Development of a wide-tuning-range two-parallel-plate tunable capacitor for integrated wireless communication systems

This paper reports on the development of a micromachined parallel-plate tunable capacitor with a wide tuning range. Different from conventional two-parallel-plate tunable capacitors, this tunable capacitor consists of one suspended top plate and two fixed bottom plates. One fixed plate and the top plate form a variable capacitor, while the other one provides necessary electrostatic actuation. Among the fabricated prototype devices, a maximum controllable tuning range of 69.8%@1 MHz has been obtained experimentally, exceeding the theoretical limit (50%) of conventional two-parallel-plate tunable capacitors. A component quality factor (Q) of 30@5 GHz and a self-resonant frequency far beyond 5 GHz have been achieved. The fabrication process is compatible with the existing standard IC (integrated circuit) technology, which makes it suitable for integrated wireless communication applications.