membrane (17) comprises (i) an insulating membrane (14) which covers the IDT electrodes (13), (ii) a metal membrane (16) which is formed on the other side of the piezoelectric substrate (12) for the insulating membrane (14) and which has a density higher than that of the insulating membrane (14). As regards the elastic surface wave sensor (10), a mass load on the coated membrane (17) is detected by the IDT electrodes (13).

Description

Surface acoustic wave sensor

The present invention relates to a surface acoustic wave sensor, and more particularly to a surface acoustic wave sensor that utilizes a change in frequency characteristics of a surface acoustic wave element.

Conventionally, various surface acoustic wave sensors that utilize changes in the frequency characteristics of surface acoustic wave elements in accordance with changes in the mass load on the surface of the surface acoustic wave element have been proposed.

For example, in Patent Document 1, as shown in the schematic diagram of FIG. 7, by comparing the oscillation frequencies of the measurement acoustic wave element 112 and the reference acoustic wave element 114 respectively formed on the piezoelectric substrate 110, A surface acoustic wave sensor for detecting the concentration of a measurement object is disclosed. The acoustic wave element 112 for measurement is formed with a sensitive film 116 that exhibits adsorptivity to the object to be measured, and the oscillation frequency of the acoustic wave element 112 for measurement changes as the sensitive film 116 adsorbs the object to be measured. To do. The reference elastic wave element 114 is formed with the same type of sensitive film 118 as the sensitive film 116, but the sensitive film 118 of the reference elastic wave element 114 is adsorbed to the object to be measured adsorbed by the sensitive film 116. It is inactivated so as not to show sex. The sensitive films 116 and 118 can be formed on the acoustic wave elements 112 and 114, respectively, with an Au film interposed.

In Patent Document 2, as shown in the explanatory diagram of FIG. 8, the thickness over the entire surface of the piezoelectric substrate 204 on which the transverse wave excitation unit 206, the reception unit 207, and the longitudinal wave excitation units 210 and 210 are formed. A guide layer layer 212 made of a SiO ₂ film having a thickness of about 3 μm is formed. Between the excitation unit 206 and the receiving unit 207 on the guide layer layer 212, a chromium film having a thickness of 20 nm and an Au film having a thickness of 100 nm are formed. And a surface acoustic wave sensor 240 in which an immobilization film 209 is formed. The surface acoustic wave sensor 240 is a delay line type surface acoustic wave sensor, and the immobilization film 209 formed between the transmission IDTs 206 a and 206 b and the reception IDTs 207 a and 207 b becomes the detection unit 208. That is, no detection unit is formed on the IDT.

In Patent Document 3, an IDT electrode 303 for surface wave excitation is formed on a piezoelectric substrate 302 and an insulating film 306 is formed so as to cover the IDT electrode 303 as shown in the cross-sectional view of the main part of FIG. An elastic surface on which a reaction film 308 that reacts with a detection target substance or a binding substance that binds to the detection target substance (hereinafter referred to as “mass-loading substance”) is formed on the film 306 via the adhesion layer 307. A wave sensor 301 is disclosed. In the surface acoustic wave sensor 301, the reaction film 308 is a metal film, and the metal film itself reacts with the mass load substance to detect the change.

JP 2006-258767 A JP 2005-351799 A International Publication No. 2008/102577

The Au films disclosed in Patent Documents 1 and 2 use a general technique for bonding the Au film to thiol groups such as protein and DNA, and the film thickness of the Au film is not considered. Since the surface acoustic wave sensor disclosed in Patent Document 2 is a transversal type, there is a problem that the element itself is large. The surface acoustic wave sensor disclosed in Patent Document 3 uses a metal film as a reaction film.

Patent Documents 1 to 3 do not disclose or suggest that the sensitivity of the surface acoustic wave sensor is improved by limiting the thickness or density of the metal film.

In view of such circumstances, the present invention intends to provide a surface acoustic wave sensor that can improve detection sensitivity using a metal film.

In order to solve the above problems, the present invention provides a surface acoustic wave sensor configured as follows.

The surface acoustic wave sensor includes (a) a piezoelectric substrate, (b) an IDT electrode formed on the piezoelectric substrate, and (c) a coating film formed so as to cover the IDT electrode. The covering film includes: (i) an insulating film that covers the IDT electrode; and (ii) a metal film that is formed on the opposite side of the insulating film from the piezoelectric substrate and has a density greater than that of the insulating film. Including. In the surface acoustic wave sensor, a mass load on the coating film is detected by the IDT electrode.

