Lateral diffusion doping of silicon for temperature compensation of MEMS resonators

Abstract

This paper reports the results of a diffusion doping-based method of controlling the temperature coefficient of frequency (TCf) of MEMS resonators. In this work, a suite of resonators from two different wafers — one with and one without diffusion doping — is characterized and compared. By diffusing dopants through exposed sidewalls of silicon resonators within an epitaxial polysilicon encapsulation process, this technique demonstrates a dramatic reduction in the resonator's frequency-temperature sensitivity, one of the significant disadvantages of silicon as a resonator material. Moreover, because thicker geometries are less affected by lateral diffusion, this method provides capability to independently manipulate frequency-temperature behaviors of different resonant systems fabricated on the same wafer.