Understanding Smart Sensors - Nomads.usp

MEMS Beyond Sensors 217+ 10°− 10°Support postMirror elementTorsion hingeSilicon substrateOffset addresselectrodesMirror landingelectrodeFigure 9.13 Digital micromirror with torsion hinge suspension.deflect the mirror without aid of external probes. Figure 9.14 shows the mirrorin the upright position.9.3.6 Heating ElementsMultijunction thermal converters (MJTC) have been fabricated using a standardCMOS process and bulk micromachining [23]. After CMOS processing,a cavity is etched by bulk micromachining that produces a suspended MJTCcantilever structure, as shown in Figure 9.15. Polysilicon resistive heating elementsand aluminum-polysilicon thermocouple junctions are encapsulated inglass. The glass protects those elements from the etchant and provides amechanical support. MJTCs have potential applications in low-cost, highprecisionRF and microwave power circuits.9.3.7 Thermionic EmittersArrays of sputtered tungsten thermionic emitters have been fabricated by surfacemicromachining [24]. An SiO 2 layer isolates sputtered tungsten from thesilicon substrate. The tungsten is patterned by wet etching, and the silicon isalso wet-etched under the filament to avoid contact. The filaments were testedin a vacuum of 5 ⋅ 10 −7 torr. The filaments changed from barely visible red towhite light once they start to emit. Operating life approaching 1 hr has been