Dynamic Q-enhancement in aluminum nitride contour-mode resonators

In this letter, we discuss a dynamic quality factor (Q)-enhancement technique for aluminum nitride (AlN) contour-mode resonators. This technique is implemented by applying an external voltage source that has a specific frequency-dependent phase relationship with respect to the driving voltage source. In this way, the effective spring, damping, and mass of the resonator become dependent on the frequency. With proper gain and phase delay between external and driving signals at resonance, 3-dB Q of the resonator's spectral admittance can be dramatically boosted beyond the fundamental limit of the AlN f-Q product. Meanwhile, the effective electromechanical coupling, k t 2, is also improved regardless of the material piezoelectricity limit. These two enhancements correspond to the reduction of the effective damping and spring, respectively. Unlike other active Q-enhancement methods, which use complex electrical circuits to convert resonator displacement/output current into a feedback signal, in this approach, the external and driving signals are generated from the same source and split via a power splitter without resorting to any closed loop operation. The external signal is amplified and shifted by an amplifier and a delay line, respectively. Thus, the demonstrated dynamic Q-enhancement method is relatively simple to implement and intrinsically immune to self-oscillations.In this letter, we discuss a dynamic quality factor (Q)-enhancement technique for aluminum nitride (AlN) contour-mode resonators. This technique is implemented by applying an external voltage source that has a specific frequency-dependent phase relationship with respect to the driving voltage source. In this way, the effective spring, damping, and mass of the resonator become dependent on the frequency. With proper gain and phase delay between external and driving signals at resonance, 3-dB Q of the resonator's spectral admittance can be dramatically boosted beyond the fundamental limit of the AlN f-Q product. Meanwhile, the effective electromechanical coupling, k t 2, is also improved regardless of the material piezoelectricity limit. These two enhancements correspond to the reduction of the effective damping and spring, respectively. Unlike other active Q-enhancement methods, which use complex electrical circuits to convert resonator displacement/output current into a feedback signal, in this approa...