A low-loss 1.8GHz monolithic thin-film piezoelectric-on-substrate filter

A 1.8GHz thin-film piezoelectric-on-substrate (TPoS) filter with insertion loss of less than 4dB and bandwidth of 18MHz (50Ω termination) is presented in this paper. Such filters are alternatives to conventional ladder-type filters working in the frequency range of up to a few GHz. A monolithic TPoS filter is a coupled mode system based on a single composite resonant structure, with a thin piezoelectric layer deposited on a high acoustic velocity, low loss substrate layer. An interdigitated top electrode structure is used that eliminates the spurious modes and provides a mechanism for adjusting the bandwidth.