JPH0514100A - Substrate for surface acoustic wave device and manufacture thereof - Google Patents

Abstract

PURPOSE:To prevent production of a spurious wave by a bulk wave reflected in the surface of a substrate and to attain high reliability in the substrate for a surface acoustic wave device used various electronic devices. CONSTITUTION:A substrate 1 consists of a uniform sintered layer 11 made of a piezoelectric ceramic material having a thickness larger than one wavelength with respect to a pass band center frequency at the side to which an input electrode 2 and an output electrode 3 are arranged and an ununiform sintered layer 12 completely molten to the uniform sintered layer 11, and as the manufacture of the substrate 1, calcinated powder reacted completely and calcinated powder reacted incompletely are manufactured in the calcination process using mixed powder of the same composition, each powder is crushed and granulated respectively and the surface is formed with a powder layer completely calcinated and the rear side is formed with a powder layer incompletely calcinated and the result is sintered, then the ununiform sintered layer 12 disperses a bulk wave to prevent production of spurious radiation and the reliability is improved because no complicated process is required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate of a surface acoustic wave device used for a surface acoustic wave filter or a surface acoustic wave resonator of various electronic devices and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, surface acoustic wave devices used for surface acoustic wave filters, surface acoustic wave resonators, etc.
It is also used in mobile communication devices such as TRs, mobile phones and pagers, and the demand for it is increasing year by year.

A surface acoustic wave device has a structure in which an input electrode for exciting the surface acoustic wave and an output electrode for receiving the surface acoustic wave are provided on the surface of a substrate made of a piezoelectric ceramic material such as PZT.
The wave excited from this input electrode becomes a surface acoustic wave propagating on the surface of the substrate, but at the same time, a bulk wave propagating inside the substrate and reflected on the back surface of the substrate is also generated, and this bulk wave is received by the output electrode. Then, it was a factor of spurious in the frequency characteristic.

In order to prevent the generation of such spurious, as shown in FIG. 4, a large number of bubbles 8 are formed from the surface of the substrate 5 in a portion deeper than about one wavelength of the center frequency of the pass band, and the input electrode 6 is formed. The bulk wave excited by was diffused by the bubble 8 so as not to reach the output electrode 7. Further, as shown in FIG. 5, a kerf 9 is provided on the back surface of the substrate 5 in a direction orthogonal to the surface wave propagation direction indicated by an arrow A or in an oblique direction. Further, as shown in FIG. 10 was formed to diffuse the bulk wave reflected on the back surface of the substrate 5 so as not to reach the output electrode 7.

[0005]

However, in the above-mentioned conventional structure, in forming the substrate 5 having a layer with a small number of bubbles 8 and a layer with a large number of bubbles, a bonding failure occurs when two types of substrates are prepared and then bonded. In addition, the reliability of the substrate 5 is lowered, and the processing steps of forming the kerf 9 and the lap surface 10 are complicated, and processing defects such as cracks and defects are generated in the substrate 5 to reduce the strength of the substrate 5. It had a problem of lowering it.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a substrate for a surface acoustic wave device which prevents spurious emission and is highly reliable, and a method for manufacturing the same.

[0007]

In order to achieve this object, a substrate of a surface acoustic wave device and a method of manufacturing the same according to the present invention are designed so that one wavelength of a center frequency of a pass band on a side where an input electrode and an output electrode are arranged is And a calcination process using a mixed powder of the same composition, with a homogeneous sintered layer of piezoelectric ceramic material having a large thickness and a heterogeneous sintered layer of piezoelectric ceramic material completely fused to this homogeneous sintered layer. Then, after producing calcined powder that completely reacted and calcined powder that reacted incompletely, crushing and granulating each, the thickness after firing is only larger than one wavelength of the pass band center frequency. The amount of the completely calcined granules and the predetermined amount of the incompletely calcined granules are filled in a mold, and the compact formed by processing is sintered.

[0008]

With this structure and manufacturing method, the inhomogeneous sintered layer disturbs bulk waves to prevent spurious emission.

[0009]

EXAMPLE 1 An example of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a substrate 1 made of a PZT type piezoelectric ceramic material is a completely sintered homogeneous sintered layer 11 having a thickness greater than one wavelength of the center frequency of the pass band, and is completely fused to this. Incompletely sintered heterogeneous sintered layer 12 having the same composition as described above. 4 in the figure is a heterogeneous sintered layer 1
The defective part in 2 is shown.

The surface acoustic wave device in which the input electrode 2 and the output electrode 3 are provided on the surface of the homogeneous sintered layer 11 is the input electrode 2
The wave excited from becomes a surface acoustic wave, propagates in the direction indicated by arrow A, and is received by the output electrode 3.