In the above configuration, the surface load is excited by the IDT electrode and the frequency characteristic is measured to detect the mass load on the coating film. At this time, the mass of the coating film itself does not change.

According to the above configuration, the coating film includes an insulating film having a relatively low density on the piezoelectric substrate side, and includes a metal film having a relatively high density on the side opposite to the piezoelectric substrate, that is, the surface side. The surface wave has a higher energy concentration on the opposite side of the piezoelectric substrate than the piezoelectric substrate side, that is, on the surface of the coating film, and the amount of displacement by the surface acoustic wave on the surface of the coating film subjected to mass load is Can be made larger than when only an insulating film is formed. Thereby, the detection sensitivity with respect to mass load can be improved.

In a preferred embodiment, a reaction that includes a reactant that specifically reacts with a mass-loading substance that is a binding substance that binds to a detection target substance or a detection target substance, on a main surface of the coating film opposite to the piezoelectric substrate. A film is formed.

In this case, the sensitivity for detecting that the mass in the reaction film has changed due to the mass-loading substance can be improved by adding a metal film.

In another preferred embodiment, the metal film is exposed on the main surface of the coating film opposite to the piezoelectric substrate.

In this case, the sensitivity to the mass loading substance deposited on the metal film can be improved by adding the metal film.

Preferably, the metal film is mainly composed of a metal having a density of 10 g / cc, that is, 10 × 10 ³ kg / m ³ at room temperature (298 K).

In this case, good resonance characteristics can be obtained without increasing the thickness of the metal film, and the sensitivity of the surface acoustic wave sensor can be easily improved.

Preferably, when the thickness of the metal film is h and the wavelength of the surface acoustic wave excited according to the pitch of the electrode fingers of the IDT electrode is λ,
0.001 ≦ h / λ ≦ 0.06
Meet.

In order to improve the sensitivity of the surface acoustic wave sensor, at least this condition must be satisfied.

Preferably, the thickness of the metal film is h, the wavelength of the surface acoustic wave excited according to the pitch of the electrode fingers of the IDT electrode is λ, and the normalized film thickness of the metal film is y = h / λ And the density of the metal film at room temperature (289 K) is x [g / cc],
y ≦ −0.004x + 0.1
Meet.

In this case, the sensitivity of the surface acoustic wave sensor can be improved by reducing the thickness of the metal film as the density of the metal film is increased. That is, it is possible to prevent the sensitivity on the surface side of the coating film from being excessively increased and the sensitivity being lowered.

Preferably, the metal layer is made of Au. When the thickness of the metal film is h, and the wavelength of the surface acoustic wave excited according to the pitch of the electrode fingers of the IDT electrode is λ,
0.003 ≦ h / λ ≦ 0.015
Meet.

In this case, the sensitivity of the surface acoustic wave sensor is 1.5 times or more as compared with the case where the coating film is made of only an insulating film and no metal film, and the deterioration of the resonance characteristics is small. Since the metal film is made of Au, it is easy to form a reaction film using a thiol bond, and the metal film is stable even in a solution.

Preferably, the IDT electrode is mainly composed of a metal having a density lower than that of the metal forming the metal film.

In this case, the mass on the surface side of the coating film can be made larger than that on the piezoelectric substrate side, and the amount of displacement due to the surface acoustic wave on the surface side of the coating film can be increased to improve the detection sensitivity.

More preferably, the IDT electrode contains Al as a main component.

In this case, the IDT electrode can be easily formed.

The surface acoustic wave sensor of the present invention can improve detection sensitivity using a metal film.

(A) It is principal part sectional drawing which shows typically the structure of a surface acoustic wave sensor, (b) The top view which shows typically the structure of a surface acoustic wave element. Example 1 It is sectional drawing which shows typically the structure of the reaction film of a surface acoustic wave sensor. Example 1 It is principal part sectional drawing which shows the structure of a surface acoustic wave sensor typically. (Example 2) It is a graph which shows the relationship between the film thickness of the uppermost metal film, and sensitivity. (Analysis example 1) It is a graph which shows the relationship between the density and film thickness of the uppermost metal film. (Analysis example 1) It is a graph which shows the film thickness of the uppermost Au film | membrane, and the relationship of a sensitivity. (Analysis example 2) It is the schematic which shows the structure of a surface acoustic wave sensor. (Conventional example 1) It is explanatory drawing which shows the structure of a surface acoustic wave sensor. (Conventional example 2) It is principal part sectional drawing which shows the structure of a surface acoustic wave sensor. (Conventional example 3)

Hereinafter, embodiments of the present invention will be described with reference to FIGS.

