Tunable Film Bulk Acoustic Resonators Research Articles

Electrically tunable film bulk acoustic resonator based on Au/ZnO/Al structure

An electrically tunable Au/N-ZnO/ZnO/Al film bulk acoustic resonator (FBAR) is proposed. The stack resonator is Au-piezoelectric ZnO layer-Al while Schottky diode junction is Au/N-ZnO semiconductor layer. The FBAR's resonance frequency changes as the junction capacitance decreases with reverse bias. Our experiments gave a frequency shift of ∼30 kHz/V at 1.46 GHz, maximum insertion loss ∼0.7 dB, and a very high Q factor above 1200. Circuit simulations indicated a tunable range of ∼3.8 MHz from optimizing the FBAR's structure and doping concentration of N-ZnO. Electrical tunability decreases from 27 kHz/V to 1.5 kHz/V with temperatures from 30 °C to 105 °C.

Electrical Frequency Tuning of Film Bulk Acoustic Resonator

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper describes the design, fabrication, and measurement of an electrically tunable film bulk acoustic resonator (FBAR) that is formed by integrating FBAR with an electrostatic microelectromechanical systems actuator. Around 1.47% tuning of the series resonant frequency (<formula formulatype="inline"> <tex>$\Delta {\rm f} \cong $</tex></formula> 22.5 MHz) at 1.5 GHz is experimentally obtained with an electrostatic actuation voltage of 7 V. This is the highest frequency tuning reported for FBAR operating at above 1 GHz without any extra power consumption. Two integration approaches of FBAR and air-gap capacitor are presented and compared, in terms of fabrication process and Q factor. The approach that minimizes any possible energy loss in the acoustic wave propagation path shows a quality factor (160–304) significantly higher than the one having a capacitor right on top surface of the FBAR's piezoelectric film. Furthermore, we have characterized the electrical tuning of FBAR through piezoelectric stiffening due to an applied dc electric field and report a linear frequency shift of about <formula formulatype="inline"><tex>${-}$</tex> </formula>8 ppm/V at 3.4 GHz.<papernumber>1755</papernumber> </para>

A surface micromachined electrostatically tunable film bulk acoustic resonator

The design, modeling, fabrication and characterization of a film bulk acoustic resonator (FBAR) that allows frequency tuning by MEMS actuation are reported. FBARs are micromachined versions of bulk acoustic wave (BAW) resonators working in the microwave regime. A small range of frequency tuning is desired to cope with drifts from different origins. In conventional approaches, this functionality has been realized by introducing a discrete element. In this paper, a different design is proposed, in which the MEMS tuning element is integrated in the FBAR structure and tuning is realized by electrostatic actuation. A first demonstration of frequency tuning is also presented.