JP2639580B2 - Surface acoustic wave resonator and method of adjusting its resonance frequency - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] PLL (Phase-Locked L) used for digital communication etc.
oop: VCO (Voltage-Cont)
Regarding a surface acoustic wave resonator used as a rolled oscillator (voltage controlled oscillator), it is possible to easily adjust the oscillation frequency of the surface acoustic wave resonator while the surface acoustic wave resonator is oscillating. By increasing the productivity of the surface acoustic wave resonator and realizing a high quality surface acoustic wave resonator, a drive electrode is formed on a piezoelectric substrate as a reflective electrode, and the piezoelectric substrate and the drive In a surface acoustic wave resonator in which a dielectric is formed on the electrode and the reflective electrode, a reflection electrode for frequency adjustment is provided on the dielectric.

[Industrial applications]

The present invention relates to a PLL (Phase
−Locked Loop (Phase Locked Loop) circuit, VCO (Vol
The present invention relates to a surface acoustic wave resonator used as a stage-controlled oscillator (voltage-controlled oscillator).

(Summary of surface acoustic wave resonator)

FIG. 7 is a plan view and a cross-sectional view illustrating a conventional surface acoustic wave resonator.

The surface acoustic wave resonator is provided with a drive electrode 2 in the shape of a barb made of aluminum or the like and a reflective electrode 3 on the surface of a piezoelectric substrate 1.
In order to protect the electrodes and improve the temperature characteristics, the surface is covered with a dielectric 4. The lead 5 is for applying a drive voltage to the drive electrode 2.

When an electric signal is applied to the drive electrode 2 of the surface acoustic wave resonator configured as described above, the piezoelectric substrate 1 is excited, and a surface acoustic liquid is generated on the piezoelectric substrate 1. Further, the elastic surface liquid is converted into an electric signal by the driving electrode 2 by a piezoelectric reaction.

That is, the interdigital drive electrode 2 is a transducer that converts an electric signal into a surface acoustic wave or converts a surface acoustic wave into an electric signal.

On the other hand, the reflection electrode 3 is for reflecting the surface acoustic wave.

Therefore, when the frequency of the excitation electric signal applied to the piezoelectric substrate 1 matches the standing wave frequency of the surface acoustic wave generated on the piezoelectric substrate 1, a large surface acoustic wave is generated on the piezoelectric substrate 1. Also, due to the piezoelectric reaction, a very large AC electric signal is generated also in the drive electrode 2, and a resonance phenomenon occurs.

At this time, the resonance frequency f of the surface acoustic wave resonator can be expressed by the following equation.

f = c / λ Here, c is the propagation speed of the surface acoustic wave in the piezoelectric substrate 1, and the wavelength λ is determined by the pattern pitch and the pattern width of the drive electrode 2 and the reflective electrode 3.

[Conventional technology]

Therefore, when manufacturing a surface acoustic wave resonator having a predetermined resonance frequency, the pattern pitch and the pattern width of the drive electrode 2 and the reflection electrode 3 are manufactured so as to have predetermined values.

However, even in a strictly controlled manufacturing process, errors occur in the pattern pitch and the pattern width, which cause variations in the resonance frequency.

Therefore, the resonance frequency of the surface acoustic wave resonator is adjusted.

An oscillation circuit using a surface acoustic wave resonator utilizes the above-described resonance phenomenon, and its oscillation frequency matches the resonance frequency of the surface acoustic wave resonator. That is, the reason for adjusting the resonance frequency of the surface acoustic wave resonator is to adjust the oscillation frequency to a predetermined frequency.

Conventionally, the oscillation frequency of a surface acoustic wave resonator has been adjusted using the following method.

The oscillation frequency is adjusted by reducing the thickness of the drive electrode or the reflective electrode by etching.

The oscillation frequency is adjusted by etching the piezoelectric substrate using the drive electrode or the reflective electrode as a mask.

The oscillation frequency is adjusted by evaporating the dielectric and increasing the thickness of the dielectric.

In each of these methods, the oscillation frequency is adjusted by changing the propagation constant of the surface acoustic wave.

[Problems to be solved by the invention]

However, these methods have the following problems.

1) All of the above methods require a vacuum device.

2) In the above method, since the surface acoustic wave resonator cannot be etched in an oscillating state, the operation of confirming the oscillating frequency after etching little by little must be repeated.

3) According to 1) and 2), the productivity of adjusting the oscillation frequency of the surface acoustic wave resonator is low.

4) In the above method, the surface acoustic wave resonator is oscillated,
The adjustment can be made while monitoring the oscillation frequency with a measuring instrument, but the deposition takes time and the productivity is low.

The technical problem of the present invention is to solve such a problem in the oscillation frequency adjustment of the conventional surface acoustic wave resonator and adjust the oscillation frequency of the surface acoustic wave resonator by oscillating the surface acoustic wave resonator. It is an object of the present invention to increase the productivity of a surface acoustic wave resonator and to realize a high-quality surface acoustic wave resonator by making it possible to perform the operation in a state easily.

