A 5.8-GHz VCO with CMOS-compatible MEMS inductors

This paper describes a low power, low phase noise 5.8 GHz voltage controlled oscillator (VCO) with on-chip CMOS MEMS inductor. The inductor was fabricated by TSMC 0.18 μm one-poly six-metal (1P6M) CMOS process and also Chip Implementation Center (CIC) micromachining post-process. During the post-process, the dry etching was utilized to remove the oxide between the winding metals and the silicon substrate under the inductor. Due to the alleviation of parasitic capacitance and lossy substrate, the quality factor and resonant frequency will be improved and extended. In this work, quality factor up to 15 was obtained for a 1.88 nH micromachined inductor at 8.5 GHz, and the improvement is up to 88% in maximum quality factor. The CMOS and micromachined inductor were both implemented with a 5.8 GHz VCO. Compared side by side with the CMOS inductor, the CMOS MEMS inductor produced a 5 dB lower phase noise improvement at 1 MHz offset in this 5.8 GHz VCO.