JP7187134B2 - Acoustic wave sensor - Google Patents

Description

The present invention relates to acoustic wave sensors. The present invention particularly relates to sensors utilizing surface acoustic waves.

A sensor is a device that converts information about the physical or chemical properties of a substance or the like present around the sensor into an electrical signal and outputs the electrical signal. A huge number of sensors are used in every field, and they are indispensable to modern society.

An elastic wave sensor that utilizes elastic waves is known as one type of sensor. When a surface acoustic wave (SAW) propagating on the surface of a surface acoustic wave element is used as the acoustic wave, the degree of reaction between the reaction film formed on the surface acoustic wave element and the substance to be detected is defined as elastic wave. It is possible to measure the type, concentration, etc. of the substance to be detected by extracting it as a change in the propagation characteristics of the surface wave. Examples of substances to be detected include biological substances contained in gases and liquids, and elastic wave sensors are used as gas sensors and biosensors.

For example, Patent Document 1 discloses a surface acoustic wave gas sensor in which two transducers are provided on a piezoelectric substrate and a gas sensing material containing a getter material is arranged between the two transducers. Have been described. According to Patent Document 1, molecules adsorbed by a getter material, such as hydrogen, change the frequency of a signal transmitted between two transducers to detect the molecules and function as a gas sensor. is stated.

Japanese Patent Publication No. 2008-518201

In the acoustic wave sensors described above, including the surface acoustic wave sensor described in Patent Document 1, a reaction film that changes the propagation characteristics of the acoustic wave by reacting with the substance to be detected is formed on the substrate through which the acoustic wave propagates. is formed.

However, such a reaction film has poor adhesion to the substrate, and during the production of the acoustic wave sensor or the operation of the acoustic wave sensor, part or all of the reaction film may be peeled off. If part or all of the reaction film is peeled off, there is a problem that the detection sensitivity is extremely lowered, or the detection becomes impossible, and the sensor cannot function.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an elastic wave sensor capable of improving the adhesion between a reaction section and a substrate.

In order to achieve the above object, the elastic wave sensor of the present invention includes:
[1] A substrate capable of propagating elastic waves;
elastic wave transmitting/receiving means provided on the substrate for exciting elastic waves in the substrate and receiving the excited elastic waves;
a reaction part arranged on the propagation path of the elastic wave and reacting with the object to be detected;
a bonding portion for bonding the substrate and the reaction portion is formed between the substrate and the reaction portion;
The elastic wave sensor is characterized in that the adhesive part contains a compound having a siloxane bond as a main skeleton.

[2] The elastic wave sensor according to [1], wherein the compound is silicon dioxide.

[3] The elastic wave sensor according to [1] or [2], wherein the reaction portion contains graphene and/or graphene oxide.

[4] The elastic wave sensor according to any one of [1] to [3], wherein the elastic wave transmitting/receiving means includes an elastic wave excitation electrode and an elastic wave receiving electrode.

According to the present invention, it is possible to provide an elastic wave sensor capable of improving the adhesion between the reaction section and the substrate.

FIG. 1(a) is a schematic perspective view showing an example of an elastic wave sensor according to an embodiment of the present invention. FIG. 1(b) is a schematic cross-sectional view of the elastic wave sensor along line Ib--Ib in FIG. 1(a). FIG. 2 is a schematic perspective view showing another example of the elastic wave sensor according to one embodiment of the present invention.

Hereinafter, the present invention will be described in detail in the following order based on specific embodiments.
1. 1. Acoustic Wave Sensor 1.1 Overall Structure of Surface Acoustic Wave Sensor 1.2 Reaction Part 1.3 Bonding Part 1.4 Substrate 1.5 Surface Acoustic Wave Excitation Electrode and Surface Acoustic Wave Receiving Electrode 1.6 Operation of Surface Acoustic Wave Sensor Principle 2. 3. Manufacturing method of surface acoustic wave sensor. 4. Effect of this embodiment. Modification

(1. Elastic wave sensor)
The acoustic wave sensor according to this embodiment is a surface acoustic wave sensor. This sensor may be mounted on a substrate with an adhesive or the like, or may be housed in a known package that communicates with the measurement atmosphere. Further, the detection target may be detected only by this sensor, or the detection target may be detected together with a sensor element for compensation, another sensor element for detecting another type of detection target, or the like.

