Development of microfabricated phononic crystal resonators based on two-dimensional silicon slab

This paper shows the design, fabrication and characterization of novel micromechanical resonators with Bloch-mode resonance by creating defects on a two-dimensional (2-D) silicon phononic crystal (PnC) slab. The PnC slab was made by etching a square array of cylindrical air holes in a 10μm thick free-standing silicon plate, while the defects are created by replacing periodically arranged three rows of air holes with one row of air holes at the centre of the PnC region. The radius of the central air holes (r') is also varied to study the effect of r' on the performance of the PnC resonators. Piezoelectric aluminium nitride (AlN) film is employed as the inter-digital transducers (IDT) to transmit and detect acoustic waves, thus making the whole microfabrication process CMOS-compatible. We also fabricate a pure PnC structure with a stopband of 140MHz < f <195MHz which agrees quite well with the simulation results. The characterized resonant frequency of microfabricated PnC resonators reaches its maximum value (174.67MHz) when central-hole radius (r') reaches 8μm, while Q factor reaches maximum (893) at r'=6μm. The Bloch-mode PnC resonators based on square lattice PnC structure show promising acoustic resonance characteristics and may be further optimized for applications such as microfluidics, biomedical devices and RF communications in GHz range.