JP2005331326A - Elastic wave sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an elastic wave sensor realizing simplifying and turning high sensitivity of the structure. <P>SOLUTION: This elastic wave sensor 1 is constituted by arranging on a substrate 2, for example, a reaction film 5 to be reacted with a specific material which is a detection object, between an input electrode 3 for exciting elastic waves and an output electrode 4 for receiving the elastic waves excited by the input electrode 3 and propagated (on a propagation route of the elastic wave). In the sensor 1 capable of detecting the specific material by the change of a propagation characteristic of the elastic wave generated accompanying the mass change of the reaction film 5 caused by a reaction with the specific material, the elastic waves are a transversal elastic wave mainly deformed in the direction parallel to the substrate 2 surface and orthogonal to the propagation direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sensor for detecting a specific substance to be detected, and more particularly to an elastic wave sensor.

  Conventionally, in various fields such as the environment, food, and medicine, a sensor using a crystal resonator, which has a simple structure and can be expected to be miniaturized, detects various substances and measures the amount and concentration of the substance. Is used.

  As shown in FIG. 6, for example, a sensor using a quartz resonator has gold electrodes disposed on the front side and the back side of a quartz substrate, and has a property of reacting with a substance to be detected on the surface of one gold electrode. (Hereinafter, referred to as a reaction film). For example, when this sensor is used as a gas sensor, a film that adsorbs a gas to be detected is coated, and when it is used as an immunosensor, an antibody film that reacts with an antigen to be detected and antigen-antibody reacts. .

Then, according to the sensor using the crystal resonator as shown in FIG. 6, when the reaction film reacts with the detection target substance, the mass on the electrode of the crystal resonator increases, and accordingly, the resonance frequency of the crystal resonator. Therefore, the mass of the detection target substance can be quantitatively measured as the frequency change of the crystal resonator. Further, it can be applied not only to mass measurement of a detection target substance but also to concentration measurement. Note that the frequency of a crystal resonator normally used for a measurement sensor or a detection sensor is about 9 MHz, and according to a sensor using such a crystal resonator, a mass of 10 ⁻⁶ to 10 ⁻⁹ g. The change can be detected as a frequency change.

  In addition, by using surface acoustic wave devices instead of quartz resonators as other types of detection sensors, surface mass waves (Rayleigh waves) propagating on the piezoelectric substrate are used to detect the mass of the detection target substance. There is a sensor that performs.

  The surface acoustic wave device has a configuration in which an input electrode and an output electrode composed of comb-shaped electrode fingers are formed on a piezoelectric substrate. When an electric signal is applied to the comb-like input electrode, an electric field is generated between the electrode fingers, and a surface acoustic wave is excited by the piezoelectric effect. In the sensor using the surface acoustic wave, as shown in FIG. 7, for example, a reaction film is formed in a region between the input electrode and the output electrode. A change in mass is detected as a change in the frequency of Rayleigh waves propagating on the substrate surface. The sensor using the Rayleigh wave is disclosed in the following prior art documents.

R. B. Haskell et al., “Effects of Film Thickness on Sensitivity of SAW Mercury Sensors”, 1999 IEEE Ultrasonics Symposium Proceedings, (USA), IEEE Ultrasonics, Ferroelectrics and Frequency Control Society, November 30, 1999, pp. 429-434

In recent years, high sensitivity of sensors has been demanded in each application field in order to realize more accurate measurement. For example, in the field of the environment and food, it is required to accurately measure a very small amount (10 ⁻⁹ to 10 ⁻¹² g) in analyzing the amount of dioxins and environmental hormones harmful to the human body. . In the medical field, for example, detection of disease markers such as CRP (C-reactive protein), which is an inflammatory marker, and detection of bacterial infections enable early detection of diseases by enabling highly accurate measurement. In addition, since it is possible to reduce the burden on the subject because the amount of blood collected from the subject can be made very small, high sensitivity of the sensor is desired.

