Invar MEMS milliactuator for hard disk drive application

High-bandwidth servo actuation of the recording head is necessary for the future high areal recording density hard-disk drives. The ''piggy-back'' actuation scheme, in which MEMS milliactuator is used as the secondary actuator, is one of the promising solutions. 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, 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.