Tunable surface acoustic wave filter using integrated micro-electro- mechanical-system based varactors made of electroplated gold

This paper describes the fabrication and preliminary evaluation of a 200 terminated, 1 GHz tunable surface acoustic wave (SAW) filter with electrostatic micro-electro-mechanical-system (MEMS) varactors. The tunable filter was constructed on a 15 Y LiNbO3 substrate to use Love wave with an electromechanical coupling coefficient as high as 25%. The bridge structure of the MEMS varactor was fabricated by Au electroplating on a sacrificial photoresist, which was finally removed by either O2 plasma ashing or O3 water etching. The measured center frequency was 1.07 GHz, and the bandwidth was 171 MHz, i.e., 16% in relative bandwidth. The MEMS varactor, which was connected to a series SAW resonator in parallel, pulled in by an actuation voltage of 150 V DC, and the right passband edge moved to lower frequency side by 15 MHz.