JPS6041808A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To obtain a surface acoustic wave element excellent also in the coupling coefficient by cutting a piezoelectric medium substrate of lithium tantalate having substantially an excellent temperature coefficient in a prescribed direction. CONSTITUTION:The X, Y and Z axes of the lithium tantalate single crystal are taken respectively as the 1st, 2nd and 3rd axes. The 2nd and 3rd axes are rotated counterclockwise by nearly 40 deg. by taking the 1st axis as the rotating axis and the Y and Z axes in this azimus is taken respectively as the 4th and 5th axes. The 1st and 4th axes are rotated counterclockwise by nearly 3 deg. by taking the 5th axis as the rotating axis and the X and Z axes in this azimuth are taken respectively as the 6th and 7th axes. The 6th axis is rotated counterclociwise slightly by taking the 7th axis as the rotating axis and the direction of the X axis in this azimuth is taken as the 8th axis. The direction of the 7th axis is used as the plane azimuth and the direction of the 8th axis is taken as the propagation direction of the surface acoustic wave so as to form the surface acoustic wave element. As a result, the characteristic curve G better than the curve H of the 40 deg. rot Y cut in the resonance characteristic is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical field of the invention The present invention relates to improvements in surface acoustic wave elements. In particular, lithium tantalate (L+Ta03) is used as the base material.

This invention relates to improvements in surface acoustic wave devices that increase the coupling coefficient and decrease the temperature coefficient.

(2) Background of the technology A surface acoustic wave element is a signal transmission means that uses an elastic wave as a signal transmission medium that propagates along the surface of a flexible body such as a piezoelectric medium, and the propagation speed of the wave is approximately that of an electromagnetic wave. Since it is one-tenth the size, the element is small and lightweight, and can be driven and detected at any location on the substrate made of an elastic body through which waves propagate, and the propagation characteristics can be easily controlled from the outside. In particular, it is widely used as a delay element, and can also be used as an amplifier 9 waveform conversion element.

Incidentally, there are a coupling coefficient and a temperature coefficient as indicators for indicating the characteristic +I of a surface acoustic wave element. The coupling coefficient is an index that indicates the efficiency with which electrical energy is converted into vibration energy, and it is an index that indicates the efficiency with which electric energy is converted into vibration energy. Let Vf be the propagation velocity of the surface wave at , and Vs be the propagation velocity of the surface wave when the surface is short-circuited by a metal layer, etc., being attracted to the surface. is k2
:JL, defined as Vf −vS 2 Vs. On the other hand, the temperature coefficient kt is the rate of change of the speed at which a surface wave propagates in the piezoelectric medium base material with respect to temperature, and the phase change that occurs when the temperature is changed by ΔT at a certain phase (H) is expressed as ΔH. If so, it is defined as kT −ΔH/H/ΔT.

For lithium niobate (L+Nb03), lithium tantalate (LiTa03), quartz, etc., which are widely used as surface acoustic wave elements, when the coupling coefficient and temperature coefficient of L are written in -, each is 1286ro.
t Y cant (lithium naiohe I), X cant
-(Lithium tantalate)1. In the case of ST cant (crystal), it is as follows.

U class Id group u' [Improvement (%) (ppm/'C) Lithium Niope-1-5, 6-72 Lithium tank rate 0.007 -20 Crystal 1.00 (3) Conventional technology and problems In the conventional technology, Y cut is used when lithium tantalate is used as a typical piezoelectric medium base material, X cut is used when lithium tantalate is used, and S'F cut is used when quartz is used. It was closed.

As a result, when lithium tantalate is used, the temperature coefficient is poor, and when lithium tantalate or quartz is used, the bonding coefficient is poor.

(4) I-J aspect of the invention The purpose of the present invention is to eliminate this drawback. The Company aims to provide surface acoustic wave devices.

(5) Structure of the Invention The structure of the present invention is as follows: (a) The X-axis direction of the lithium tantalate i-mourning crystal is the first axis of the orthogonal coordinates, and the Y-axis direction is the second axis.
axis, and the X-axis direction is the third @l+ binding, (b) the first
111b as the rotation axis, the second axis and the third @I+ are rotated approximately 40 degrees counterclockwise, and the Y-axis direction and the X-axis direction in this direction are respectively made the fourth axis and the fifth axis, ( c) The first +lib and the fourth axis with the fifth axis as the rotational axis.
jilt counterclockwise by approximately 3 degrees, and the X-axis direction and Z1lif+ direction in this direction are respectively
611 and the seventh axis, (d) Rotate the seventh axis -1111
, the sixth axis is slightly rotated counterclockwise, the X-axis direction at this force position is set as the eighth axis, and (e) the direction of the seventh axis is changed from the plane orientation to the direction of the eighth axis In the elastic table + RTI wave element, where is the propagation direction of the surface acoustic wave.

