Low voltage tunable capacitors for RF MEM filters and antenna applications

The design and experimental evaluation of a very low voltage tunable capacitor is presented in this paper. Interdigital capacitors are designed and fabricated on high resistance silicon substrate. Tunable ferroelectric thin film is deposited on to the device and its tunability is measured using an RF network analyzer. It is observed that the capacitor has 80% tunability at 6 volts. In conventional micro fabrication techniques, metal is deposited on the top of a ferroelectric thin film and then develops the device layout by photolithographic and etching technique. However, in this paper, the thin film is deposited on the top of IDT. This helps to reduce the bias voltage and to eliminate the device micro fabrication problems on ferroelectric films. High dielectric constant films can dramatically reduce the device size and it could be possible to achieve desired size of microsensors using these devices. These low voltage tunable ferroelectric films are also useful for the design of phase shifters for phased array antennas and tunable RF MEM filters.