Localized, degenerately doped epitaxial silicon for temperature compensation of resonant MEMS systems

A new fabrication method for locally doped silicon resonators is demonstrated within an epitaxial polysilicon encapsulation process (consistent with the established low cost, high yield, high volume manufacturing at SiTime Corporation). Using a cavity etch followed by a selective epitaxial silicon refill with in situ degenerate doping, distinct locally doped regions on a 40-μm thick silicon device layer were obtained. Resonators from two different families were characterized for a couple of doping levels and show that temperature sensitivity can be suppressed. This capability removes one of the last remaining disadvantages of silicon as a resonator material, relative to quartz, and should directly enable improvements in the performance, power consumption, and cost of MEMS-based timing products.