Variable RF MEMS capacitors with extended tuning range

Three distinct designs of variable RF MEMS capacitors are presented and a comparison is made in terms of their continuous tuning range. Among these designs are the classical parallel-plate capacitor, as well as the so-called two-gap structure and a novel device with torsion-beam suspensions and double actuation. This allows the capacitance to be tuned over a larger range compared to a single-driven device. As a result of this, the tuning range of the device exceeds the theoretical 50%-limit for parallel-plate capacitors. The tuning ranges of all three devices have been determined experimentally and were found to be 39% for the parallel-plate capacitor, 310% for the two-gap structure and 61% for the torsion-suspension device. The measured tuning voltages are 17 V, 22 V and 11 V respectively.