Microfabricated Electrostatic Actuators for Magnetic Disk Drives

This dissertation describes microfabricated electrostatic actuators which have been designed to serve as the secondary actuator in a dual-stage servo system for magnetic hard disk drives. Both translational and rotational designs are presented, each of which consists of a flexurally suspended moving shuttle that may be actuated over a range of up to + 3 umusing electrostatic force. To allow closed-loop controller design, a complete electro-mechanical model is developed. The resulting nonlinear model is then simplified, resulting in a second-order, linear actuation model. The various parameters of this model are identified using experimental actuation data obtained with a laser-doppler vibrometer (LDV).
The measured first mechanical resonance of the translational actuator is at 532 Hz, well within the intended control bandwidth. In order to use feedback control to extend the actuation bandwidth, both proportional-derivative (PD) and phase-lead control design techniques are described. The design trade-offs presented by the compromise between actuation gain and bandwidth are explored. The results of closed-loop actuation experiments, performed using both capacitive and laser-based displacement measurements, are presented, and positioning of a 1.6 mg ceramic slider from a conventional disk drive is demonstrated over a 2.5 kHz bandwidth.  
Prototype actuators are fabricated from a 3 um thick film of chemical-vapor deposited (CVD) polysilicon which is molded to form the 45 um thick actuator. This molding technique, referred to as the HexSil process, relies on the use of a re-usable silicon mold wafer which is fabricated using a deep reactive ion etching (DRIE) process. The completed actuators are released from the mold wafer and assembled onto a target substrate using a solder-bump assembly process. This assembly method will allow separately fabricated actuators and CMOS signal-processing electronics to be combined on the same substrate die, resulting in reduced parasitics and increased position measurement sensitivity. The complete fabrication process flow is described, and fabrication results are used to highlight the advantages and limitations of this process.
Albert P. Pisano
Roberto Horowitz
Roger T. Howe
Publication date: 
May 31, 1998
Publication type: 
Ph.D. Dissertation
Horsley, D. A. (1998). Microfabricated Electrostatic Actuators for Magnetic Disk Drives. United States: University of California, Berkeley.

*Only registered BSAC Industrial Members may view project materials & publications. Click here to request member-only access.