Switchable and Tunable BAW Duplexer Based on Ferroelectric Material

A switchable and tunable bulk acoustic wave (BAW) duplexer for RF applications is presented in this paper. The fabricated BAW duplexer was built on sapphire substrate using solidly mounted resonators. A metal-organic solution deposition technique was used to form resonators with barium strontium titanate (BST) thin film and six layers of silicon dioxide and tantalum oxide as Bragg reflector. By applying dc bias, the BST thin film shows an electrostrictive effect, and the two filter paths of the BAW duplexer switch to a bandpass response with center frequencies at 4.635 and 4.878 GHz, showing a bandwidth of 119 and 154 MHz for the transmitting (Tx) and receiving (Rx) filters, respectively. Further, the BAW duplexer was simulated using the circuit, Butterworth-van-Dyke, and electromagnetic models. The simulated results are in agreement with the measurements and show the response of bandpass filters at center frequencies of 4.633 and 4.876 GHz for Tx and Rx, respectively.