Active solid-state devices (e.g. – transistors – solid-state diode – Physical configuration of semiconductor – Mesa structure
Reexamination Certificate
1999-05-25
2001-03-27
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Physical configuration of semiconductor
Mesa structure
C257S415000, C310S309000
Reexamination Certificate
active
06208013
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a microactuator and a method of forming the same, and more particularly to a micro-actuator suitable for driving a small size device such as optical devices, optomagnetic and magnetic devices.
A convention small actuator is mounted on a top of a suspension of a magnetic head for driving a slider. This was proposed by L. S. Fan and is disclosed in IEEE Transactions On Industrial Electronics, vol. 42, No. 3, pp. 222-233, June 1995 entitled “Magnetic Recording Head Positioning At Very High Track Densities Using A Microactuator Based Two-Stage Servo System”.
FIG. 1
is a plane view illustrative of a conventional microactuator.
FIG. 2
is a partially enlarged view of an area “A” in
FIG. 1
illustrative of the conventional microactuator.
FIG. 3
is a cross sectional elevation view illustrative of the conventional microactuator taken along an A—A line in FIG.
2
. In
FIGS. 1 and 2
, illustrations of a structure of a platform are eliminated. The microactuator has a pair of stators
83
and
84
provided on opposite sides of a silicon substrate
100
and separated from each other in a first direction, and a movable part
82
positioned between the stators
83
and
84
. The movable part
82
is supported by spring members
81
which are provided on spring fixing stages
80
fixed to the silicon substrate
100
so that he movable part
82
is floated or isolated from the silicon substrate
100
.
Each of the stators
83
and
84
has a stator extending portion which extends toward inside regions and in the first direction and also extends along a longitudinal center line. The stator extending portion has many stator comb-tooth portions
91
which extend from both sides of each of the stator extending portions in a second direction perpendicular to the first direction, thereby to form a comb-shape, wherein the stator comb-tooth portions
91
are arranged at a first constant pitch in the first direction and extend in the second direction. Each of the stator comb-tooth portions
91
has comb-tooth shaped stator electrodes
93
which extend from one side of the stator comb-tooth portion
91
, wherein the comb-tooth shaped stator electrodes
93
extend in the first direction at a second constant pitch.
Each of the movable part
2
comprises first and second side frame portions extending in the first direction and separated from each other in the second direction and a center frame portion extending in the second direction to connect the first and second side frame portions to each other. Each of the first and second side frame portions has many movable comb-tooth portions
92
which extend from the side toward the longitudinal center line in the second direction, thereby to form a comb-shape, wherein the movable comb-tooth portions
92
are arranged at a third constant pitch in the second direction and extend in the first direction. The many movable comb-tooth portions
92
and the many stator comb-tooth portions
91
are alternately aligned in the first direction, whereby each of the many movable comb-tooth portions
92
is positioned between adjacent two of the many stator comb-tooth portions
91
. Each of the movable comb-tooth portions
92
has comb-tooth shaped movable electrodes
94
which extend from one side of the movable comb-tooth portion
92
, wherein the comb-tooth shaped movable electrodes
94
extend in the first direction at a fourth constant pitch, so that the comb-tooth shaped movable electrodes
94
and the comb-tooth shaped stator electrodes
93
are alternately aligned in the second direction, whereby each of the comb-tooth shaped movable electrodes
94
is positioned between adjacent two of the comb-tooth shaped stator electrodes
93
. The stator comb-tooth portion
91
is wider in width than the movable comb-tooth portion
92
. The comb-tooth shaped stator electrodes
93
are wider in width than the comb-tooth shaped movable electrodes
94
. The comb-tooth shaped stator electrodes
93
are adhered onto the silicon substrate
100
together with the many stator comb-tooth portions
91
. The comb-tooth shaped movable electrodes
94
are separated or floated from the silicon substrate
100
together with the movable comb-tooth portion
92
.
A voltage is applied across the comb-tooth shaped movable electrodes
94
and the comb-tooth shaped stator electrodes
93
so that the movable part
82
is driven to be moved in the first direction. The voltage application across the comb-tooth shaped movable electrodes
94
of the movable part
82
and the comb-tooth shaped stator electrodes
93
of the second stator
84
causes the movable part
82
to move toward the second stator
84
. The voltage application across the comb-tooth shaped movable electrodes
94
of the movable part
82
and the comb-tooth shaped stator electrodes
93
of the first stator
83
causes the movable part
82
to move toward the first stator
83
.
The above conventional microactuator has been fabricated a follows. A phospho silicate pattern of 2 micrometers in thickness if formed on a first region of the silicon substrate
100
, wherein the first region is for later formation of the above movable part
82
. A photo-resist pattern is then formed on the phospho silicate glass pattern by use of a photo-lithography technique. A copper plating method is carried out to form copper films between apertures of the photo-resist pattern. A platform pattern is then formed by use of other photo-lithography technique and subsequent copper plating method before the phospho silicate glass pattern is removed by an etchant of hydrofluoric acid solution so as to isolate the movable part
82
and the comb-tooth shaped movable electrodes
94
from the silicon substrate
100
, whereby the microactuator and the platform are formed. Namely, this actuator is formed by the electro-plating technique.
By the way, it has been known in the part that a polysilicon thin film is used for the microactuator fabricated by utilizing a silicon IC process. This microactuator having the polysilicon thin film is superior in conformability with the silicon IC process and also in mechanical characteristics as compared to the above electroplate microactuator. In order to apply this second microactuator having the polysilicon film to the magnetic had or the optomagnetic head, it is, however, necessary to suppress motion of the head in other directions to the intended direction. For example, the microactuator shown in
FIG. 1
is required to cause the movable part
82
to move in the first direction but required to suppress any motion of the movable part
82
in a vertical direction to the first and second directions. In order to suppress the motion of the movable part
82
in the vertical direction, it is effective to increase the thickness of the springs
81
. In view of utilizing a large electrostatic force, it is also important to increase the thicknesses of the comb-tooth shaped movable electrodes
94
and the comb-tooth shaped stator electrodes
93
.
Accordingly, it had been required to form the actuator having a thickness of not less than 20 micrometers. Notwithstanding, a practically possible maximum thickness of the polysilicon film is about 4 micrometers which is much thinner than the required thickness. For those reasons, the above plating technique for forming the electro-plated actuator and the following other type microactuator had been developed. The other type microactuator may be formed by etching technique for etching a single crystal silicon layer.
The actuator having the silicon crystal silicon film may be formed by use of an silicon-on-insulator substrate. This technique was proposed by A. Benitez et al. and is disclosed in Sensors and Actuators, A50, pp. 99-103, 1995, entitled “bulk silicon microelectromechanical devices fabricated from commercial bonded and etched-back silicon-on-insulator substrates”. The use of this technique allows the comb-tooth shaped movable electrodes
94
and the comb-tooth shaped stator electrodes
93
to be formed from a single crystal s
Chaudhuri Olik
Ha Nathan W.
NEC Corporation
Young & Thompson
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