Poly-Wire-Coupled Single Crystal Silicon HARPSS Micromechanical Filters Using Oxide Islands

This paper reports on the implementation of single crystal silicon micromechanical filters coupled through a thin polysilicon wire using a SOI-based HARPSS process. The formation of suspended thin poly wires, which provide weak mechanical coupling between high quality factor thick microresonators, are enabled by the use of thick sacrificial oxide islands created between adjacent single crystal silicon resonators. The oxide islands are also used beneath the input and output pads of the filters to reduce the parasitic capacitances to substrate. Mechanical coupling of microresonators using thin-film wires provides superior design flexibility since the material and thickness of the coupling element can be chosen independent of those of the resonators. Measurement results obtained from 800kHz two-pole HARPSS micromechanical filters with thin poly wire are presented.