Input-output insulation in thermal-piezoresisitive resonant microsctructures using embedded oxide beams

This paper reports on the design, fabrication and testing of silicon based monolithic thermally actuated MEMS resonators with electrically insulated input and output ports. Promising results lately achieved for thermally actuated micromechanical resonators show that they could be viable candidates for frequency referencing and sensory applications. However, most of such devices utilizing monolithic fully silicon structures demonstrated so far use the same elements as both thermal actuators and piezoresistive sensors simultaneously. This leads to significantly high transmission feedthrough necessitating post-measurement data processing and de-embedding the effect of the large feedthrough conductance in order to extract the pure resonance behavior. The large feedthrough also complicates using such devices as frequency selective electronic components. The presented approach in this work takes advantage of embedded silicon oxide beams in the resonator structure formed through a long thermal oxidation process. The oxide beams electrically isolate the input and output ports of the resonator while maintaining its mechanical integrity. Characterization of resonators fabricated using this technique shows significantly suppressed feedthrough levels in the measured transmission data.