Thin film piezoelectric resonator (FBAR) with improved mode suppression

摘要

The resonator includes a thin-film portion having at least one piezoelectric thin-film layer 4 disposed on the substrate and at least one pair of upper 6 and lower 5 electrodes disposed on the substrate. The upper and lower electrodes oppose each other in the depth direction and their overlapping portion has a tetragonal shape, when viewed in the depth direction, other than a rectangle and a square, the tetragonal shape having substantially parallel sides having a longitudinal length equal to or smaller than about 10 times the oscillatory wavelength and also having at least one portion in which the distance between opposing electrode edges varies. Another embodiment requires the shape of the electrode overlap region to have no pair of parallel sides and to be symmetric about a line when viewed in the depth direction, eg an isosceles triangle or heptagon.