JPS63132514A - Surface acoustic wave element using high polymer piezoelectric body - Google Patents

Abstract

PURPOSE:To form a high polymer surface acoustic wave element which is easily reduced in thickness, superior in molding workability, and high in transparency and elasticity and has high piezoelectricity by using a high polymer piezoelectric body which has couples of electrodes provided alternately on one surface of a piezoelectric film made of a vinylidene silicate copolymer. CONSTITUTION:The piezoelectric film 2 of 40 mum in film thickness is formed of an alternate copolymer of vinylidene silicate and vinyl acetate and inter- digital electrodes 3 and 3 are arrayed on the film 2 at specific intervals and connected to one terminal of a transmitter 5. Further, the other electrodes 4 and 4 are arrayed between the electrodes 3 and 3 and grounded while the electrode 3 and 4 are arranged alternately. The left group operates as a transmission part and the other group of electrodes 6 and 7 formed on the right on the piezoelectric film 2 operates as a reception part and the electrodes 6 and 6, and 7 and 7 are connected to a receiver 8.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is a thermal electret film having a pair of electrodes provided on one surface of a piezoelectric film, which is made by converting vinylidene cyanide copolymer into piezoelectricity. The present invention relates to a surface acoustic wave device using a stable polymer piezoelectric material.

[Conventional technology]

Conventionally, surface acoustic wave elements include single crystals such as LiNbO5 and quartz, piezoelectric ceramics such as PZT, ZnO,
Some use piezoelectric thin films such as ZnS. Using these elements, filters for TVs, FM tuners, and communication devices have already been put into practical use, and various other devices such as delay lines, surface wave convolvers, and surface wave memories are being studied.

[Problem that the invention seeks to solve]

However, among these inorganic materials, LiNbO5 has high piezoelectricity and high reliability, but it is difficult to process and expensive, and P
AT-based piezoelectric ceramics have high piezoelectricity and are inexpensive, but have low reliability and poor workability. Piezoelectric thin films are relatively inexpensive, but each material has its advantages and disadvantages, such as poor mass production and reliability.

[Summary of the invention]

The present invention solves the problems of existing inorganic materials and provides a polymeric surface acoustic wave element that can be easily made into a thin film, has excellent moldability, is highly transparent and flexible, and has high piezoelectricity. It is something. There are 150 application fields for this material.
Surface acoustic wave sensors (temperature sensors, pressure sensors, etc.) that take advantage of stable characteristics even at ℃ temperatures, medical ultrasonic transducers, and optical waveguide type surface acoustic wave devices (acousto-optic devices) that take advantage of their high transparency. Conceivable.

That is, the present invention is composed of a copolymer of vinylidene cyanide represented by the following formula and another vinyl compound, a vinylidene compound, or a diene; The present invention relates to a polymeric surface acoustic wave element in which a stretched film or sheet is made into an electret to impart piezoelectricity, and an electrode is formed on one surface of the piezoelectric film by sputtering, vapor deposition, or photolithography.

[Detailed description of the invention]

Next, the present invention will be explained in detail. The polymer compound used as the surface acoustic wave device in the present invention is obtained by copolymerization or alternating copolymerization of vinylidene cyanide and other vinyl compounds, vinylidene compounds, or dienes.

Other vinyl compounds, vinylidene compounds, or dienes include vinyl acetate, vinyl formate, vinyl chloroacetate, vinyl monofluoroacetate, vinyl difluoroacetate, vinyl trifluoroacetate, styrene, dichlorostyrene, acrylic acid and its esters, and methacrylic acid. and its esters, vinyl alcohol and its esters, vinyl chloride,
Examples include vinylidene chloride, vinyl fluoride, vinylidene fluoride, trifluoroethylene, and butadiene. For ester compounds, it is also possible to chemically modify part or all of them after polymerization, such as hydrolysis.

The composition ratio in the copolymer of vinylidene cyanide and other heptamers is from 0.5:1 to 1.5:1 in molar terms, preferably from O, a:t to 1.2:1. , particularly preferably a 1:1 alternating copolymerization is used.

The above monomer can be polymerized using a known method for polymerizing this type of monomer, and can be carried out in the presence or absence of a radical polymerization initiator, such as α,α'-azobisisobutyronitrile. Polymerization can be carried out by applying heat in the coexistence of these substances.

As a molding method for these vinylidene cyanide copolymers, a press molding method, a calendar molding method, a solvent casting method, etc. can be used. It is preferable to stretch the molded product obtained by either method to improve orientation. In this case, stretching methods include rolling with rolls or calendars, and mechanical stretching in uniaxial or biaxial directions using a stretching device. I do. Further, a stretched film can also be produced by simultaneously stretching the film by inflation molding or the like.

In order to impart piezoelectricity to the molded product, the molded product is heated to a predetermined temperature, a DC electric field or a DC and AC electric field is applied to the molded product for a certain period of time, and then slowly or rapidly cooled. electretization is performed. The optimal conditions for electretization vary depending on the polymer, but
For crystalline polymers, it is desirable to form electrets at a temperature higher than the crystal relaxation temperature, and for non-grade polymers, it is desirable to form electrets near the glass transition temperature, generally in the range of room temperature to 250°C, preferably 80°C to 180°C. temperature is used.

