A robust high-Q micromachined RF inductor for RFIC applications

In this paper, a robust micromachined spiral inductor with a cross-shaped sandwich membrane support is proposed and fabricated with fully CMOS compatible post-processes for radio frequency integrated circuit (RFIC) applications. Via the incorporation of a sandwich dielectric membrane (0.7 μm SiO₂/0.7 μm Si₃N₄/0.7 μm TEOS) to enhance the structure rigidity, the inductor can have better signal stability. In comparison, the new design of a ∼5-nH micromachined inductor can have 45% less inductance variation than the one without the dielectric support while both devices are operated with 10 m/s² acceleration. Meanwhile, using a cross shape instead of blanket membrane can also effectively eliminate the inductance variation induced by the working temperature change (20 °C to 75 °C). The measurement results show the robust inductor can have similar electrical performance to the as-fabricated freely suspended inductor, which has five times Q (quality factor) improvement than the inductor without the substrate removal. It is our belief that the new micromachined inductors can have not only high-Q performance but also better signal stability suitable for wide-range RFIC applications.