WO2023189334A1 - Elastic wave sensor and method for manufacturing same - Google Patents

Abstract

An elastic wave sensor 100 comprises: a piezoelectric substrate 10; a pair of comb electrodes 24a and 24b which are provided on the piezoelectric substrate 10 and have a plurality of electrode fingers 22a and 22b, spaces between adjacent electrode fingers 22a and 22b on the piezoelectric substrate 10 being gaps 15; a first insulator layer 16 provided on the plurality of electrode fingers 22a and 22b; and a sensitive membrane 18 provided on the first insulator layer 16.　

Description

Acoustic wave sensor and its manufacturing method

The present invention relates to an acoustic wave sensor and a method for manufacturing the same, and for example, to an acoustic wave sensor having a sensitive film and a method for manufacturing the same.

2. Description of the Related Art Acoustic wave sensors using surface acoustic waves are known as sensors for detecting specific substances in gas or liquid. An elastic wave sensor is known that uses Love waves as surface acoustic waves by depositing a PMMA (Poly Methyl Methacrylate) layer on a crystal substrate (for example, Non-Patent Document 1). In an elastic wave sensor using Love waves, it is known to provide a SiO ₂ layer between a crystal substrate and a PMMA layer (for example, Non-Patent Document 2). It is known to provide two layers of SiO ₂ on a piezoelectric substrate and to provide a resin layer as a hydrophobic material on the two layers of SiO ₂ (for example, Patent Document 1).

Japanese Patent Application Publication No. 2006-38584

E. Gizeli et al. “A Novel Love-Plate Acoustic Sensor Utilizing Polymer Overlayers”, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Cintrol, Vol. 39, No. 5, pp657-659, (1992). J. Du etal. “A multilayers structure for Love-mode acoustic sensors”, Sensors and Actuators, Vol, A65 pp152-159, (1998)

As in Non-Patent Document 1, by providing a PMMA layer with low acoustic impedance under the sensitive film, the sensitivity of the acoustic wave sensor can be improved. However, since a material with low acoustic impedance has a small Young's modulus, the elastic loss in the PMMA layer increases, and the characteristics of the acoustic wave sensor deteriorate. By providing a SiO ₂ layer between the crystal substrate and the PMMA layer as in Non-Patent Document 2, elastic loss can be suppressed. However, further suppression of elastic loss is required.

The present invention was made in view of the above problems, and an object of the present invention is to suppress elastic loss of an elastic wave sensor.

The present invention includes a piezoelectric substrate, a pair of comb-shaped electrodes provided on the piezoelectric substrate and having a plurality of electrode fingers, and having a gap between adjacent electrode fingers on the piezoelectric substrate, and the plurality of electrode fingers. The present invention is an acoustic wave sensor including a first insulator layer provided above and a sensitive film provided on the first insulator layer.

In the above configuration, the resonator includes the piezoelectric substrate, the pair of comb-shaped electrodes, and the sensitive film, and has a resonant frequency that changes with changes in the environment; The configuration may include a detector that detects a change.

In the above structure, the first insulator layer and the sensitive film may not be provided between the adjacent electrode fingers.

The present invention includes a piezoelectric substrate, a pair of first comb-shaped electrodes provided on the piezoelectric substrate, a pair of second comb-shaped electrodes provided on the piezoelectric substrate, and a pair of first comb-shaped electrodes provided on the piezoelectric substrate. provided between the first comb-shaped electrodes and the pair of second comb-shaped electrodes, arranged in the arrangement direction of the pair of first comb-shaped electrodes and the pair of second comb-shaped electrodes, and arranged on the piezoelectric substrate. A plurality of electrode fingers having spaces between adjacent electrode fingers, a first insulator layer provided on the plurality of electrode fingers, and a sensitive film provided on the first insulator layer. , an acoustic wave sensor in which the first insulator layer and the sensitive film are not provided between the adjacent electrode fingers.

The above configuration includes a detector that detects a change in the environment based on a change in phase difference between a high frequency signal applied to the pair of first comb-shaped electrodes and a high frequency signal outputted from the pair of second comb-shaped electrodes. It can be configured as follows.

In the above configuration, the acoustic impedance of the first insulating layer may be smaller than the acoustic impedance of the plurality of electrode fingers.

In the above structure, a second insulating layer may be provided between the plurality of electrode fingers and the first insulating layer and having a Young's modulus larger than the Young's modulus of the first insulating layer. .

In the above structure, the first insulating layer may be separated above the gap.

In the above structure, the width of the first insulating layer may be larger than the width of each of the adjacent electrode fingers in the direction in which the plurality of electrode fingers are arranged.

In the above configuration, the plurality of electrode fingers may be embedded in the piezoelectric substrate.

In the above structure, the first insulator layer may be continuously provided on the plurality of electrode fingers so as to form a gap between the plurality of electrode fingers.

In the above structure, the first insulating layer may be provided with a hole connecting the void and the outside on the first insulating layer.

In the above configuration, a second insulating layer is provided continuously between the plurality of electrode fingers and the voids and the first insulating layer, and the hole is provided in communication with the first insulating layer. The diameter of the hole in the body layer may be larger than the diameter of the hole in the second insulator layer.

In the above structure, a second insulating layer is provided continuously between the plurality of electrode fingers and the void and the first insulating layer, and the surface on the void side is arch-shaped. I can do it.

The present invention includes a piezoelectric substrate, a pair of first comb-shaped electrodes provided on the piezoelectric substrate, a pair of second comb-shaped electrodes provided on the piezoelectric substrate, and a pair of first comb-shaped electrodes provided on the piezoelectric substrate. a metal layer provided between the first comb-shaped electrodes and the pair of second comb-shaped electrodes; and a metal layer provided on the metal layer, the pair of first comb-shaped electrodes and the pair of second comb-shaped electrodes; an acoustic wave sensor comprising: a plurality of insulator fingers arranged in the arrangement direction of the metal layer, with gaps between adjacent insulator fingers on the metal layer; and a sensitive film provided on the plurality of insulator fingers. It is.

The above configuration includes a detector that detects a change in the environment based on a change in phase difference between a high frequency signal applied to the pair of first comb-shaped electrodes and a high frequency signal outputted from the pair of second comb-shaped electrodes. It can be configured as follows.

The present invention includes a step of forming a plurality of electrode fingers and a sacrificial layer between the plurality of electrode fingers on a piezoelectric substrate, and a step of forming a first insulator layer on the plurality of electrode fingers and the sacrificial layer. a step of forming a sensitive film on the first insulating layer; a step of forming a hole that penetrates the first insulating layer and contacts the sacrificial layer; and an etching step of removing the sacrificial layer through the hole. The method of manufacturing an acoustic wave sensor includes the step of forming gaps between a plurality of electrode fingers between the piezoelectric substrate and the first insulator layer by introducing a liquid.

In the above structure, the step of forming a second insulator layer on the plurality of electrode fingers and the sacrificial layer includes the step of forming the first insulator layer on the second insulator layer. The step of forming the hole includes the step of forming an insulator layer, and the step of forming the hole includes the step of forming the hole so that the diameter of the hole penetrating the first insulator layer is larger than the diameter of the hole penetrating the second insulator layer. The method may include a step of forming the hole penetrating the first insulator layer and the second insulator layer.

In the above structure, the step of forming the hole may include the step of forming the hole outside a region of the piezoelectric substrate in which an elastic wave propagates in a direction in which the plurality of electrode fingers extend.

According to the present invention, elastic loss of an elastic wave sensor can be suppressed.

FIG. 1(a) is a plan view of the elastic wave sensor according to Example 1, and FIG. 1(b) is a sectional view taken along line AA in FIG. 1(a). FIGS. 2A to 2D are cross-sectional views of elastic wave sensors according to Modifications 1 to 4 of the first embodiment. 3(a) is a plan view of an elastic wave sensor according to a fifth modification of the first embodiment, and FIG. 3(b) is a sectional view taken along line AA in FIG. 3(a). FIGS. 4(a) to 4(d) are cross-sectional views of sensors A to D, respectively, in the simulation. FIG. 5(a) is a diagram showing |Y| with respect to the frequencies of sensors A to C in the simulation, and FIG. 5(b) is a diagram showing |Y| with respect to the frequencies of sensors B and D in the simulation. FIGS. 6A and 6B are diagrams showing the magnitude of displacement in the Y direction with respect to the X coordinate in sensors B and D, respectively. 7(a) to 7(f) are cross-sectional views showing a method of manufacturing an elastic wave sensor according to the first embodiment. FIGS. 8(a) to 8(f) are cross-sectional views showing a method of manufacturing an elastic wave sensor according to the first embodiment. 9(a) to 9(f) are cross-sectional views showing a method of manufacturing an elastic wave sensor according to Example 1. FIG. 10(a) to 10(d) are cross-sectional views showing a method of manufacturing an elastic wave sensor according to a sixth modification of the first embodiment. FIG. 11 is a cross-sectional view of an elastic wave sensor according to Modification Example 7 of Example 1. FIG. 12(a) is a plan view of the elastic wave sensor according to Example 2, and FIG. 12(b) is a sectional view taken along line AA in FIG. 12(a). 13(a) and 13(b) are cross-sectional views of elastic wave sensors according to modified examples 1 and 2 of the second embodiment. FIG. 14(a) is a plan view of an elastic wave sensor according to Example 3, and FIG. 14(b) is a sectional view taken along line AA in FIG. 14(a). 15(a) and 15(b) are block diagrams of a detection system according to the fourth embodiment and the first modification thereof.

