Tunability and Calculation of the Dielectric Constant of Capacitor Structures with Interdigital Electrodes

The voltage dependence of the dielectric constant of ferroelectricmaterials makes them attractive for use as tuning elements in microwavecircuits. In this study, capacitance tuning and loss measurements wereperformed on ferroelectric materials prepared by the sol-gel process and RFmagnetron sputtering. We find that Pb(Zr,Ti)O^sub 3^ (PZT) thinfilms with interdigital electrodes can be fabricated with reasonably lowloss to make them useful for room temperature tuning applications. Inaddition, it is found that high temperature post-deposition annealing ofboth sputtered SrTiO^sub 3^ (ST) and sol-gel derivedBaTiO^sub 3^ (BT) films markedly improves their tuning and lossfactor characteristics. By annealing the samples in the range of1000-1100°C, the tunability was increased by as much as a factorof seven, while the dissipation factors were decreased to values of0.3-0.5%. In addition, it is shown that the permittivity of thefilms in these interdigitated capacitor structures can be calculated usingan analytical model previously described by Farnell et al. [1]. [PUBLICATION ABSTRACT]