(1.1 Overall Configuration of Surface Acoustic Wave Sensor)
As shown in FIG. 1A, a surface acoustic wave sensor 1 according to this embodiment has a substrate 2, a surface acoustic wave excitation electrode 3, a surface acoustic wave receiving electrode 4, and a reaction section 5. As shown in FIG. Further, as shown in FIG. 1B, a bonding portion 6 is formed between the substrate 2 and the reaction portion 5 . The surface acoustic wave excitation electrode 3 , the surface acoustic wave reception electrode 4 , the reaction portion 5 and the adhesive portion 6 are all provided on one main surface of the substrate 2 . The reaction portion 5 and the bonding portion 6 have substantially the same shape in plan view, and are arranged between the surface acoustic wave excitation electrode 3 and the surface acoustic wave reception electrode 4 . Each component will be described in detail below.

(1.2 Reaction section)
The reaction section 5 is provided on one main surface of the substrate 2 . The reaction section 5 can react with the detection target to change the propagation speed of surface acoustic waves propagating on the reaction section. A change in the propagation velocity of the surface acoustic wave is detected as a change in frequency of the surface acoustic wave by the surface acoustic wave receiving electrode 4, which will be described later. Therefore, the presence/absence, mass, concentration, and the like of the detection target can be taken out as the amount of frequency change, and information regarding the detection target can be detected.

In the present embodiment, "reaction" means that the reaction section 5 can reversibly capture and release a detection target, such as reversible adsorption and desorption.

The reaction section 5 is not particularly limited as long as it contains a substance capable of reacting with the detection target to change the propagation speed of surface acoustic waves propagating on the reaction section. In the present embodiment, the reaction section 5 preferably contains modified graphene and/or graphene oxide, and more preferably contains graphene oxide.

Graphene has a structure in which one layer of a two-dimensional sheet structure is extracted from graphite, which has a layered structure in which two-dimensional sheets composed of carbon atoms are stacked. Modified graphene is graphene introduced with a modifying functional group capable of reacting with a detection target. In addition, graphene oxide has a structure in which oxygen or a functional group containing oxygen capable of reacting with a detection target is bonded.

Since graphene is a two-dimensional sheet for one layer, almost all of the modified functional groups in graphene and oxygen in graphene oxide are exposed to the outside. Therefore, even if the amount of the detection target is very small, the detection target can be detected with high sensitivity because the detection target is easily adsorbed. In addition, even if the area of the reaction section 5 is small, since there are many modifying functional groups or oxygen involved in adsorption and desorption, the detection target can be efficiently adsorbed and desorbed. Therefore, even if the surface acoustic wave sensor is miniaturized, the detection target can be detected with high accuracy.

In addition, since graphene and graphene oxide are both thermally and chemically stable, by using modified graphene and/or graphene oxide as a material constituting the reaction portion, it can be placed under various environments. It is possible to obtain a sensor that undergoes little change over time and has high reproducibility of the reaction of the object to be detected.

Note that the degree of oxidation of graphene oxide is preferably 5% or more, more preferably 10% or more, and even more preferably 30% or more. On the other hand, the upper limit of the degree of oxidation of graphene oxide is 80%. Further, when the reaction portion 5 contains both graphene and graphene oxide, the degree of oxidation is the oxygen content when the total of graphene and graphene oxide is 100%.

In this embodiment, the detection target of the reaction section 5 can be set according to the type of the modifying molecule and the type of the functional group containing oxygen. For example, when the detection target is gas, hydrogen gas ( _H2 gas), water vapor ( _H2O gas), carbon monoxide gas (CO gas), carbon dioxide gas ( _CO2 gas), nitrogen monoxide gas (NO gas), nitrogen dioxide gas (NO ₂ gas), ammonia gas (NH ₃ ), and the like. Note that when the detection target is water vapor, the sensor functions as a humidity sensor.