Examples will be described below with reference to the drawings.

As Example 1, an example will be described in which a surface acoustic wave resonator is employed as an acoustic wave sensor that detects environmental changes in gas or liquid. FIG. 1(a) is a plan view of an elastic wave sensor 100 according to Example 1, and FIG. 1(b) is a cross-sectional view taken along line AA in FIG. 1(a). The direction in which the electrode fingers 22a and 22b are arranged is the X direction, the extending direction of the electrode fingers 22a and 22b is the Y direction, and the normal direction of the piezoelectric substrate 10 is the Z direction. The X, Y, and Z directions do not necessarily match the crystal orientation of the piezoelectric substrate 10. When the piezoelectric substrate 10 is a rotating Y-cut X-propagation substrate, the X direction is the X-axis direction of the crystal orientation. FIG. 1(a) mainly shows an IDT 20 (interdigital transducer), pads 25a, 25b, insulator layers 14, 16, reflector 21, sensitive film 18, and hole 26, and shows the sensitive film 18 with a thick broken line, Reflector 21, IDT 20, and pads 25a and 25b are shown by cross hatching.

As shown in FIGS. 1(a) and 1(b), in the acoustic wave sensor 100, a metal film 12 is provided on a piezoelectric substrate 10. Metal film 12 forms IDT 20, reflector 21, and pads 25a and 25b. IDT 20 has comb-shaped electrodes 24a and 24b. The comb-shaped electrode 24a (first comb-shaped electrode) has a plurality of electrode fingers 22a (first electrode fingers) and a bus bar 23a. The +Y side ends of the plurality of electrode fingers 22a extending in the Y direction are connected to the bus bar 23a, and the bus bar 23a extends in the X direction. The comb-shaped electrode 24b (second comb-shaped electrode) has a plurality of electrode fingers 22b (second electrode fingers) and a bus bar 23b. The −Y side ends of the plurality of electrode fingers 22b extending in the Y direction are connected to the bus bar 23b, and the bus bar 23b extends in the X direction. A region of the IDT 20 where the electrode fingers 22a and 22b overlap when viewed from the X direction is a crossing region 50. In at least a part of the region 50, the electrode fingers 22a and 22b are provided alternately. Although the elastic waves propagate outside the region 50, they mainly propagate within the region 50. A gap region 52 exists between region 50 and bus bars 23a and 23b.

Reflectors 21 are formed on both sides of the IDT 20 in the X direction. Each reflector 21 includes a plurality of electrode fingers 22c and a pair of bus bars 23c. The plurality of electrode fingers 22c are connected to one bus bar 23c at the +Y end, and connected to the other bus bar 23c at the -Y end. Within the region 50, the elastic waves excited by the IDT 20 mainly propagate in the X direction, and the reflector 21 reflects the elastic waves. Let the pitch of the electrode fingers 22a and the pitch of the electrode fingers 22b be λ. λ corresponds to the wavelength of the surface acoustic wave excited by the IDT 20. λ is twice the pitch P of the plurality of electrode fingers 22a and 22b.

A gap 15 is provided on the piezoelectric substrate 10 between the electrode fingers 22a and 22b and between the electrode fingers 22c. The space 15 is filled with gas such as air. An insulator layer 14 is provided on the piezoelectric substrate 10 so as to cover the metal film 12 and the void 15 . An insulator layer 16 is provided on the insulator layer 14. Insulator layers 14 and 16 are provided to cover IDT 20 and reflector 21. In the cross-sectional view in the XZ plane, in the IDT 20, the gap 15 is surrounded by the piezoelectric substrate 10, the insulator layer 14, and the electrode fingers 22a and 22b, and in the reflector 21, the gap 15 is surrounded by the piezoelectric substrate 10, the insulator layer 14, and and surrounded by electrode fingers 22c. A sensitive film 18 is provided on the insulator layer 14. The sensitive film 18 is provided on the region 50 of the IDT 20 and is not provided anywhere other than the region 50.

In the IDT 20, a hole 26 penetrating through the insulator layers 14 and 16 is provided in a gap region 52 outside the region 50 in the Y direction. Hole 26 connects void 15 and the outside on insulator layer 16 . The hole 26 is provided between the tip of the electrode finger 22b and the bus bar 23a, and between the tip of the electrode finger 22a and the bus bar 23b. In the reflector 21, a hole 26 penetrating through the insulator layers 14 and 16 is provided between the electrode fingers 22c in the gap region 52. As will be described later, the hole 26 is a hole for etching the sacrificial layer formed to form the void 15. A pad 25a is connected to the +Y side of the bus bar 23a, and a pad 25b is provided to the -Y side of the bus bar 23b. Pads 25a and 25b are terminals for electrically connecting comb-shaped electrodes 24a and 24b to the outside, respectively.

The piezoelectric substrate 10 is, for example, a lithium tantalate (LiTaO ₃ ) substrate, a lithium niobate (LiNbO ₃ ) substrate, or a quartz (single-crystal SiO ₂ ) substrate, and is, for example, a single-crystal rotating Y-cut, It is a crystal rotation Y cut X propagation lithium niobate substrate. The piezoelectric substrate 10 may be bonded to a supporting substrate such as a sapphire substrate, a silicon substrate, a spinel substrate, a quartz substrate, or a quartz substrate directly or via an insulating layer. The metal film 12 has at least one metal as a main component, for example, aluminum (Al), copper (Cu), gold (Au), and molybdenum (Mo). An adhesion layer or barrier layer such as a titanium (Ti) layer or a chromium (Cr) layer may be provided between the metal film 12 and the piezoelectric substrate 10.

The insulator layer 14 is made of, for example, a silicon oxide (SiO ₂ ) film, an aluminum oxide (Al ₂ O ₃ ) film, a zinc oxide (ZnO) film, a tantalum oxide (Ta ₂ O ₅ ) film, a silicon nitride (SiN) film, or a nitride film. This is an insulating film such as a silicon oxide (SiON) film. The insulator layer 16 is, for example, a polymer resin such as PMMA, PDMS (dimethylpolysiloxane), or polyimide. The acoustic impedance of the insulator layer 16 is smaller than the acoustic impedance of the metal film 12 and the acoustic impedance of the insulator layer 14.

The sensitive film 18 is, for example, an organic polymer film, an organic low molecular film, or an inorganic film. Examples of polymers such as organic polymer materials include polystyrene, polymethyl methacrylate, 6-nylon, cellulose acetate, poly-9,9-dioctylefluorene, polyvinyl alcohol, polyvinylcarbazole, polyethylene oxide, polyvinyl chloride, and polyvinyl chloride. - A homopolymer or copolymer of two or more homopolymers consisting of a single structure such as p-phenylene ether sulfone, poly-1-butene, polybutadiene, polyphenylmethylsilane, polycaprolactone, polybisphenoxyphosphazene, and polypropylene. Copolymers, blend polymers made by mixing these, and the like can be used.

For example, organic low-molecular materials include tris(8-quinolinolato)aluminum (Alq3), naphthyldiamine (α-NPD), BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), and CBP. (4,4'-N,N'-dicarbazole-biphenyl), copper phthalocyanine, fullerene, pentacene, anthracene, thiophene, Ir(ppy(2-phenylpyridinato)) ₃ , triazinethiol derivative, dioctylfluorene derivative, tetratetracontane, Parylene or the like can be used.

For example, inorganic materials include alumina, titania, vanadium pentoxide, tungsten oxide, lithium fluoride, magnesium fluoride, aluminum, gold, silver, tin, indium tin oxide (ITO), carbon nanotubes, sodium chloride, chloride Magnesium or the like can be used.

Furthermore, when the acoustic wave sensor detects an antigen such as a virus or bacteria, the sensitive membrane 18 may contain antibodies. For example, the sensitive film 18 may include a connection layer provided on the insulator layer 16 and an antibody provided on the connection layer. Examples of the connection layer include a titanium layer with a thickness of 10 nm provided on the insulator layer 16 and a gold layer with a thickness of 20 nm provided on the titanium layer. A self-assembled monolayer may be provided between the antibody and the connection layer. The thickness of the self-assembled monolayer is, for example, 1 nm to 2 nm, and the thickness of the antibody is, for example, 10 nm to 20 nm.

