JPH02104120A - surface acoustic wave resonator - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a surface acoustic wave resonator in which a driving electrode and a reflecting electrode are formed on a piezoelectric material cut out from a 36-degree rotated Y plate of lithium tantalate (LiTaO+) single crystal, especially in a high frequency band. The aim of this project is to provide a highly stable resonator with a wide frequency variable range for use in a voltage controlled oscillator (VCO). The pitch of the electrode fingers of the reflective electrode, the pitch of the electrode fingers of the reflective electrode, and the pitch of the electrode fingers between the driving electrode and the reflective electrode facing each other are set to a surface acoustic wave wavelength.

[Industrial application field]

The present invention provides LiTa0. A surface acoustic wave resonator in which at least a driving electrode and a reflecting electrode are formed on the surface of a piezoelectric body cut out from a 36-degree rotated Y plate of single crystal, especially in a high frequency band.
This invention relates to the configuration of a CO resonator.

As digital technology has progressed in recent years, it has come to be widely used in audio equipment and communication equipment.

Along with this, it has become necessary to synchronize the frequencies of these devices, which requires a high-performance phase synchronization circuit and a high-performance VCO that is its central component, and the operating frequency is also increasing to several tens of megawatts.
High frequencies of Hz or higher are now required.

[Conventional technology]

The high-frequency VCO is composed of an oscillation section using a resonant element such as a crystal or LC, and a control element using a variable capacitance diode or the like. However, V using a crystal resonator
CO has excellent temperature characteristics, but has a small frequency variation range.
Although a VCO using an LC oscillator circuit can have a wide variable frequency range, it has the drawback of poor stability.

Therefore, as a resonator for a high-frequency VCO, LiTaO3, which has a wide frequency variable width and has an electro-mechanical coupling coefficient Kz of about 5% and a temperature characteristic of about -30 ppm/'C, is used.
Resonators made from piezoelectric material cut from a single crystal Y-plate rotated 36 degrees have started to attract attention.

Figure 3 is a schematic plan view (A) showing the electrodes of a conventional surface acoustic wave resonator using a piezoelectric material cut out from a 36° rotated Y plate of LiTaO3 single crystal, and the electrodes of the resonator and the surface acoustic wave. FIG. 2 is an explanatory diagram (b) of the relationship between the two, and an impedance characteristic diagram (c) of the resonator.

In FIG. 3(a), the surface acoustic wave resonator 1 is made of LiTa
0=A drive electrode 3 and a pair of reflective electrodes 4 are formed on the surface of a piezoelectric body 2 cut out from a 36-degree rotated Y plate of single crystal.

The drive electrode 3 is formed so that the electrode fingers 5a of the pair of interdigital electrodes 5 are inserted alternately, and the reflective electrodes 4 formed on the left and right sides of the drive electrode 3 are formed by a ladder in which the electrode fingers 4a are connected in parallel. It is the shape. Pitch pI of electrode fingers 5a
and the pitch p2 of the electrode fingers 4a are both A of the wavelength λ of the surface acoustic wave, and the pitch p of the electrode fingers 5a and 4a facing each other between the driving electrode 3 and the reflective electrode 4 is the pitch p2 of the surface acoustic wave. 7/8λ or 1/8λ in order to satisfy the resonance condition using multiple reflections. As shown in FIG. 3(B), the electrode finger 5a of the driving electrode 3 coincides with the antinode of the surface acoustic wave 6, and the inner edge of the electrode finger 4a of the reflective electrode 4 coincides with the node of the surface acoustic wave 6. He almost loses once.

The impedance characteristic of the surface acoustic wave resonator 1 configured in this way is such that, as shown in FIG. .

[Problem to be solved by the invention]

As explained above, a conventional resonator using a piezoelectric material cut from a 36-degree rotated Y plate of LiTaO3 single crystal is
V
When used for CO, there was a problem that the frequency variable range was wide (not possible).

In addition, in order to widen the frequency variable range, lithium niobate (
An energy-confined surface acoustic wave resonator with an electro-mechanical coupling coefficient of 2 of about 30% has been reported by forming gold electrodes on a piezoelectric material cut from a rotating (LiNbOs) single crystal. However, the temperature characteristic of this resonator is about -100 ppm, and therefore it cannot be used as a resonator for a VCO.

An object of the present invention is to eliminate the above-mentioned problems in conventional resonators using quartz or LiTaO5 single crystals, and resonant circuits using LC, etc., and to provide a highly stable resonator for VCOs with a large frequency variable width. It is to be.