[Means for solving the problem]

FIG. 1 is a plan view and a sectional view for explaining the basic principle of the present invention.

A drive electrode 2 and a reflective electrode 3 are formed on a piezoelectric substrate 1a, and a surface acoustic wave resonator having a dielectric 4 formed on the piezoelectric substrate 1a, the drive electrode 2 and the reflective electrode 3 is provided with a frequency adjusting reflective electrode. 6 is provided.

However, in this case, the reflection electrode 6 for frequency adjustment is provided on the dielectric 4.

[Action]

The resonance frequency or oscillation frequency of the surface acoustic wave resonator is a value specific to the surface acoustic wave resonator, and its frequency f
Can be expressed by the following equation.

f = c / λ Here, c is the propagation speed of the surface acoustic wave in the piezoelectric substrate 1, and the wavelength λ is determined by the pattern pitch and the pattern width of the drive electrode 2 and the reflective electrode 3.

The above is as described in the outline of the surface acoustic wave resonator.

Therefore, in order to change the oscillation frequency f, c or λ may be changed.

In the present invention, in order to change c or λ, a reflection electrode 6 dedicated to frequency adjustment is provided, and the oscillation frequency can be adjusted while the surface acoustic wave resonator is oscillating.

FIG. 2 is an enlarged cross-sectional view of FIG. 1 (b), illustrating the operation of the surface acoustic wave resonator according to the present invention.

C ₁ , C ₂ , C ₃ , and C ₄ in the figure indicate the propagation speed of surface acoustic waves generated in the piezoelectric substrate 1 a and the dielectric 4. The standing wave described in the figure represents the distribution of the standing wave in terms of the amplitude, and the wavelength λ of the standing wave is twice the distance from the antinode to the antinode of the standing wave. .

In such a surface acoustic wave resonator, the propagation speed C _{1 of the} surface acoustic wave in the piezoelectric substrate 1a at the position of the drive electrode 2
And the propagation velocity C _{2 of} the surface acoustic wave in the dielectric 4, the propagation velocity C _{3 of the} surface acoustic wave in the piezoelectric substrate 1 a at the position of the reflective electrode 3, and the propagation velocity C of the surface acoustic wave in the dielectric 4 _4. Each of these speeds is different, but constant.

However, when the reflection electrode 6 for frequency adjustment is cut or removed, the energy of the surface acoustic wave reflected by the reflection electrode 6 for frequency adjustment changes, and as a result, the propagation velocities C ₃ and C _{4 of the} surface acoustic wave become constant. The wavelength λ of the standing wave changes.

Therefore, the resonance frequency of the surface acoustic wave resonator changes.

In the surface acoustic wave resonator according to the present invention, the reflection electrode 6 for adjusting the oscillation frequency is provided on the dielectric 4.

Therefore, by using a laser beam or the like as a means for cutting or removing the frequency adjusting reflection electrode 6, the surface acoustic wave resonator is oscillated by the oscillation circuit,
The cutting or removing operation can be performed.

Therefore, it is possible to adjust the oscillation frequency of the surface acoustic wave resonator to a predetermined frequency while measuring the change.

FIG. 3 is a plan view illustrating an example of cutting a reflection electrode for frequency adjustment.

As shown in the figure, the oscillation frequency of the surface acoustic wave resonator can be adjusted by sequentially moving the cut portion of the frequency adjusting reflective electrode 6 in the order of 7a → 7b → 7c → 7d → 7e →. .

〔Example〕

 FIG. 4 is a plan view and a sectional view for explaining the embodiment.

A drive electrode 2 and an oscillation frequency 3 are formed on a piezoelectric substrate 1b,
A dielectric protective film 4 is formed on the upper surface.

In this case, aluminum or the like having a small propagation loss is used as the electrode, and SiO ₂ or the like is used as the dielectric.

Next, a reflection electrode 6a for frequency adjustment is formed on the dielectric 4. In this case, the frequency-adjusting reflective electrode 6a is provided at a position arranged side by side with the reflective electrode 3.

With such an arrangement, when the frequency adjusting reflective electrode 6a is cut or removed by a laser beam or the like, even if the laser beam or the like penetrates through the dielectric 4, the reflective electrode 3 is damaged. There is an advantage that it is not done.

The lead 5 is for connecting to an external circuit.

FIG. 5 is an enlarged sectional view of FIG. 4 (b), and is an explanatory view of the operation of the embodiment.

C ₁ , C ₂ , C ₃ , C ₄ , C ₅ , C ₆ in the figure are the piezoelectric substrate 1 b and the dielectric 4
Shows the propagation speed of the surface acoustic wave generated in FIG. The standing wave described in the figure represents the distribution of the standing wave in terms of the amplitude, and the wavelength λ of the standing wave is twice the distance from the antinode to the antinode of the standing wave. .

