Variable RF Inductor on Si CMOS Chip

Abstract

We propose a novel variable inductor on a Si complementary metal oxide semiconductor (CMOS) chip, whose inductance is of nH-order, for GHz applications. The inductance value can be varied by moving a metal plate above the inductor. The magnetic flux penetrating the spiral inductor continuously varies depending on the position of the metal plate. The metal plate is slid horizontally using a micro electro mechanical system (MEMS) actuator. We present the measured and simulated results. At 2.45 GHz, the inductance is varied from 6.6 nH to 5.7 nH, i.e., the variable range is 13%. These results show that the effect of parasitic capacitance between the spiral inductor and the metal plate can be ignored. The proposed variable inductor can be applied to RF circuits.