High-Quality-Factor and Low-Temperature-Dependence SMR FBAR Based on BST Using MOD Method

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.