The reaction unit 5 may contain substances other than graphene and graphene oxide to the extent that the detection of the detection target is not hindered. In this embodiment, graphite is exemplified as a substance other than graphene and graphene oxide. Graphite may be a raw material for producing graphene and graphene oxide and is likely to be included in the reaction portion.

The thickness of the reaction section 5 is not particularly limited as long as the detection target can be sufficiently detected and the propagation loss of surface acoustic waves propagating on the reaction section is suppressed. In this embodiment, it is about 1 nm to 2 μm.

(1.3 Adhesion part)
The bonding portion 6 is formed between the substrate 2 and the reaction portion 5 and serves to bond the substrate 2 and the reaction portion 5 together and improve their adhesion. In this embodiment, the bonding portion 6 and the reaction portion 5 have substantially the same shape when viewed from above. In addition, in the present embodiment, the bonding portion 6 contains at least a compound having a siloxane bond as a main skeleton.

A siloxane bond is a bond between silicon (Si) and oxygen (O), and examples of compounds having a siloxane bond as a main skeleton include silicon dioxide (silica) and silicone resins. Therefore, although the adhesive portion 6 may contain a resin component, in the present embodiment, the adhesive portion 6 is preferably made of silicon dioxide, which is composed only of siloxane bonds.

However, when trying to configure the bonding portion 6 with silicon dioxide, it is difficult to form the bonding portion 6 that bonds the substrate 2 and the reaction portion 5 using silica itself, for example. Therefore, in the present embodiment, when the bonding portion 6 is to be composed of silicon dioxide, a compound having a siloxane bond is used, and silicon dioxide composed only of siloxane bonds is finally formed as the bonding portion 6.

Specifically, by heating a compound having a siloxane bond, the bonding portion 6 can be formed by leaving silicon dioxide composed only of the siloxane bond.

In this embodiment, silanol and derivatives thereof are preferable as the compound having a siloxane bond capable of forming silicon dioxide. Examples of silanol derivatives include those obtained by introducing a functional group such as a methyl group or a phenyl group into silanol. When silicon dioxide is formed using a silanol derivative, the adhesive portion 6 may contain a resin component in addition to silicon dioxide.

When the silanol is heated, the following main reaction occurs, and silicon dioxide that plays a role in improving the adhesion between the substrate 2 and the reaction portion 5 remains in the adhesion portion 6 .
_2SiH3OH + _3O2 → _2SiO2 + _4H2O

The thickness of the bonding portion 6 is not particularly limited as long as it is thick enough to improve the adhesion between the substrate 2 and the reaction portion 5 . In this embodiment, it is about 0.05 to 5 μm.

(1.4 Substrate)
The substrate 2 shown in FIG. 1 has a strength capable of supporting the reaction portion 5, the bonding portion 6, the surface acoustic wave excitation electrode 3, and the surface acoustic wave reception electrode 4, and the surface acoustic wave excited on the substrate has a predetermined thickness. There is no particular limitation as long as the substrate can propagate in any direction. In this embodiment, it is composed of a material having piezoelectricity, and examples thereof include lithium tantalate (LiTaO ₃ ), lithium niobate (LiNbO ₃ ), and crystal, with LiTaO ₃ being preferred. This is because the propagating surface acoustic waves have excellent frequency-temperature characteristics and a high mechanical coupling coefficient.

The crystal orientation of these substrates 2 may be determined according to the type of surface acoustic wave to be excited. In this embodiment, examples of surface acoustic waves to be excited include Rayleigh waves, leaky waves, and Love waves. For example, when exciting leaky waves, the crystal orientation of _LiTaO3 is a 36° rotated Y-cut cut angle, the crystal orientation of _LiNbO3 is a 64° rotated Y-cut cut angle, and the crystal orientation of LiNbO3 is a 64° rotated Y-cut. The orientation is a -7.5° rotated Y-cut with a cut angle.

