An X-band Lithium Niobate Acoustic RFFE Filter with FBW of 3.45% and IL of 2.7 dB

This paper presents a micro-electro-mechanical system (MEMS) radio frequency front-end (RFFE) filter at 8.4 GHz. The center frequency of 8.4 GHz is achieved by resorting to the third-order antisymmetric Lamb wave mode (A3) in 650 nm thick Z-cut lithium niobate thin film. For the first time, a novel bandwidth-widening technique based on the utilizing of the self-inductance of the top interdigital electrodes is proposed to overcome the limitations set by the electromechanical coupling and satisfy the demands in miniaturization and wide bandwidth. The fabricated filter has demonstrated a 3 dB fractional bandwidth (FBW) of 3.45% (BW=290 MHz), a minimum insertion loss (IL) of 2.7 dB, and a compact footprint of 0.56 mm(2). After utilizing bonding wires as matching inductors, the minimum IL can be decreased to be 2 dB in 50 Omega system.