Evidence on simultaneous improvement of motional impedance and Q-factor of silicon phononic crystal micromechanical resonators by variously engineering the cavity defects

In this work, we report the experimental evidence on the capability to simultaneously improve the Q-factor (Q) and motional impedance (Z) of silicon phononic crystal (PnC) micromechanical (MM) resonators by properly engineering the cavity defects on an otherwise perfect two-dimensional (2D) silicon PnC slab. The cavity defects of the resonators in the current study are engineered by patterning additional scattering holes to the pure Fabry-Perot resonant cavity, which is created by deleting two rows of scattering air holes from the centre of the 2D square air-hole array. Experimental results show that by varying the radii of the additional scattering holes patterned in the cavity, the fabricated silicon PnC MM resonators can have their Q and Z improved simultaneously, showing great potential in overcoming the trade-off between Z and Q in conventional resonators of piezoelectric type and capacitive type.