Understanding Smart Sensors - Nomads.usp

220 Understanding Smart SensorsPolyimidePolysiliconPolysiliconPSGSilicon wafer(a)(b)Figure 9.16 (a) Three-dimensional structure with elastic joint (after: [27]), and (b) roboticbug (courtesy of BSAC, University of California, Berkeley).pin-and-staple system and scissor-hinge design. The pin-and-staple systemrequired three structural layers to achieve a base, axle pin, and retaining staplewhere the foldout movable structure was attached to the substrate. The scissorhingeweaves a second polysilicon layer under and then over the first polysiliconlayer. Weaving allows the retaining structure to be deposited with the first layerbut not connected to it. The most recent development makes use of cantileversto press on and then fix the axle pin. The axle is designed with a self- limitingmechanism that prevents the axle from protruding beneath the first layerof polysilicon. The hinge was designed, built, and tested in a surface-micromachinedmicrophotonic system. The hinge could be opened to 90 ±0.8degrees.