JPH07198428A - Surface acoustic wave sensor - Google Patents

Abstract

PURPOSE:To assemble sensor members easily and to eliminate the contact between the sensor members and an IDT electrode. CONSTITUTION:A piezoelectric substrate 1 is made of a material for propagating leakage surface acoustic wave, and IDT electrode 2 for exciting the surface acoustic wave and an IDT electrode 3 for converting the leakage surface acoustic wave propagated on the substrate 1 are formed on the surface, a recessed part 1A is formed at the center of the inverse side of the substrate 1, and a sensor member 4 is applied to the recessed part 1A, thus constituting a sensor which changes the sound velocity of the leakage surface acoustic wave propagated on the substrate 1 depending on the sensing state of the sensor member 4. The sensor member 4 and the IDT electrode 2 are positioned on mutually separated surfaces for eliminating contact, thus preventing the damage and at the same time facilitating the manufacture. By providing the recessed part 1A, the sensor member 4 is positioned at a shallow location from the substrate surface, thus improving the sensor sensitivity for the leakage surface acoustic wave.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor utilizing surface acoustic waves.

[0002]

2. Description of the Related Art A sensor of this type, as shown in FIG.
Interdigital transducer (IDT) electrodes 2 and 3 are formed on both sides of the piezoelectric substrate 1, and the sensor member 4 is attached to the surface of the substrate 1 between the electrodes.

In this structure, a signal of a predetermined frequency is applied to the IDT electrode 2 from the high frequency signal source 5 to propagate the surface acoustic wave excited by the IDT electrode 2 to the IDT electrode 3.
The output frequency by electromechanical coupling of the IDT electrode 3 is measured by the measuring instrument 6.

The sensor member 4 attached to the surface of the substrate 1 reduces the sound velocity of the surface acoustic wave propagating through the substrate 1.
The degree corresponds to the sensing state of the sensor member 4. As a result, the frequency measured by the measuring device 6 changes depending on the sensing state of the sensor member 4, and this frequency change can be used as the sensor output.

For example, to construct a humidity sensor, the sensor member 4 is made of a selenium thin film or a carbon film, and the sound velocity of the substrate 1 is changed according to the degree of water absorption. Further, the gas sensor detects formaldehyde concentration as a frequency change by using formaldehyde dehydrogenase and its coenzyme as coating films on a quartz substrate. In addition, the odor sensor detects a chemical substance that is a source of odor as a frequency change by utilizing the high detection sensitivity of a minute amount of a crystal oscillator. Furthermore, the application using each sensor member is made also to a bitterness sensor, a metal corrosion sensor, etc.

[0006]

In the conventional configuration, I
In the method of performing sensing on the surface of the substrate provided with the DT electrode, since the substrate 1 itself becomes extremely small, the IDT electrodes 2 and 3 and the sensor member 4 may come into contact with each other when manufacturing the sensor.

Therefore, the IDT electrode and the sensor member may be damaged. Further, it is necessary to take measures such as forming a protective film for protecting the IDT electrodes so that a short circuit between the electrodes does not occur.

An object of the present invention is to provide a surface acoustic wave sensor having a structure which facilitates the assembly of the sensor member and eliminates the contact between the sensor member and the IDT electrode.

[0009]

According to the present invention, in order to solve the above-mentioned problems, one surface is made flat and the other back is made flat, and a recess is formed in the central portion thereof, and the surface has leakage elasticity. A piezoelectric substrate for propagating a surface wave, a first IDT electrode for generating a surface acoustic wave excited by a signal source by obtaining electromechanical coupling at one site on both sides of the surface of the substrate, and a substrate for the substrate. A second IDT electrode that obtains electromechanical coupling at the other part of both sides of the surface and obtains a frequency change of the leaky surface acoustic wave propagating through the substrate as a sensor output, and is provided in the recessed portion of the substrate, And a sensor member for changing the sound velocity of the leaky surface acoustic wave propagating through the substrate according to the sensing state.

[0010]

Function: As the surface acoustic wave propagating through the piezoelectric substrate, the energy of the wave is concentrated on the substrate surface, but when the wave propagates, the leaky surface acoustic wave (leaky surface wave propagating while radiating the bulk wave into the substrate) Wave, pseudo surface acoustic wave) is used.

Thus, the restriction that the sensor member is located on the surface on which the IDT electrode is provided is eliminated, and the sensor member is provided on the back surface of the substrate to serve as the frequency changing operator of the leaky surface acoustic wave, and on the surface of the substrate opposite to the IDT electrode. It is provided to eliminate contact with the IDT electrode.

The effect of the sensor member on the leaky surface acoustic wave is more effective when the substrate is thinner, but when the substrate is made thin, the holding structure and the substrate strength become problems. Therefore, the substrate is made relatively thick, and a depression is formed in the central portion of the substrate to provide the sensor member at that portion.