<Example 1> The structure of the surface acoustic wave sensor 10 of Example 1 will be described with reference to FIGS. FIG. 1A is a main part sectional view schematically showing the configuration of the surface acoustic wave sensor 10. FIG. 1B is a plan view schematically showing the configuration of the surface acoustic wave element. FIG. 2 is a cross-sectional view schematically showing the configuration of the reaction film of the surface acoustic wave sensor 10.

As shown in FIG. 1A, the surface acoustic wave sensor 10 includes a surface acoustic wave element 11 (see FIG. 1B) including an IDT electrode 13 formed on a piezoelectric substrate 12 so as to cover the IDT electrode 13. An insulating film 14 is formed thereon, and an adhesion layer 15, a metal film 16, and a reaction film 18 are sequentially formed thereon. The surface 18s of the uppermost reaction film 18 is exposed. When the sample 2 is supplied, the surface 18s comes into contact with the sample 2 and reacts with, adsorbs or binds to the mass-loading substance 4 such as DNA or protein in the sample 2. . As a result, the mass of the reaction film 18 changes, but the mass of the coating film 17 itself formed by the insulating film 14, the adhesion layer 15, and the metal film 16 does not change.

As schematically shown in FIG. 1B, the surface acoustic wave element 11 includes two IDT electrodes 13 arranged in the vibration propagation direction (left-right direction in the figure) of the surface acoustic wave and both sides of the vibration propagation direction. And a reflector 13x arranged. The IDT electrode 13 is composed of a pair of comb electrodes each having a plurality of electrode fingers 13s that are interleaved with each other. A voltage is applied between a pair of comb electrodes of one IDT electrode 13 to excite the surface acoustic wave, and the surface acoustic waves are detected by a voltage change between the pair of comb electrodes of the other IDT electrode 13. The surface acoustic wave is confined between the reflectors 13x. The insulating film 14 (see FIG. 1A) is formed so as to cover the IDT electrode 13 and the reflector 13x.

The insulating film 14, the adhesion layer 15, and the coating film 17 formed of the metal film 16 include an insulating film 14 having a relatively low density on the piezoelectric substrate 12 side, and is relatively opposite to the piezoelectric substrate 12, that is, on the surface side. Since the metal film 16 having a high density is included, the surface acoustic wave has a higher energy concentration on the surface side, and the displacement amount of the reaction film 18 formed on the surface side of the coating film 17 due to the surface acoustic wave is covered. The film 17 is made of only the insulating film 14 and can be made larger than when the metal film 16 is not included. Thereby, the detection sensitivity with respect to the change of the mass load due to the reaction between the mass load substance and the reaction film 18 can be improved.

In the surface acoustic wave sensor 10, for example, an IDT electrode 13 is formed of an Au film on a piezoelectric substrate 12 such as a 36 ° rotated Y-plate X-propagating LiTaO ₃ , and an SiO ₂ film is formed thereon as an insulating film 14. Is done. As will be described in detail later, the SiO ₂ film of the insulating film 14 is a standardized film when the film thickness is h ₀ and the wavelength of the surface acoustic wave excited according to the pitch of the electrode fingers of the IDT electrode 13 is λ. The thickness h ₀ / λ is preferably formed to be about 0.05 to 0.4.

A metal film 16 is formed on the insulating film 14 via an adhesion layer 15 such as Ti having a thickness of about 10 nm. The metal film 16 is formed using a metal material such as Au, Pt, Ag, Ta, or the like that has a density exceeding 10 g / cc at room temperature (293 K). As will be described in detail later, the adhesion layer 15 and the metal film 16 have a standardized film thickness when the thickness is h and the wavelength of the surface acoustic wave excited according to the pitch of the electrode fingers of the IDT electrode 13 is λ. The h / λ is preferably formed to be 0.001 or more and 0.06 or less.

