Film bulk acoustic resonator (FBAR) devices with temperature compensation layers

The temperature-compensated film bulk acoustic resonator (FBAR) device comprises an FBAR stack that comprises an FBAR characterized by a resonant frequency having a temperature coefficient and a temperature-compensating layer 115 comprising doped silicon dioxide. The silicon dioxide may be doped with Group III elements, e.g. Boron, Aluminium, Gallium and Indium. The temperature-compensating layer 115 may lie beneath or on top of the top electrode 114 (fig 3C), between each electrode and the piezoelectric layer 116 (fig 3D) or in the piezoelectric layer (fig 3E). Embodiments relating to DSBARs and DSBARs coupled as transformers (FACTs) are shown (figs 4 and 5).