JPS6173409A - Elastic surface wave device - Google Patents

Abstract

PURPOSE:To set up a pitch between electrodes to a large value and to set up frequency to a high level easily by setting up the Euler's angle of the ST cut to about 90 deg. and forming an electrode body on a crystal substrate so that the transmitting direction of a surface wave transmitting on the crystal substrate makes about 90 deg. with the transmitting direction due to the ST cut. CONSTITUTION:Euler's angle display consisting of three parameters PHI, THETA, psito X, Y and Z axes is used for the separating method of the crystal substrate similarly to the ordinary method. The Euler's angle indicating the transmitting direction of the surface wave out of the Euler's angles PHI=0 deg., THETA=132.75 deg. and psi=0 deg. in the ordinary ST cut is changed to 90 deg. to cut off the crystal body 5, to form a crystal substrate 1' and a comb type electrode 2'. Consequently, the transmitting direction of the surface wave is obtained in the direction rectan gular to that of a surface wave on a crystal substrate 1' separated by the ordi nary ST cut and the transmitting speed V of the surface wave can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave device, and more particularly to a surface acoustic wave resonator used as a resonant element.

In general, surface acoustic wave devices utilize surface acoustic waves caused by the piezoelectric effect of piezoelectric substrates made of single crystals such as quartz, lithium tantalate, or ceramics. In surface wave resonators (hereinafter referred to as SAW resonators), a crystal substrate is often used as the piezoelectric substrate.

For example, a specific example of a SAW resonator using a crystal substrate is shown in the fifth section.
To explain with reference to the figures and FIG. 6, (1) is a quartz crystal substrate which is a piezoelectric substrate, and (2) is a quartz crystal substrate in which a pair of comb-shaped electrode bodies separated at regular intervals λ are interlocked with each other. A comb-shaped electrode made of an A4 vaporized M film formed on the substrate (1),
(3) (3) is a reflector for surface waves excited by the comb-shaped electrode (2), and is a reflector for the surface waves excited by the comb-shaped electrode (2).
), a grating electrode (4) made of an Al vapor-deposited film formed in a vertical pattern perpendicular to the propagation direction of surface waves (
4).

When a pulse voltage is applied to the comb-shaped electrode (2) in the SAW resonator, a piezoelectric effect causes distortions in opposite phases to occur on the substrate surface between adjacent electrodes, and a surface wave with a wavelength λ is excited. This surface wave propagates on the crystal substrate (1) and is separated into a reflected wave and a transmitted wave each time it reaches each grating electrode (4) (4) of the reflector (3) (3). Therefore, if the spacing between each grating electrode <4) (4) is determined so that the phases of the reflected waves from each grating electrode (4) (4> are aligned, each reflector (3) (3)
A standing wave of wavelength λ is excited between them and becomes a resonator. The resonance frequency f of the surface wave or reflected wave is given by f=V/λ (V is the propagation velocity), the wavelength λ is determined by the pinch between the electrodes, and the propagation velocity V is determined by the material of the piezoelectric substrate. Ru.

By the way, in manufacturing the above-mentioned SAW resonator, a crystal substrate (1) which is a piezoelectric substrate is manufactured by cutting out a crystalline body (5) having crystal axes consisting of XYZ axes as shown in FIG. The propagation velocity (■) of the surface wave propagating on the crystal substrate (1) is determined by the way the crystal substrate (1) is cut out from the crystalline lens (5). A crystal substrate (1) having the following structure is cut out. Crystal substrate by this ST cut (1)
To explain how to cut out the crystalline lens (5), first, as shown in Fig. 8, in order to display the cut plane (m),
An Euler angle representation consisting of 31 parameters Φ, Θ, and Ψ is used for the axis. The Euler angle φ is the rotation angle from the X axis around the Z axis, that is, the angle made with the X axis on the Z-0 reference plane (mo>), and the Euler angle θ is the rotation angle from the
The angle between the normal n of m) and the Z axis, and the Euler square shape is the angle between the reference plane (no) and the cuff) on the cut surface (m).
The cut plane (m) is determined by the above Euler angles Φ, Θ, Ψ, which indicate the propagation direction of the surface wave by the angle formed with the intersection line l of the plane (m). For example, in the case of ST Kapto, Φ-〇°, e -13
The cut plane (m') is determined by the Euler angle of 2.75° and 'F-0' as shown in Fig. 9, and the cut plane (m') is the plate surface. °) is cut out from the crystalline lens (5).At this time, the above Euler angle !=
0°, the propagation direction of the surface wave propagating on the crystal substrate (1') is in the X-axis direction as shown by the arrow in Figure 10, and the comb teeth are interlocked in a direction perpendicular to this X-axis direction. A comb-shaped electrode (2') is formed on the crystal substrate (1'') and the first
The SAW resonator shown in Figure 1 is obtained.

■ ()I' Seat. Conventionally, as mentioned above, the propagation velocity V of the surface teeth in the ST-cut crystal substrate (1゛) is about 3158 m/s, and as the resonant frequency f of SAW resonators has become higher in recent years, for example in the UHF band. In the case of the SAW resonator used in , in order to reduce the wavelength λ of the surface wave, the interelectrode pinch must be set to about 1 μm to form comb-shaped electrodes (2°). In order to form comb-shaped electrodes (2°) with an inter-electrode pitch of about 1 μm on a crystal substrate (1°), advanced photolithography technology is required.
It has been difficult to increase the frequency of the SAW resonator due to difficulties in process technology.

