Ferroelectric MIM Capacitors for Compact High Tunable Filters

The voltage- and frequency-dependent material properties of (Ba,Sr)TiO3 (BST) thin film have been extracted up to 67 GHz by means of a lumped elements equivalent circuit validated by fitting on de-embedded experimental data. The tunability is 73% (0-10 V bias), and the loss tangent is better than 0.06 (value at 0 V at 1 GHz). This varactor has been exploited in the design of a compact tunable filter implemented by using coupled resonators in lumped element in silicon planar technology. This solution yields a very compact size, and experimental results show a filter center frequency tuning of 83% (997 MHz - 1830 MHz) while maintain almost constant the fractional bandwidth at 35% upon the application of a 0-10 V bias. The insertion loss is between 3.8 and 4.4 dB, and the return loss is better than 14 dB.