JPH0349310A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To minimize the effect of thermal stress due to ambient temperature, by making a piezoelectric crystal substrate and a coating member covering a surface acoustic wave propagation part of the piezoelectric crystal substrate and adhered to the piezoelectric crystal substrate, with the same type of material, cutting the members at the same cut angle and arranging them in a direction whose crystal axes are coincident. CONSTITUTION:For example, a surface acoustic wave resonator 12 is used as a surface acoustic wave element. The surface acoustic wave resonator 12 includes a crystal substrate 14 as a piezoelectric crystal substrate. A coated member 24 is fitted on one major face of the surface acoustic wave resonator 12. The coated member 24 is fitted to cover a forming part of a surface acoustic wave propagation part, i.e., an interdigital transducer 16 and a forming part of a reflector 18. The coated member 24 is made of the same material as that of the crystal substrate 14, cut at the same cut angle and arranged so that the direction of both the crystal axes is the same. The coated member 24 is fitted to the crystal plate 14 by using an adhesive layer 26. A gap 28 is formed between the coated member 24 and the crystal substrate 14 by the adhesive layer 26.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to surface acoustic wave devices.

(Prior Art) Conventionally, as surface acoustic wave devices, there have been devices in which an ink digital transducer or the like is formed on a quartz crystal substrate as a piezoelectric crystal substrate, for example. In such a surface acoustic wave device, a covering member is attached in order to protect the surface acoustic wave propagation portion of the crystal substrate and to facilitate surface mounting of the surface acoustic wave device. This covering member is attached so that a gap portion is formed over the surface acoustic wave propagation portion of the crystal substrate. The purpose of this gap is to prevent propagation of surface acoustic waves.

(Problem to be Solved by the Invention) However, such conventional surface acoustic wave devices are susceptible to thermal stress during manufacturing and mounting, for example, because the thermal expansion coefficients of the crystal substrate and the covering member are different. Therefore, depending on the ambient temperature, warping or cranking may occur, or the airtightness may deteriorate.

Therefore, the main object of the present invention is to provide a surface acoustic wave device that is less susceptible to thermal stress caused by ambient temperature.

(Means for Solving the Problems) The present invention provides a surface acoustic wave element using a piezoelectric crystal substrate,
a covering member adhered to the piezoelectric crystal substrate so as to cover the surface acoustic wave propagating portion of the piezoelectric crystal substrate and to form a void portion over the surface acoustic wave propagating portion, the covering member being made of the same material as the piezoelectric crystal substrate; This is a surface acoustic wave device in which the covering member is cut at the same cut angle as the piezoelectric crystal substrate and is arranged in a direction in which the crystal axis of the covering member and the crystal axis of the piezoelectric crystal substrate coincide.

(Function) The covering member and the piezoelectric crystal substrate have substantially the same coefficient of thermal expansion in the same direction.

(Effects of the Invention) According to the present invention, it is possible to obtain a surface acoustic wave device that does not cause warping or cracks in the piezoelectric crystal substrate and does not cause deterioration of airtightness even when the ambient temperature changes. can.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

(Embodiment) FIG. 1 is a perspective view showing an embodiment of the present invention, and FIG.
The figure is a sectional view taken along the line n-rr of the embodiment of FIG.

Surface acoustic wave device 10 includes a surface acoustic wave element. As the surface acoustic wave element, for example, a surface acoustic wave resonator 12 as shown in FIG. 3 is used. Surface acoustic wave resonator 12
includes, for example, a crystal substrate 14 as a piezoelectric crystal substrate. The crystal substrate 14 is formed, for example, into a rectangular plate shape.

An ink digital transducer 16 is formed on one main surface of the crystal substrate 14 at the center thereof.

Reflectors 18 are formed on one main surface of the crystal substrate 14 at intervals in the longitudinal direction so as to sandwich the ink digital transducer 16 therebetween. Reflector 1
8 is formed by arranging a plurality of mutually parallel electrode fingers in the longitudinal direction of the crystal substrate I4. These ink digital transducer 16 and reflector 18 are
For example, it is made of aluminum.