(1.5 Surface Acoustic Wave Excitation Electrode and Surface Acoustic Wave Reception Electrode)
As shown in FIG. 1, a surface acoustic wave excitation electrode 3 and a surface acoustic wave reception electrode 4 as acoustic wave transmitting/receiving means are arranged on the main surface of the substrate 2 on which the reaction portion 5 is formed so as to sandwich the reaction portion 5 therebetween. are placed in

The surface acoustic wave excitation electrode 3 and the surface acoustic wave reception electrode 4 are arranged such that a pair of comb-shaped electrodes intersect each other at a predetermined interval without contact. The arrangement state of the electrodes, the spacing of the electrodes and the intersecting length of the electrodes are determined according to the frequency of the surface acoustic wave to be excited, the propagation direction of the surface acoustic wave, and the like.

The surface acoustic wave excitation electrode 3 inputs electrical energy input as an electrical signal having a predetermined frequency from an external circuit to the substrate. A substrate to which electrical energy is applied vibrates due to the inverse piezoelectric effect, and can excite a surface acoustic wave having a frequency input onto the substrate.

The surface acoustic wave receiving electrode 4 receives the surface acoustic wave that has been excited and propagated by the surface acoustic wave excitation electrode 3, converts the energy of the surface acoustic wave according to the frequency into electrical energy, and converts it into electrical energy. Output to an external circuit as an electrical signal having a frequency.

The material constituting the surface acoustic wave excitation electrode 3 and the surface acoustic wave reception electrode 4 is not particularly limited as long as it is a conductive material and can withstand the processing temperature during the production of the surface acoustic wave sensor element. In this embodiment, gold (Au), platinum (Pt), nickel (Ni), copper (Cu), or alloys containing two or more of these are exemplified, with Au being preferred. When Au is used as a material for forming the surface acoustic wave excitation electrode 3 and the surface acoustic wave receiving electrode 4, an adhesion layer such as titanium (Ti) is provided between the Au and the substrate in order to improve adhesion to the substrate. may be formed.

A cover electrode may be formed on the surface acoustic wave excitation electrode 3 and surface acoustic wave reception electrode 4 . Examples of the material forming the cover electrode include aluminum (Al).

The thickness of the surface acoustic wave excitation electrode 3 and the surface acoustic wave reception electrode 4 is not particularly limited as long as the surface acoustic wave can be excited on the substrate and the excited surface acoustic wave can be received. In this embodiment, the thickness is about 50-200 nm.

(1.6 Operation Principle of Surface Acoustic Wave Sensor)
In this embodiment, a case where the detection target is gas and the reaction unit 5 is made of graphene oxide will be described. In the surface acoustic wave sensor 1, the surface acoustic wave exciting electrode 3 and the surface acoustic wave receiving electrode 4 are connected to an external circuit (not shown). When the surface acoustic wave sensor 1 is placed in a predetermined atmosphere and a high-frequency voltage having a predetermined frequency is applied to the surface acoustic wave excitation electrode 3, surface acoustic waves are excited on the substrate. That is, the applied electrical energy is converted into surface acoustic wave energy. The excited surface acoustic wave propagates toward the surface acoustic wave receiving electrode 4, is received by the surface acoustic wave receiving electrode 4, is converted into electrical energy, and is taken out as a high frequency voltage.

If there is no substance in the atmosphere that reacts with the reaction portion 5 of the surface acoustic wave sensor 1, the frequency f of the high frequency voltage applied is the same as the frequency f of the high frequency voltage taken out. When a gas to be detected is introduced into this atmosphere (when the gas concentration increases), molecules of the gas are adsorbed to oxygen in graphene oxide forming the reaction portion 5 . As a result, the electron orbits of carbon atoms forming graphene oxide change, and the conductivity of graphene oxide changes.