1 The present invention was proposed in view of the above problem, and the technical means to solve this problem is to convert the crystalline lens having crystal axes consisting of XYZ axes into Eulerian A thin film electrode body is formed on a quartz crystal substrate cut by an ST cut determined by the angle, and the Euler angle ψ of the ST cart is set to around 90°. As a result, the electrode body is formed on the crystal substrate so that the propagation direction of the surface wave propagating on the crystal substrate forms an angle of approximately 90° with the propagation direction due to the 3T force.

One embodiment of the present invention applied to the SAW resonator shown in FIGS. 5 and 6 will be described below with reference to FIGS. 1 to 4. A feature of the present invention lies in the use of a crystal substrate cut out from a crystalline lens so that the propagation velocity V of surface waves is increased. That is, the crystal substrate used in the present invention is a crystalline substance having crystal axes consisting of the XYZ axes as shown in FIG.
5) Manufactured by cutting out from. This crystal substrate is cut out in the same way as the conventional method, with Φ, e, v
An Euler angle representation consisting of three parameters is used. As mentioned above and shown in Figure 8, Euler's horn is the rotation angle from the X-axis around the Z-axis, and the X-axis on the Z = CI reference plane (mo), which coincides with the XY plane. and the Euler angle e is the modulus of the cut surface (m) Ijtn
In addition, the Euler square shape has a cut surface (
on the reference plane (mo) and the cut plane (m)
The propagation direction of the surface wave is indicated by the angle formed with the intersection line β, and the cut plane (m) is determined by this Euler angle Φ, o1A. In the case of the present invention, φ=0゛, θ-132,75°,! −
The cut plane (m-) is determined by the Euler angle of 90' as shown in the first review, and the crystal substrate (1") is cut out from the crystalline lens (5) such that this cut plane (m") becomes the plate surface. , At this time, since the above Euler angle 'P=90'', the propagation direction of the surface wave propagating on the crystal substrate (1'') is perpendicular to X!IlI as shown by the arrow in Figure 2, and this A comb-shaped electrode (2') is formed on a crystal substrate (1'') so that the comb teeth are interlocked in a direction perpendicular to the propagation direction to obtain the S A W resonator shown in FIG. 3. In this way, the conventional ST Euler angle at the cuft Φ=O°, θ=132.75°
, the Euler angle indicating the propagation direction of the surface wave is changed to 90°, and the crystalline lens (5) is cut to form a crystal substrate (1"), and the comb-shaped electrode (2' ), the crystal substrate (1') cut out using the conventional ST cup
The propagation direction of the surface waves can be obtained in a direction perpendicular to the propagation direction of the surface waves (X-axis direction) above, and the propagation speed (2) of the surface waves can be increased. According to the applicant's experimental results, as shown in Fig. 4, in the resonant frequency characteristic, the resonant frequency [shows approximately the peak value when the above-mentioned Euler angle is around 90°, and the Euler angle in the conventional ST cut It is possible to obtain a resonance frequency f that is approximately 1.6 times that when the mold is at 0°.

11 of 41 According to the present invention, the Euler angle ゛y in the conventional ST cut
Since the electrode body is formed on the crystal substrate so that the propagation direction of the surface wave propagating on the crystal substrate forms an angle of approximately 90 degrees with the X-axis direction by setting the If desired, the inter-electrode pitch can be set large, and in other words, high frequency can be easily achieved in terms of process technology without requiring sophisticated photolithography technology.

[Brief explanation of the drawing]

1 to 4 are for explaining one embodiment of the present invention. FIG. 1 is an explanatory diagram showing a cut surface according to the O(R) angle representation in the present invention, and FIG. 2 is an explanatory diagram showing a cut surface in the present invention. FIG. 3 is a plan view showing a surface acoustic wave device (SAW resonator) according to the present invention, and FIG. 4 is a characteristic diagram showing resonance frequency characteristics. FIG. 5 is a perspective view showing a specific example of a general surface acoustic wave device (SAw resonator), FIG. 6 is a sectional view taken along line A-A in FIG. 5,
Fig. 7 is a perspective view showing an example of a crystalline lens, Fig. 8 is an explanatory drawing for explaining Euler angle display, Fig. 9 is an explanatory drawing showing an ST cut surface by conventional Euler angle display,
FIG. 0 is an explanatory view showing a conventional comb-shaped electrode formed on an ST cupto surface, and FIG. 11 is a plan view showing a conventional surface acoustic wave device (SAW resonator). (1) (1')-m-crystal substrate, (2) (2°
)--electrode body comb-shaped electrode), (5)-- crystalline lens. and: 115 Figure 116 Figure s 8 Figure 99 X-axis direction -

Claims (1)

[Claims] (1) From a crystalline lens with crystal axes consisting of XYZ axes, Φ
, Θ, Ψ A thin film-like electrode body is formed on a quartz crystal substrate cut out with an ST cut determined by the Euler angles of , Θ, and Ψ so that the comb teeth engage with each other. The electrode body is formed on the crystal substrate so that the propagation direction of the surface wave propagating on the crystal substrate forms an angle of approximately 90 degrees with the propagation direction by the ST cut by setting the electrode body near 90°. surface wave device.