The enhanced Q spiral inductors with MEMS technology for RF applications

The quality (Q) factor and self-resonant frequency (SRF) of the spiral inductor in CMOS IC technologies are limited by both high substrate capacitance and substrate loss. In this letter, a post-fabrication maskless etching procedure is used to selectively remove the silicon substrate and suspend inductors in air. Using this technique, a lot of inductors suitable for 2.4 GHz ISM band are investigated. The Q factor increased from 3.9 to 6.5 at 2.4 GHz for a small inductor 2.14-nH and 2.55 to 5.88 for a large inductor 9-nH at 1.5 GHz. Also the SRF of the 9-nH inductor is raised from 3.5 GHz to 6.1 GHz.