When the conductivity of the reaction portion 5 changes, the characteristics of the substrate change, and the propagation velocity (v=fλ) of the surface acoustic wave propagating on the reaction portion 5 formed on the substrate changes, so the frequency also changes. . As a result, the frequency f' of the high-frequency voltage taken out at the surface acoustic wave receiving electrode 4 is different from the frequency f of the applied high-frequency voltage, and the amount of frequency change (Δf) caused by the change in conductivity can be detected. can be done. Since this frequency change amount has a predetermined correlation with the gas molecular weight adsorbed in the reaction section 5, this frequency change amount can be detected as the gas concentration.

On the other hand, when the gas concentration decreases, gas molecules adsorbed to oxygen in graphene oxide desorb from oxygen as the concentration decreases. As a result, the electrical conductivity of the reaction section 5 changes, and the amount of frequency change (Δf) caused by this electrical conductivity change is detected, and the fact that the gas concentration has decreased is output.

The factor for changing the propagation speed of the surface acoustic wave propagating on the reaction section 5 is not limited to the change in conductivity of the reaction section 5 , but may be the change in the mass of the reaction section 5 . In this case, the object to be detected is adsorbed on oxygen in graphene oxide, so that the mass of the reaction portion 5 increases. frequency changes.

Similarly, when the reaction portion 5 is composed of graphene, the atoms in the modified functional group introduced into the graphene are adsorbed and desorbed from the detection target, thereby changing the conductivity of the reaction portion 5, or A mass change occurs. Therefore, the change in conductivity or the change in mass can be taken out as the amount of change in the frequency of the surface acoustic wave propagating on the reaction section 5 to obtain information on the object to be detected.

Even if the object to be detected is a liquid, information on the object to be detected can be extracted as the amount of change in the frequency of the surface acoustic wave based on the same principle as described above.

(2. Manufacturing method of surface acoustic wave sensor)
Next, an example of a method for manufacturing the surface acoustic wave sensor shown in FIG. 1 will be described below.

First, prepare the substrate. A thin film of a conductive material that constitutes the surface acoustic wave excitation electrode 3 and the surface acoustic wave reception electrode 4 is formed on the prepared substrate using a known film formation method. When the electrodes 3 and 4 are formed by laminating a plurality of conductive materials, a plurality of thin films may be formed and laminated. Next, the thin film is etched so that the electrodes 3 and 4 have the comb-shaped electrode pattern shown in FIG. The etching may be wet etching or dry etching. An example of dry etching is ion milling.

When the cover electrode is formed on the surface acoustic wave excitation electrode 3 and the surface acoustic wave reception electrode 4, the cover electrode is formed by forming a vapor deposition film on the exposed and developed resist pattern and then lifting off the film. be.

In this embodiment, a bonding portion 6 for improving adhesion between the substrate 2 and the reaction portion 5 is formed on the substrate 2 on which the surface acoustic wave excitation electrodes 3 and the surface acoustic wave receiving electrodes 4 are formed.

First, a resist is formed on the substrate 2, and the resist is exposed and developed so as to form a resist pattern exposing the region where the reaction portion is to be formed. The resist may be a positive type resist or a negative type resist, but in this embodiment, it is preferable to use a negative type resist.

By exposing and developing the resist, the reaction portion formation scheduled region is exposed and the reaction portion formation scheduled region is patterned. After patterning, a solution of a compound having a siloxane bond is applied to the regions where reaction portions are to be formed. The coating method is not particularly limited, but spin coating and spray coating are preferable in this embodiment. After application, the adhesive is dried to form the adhesive portion 6 . In this embodiment, the drying conditions are preferably a temperature of 80 to 150° C. and a holding time of 30 seconds to 5 minutes.

Moreover, in the present embodiment, it is preferable to cure the compound after drying by irradiating energy rays. By doing so, it is possible to increase the adhesive force between the bonding portion 6 and the substrate 2 and the reaction portion 5 . After forming the bonding portion 6 , the reaction portion 5 is formed on the bonding portion 6 .

