A micro variable inductor chip using MEMS relays

An adjustable inductor which is digitally controlled by microrelays has been made using combined surface and bulk micromachining technology. The microrelays were fabricated using a TaSi/sub 2//SiO/sub 2/ bimorph cantilever beam, a gold-to-gold electrical contact, aluminum as sacrificial layer, and a combined electrostatic and thermal actuation mechanism. The silicon substrate underneath the inductor region was etched out to reduce the substrate eddy current loss. Sixteen different inductance values ranging from 2.5 nH to 324.8 nH were obtained using four microrelays. The minimum self-resonant frequency is 1.9 GHz. The lowest measured thermal power and electrostatic voltage for the combined actuation of microrelays are 8.0 mW and 20 V, respectively. The measured contact resistance is typically 0.6 to 0.8 ohms.