JPS5884516A - Manufacture of substrate for surface acoustic wave element - Google Patents

Abstract

PURPOSE:To grow crystal of a specific composition around the surface of a flat plate with arranged crystal axes, by thermally treating a glass component on the flat plate consisting of BaO, SrO, TiO2 and SiO2, through the provision of temperature gradient vertically to the plate surface. CONSTITUTION:BaO, SrO, TiO2 and SiO2 are weighed to obtain the composition indicated by formula (Ba1.0, Sr1.0)TiSi2O8 and mixed with the wet process. After the mixture is dried, it is ground and formed under pressure. A sintered body obtained by sintering it is subjected to high frequency heating, and the molten substance is rapidly cooled to obtain a transparent glassy lump. The lump is cut into a flat plate and one side is optically polished. This flat plate is arranged on the plate surface with a temperature gradient and subjected to heat treatment. Thus, piezoelectric crystal expressed by (Ba2-xSrx)TiSi2O8 (0<x<=2.0) is grown around the surface of the plate, allowing to obtain a substrate member used for a surface acoustic wave element such as a filter and a delay line.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention ti. This article relates to a method for producing pressure xi plate materials used for elastic table 119 elements such as 7 ilters and slow-falling wires. Takumi rice. As the substrate material for the 911L hexagonal wave element, lithium diopate LiNbO. , crystal, etc. are often used. However, although lithium niobate has a large electromechanical coupling coefficient, it has poor temperature hardness.

On the other hand, quartz has good temperature resistance but low electromechanical coupling coefficient, and each has its advantages and disadvantages. The search for compression materials that have a large air-mechanical coupling coefficient and good temperature and properties is currently being actively conducted.

"t'? 11 out of 70 (Ba.-gsrJTts!1
o. Applied Physics Letters, Vol. 36, No. 11, 894~
Reported on page 895 (1980). This single crystal has a symmetry of 4m. Like crystal, it is a piezoelectric material of 1 lc and does not require polarization treatment. It has also been reported that as the amount of S-r increases, the temperature % property improves. but,
This is because this crystal does not have a so-called congruent melting composition. When single crystals are grown using the pulling method suitable for mass production, compositional deviations occur and uniform crystals cannot be obtained.

Therefore, the object of the present invention is to provide a uniform (Bag-xsrm) Ti841 08 suitable as a substrate for a bottom acoustic wave device.
The object of the present invention is to provide a method for producing crystals. The manufacturing method of the present invention is based on growing crystals of the same composition from a glass state with their crystal axes aligned. Until now, we have used technology to grow crystals from a glassy state.
sOst and Lt. st. Crystals such as os have been obtained. Especially regarding L import 8'*Os K.

By heat-treating a glass plate of L'lS'*Ol with a temperature gradient perpendicular to the plate surface, L'S+, O1 with the C axis, which is the polar axis, aligned perpendicular to the plate surface. , has been reported to be fried near the surface (Applied Physics Letters, Vol. 36, No. 10 (1980), pp. 817-818). By using this method, the present invention can be applied to (Bag, xsrx)T'8'*Os
(0<x<2.0)
Despite the difference in Katsucho Irl1 Hirozo, the C-axis is perpendicular to the board surface by heat treatment with a gradient of 50 to 150 C/m perpendicular to the board surface once in the summer. It is based on the discovery that the

Also,! As a substrate material for an 11-dimensional surface wave element, one point of interest is that it is good to have crystallization near the substrate, that is, to piezoelectrically activate it. The present invention will be explained in detail below using examples.

Based on Example 1 Bad, 8rO, TtO, and StO were weighed and wet-mixed so that the composition formula was (Ba1.ls'Ll), Tj19i, O. After drying, pulverize to 350Kf/c
The powder was press-molded at a pressure of 90 m" and then
The sintered body obtained by sintering under the conditions of 3 hours was placed in a platinum crucible and bath-melted by high frequency heating. Turn off the power suddenly.

When the rutsuho was removed from the furnace and quenched, a colorless and transparent glassy mass was obtained.

From this, cut out a 10 x 10' x 5' (D) square plate and optically polish one side.
Place it on a hot plate and heat it to 700C so that there is a m degree gradient of 0tll'/saw, then increase the temperature to 2C/II!
After death, the body was gradually raised to 850C at a rate of I and rapidly cooled to room temperature by taking it out into the air.

After taking it out from the hot plate (V-), the optically polished surface was examined using an X-ray diffractometer.

It was found that a Ba1Ti8i10@ type crystal in which the C axis was oriented was obtained. As a result of conducting a compositional analysis of the crystal grown near the surface, it was found that it was a (Bat, sS'e, 5)Ti81tOsTeNwasatLruffi+7) crystal. Next, the cross section was optically polished and the thickness of the crystallized particles was measured using an optical microscope, and it was found that the crystals were crystallized to a depth of about 100 μm from the surface.

Therefore, after briefly polishing the narrow surface, we used two At interdigital electrodes (elastic surface n-wave v
(J-shape and keiki) were roasted (Fig. 1). The width of the finger of the valley blind is 20 μm.

10 pairs of i! with a gap of 20 μm! From the Ilc finger,
There are 3 ■ in the crossover. Using such interdigital electrodes,
54, the basic characteristics of the two-sided wave. the result.

The square of the electromechanical coupling coefficient is approximately 1.5%, the delay time temperature coefficient is 33 ppm IC, and two single crystals of the same composition)
110>The characteristics of propagation and th are all the same.

This is because the anisotropy of the narrow plane wave characteristics is very small in the two-cut direction in the single crystal of (Ba, -mSrs)'rtst,o, and the C axis is aligned perpendicular to the plate surface. It is considered that sufficient characteristics are obtained.

actually,! It has been reported that the characteristics of surface waves propagating in two planes depend almost on the propagation direction (Journal of Abrid Physics). Tsukusu magazine #g49 volume 12 issue 61
62-6164 (1978)).

Example 2 Bad, 8rO, Tie, and 8i0. As a child prodigy, he created a glass plate using exactly the same method as in Example 1.

This square plate was placed on a hot plate with a temperature gradient of 70tl:'/wm perpendicular to the plate surface and heated to 650t:', and then the temperature was gradually increased to 800C at a rate of 2C/Mill. The glass was poured into 1g of air and rapidly cooled to room temperature. As a result, it was found that Ba, TiS crystals with C-axes oriented had grown to a depth of about 100 μm from the surface of the glass plate. The composition also has a Ba to BrO ratio of about 1
:L and the desired one, 1W14 with the 1W14 of Example 1
When the narrow-plane wave characteristics were investigated using the 1I method, the square of the m'fA modest coupling coefficient was 1.3%, and the delay time temperature coefficient was 20.
PI) m/C failed. Compared to other single-crystal materials, this material has excellent properties in that it has both a high coupling coefficient and a low temperature coefficient at the same time.Production method of the present inventionCrystal growth from the same phase of mineral and glass states tame* (bat-xsrx) tisi*o.

It is clear that crystals can be obtained over the entire range O<X<'10. Ceramics actually obtained by in-phase reaction have desired compositions for all values of X.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a method for evaluating surface wave characteristics. l... interdigital electrode for exciting and receiving the mass 111tR.

Claims (1)

[Claims] A flat glass-state composition consisting of Bad, sro, 'rio, and 5t□ is heat-treated with a temperature gradient perpendicular to the plate surface, and the general formula (
Bag-x8' II )'pi 8 '10@ (0
< 20) A method for manufacturing a substrate for a secondary enclosure element patented for lengthening a piezoelectric crystal represented by < 20).