[0013]

FIG. 1 is a sectional view of an element showing an embodiment of the present invention.

One surface of the piezoelectric substrate 1 is flat, and the IDT electrodes 2 and 3 are formed on both sides thereof. Further, the piezoelectric substrate 1 has a recessed portion 1A at the center on the other back surface.
And has a flat shape. The sensor member 4 is attached to the recess 1A.

The piezoelectric substrate 1 is made of a material that propagates a leaky surface acoustic wave. For example, a quartz substrate or LiTaO ₃
There is a substrate, a Li ₂ B ₄ O ₇ substrate, and an LST-cut quartz substrate that cuts a zero temperature coefficient is particularly preferable.

In this embodiment, a high frequency signal source is connected to the IDT electrode 2 and the piezoelectric substrate 1 is electromechanically coupled.
Generates leaky surface acoustic waves. The IDT electrode 3 converts the leaky surface acoustic wave propagating on the surface of the piezoelectric substrate 1 into an electric signal by electromechanical coupling, and obtains an output to a measuring instrument.

Here, the leaky surface acoustic wave propagating through the piezoelectric substrate 1 radiates to the inner surface of the substrate 1 and the bulk wave radiates into the sensor member 4.
Is affected by the sensing state of, and as a result, the propagation velocity of the leaky surface acoustic wave changes. A sensor that can be regarded as a frequency change of a signal converted by the IDT electrode 3 by this speed change can be configured.

According to this embodiment, the sensor member 4 and the IDT
The electrodes 2 and 3 are separated into a front surface and a back surface of the piezoelectric substrate 1. As a result, the damage due to the contact between the sensor member and the IDT electrode, which is a problem in the conventional structure, is eliminated, and the formation of the protective film is unnecessary.

Further, in this embodiment, since the sensor member 1 is attached to the recess 1A of the piezoelectric substrate 1, the sensor member 1 can be arranged at a relatively shallow position from the surface of the piezoelectric substrate 1, and the sensor member 1 The effect of 1 on the propagation velocity change of the leaky surface acoustic wave is enhanced, and the sensor sensitivity is not lowered.

FIG. 2 shows another embodiment of the present invention. 1 is different from FIG. 1 in that only the surface portion to which the sensor member 4 is attached is formed in the formation of the recessed portion 1A of the piezoelectric substrate 1.

That is, the recessed portion 1A of the piezoelectric substrate 1 is
The structure is such that it surrounds the sensor member 4, and also has a wall portion 1B in the width direction of the sensor member 4. This structure is realized by forming the recessed portion 1A of the piezoelectric substrate 1 by etching.

In this embodiment, in addition to obtaining the same effects as the above-mentioned embodiment, since the wall 1B is provided, the surface of the recess 1A is formed shallower than the surface of the IDT electrode side. 1 can have a sufficient bending strength. Thereby, the sensor member 4 can be arranged closer to the surface of the substrate, which has the effect of increasing the sensor sensitivity.

[0023]

As described above, according to the present invention, the structure in which the surface on which the IDT electrode is formed and the surface on which the sensor member is arranged are separated into the front surface and the back surface of the piezoelectric substrate by utilizing the leaky surface acoustic waves. Therefore, there is no contact between the IDT electrode and the sensor member, and there is an effect that the IDT electrode and the sensor member are easily manufactured, and moreover, damage due to mutual contact is surely prevented.

Since the sensor member is adhered to the piezoelectric substrate by providing the recessed portion, the thickness of the substrate is made relatively thick to obtain sufficient strength, and the sensor member is leaked by a surface acoustic wave. The sensor sensitivity can be increased by positioning the sensor relatively shallowly from the propagation surface of.

[Brief description of drawings]

FIG. 1 is a sectional view of an element showing an embodiment of the present invention.

FIG. 2 is a sectional view of an element showing another embodiment.

FIG. 3 is a perspective view of a conventional element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Piezoelectric substrate 2, 3 ... IDT electrode 4 ... Sensor member 5 ... Signal source 6 ... Measuring instrument 1A ... Recess 1B ... Wall

Claims (1)

[Claims] 1. A piezoelectric substrate, one surface of which is flat and the other back surface is flat, and a recess is formed in the center thereof, and a piezoelectric substrate for propagating leaky surface acoustic waves on the surface, and both sides of the surface of the substrate. Electromechanical coupling is obtained at one part of the part, and a first IDT electrode that generates a surface acoustic wave excited by a signal source, and electromechanical coupling is obtained at the other part of both sides of the surface of the substrate, A second IDT electrode that obtains a frequency change of the leaky surface acoustic wave propagating through the substrate as a sensor output, and a sound velocity of the leaky surface acoustic wave propagating through the substrate depending on the sensing state. A surface acoustic wave sensor, comprising: