A monolithic variable inductor network using microrelays with combined thermal and electrostatic actuation

An adjustable inductor which is digitally controlled by microrelays has been made using combined surface and bulk micromaching technology. The microrelays were fabricated using a TaSi₂/SiO₂ bimorph cantilever beam, a gold-to-gold electrical contact, aluminum as sacrificial layer and a combined thermal and electrostatic actuation mechanism. The silicon substrate under the inductor region was etched out to reduce the parasitic oxide capacitors and the eddy current power loss in the substrate semiconductor bulk. Sixteen different inductance values ranging from 2.5 nH to 324.8 nH were obtained using a planar rectangular spiral coil and four microrelays. The minimum self-resonant frequency is 1.9 GHz. The lowest measured combined thermal power and electrostatic voltage for the actuation of microrelays are 8.0 mW and 20 V, respectively. The highest operation frequency of microrelays is 10 kHz limited by the mechanical self-resonance. The measured contact resistance typically ranges from 0.6 ohms to 0.8 ohms. The dimensions of the chip measure 3150×930 µm².