  At present, detection methods using magnetic sensors, detection methods using radio wave sensors, and detection methods using biosensors are being investigated as methods for sensing explosives such as landmines. Among these, detection methods using biosensors have a sensor structure. It is attracting attention because it is easy and portable. As a biosensor, a sensor in which a reaction film that reacts with a small amount of vapor of TNT (trinitrotoluene) is coated on a gold electrode of a crystal resonator has been studied. However, in gas sensing using a biosensor with such a configuration, the sensitivity of the sensor is insufficient at present, and the high sensitivity of the sensor is still an issue for practical use.

Here, in order to improve the sensitivity of a sensor using a crystal resonator, it is effective to increase the resonance frequency of the crystal resonator. The resonance frequency f ₀ of the crystal resonator is determined by the thickness d of the substrate. Since it is determined (f ₀ = v / 0.5d: v is the acoustic velocity of the elastic wave), the resonance frequency can be increased by reducing the thickness of the quartz substrate, thereby improving the sensitivity of the sensor. Can do. However, since it is difficult to reduce the thickness of the quartz substrate due to mechanical processing difficulties, it is difficult to increase the frequency, and thus it is very difficult to improve the sensitivity of the sensor using the quartz resonator. Met.

  On the other hand, in a sensor using a surface acoustic wave device, a reaction film is usually formed on a gold film via a self-assembled monolayer, and as a result of the reaction film being formed in this way, a Rayleigh wave is formed. There is a disadvantage that the propagation loss of the device becomes large. Even if the frequency is increased to improve the sensitivity of the sensor, the above-mentioned propagation loss due to the gold film becomes noticeable because the wavelength of the elastic wave becomes shorter. As a result, the conventional method using the Rayleigh wave has a high frequency. It was difficult to improve the sensitivity of the sensor.

  An object of the present invention is to provide an elastic wave sensor having a simple structure and high sensitivity.

  In order to achieve the above object, an elastic wave sensor according to the present invention is arranged on an elastic wave propagation means for exciting an elastic wave and propagating the elastic wave to and near the surface of the substrate, and on the propagation path of the elastic wave. And a reaction film that reacts with the specific substance to be detected, and the specific substance can be detected by a change in the propagation characteristics of the elastic wave caused by a change in the reaction film due to the reaction with the specific substance. The acoustic wave is a transverse acoustic wave whose displacement is mainly parallel to the substrate surface and perpendicular to the propagation direction.

  Here, in the elastic wave sensor, the elastic wave propagation means is an input electrode for exciting the elastic wave on the substrate, and an output for receiving the elastic wave excited on the input electrode and propagating on the substrate. An electrode, and the reaction film may be disposed between the input electrode and the output electrode. Further, a film of the same type as the reaction film may be further formed on at least one of the input electrode and the output electrode, and the reaction film may have a lattice shape.

  The elastic wave sensor according to the present invention includes an input electrode that excites an elastic wave on a substrate, and an elastic wave that is disposed adjacent to the input electrode and that is excited by the input electrode and propagates on the substrate. An output electrode for receiving; and a reaction film that reacts with a specific substance to be detected; the reaction film is formed on at least one of the input electrode and the output electrode; and A transverse acoustic wave having a displacement in a direction parallel to the substrate surface and perpendicular to the propagation direction is used.

  The elastic wave sensor according to the present invention includes an input electrode that excites an elastic wave on a substrate, and an elastic wave that is disposed adjacent to the input electrode and that is excited by the input electrode and propagates on the substrate. An output electrode to receive, two reflectors arranged along the propagation direction of the elastic wave so as to sandwich the input electrode and the output electrode, a reaction film that reacts with a specific substance to be detected, The reaction film is formed on at least one of the input electrode, the output electrode, and both reflectors, and the elastic wave is displaced in a direction parallel to the substrate surface and perpendicular to the propagation direction. It is a transverse elastic wave having

  Here, the reaction film may be formed on the input electrode, the output electrode, and each reflector, or may be formed only on each reflector.

