JPH0637574A - Surface acoustic wave oscillator and surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To obtain a desired resonance frequency or pass band frequency without requiring high manufacturing accuracy by providing a comb-line reed screen type electrode formed by applying mask vapor-deposition on the surface of organic system macromolecule thin film formed on the surface of a piezoelectric monocrystal substrate by vapor-deposition, and electrodes to apply a DC voltage for use of resonance frequency adjustment at both terminals of the organic system macromolecule thin film. CONSTITUTION:In a surface acoustic wave oscillator, it is required to regulate the width and interval of the electrode so as to accurately establish relation a0=S0 assuming the width of the reed screen type electrode 1 as a0, and the interval as S0 to accurately take out the resonance frequency of the surface acoustic wave oscillator. The DC voltage from a power source 3 is applied to the organic system macromolecule thin film 3 vapor-deposited on the piezoelectric monocrystal substrate 8. In such a case, the propagation velocity of a surface acoustic wave is varied by a tensile force according to the shrinkage/expansion of the thin film in the length direction generated by high voltage property. In other words, since the resonance frequency is varied, it can be adjusted by varying the DC voltage. Thereby, the manufacturing accuracy can be moderated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave oscillator having a comb-shaped electrode and a surface acoustic wave filter.

[0002]

2. Description of the Related Art Conventionally, a surface acoustic wave oscillator of this type has a comb-shaped interdigital transducer formed on the surface of a piezoelectric crystal substrate so that the width of the electrode and the distance between the electrodes are all equal. Are arranged along the propagation direction of. The width and the interval are usually designed to be 1/4 of the wavelength of the surface acoustic wave. In principle, the resonance frequency is determined by the width and the interval. However, in order to obtain a desired resonance frequency, such an interdigital electrode having a uniform width and interval is not enough, and various electrode designs are required. Is devised.

A surface acoustic wave filter to which this type of surface acoustic wave element is applied is one in which two sets of surface acoustic wave elements are arranged on the left and right on the same piezo-voltage substrate to form an interdigital electrode. The Q of the resonator is lowered by the distance between the surface acoustic wave elements to secure the pass band width.

[0004]

Generally, the speed of sound of a surface acoustic wave composed of interdigital electrodes is different from the speed of sound when only a piezoelectric crystal substrate is used and the speed of sound on the metal surface forming the interdigital electrode, and therefore the interdigital shape is used. The sound velocity of the surface acoustic wave passing through the electrode portion is different from the sound velocity of the surface acoustic wave propagating through the piezoelectric crystal portion without the interdigital transducer. In the configuration of the interdigital electrodes, the electrodes facing each other in a comb shape are usually provided on the piezoelectric crystal substrate. In this interdigital electrode region, when the area of the metal surface is a and the area of the piezoelectric portion is S,
The sound velocity decreases as a / (a + S) increases.
The value is such that when a / (a + S) changes by 0.1, the sound speed changes by about 1 to 6 m / sec, and the sound speed decreases as the ratio of the metal surface becomes higher than that of the piezoelectric crystal part of the electrode part. Show.

Since the acoustic velocity of the surface acoustic wave varies depending on the surface condition of the element and the manufacturing precision of the dimensions of the electrode itself, conventionally, in this type of surface acoustic wave oscillator, the gap between the interdigital electrodes is different. When a difference in sound velocity occurs due to the above, the resonance frequency is affected and the resonance frequency shifts, so that there is a problem that a high manufacturing precision is required.

An object of the present invention is to solve the above problems and provide a surface acoustic wave oscillator and a surface acoustic wave filter that can obtain a desired resonance frequency or pass band frequency without requiring much manufacturing precision. is there.

[0007]

A surface acoustic wave oscillator according to the present invention comprises a piezoelectric single crystal substrate, an organic polymer thin film formed on the surface of the piezoelectric single crystal substrate by vapor deposition, and the organic polymer thin film. Is provided with comb-shaped interdigital electrodes formed by mask vapor deposition on the surface thereof and electrodes for applying a DC voltage for adjusting the resonance wave number to both ends of the organic polymer thin film.

The surface acoustic wave filter includes a piezoelectric substrate, a comb-shaped first interdigital electrode provided on the left surface of the piezoelectric substrate, and the piezoelectric substrate and the first interdigital electrode. Further, a first organic polymer thin film provided over the entire length of the comb tooth portion of the first interdigital electrode, and a resonance frequency adjusting device provided at both ends of the first organic polymer thin film. A first electrode for applying a DC voltage, a first DC power source for generating the first DC voltage, a right surface of the piezoelectric substrate, and an interdigital electrode with the first electrode. A second comb-shaped comb-shaped electrode provided and a second comb-shaped electrode provided between the piezoelectric substrate and the second comb-shaped electrode and over the entire length of the comb-teeth portion of the second comb-shaped electrode. Both the organic polymer thin film of the above and the second organic polymer thin film And a second DC power supply for generating the DC voltage and the second electrodes for applying a DC voltage for adjusting the resonance frequency provided.

The organic polymer thin film may be made of polyvinylidene fluoride (PVDF), for example.

[0010]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a (a) top view and (b) a sectional view taken along line AA of a surface acoustic wave resonator as a first embodiment.

In FIG. 1A, the comb-shaped electrodes of the interdigital electrode 1 are arranged on the plate surface of the piezoelectric crystal substrate 8 so as to face each other, and a metal electrode such as aluminum is provided at one end as the input terminal 14 and the output terminal 15. ing. A uniaxially stretchable organic polymer thin film 2 is formed by vapor deposition between the interdigital electrode 1 and the piezoelectric crystal substrate 8, and electrodes 6 are provided at both ends thereof.