In addition, the voltage is applied by using metal foil, metal plate, conductive paste, conductive polymer, conductive rubber, or vacuum-deposited or chemically plated metal thin film as electrodes, which are closely adhered to both sides of the molded product. In general, electric field strength of 10 kV/cm or more does not cause dielectric breakdown, preferably 100 kV/cm or more.
kV/cs to 1000 kV/cm, and the treatment time is not particularly limited, but it is preferable to conduct the treatment for 30 minutes or more.

Next, in order to produce a surface acoustic wave element, an electrode is formed on one surface of the piezoelectric molding.

As shown in FIG. 1, the element 1 has one electrode 3.3 arranged in a row at a predetermined interval on one surface of the piezoelectric film 2, and connects them to one side of the transmitter 5. The other electrodes 4, 4 are arranged in a row with a gap of .3, the electrodes 3, 4 are arranged alternately, and the electrode 4.4 is grounded.

In FIG. 1, one set on the left acts as a transmitter, and the other set of electrodes 6, formed on the right side of the continuous piezoelectric film 2,
7 system acts as a receiving section, electrode 6.6, electrode 7
．． 7 is connected to receiver 8.

The electrodes are created by mask evaporation, sputtering, photolithography, or the like. When the period of the electrode is d and the velocity of the surface acoustic wave is V, the center frequency f of the excited surface acoustic wave is expressed by the following equation.

f = v / d In general, f is I MHz to I GHz, and the gap d/2 between the electrodes 3 and 4 and the electrodes 6 and 7 is about 1 to 0,001 mm.

When an ultrasonic wave is emitted by the transmitter formed by the electrode systems 3 and 4, the reflected wave is transmitted through the surface of the piezoelectric film 2 or propagated through the water when the surface wave element is underwater, and the reflected wave is transmitted to the electrode. 6.7, and is received by the receiving section formed by 6.7.

At that time, the propagation speed changes depending on environmental conditions such as temperature, humidity, and concentration of dissolved substances in water. Therefore, by measuring the change over time, temperature, humidity, concentration, etc. can be detected.

In addition, when detecting the concentration etc. by immersing it in water, the second
As shown in the figure, an element 1 is placed in a cell 10 through which a sample liquid 9 passes.
is immersed in the element 1, and a reflector 11 is installed opposite the element 1.

Vinylidene cyanide has high piezoelectricity and excellent moldability, so it is easy to manufacture elements and has excellent practicality.

In addition, vinylidene cyanide is highly transparent, so by transmitting light into the piezoelectric film and applying high frequency to the electrodes, it is possible to control the amount of light transmitted and polarized light, making it possible to use it as an optical element. can.

EXAMPLES Hereinafter, the present invention will be explained with reference to Examples, focusing on alternating copolymers of vinylidene cyanide and other monomers, but the present invention is not limited thereto.

<Example 1> A piezoelectric film 2 with a thickness of 40 μm made of an alternating copolymer of vinylidene cyanide and vinyl acetate was prepared, and a 2M interdigital electrode having the shape shown in FIG. 1 was formed on this film 2 by mask vapor deposition. establish. A burst wave Si as shown in FIG. 3 is input between a pair of electrodes 3 and 4 of the fabricated surface acoustic wave element 1, and the surface acoustic wave So propagated from between the interdigital electrodes 6 and 7 of the ground assembly is was detected. t is the delay time. When the period d of the interdigital electrodes was changed to 0.4.1 and 2 m,
Table 1 shows the results of measuring the center frequency and sound speed of the generated surface acoustic waves.

Table 1 <Example 2> As in Example 1, two sets of interdigital electrodes were provided on a 40 μm thick piezoelectric film made of an alternating copolymer of vinylidene cyanide and vinyl formate. As in Example 1, the period d of the interdigital electrodes was set to 0.4.1. Table 2 shows the results of measuring the center frequency and sound speed of the generated surface acoustic waves when the distance was changed to 2 mm.

Table 2 <Example 3> In the same manner as in Example 1, interdigital electrodes were provided on a piezoelectric film having a thickness of 40 IIIa made of an alternating copolymer of vinylidene cyanide and vinyl chloroacetate. Table 3 shows the results of measuring the center frequency and sound speed of the generated surface acoustic waves when the period d of the interdigital electrodes was changed to 0.4 and 1.2 m as in Example 1.

Table 3 <Example 4> As in Example 1, interdigital electrodes were provided on a piezoelectric film coated with an alternating copolymer of vinylidene cyanide and vinyl benzoate and having a thickness of 40 μm. Table 4 shows the results of measuring the center frequency and sound speed of the generated surface acoustic waves when the period d of the interdigital electrodes was changed to 0.4.1 and 2 ta as in Example 1.

Table 4

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram of an embodiment of the device of the present invention, and FIG. 2 is a cross-sectional view of a detector when concentration detection is performed by the device of the present invention.
FIG. 3 is a waveform diagram of transmitted and received signals. l...Surface acoustic wave element, 3.4...1
Set of electrodes, 5... Transmitter, 6, 7...
Shingle's electrode, 8...Receiver. Note 10 Arithmetic 2 Drama No.1

Claims (1)

[Claims] A surface acoustic wave element using a polymeric piezoelectric material in which electrodes forming pairs are alternately provided on one surface of a piezoelectric film made of vinylidene cyanide copolymer.