Fabrication of an electrostatic track-following micro actuator for hard disk drives using SOI wafer

Abstract

This paper presents track-following control using an electrostatic microactuator for super-high density hard disk drives (HDDs). The electrostatic microactuator, a high aspect ratio track-following microactuator (TFMA) which is capable of driving 0.3 µg magnetic head for HDDs, is designed and fabricated by a microelectromechanical systems process. It was fabricated on a silicon on insulator wafer with a 20 µm thick active silicon layer and a 2 µm thick thermally grown silicon dioxide layer; a piggyback electrostatic principle was used for driving the TFMA. The first vibration mode frequency of the TFMA was 18.5 kHz, which is enough for a recording density of higher than 10 Gb in −2 . Its displacement was 1.4 µm when a 15 V dc bias plus a 15 V ac sinusoidal driving input was applied and its electrostatic force was 50.4 µN when the input voltage was 30.7 V. A track-following feedback controller is designed using a feedback nonlinear compensator, which is derived from the feedforward nonlinear compensator. The fabricated actuator shows 7.51 dB of gain margin and 50.98 • of phase margin for a 2.21 kHz servo bandwidth.

Degradation of Mechanical Strength at Si/SiO<inf>2</inf> Interface on SOI Wafers under Cyclic Loading

“…Because of the advantages they provide, MEMS devices on SOI wafers are being manufactured in increasing quantities despite their higher cost compared to that of conventional bulk silicon wafers [1]. For example, the microactuators in SOI-MEMS devices have a high-aspect ratio structure that achieves high driving force with low consumption energy [2]. AFM probes are typical examples of SOI-MEMS devices in which the cantilever or the tip is fabricated on the SOI layer [3,4].…”

MEMS Based on Thin Ferroelectric Layers

“…The parameters of the capacitance electromechanical devices such as driving force, power, reaction time with respect to voltage pulse can be improved by the increase in the field strength in the gaps, as they are proportional to the energy density of the field εε 0 Е 2 /2, where ε and ε 0 are the dielectric permeabilities of the medium and the vacuum. Use of the micromachining for the manufacturing of the electrostatic micromotors allows one to reach significantly smaller gaps (on the order of several micrometers), and to get higher values of electric field strength and energy density (Harness& Syms, 2000;Wallrabe et al,1994;Zappe et al, 1997;Kim & Chun, 2001). The estimates of specific energy output based on the energy density of electric and magnetic fields can be used to determine the gap width necessary for the electric field energy density to be comparable to or higher than magnetic field energy density (~4-5·10 5 J/m 3 with 1 T induction and very high quality of magnetic material).…”

Design, Fabrication, and Control of a High-Aspect Ratio Microactuator for Vibration Suppression in a Hard Disk Drive

“…Electrostatic (Horsley et al, 1999) (White et al, 2004), piezoelectric (Soeno et al, 1999) (Kuwajima and Matsuoka, 2002), and electromagnetic (Tang et al, 1996) actuation forces have been proposed for this configuration. The final approach places the second stage actuator in the slider itself at the read-write head (Nakamura et al, 1998) (Kim and Chun, 2001). This "actuated head" arrangement gives dual-stage instrumented servo assembly ideal actuation location, but the integration of head, slider, and actuator fabrication is very difficult.…”