MEMS MILLIACTUATOR FOR HARD-DISK-DRIVE TRACKING SERVO

This paper describes the design, fabrication, and operational characte ristics of a MEMS milliactuator designed for servo tracking in a hard- disk drive (HDD), The actuator is designed to increase the bandwidth o f an HDD tracking servo and pack more recording tracks on a disk. An I nvar (low thermal expansion metal) electrode position process was deve loped to meet the thermal stability requirement. The electroplated Inv ar's thermal coefficient of expansion is as low as 6.3 x 10(-6)/K, whi ch is almost half of that of pure nickel. For the plating mold pattern definition, a high-aspect-ratio polymer etching technique was develop ed. A high-aspect-ratio structure line-and-gap definition is required to achieve both a high directional stiffness ratio and electrode effic iency for the actuator, The etching technique described can etch throu gh a thick (<40 mu m) polymer layer with an aspect ratio of 16:1. at a n etch rate of <2 mu m/min. Low-cost/high-volume manufacturing is achi evable by this batch fabrication technique. A milliactuator was fabric ated and assembled with a suspension and a slider weighted at around 2 mg, The slider was successfully driven by the milliactuator while the slider was flying on a spinning disk. The operational characteristics (frequency response) of the in-flight milliactuator were measured, an d the results indicate that the actuator is suitable for high-bandwidt h HDD servo-tracking applications.