A 1.3–2.4-GHz 3.1-mW VCO Using Electro-Thermo- Mechanically Tunable Self-Assembled MEMS Inductor on HR Substrate

This paper reports implementation and wafer-level testing of a self-assembled tunable microelectromechanical systems (MEMS) inductor with electrostatic, electrothermal, and thermal tuning capability. The surface micromachined inductor was fabricated on a high-resistivity (HR) substrate ( ρ = 5 kΩ·cm) using a doped polysilicon and Au-Cr metal combination as a bimorph structural layer for providing self-assembled elevation with an enhanced Q factor. Extensive electro-thermo-mechanical and RF characterization was carried out for the inductor, the latter over a temperature range from -30 ^°C to 150 ^°C. Furthermore, the tunable inductor was integrated in the tank circuit of a CMOS oscillator and wafer-level MEMS-CMOS voltage-controlled oscillator testing revealed a best figure-of-merit of -197.6 dB with a frequency tuning range of 1.3-2.4 GHz with a power consumption of 3.07 mW.