When a specific object such as a substance such as a specific atom or molecule in a gas or liquid or an antigen such as a virus or bacteria is adsorbed or bonded to the sensitive membrane 18, the mass of the sensitive membrane 18 increases. Further, when the humidity changes, moisture binds to the sensitive film 18, and the mass of the sensitive film 18 changes. In this way, the mass of the sensitive film 18 changes due to changes in the environment. Corresponding to this change in mass, the sound speed of the elastic wave propagating through the region 50 changes. This changes the resonant frequency of the surface acoustic wave resonator. For example, when the sensitive film 18 becomes heavier, the sound speed of the elastic wave propagating through the region 50 becomes slower, and the resonant frequency becomes lower. Based on this change in resonance frequency, a specific object such as a specific substance or antigen can be detected.

In Example 1, a gap 15 is provided between the electrode fingers 22a and 22b on the piezoelectric substrate 10, and insulator layers 14 and 16 are provided on the electrode fingers 22a and 22b and the gap 15. By using a polymer resin having lower acoustic impedance than the electrode fingers 22a and 22b for the insulator layer 16, the sensitivity of the acoustic wave sensor is improved. By making the Young's modulus of the insulating layer 14 larger than the Young's modulus of the insulating layer 16, elastic loss can be suppressed. Furthermore, by providing the gap 15 between the electrode fingers 22a and 22b, the elastic waves propagate within the insulator layers 14 and 16 near the surface of the piezoelectric substrate 10, and the gap 15 between the electrode fingers 22a and 22b is propagated. Not propagated. Thereby, the number of elastic waves propagating through the insulator layers 14 and 16 having a low Young's modulus is reduced, and elastic loss can be suppressed.

The insulator layers 14 and 16 do not need to be provided on the reflector 21. In order to match the sound speed of the elastic wave excited by the IDT 20 and the sound speed of the elastic wave reflected by the reflector 21, and for the reflector 21 to efficiently reflect the elastic wave excited by the IDT 20, an insulating layer 14 is also provided on the reflector 21. and 16 are preferably provided. Further, it is preferable that a gap 15 is provided between the electrode fingers 22c of the reflector 21.

[Modification 1 of Example 1]
FIG. 2A is a cross-sectional view of the elastic wave sensor 101 according to Modification 1 of Example 1. As shown in FIG. 2A, in the acoustic wave sensor 101, the insulator layer 14 is not provided, and the insulator layer 16 is directly provided on the electrode fingers 22a and 22b and the void 15. The other configurations are the same as in Example 1, and their explanation will be omitted.

[Modification 2 of Example 1]
FIG. 2(b) is a cross-sectional view of the elastic wave sensor 102 according to the second modification of the first embodiment. As shown in FIG. 2(b), the insulator layers 14 and 16 are provided only on the electrode fingers 22a to 22c, and the insulator layers 14 and 16 are not provided on the void 15. The sensitive film 18 is provided only on the electrode fingers 22a and 22b, and the sensitive film 18 is not provided on the gap 15. The other configurations are the same as in Example 1, and their explanation will be omitted.

[Modification 3 of Example 1]
FIG. 2C is a cross-sectional view of the elastic wave sensor 103 according to the third modification of the first embodiment. As shown in FIG. 2C, the insulator layer 14 is not provided, and the insulator layer 16 is provided directly on the electrode fingers 22a and 22b. The other configurations are the same as the second modification of the first embodiment, and the explanation will be omitted.

[Modification 4 of Example 1]
FIG. 2D is a cross-sectional view of the elastic wave sensor 104 according to the fourth modification of the first embodiment. As shown in FIG. 2(d), the IDT 20 including electrode fingers 22a to 22c is embedded in the piezoelectric substrate 10. The other configurations are the same as the second modification of the first embodiment, and the explanation will be omitted. In the acoustic wave sensor 104 of the fourth modification of the first embodiment, the side surfaces of the electrode fingers 22a to 22c are not exposed from the piezoelectric substrate 10, so even when a sample liquid containing a sample is supplied to the sensitive membrane 18, the electricity of the IDT 20 is It is possible to suppress short-circuits, etc.

[Modification 5 of Example 1]
3(a) is a plan view of an elastic wave sensor according to a fifth modification of the first embodiment, and FIG. 3(b) is a sectional view taken along line AA in FIG. 3(a). As shown in FIGS. 3(a) and 3(b), in the IDT 20, in the region 50, between the electrode fingers 22a and 22b, and in the gap region 52, between the electrode fingers 22a and 22b and the bus bars 23b and 23a, respectively. A slit 28 is provided in the insulator layers 14 and 16 at. As a result, slits 28 are provided on the +Y side and ±X side of the electrode finger 22a, and slits 28 are provided on the -Y side and ±X side of the electrode finger 22b. In the reflector 21, a slit 28 is provided in the insulator layers 14 and 16 between the electrode fingers 22c. The slit 28 penetrates the insulator layers 14 and 16 and is connected to the void 15. The width of the slit 28 is smaller than the width of the hole 26. The other configurations are the same as in Example 1, and their explanation will be omitted.

[simulation]
A simulation was performed using the finite element method for sensors A to D. FIGS. 4(a) to 4(d) are cross-sectional views of sensors A to D, respectively, in the simulation. As shown in Figures 4(a) to 4(d), in the simulation, one wavelength λ of the elastic wave is extracted in the X direction, the boundary condition in the X direction is a mirror condition, and the boundary condition in the Y direction is continuous. It was made a condition. Although not shown, a thick sensitive film 18 was not provided as the sensitive film 18, but a pseudo sensitive film 18 was provided by adding mass with a certain areal density to the upper surface of the insulating layer 16. Sensor A corresponds to Comparative Example 1, sensor B corresponds to Example 1, sensor C corresponds to Modification 2 of Example 1, and sensor D corresponds to Modification 5 of Example 1.

As shown in FIG. 4(a), in sensor A, electrode fingers 22a and 22b are provided on the piezoelectric substrate 10, and an insulator layer 14 is provided on the piezoelectric substrate 10 so as to cover the electrode fingers 22a and 22b. ing. No gap 15 is provided between the electrode fingers 22a and 22b, and an insulator layer 14 is provided. An insulator layer 16 is provided on the insulator layer 14.

As shown in FIG. 4(b), in sensor B, a gap 15 is provided between the electrode fingers 22a and 22b, and insulator layers 14 and 16 are provided on the electrode fingers 22a, 22b and the gap 15. . The other configurations are the same as sensor A, and the explanation will be omitted.

As shown in FIG. 4(c), in sensor C, insulator layers 14 and 16 are provided only on electrode fingers 22a and 22b, and are not provided on gap 15. The width of the insulator layers 14 and 16 in the X direction is the same as the width of the electrode fingers 22a and 22b in the X direction. The other configurations are the same as sensor B, and the explanation will be omitted.

As shown in FIG. 4(d), in the sensor D, a slit 28 penetrating the insulator layers 14 and 16 above the gap 15 is provided in the insulator layers 14 and 16. The width G1 of the slit 28 is smaller than the distance G2 between the electrode fingers 22a and 22b. The width W2 of the insulator layers 14 and 16 in the X direction is larger than the width W1 of the electrode fingers 22a and 22b in the X direction. The other configurations are the same as sensor B, and the explanation will be omitted.

In sensors A to D, the thickness of electrode fingers 22a and 22b is T1, the thickness of insulator layer 14 is T2, and the thickness of insulator layer 16 is T3. As shown in FIGS. 4(b) and 4(d), the X coordinate of the end face of the piezoelectric substrate 10 in the −X direction is set to 0, and the +X direction is set to the X coordinate. Let the X coordinate of the midpoint between the electrode fingers 22a and 22b be X1, and the X coordinate of the end surface of the piezoelectric substrate 10 in the +X direction be X2. X1 is 1/2λ and X2 is λ. Let the X coordinates of the centers of electrode fingers 22a and 22b in the X direction be X3 and X4, respectively. X3 is λ/4 and X4 is 3λ/4.

The piezoelectric substrate 10 was a 42° rotated Y cut X propagation lithium tantalate substrate, the electrode fingers 22a and 22b were aluminum layers, the insulator layer 14 was a silicon oxide layer, and the insulator layer 16 was a PMMA layer. λ was set to 2.20 μm, and the width of the electrode fingers 22a and 22b in the X direction was set to 0.55 μm. Table 1 is a table showing thicknesses T1 to T3, sensitivity |Δf|/f ² and admittance ratio ΔY.

The thicknesses T1 to T3 of sensors A to D were set to the values shown in Table 1. Sensitivity |Δf|/f Of ² , Δf is the amount of change in the resonant frequency f when a mass having a surface density on the upper surface of the insulating layer 16 is added. Since |Δf| is proportional to the square of the resonance frequency f, it is normalized by ^f2 . A large sensitivity |Δf|/f ² indicates that the resonant frequency f changes greatly when the same areal density is applied to the upper surface of the insulating layer 16. ΔY is the difference between the absolute value of the admittance at the resonant frequency |Y| and the absolute value of the admittance at the anti-resonant frequency |Y|. A large ΔY indicates a small elastic loss.

