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1. (WO1998052279) ELASTIC WAVE DEVICE

Pub. No.:    WO/1998/052279    International Application No.:    PCT/JP1997/001584
Publication Date: Fri Nov 20 00:59:59 CET 1998 International Filing Date: Tue May 13 01:59:59 CEST 1997
IPC: H03H 3/08
H03H 9/05
Applicants: HITACHI, LTD.

ISOBE, Atsushi

HIKITA, Mitsutaka

SHIBAGAKI, Nobuhiko

ASAI, Kengo

TAKUBO, Chisaki

Inventors: ISOBE, Atsushi

HIKITA, Mitsutaka

SHIBAGAKI, Nobuhiko

ASAI, Kengo

TAKUBO, Chisaki

Title: ELASTIC WAVE DEVICE
Abstract:
In order to realize a subminiature elastic wave device, which has an electric property comparable to at least that of a conventional elastic surface wave device and of which reliability is not degraded even when undergoing resin sealing or bare chip packaging, an elastic boundary wave device of three-medium construction, in which films (29, 30) of two or more kinds are formed on a piezoelectric substrate (28), is excited. Formed on the piezoelectric substrate formed with an interdigital electrode (14) are a polycrystal silicon dioxide film (29) and a polycrystal silicon film (30). The piezoelectric substrate is formed from a single crystal substance. The polycrystal silicon dioxide film and the polycrystal silicon film are formed as by a sputtering method, CVD method and a coating method. Formation of the polycrystal silicon film enables elastic wave excited by the interdigital electrode to be confined to the polycrystal silicon dioxide film, and even when the polycrystal silicon film is deteriorated in its film quality, the elastic boundary wave device exhibits an electric property superior to that of a conventional elastic surface wave device. Also, since the polycrystal silicon dioxide film and the polycrystal silicon film protect the interdigital electrode, the elastic boundary wave device can have a high reliability.