Micromachined GaAs MMIC-Based Spiral Inductors With Metal Shores and Patterned Ground Shields

This paper presents micromachined GaAs monolithic microwave integrated circuits (MMIC)-based radio frequency (RF) planar spiral inductors with metal shores (MS) and patterned ground shields (PGS). The inductors are fabricated using a GaAs MMIC process without any additional step. MS and PGS are located and inserted between the planar spiral inductors and the GaAs substrate respectively for depressing substrate losses. To further improve its performance, the backside substrate of each inductor is processed to form the membrane structure by the via-hole etching technology. Based on the parameter extraction about a single-ended method, the characteristics of two-type RF spiral inductors (3.5- and 4.5-turn) are investigated. The measured quality factor (Q) of 4 nH on-chip spiral MMIC inductors (4.5-turn) with MS and PGS are 13 at 5.8 GHz and 14.2 at 6.6 GHz, respectively. Measurement results demonstrate that the effects of MS and PGS on the Q of MMIC inductors have resulted in the improvement of about 6% and 15%, respectively, and on the inductance and the metal losses are almost constant in interested frequencies. These improved inductors applied to GaAs MMIC-based passive lowpass filters reduce insertion losses of the filters.