On the metal film 16, a reaction film 18 made of protein, DNA, or the like that specifically adsorbs a mass-loading substance such as protein or DNA to be detected is formed. As schematically shown in FIG. 2, the reaction film 18 is, for example, an antibody 19 fixed to the metal film 16, and the mass load substance 4 is an antigen that binds to the antibody 19.

The surface acoustic wave sensor 10 detects the mass load substance 4 by changing the frequency characteristic (for example, resonance frequency) when the mass load changes when the mass load substance 4 contained in the sample 2 is coupled to the reaction film 18. can do.

Example 2 The configuration of the surface acoustic wave sensor 10a of Example 2 will be described with reference to FIG. FIG. 3 is a cross-sectional view of an essential part schematically showing the configuration of the surface acoustic wave sensor 10a.

The surface acoustic wave sensor 10a according to the second embodiment is configured in substantially the same manner as the surface acoustic wave sensor 10 according to the first embodiment. In the following, the same reference numerals are used for the same components as in the first embodiment, and differences from the first embodiment will be mainly described.

As shown in FIG. 3, the surface acoustic wave sensor 10 a according to the second embodiment is formed so that the surface acoustic wave element 11 including the IDT electrode 13 is formed on the piezoelectric substrate 12 and covers the IDT electrode 13, as in the first embodiment. Although the insulating film 14 is formed, and the adhesion layer 15 and the metal film 16 are sequentially formed thereon, the reaction film is not formed unlike the first embodiment. That is, the metal film 16 is the uppermost layer, and the surface 16s of the metal film 16 is exposed.

The surface acoustic wave sensor 10a can detect the mass load material 4 by changing the frequency characteristics when the mass load material 4 included in the sample 2 is deposited on the surface 16s of the uppermost metal film 16. .

In the surface acoustic wave sensor 10a, for example, an IDT electrode 13 is formed of an Au film on a piezoelectric substrate 12 such as a 36 ° rotated Y-plate X-propagating LiTaO ₃ , and an SiO ₂ film is formed thereon as an insulating film 14. Is done. As will be described in detail later, the SiO ₂ film of the insulating film 14 is a standardized film when the film thickness is h ₀ and the wavelength of the surface acoustic wave excited according to the pitch of the electrode fingers of the IDT electrode 13 is λ. The thickness h ₀ / λ is preferably formed to be about 0.05 to 0.4.

A metal film 16 is formed on the insulating film 14 via an adhesion layer 15 such as Ti having a thickness of about 10 nm. The metal film 16 is formed using a metal material such as Au, Pt, Ag, Ta, or the like that has a density exceeding 10 g / cc at room temperature (293 K). As will be described in detail later, the adhesion layer 15 and the metal film 16 have a standardized film thickness when the thickness is h and the wavelength of the surface acoustic wave excited according to the pitch of the electrode fingers of the IDT electrode 13 is λ. The h / λ is preferably formed to be 0.001 or more and 0.06 or less.

On the metal film 16, a precipitate generated by the enzyme / substrate reaction is deposited as the mass load substance 4. For example, ALP (alkaline phosphatase) is used as the enzyme, and BCIP / NBT is used as the substrate.

<Analysis Example 1> Next, analysis results of the surface acoustic wave sensors 10 and 10a will be described.

Whether the mass load substance 4 is bonded to the reaction film 18 as in the first embodiment or the mass load substance 4 is deposited on the metal film 16 as in the second embodiment, the surface mass of the surface acoustic wave sensor is changed. In any case, analysis can be performed using an analysis model in which mass is added to the uppermost metal film.

In the analysis model, the piezoelectric substrate 12 is a 36 ° rotated Y-plate X propagation LiTaO ₃ substrate, the IDT electrode 13 is an Au film, and the insulating film 14 is a SiO ₂ film. When the film thickness of the IDT electrode 13 (Au film) is h ₁ , h ₁ /λ=0.03, and when the film thickness of the insulating film 14 (SiO ₂ film) is h ₀ , h ₀ /λ=0.3. . λ is the wavelength of the surface acoustic wave excited according to the pitch of the electrode fingers of the IDT electrode 13 (Au film). The thicknesses of the adhesion layer 15 and the reaction film 18 are negligible because they are sufficiently smaller than the metal film 16.

