| 摘要 |
A piezoelectric thin film resonator in which spurious of short wavelength can be suppressed. In a part of a thin film portion supported partially on a substrate (12) while isolated acoustically therefrom, a) an oscillatory portion (24) consisting of a pair of electrodes (14, 18) superposed in plan view while sandwiching a piezoelectric film (16), and b) an extra film (20) provided on the piezoelectric film (16) or the electrode (18) at least along a portion of the outer circumference of the oscillatory portion (24) are included. Assuming the acoustic impedance of the extra film (20) defined by the root of product of density and Young's modulus is x(MN sec/m3), product of the density and thickness of the extra film (20) is A, product of the density and thickness of the electrodes (14, 18) is B, and y=A/B, following relations are satisfied; (i) for 9.0<=x<44.0, 0.0092.x+0.88<=y<0.067.x+0.60 (1a), and (ii) for 44.0<=x<79.0,-0.0035.x+1.45<=y<0.015.x+2.9 (1b). |
