Parallel Plate Varactors Employing Bi1.5Zn1.0Nb1.5O7/Ba0.5Sr0.5TiO3 Bilayered Thin Films

Parallel plate capacitors based on Bi1.5Zn1.0Nb1.5O7 (BZN) / Ba0.5Sr0.5TiO3 (BST) bilayered thin films were fabricated on sapphire substrates. The BZN/BST bilayered thin films were deposited by radio frequency magnetron sputtering, from two individual Bi1.5Zn1.0Nb1.5O7 and Ba0.5Sr0.5TiO3 stoichiometric ceramic targets. Dielectric measurements indicated that the capacitors exhibited device quality-factor of up to 200, with a relative tunability of 40% at a bias field of 1.6 MV/cm.The figure of merit was about 80. Compared with the parallel plate capacitors with single BST thin film configuration, the leakage current of the BZN/BST capacitors was observed to be much lower. It was also found that the capacitance was frequency independent in the range from 100 kHz to 100 MHz, while the device quality-factor dropped down as frequency increasing. The decrease of device quality-factor accompanied with frequency independent capacitance could be attributed to the conductor loss of electrodes.