In the present invention, we make use of the property that the characteristics such as the coupling coefficient and temperature coefficient of the beam chum tantare I greatly depend on the direction in which they are cut out, and we prototype a large number of samples with different cutting directions. After repeating the experiment, the coupling coefficient was 4.
．． It is as large as 6%, and the temperature coefficient is -29ppm
We discovered the direction in which C and J protrude, and decided to manufacture a surface acoustic wave element by using the pressed media base cut in this direction.In addition, this 9J
FIG. 1 shows a graph showing the relationship between the phase change and the temperature change in the free state and the short-circuited state of the piezoelectric medium substrate extended in the extending direction. In the figure, A shows the case where the string is shortened, and B shows the case where it is free. and,
The temperature coefficient of the bender is -29 ppm/°C, and the temperature coefficient of the latter is -43 ppm/°0, and it is clear that the temperature coefficient is extremely small. Further, the coupling coefficient at this time was 4.6%, and the sound speed was 4,200 m/sec. The sample used in this test, as shown in Figure 2, has a pinch of 44 m, a cross width of 2 IoII+, 25 pairs of double ゛i[z model I transducer, and a lithium tandem transducer. Tare 1 RP crystal is made into 9 pieces as shown in L. In addition, in the figure, C
is the crossover width, and D is the input and output!・Transducer distance #
(5 mm), ■ is a substrate, 2 is a transducer, and 3 is a shorting metal plate.

(6) Embodiments of the Invention Hereinafter, surface acoustic wave elements (filters and resonators) according to embodiments of the present invention will be further described with reference to the drawings.

Using a substrate cut out from a single crystal Lithumtan crystal as shown in the above structure, we prototyped an intermediate frequency filter that uses a multi-channel filter to improve the pukablur. Since the manufacturing process is well known, the description thereof will be omitted. To compare the characteristics,
A 40 DEG rot Y-Lithium Niohe I filter was also produced using the same mask, and its characteristics were also determined, and the characteristic curves of both are shown in FIG. The curve E is the characteristic of the filter according to the embodiment of the present invention, and the curve F is the characteristic of the Tuumniobate filter.The coupling coefficients of both curves are almost the same.

A resonator was prototyped using a substrate with a lithum tantalate single crystal as shown in the configuration shown in the following.

Since the manufacturing process is well known, the description thereof will be omitted. 40°rot manufactured using a circular mask to compare characteristics.
A prototype Y-lithum tantalate resonator was also manufactured and its characteristics were measured, and the characteristic curves of both are shown in FIG. The curve G is the characteristic of the resonator according to the embodiment of the present invention, and the curve G is the characteristic of the resonator according to the embodiment of the present invention.
This is a characteristic of the resonator, and the effects of the present invention are clear.

(7) Effects of the invention - As explained, according to the present invention, lithium tantalate 1.
It is possible to provide a surface acoustic wave element using a medium-based material and having a large coupling coefficient.

[Brief explanation of drawings]

Figure 1 shows test l'#+'i of the test for confirming the effectiveness of the present invention.
2 is a graph showing the results, and FIG. 2 is a plan view of the sample used in the test. FIGS. 3 and 4 are graphs comparing the characteristics of a filter and a resonator, respectively, according to an embodiment of the present invention. A... As a result of short circuit condition, B... Free condition.

Claims (1)

[Claims] (b) The X-axis direction of the lithium tank crate single crystal is the 1611th orthogonal coordinate, the Y-axis direction is the second axis, and the X-axis direction is the third axis, (b) the first axis is the rotation axis, and the The second and third axes are rotated approximately 40 degrees counterclockwise, and the Y-axis direction and Z4:bJ direction in this direction are respectively made the fourth and fifth axes, and (c) the corresponding Rotating the first shaft and the fourth shaft approximately 3 degrees counterclockwise using the fifth shaft as the rotation axis,
The X-axis direction and the second axis direction in this direction are respectively
(d) Slightly rotate the 611jl+ counterclockwise using the 7th axis as the rotation axis, and make the X-axis direction in this direction the 8th axis; (e) the fJ
, 711111 is the surface orientation, and the direction of the eighth axis is the propagation direction of the elastic table +f+i waves.