Invar MEMS milliactuator for hard disk drive application

High-bandwidth servo actuation of the recording head is necessary for future high areal recording density hard-disk drives. The “piggy-back” actuation scheme, in which a MEMS milliactuator is used as the secondary actuator, is a promising solution. There are several requirements for the milliactuator in this application, including thermal stability to ensure wide-range operation temperature, and a vertical/horizontal directional selectivity of the stiffness, which needs high-aspect-ratio structures. To meet the thermal stability requirement, a low-thermal-expansion-alloy (Invar) electro-deposition process was developed. High-aspect-ratio etching technology was also established to define a thick and high-aspect-ratio structure. The milliactuator was designed, fabricated and characterized, and the measured frequency response indicated that the device is suitable for use as a servo actuator