Design, fabrication and characterization of single crystal silicon microactuator for hard disk drives

In this paper, a single crystal silicon electrostatic microactuator for hard disk drives' (HDD) dual stage servo systems is presented. The microactuator is mounted between the slider and suspension and drives the slider on which a magnetic head element is attached. The microactuator has electrically isolated microstructures with an aspect ratio of 20:1 directly processed from a single crystal silicon substrate. It consists of a stator attached to the silicon substrate by a bus bar and a movable rotor connected to an anchored central column via spring beams. Both the stator and the rotor are suspended from the silicon substrate. Parallel plate capacitor pairs are used for the electrostatic actuation. When a voltage is applied to the microactuator, the head element will be driven to move in the tracking direction because of the rotational motion of the rotor. The microactuator prototype with overall dimensions 1.4 mm × 1.4 mm × 0.18 mm has been successfully fabricated. The techniques for integration of the microactuator with a head gimbal assembly (HGA) have been investigated. Experiments show that ±0.6 µm equivalent displacement of the head element in the tracking direction is achieved at the driving voltage 28.5 V. Dynamic frequency response testing of the microactuator bonded with the slider has been carried out. The test results demonstrate that the first in-plane resonance frequency of the electrostatic microactuator bonded with the slider is 1.9 kHz and the damping ratio is 2.8%, and the device is equivalent to a single spring mass system up to 50 kHz. The single crystal silicon electrostatic microactuator has a small mass, good thermal stability and dynamic performance, and is feasible to operate as a fine actuator in dual stage servo systems for high density HDD.