The graph of FIG. 4 is a graph showing the sensitivity Δf / f ₀ when the material (Al, Ag, Ta, Au) of the metal film 16 and the film thickness h are changed. The density of Al is less than 10 g / cc. The densities of Ag, Ta, and Au all exceed 10 g / cc, and the density is higher than that of SiO ₂ . λ is the wavelength of the surface acoustic wave excited according to the pitch of the electrode fingers of the IDT electrode 13. f ₀ is an initial resonance frequency, Δf is a fluctuation amount of the resonance frequency f ₁ with respect to the initial resonance frequency f ₀ , and Δf = f ₁ −f ₀ . The resonance frequency f ₁ is a resonance frequency when a mass load is added on the uppermost metal film 16 in the analysis model. That is, when the mass load substance 4 contained in the sample 2 is combined with the reaction film 18 in the surface acoustic wave sensor 10 of the first embodiment, or when the mass load is applied on the metal film 16 in the surface acoustic wave sensor 10a of the second embodiment. This is the resonance frequency when the substance 4 is deposited.

From FIG. 4, the addition of the metal film 16 can improve the detection sensitivity to the mass load on the surface of the surface acoustic wave sensors 10 and 10a. That is, in the surface acoustic wave sensor 10 according to the first embodiment, the addition of the metal film 16 can improve the sensitivity of detecting that the mass in the reaction film 18 has changed due to the mass load substance 4. In the surface acoustic wave sensor 10a according to the second embodiment, the addition of the metal film 16 improves the sensitivity of detecting a mass change caused by the mass load substance 4 being deposited on the sensor surface (the surface 16s of the metal film 16). it can.

As shown in FIG. 4, when the material of the metal film 16 is Al, the sensitivity is not improved even if the thickness of the metal film 16 is increased.

However, when the material of the metal film 16 is Ag, Ta, or Au having a density exceeding 10 g / cc, the sensitivity increases as the film thickness of the metal film 16 increases while the film thickness of the metal film 16 is small. Furthermore, when the film thickness of the metal film 16 is increased, the sensitivity is lowered, and even if the film thickness of the metal film 16 is increased, a sensitivity improvement effect cannot be obtained. This is because the resonance characteristics deteriorate when the thickness of the metal film 16 becomes too large. In FIG. 4, when the material of the metal film 16 is Ag, Ta, or Au, the range of the film thickness of the metal film 16 that can be suitably used as a surface acoustic wave sensor is plotted.

FIG. 5 shows the relationship between the maximum value of the preferred thickness of the metal film 16 and the density of the metal film 16 when the metal film 16 plotted in FIG. 4 is Ag, Ta, or Au. The vertical axis in FIG. 5 represents the film thickness y = h / λ of the metal film 16 normalized by the wavelength λ of the surface acoustic wave excited according to the pitch of the electrode fingers of the IDT electrode 13. 5 represents the density x [g / cc] of the metal of the metal film 16 at normal temperature.

In FIG. 5, since each plotted point is included in a region below the solid line 80, the metal film 16 is formed so that its density x and film thickness y are included in a region below the solid line 80. It is preferred that This solid line 80 is
y = −0.004x + 0.1
Is represented by

Also, as the density x of the metal film 16 decreases, the film thickness y of the metal film 16 needs to be increased in order to increase sensitivity. However, when the film thickness y of the metal film 16 increases, the resonance characteristics deteriorate. When the density x of the metal film 16 exceeds 10 g / cc, the film thickness y of the metal film 16 does not need to be increased until the resonance characteristics are deteriorated. This is preferable because it is easy to improve the sensitivity. That is, the region on the right side of the broken line 82 in FIG.

Therefore, it is preferable that the metal film 16 is formed so that the density x and the film thickness y are included in the inside (excluding the boundary line) of the triangular region 84 which is hatched in FIG.

In FIG. 5, since the solid line 80 and the broken line 82 intersect at h / λ = 0.06, it is preferable that h / λ ≦ 0.06. Further, from FIG. 4, when h / λ <0.001, the effect of improving the sensitivity due to the addition of the metal film 16 cannot be expected so much, so it is preferable that h / λ ≧ 0.01.

