Optical: systems and elements – Deflection using a moving element – By moving a reflective element
Reexamination Certificate
2002-02-13
2004-12-14
Phan, James (Department: 2872)
Optical: systems and elements
Deflection using a moving element
By moving a reflective element
C359S198100, C359S199200, C248S560000, C310S066000
Reexamination Certificate
active
06831765
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tiltable-body apparatus with a tiltable body which can be reciprocally tilted about a twisting longitudinal axis, such as micro-sensors for sensing mechanical amounts, micro-actuators, and optical micro-scanners, and a method of fabricating the tiltable-body apparatus.
2. Description of the Related Background Art
It is well known that surface forces become more dominant than volume forces as the size of mechanical elements decreases and the influence of friction thus increases in such machines more than in normally-sized machines. Accordingly, in designing micro-machines, it is generally necessary to consider the reduction of the number of sliding portions and rotating portions as much as possible.
A conventional optical scanner with a tiltable body oscillating about a twisting longitudinal axis will be described.
FIG. 1
illustrates the optical scanner disclosed in U.S. Pat. No. 4,317,611.
FIG. 2
illustrates a disassembled view of this optical scanner to clearly show its internal structure.
FIGS. 3 and 4
illustrate cross sections of a silicon thin plate
2020
taken along lines
2003
and
2006
in
FIG. 1
, respectively.
In the above optical scanner, a recess
2012
is formed in a substrate
2010
of an insulating material. A pair of driver electrodes
2014
and
2016
and a mirror support portion
2032
are provided on the bottom of the recess
2012
. A pair of torsion bars
2022
and
2024
and a mirror
2030
are integrally formed in the silicon plate
2020
. An upper surface of the mirror
2030
is coated with a highly-reflective material, and the mirror
2030
is rotatably supported by the torsion bars
2022
and
2024
. The silicon plate
2020
is disposed above the substrate
2010
with a predetermined distance between the silicon plate
2020
and the driver electrodes
2014
and
2016
being set as illustrated in FIG.
3
.
The silicon plate
2020
is electrically grounded. A voltage is alternately applied to each of the driver electrodes
2014
and
2016
to attract the mirror
2030
by an electrostatic force. The mirror
2030
is thus tilted about the longitudinal axis of the torsion bars
2022
and
2024
.
The cross section of the torsion bars
2022
and
2024
has a shape of trapezoid as illustrated in FIG.
4
. In a microstructure with such torsion bars, however, since the torsion bar is likely to bend in a direction perpendicular to its longitudinal axis, the microstructure can be easily affected by external vibrations and the longitudinal axis of the torsion bar can be easily shifted. Accordingly, it is difficult to attain an accurate driving in such a microstructure.
Therefore, when the above optical scanner is used in an optical scanning type display, its image and spot profile are likely to shift and vary due to the external vibrations. This disadvantage increases when the scanning type display is constructed in a small portable form.
The following structure has been proposed to solve the above-discussed disadvantage of the torsion bar.
FIG. 5
illustrates a gimbal plate
2120
for a hard disc head disclosed in “10th International Conference on Solid-State Sensors and Actuators (Transducers '99) pp. 1002-1005”. This gimbal plate
2120
is mounted on a tip portion of a suspension for the hard disc head so that rolling and pitching motions of a magnetic head are flexibly allowed. The gimbal plate includes a support frame
2131
which is rotatably supported by rolling torsion bars
2122
and
2124
. There is also arranged inside the support frame
2131
a head support
2130
rotatably supported by pitching torsion bars
2126
and
2128
. Twisting axes (indicated by dot-and-dash lines in
FIG. 5
) of rolling torsion bars
2122
and
2124
and pitching torsion bars
2126
and
2128
are orthogonal to each other, and hence, those torsion bars can achieve rolling and pitching motions of the head support
2130
.
FIG. 6
is a cross-sectional view taken along a line
2106
of FIG.
5
. As illustrated in
FIG. 6
, the cross section of each of the torsion bars
2122
and
2124
is T-shaped, and the gimbal plate
2120
has a structure with ribs.
A fabrication method of the above gimbal plate
2120
will be described with reference to
FIGS. 7A
to
7
E. As illustrated in
FIG. 7A
, initially, a silicon wafer
2191
for molding is perpendicularly etched using an etching method such as ICP-RIE (Inductively Coupled Plasma-Reactive Ion Etching). The silicon wafer
2191
for molding can be re-used. A sacrificial layer
2192
of silicon oxide and phosphosilicate glass is then deposited on the silicon wafer
2191
, as illustrated in FIG.
7
B. After that, a poly-silicon layer
2193
, which is to be the structure of the gimbal plate
2120
, is formed as illustrated in FIG.
7
C. The poly-silicon
2193
is then patterned as illustrated in FIG.
7
D. Finally, the sacrificial layer
2192
is removed, and the poly-silicon layer
2193
is bonded to a patterned pad
2195
with an epoxy resin
2094
, as illustrated in FIG.
7
E.
The thus-fabricated torsion bar with the T-shaped cross section has the feature that its geometrical moment of inertia I is large while its polar moment of inertia J is relatively small, in contrast to a torsion bar having a circular or rectangular cross section. Therefore, the above torsion bar is relatively easy to twist while hard to bend. That is, this torsion bar has a sufficient compliance in a twisting direction and a high rigidity in a direction perpendicular to the twisting axis.
Further, in the above T-shaped torsion bar, the length for obtaining necessary compliance and permissible twisting angle is small, and hence, the torsion bar can be made compact in size.
Thus, a compact micro-gimbal plate with sufficient compliance in rolling and pitching directions and sufficient rigidity in other directions can be obtained.
However, the above-discussed microstructure has the following disadvantages.
1. In the torsion bar with the T-shaped cross section, a stress concentration is likely to occur at a portion
2150
of
FIG. 6
when the torsion bar is twisted. Accordingly, the torsion bar is easy to break.
2. When the torsion bar with the T-shaped cross section is used, a twisting center of the torsion bar deviates from a center of gravity of the tiltable body. This phenomenon will be described with reference to
FIGS. 8 and 9
.
FIG. 8
illustrates a T-shaped torsion bar
2922
one end of which is fixed and the other end of which supports a tiltable body
2930
.
FIG. 9
illustrates a side of the torsion bar
2922
viewed from a direction of view indicated by an arrow in FIG.
8
. As illustrated by arrows in
FIG. 9
, since the twisting center of the T-shaped torsion bar
2922
deviates from the center of gravity of the tiltable body
2930
, a vibratory force occurs in a direction perpendicular to the twisting longitudinal axis when the tiltable body
2930
is tilted. This causes unwanted noises in micro-sensors for mechanical amounts, unnecessary actions in micro-actuators, and deflection shifts of light in micro-optical scanners.
3. Internal loss of poly-silicon is larger than that of single crystal silicon. Accordingly, a mechanical Q-value of the poly-silicon is relatively small. The vibration amplitude cannot hence be increased when the tiltable body is driven by employing its mechanical resonance. Further, its energy efficiency is small since the driving loss is large.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a tiltable-body apparatus with good strength and performance including a tiltable body which can be reciprocally tilted about a twisting longitudinal axis, such as micro-sensors for sensing mechanical amounts, micro-actuators, and optical micro-scanners, and a method of fabricating the tiltable-body apparatus.
The present invention is generally directed to a tiltable-body apparatus including a frame member, a tiltable body, and a pair of torsion springs having a twisting longitudinal axis. The torsion springs are
Hirose Futoshi
Kato Takahisa
Mizutani Hidemasa
Shimada Yasuhiro
Yagi Takayuki
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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