Tunable dual-mode filter using varactor and variable ring resonator on integrated BST/TiO2/Si substrate

A RF tunable dual-mode filter employing a BST (BaxSr1-xTiO3)-based ring resonator and a capacitor is proposed. BST thin film was deposited on TiO2/Si substrate and a TiO2 buffer layer grown by ALD (atomic layer deposition). The device with a BST varactor capacitance of 0.5 pF and 40% of tunability applied voltage of 40 V, and a tunable ring resonator frequency of 1.53-2.02 GHz with a bias of up to 40 V, has been realised. The fabricated bandpass filter has a centre frequency of 1.53 GHz and shows a tunability of approximately 20% with an applied voltage of 40 V. It also has a bandwidth of 74 MHz and shows a tunability of approximately 27% with an applied voltage of 40 V.