Dartmouth Thayer School Stress Engineered Microsystems

A new technique of creating out-of-plane microstructures has been devised at the Dartmouth Thayer School of Engineering, and has been used to fabricate three-dimensional microturbines which are free from any post-processing assembly.

Stress engineering of microstructures (SEMS), involves lithographic control over the stress between two films to design self-assembling three-dimensional microstructures. To quantify SEMS design criteria, stress engineered silicon nitride/polysilicon beams, with wide ranges of thin film thickness ratio were fabricated and show large out-of-plane deflections (Figures 1 and 2). As an example of the utility of this new technique, we then fabricated a three-dimensional microturbine (the world's smallest) which free from any post-processing assembly (Figures 3 and 4).

The microturbine fabrication process consists primarily of surface micromachining technology, with a bulk micromachining step to create the turbine flow channel normal to the wafer surface. The SEMS bending force in the turbine vanes simultaneously prevents stiction to the substrate, and allows the vanes to self-form their final shape. Stators, similar to those found in surface micromachined motors, allow electrical sensing or actuation of fluid flow.

The microturbine fabrication was executed using the facilities of the Microsystems Technology Laboratories at MIT, and the Microengineering Laboratory at the Dartmouth College Thayer School of Engineering.

Full details are reported in the Ph.D. dissertation: "Three Dimensional Streess Engineered MicroStructures", Chia-lun Tsai, Thayer School of Engineering, Dartmouth College, Hanover, NH, December 1997.

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