Materials Engineering Department
BS in Materials Engineering
Seven different actuating micro-mirror designs were created and verified via finite element analysis. Two were straight torsion beam hinge designs representative of previous work at Cal Poly; the remaining five were new designs incorporating serpentine hinges. The surface area of these mirror devices ranged from 0.5 square millimeters to 12.5 square millimeters. Geometric patterns representing the device profiles were created and used to obtain photolithographic masks. Beginning with a 400μm thick, 100mm diameter silicon on insulator wafer, a silicon dioxide layer was thermally grown on the surface at 1050 degrees Celsius. Positive photoresist was then spun onto the wafer at 4000 RPM for 20 seconds. Using an exposure dose of 180 millijoules per square centimeter, this photoresist was exposed through the photomask and developed, then used to transfer the geometry into the oxide. The wafer was placed in a reactive ion etcher for 5 minutes at a power throughput of 300 watts and a mixture of 300mTorr of 80% sulfur hexafluoride and 20% oxygen to create a device thickness of 10 microns. After producing the top-side geometry, additional photoresist was spun onto the bottom side of the wafer and a different photo mask was used to expose geometries for “windows” through the wafer to allow mirror rotation. Using 25% tetramethylammonium hydroxide solution, these “windows” were etched through the entire wafer substrate. A turntable arm counterweighted with a micrometer was used to apply extremely accurate forces to the devices with a resolution of 40 micronewtons. Using a laser and a position sensitive detector, the displacements corresponding to various applied forces were measured, but electronic noise prevented effective comparison between designs.