The organic polymer thin film 2 is made of, for example, polyvinylidene fluoride (PVDF) having a large piezoelectric constant, and a DC voltage from a DC power source 3 serving as a modulation means is applied to the electrode 1.
By applying to No. 6, the thin film 12 expands and contracts in the length direction. In this interdigital transducer 1, in order to eliminate transient echoes as much as possible, the intervals between the electrodes are made uniform, and the width and the intervals of the electrodes are made equal.

In the case of this surface acoustic wave oscillator, assuming that the width of the interdigital electrode 1 is a ₀ and the interval is S ₀ as shown in FIG. 2, the ratio R of the metal surface in the electrode portion is given by the following equation. Become.

R = m · a ₀ / m · a ₀ + (m−1) · S ₀ Here, in order to accurately extract the resonance frequency of the surface acoustic wave oscillator, a ₀ = S ₀ is accurate. It is necessary to define the width and spacing of the electrodes so that they hold.

When a direct current voltage is applied to the organic polymer thin film 2 deposited on the piezoelectric crystal substrate 8 from the power source 3, the surface acoustic wave is generated by the tension caused by the expansion and contraction of the thin film in the length direction caused by its high piezoelectricity. The propagation speed changes continuously. That is, since the resonance frequency changes, the resonance frequency can be adjusted by changing the DC voltage.

This is made possible by using an organic polymer material having a relatively high acoustic impedance and a large electromechanical coupling coefficient as compared with an inorganic polymer material, and at the same time, the metal of the electrode material and the inorganic material of the piezoelectric crystal substrate are used. It also serves to improve characteristics such as transient response characteristics and propagation loss due to differences in the media of the system materials (eg, quartz substrate, alumina, etc.). Although the present embodiment has been described for the case where the intervals between the interdigital electrodes 11 are uniform and equal to each other, the present invention can be applied to the interdigital electrodes that are phase-modulated and arranged at predetermined intervals so as to obtain desired characteristics.

FIG. 2 is a (a) top view of the surface acoustic wave filter of the second embodiment, and (b) a sectional view taken along line AA. FIG. 2 is an application of the surface acoustic wave resonator described in FIG. 1, in which two surface acoustic wave resonators are arranged on the left and right, and the Q of the resonator is lowered by the distance between them to set the pass band width. Is. The structure and operation are the same as in the case of FIG. 1, so description thereof will be omitted, but characteristics will be described with reference to FIG. FIG. 3 is a characteristic diagram of FIG. When the DC power supplies 16 and 17 in FIG. 2 are simultaneously changed in the same direction, FIG.
The passing frequency shifts as shown in (a). When the DC power supplies 16 and 17 are individually changed, the pass band width can be changed as shown in FIG. Figure 3
(B) is a characteristic diagram when only the DC power supply 17 is changed.

[0018]

As described above, in the surface acoustic wave oscillator according to the present invention, the resonance frequency can be adjusted by the DC voltage applied to the organic polymer thin film, so that the degree of freedom in designing the resonance frequency is reduced. There are effects such as enlargement and ease of manufacturing accuracy.

[Brief description of drawings]

FIG. 1A is a top view and FIG. 1B is a sectional view taken along the line AA of the first embodiment of the present invention.

FIG. 2A is a top view of the second embodiment and FIG.
It is a line sectional view.

FIG. 3 is a characteristic diagram in FIG.
(B) Bandwidth characteristics.

[Explanation of symbols]

 1,22 Interdigital electrodes 2,15 Organic polymer thin film 3,16,17 DC power source 4,13 Input terminal 5,14 Output terminal 6,7,18-21 Electrode 8,11 Piezoelectric single crystal substrate

Front page continuation (72) Inventor Hiroyuki Kudo No.2 Raijin, Yoshioka, Yamato-cho, Kurokawa-gun, Miyagi Miyagi NEC Corporation

Claims (3)

[Claims] 1. A piezoelectric substrate, a comb-shaped interdigital electrode provided on the surface of the piezoelectric substrate, between the piezoelectric substrate and the interdigital electrode, and over the entire length of the comb-teeth portion of the interdigital electrode. An organic polymer thin film provided as an electrode, electrodes for applying a DC voltage for resonance frequency adjustment to both ends of the organic polymer thin film, and a DC power source for generating the DC voltage. Surface acoustic wave oscillator. 2. A piezoelectric substrate, a comb-shaped first interdigital transducer electrode provided on the left surface of the piezoelectric substrate, and between the piezoelectric substrate and the first interdigital electrode and the first interdigital transducer. A first organic polymer thin film provided over the entire length of the comb tooth portion of the electrode, and a DC voltage for adjusting resonance frequency provided at both ends of the first organic polymer thin film Of the first electrode, the first DC power source for generating the first DC voltage, and the comb-shaped second electrode provided on the right surface of the piezoelectric substrate and so as to form the interdigital electrode with the first electrode. The interdigital transducer, the piezoelectric substrate, and the second electrode
A second organic polymer thin film provided between the interdigital electrode and the entire length of the comb-teeth portion of the second interdigital electrode, and on both ends of the second organic polymer thin film. A surface acoustic wave filter comprising: a provided second electrode for applying a DC voltage for resonance frequency adjustment; and a second DC power supply for generating the DC voltage. 3. The organic polymer thin film is made of polyvinylidene fluoride (PVDF).
And the surface acoustic wave oscillator and the surface acoustic wave filter according to 2.