Therefore, when the film thickness of the metal film 16 is h and the wavelength of the surface acoustic wave excited according to the pitch of the electrode fingers of the IDT electrode 13 is λ,
0.001 ≦ h / λ ≦ 0.06
It is preferable that

Particularly in the case where the metal film 16 is an Au film, it can be seen from FIG. 4 that the characteristic deterioration of the surface acoustic wave element can be suppressed by setting h / λ ≦ 0.015. It can also be seen that by setting h / λ ≧ 0.003, the sensitivity of 1.5 times or more can be secured as compared with the case where there is no metal film (h / λ = 0).

Therefore, when the metal film 16 is an Au film,
0.003 ≦ h / λ ≦ 0.015
It is preferable to satisfy.

When the metal film 16 is made of an Au film, the metal film 16 is stable even in contact with the solution of the sample 2, and an Au-thiol bond between the thiol group and the Au film can be used when proteins are fixed.

Analysis Example 2 The graph of FIG. 6 shows the sensitivity Δf / f ₀ when the thickness h of the metal film 16 of the Au film is changed in the case where the IDT electrode 13 is formed of Al, Ag, and Au. It is.

From FIG. 6, when the IDT electrode 13 is formed of Al having a relatively low density, the sensitivity for detecting the mass load substance 4 is improved as compared with the case where the IDT electrode 13 is formed of Ag or Au having a relatively high density. I understand that This is because if the IDT electrode 13 is mainly composed of a metal having a density lower than that of the metal forming the metal film 16, the mass on the surface side becomes relatively large, and the displacement due to the surface acoustic wave on the surface side becomes large. As a result, the sensitivity is improved.

The IDT electrode 13 mainly composed of Al has a low resistivity, is inexpensive, and can be easily finely processed by photolithography.

<Summary> As described above, the sensitivity of the surface acoustic wave sensors 10 and 10a can be improved by providing the metal film 16 having a density exceeding 10 g / cc.

It should be noted that the present invention is not limited to the above embodiment, and can be implemented with various modifications.

2 Sample 4 Mass load material 10, 10a Surface acoustic wave sensor 11 Surface acoustic wave element 12 Piezoelectric substrate 13 IDT electrode 13x reflector 14 Insulating layer 15 Adhesion layer 16 Metal film 17 Coating film 18 Reaction film 19 Antibody

Claims (9)

A piezoelectric substrate;
An IDT electrode formed on the piezoelectric substrate;
A coating film formed to cover the IDT electrode;
With
The coating film is
An insulating film covering the IDT electrode;
The insulating film is formed on the opposite side of the piezoelectric substrate, and includes a metal film having a density higher than that of the insulating film,
A surface acoustic wave sensor, wherein a mass load on the coating film is detected by the IDT electrode. On the main surface of the coating film opposite to the piezoelectric substrate, a reaction film including a reaction substance that specifically reacts with a substance to be detected or a mass loading substance that is a binding substance that binds to the substance to be detected is formed. The surface acoustic wave sensor according to claim 1, wherein: The surface acoustic wave sensor according to claim 1, wherein the metal film is exposed on a main surface of the coating film opposite to the piezoelectric substrate. The surface acoustic wave sensor according to claim 1, 2 or 3, wherein the metal film is mainly composed of a metal having a density at room temperature exceeding 10 g / cc. When the thickness of the metal film is h, and the wavelength of the surface acoustic wave excited according to the pitch of the electrode fingers of the IDT electrode is λ,
0.001 ≦ h / λ ≦ 0.06
The surface acoustic wave sensor according to claim 1, wherein: The thickness of the metal film is h, the wavelength of the surface acoustic wave excited according to the pitch of the electrode fingers of the IDT electrode is λ, the normalized film thickness of the metal film is y = h / λ, When the density of the metal film at room temperature (289 K) is x [g / cc],
y ≦ −0.004x + 0.1
The surface acoustic wave sensor according to claim 1, wherein: The metal layer is made of Au;
When the thickness of the metal film is h, and the wavelength of the surface acoustic wave excited according to the pitch of the electrode fingers of the IDT electrode is λ,
0.003 ≦ h / λ ≦ 0.015
The surface acoustic wave sensor according to claim 1, wherein: The surface acoustic wave sensor according to any one of claims 1 to 7, wherein the IDT electrode is mainly composed of a metal having a density lower than that of the metal forming the metal film. The surface acoustic wave sensor according to claim 8, wherein the IDT electrode contains Al as a main component.

Images