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 (
$\rho = 5$

${\hbox{k}}\Omega\!\cdot \!{\hbox{cm}}$
) 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
${-}{\hbox{30}}\ ^{\circ}{\hbox{C}}$
to 150
$^{\circ}{\hbox{C}}$
. 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
${-}{\hbox{197.6}}$
dB with a frequency tuning range of 1.3–2.4 GHz with a power consumption of 3.07 mW.