The reaction section 5 can be formed by a known film forming method. After the bonding portion 6 is formed, a paste containing a substance constituting the reaction portion 5 is applied onto the substrate 2 to form the bonding portion 6 . The method of application is not particularly limited, but in the present embodiment, spray coating, ultrasonic nozzle spray coating, application coating using a brush or the like, and the like are exemplified.

After application of the paste, the substance constituting the reaction portion 5 is cured by heating. In the present embodiment, when the substance forming the reaction unit 5 is graphene oxide, the heating conditions are preferably a temperature of 80 to 200° C. and a holding time of 5 to 120 minutes.

After heating, the substance is cooled. In the present embodiment, the cooling rate after heating is preferably 10° C./min or less. By performing such slow cooling, it is possible to suppress cracking of the substance contained in the reaction section 5 during cooling. After cooling, the resist pattern is lifted off using a stripping solution, so that the adhesive portion and the reaction portion can be patterned in this order on the reaction portion formation planned region on the substrate.

Through the above steps, a surface acoustic wave sensor having surface acoustic wave excitation electrodes 3, surface acoustic wave reception electrodes 4, reaction portions 5 and bonding portions 6 formed on substrate 2 can be obtained.

(3. Effects of this embodiment)
In this embodiment, in a sensor that utilizes surface acoustic waves, an adhesive portion containing a compound having a siloxane bond as a main skeleton is formed between the reaction portion and the substrate. In this adhesive part, the siloxane bond is firmly attached to both the reaction part and the substrate, so that the adhesion between the reaction part and the substrate can be improved, and the peeling of the reaction part can be effectively suppressed. . In particular, when the compound is silicon dioxide composed only of siloxane bonds, the adhesion is further improved.

When the bonding portion is composed of silicon dioxide, the bonding portion is formed by heating silanol and a silanol derivative to leave silicon dioxide, thereby obtaining the effect obtained by containing silicon dioxide in the bonding portion 6. can be reliably obtained.

In addition, when the substance forming the reaction portion is graphene and/or graphene oxide, the above effects can be further enhanced.

(4. Modification)
In the above-described embodiments, a sensor having a surface acoustic wave excitation electrode, a surface acoustic wave receiving electrode, a reaction portion, and an adhesive portion on a substrate has been described. Compensating surface acoustic wave excitation electrodes and surface acoustic wave receiving electrodes may be formed in other regions on the main surface where the bonding portion is formed. Since no reaction portion is formed between the compensating surface acoustic wave excitation electrode and the surface acoustic wave receiving electrode, it is possible to calibrate the reference frequency for calculating the frequency change.

In order to increase the detection sensitivity, a reflector 7 may be installed outside the surface acoustic wave excitation electrode 3 and the surface acoustic wave reception electrode 4, as shown in FIG. By installing the reflector 7, surface acoustic wave resonance occurs, and filter characteristics and resonance characteristics with a sharp rise and low insertion loss can be obtained. As a result, the gas detection sensitivity of the sensor is improved.

In addition, in the above-described embodiments, surface acoustic waves are used as elastic waves, but elastic waves other than surface acoustic waves may be used.

Although the embodiments of the present invention have been described above, the present invention is by no means limited to the above embodiments, and may be modified in various ways within the scope of the present invention.

The present invention will be described in more detail below using examples. However, the present invention is not limited to the following examples.

First, a titanium thin film (thickness: 20 nm) and a gold thin film (thickness: 80 nm) were sequentially deposited on the main surface of a rotated Y-cut lithium tantalate (LiTaO ₃ ) wafer with a cut angle of 36° using a sputtering method. An Au/Ti film was formed as a surface acoustic wave excitation electrode and a surface acoustic wave reception electrode. Thereafter, the Au/Ti film was subjected to ion milling to form surface acoustic wave excitation electrodes and surface acoustic wave reception electrodes having a logarithm of 32, an electrode spacing of 9.4 μm, and a cross length of 2730 μm. Next, Al was formed as a cover electrode by a lift-off method.