First, the thickness T3 of the insulator layer 16 was adjusted so that the sensitivities |Δf|/f ² were approximately the same for the sensors A to C. As shown in Table 1, the sensitivities |Δf|/f ² of sensors A to C are almost the same.

FIG. 5(a) is a diagram showing |Y| with respect to the frequencies of sensors A to C in the simulation. The horizontal axis represents frequency, and the vertical axis represents the absolute value of admittance |Y| in dB.

As shown in FIG. 5(a), the absolute value of admittance |Y| becomes maximum at the resonant frequency fr, and |Y| becomes minimum at the anti-resonance frequency fa. The resonance frequency fr and the anti-resonance frequency fa are lower in sensor B than in sensor A, and lower in sensor C than in sensor B. ΔY, which is the difference between |Y| at the resonant frequency fr and |Y| at the anti-resonant frequency fa, is larger for sensor B than for sensor A, and larger for sensor C than for sensor B.

In sensor A, Love waves as elastic waves propagate near the surface of piezoelectric substrate 10 and through insulator layers 14 and 16. The sensitivity |Δf|/f ² becomes larger as the acoustic impedance of the insulating layer 16 in contact with the sensitive film 18 is smaller. The acoustic impedance Za of the transverse wave is Za=ρ·V. ρ is the density and V is the transverse sound velocity. V=√(E/(2(1+ν)×ρ). E is Young's modulus and ν is Poisson's ratio. Therefore, Za=√{(ρ·E)/(2(1+ν)). In this way, the insulator layer 16 with a small acoustic impedance Za has a small Young's modulus E. When an elastic wave propagates through a medium with a small Young's modulus E, the vibration of the elastic wave is weakened. Therefore, the vibration energy is lost, and the elastic wave Therefore, the insulating layer 14 has a larger Young's modulus than the insulating layer 16. However, some of the elastic waves are transmitted to the electrode fingers 22a and 22b. Since the elastic wave propagates through the insulator layer 14 between the two, the loss of the elastic wave cannot be sufficiently reduced.

In sensor B, since the gap 15 is provided between the electrode fingers 22a and 22b, the elastic waves propagate near the surface of the piezoelectric substrate 10 and through the insulator layers 14 and 16, and the elastic waves propagate between the electrode fingers 22a and 22b. There is no propagation in the air gap 15 between them. As a result, compared to sensor A, the proportion of elastic waves propagating through the piezoelectric substrate 10 increases, and the proportion of elastic waves propagating through the insulator layers 14 and 16, which have a small Young's modulus and a large elastic loss, decreases. Thereby, loss is suppressed more than sensor A.

In the sensor C, a gap 15 is also provided between the insulator layers 14 and 16 provided on the electrode fingers 22a and 22b. As a result, the elastic waves do not propagate through the insulator layers 14 and 16, but propagate near the surface of the piezoelectric substrate 10. Therefore, since almost no elastic waves propagate through the insulator layers 14 and 16, which have a small Young's modulus and a large elastic loss, loss of elastic waves can be suppressed. Note that since most of the elastic waves propagate through the piezoelectric substrate 10, the elastic waves of the sensor C are not Love waves but SH (Shear Horizontal) waves, which are sometimes referred to as Love wave-type SH surface acoustic waves.

In sensor D, the thicknesses T1 to T3 were the same as those in sensor B, and a slit 28 was provided in the insulator layers 14 and 16 at the midpoint between the electrode fingers 22a and 22b in the X direction. The width G1 of the slit 28 in the insulator layers 14 and 16 in the sensor D is 110 nm. FIG. 5(b) is a diagram showing |Y| with respect to the frequencies of sensors B and D in the simulation. The horizontal axis represents frequency, and the vertical axis represents |Y| in dB.

As shown in FIG. 5(b), the resonance frequency fr and the anti-resonance frequency fa are lower in the sensor D than in the sensor B. As shown in Table 1, ΔY is almost the same for sensors B and D. The sensitivity of sensor D |Δf|/f ² is approximately 1.3 times the sensitivity of sensor B |Δf|/f ² .

In order to investigate the reason why sensor D has higher sensitivity than sensor B, we simulated the displacement of the upper surface of the insulator layer 16 in the Y direction with respect to the X coordinate. FIGS. 6A and 6B are diagrams showing the magnitude of displacement in the Y direction with respect to the X coordinate in sensors B and D, respectively. The horizontal axis is the X coordinate in FIG. 4(b) and FIG. 4(d). The vertical axis indicates the magnitude of displacement in the Y direction on the upper surface of the insulator layer 16 when the elastic wave vibrates. Since the elastic waves vibrate in the Y direction, the upper surface of the insulator layer 16 vibrates in the positive and negative Y directions. The vertical axis indicates the magnitude of displacement in the Y direction when the displacement in the Y direction is the largest.

As shown in FIG. 6(a), in sensor B, the magnitude of the displacement in the Y direction is is 0. This is because when the electrode finger 22a is displaced in the +Y direction, the electrode finger 22b is displaced in the -Y direction. This is because X1 and X2) become nodes of vibration. The displacement in the Y direction is maximum at the X coordinates X3 and X4 of the centers of the electrode fingers 22a and 22b. When the insulator layer 16 is displaced in the +Y direction at X3, the insulator layer 16 is displaced in the -Y direction at X4. When the insulator layer 16 is displaced in the -Y direction at X3, the insulator layer 16 is displaced in the +Y direction at X4.

As shown in FIG. 6(b), in sensor D, the displacement in the Y direction is largest near the X coordinates of 0, X1, and X2. When the X coordinates are X3 and X4, the magnitude of displacement in the Y direction is the smallest, but not zero. In sensor D, slits 28 are provided in insulator layers 14 and 16 near 0, X1, and X2. Therefore, the X coordinates of 0, X1, and X2 do not become nodes of vibration within the insulator layers 14 and 16. When the insulator layers 14 and 16 on the electrode finger 22a are displaced in the +Y direction, the insulator layers 14 and 16 on the electrode finger 22b are not limited to the insulator layers 14 and 16 on the electrode finger 22a. , -Y direction. Therefore, in the sensor D, compared to the sensor B, the displacement of the upper surface of the insulating layer 16 in the Y direction can be made larger. Thereby, sensor D can have greater sensitivity than sensor B.

In sensor C, when the insulator layers 14 and 16 on the electrode finger 22a are displaced in the +Y direction, the insulator layers 14 and 16 on the electrode finger 22b are limited to the insulator layers 14 and 16 on the electrode finger 22a. It can be displaced in the -Y direction without being affected. However, in sensor C, the width of electrode fingers 22a and 22b in the X direction and the width of insulator layers 14 and 16 are almost the same. In this case, the displacement of the upper surface of the insulator layer 16 in the Y direction does not become very large. On the other hand, in sensor D, the width W2 of the insulator layers 14 and 16 is larger than the width W1 of the electrode fingers 22a and 22b in the X direction. Therefore, the insulator layers 14 and 16 act as pendulums, and the displacement of the upper surface of the insulator layer 16 in the Y direction becomes larger than the displacement of the sensor C in the Y direction. Therefore, the sensitivity of sensor D is greater than that of sensor C.

According to the first embodiment and its modifications, the gap 15 is provided between the electrode fingers 22a and 22b on the piezoelectric substrate 10, and the insulator layer 16 (first insulator layer) is provided on the electrode fingers 22a and 22b and the gap 15. is provided. A sensitive film 18 is provided on the insulator layer 16. By using a polymer resin whose acoustic impedance is smaller than that of the electrode fingers 22a and 22b for the insulating layer 16 on which the sensitive film 18 is provided, the sensitivity of the acoustic wave sensor is improved. Furthermore, by providing the air gap 15 between the electrode fingers 22a and 22b, the elastic waves propagate near the surface of the piezoelectric substrate 10 and within the insulator layers 14 and 16, and the air gap 15 between the electrode fingers 22a and 22b propagates. does not propagate. This reduces the number of elastic waves propagating through the insulator layer 16 having a low Young's modulus. Therefore, as in sensor B in FIG. 5(a), compared to sensor A, elastic loss can be suppressed and ΔY becomes larger.

It is only necessary that a gap 15 be provided in a part between the electrode fingers 22a and 22b on the piezoelectric substrate 10. Preferably, the insulator layers 14, 16 and the sensitive film 18 are not provided between adjacent electrode fingers 22a and 22b. Thereby, there is no elastic wave propagating through the insulator layers 14, 16 and the sensitive film 18 between the electrode fingers 22a and 22b, and loss can be suppressed. More preferably, only the gap 15 is provided between adjacent electrode fingers 22a and 22b, and members such as the insulator layers 14 and 16 and the sensitive film 18 are not provided. Thereby, loss can be further suppressed.

