Design and fabrication of high torque electrostatic micromotors using micromachining of thin polysilicon sheets

This paper investigates new design rules that will allow the development of high torque electrostatic micromotors through the cooperation of arrayed direct drive actuators. Electrostatic scratch drive actuators, which combine active frictional contact mechanisms with the electrostatic actuation are particularly analyzed because previous achievements have pointed their ability to develop, at a low speed, high driving forces comparatively to their little size. Scratch drive actuators (SDA) have been already successfully applied, as an example for self assembling microstructures and micro optical bench actuation. Such interesting results which have been performed by using an individual or a few number of SDA, led us to make further investigations in order to optimize this new promising actuator technology. Consequently, we have mainly focused on new mechanisms which integrate combinations of a large number of SDA, (from some tens to several thousands), in such a way to allow powerful annular and tubular micromotors to be designed, machined, and then characterized. This paper points out the main physical and technological principles that will allow high torque electrostatic micromotors to be realized in a near future. It also gives the first results that have been obtained on the design and surface-micromachining of annular and tubular micromotors. The previous results related to the batch fabrication of large and thin polysilicon sheets (thickness on the order of 1 mu m, surface on the order of a few mm(2)), which integrate up to several thousands of microactuators are also given. New concepts which will allow large size and high torque 3D electrostatic micromotors to be realized through the forming of thin polysilicon sheets, are finally described The expected driving characteristics show the interest of both cooperative arrayed microactuators and direct drive frictional mechanisms.