Fabrication and characterization of ferroelectric varactors for tunable wireless front-ends

Using a tunable wireless front-end is a competitive solution for implementing multistandard radios. To realize tunable wireless front-ends, varactors are indispensible building blocks. Ferroelectric varactors, offering high tunability, low bias voltage, high power handling capability, good quality factor, fast tuning speed, and low cost, are suitable for making tunable microwave circuits. In this paper, we present our work on the fabrication and characterization of the ferroelectric varactors based on RF-sputtered BST thin films. Both MIM and interdigitated capacitors are fabricated and characterized. The measurement results of the MIM structure show that 45% variation in capacitance can be obtained with a bias voltage of 10 V. For the interdigitated varactor, capacitance variation of 20% and leakage current lower than 30 nA are observed under a 50-V bias. The maximum quality factor of the interdigitated varactor measured at 500 MHz is above 10.