Table 2 is a table showing the density ρ, Young's modulus E, Poisson's ratio ν, and acoustic impedance Za of materials that may be used for the electrode fingers 22a, 22b and the insulator layers 14 and 16.

As shown in Table 2, in the simulation, the acoustic impedance of aluminum (Al) used for the electrode fingers 22a and 22b was 8.37×10 ⁶ Pa/(m/s), and the acoustic impedance of PMMA used for the insulator layer 16 was 8.37×10 6 Pa/(m/s). The acoustic impedance is 1.13×10 ⁶ Pa/(m/s). To improve sensitivity, the acoustic impedance Za of the insulator layer 16 is smaller than the acoustic impedance of the electrode fingers 22a and 22b. The acoustic impedance Za of the insulating layer 16 is preferably 1/2 times or less, more preferably 1/5 times or less, the acoustic impedance of the electrode fingers 22a and 22b. The acoustic impedance of the insulator layer 16 is preferably 5×10 ⁶ Pa/(m/s) or less, more preferably 2×10 ⁶ Pa/(m/s) or less. If the acoustic impedance of the insulator layer 16 is too small, the strength of the insulator layer 16 will be weakened. From this viewpoint, the acoustic impedance Za of the insulator layer 16 is preferably 1/100 times or more the acoustic impedance of the electrode fingers 22a and 22b. In order to reduce the loss of elastic waves, the thickness T3 of the insulating layer 16 is preferably equal to or less than the thickness T1 of the electrode fingers 22a and 22b, and more preferably equal to or less than 1.5 times the thickness T1.

When the acoustic impedance of the insulator layer 16 is reduced, the Young's modulus of the insulator layer 16 is reduced. In particular, if a resin having an acoustic impedance of 2×10 ⁶ Pa/(m·s) or less is used as the insulator layer 16, the Young's modulus will be about 3 GPa or less. When the insulating layer 16 is provided directly on the electrode fingers 22a and 22b as in the elastic wave sensor 101 of the first modification of the first embodiment shown in FIG. propagates, resulting in a large elastic loss.

Therefore, as in the acoustic wave sensor 100 of Example 1 shown in FIGS. 1(a) and 1(b), the Young's modulus of the insulating layer 16 is An insulator layer 14 (second insulator layer) having a larger Young's modulus is provided. In the elastic wave sensor 100 of Example 1 (FIG. 1(b)) and the elastic wave sensor 101 of Modification 1 of Example 1 (FIG. 2(a)), the thickness of the insulating layer 16 was changed to achieve the same sensitivity. In order to achieve this, in the acoustic wave sensor 100 of the first embodiment, the insulator layer 16 can be made thinner. Thereby, the proportion of elastic waves propagating within the insulator layer 16 is reduced, and elastic loss can be suppressed. In order to increase sensitivity, the thickness T2 of the insulating layer 14 is preferably twice or less the thickness T3 of the insulating layer 16. In order to suppress elastic loss, the thickness T2 of the insulating layer 14 is preferably 1/2 or more times the thickness T3 of the insulating layer 16. The Young's modulus of the insulating layer 14 is preferably 10 times or more, more preferably 20 times or more, and even more preferably 50 times or more the Young's modulus of the insulating layer 16.

As in the acoustic wave sensor 100 of Example 1 shown in FIGS. 1(a) and 1(b) and the sensor B shown in FIG. 15 may be provided continuously.

In the elastic wave sensors 102 to 105 of the modified examples 2 to 5 of the first embodiment shown in FIGS. 2(b) to 3(b) and the sensors C and D shown in FIGS. 4(c) and 4(d), Insulator layers 16 provided on adjacent electrode fingers 22a and 22b are separated. As a result, elastic waves cannot propagate within the insulator layer 16 in the X direction. Therefore, like sensor C in FIG. 5(a), elastic loss can be suppressed and ΔY can be increased.

Although the sensitive film 18 may be continuously provided on the separated insulating layer 16, it is preferable that the sensitive films 18 on the separated insulating layer 16 are separated from each other. As a result, elastic waves cannot propagate within the sensitive film 18. Therefore, elastic loss can be suppressed.

In the acoustic wave sensor 105 of the fifth modification of the first embodiment shown in FIGS. 3(a) and 3(b) and the sensor D shown in FIG. 4(d), the width W2 of the insulator layers 14 and 16 in the X direction is It is larger than the width W1 of each of fingers 22a and 22b. Thereby, the sensitivity can be increased as shown in FIG. 5(b) and Table 1. The width W2 of the insulator layers 14 and 16 is preferably 1.1 times or more, more preferably 1.2 times or more, and even more preferably 1.5 times or more the width W1 of each of the electrode fingers 22a and 22b. The width G1 of the slit 28 is preferably 1/2 or less, more preferably 1/3 or less, and even more preferably 1/5 or less of the distance G2 between the electrode fingers 22a and 22b. As the gap G2 becomes smaller, the portions of the insulator layers 14 and 16 that protrude from the electrode fingers 22a and 22b become larger. This increases the weight of the pendulum and improves its sensitivity.

[Production method of Example 1]
The manufacturing method of Example 1 will be explained. FIGS. 7(a) to 9(f) are cross-sectional views showing a method of manufacturing an elastic wave sensor according to the first embodiment. 7(a) to 7(c), FIG. 8(a) to FIG. 8(c), and FIG. 9(a) to FIG. 9(c) show the BB in the gap region 52 of FIG. 7(d) to 7(f), FIG. 8(d) to FIG. 8(f), and FIG. 9(d) to FIG. 9(f) are cross-sectional views corresponding to the cross-sections of FIG. ) is a cross-sectional view corresponding to a CC cross section in a region 50.

As shown in FIGS. 7(a) and 7(d), a metal film 12 is formed on the piezoelectric substrate 10 using, for example, a vacuum evaporation method or a sputtering method. The metal film 12 is, for example, an aluminum film. For example, by patterning the metal film 12 using a photolithography method and an etching method, the IDT 37 including the electrode fingers 22a and 22b and the reflector 21 are formed. A sacrificial layer 38 is formed on the piezoelectric substrate 10 using, for example, a vacuum evaporation method or a sputtering method so as to cover the electrode fingers 22a and 22b. The sacrificial layer 38 is, for example, a magnesium oxide layer. If the upper surface of the sacrificial layer 38 is not flat, the upper surface of the sacrificial layer 38 is planarized using, for example, a CMP (Chemical Mechanical Polishing) method.

As shown in FIG. 7(b) and FIG. 7(e), a recess 41 is formed on the top surface of the sacrificial layer 38 using a photolithography method and an etching method so that the top surface of the electrode fingers 22a and 22b is exposed. . As a result, a convex portion 40 is formed on the upper surface of the sacrificial layer 38 in a region where the hole 26 is to be formed. In the region 50 in FIG. 1A, the recess 41 of the sacrificial layer 38 is formed as shown in FIG. 7E, and the upper surfaces of the electrode fingers 22a and 22b are exposed from the upper surface of the sacrificial layer 38.

As shown in FIGS. 7(c) and 7(f), the insulating layer 14 is deposited on the sacrificial layer 38 by, for example, sputtering, vacuum evaporation, or CVD (Chemical Vapor Deposition) so as to cover the convex portions 40 and concave portions 41. ) method. The insulator layer 14 is, for example, a silicon oxide layer. The upper surface of the insulating layer 14 is polished using, for example, a CMP method so that the upper surface of the convex portion 40 of the sacrificial layer 38 is exposed from the upper surface of the insulating layer 14. At this time, the upper part of the protrusion 40 of the sacrificial layer 38 is also polished so that the upper surface of the protrusion 40 of the sacrificial layer 38 is reliably exposed. As a result, the insulating layer 14 is embedded in the recess 41 on the upper surface of the sacrificial layer 38, and a hole 26a through which the convex part 40 of the sacrificial layer 38 passes is formed in the insulating layer 14. The upper surface of the insulator layer 14 and the upper surface of the convex portion 40 of the sacrificial layer 38 form a flat plane. As shown in FIG. 7F, in the region 50, the insulator layer 14 is formed on the electrode fingers 22a, 22b and the sacrificial layer 38.

As shown in FIGS. 8(a) and 8(d), the insulating layer 16 is formed on the upper surface of the insulating layer 14 and the upper surface of the convex portion 40 of the sacrificial layer 38. When the insulator layer 16 is made of resin, the insulator layer 16 is formed by spin-coating a solution containing resin on the upper surfaces of the insulator layer 14 and the sacrificial layer 38 and then curing it. The insulator layer 16 is, for example, a PMMA layer. A mask layer 17 is formed on the insulator layer 16 using, for example, a sputtering method or a vacuum evaporation method. The mask layer 17 is, for example, a metal layer such as a chromium film, and functions as a mask when etching the insulator layer 16.

