Surface micromachined mechanisms and micromotors

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Abstract
Electric micromotors are sub-millimeter sized actuators capable of unrestrained motion in at least one degree of freedom. Polysilicon surface micromachining using heavily phosphorus-doped LPCVD polysilicon for the structural material, LPCVD silicon nitride for the electrical isolation and deposited silicon dioxide for the sacrificial material has formed the fabrication technology base for the development of these micromotors. Two polysilicon surface micromachining processes, referred to here as the center-pin and flange, have been demonstrated for the fabrication of passive mechanisms and micromotors. Passive mechanisms such as gear trains, cranks and manipulators have been implemented on silicon. Reported operational micromotors have been of the rotary variable-capacitance salient-pole and harmonic (or wobble) side-drive designs. These micromotors are capable of motive torques in the 10 pN m order of magnitude range. Preliminary progress has been made in studying the operational, friction and wear characteristics of these micromechanical devices. Typical operational voltages have been as low as 37 V and 26 V across 1.5 mu m air gap salient-pole and harmonic micromotors. These excitations correspond to electric field intensities above 108 Vm-1 in the micromotor air gaps. Salient-pole and wobble micromotors have been reported to operate at speeds as high as 15000 rpm and 700 rpm, respectively. Micromotor lifetimes of at least many millions of cycles over a period of several days have been reported.