Dynamic magnetic information storage or retrieval – Head mounting – For adjusting head position
Reexamination Certificate
1998-05-21
2001-01-23
Ometz, David L. (Department: 2754)
Dynamic magnetic information storage or retrieval
Head mounting
For adjusting head position
C360S294200, C310S0400MM
Reexamination Certificate
active
06178069
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a microactuator used to drive optical components and small-size magneto-optical/magnetic disk components, and a method of manufacturing the same.
A microactuator (electrostatic actuator) is generally proposed in which a movable element made of an insulating substance is moved by an electrostatic force generated between a plurality of stationary electrodes and the charges induced by the movable element when a voltage is applied to the plurality of stationary electrodes opposing the movable element at a small gap.
A microactuator mounted at the distal end of a suspension supported by an arm in a magnetic disk apparatus to drive a magnetic head formed integrally with a slider is proposed in L.S. Fan et al., “Magnetic Recording Head Positioning at Very High Track Densities Using a Microactuator-Based, Two-Stage Servo System”, IEEE Transactions on Industrial Electronics, Vol. 42, No. 3, pp. 222-233, June 1995 (reference 1).
FIG. 9
shows a microactuator described in reference 1.
In
FIG. 9
, the conventional microactuator is constituted by a pair of T-shaped stationary elements
83
and
84
which are formed on a silicon substrate (to be described later) and have the distal ends of leg portions opposing each other, and an H-shaped movable element
82
formed between the stationary elements
83
and
84
. The movable element
82
is supported by four springs
81
to float above the silicon substrate. One end of each spring
81
is fixed to a corresponding one of a pair of spring bases
80
fixed to the silicon substrate, and the entire spring
81
is separated from the silicon substrate.
The stationary elements
83
and
84
are respectively made up of support portions
83
a
and
84
a
, and support portions
83
b
and
84
b
constituting leg portions vertically extending from the centers of the support portions
83
a
and
84
a
. The end portions of the support portions
83
b
and
84
b
oppose each other. Many comb tooth portions
91
are formed in a comb tooth shape at a predetermined pitch in two lines on the two sides of each of the support portions
83
b
and
84
b
. As shown in
FIG. 10
, many stationary element electrodes
93
are formed at a predetermined pitch in a comb tooth shape on one side of each comb tooth portion
91
.
The movable element
82
is made up of a pair of parallel support portions
82
a
and a coupling portion
82
b
coupling the centers of the support portions
82
a
. The movable element
82
is combined with the stationary elements
83
and
84
to constitute an actuator. That is, the support portions
82
a
of the movable element
82
are arranged parallel to sandwich the support portions
83
b
and
84
b
of the stationary elements
83
and
84
. The coupling portion
82
b
of the movable element
82
vertically crosses the gap formed by the end portions of the support portions
83
b
and
84
b
of the stationary elements
83
and
84
.
The movable element
82
comprises many comb tooth portions
92
formed in a comb tooth shape at the same pitch as that between the comb tooth portions
91
of the stationary elements
83
and
84
. The comb tooth portions
91
of the stationary elements
83
and
84
and the comb tooth portions
92
of the movable element
82
overlap and interdigitated with each other. As shown in
FIG. 10
, movable element electrodes
94
to be inserted between the stationary element electrodes
93
are formed on one side of each comb tooth portion
92
.
As shown in
FIG. 11
, the comb tooth portion
91
formed integrally with the stationary element electrode
93
is fixed to a silicon substrate
100
via a stationary element base
101
. In contrast to this, the comb tooth portion
92
formed integrally with the movable element electrode
94
is separated from the silicon substrate
100
, i.e., floats above the surface of the semiconductor substrate
100
at a predetermined interval.
In this arrangement, the movable element
82
can be moved right or left in
FIG. 9
, i.e., the comb tooth portion
92
can be moved in a direction to come close to and separate from the comb tooth portions
91
by applying a voltage across the movable element electrode
94
of the comb tooth portion
92
and the stationary element electrodes
93
of the stationary elements
83
and
84
. In this case, the movable element
82
can be moved left by applying a voltage to the left stationary element
84
in
FIG. 9
, or right by applying a voltage to the right stationary element
83
.
A method of manufacturing the microactuator having this arrangement will be explained. A 2-&mgr;m thick PSG (PhoshoSilicate Glass) film is patterned in a region on the silicon substrate
100
where the movable element
82
is to be formed. Copper is plated between resist patterns formed on the PSG film using photolithography.
The PSG film is removed using hydrofluoric acid to separate the movable element
82
including the movable element electrode
94
from the silicon substrate
100
, thereby forming the copper-plated movable element
82
. In this way, the microactuator in reference 1 using a 20-&mgr;m thick copper material is manufactured.
In a microactuator using a silicon IC process, a structure using a polysilicon thin film has conventionally been known well. Compared to the electroplated actuator, the microactuator with a polysilicon structure has good matching with the silicon IC process and exhibits excellent mechanical characteristics. Note that in applications to a magnetic/magneto-optical head and the like, movement of the head in directions other than a desired direction must be suppressed small.
In the microactuator shown in
FIG. 9
, the movable element
82
must move right and left in
FIG. 9
, but its movement in a direction perpendicular to the surface of the silicon substrate
100
must be suppressed as small as possible. From this condition, the spring
81
must be made thick. The movable element electrode
94
and the stationary element electrode
93
must also be made thick in order to use a large electrostatic force.
From these conditions, a microactuator having an electrode thickness of 20 &mgr;m or more must be manufactured for practical use. Since the polysilicon thin film has a thickness of about 4 &mgr;m at most, microactuators using the above-described plating technique and a single-crystal silicon etching technique (to be described later) are being developed.
To manufacture a microactuator made of single-crystal silicon, the method using an SOI (Silicon On Insulator) substrate described in A. Benitez et al., “Bulk Silicon Microelectromechanical Devices Fabricated from Commercial Bonded and Etched-Back Silicon-on-Insulator Substrates”, Sensors and Actuators, A50, pp. 99-103, 1995 (reference 2) can be employed.
According to this method, the movable element electrode
94
and the stationary element electrode
93
in
FIG. 11
are formed of a 20-&mgr;m thick single-crystal silicon film, and the stationary element base
101
is formed of a silicon oxide film. By removing the silicon oxide film positioned below the movable element electrode
94
using hydrofluoric acid, the movable element electrode
94
can be separated from the silicon substrate
100
.
In this case, since the movable element electrode
94
is narrower in width than the stationary element electrode
93
, the silicon oxide film is still left below the stationary element electrode
93
even upon etching using hydrofluoric acid, and forms the stationary element base
101
. In this manner, the movable element electrode
94
and the stationary element electrode
93
each made of, e.g., a 20-&mgr;m thick single-crystal silicon film are formed on the silicon substrate
100
.
The method of manufacturing a thick microactuator has been briefly described. The conventional microactuator shown in
FIG. 9
is undesirably easily destructed by external shock, as will be described below.
I) To enable the microactuator to use a very weak electrostatic energy, the spring
81
is formed of a wire having a width of 2 &mgr;m and a length of 200
NEC Corporation
Ometz David L.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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