JPH0755680A - Lamb wave device - Google Patents

Abstract

PURPOSE:To immerse a lamb wave device entirely in a solution while eliminating the influence of variation in the impedance of the solution. CONSTITUTION:A lamb wave device comprises a silicon substrate 1, a piezoelectric film 2, a comb-toothed electrode 3, an insulating film 4 and a flat electrode 5, the piezoelectric film 2 being formed on the comb-toothed electrode 3, sandwiched between the insulating film 4 and the flat electrode 5 from both sides. The comb-toothed electrode 3 excites lamb wave by application of voltage to the piezoelectric film 2. Because of the flat electrode 5, the piezoelectric film 2 is not affected by variation in impedance.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the structure of Lamb wave devices.

[0002]

2. Description of the Related Art Since an acoustic device causes a shift in resonance frequency and phase difference with respect to changes in temperature, humidity, etc.,
It has been widely used as a temperature sensor and a humidity sensor. The acoustic device causes a shift of the resonance frequency and a phase difference even when the mass attached to the surface of the acoustic device changes. But,
In the case of measurement in a solution, the acoustic wave often escapes into the liquid, and the acoustic wave in a mode that can perform the measurement in the liquid is limited. Acoustic waves that can be measured in liquid include Lamb waves and SH surface waves. In particular, acoustic devices using Lamb wave mode are expected to have good sensitivity (RMWhite and SWWenzel, Appl.Phys.Lett. 52, 16).
53 (1988)). A Lamb wave device operating in solution has already been proposed by Kuriyama (Japanese Patent Laid-Open No. 3-25343).
Issue).

[0003]

When a Lamb wave device is used in a liquid, a change in the impedance of the solution and a change in the electric field in the piezoelectric film due to the coupling between the comb-teeth electrode and the solution cause a vibration state of the piezoelectric film. Influences the characteristics of the Lamb wave device. In the sensor device proposed by Kuriyama, since the comb-teeth-shaped electrode is provided inside the piezoelectric layer, opposite-phase sound waves are excited on both sides of the piezoelectric layer sandwiching the comb-teeth-shaped electrode. Therefore, the two sound waves cancel each other. It is an object of the present invention to solve such a conventional problem and provide a Lamb wave device that can be used in a liquid without being affected by a change in the impedance of the solution.

[0004]

According to the present invention, a piezoelectric film is formed on a comb-teeth electrode, and two flat plate electrodes sandwiching the comb-teeth electrode and the piezoelectric film from both sides are formed. It is a Lamb wave device.

[0005]

According to the present invention, a Lamb wave device composed of an acoustic element having a Lamb wave mode operating in a liquid can be obtained. In the present invention, even if the device is immersed in a liquid, the comb-teeth-shaped electrode and the piezoelectric layer are surrounded by the plate electrodes and electrically shielded. In addition, since the entire device is immersed in the liquid without being affected, the influence of the pressure change of the liquid is small, and only the mass change of the device surface can be detected, and accurate measurement is possible. Further, since the piezoelectric layer is provided only on one side of the comb-teeth electrode, the sound wave is not canceled. Receptors that adsorb or absorb a specific substance provided on the surface, such as antibodies immobilized on the surface, can cause mass changes on the device surface, and an immunosensor that detects an antigen-antibody reaction can be obtained. . In this case, by attaching an antibody film to both sides of the flat plate electrode, the amount of adsorbed antigen as a sample is doubled and the sensitivity is increased.

[0006]

EXAMPLES Next, examples of the present invention will be described. FIG. 1 (a) is a side view of an embodiment of the Lamb wave device of the present invention, and FIG. 1 (b) is an enlarged sectional view of a portion A in FIG. 1 (a). 2 (a) is a plan view thereof, and FIG. 2 (b) is an enlarged view of a B portion in FIG. 2 (a). The Lamb wave device is composed of a silicon substrate 1, a piezoelectric film 2, a comb electrode 3, an insulating film 4 and a plate electrode 5. The piezoelectric film 2 is formed on the comb-teeth electrode 3, and the piezoelectric film 2 is sandwiched between the insulating film 4 and the plate electrode 5 from both sides to form a sandwich structure. The comb electrode 3 applies a voltage to the piezoelectric film 2 to excite a Lamb wave. 3 and 4 are graphs showing frequency characteristics of a quartz Lamb wave device having no plate electrode in air and solution. In the air, a good resonance characteristic was obtained as shown in FIG. 3, but in water, the resonance characteristic collapses as shown in FIG. However, as shown in FIG. 5, by adding a plate electrode, the shape of the resonance characteristic becomes the same as that in air.

[0007]

By applying the present invention, the Lamb wave device can be used in the liquid without being affected by the impedance change of the solution.

[Brief description of drawings]

FIG. 1 is a side view and a sectional view of an embodiment of a Lamb wave device according to the present invention.

FIG. 2 is a plan view of an embodiment of a Lamb wave device according to the present invention.

FIG. 3 is a frequency characteristic diagram in air of a Lamb wave device having no plate electrode.

FIG. 4 is a frequency characteristic diagram in water of a Lamb wave device having no plate electrode.

FIG. 5 is a frequency characteristic diagram in water of a Lamb wave device having a plate electrode.

[Explanation of symbols]

 1 Silicon substrate 2 Piezoelectric film 3 Comb-shaped electrode 4 Insulating film 5 Flat plate electrode

[Procedure amendment]

[Submission date] April 27, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

Claims (1)

[Claims] 1. A Lamb wave device characterized in that a piezoelectric film is formed on a comb-teeth electrode, and two flat plate electrodes sandwiching the comb-teeth electrode and the piezoelectric film from both sides are formed.