PERFORMANCE IMPACT OF MONOLAYER COATING OF POLYSILICON MICROMOTORS

This paper reports the impact on performance of flange-bearing polysil icon micromotors for different self-assembled monolayer coatings on th e surface of released motors. Octadecyltrichlorosilane (OTS) and (3,3, 3-trifluoropropyl) trichlorosilane (TFP) are found to be promising as they significantly improve micromotor performance. Micromotors coated with OTS show a stable rotor speed and minimum operating voltage durin g a nine-month testing period. The experiments on gear ratio as a func tion of wobble cycles indicate that wear in a bearing without OTS coat ing is significant and results in changes in the gear ratio from the s tart of micromotor operation by as much as 40%, while the change of ge ar ratio is within 4% for near 80 million wobble cycles over a nine-mo nth testing perod for motors with OTS coating. For motors coated with TFP, no stiction and no significant change of the gear ratio are obser ved for the testing duration. However, the study of gear ratio as a fu nction of wobble cycles shows that the rotor speed fluctuates in the b eginning and then stabilizes for wobble micromotors coated with TFP. O TS coating is found to decrease the flange frictional force/torque by a factor of about 1.5. This net reduction of the flange friction force /torque comes about from the combined action of increasing the frictio nal coefficient from 0.36 to 0.55 and decreasing the normal contact fo rce associated with the rotor/flange contact friction from near 0.8 mu N to near 0.3 mu N.