About 90% of the surface acoustic wave energy is 1 at the center frequency of the pass band in the depth direction from the surface of the substrate 1.
It is known to propagate within a range of wavelengths. In this embodiment, since the dense homogeneous sintered layer 11 is formed within the depth range, the surface acoustic wave propagates with a very small energy loss. At the same time, about 10% of the energy that propagates inside the substrate 1 and is reflected on the surface of the substrate 1 to form a bulk wave is sufficiently disturbed by the defect portion 4 of the heterogeneous sintered layer 12 as shown in FIG. It is possible to prevent the spurious response of the frequency characteristic that is suppressed by the output electrode 3 and is received by the output electrode 3.

Example 2 A method for manufacturing a substrate of a surface acoustic wave device according to the present invention will be described below.

As shown in FIG. 3, first, the raw material is made into a predetermined PZ.
The T-type piezoelectric ceramic material was weighed so as to have a composition and mixed by a ball mill. Part of the mixed powder is calcined at the optimum calcination temperature, and the remaining mixed powder is 50 to 2 from the optimum calcination temperature.
After calcining at a low temperature of 00 ° C., each calcined powder was crushed and granulated. Of the two types of granulated powder thus obtained, the granulated powder obtained by calcining at the optimum calcining temperature is such that the thickness after firing is greater than one wavelength of the pass band center frequency. Fill the amount into the mold, and then add 5 from the optimum calcination temperature.
The granulated powder obtained by calcining at a low temperature of 0 to 200 ° C. was filled and then pressure-molded. This two-layered compact was sintered at the optimum firing temperature and then polarized. By this manufacturing method, a homogeneous sintered layer of a piezoelectric ceramic material having a thickness larger than one wavelength of the pass band center frequency and a heterogeneous sintered layer of a piezoelectric ceramic material of the same composition completely fused to the homogeneous sintered layer are formed. It is possible to obtain a substrate of the surface acoustic wave device.

The method of manufacturing the substrate of the surface acoustic wave device according to the present invention is not limited to the second embodiment and can be modified within the scope of the present invention.

[0016]

As described above, the present invention provides a homogeneous sintered layer of a piezoelectric ceramic material having a thickness larger than one wavelength of the center frequency of the pass band on the side where the input electrode and the output electrode are arranged, and the homogeneous sintered layer. A structure with an inhomogeneous sintered layer of piezoceramic material completely fused to the layers, and a calcination process using a mixed powder of the same composition, a calcination powder that was completely reacted and a calcination powder that was incompletely reacted. After making burned powder, crushing and granulating each, completely calcined granulated powder in an amount such that the thickness after firing is greater than one wavelength of the passband center frequency, and a predetermined amount of incomplete Substrate of high-reliability surface acoustic wave device that prevents spurious generation and is manufactured by a method of filling a die with the granulated material calcined in a mold and sintering the molded body that has been pressure-molded The method can be realized.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a concept of a substrate of a surface acoustic wave device according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing the concept of a bulk wave confusion state in the substrate of the surface acoustic wave device.

FIG. 3 is a diagram showing a flowchart of a manufacturing process of a substrate of a surface acoustic wave device according to a second embodiment of the present invention.

FIG. 4 is a schematic sectional view showing the concept of a substrate of a conventional surface acoustic wave device.

FIG. 5 is a schematic sectional view showing the concept of a substrate of another conventional surface acoustic wave device.

FIG. 6 is a schematic sectional view showing the concept of a substrate of still another conventional surface acoustic wave device.

[Explanation of symbols]

1 substrate 2 input electrodes 3 output electrodes 11 Homogeneous sintered layer 12 Heterogeneous sintered layer

Claims (2)

[Claims] 1. A substrate of a surface acoustic wave device having an input electrode and an output electrode disposed on a surface thereof, the thickness being greater than one wavelength of a center frequency of a pass band on the side where the input electrode and the output electrode are disposed. A substrate of a surface acoustic wave device, comprising: a homogeneous sintered layer of the piezoelectric ceramic material; and a heterogeneous sintered layer of the piezoelectric ceramic material completely fused to the homogeneous sintered layer. 2. A calcining step using a mixed powder of the same composition to prepare a completely calcined powder and an incompletely reacted calcined powder, crushing and granulating each, and then firing. The mold is filled with a quantity of completely calcined granules and a predetermined quantity of incompletely calcined granules such that the subsequent thickness is greater than one wavelength of the pass band center frequency and the pressure is applied. A method of manufacturing a substrate of a surface acoustic wave device, comprising sintering a molded body.