  In the acoustic wave sensor of the present invention, it is preferable that the substrate is a quartz substrate, and the quartz substrate has a cut angle from 30 degrees rotation Y cut to 60 degrees rotation Y cut, and the input electrode is The propagation direction of the elastic wave is preferably formed to be a direction perpendicular to the X direction.

  Since the elastic wave sensor of the present invention uses transverse elastic waves, the propagation loss due to the formed reaction film is small, and surface waves can be efficiently propagated and detected. In addition, the transverse elastic wave is excellent in frequency temperature characteristics and has a high propagation speed, and is therefore suitable for high frequency. Therefore, it is possible to achieve high sensitivity of the sensor, which has been difficult to realize with a conventional sensor using a crystal resonator or a surface acoustic wave device.

  Further, by arranging the reaction film on the surface of the excitation electrode, the frequency change rate of the elastic wave accompanying the mass change (mass increase) of the reaction film generated when the reaction film reacts with the specific detection substance is improved ( Therefore, the sensitivity of the sensor can be further increased.

  First, a first embodiment of the present invention will be described with reference to FIGS.

  As shown in FIGS. 1 and 2, the acoustic wave sensor 1 according to the present embodiment includes a substrate 2, an input electrode 3, an output electrode 4, a reaction film 5, and a gold film 6. It has become.

The substrate 2 may be any material that can propagate a transverse elastic wave (e.g., STW: surface transverse wave) having a displacement in a direction parallel to the substrate surface and perpendicular to the propagation direction. Although there is lithium tantalate (LiTaO ₃ ) or the like, in this embodiment, quartz is selected as the substrate material because the frequency temperature characteristics of the propagating elastic wave are excellent. Further, the quartz substrate has a cut angle and a propagation direction in which the transverse acoustic wave can be efficiently excited and propagated. For example, the cut angle is from a 30-degree rotation Y-cut to a 60-degree rotation Y-cut. There are suitable conditions for propagating a transverse elastic wave such as that the wave propagation direction is perpendicular to the X direction. However, in the quartz substrate 2 used in this embodiment, the cut angle is 38 degrees. A rotation Y cut is used, and the propagation direction of the elastic wave is a direction perpendicular to the X direction.

  The input electrode 3 uses a comb-shaped electrode as an electrode for exciting an elastic wave, and is disposed on the surface of the substrate 2 so that the propagation direction of the elastic wave is perpendicular to the X direction. The output electrode 4 is a comb-shaped electrode that receives the elastic wave excited and propagated by the input electrode 3. In the present embodiment, each electrode is made of aluminum from the viewpoint of weight reduction of the sensor.

  And since the conditions of the board | substrate 2 are set as mentioned above and each said electrodes 3 and 4 are arrange | positioned so that the conditions of this board | substrate 2 may be met, it is parallel to the surface of the board | substrate 2, and it is in a propagation direction. On the other hand, a transverse elastic wave having a vertical displacement propagates from the input electrode 3 toward the output electrode 4.

  The reaction film 5 has a property of reacting with a specific substance to be detected, and is disposed on a propagation path of a transverse acoustic wave between the input electrode 3 and the output electrode 4. The reaction film 5 is formed on the gold film 6 via a self-assembled monomolecular film (not shown) as shown in FIG. The reaction film 5 on the propagation path may be a single layer film or a lattice-like shape (grating structure) as shown in FIG. Since energy propagates while being trapped on the surface of the substrate 2, there is an advantage that propagation loss can be suppressed. Therefore, in this embodiment, the reaction film 5 on the propagation path has a grating structure.

  Further, a titanium film or a chromium film is preferably formed between the gold film 6 and the substrate 2 in order to enhance the adhesion between the gold film 6 and the substrate 2. Further, since the mass of gold is large, the gold film 6 may be replaced with a light-mass material such as aluminum and a gold or two-layer or multilayer film. In this case, the outermost surface is a gold layer. good.