As shown in FIGS. 8(b) and 8(e), a mask layer 42 is formed on the mask layer 17. The mask layer 42 is made of, for example, a photoresist, and is formed using a photolithography method. The mask layer 42 has an opening 43 that overlaps the hole 26a. The width W4 of the opening 43 is larger than the width W3 of the hole 26a. As shown in FIG. 8E, no opening is formed in the mask layer 42 in the region 50.

As shown in FIGS. 8(c) and 8(f), the mask layer 17 and the insulator layer 16 are etched using the mask layer 42 as a mask. For example, an ion milling method is used for etching the mask layer 17 and the insulator layer 16. Thereby, a hole 26b defined by the opening 43 and penetrating the mask layer 17 and the insulator layer 16 is formed. Mask layer 17 and insulator layer 16 are over-etched so that the upper surface of sacrificial layer 38 is exposed in hole 26b. The holes 26a and 26b communicate with each other to form the hole 26. As shown in FIG. 8F, no hole 26b is formed in the insulator layer 16 and mask layer 17 in the region 50. In FIGS. 8(c) and 8(f), the mask layer 17 may be removed.

As shown in FIGS. 9(a) and 9(d), the mask layer 42 is removed. As shown in FIGS. 9(b) and 9(e), the etching solution is introduced through the holes 26b and 26a as indicated by an arrow 44. The sacrificial layer 38 is etched and removed by the etching solution. As shown in FIG. 9E, the sacrificial layer 38 between the electrode fingers 22a and 22b is removed, and a gap 15 is formed between the electrode fingers 22a and 22b. For example, nitric acid or acetic acid is used as the etching solution. Nitric acid etches magnesium oxide, but not PMMA, silicon oxide, and aluminum. Therefore, by using nitric acid as the etching solution, the sacrificial layer 38 can be removed without corroding the electrode fingers 22a, 22b and the insulator layers 14 and 16. The etching solution may be acetic acid. Acetic acid can also be slightly corrosive to PMMA and aluminum. Therefore, nitric acid is preferable as the etching solution.

As shown in FIGS. 9(c) and 9(f), a sensitive film 18 is formed on the mask layer 17 in the region 50. When the lowest layer of the sensitive film 18 is a gold layer, the mask layer 17 also functions as an adhesion layer between the gold layer and the insulator layer 16. The formation of the sensitive film 18 may be performed before the step of removing the sacrificial layer 38.

In the manufacturing method of Example 1, as shown in FIGS. 7(a) and 7(d), a plurality of electrode fingers 22a and 22b are provided on the piezoelectric substrate 10, and a sacrificial layer 38 is provided between the plurality of electrode fingers 22a and 22b. Form. As shown in FIGS. 7(c) and 7(f), the insulating layer 14 is formed on the plurality of electrode fingers 22a, 22b and the sacrificial layer 38. As shown in FIGS. 9(c) and 9(f), a sensitive film 18 is formed on the insulating layer 16. As shown in FIG. 7(c), a hole 26a is formed in the insulating layer 14, and a hole 26b is formed in the insulating layer 16 as shown in FIG. 8(c). This creates a hole that penetrates the insulator layers 14 and 16 and contacts the sacrificial layer 38 on the outside (gap region 52) in the direction in which the plurality of electrode fingers 22a and 22b extends in the region 50 in which the elastic waves propagate in the piezoelectric substrate 10. 26 is formed. As shown in FIGS. 9(b) and 9(e), by introducing an etching solution to remove the sacrificial layer 38 through the hole 26, a plurality of electrodes between the piezoelectric substrate 10 and the insulator layers 14 and 16 are removed. A gap 15 is formed between fingers 22a and 22b.

The hole 26 may be provided between the electrode fingers 22a and 22b in the region 50 instead of in the gap region 52. When the holes 26 are provided in the insulator layers 14 and 16 between the electrode fingers 22a and 22b, the elastic waves propagating in the X direction through the insulator layers 14 and 16 are reduced, so that loss of elastic waves can be suppressed. However, if the holes 26 are provided in the region 50, the sensitive film 18 may penetrate into the void 15 through the holes 26 when forming the sensitive film 18. This may increase the loss of elastic waves. Therefore, it is preferable that the hole 26 be provided outside the region 50. When introducing the etching solution through the holes 26, if two or more holes 26 are not provided, it becomes difficult for air to escape from the gaps 15, and it becomes difficult for the etching solution to enter the gaps 15. Therefore, it is preferable to provide two or more holes 26 per pair of electrode fingers 22a and 22b. Furthermore, displacement due to elastic waves also exists outside the region 50. Therefore, even when the holes 26 are provided in the gap region 52, the number of elastic waves that propagate is reduced, and the loss of elastic waves can be reduced.

[Manufacturing method of modification 6 of example 1]
10(a) to 10(d) are cross-sectional views showing a method of manufacturing an elastic wave sensor according to a sixth modification of the first embodiment. 10(a) to 10(c) are cross-sectional views corresponding to the BB cross-section in FIG. 1(a), and FIG. 10(d) is a cross-sectional view corresponding to the CC cross-section in FIG. 1(a). FIG.

As shown in FIG. 10(a), the widths of the holes 26a formed in the insulating layer 14 and the holes 26b formed in the insulating layer 16 may be approximately the same.

The problems of the sixth modification of the first embodiment will be explained. FIG. 10(b) is a diagram corresponding to FIG. 9(a) of the first embodiment. As shown in FIG. 10(b), the holes 26b in the insulator layer 16 are misaligned with respect to the holes 26a in the insulator layer 14 as shown by arrows 45. As a result, a portion of the hole 26a is blocked by the insulator layer 16.

FIG. 10(c) and FIG. 10(d) are diagrams corresponding to FIG. 9(b) and FIG. 9(e) of Example 1. As shown in FIG. 10(c), if the hole 26b is shifted relative to the hole 26a, the width of the hole 26 will become narrower. As indicated by a broken line arrow 46, when the etching liquid is introduced through the hole 26, the etching liquid is not sufficiently introduced. As a result, as shown in FIG. 10D, the etching solution may not sufficiently penetrate between the electrode fingers 22a and 22b in the region 50, and the sacrificial layer 38 may remain.

In the manufacturing method of Example 1, as shown in FIGS. 9(a) and 9(b), the diameter of the hole 26b penetrating the insulating layer 16 is made larger than the diameter of the hole 26a penetrating the insulating layer 14. A hole 26 is formed through the insulator layers 14 and 16. Thereby, even if the holes 26b of the insulator layer 16 are formed out of alignment with the holes 26a of the insulator layer 14, it is possible to prevent the insulator layer 16 from blocking the holes 26a. Therefore, remaining of the sacrificial layer 38 can be suppressed. The diameter of the hole 26b is preferably 1.1 times or more the diameter of the hole 26a.

[Modification 7 of Example 1]
FIG. 11 is a cross-sectional view of an elastic wave sensor according to Modification Example 7 of Example 1. As shown in FIG. 11, the surface 56 of the insulating layer 14 on the gap 15 side between the electrode fingers 22a and 22b has an arch shape. If the height of the gap 15 at the point where the insulator layer 14 touches the ends of the electrode fingers 22a and 22b is H1, and the height of the gap 15 at the midpoint between the electrode fingers 22a and 22b in the X direction is H2, then the height is The height H2 is greater than H1. Thereby, the volume of the void 15 becomes larger, so that loss of elastic waves can be suppressed. Furthermore, the arched shape has high strength against stress from above. Therefore, even if the insulator layers 14 and 16 vibrate minutely, the insulator layer 14 can be prevented from being crushed. The height H2 is preferably 1.1 times or more and twice or less the height H1.

As a second embodiment, an example of a delay line type elastic wave sensor that employs a propagation path through which elastic waves propagate will be described. FIG. 12(a) is a plan view of the elastic wave sensor according to Example 2, and FIG. 12(b) is a sectional view taken along line AA in FIG. 12(a). FIG. 12A mainly shows the IDTs 20a, 20b, pads 25a to 25d, insulator layers 14, 16, sensitive film 18, metal layer 30, and hole 26, with the sensitive film 18 indicated by a thick broken line, and the IDT 20a, 20b, pads 25a to 25d, and metal layer 30 are shown by cross hatching.

As shown in FIGS. 12(a) and 12(b), in the acoustic wave sensor 108, IDTs 20a and 20b are provided on the piezoelectric substrate 10. IDTs 20a and 20b are spaced apart. A region between a region 50 in which electrode fingers 22a and 22b are alternately provided in the IDT 20a and a region 50 in which electrode fingers 22a and 22b are alternately provided in the IDT 20b is a propagation path 54 through which elastic waves propagate. be.

Bus bars 23a and 23b of IDT 20a are electrically connected to pads 25a and 25b, respectively, and bus bars 23a and 23b of IDT 20b are electrically connected to pads 25c and 25d, respectively.