Subsequently, a negative type resist was formed on the LiTaO ₃ wafer on which the electrodes were formed, and the resist was exposed and developed to form a resist pattern in which the reaction portion formation planned regions were exposed. Further, the area to be formed with the reaction portion was irradiated with UV for 5 minutes to activate the LiTaO ₃ wafer bonding surface. A compound having a siloxane bond was applied by spin coating onto the LiTaO ₃ wafer on which a resist pattern was formed and activated, and dried by heating in an oven at 80° C. for 180 seconds to form an adhesive portion.

After drying, the LiTaO ₃ wafer was coated with graphene oxide as a reaction part by spray coating, heated in an oven at 150°C for 30 minutes, and then placed in an oven at a cooling rate of 10°C/min or less. Cooling was performed to harden the graphene oxide to form a reaction portion. After curing the graphene oxide, the resist pattern was lifted off using a stripping solution to obtain a patterned reaction portion.

Next, the LiTaO ₃ wafer on which graphene oxide was formed as electrodes and reaction parts was singulated to obtain sensors.

For the obtained sensor, a peeling test and an ultrasonic cleaning test were performed as follows in order to evaluate the adhesion between the substrate and the reaction portion.

The peeling test was conducted according to the tape test method of the peel test method specified in JIS H8504. First, an adhesive tape specified in JIS Z 1522 was used as a test tape. The adhesive force was about 8 N per 25 mm width.

Apply a part of the test tape to the reaction area by pressing it with your finger for 10 seconds. was pulled off momentarily. It was confirmed that the reaction portion was not adhered to the test tape after it was peeled off. That is, it was confirmed that the sensor according to the present example had good adhesion between the substrate and the reaction portion.

The ultrasonic cleaning test was carried out by placing the sensor in the container of the ultrasonic cleaning machine W-113, outputting 100 W, testing time of 10 minutes, and transmitting frequencies of 28 kHz, 45 kHz, and 100 kHz. Peeling of the reaction portion was evaluated. It was confirmed that no peeling of the reaction portion occurred at any frequency. That is, it was confirmed that the sensor according to the present example had good adhesion between the substrate and the reaction portion.

Two different tests were conducted to evaluate the adhesion, but no peeling of the reaction portion occurred in either test, confirming that the adhesion between the substrate and the reaction portion was good.

Subsequently, after flowing dry air at a flow rate of 500 sccm for 60 minutes, the hydrogen concentration was changed to 0.1%, 0.2%, 0.5%, 0.75%, and 1.0%, respectively. % of hydrogen gas was flowed and the frequency change was evaluated when the input frequency was 109.5 MHz. As a result, it was confirmed that the amount of frequency change increased as the hydrogen concentration changed. That is, it was confirmed that the concentration of hydrogen gas can be detected by measuring the amount of change in frequency when hydrogen gas is used as a detection target.

INDUSTRIAL APPLICABILITY The elastic wave sensor according to the present invention can be suitably used as a sensor because it has excellent adhesion between the substrate and the reaction section.

DESCRIPTION OF SYMBOLS 1... Surface acoustic wave sensor 2... Substrate 3... Surface acoustic wave excitation electrode 4... Surface acoustic wave receiving electrode 5... Reaction part 6... Bonding part 7... Reflector

Claims (4)

a substrate capable of propagating elastic waves;
elastic wave transmitting/receiving means provided on the substrate for exciting elastic waves in the substrate and receiving the excited elastic waves;
a reaction unit arranged on the propagation path of the elastic wave and reacting with a detection target;
a bonding portion for bonding the substrate and the reaction portion is formed between the substrate and the reaction portion;
The adhesive part contains a compound having a siloxane bond as a main skeleton,
The elastic wave sensor , wherein the bonding portion and the reaction portion have substantially the same shape when viewed from above . 2. The acoustic wave sensor according to claim 1, wherein said compound is silicon dioxide. 3. The acoustic wave sensor according to claim 1, wherein the reaction portion contains graphene and/or graphene oxide. 4. The elastic wave sensor according to claim 1, wherein said elastic wave transmitting/receiving means includes an elastic wave exciting electrode and an elastic wave receiving electrode.

Images