JPH11186870A - Langasite single crystal wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a smaller power flow angle, a large electromechanical coupling factor and excellent temperature characteristics by using La3 Ga5 SiO14 worked so as to propagate the surface acoustic waves of a specified value by Eulerian angle display. SOLUTION: This langasite single crystal wafer 1 for a surface acoustic wave device is worked so as to propagate the surface acoustic waves of (0 deg., >=45 deg. and <=54 deg., 0 deg.) by the Eulerian angle display and the propagation direction 2 of the surface acoustic waves is the direction for which θ is turned to be >=45 deg. and <=54 deg.. When Eulerian angle is out of the range, the power flow angle is increased and the large electromechanical coupling factor and the excellent temperature characteristics are not obtained. The langasite single crystal wafer is obtained by preparing a raw material for signal crystal by weighing and mixing La2 O3 , Ga2 O3 and SiO2 powder so as to be a stoichiometric composition, filling it inside a crucible and growing langasite single crystal indicated by a formula La3 Ga5 SiO14 by a Czochralski method by high frequency heating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a langasite (La ₃ Ga ₅ SiO ₁₄ ) single crystal wafer for a surface acoustic wave device.

[0002]

2. Description of the Related Art A surface acoustic wave device is a circuit element that performs signal processing by converting an electric signal into a surface wave, and is used for a filter, a resonator, a delay line, and the like. A surface acoustic wave device grows a single crystal having piezoelectricity by an appropriate single crystal growth method, cuts it into a wafer with a certain crystal orientation, and mirror-processes the wafer surface to form electrodes for transmitting and receiving surface acoustic waves. It is made by forming an interdigital electrode mainly made of aluminum in a certain direction and then cutting it out into chips. The performance of a surface acoustic wave device is determined by the wafer material used and the crystal orientation, in other words, the direction of propagation of the surface acoustic wave. Used.

In recent years, La ₃ Ga ₅ Si has been used as a material having a large electromechanical coupling coefficient and a zero temperature coefficient in an elastic bulk wave.
O ₁₄ (written as Langasite) reported (VVBezdelki
n and EEAntonova, JOURNAL DE PHYSIQUE, 4,139 -15
6,1994). On the other hand, for surface acoustic waves, it was reported that Langasite has a large electromechanical coupling coefficient and good temperature characteristics in the propagation direction of (90 °, 90 °, 21 °) in Euler angles (Sato, Mori, Technology No. 150
Committee, 51st Research Material, 21-27, 1997).

[0004]

In the above-mentioned report, the propagation directions of all surface acoustic waves at langasite are not considered. In addition, the propagation direction is represented by Euler angles (90 °, 90 °,
(21 °) surface acoustic wave has a large power flow angle of 11 °,
This is disadvantageous for the design and manufacture of a surface acoustic wave device. It is an object of the present invention to provide a langasite single crystal wafer in the propagation direction having a smaller power flow angle, a large electromechanical coupling coefficient and good temperature characteristics.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems and completed the present invention.
The present invention provides a langasite comprising La ₃ Ga ₅ SiO ₁₄ processed so that a surface acoustic wave (0 °, 45 ° or more and 54 ° or less, 0 °) in Euler angle representation can propagate. The subject matter of the present invention is a single crystal wafer, which has a small power flow angle, a large electric coupling coefficient, and good temperature characteristics.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The relationship between the crystal orientation of langasite and the Euler angle will be described. Langasite belongs to a trigonal system and a point group 32. In the case of hexagonal system, one c-axis (optical axis) and three perpendicular to the c-axis (optical axis) are displayed. It has an a-axis (electric axis). The relationship between the coordinate axis and the azimuth is the same as that of quartz, in which the Z axis is coincident with the c axis, the X axis is coincident with one of the three a axes, and the axis perpendicular to the Z axis and the X axis is the Y axis. X, Y,
Since the lattice constant is known, the Z axis can be determined by X-ray diffraction measurement. The direction perpendicular to {110} is the X axis,
The direction perpendicular to 0} is the Y axis, and the direction perpendicular to {001} is Z
Axis and the X-ray diffraction angle of the main surface is JCPDS card 4101
55. The positive and negative axes are simple directions using an oscilloscope (Ninomiya, NHK Technical Research, 24, 215-23
3, 1972). Further, the coordinate axes (X, Y, Z) and the Euler angles (φ, θ, ψ) of the right-handed system are shown in FIG. 2 (elastic wave element technology handbook, 549−).
550). Where X ₁ is the propagation direction of the surface acoustic wave,
X ₂ indicates the direction of the beam axis of the surface acoustic wave, and X ₃ indicates the depth direction of the substrate.

