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

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 mug 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 mum thick active silicon layer and a 2 mum 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 mum when a 15 V dc bias plus a 15 V ac sinusoidal driving input was applied and its electrostatic force was 50.4 muN 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 degrees of phase margin for a 2.21 kHz servo bandwidth.