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

Abstract

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 ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\rho = 5$</tex></formula> <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\hbox{k}}\Omega\!\cdot \!{\hbox{cm}}$</tex></formula> ) using a doped polysilicon and Au–Cr metal combination as a bimorph structural layer for providing self-assembled elevation with an enhanced <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$Q$</tex></formula> factor. Extensive electro-thermo-mechanical and RF characterization was carried out for the inductor, the latter over a temperature range from <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\hbox{30}}\ ^{\circ}{\hbox{C}}$</tex></formula> to 150 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}{\hbox{C}}$</tex> </formula> . 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 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\hbox{197.6}}$</tex> </formula> dB with a frequency tuning range of 1.3–2.4 GHz with a power consumption of 3.07 mW.