This paper presents the design and fabrication of a switchable band pass filter based on barium strontium titanate (Ba 0.7 Sr 0.3 TiO 3 ) thin film materials. This filter is designed and fabricated as a solidly mounted resonator (SMR) using spin-on metal organic solution decomposition. It consists of six film bulk acoustic resonators (FBARs), two series and four shunt. Without voltage biasing, there is no frequency switching and the filter has shown capacitive response of return loss S11 at -3 dB and insertion loss of -21 dB. By applying 10.8 dc voltage to the six resonators, the filter has exhibited band pass response at 4.67 GHz with 150 MHz band width and insertion loss of 3.8 dB and shown an agreement between the simulation and measurement results.
This paper presents the design, fabrication, and experimental evaluation of switchable and tunable thin-film bulk acoustic wave (BAW) resonators and filters with metal-organic solution deposited barium strontium titanate (BST) for radio-frequency (RF) applications. The switchability and tunability of these devices come from utilizing the electrostrictive effect of ferroelectric materials such as BST with the application of an external dc bias voltage. The BAW resonators and filters in this paper were fabricated on a high-resistivity silicon substrate as a solidly mounted resonator structure with eight layers of silicon dioxide and tantalum pentoxide as a Bragg reflector. A 170-nm BST thin-film thickness with Br/Sr (70/30) composition was deposited using the metal-organic deposition solution chemical technique. The measurements of the RF transmission characteristics showed no resonance (OFF state) with zero bias voltage across the terminals of the resonator. At nonzero applied bias, a switching response (ON state) was observed at near 5.44 GHz. With the increasing magnitude of the applied bias across the film, the resonance increased in intensity by showing a quality factor of 746 and shifted to a lower frequency of 5.375 GHz with a tunability of 1.3%. The temperature dependence of the fabricated device was measured from room temperature up to 80 °C and showed a temperature coefficient of frequency of -12.595 ppm/°C.
A solidly mounted acoustic resonator was fabricated using a Ba0.60Sr0.40TiO3 (BST) film deposited by metal organic chemical vapor deposition. The device was acoustically isolated from the substrate using a Bragg reflector consisting of three pairs of Ta2O5/SiO2 layers deposited by chemical solution deposition. Transmission electron microscopy verified that the Bragg reflector was not affected by the high temperatures and oxidizing conditions necessary to process high quality BST films. Electrical characterization of the resonator demonstrated a quality factor (Q) of 320 and an electromechanical coupling coefficient (Kt2) of 7.0% at 11 V.
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.
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