A fully-printed, BST MIM varactor for low ISM-band matching networks up to 1000 W

This work presents a fully-printed metal-insulator-metal (MIM) thick film varactor capable of operation in matching circuits rated with up to 1 kW. The varactor utilizes a 20 μm thick layer of barium strontium titanate (BST) as tunable ferroelectric material. The design is based on a serial stack of capacitive MIM structures. The obtained overall capacitance is 1.9 nF with a maximum tunability of 37 % for a biasing voltage of 200 V and a quality factor of 58 at room temperature and 13.56 MHz. At 70 °C the tunability of the varactor is decreased to 22 %, while the quality factor increases to its maximum of 93. With 1 kW of input power, the varactor shows a tunability of 19 % for 150 V of DC biasing voltage, withstanding 121V and 17 A of RMS RF voltage and current, respectively. The varactor with integrated resistive matching dissipates 37 W of power, equal to 3.7 %.