[Means to solve the problem]

According to FIG. 1 showing an embodiment of the surface acoustic wave resonator of the present invention, electrode fingers of a drive electrode 3 are formed on the surface of a piezoelectric body 2 cut out from a 36 degree rotated Y plate of LiTa0:+ single crystal. 5a, the pitch p2 of the electrode fingers 4a of the reflective electrode 4, and the electrode finger pitch p3 between the driving electrode 3 and the reflective electrode 4 facing each other are set to 1/2 of the surface acoustic wave wavelength λ.
It is characterized by the following features:

[Effect]

According to the above means, the piezoelectric body is made of LiTaO3 single crystal 36
By using a degree-rotated Y plate and constructing an energy-trapped resonator that takes advantage of the difference in speed of surface acoustic waves,
It is possible to eliminate spurious noise that occurs in a conventional resonator using a 36-degree rotated Y plate of LiTaO3 single crystal. Therefore, when the surface acoustic wave resonator according to the present invention is used in a VCO, the VCO becomes stable and has a wide frequency variation range.

〔Example〕

Below, surface acoustic wave resonators according to embodiments of the present invention will be explained using the drawings.

FIG. 1 is a schematic plan view (a) showing electrodes of a surface acoustic wave resonator according to an embodiment of the present invention, an explanatory diagram (b) of a surface wave propagating on the surface of the resonator, and a schematic plan view of the surface acoustic wave resonator according to an embodiment of the present invention. A driving electrode 3 in which electrode fingers 5a of a pair of interdigital electrodes 5 are inserted alternately into the surface of a piezoelectric body 2 cut out from a 36-degree rotated Y temporary crystal.
A pair of reflective electrodes 4 are formed on the left and right sides of the drive electrode 3.

The driving electrode 3 and the reflecting electrode 4 are formed by vacuum-depositing an aluminum film having a thickness of 1% or more of the wavelength λ of the surface acoustic wave on the surface of the piezoelectric body 2, and removing unnecessary parts using photolithography. The pitch p1 of the electrode fingers 5a of the electrode 3, the pitch p2 of the electrode fingers 4a of the reflective electrode 4, the electrode fingers 5a located at the left and right ends of the drive electrode 3, and the electrode fingers 4a of the reflective electrode 4 facing the electrode fingers 5a. The pitch p3 is A2 of the wavelength λ of the surface acoustic wave, that is, p+ −pz −p+ =′A·λ.

LiTa0. As shown in FIG. 1 (TI), the surface acoustic wave 6 of the surface acoustic wave resonator 11 propagating in the X-axis direction of the single crystal is caused by the electrode finger 5a of the drive electrode 3 and the electrode finger 4a of the reflective electrode 4, It comes to match the antinode of the surface wave.

Furthermore, by connecting a capacitor in series with the drive electrode 3, the sound speed of the surface acoustic wave propagating through the drive electrode 3 becomes faster than that of the reflection electrode 4, and the energy of the surface acoustic wave is transferred to the drive electrode 3.
will be confined to the department.

The impedance characteristic of the surface acoustic wave resonator 11 constructed in this way is such that the conventional spurious S generated near the main resonance "m" disappears, as shown in FIG. 1(C).

FIG. 2 is a characteristic diagram of a VCO in which a series capacitance is connected to the drive electrode of the surface acoustic wave resonator according to the present invention.

In Figure 2, the vertical axis is the rate of change of oscillation frequency Δf/f
(%), the horizontal axis is the control voltage (V), and the solid line connects the measurement points with V
CO characteristic A is the one using the surface acoustic wave resonator 11 of the present invention, and VCO characteristic B, which connects the measurement points with a broken line, is the one using the conventional resonator 1. For example, at the control voltage 3■, the characteristic A is the oscillation frequency change rate Δf/f with respect to characteristic B
will increase by approximately 40%.

〔Effect of the invention〕

As explained above, according to the present invention, LiTa0. In a surface acoustic wave resonator using a piezoelectric material cut from a single-crystal 36-degree rotated Y plate, we have achieved high stability and a wide frequency variable range by eliminating the spurious that occurs near the main resonance, for example. It has the effect of increasing the performance of high-frequency VCOs.

[Brief explanation of drawings]

FIG. 1 shows a surface acoustic wave resonator according to an embodiment of the present invention, and FIG. 2 shows a VC using the surface acoustic wave resonator according to the present invention.
The characteristic diagram of O is shown in Fig. 3, which is a conventional surface acoustic wave resonator. In the figure, 2 is a piezoelectric body, 3 is a drive electrode, 4 is a reflective electrode, 4a is an electrode finger of the reflective electrode, 5a is an electrode finger of a drive electrode, 11 is a surface acoustic wave resonator, and pl is a pitch of the electrode fingers 5a. , p! is the pitch of the electrode fingers 4a, p3 is the electrode finger pitch between the opposing drive electrode and reflective electrode, 6) C hull

Claims (1)

[Claims] Pitch (p_1) of the electrode fingers (5a) of the drive electrode (3) formed on the surface of the piezoelectric body (2) cut out from a 36-degree rotated Y plate of lithium tantalate single crystal and the reflective electrode (4)
The pitch (p_2) of the electrode fingers (4a) and the electrode finger pitch (p_2) between the opposing electrode fingers (4a) of the drive electrode and the reflective electrode.
3) is set to 1/2 of the surface acoustic wave wavelength (λ).