Performance Impact of Monolayer Coating of Polysilicon Micromotors

Abstract

This paper reports the impact on performance of flange‐bearing polysilicon micromotors for different self‐assembled monolayer coatings on the 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 during a nine‐month testing period. The experiments on gear ratio as a function of wobble cycles indicate that wear in a bearing without OTS coating is significant and results in changes in the gear ratio from the start of micromotor operation by as much as 40%, while the change of gear ratio is within 4% for near 80 million wobble cycles over a nine‐month testing perod for motors with OTS coating. For motors coated with TFP, no stiction and no significant change of the gear ratio are observed for the testing duration. However, the study of gear ratio as a function of wobble cycles shows that the rotor speed fluctuates in the beginning and then stabilizes for wobble micromotors coated with TFP. OTS 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 frictional coefficient from 0.36 to 0.55 and decreasing the normal contact force associated with the rotor/flange contact friction from near 0.8 μN to near 0.3 μN.

Accurate method for determining adhesion of cantilever beams

“…We shall refer to these as the hydrophobic samples. ODTS has been investigated as a promising molecule for minimization of adhesion in MEMS [8,22,29,30]. The head group of the organosilane is hydrolyzable, which facilitates the formation of covalent siloxane bonding to the substrate hydroxyl groups as well as between neighboring silane molecules to form a well attached organosilane layer [3 11.…”

Tunable water-based lubrication behavior of alkyl- and fluoroalkyl-silanes

“…These properties make them good candidates for use in micro/nano devices. Alkylsilane SAM films have therefore been extensively studied, and proposed as lubricants for MEMS [15][16][17][18]. It is…”

“…These properties make them good candidates for use in micro/nano devices. Alkylsilane SAM films have therefore been extensively studied, and proposed as lubricants for MEMS [15][16][17][18]. It is known that roughness has a significant effect on the friction characteristics of solid surfaces [19][20][21].…”

Recent Advances in Surface Micromachining

“…1, or by roughening the underlying surface [64]. Self-assembled monolayer coatings have been shown to reduce surface adhesion and to be effective at friction reduction in bearings, as well [63,65]. Recently, a process that results in a hydrogen-terminated, extremely hydrophobic silicon surface has been shown to be effective in reducing post-release stiction [66].…”