Fabrication of edge-suspended microwave passive components using CMOS-compatible micromachining

The paper reports the fabrication of the edge-suspended RF/microwave passive components using CMOS-compatible micromachining. The edge-suspended structure can effectively improve the performance of microwave passive components without sacrificing their mechanical strength and reliability at the same time. Combination of ICP-DRIE (inductively coupled plasma deep reactive ion etching) dry etching and TMAH anisotropic etching are chosen to realize this edge-suspended structure and both of them are CMOS compatible. A TMAH solution consisting of 5 wt% TMAH, 1.6 wt% Si and 0.5 wt% (NH₄)₂S₂O₈ offers effective etching of silicon along the {100} and {110} planes, while having negligible etching on aluminum and {111} planes. Layout requirements for achieving the edge-suspended passive components is also discussed. Edge-suspended spiral inductors and coplanar waveguides (CPW) with enhanced performance are fabricated successfully.