At both ends of the crystal substrate 14 in the longitudinal direction, pads 20 are attached.
is formed. The reason why the mounting pads 20 are formed at both ends of the crystal substrate 14 is that the propagation of surface acoustic waves is limited to between the two benders 18. These mounting pads 20 are connected to the interdigital transducer 16 by connection electrodes 22. Therefore, this surface acoustic wave resonator 12 is a one-boat type surface acoustic wave resonator.

A covering member 24 is provided on one main surface of the surface acoustic wave resonator 12.
can be installed. The covering member 24 is attached so as to cover the surface acoustic wave propagation portion, that is, the portion where the ink digital transducer 16 is formed and the portion where the reflector 18 is formed. This covering member 24 is made of the same material as the crystal substrate 14. These covering member 24 and crystal substrate 14 are cut at the same cut angle and are arranged so that both crystal axes are oriented in the same direction.

Covering member 24 is attached to quartz substrate 14 by adhesive layer 26 . As the adhesive, for example, glass frit or a high temperature cure type sealant is desirable. This adhesive layer 26 forms a gap 28 between the covering member 24 and the crystal substrate 14 . By forming this void portion 28, propagation of surface acoustic waves on the crystal substrate 14 is not hindered.

Such a surface acoustic wave device IO is attached to a printed circuit board 30, as shown in FIG. 4, for example. In this case, a hole 32 is formed in the pudding 5 plate 30 at a portion corresponding to the covering member 24. Covering member 2 is inserted into this hole 32.
The surface acoustic wave device IO is arranged so that 4 is fitted into the surface acoustic wave device IO. Then, the pad 20 and the electrode pattern 34 of the Pudding IIJ board 30 are connected by soldering or the like.

In this case, for example, nickel, silver, or the like may be deposited on the pad 20 as a bump to facilitate soldering. Note that if the covering member 24 is formed thinly, there is no need to form holes in the printed circuit board 30.

In such a surface acoustic wave device 10, the crystal substrate 14
and the covering member 24 have substantially the same coefficient of thermal expansion in the same direction. Therefore, when manufacturing the surface acoustic wave device 10 or mounting it on a printed circuit board, even if heat is applied from the outside, warping or cranking will not occur.
Airtightness is also less likely to deteriorate. In addition, the surface acoustic wave device 10
Even after it is mounted on a printed circuit board, etc., it is less susceptible to thermal stress caused by changes in ambient temperature.

In the above embodiment, a quartz crystal substrate was used as the piezoelectric crystal substrate, but other single crystal substrates may be used as long as they have heat resistance as a surface acoustic wave device.

In addition to the resonator, other surface acoustic wave elements such as a two-port filter can be used as the surface acoustic wave element.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention. FIG. 2 is a cross-sectional view of the surface acoustic wave device shown in FIG. 1 taken along line 1--2. FIG. 3 is a plan view showing an example of a surface acoustic wave element used in the surface acoustic wave device shown in FIGS. 1 and 2. FIG. FIG. 4 is an illustrative view showing a state in which the surface acoustic wave device shown in FIG. 1 is mounted on a printed circuit board. In the figure, 10 is a surface acoustic wave device, 12 is a surface acoustic wave resonator as a surface acoustic wave element, 14 is a crystal substrate as a piezoelectric crystal substrate, 24 is a covering member, and 28 is a gap portion.

Claims (1)

[Scope of Claims] 1. A surface acoustic wave element using a piezoelectric crystal substrate, and a surface acoustic wave element that covers a surface acoustic wave propagation portion of the piezoelectric crystal substrate and forms a void portion on the surface acoustic wave propagation portion. a covering member adhered to the crystal substrate, the covering member being formed of the same material as the piezoelectric crystal substrate, the covering member being cut at the same cut angle as the piezoelectric crystal substrate, and the crystal axis of the covering member and the A surface acoustic wave device arranged in a direction that matches the crystal axis of a piezoelectric crystal substrate. 2. The surface acoustic wave device according to claim 1, wherein the covering member and the piezoelectric crystal substrate are formed to have substantially the same thickness.