High Quality Factor and Low Motional Impedance Aluminum Nitride Tuning Fork Resonators Vibrating in In-Plane Flexural Mode

Abstract

This letter presents a piezoelectric tuning fork resonator vibrating in in-plane flexural mode with a high quality factor (Q) and low motional impedance. A novel double-sided actuating design is implemented based on unimorph structure with a 2.5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> -thick AlN film as passive layer. The design significantly improves the Q and motional impedance compared with the conventional single-sided actuating design thanks to an increase of static capacitance without change of material interfaces. The proposed double-sided actuating device shows an excellent Q measured as 11272 with an extracted motional impedance of 7.2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{k}\Omega $ </tex-math></inline-formula> in vacuum. The measured Q-pressure relationship shows that a vacuum level <100 Pa would ensure a sufficiently high Q value, which can be easily achieved through wafer-to-wafer bonding with getters in the future. Furthermore, the impact of AlN passive layer thickness on the resonator performance is analyzed. The proposed device would find applications in sensing fields as miniaturized and high-performance resonator-based solutions, such as gyroscopes, accelerometers and pressure sensors.