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

An adjustable inductor which is digitally controlled by microrelays has bee n made using combined surface and bulk micromaching technology. The microre lays were fabricated using a TaSi2/SiO2 bimorph cantilever beam, a gold-to- gold electrical contact, aluminum as sacrificial layer and a combined therm al and electrostatic actuation mechanism. The silicon substrate under the i nductor region was etched out to reduce the parasitic oxide capacitors and the eddy current power loss in the substrate semiconductor bulk. Sixteen di fferent inductance values ranging from 2.5 nH to 324.8 nH were obtained usi ng a planar rectangular spiral coil and four microrelays. The minimum self- resonant frequency is 1.9 GHz. The lowest measured combined thermal power a nd 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 t ypically ranges from 0.6 ohms to 0.8 ohms. The dimensions of the chip measu re 3150 x 930 mu m(2).