Discrete RF-power MIM BST thick-film varactors

Discrete high power RF varactors based on bariumstrontium-titanate are presented in this paper. They are targeting high power applications up to 3 GHz and feature power handling capabilities up to 50 W as well as promising tunability, due to the novel metal-insulator-metal configuration. The varactors are fabricated on Al2O3 in screen-print thick-film technology and mounted in RF-power transistor packages. Capacitances in the range from 1.4 pF to 28 pF were designed. Small- and large-signal measurements show a maximum insertion loss of 0.3 dB to 0.5 dB and a tunability of 7% to 30% at 1/3 of the resonance frequency. The exceptional linearity of BST was verified using two-tone measurements, resulting in 65 dBm OIP3.