FIG. 1 shows the processing orientation of a langasite single crystal wafer 1 for a surface acoustic wave device according to the present invention.
It is processed so that surface acoustic waves (0 °, 45 ° or more and 54 ° or less, 0 °) in Euler angle display can be propagated.
In the propagation direction 2 of the surface acoustic wave, θ is 45 ° or more and 54 ° or more.
The direction is as follows. If the Euler angle is out of the above range, the power flow angle increases, and a large electric coupling coefficient and good temperature characteristics cannot be obtained. For example, in FIG. 1, if a Langasite wafer of (0 °, 50 °, 0 °) in θ = 50 ° and Euler angle display is represented by coordinate axes (X, Y, Z), 140
° It becomes a Langasite wafer of rotation Y cut X propagation.
Assuming that a surface acoustic wave propagates in parallel to the X-axis direction on a Langasite wafer having θ of 45 ° or more and 54 ° or less in FIG. 1, that is, assuming that the power flow angle is 0 °, an interdigital aluminum electrode is formed, and resonance occurs. When the resonator is manufactured, this resonator can transmit and receive surface acoustic waves well, and the power flow angle becomes almost 0 °.

[0008] The langasite single crystal wafer of the present invention comprises:
La ₂ O ₃ , Ga ₂ O ₃ , and SiO ₂ powders are weighed and mixed so as to have a stoichiometric composition to prepare a single crystal raw material, and the single crystal raw material is filled in a crucible and heated by high frequency heating. A langasite single crystal represented by the formula La ₃ Ga ₅ SiO ₁₄ is grown by the Czochralski method, and then the langasite single crystal is processed into a circular shape, and expressed as (0
(45 ° or more, 54 ° or less, 0 ° or less), the surface is cut so that the surface acoustic wave can propagate, the surface of the wafer on which electrodes for transmitting and receiving the surface acoustic wave are formed is mirror-finished, and the other surface is roughened. And it is produced.

Thus, the Euler angle display (0 °, 45 °
(54 ° or less, 0 °) The use of a langasite single crystal wafer processed so that surface acoustic waves can be propagated makes it easy to design and manufacture surface acoustic wave devices and has good characteristics. A surface acoustic wave device can be provided.

[0010]

EXAMPLES (Examples) La ₂ O ₃ , Ga ₂ O ₃ , SiO
_{2 The} powder was weighed and mixed so as to have a stoichiometric composition to prepare a single crystal raw material.The single crystal raw material was filled in a crucible, and the diameter was adjusted to 80 mm by Czochralski method using high frequency heating.
A langasite single crystal represented by the formula La ₃ Ga ₅ SiO ₁₄ having a length of 50 mm and a length of 50 mm was grown. This langasite single crystal was processed into a circular shape, and further expressed in Euler angles (0 °, 50 °).
(0 °, 0 °) in a direction that allows surface acoustic waves to propagate, mirror-finish the wafer surface on which electrodes for transmitting and receiving surface acoustic waves are to be formed, and roughen the other surface, and have a diameter of 3 inches and a thickness of 3 inches. Twenty 0.5 mm wafers having a θ of 50 ° shown in FIG. 1 were manufactured.

Assuming that a surface acoustic wave propagates parallel to the X-axis direction on this langasite wafer, an interdigital aluminum electrode is formed and a resonator is manufactured. This resonator can transmit and receive surface acoustic waves favorably. And the power flow angle was almost 0 °. In addition, when the resonance frequency change was observed in the temperature range from -25 ° C to + 75 ° C, it was found that the frequency temperature change was small at 260 ppm or less for all resonators. In addition, a method of measuring the electromechanical coupling coefficient from the difference in propagation speed (see Elastic Wave Device Technology Handbook, 338-339)
As a result, a large electromechanical coupling coefficient of 0.2% or more and 0.3% or less was obtained for all the resonators.

[0012]

According to the present invention, the power flow angle is small, the electric coupling coefficient is large, the temperature characteristics are good, and the design,
A surface acoustic wave device that can be easily manufactured can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the processing orientation of a langasite single crystal wafer of the present invention.

FIG. 2 is a diagram illustrating a relationship between coordinate axes (X, Y, Z) and Euler angles of a right-handed system.

[Explanation of symbols]

 1. Langasite single crystal wafer 2. Propagation direction of surface acoustic wave

Claims (1)

[Claims] 1. An Euler angle display (0 °, 45 ° or more and 54 ° or more)
A langasite single crystal wafer made of La ₃ Ga ₅ SiO ₁₄ processed so that a surface acoustic wave of 0 °) can be propagated.