A metal layer 30 is provided on the piezoelectric substrate 10 between the IDTs 20a and 20b. The metal layer 30 includes a plurality of electrode fingers 32 and a pair of bus bars 33. The electrode fingers 32 extend in the Y direction and are arranged in the X direction in the propagation path 54. The pair of bus bars 33 are provided outside the propagation path 54 in the Y direction. The electrode finger 32 is connected to one bus bar 33 at the +Y end, and connected to the other bus bar 33 at the -Y end. The bus bar 33 on the +Y side is connected to the bus bar 23a of the IDT 20b. The -Y side bus bar 33 is connected to the bus bar 23b of the IDT 20a.

The electrode fingers 32 are provided for electric field short-circuiting to suppress electrical sensitivity in the propagation path 54. The pitch Pa of the electrode fingers 22a and 22b in the IDT 20a is approximately equal to the pitch Pb of the electrode fingers 22a and 22b in the IDT 20b. If the pitch Pc of the electrode fingers 32 is equal to the pitches Pa and Pb, the electrode fingers 32 will reflect the elastic waves excited by the IDT 20a. For this reason, the pitch Pc is preferably different from the pitches Pa and Pb, and the pitch Pc is preferably 1/2 or less or twice or more of the pitches Pa and Pb.

There is a gap 15 between the electrode fingers 22a and 22b of the IDTs 20a and 20b. Insulator layers 14 and 16 are provided on electrode fingers 22a, 22b and void 15. A gap 15 exists between the metal layer 30 and the electrode finger 32 . Insulator layers 14 and 16 are provided on electrode fingers 32 and voids 15 . A sensitive film 18 is provided on the insulator layer 16 in the propagation path 54 .

In the IDTs 20a and 20b, holes 26 are provided in the insulator layers 14 and 16 in the gap region 52 between the tip of the electrode finger 22a and the bus bar 23b, and in the gap region 52 between the tip of the electrode finger 22b and the bus bar 23a. ing. Holes 26 are provided in the insulator layers 14 and 16 between the electrode fingers 32 between the propagation path 54 and the bus bar 33 in the metal layer 30 . The hole 26 is also a hole for removing the sacrificial layer as in the first embodiment.

The materials of the piezoelectric substrate 10, metal film 12, insulator layers 14 and 16, and sensitive film are the same as in Example 1.

[Modification 1 of Example 2]
FIG. 13(a) is a cross-sectional view of an elastic wave sensor 109 according to a first modification of the second embodiment. As shown in FIG. 13A, the insulator layers 14 and 16 are provided only on the electrode fingers 22a, 22b, and 32, and the insulator layers 14 and 16 are not provided on the gap 15. The sensitive film 18 is provided only on the electrode fingers 22a and 22b, and the sensitive film 18 is not provided on the gap 15. Similar to the sensor C in FIG. 4C, in the propagation path 54, the width of the electrode finger 32 in the X direction and the width of the insulator layers 14 and 16 in the X direction are the same. In IDTs 20a and 20b, the widths of electrode fingers 22a and 22b in the X direction and the widths of insulator layers 14 and 16 in the X direction are the same. The other configurations are the same as in the second embodiment, and their explanation will be omitted.

[Modification 2 of Example 2]
FIG. 13(b) is a cross-sectional view of an elastic wave sensor 110 according to a second modification of the second embodiment. As shown in FIG. 13(b), in the IDTs 20a and 20b, slits 28 are provided in the insulator layers 14 and 16 between the electrode fingers 22a and 22b. In the propagation path 54, a slit 28 is provided in the insulator layers 14 and 16 between the electrode fingers 32. The slit 28 penetrates the insulator layers 14 and 16 and is connected to the void 15. Similar to the sensor D in FIG. 4(d), in the propagation path 54, the width of the slit 28 in the X direction is smaller than the width of the gap 15 between the electrode fingers 32 in the X direction. In the IDTs 20a and 20b, the width of the slit 28 in the X direction is smaller than the width of the gap 15 between the electrode fingers 22a and 22b in the X direction. The width of the slit 28 is smaller than the width of the hole 26. The other configurations are the same as in the second embodiment, and their explanation will be omitted.

According to the second embodiment and its modifications, a plurality of electrodes are arranged in the X direction between the IDT 20a (a pair of first comb-shaped electrodes) and the IDT 20b (a pair of first comb-shaped electrodes) on the piezoelectric substrate 10. Fingers 32 are provided, and gaps 15 are provided between adjacent electrode fingers 32 on the piezoelectric substrate 10 . An insulator layer 16 is provided on the plurality of electrode fingers 32, and a sensitive film 18 is provided on the insulator layer 16.

It is only necessary that a gap 15 be provided in a part between the plurality of electrode fingers 32 on the piezoelectric substrate 10. Preferably, the insulator layers 14 and 16 and the sensitive film 18 are not provided between adjacent electrode fingers 32. Thereby, loss can be suppressed. Furthermore, it is more preferable that only the gap 15 is provided between adjacent electrode fingers 32 and that members such as the insulator layers 14 and 16 and the sensitive film 18 are not provided. Thereby, loss can be further suppressed.

When a ground potential is supplied to the pads 25b and 25c and a high frequency signal is applied to the pad 25a with respect to the pad 25b at the ground potential, the IDT 20a excites elastic waves near the surface of the piezoelectric substrate 10. The elastic wave propagates near the surface of the piezoelectric substrate 10 in the propagation path 54 and reaches the IDT 20b. In the IDT 20b, a high frequency signal is outputted to the pad 25b using an elastic wave with respect to the pad 25c at the ground potential.

When the environment changes, such as when the concentration of a specific substance or antigen changes, and the mass of the sensitive membrane 18 changes, the mass added to the propagation path 54 changes, and the speed of the elastic wave propagating through the propagation path 54 changes. Change. The phase difference between the high frequency signal input to the IDT 20a and the high frequency signal output to the IDT 20b changes. Based on changes in this phase difference, changes in the environment such as the concentration of a specific substance or specific object such as an antigen can be detected.

Similarly to the first embodiment and its modifications, the sensitivity of the elastic wave sensor can be improved by making the acoustic impedance of the insulator layer 16 smaller than the acoustic impedance of the plurality of electrode fingers 32. By providing the insulator layer 14 having a Young's modulus larger than the Young's modulus of the insulator layer 16 between the plurality of electrode fingers 22c and the insulator layer 16, elastic loss can be suppressed. By separating the insulator layers 16 provided on adjacent electrode fingers 22c over the gaps 15, loss can be suppressed. Sensitivity can be improved by making the width of the insulator layer 16 larger than the width of the electrode finger 22c in the X direction.

As Example 3, another example of a delay line type elastic wave sensor that employs a propagation path through which elastic waves propagate will be described. FIG. 14(a) is a plan view of an elastic wave sensor according to Example 3, and FIG. 14(b) is a sectional view taken along line AA in FIG. 14(a). FIG. 14A mainly shows the IDTs 20a, 20b, pads 25a to 25d, insulator layers 14, 16, sensitive film 18, metal layer 30a, and hole 26, with the sensitive film 18 indicated by a thick broken line, and the IDT 20a, 20b, pads 25a to 25d, and metal layer 30a are shown by cross hatching.

As shown in FIGS. 14(a) and 14(b), in the acoustic wave sensor 111, the metal layer 30a is a solid film, and the propagation path 54 is not provided with electrode fingers. A plurality of insulator fingers 19 are provided on the metal layer 30a, extending in the Y direction and arranged in the X direction. The insulator finger 19 includes an insulator layer 14 provided on the metal layer 30a and an insulator layer 16 provided on the insulator layer 14. A gap 15 exists between adjacent insulator fingers 19 on the metal layer 30a. The sensitive film 18 is provided only on the plurality of insulator fingers 19.

The metal layer 30a is provided for electric field short-circuiting to suppress electrical sensitivity in the propagation path 54. The pitch Pc of the insulator fingers 19 may be approximately equal to or different from the pitch Pa in the IDT 20a and the pitch Pb in the IDT 20b. The rest of the configuration is the same as in the second embodiment, and the explanation will be omitted.

In the acoustic wave sensor according to the third embodiment, when the environment changes such as the concentration of a specific substance or a specific substance such as an antigen changes, and the mass of the sensitive film 18 changes, the mass added to the propagation path 54 changes. However, the speed of the elastic wave propagating through the propagation path 54 changes. Therefore, based on the change in the phase difference of the elastic waves propagating through the propagation path 54, changes in the environment such as the concentration of a specific substance or a specific object such as an antigen can be detected.

Similarly to Example 2 and its modifications, by providing the insulating layer 16, the sensitivity of the acoustic wave sensor can be improved. By creating a gap 15 between adjacent insulator fingers 19 on the metal layer 30a, elastic waves cannot propagate through the insulator layer 16. Therefore, elastic loss can be suppressed. By providing the insulator layer 14 having a Young's modulus larger than the Young's modulus of the insulator layer 16 between the metal layer 30a and the insulator layer 16, elastic loss can be suppressed.

