Temperature-Regulated Nonlinear Microvalves for Self-Adaptive MEMS Cooling

In this paper, thermal buckling of doubly clamped microfabricated nickel beams is implemented as a passive actuation mechanism to drive temperature-regulated nonlinear micro-valves for adaptive microcooling applications. The nonlinear buckling phenomenon is combined with the nonlinear change in flow rate through parallel plates with a variable spacing. The thermal buckling mechanism and parallel plate flow are modeled analytically, and nondimensional characteristic design curves have been generated. Passive flow-control microvalves were fabricated using deep reactive ion etching and a through-mold nickel electroplating process over a thin sacrificial layer. The model is validated with experimental results from the microfabricated temperature-regulated microvalves. Experimental characterization using an integrated micromachined heat exchanger with air as the working fluid shows the desired nonlinear valving behavior with mass flow rates of up to 5 mg/s for a temperature increase of 50degC, corresponding to 0.25 W of heat removal. It is shown that temperature-induced elastic instabilities in microfabricated structures can be modeled and manipulated to create a nonlinear adaptive valving mechanism. The modeling approach, microfabrication process, and full characterization of the microvalves are presented.