Strength Differences of Lateral, Top and Bottom Surface in Monocrystalline Silicon Micromachining

The research presents two structures designed to compare the strength of lateral sidewalls against the strength of top and bottom surfaces in a monocrystalline silicon process for MEMS inertial sensors. The first task is achieved through an in-plane driver, with actuation and position-sensing combs, which, through a lever, stresses the vertical surface of a notched specimen. The novel, second task is much harder to accomplish, as vertical gaps and pull-in limit the maximum travel range and achievable stress on horizontal surfaces: it is nevertheless possible to identify a range of strengths between pull-in and the following contact to stoppers in torsional structures with a central notch. Results show a remarkable difference: About 10 GPa strength for lateral surfaces but a noticeably lower value, in the range of 3 GPa to 6 GPa for top and bottom surfaces.