Micromachined Variable capacitors using copper have been designed and fabricated as the tuning element in voltage-controlled oscillatrs, VCOs, in RF applications such as cellular phones. Compared with the traditional solutions relying on varactor diode, this approach is amenable to monolithic integration in a standard electronic circuit process without sacrificing performance. Experimental devices consisting of two parallel micro copper plates supported by copper springs have shown 50% variation of the capacitance with DC tuning voltages below 5 volts. At 4.5GHz, the quality factor, Q, has been measured as 15 after de-embedding. This quality factor is considered to be limited by the substrate loss in silicon substrate.