  Then, for example, as shown in FIG. 3, the acoustic wave sensor 1 having the above configuration, the amplifier 7 and the phase shifter 8 are connected to perform feedback to a frequency counter (not shown) that measures the frequency of the propagation wave. When a specific substance is detected by configuring a type oscillation circuit, the propagation speed of the transverse elastic wave propagating on the substrate surface with the mass change (mass increase) of the reaction film 5 due to the reaction with the specific substance to be detected is Therefore, the mass change due to the reaction is output as a frequency change based on a change in the propagation velocity of the transverse elastic wave. Therefore, according to the elastic wave sensor 1, it is possible to measure a mass change as a frequency change. Based on the measurement result, the presence / absence, mass, or concentration of a specific substance to be detected is detected. It is also possible.

  In addition, since the elastic wave sensor 1 according to the present embodiment uses a transverse elastic wave, even if an antibody film or the like is present on the surface of the substrate 2, the propagation loss is reduced, and the surface wave is efficiently propagated and detected. can do. Furthermore, since the transverse acoustic wave is excellent in frequency temperature characteristics and has a high propagation speed, it is suitable for high frequency, so that high sensitivity of the sensor can be achieved.

  Next, a second embodiment of the present invention will be described below with reference to FIGS.

  The elastic wave sensor 11 according to the present embodiment includes a quartz substrate 12, an input electrode 13, an output electrode 14, a reaction film 15, and two reflectors 16. As in the first embodiment, the substrate 12 used in the present embodiment is a crystal substrate that satisfies the conditions of the cut angle and the propagation direction in which the transverse acoustic wave can be efficiently excited and propagated.

  The input electrode 13 uses a comb-shaped electrode as an electrode for exciting an elastic wave, and is arranged on the surface of the substrate 12 so that the propagation direction of the elastic wave satisfies the above conditions. The output electrode 14 is a comb-shaped electrode that receives the elastic wave excited and propagated by the input electrode 13, and is disposed adjacent to the input electrode 13. Furthermore, two reflectors 16 are arranged along the propagation direction of the elastic wave so as to sandwich the input electrode 13 and the output electrode 14.

  In the present embodiment, the surfaces of the input electrode 13, the output electrode 14, and each reflector 16 are made of gold, and on the input electrode 13, the output electrode 14, and each reflector 16, The reaction film 15 is formed through a self-assembled monomolecular film (not shown). The input electrode 13, the output electrode 14, and each reflector 16 may be made of gold, or may be a two-layer or multi-layer film of a material such as light aluminum and gold. The outermost surface may be a gold layer.

  When the specific substance is detected by configuring the oscillation circuit using the elastic wave sensor 11 configured as described above, the mass change (mass increase) of the reaction film 15 due to the reaction with the specific substance occurs. Not only does the propagation speed decrease due to the increase in the apparent thickness of the electrode finger, but also the center frequency decreases due to an increase in the reflectance per electrode finger as the mass increases. Therefore, the center frequency of the transverse acoustic wave changes more than the center frequency change caused by the decrease in the propagation speed accompanying the mass change. Similarly, in each reflector 16, the rate of change of the center frequency of the transverse elastic wave accompanying the mass change is also increased. Therefore, since the frequency change rate of the transverse acoustic wave accompanying the mass change is larger than that of the elastic wave sensor 1 according to the first embodiment, the elastic wave sensor 11 according to the present embodiment has higher sensitivity. Measurement can be performed.

  In the second embodiment, the reaction film 15 is disposed on the input electrode 13, the output electrode 14, and each reflector 16, but the reaction film 15 is provided on the input electrode 13 and the output electrode 14. The reaction film 15 may be disposed only on each reflector 16 without arranging the reflector 15, and the frequency change of the transverse acoustic wave in the reflector 16 may be measured. In the case of this configuration, since the reaction film 15 is not disposed on the electrode, there is an advantage that the input impedance of the input electrode 13 does not change.

