A MICRO-ACTUATOR FOR A HARD-DISK DRIVE FINE TRACKING SERVO

Abstract

This paper reports on the design, fabrication and testing of an electrostatic micro-actuator for a magnetic Hard-Disk Drive (HDD) tracking servo. First, the design requirements for a micro-actuator in this application were investigated. These include high Z-directional stiffness, low in-plane stiffness, high structural aspect ratio, large output force, high area-efficiency, low cost, and mass-production by a batch process. A novel area-efficient rotary micro-actuator design was devised, and micro-actuators were successfully fabricated using innovative processing technologies such as high-aspect ratio polymer etching and thick metal electro-deposition. The fabricated micro-actuator has a structural thickness of 40 μm with a minimum gap/structure width of approximately 2 μm (aspect ratio of 20:1). The micro-actuator's frequency response was measured and it was confirmed that the micro-actuator has extremely clean response up to very high frequency region, and this fact enables the design of a servo system that exceeds a 5 kHz servo bandwidth, which is adequate to achieve a track density of more than 25 kilo-track-per-inch (kTPI). The micro-actuator/slider assembly was also tested on a spinning disk, with its position controlled by a PID controller using the magnetic position error signal (PES) written on the disk. A position accuracy of about 0.05 μm was observed when the servo controller was turned on. This result confirms that this micro-actuator can be used in a servo system which is capable of more than 25 kTPI.