Patent ID: 6111341
Filing Date: 2000-08-29
Classification: H03H

Abstract:
A piezoelectric vibrator on which excitation electrodes are respectively disposed on a top surface and undersurface of a piezoelectric substrate, and at least one of said excitation electrodes is an inverted-mesa electrode comprising a projecting circular portion and a circular recess provided in said projecting circular portion, and wherein:a ratio of mesa thickness .mu. and a ratio of mesa length are set to satisfy the equation defined as k.sub.3 tanh k.sub.3 (b-a) =k.sub.2 tan k.sub.2 (a -p), so that a capacitance ratio .gamma. of said piezoelectric vibrator is less than 200, whereinsaid circular recess in said projecting circular portion of said inverted mesa electrode is defined as region I,said projecting circular portion surrounding said recess is defined as region II,a region outside of said projecting circular portion of said piezoelectric substrate is defined as region III,f.sub.1 is a cut-off frequency in said region I,f.sub.2 is a cut-off frequency in said region II,f.sub.3 is a cut-off frequency in said region III,f is a resonance frequency of said piezoelectric vibrator,k.sub.2 is a propagation constant for said region II and obtained by equation: ##EQU13## k.sub.3 is a propagation constant for said region III and obtained by equation: ##EQU14## p is a distance from a center of said circular recess surrounded by said projecting circular portion to an inner edge of said projecting circular portion,a is a distance from said center to an outer edge of said projecting circular portion,b is a distance from said center to an outer edge of said piezoelectric substrate,H is a thickness of said region III,said ratio of mesa thickness .mu. is obtained by equation:.mu.=(f.sub.1 -f.sub.2)/f.sub.3 -f.sub.1), andsaid ratio of mesa length is equal to p/a.