The propagation speed C _{1 of the} surface acoustic wave in the piezoelectric substrate 1 b at the position of the drive electrode 2 and the propagation speed C _{2 of} the surface acoustic wave in the dielectric 4 at the position of the drive electrode 2, and the piezoelectric substrate 1 b at the position of the reflective electrode 3
The propagation velocity C ₃ of the surface acoustic wave in the inside, the propagation velocity C _{4 of} the surface acoustic wave in the dielectric ₄ , and the propagation velocity C _{5 of the} surface acoustic wave in the piezoelectric substrate 1 b at the position of the reflection electrode 6 a for frequency adjustment. And the propagation speed C _{6 of} the surface acoustic wave in the dielectric 4, which are different but constant values.

However, when cutting or removing frequency adjusting reflective electrode 6a, the energy of the surface acoustic wave reflected by said frequency adjusting reflective electrode 6a is changed, as a result, the propagation velocity C _5, C ₆ of the surface acoustic wave constant The wavelength λ of the standing wave changes, and the resonance frequency of the surface acoustic wave resonator changes.

FIG. 6 is a view for explaining another example of a reflection electrode for frequency adjustment, wherein (a) and (c) are plan views and (b) and (d) are cross-sectional views.

As shown, the rod-shaped electrode 6b ₁ ~6b ₈ placed on the dielectric 4 at a predetermined interval, and the frequency adjustment reflecting electrode 6b.

At first, they are arranged as shown in the figures (a) and (b), but when adjusting the oscillation frequency, for example, (c),
(D) as shown in the illustration, the removal of the electrode 6b ₁ with a laser beam. Also, by sequentially removing 6b ₁ → 6b ₂ → 6b ₃ →..., The oscillation frequency is adjusted to a predetermined oscillation frequency.

〔The invention's effect〕

As described above, according to the present invention, the surface acoustic wave resonator is provided with the reflection electrode for frequency adjustment, and the reflection electrode for frequency adjustment is cut or removed little by little by a laser beam or the like, whereby the surface acoustic wave The resonance frequency of the resonator can be adjusted.

Therefore, a vacuum device is not necessary for adjusting the oscillation frequency of the surface acoustic wave resonator, and the frequency can be adjusted while measuring the oscillation frequency while the surface acoustic wave resonator is oscillating.

Therefore, the productivity of adjusting the oscillation frequency of the surface acoustic wave resonator is greatly improved, and the accuracy of the adjustment of the oscillation frequency is increased, so that a high quality surface acoustic wave resonator can be realized.

[Brief description of the drawings]

FIG. 1 is a plan view and a cross-sectional view illustrating the basic principle of a surface acoustic wave resonator according to the present invention. FIG. 2 is a cross-sectional view illustrating the operation of the present invention. FIG. 4 is a plan view and a cross-sectional view for explaining the embodiment, FIG. 5 is a cross-sectional view for explaining the operation of the embodiment, and FIG. FIGS. 7A and 7C are plan views, FIGS. 7B and 7D are cross-sectional views, and FIG. 7 is a plan view illustrating a conventional surface acoustic wave resonator. It is sectional drawing. In FIG, 1, 1a, 1b piezoelectric substrate, 2 is the drive electrode, the reflective electrode 3, the dielectric 4, 5 lead wire, 6, 6a, 6b is frequency adjusting reflective electrode, 6b ₁ ~6b ₈ is The individual electrodes 7a to 7e of the reflection electrode for frequency adjustment indicate cut portions, respectively.

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-52-105752 (JP, A) JP-A-61-269509 (JP, A) JP-A-61-89708 (JP, A)

Claims (2)

(57) [Claims] 1. A driving electrode (2) and a reflecting electrode (3) are formed on a piezoelectric substrate (1a), and the driving electrode (2) and the reflecting electrode (3) are formed on the piezoelectric substrate (1a), the driving electrode (2) and the reflecting electrode (3). A surface acoustic wave resonator comprising a dielectric (4), wherein a reflection electrode (6) for frequency adjustment is provided on the dielectric (4). 2. A driving electrode (2) and a reflecting electrode (3) are formed on a piezoelectric substrate (1a), and the driving electrode (2) and the reflecting electrode (3) are formed on the piezoelectric substrate (1a), the driving electrode (2) and the reflecting electrode (3). In the surface acoustic wave resonator on which the dielectric (4) is formed, a reflection electrode for frequency adjustment (6) is provided on the dielectric (4), and the reflection electrode for frequency adjustment (6) is connected to the surface acoustic wave resonator. A method of adjusting the resonance frequency of a surface acoustic wave resonator, wherein the resonator is cut and removed at predetermined intervals while measuring the resonance frequency of the resonator.