Micromachined Passive Bandpass Filters Based on GaAs Monolithic-Microwave-Integrated-Circuit Technology

This paper presents micromachined on-chip RF passive bandpass filters at 1-8 GHz based on utilizing a three-pole LC low-pass filter and two dc-blocking capacitors, which is accomplished with a GaAs monolithic-microwave-integrated-circuit process. The microwave design model of the bandpass filters that take into account conductor losses is given and verified. Using this model, the RF bandpass filter with a tunable center frequency and a desirable bandwidth can be realized. Due to only a planar spiral inductor required in the design, the layout size of the filter is less than 700μm × 400μm. Furthermore, in order to minimize the effect of substrate losses caused by the inductor on the bandpass filter, metal shores (MSs) and patterned ground shields (PGSs) are located and inserted between the inductor and the GaAs substrate, respectively, and a cavity on the backside of the inductor substrate is processed by the via-hole etching technique. Measurement results demonstrate that RF bandpass filters without MS and PGS show agreement with the design performance and those with MS and PGS have resulted in the improvement of about 24% insertion loss and a slight effect on the center frequency.