Understanding Smart Sensors - Nomads.usp

MEMS Beyond Sensors 215Over-range protectorOpen driverExtension armOpen driverDrive armGripper tipOpen driverL drL ext=> AnchorFigure 9.11 Schematic of a microgripper with an electrostatic comb drive. (After: [20].)t=2mm. The calculated spring constant of this structure is 4 N/m. The AFMprobe was used to measure a silicon dioxide grating that had a depth of 270 Åand repeated every 6.5 mm. These types of devices may be useful in profilometryand IC inspection. An AFM probe produced by Park Scientific Instrumentsis shown in Figure 9.12(b).9.3.5 MicromirrorsMicromachined digital micromirror devices can be used for displays. As shownin Figure 9.13, the micromirror element is an aluminum mirror suspendedover an air gap by two thin, post-supported hinges [22]. The mechanicallycompliant hinges permit the mirror to rotate 10 degrees in either direction.The posts provide the connections to a bias/reset bus that connects all the mirrorsof the arrays to a bond pad. The mirrors are fabricated over conventionalCMOS SRAM cells that provide an address circuit for each mirror. The mirrorshave a response time of approximately 10 ms and can be pulse-widthmodulated to provide a gray-scale output in a black-and-white display. Monolithicarrays with 768 by 576 pixels have been produced.A hinged micromirror device has been fabricated using surfacemicromachining [11]. The hinged micromirror is driven by a microengine coupledto a three-gear torque-increasing system. The combination is sufficient to