Development of miniature filters for wireless applications

TLDR

Miniature filters for wireless applications from 500 MHz to over 6 GHz have been developed using thin piezoelectric films on common substrates. The paper investigates the development of miniature filters based on a solidly mounted resonator (SMR) concept that isolates the acoustic resonator from the substrate using quarter‑wavelength reflector layers. The filters are built as ladder structures of interconnected series and shunt SMR resonators on a single die, with the resonators isolated by quarter‑wavelength reflector layers. Demonstrated ladder filters achieve insertion losses around 3 dB using aluminum nitride piezoelectric films on substrates such as silicon, sapphire, and glass.

Abstract

Miniature filters have been under development for wireless applications from 500 MHz to over 6 GHz using thin piezoelectric films on common substrates. This paper discusses recent results in the development of miniature filters using a solidly mounted resonator (SMR) concept wherein the acoustic resonator is isolated from the substrate with a sequence of quarter wavelength thick layers that form a reflector. The SMR concept is discussed in detail and applications to filters is presented. Ladder filters have been demonstrated with insertion losses in the 3 dB range using aluminum nitride films for the piezoelectric and appropriate substrates such as silicon, sapphire, and glass. The ladder filters reported consist of interconnected series and shunt resonators forming a monolithic structure on a single die of comparable size to an integrated circuit.