It is only necessary that a gap 15 be provided in a portion between the plurality of insulator fingers 19 on the piezoelectric substrate 10. Preferably, the insulator layers 14, 16 and the sensitive film 18 are not provided between adjacent insulator fingers 19. Thereby, loss can be suppressed. Furthermore, it is more preferable that only the gap 15 is provided between adjacent insulator fingers 19 and that members such as the insulator layers 14 and 16 and the sensitive film 18 are not provided. Thereby, loss can be further suppressed.

Example 4 is an example of a detection system using Example 1 and its modification. FIG. 15(a) is a block diagram of the detection system 112 according to the fourth embodiment. As shown in FIG. 15(a), in the detection system 112 of the fourth embodiment, the oscillation circuit 62 includes an elastic wave sensor 60. The elastic wave sensor 60 is a surface acoustic wave resonator in the first embodiment and its modifications. The oscillation circuit 62 outputs an oscillation signal having an oscillation frequency corresponding to the resonance frequency of the surface acoustic wave resonator. The oscillation frequency does not need to be the same as the resonant frequency, and it is sufficient that the oscillation frequency changes based on a change in the resonant frequency. That is, the oscillation circuit 62 outputs an oscillation signal having an oscillation frequency that changes in response to changes in the environment. The detector 64 includes a measuring device 66 and a calculating device 68. The measuring device 66 measures the frequency of the oscillation signal output by the oscillation circuit 62. The calculator 68 detects a specific substance or antigen based on the amount of change in the frequency of the oscillation signal measured by the measuring device 66. As described above, when a specific object such as a specific substance or an antigen is adsorbed or bonded to the sensitive membrane 18, the mass of the sensitive membrane 18 changes. Therefore, since the frequency of the oscillation signal changes, a specific substance or antigen can be detected based on the amount of change.

[Modification 1 of Example 4]
Modification 1 of Embodiment 4 is an example of a detection system using Embodiments 2 and 3 and their modifications. FIG. 15(b) is a block diagram of the detection system 114 according to the first modification of the fourth embodiment. As shown in FIG. 15(b), in the detection system 114 of the first modification of the fourth embodiment, the transmitter 71 transmits a high frequency signal to the IDT 20a of the elastic wave sensor 70 of the second and third embodiments and their modifications. . The receiver 72 receives a high frequency signal from the IDT 20b of the elastic wave sensor 70. Detector 74 includes a measuring device 76 and a calculating device 78. The measuring device 76 measures the phase difference between the high frequency signal transmitted by the transmitter 71 and the high frequency signal received by the receiver 72. The calculator 78 detects the specific substance or antigen based on the amount of change in phase difference measured by the measuring device 76.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and variations can be made within the scope of the gist of the present invention as described in the claims. Changes are possible.

10 piezoelectric substrate 12 metal film 14, 16 insulator layer 15 void 17, 42 mask layer 18 sensitive film 19 insulator finger 20, 20a, 20b IDT
21 Reflector 22a to 22c, 32 Electrode fingers 23a, 23b, 33 Bus bar 24a, 24b Comb-shaped electrode 25a to 25d Pad 26, 26a, 26b Hole 28 Slit 30, 30a Metal layer 38 Sacrificial layer 40 Convex portion 41 Concave portion 50 Region 52 Gap region 54 Propagation path 60, 70 Elastic wave sensor 62 Oscillation circuit 64, 74 Detector

Claims (19)

a piezoelectric substrate;
a pair of comb-shaped electrodes provided on the piezoelectric substrate, having a plurality of electrode fingers, and having a gap between adjacent electrode fingers on the piezoelectric substrate;
a first insulator layer provided on the plurality of electrode fingers;
a sensitive film provided on the first insulator layer;
An elastic wave sensor equipped with a resonator comprising the piezoelectric substrate, the pair of comb-shaped electrodes, and the sensitive film, and whose resonant frequency changes with changes in the environment;
a detector that detects a change in the environment based on a change in the resonant frequency of the resonator;
The elastic wave sensor according to claim 1, comprising: The acoustic wave sensor according to claim 1, wherein the first insulator layer and the sensitive film are not provided between the adjacent electrode fingers. a piezoelectric substrate;
a pair of first comb-shaped electrodes provided on the piezoelectric substrate;
a pair of second comb-shaped electrodes provided on the piezoelectric substrate;
provided between the pair of first comb-shaped electrodes and the pair of second comb-shaped electrodes on the piezoelectric substrate, and an arrangement direction of the pair of first comb-shaped electrodes and the pair of second comb-shaped electrodes; a plurality of electrode fingers arranged on the piezoelectric substrate, with gaps between adjacent electrode fingers on the piezoelectric substrate;
a first insulator layer provided on the plurality of electrode fingers;
a sensitive film provided on the first insulator layer;
Equipped with
An acoustic wave sensor in which the first insulator layer and the sensitive film are not provided between the adjacent electrode fingers. 5. The method according to claim 4, further comprising a detector that detects a change in the environment based on a change in phase difference between a high frequency signal applied to the pair of first comb-shaped electrodes and a high frequency signal outputted from the pair of second comb-shaped electrodes. The described elastic wave sensor. The acoustic wave sensor according to claim 1 or 4, wherein the acoustic impedance of the first insulating layer is smaller than the acoustic impedance of the plurality of electrode fingers. The acoustic wave sensor according to claim 6, further comprising a second insulator layer that is provided between the plurality of electrode fingers and the first insulator layer and has a Young's modulus larger than the Young's modulus of the first insulator layer. The acoustic wave sensor according to claim 1 or 4, wherein the first insulator layer is separated above the gap. The acoustic wave sensor according to claim 8, wherein the width of the first insulating layer is larger than the width of each of the adjacent electrode fingers in the direction in which the plurality of electrode fingers are arranged. The acoustic wave sensor according to claim 8, wherein the plurality of electrode fingers are embedded in the piezoelectric substrate. The acoustic wave sensor according to claim 1, wherein the first insulator layer is continuously provided on the plurality of electrode fingers so as to form a gap between the plurality of electrode fingers. The acoustic wave sensor according to claim 11, wherein the first insulator layer is provided with a hole connecting the void and the outside on the first insulator layer. a second insulator layer provided continuously between the plurality of electrode fingers and the voids and the first insulator layer, and in which the hole is provided in communication;
The acoustic wave sensor according to claim 12, wherein the diameter of the hole in the first insulator layer is larger than the diameter of the hole in the second insulator layer. The elastic wave according to claim 11, further comprising a second insulating layer that is continuously provided between the plurality of electrode fingers and the void and the first insulating layer, and has an arched surface on the void side. sensor. a piezoelectric substrate;
a pair of first comb-shaped electrodes provided on the piezoelectric substrate;
a pair of second comb-shaped electrodes provided on the piezoelectric substrate;
a metal layer provided between the pair of first comb-shaped electrodes and the pair of second comb-shaped electrodes on the piezoelectric substrate;
A plurality of insulator fingers provided on the metal layer, arranged in the arrangement direction of the pair of first comb-shaped electrodes and the pair of second comb-shaped electrodes, and having gaps between adjacent insulator fingers on the metal layer. Insulator fingers;
a sensitive film provided on the plurality of insulator fingers;
An elastic wave sensor equipped with 16. The method according to claim 15, further comprising a detector that detects a change in the environment based on a change in a phase difference between a high-frequency signal applied to the pair of first comb-shaped electrodes and a high-frequency signal outputted from the pair of second comb-shaped electrodes. The described elastic wave sensor. forming a plurality of electrode fingers and a sacrificial layer between the plurality of electrode fingers on the piezoelectric substrate;
forming a first insulator layer on the plurality of electrode fingers and the sacrificial layer;
forming a sensitive film on the first insulator layer;
forming a hole that penetrates the first insulator layer and contacts the sacrificial layer;
forming a gap between the plurality of electrode fingers between the piezoelectric substrate and the first insulator layer by introducing an etching solution for removing the sacrificial layer through the hole;
A method of manufacturing an elastic wave sensor including: forming a second insulator layer on the plurality of electrode fingers and the sacrificial layer,
The step of forming the first insulator layer includes the step of forming the first insulator layer on the second insulator layer,
The step of forming the hole includes forming the first insulator layer and the second insulator layer such that the diameter of the hole penetrating the first insulator layer is larger than the diameter of the hole penetrating the second insulator layer. The method for manufacturing an acoustic wave sensor according to claim 17, comprising the step of forming the hole that penetrates a body layer. The acoustic wave sensor according to claim 17 or 18, wherein the step of forming the hole includes the step of forming the hole outside a region in the piezoelectric substrate in which elastic waves propagate in a direction in which the plurality of electrode fingers extend. manufacturing method.

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