Investigation on the optimized design of alternate-hole-defect for 2D phononic crystal based silicon microresonators

Abstract

This paper shows the design, fabrication, and characterization of the Bloch-mode micromechanical resonators made by creating alternate defects to form a resonant cavity on a two-dimensional silicon phononic crystal slab of square lattice. The length of the resonant cavity (L) and the central-hole radius (r′) are varied to optimize the performance of the resonators. CMOS-compatible aluminium nitride is used as the piezoelectric material of the interdigital transducer to launch and detect acoustic waves. The extent of energy confinement within the cavity, as shown by the simulated displacement profiles of the resonators, agrees with the measured Q factors. We also quantitatively analysed the band structure of the proposed resonators and found that the Q factors are generally in an inverse relationship with the standard deviation of the band, due to the slow sound effect brought by flat bands which reduces the energy loss along the lateral direction (Y direction) and enhances the Q factor.

Research on bandgaps in two-dimensional phononic crystal with two resonators

“…Wang et al investigated the optimized design of alternate-hole-defect on a silicon PC slab in a square lattice. They found out that the Q factors are generally in an inverse relationship with the standard deviation of the band [39]. Leamy studied the dispersion relations of the honeycomb structures with square, diamond and hexagonal lattices and found out that only the hexagonal honeycomb exhibits a low frequency bandgap [40].…”

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

“…By adding certain defects within the PnC structure, the confinement and control of elastic waves, such as elastic waveguides and mechanical resonators, [17][18][19][20] can be achieved. For example, PnCs with a line defect created can be the basis to form a waveguide 21,22 or a cavity-mode resonator in the form of a Fabry-Perot (FP) cavity structure; [23][24][25] Bloch-mode resonators can be formed by adding an extra row of scattering holes, 26 reducing the central three rows of scattering holes, 27 or introducing alternate defects 28,29 to the FP cavity structure.…”

Approaching the intrinsic quality factor limit for micromechanical bulk acoustic resonators using phononic crystal tethers

“…The ideal phononic bandgaps are found using finite element analysis with 1-D Floquet periodic symmetry (i.e., an infinite chain of unit cells) and a wide parametric sweep for a, b and c . 15, 30 Design details of the resulting resonator and PnC tethers are provided in Table I. While the fabricated PnC tethers are not infinite chains, as assumed in the finite element analysis, the design procedure does result in highly reflective phononic crystals, even for 1 unit PnCs, as described shortly 30 .…”

“…15, 30 Design details of the resulting resonator and PnC tethers are provided in Table I. While the fabricated PnC tethers are not infinite chains, as assumed in the finite element analysis, the design procedure does result in highly reflective phononic crystals, even for 1 unit PnCs, as described shortly 30 . The complete bandgaps shown in Fig.…”