Fabrication of a novel micromachined solenoid inductor and delay line and investigation of substrate influence on their characteristics

Abstract

We have designed, fabricated and characterized a novel solenoid inductor and delay line based on our own RF MEMS process module, which have been proposed to realize simultaneous implementation of various RF MEMS devices. The solenoid inductor and delay line were developed at the same time on a Si substrate and their high frequency characteristics were measured. In the case of a 1050 µm long 12-turn delay line, the effective permittivity corresponding to the straight line was 154 at 20 GHz, which is 22.8 times bigger than the typical coplanar waveguide formed on the GaAs substrate. Consequently, we were able to achieve compact-sized devices with the aid of our three-dimensional novel device structure and process module. To improve the characteristics, we have investigated the substrate effect. The substrate was etched by a bulk-micromachined post-process, and thus we were able to obtain at least a 20% improved Q value and self-resonant frequency for each solenoid inductor due to the reduction of parasitic capacitance. Moreover, we have fabricated a conventional planar spiral inductor and its substrate effect was also investigated. Finally, we compare and discuss the substrate effects and high frequency characteristics for two different types of inductors.