  In the second embodiment, the two reflectors 16 are not provided, and the reaction film 15 is disposed on the adjacent input electrode 13 and output electrode 14 to measure the frequency change of the transverse acoustic wave. You may comprise. Thereby, further downsizing of the sensor can be realized.

  Further, in consideration of the improvement in the frequency change rate in the second embodiment, in the elastic wave sensor 1 according to the first embodiment, the reaction film 5 is disposed on at least one of the input electrode 3 and the output electrode 4. Also good.

It is a schematic block diagram of the elastic wave sensor which concerns on the 1st Embodiment of this invention. It is the sectional view on the AA line of FIG. It is a figure which shows an example of the oscillation circuit using the elastic wave sensor which concerns on the 1st Embodiment of this invention. It is a schematic block diagram of the elastic wave sensor which concerns on the 2nd Embodiment of this invention. It is the BB sectional view taken on the line of FIG. It is a schematic block diagram of the sensor using the conventional crystal oscillator. It is a schematic block diagram of the sensor using the conventional elastic wave device.

Explanation of symbols

  1,11 Elastic wave sensor, 2,12 Substrate, 3,13 Input electrode, 4,14 Output electrode, 5,15 Reaction film, 6 Gold film, 7 Amplifier, 8 Phase shifter, 16 Reflector.

Claims (10)

There is provided an elastic wave propagation means for exciting an elastic wave and propagating the elastic wave to and near the substrate surface, and a reaction film disposed on the propagation path of the elastic wave and reacting with a specific substance to be detected. An acoustic wave sensor that enables detection of the specific substance by a change in propagation characteristics of the elastic wave that occurs with a change in the reaction film due to a reaction with the specific substance,
An acoustic wave sensor characterized in that the acoustic wave is a transverse acoustic wave whose displacement is mainly parallel to the substrate surface and orthogonal to the propagation direction.   The elastic wave propagation means includes an input electrode for exciting an elastic wave on a substrate, and an output electrode for receiving an elastic wave excited by the input electrode and propagating on the substrate. The elastic wave sensor according to claim 1, wherein the reaction film is disposed between the electrode and the output electrode.   The elastic wave sensor according to claim 2, wherein a film of the same type as the reaction film is further formed on at least one of the input electrode and the output electrode.   The elastic wave sensor according to any one of claims 1 to 3, wherein the reaction film has a lattice shape. An input electrode for exciting an elastic wave on the substrate, an output electrode arranged adjacent to the input electrode, receiving an elastic wave excited on the input electrode and propagating on the substrate, and a detection target A reaction film that reacts with a specific substance,
The reaction film is formed on at least one of the input electrode and the output electrode, and the elastic wave is a transverse elastic wave having a displacement in a direction parallel to the substrate surface and perpendicular to the propagation direction. An elastic wave sensor characterized by the above. An input electrode for exciting an elastic wave on a substrate, an output electrode disposed adjacent to the input electrode, receiving an elastic wave excited on the input electrode and propagating on the substrate, and the input electrode Two reflectors arranged along the propagation direction of the elastic wave so as to sandwich the electrode and the output electrode, and a reaction film that reacts with a specific substance to be detected,
The reaction film is formed on at least one of the input electrode, the output electrode, and both reflectors, and the elastic wave has a transverse wave elasticity having a displacement in a direction parallel to the substrate surface and perpendicular to the propagation direction. An elastic wave sensor characterized by being a wave.   The acoustic wave sensor according to claim 6, wherein the reaction film is formed on the input electrode, the output electrode, and each reflector.   The elastic wave sensor according to claim 6, wherein the reaction film is formed only on each of the reflectors.   The acoustic wave sensor according to claim 1, wherein the substrate is a quartz substrate. The quartz substrate has a cut angle of 30 ° rotation Y cut to 60 ° rotation Y cut, and the input electrode is formed so that the propagation direction of the elastic wave is perpendicular to the X direction. The elastic wave sensor according to claim 9.

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