$W$ -Band Bandpass Filter Using Micromachined Air-Cavity Resonator With Current Probes

This letter presents a W -band micromachined air-cavity bandpass filter (BPF) using a novel integration method of a micromachined silicon air-cavity resonator with silicon pillars. With silicon pillars, which were fabricated simultaneously with a deep reactive ion etching process for forming a cavity structure, a micromachined silicon air-cavity can be easily integrated on a package substrate with a flip-chip interconnection. In this work, a thin-film substrate with a flip-chip interconnection was employed as a package substrate, in which the silicon pillars were used as the current probe between the air-cavity resonator and TFMS input/output feeding lines. With the novel integration of the air-cavity resonator, a W-band four-pole BPF has been successfully demonstrated on a thin-film substrate with a flip-chip interconnection, which exhibits a minimum insertion loss of 1.3 dB and return loss better than 16 dB with a 4.9% 3-dB fractional bandwidth at a center frequency of 93.7 GHz.