Electrostatic Piggyback Microactuators for Head Element Positioning
Makoto Mita*1, Hiroshi Toshiyoshi*1*2, Hiroyuki Fujita*1
*1
Institute of Industrial Science (IIS), University of Tokyo
4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
*2
VLSI Design and Education Center (VDEC), University of Tokyo
Abstract --- We propose a new types of the 3rd generation added cost for head-gimbal assembly (HGA) cannot be
MEMS piggyback actuator mechanism, which is suitable
negligible.
for integration with read/write head device. An SOI
In the third generation approach, on the other hand, the
wafer is patterned into a multiple-plate electrostatic
actuator can be fully integrated by batch processes with
actuator (2-um gap) by Deep RIE process. Prototype
the read/write devices and the air-bearing slider. In a
actuators (2 mm x 3 mm x 0.6 mm) without head device
past few years, several types have been reported [11-14].
have been developed to test electromechancial
However, no practical method of integrating actuators
characteristics. Typical mechanical stroke of 0.5 microns
with head devices has been proposed.
with a dc 60 V and resonant frequency of 16 kHz have
This paper proposes a simple fabrication method for
been obtained. Analytical model have predicted that
integrating the MEMS microactuator with head element
0.15-micron-displacement would be possible for 200
devices. Prototype actuators have been developed
Gbit/in2 model when the electrostatic gap is designed to be
without the head element parts for testing
0.5 microns.
electromechanical performance.
Index Terms -- MEMS, microactuator, electrostatic, hard-
II. Silicon Microactuator for HDD Positioning
disk drive, piggyback actuator, SOI.
Figure 1 illustrates a schematic picture of our piggyback
actuator. The actuator and the head element are
I. Introduction
As the recording density of hard-disk drives (HDD) is
increasing over 100 Gbit/in2, the conventional voice-
coil motor (VCM) mechanisms are facing difficulty in
positioning the slider chip at fast response (20 kHz in
terms of resonance) and high accuracy (< 0.5 microns
or 150 kTPI). Sev eral different types of MEMS
(Micro Electro Mechanical Systems) piggyback
mechanism, in which a small actuator moves in
cooperation with a VCM to move a slider, have been
developed to overcome these problems [1].
The first generation MEMS piggyback approaches use
an electromagnetic or PZT actuators in the middle of
the suspension, while the second generation has an
actuator in between the slider and the gimbal. These
two approaches can be immediately applied to the
present manufacturing of HDD, because no alternation
is needed in the read/write-head processes. However,
Fig. 2: Processes for monolithically integrating MEMS
Fig. 1: Schematic view of monolithically integrated
piggyback actuator with head element devices.
MEMS piggyback actuator.
assembly. The process here is very simple and
straightforward compared with those previously
reported. It does not require wafer bonding or device-
level assembly of different materials.
III. Prototype Results
Figure 3 (a) shows a piggyback actuator chip which is 2
mm in width, 2.5 mm in length, and 0.6 mm in height.
A close-up view of the electrodes is shown in Fig. 3 (b).
Each movable electrode has identical dimensions of 50
microns in width, 500 microns long, and 50 microns in
height.
The electromechanical performance of the actuator has
been tested by the laser Doppler velocimetry. Figure 4
shows the dc transfer curve of the actuator under a
triangular wav e v oltage of 20 Hz. Pull-in has been
observed at 63 V. Target stroke 0.5-um is possible at a
dc voltage of 60 V. Fundamental resonance has been
found at 16 kHz.
IV. Conclusions
HDD read/write heads today are made on AlTiC
substrates, which are very hard material to make
microactuators by any etching methods. Using a
Fig. 3: (a) Chip photograph and (b) close-up view of the
silicon wafer has compatibility with micromachining as
electrostatic actuator part.
well as read/write head processes. In this paper, we
have proposed an electrostatic microactuator compatible
with monolithically integration with head element on an
SOI wafer. This approach is good for practical use
because (1) high-resolution patterning of actuator and
head element can be done on the initial surface of wafer,
and that (2) fine polishing for head element and air
bearing is possible.
Acknowledgement
This work has been supported in part by the 2001
contract with Japan Storage Research Consortium.
References
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Fig. 4: DC transfer curve of electrostatic actuator
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