Hydrogen diffusion and pressure control of encapsulated MEMS resonators

R.N. Candler, Woo-Tae Park, M. Hopcroft, Bongsang Kim, T.W. Kenny
The 13th International Conference on Solid-State Sensors, Actuators and Microsystems, 2005. Digest of Technical Papers. TRANSDUCERS '05.  
We have investigated the diffusion of hydrogen through the oxide and silicon of our singlewafer vacuum package. We have encapsulated micromechanical silicon resonators in vacuum beneath a 20 µm polysilicon layer. While we have not been able to measure any change in pressure of parts at room temperature over a period of nine months, we have been able to accelerate the diffusion of hydrogen through the encapsulation using elevated temperatures. While placing encapsulated resonators in elevated
more » ... tors in elevated temperature, we select the furnace gas condition to diffuse hydrogen gas in or out. This is an enabling step toward forecasting long-term hermiticity of the encapsulation, and it provides the ability to set the pressure inside the encapsulation with a simple set of furnace processes. Also, the ability of the encapsulation to withstand more than twenty of these temperature cycles between room temperature and 300 °C -400 °C is evidence of the robustness of the package. K e y w o r d s : Hermetic packaging, Resonator, Hydrogen diffusion, Quality factor
doi:10.1109/sensor.2005.1496568 fatcat:53gvqkj555fcnmsh6ndoz3nu6u