U.S. patent application number 12/788065 was filed with the patent office on 2011-12-01 for biaxial scanning mirror having resonant frequency adjustment.
Invention is credited to Ho Yin Chan, Francis Chee-Shuen Lee, Wei Ma.
Application Number | 20110292480 12/788065 |
Document ID | / |
Family ID | 45021911 |
Filed Date | 2011-12-01 |
United States Patent
Application |
20110292480 |
Kind Code |
A1 |
Ma; Wei ; et al. |
December 1, 2011 |
BIAXIAL SCANNING MIRROR HAVING RESONANT FREQUENCY ADJUSTMENT
Abstract
A biaxial micro-electromechanical (MEMS) device is disclosed.
The device includes a gimbal rotatable about a gimbal axis of
rotation. A pair of gimbal torsion bars connects the gimbal to a
support along the gimbal rotation axis. A mirror plate is rotatable
about a mirror axis of rotation, the mirror plate rotation axis
being substantially perpendicular to the gimbal rotation axis. A
pair of mirror plate torsion bars connects the mirror plate to the
gimbal along the mirror plate axis of rotation. One or more gimbal
moment-of-inertia-altering blocks are positioned on a surface of
the mirror plate away from the gimbal axis of rotation.
Additionally, one or more mirror plate moment-of-inertia-altering
blocks are positioned on a surface of the mirror plate away from
the mirror plate rotation axis such that the distance from the
mirror plate axis determines a resonant frequency of the biaxial
MEMS device.
Inventors: |
Ma; Wei; (Hong Kong, HK)
; Lee; Francis Chee-Shuen; (Hong Kong, HK) ; Chan;
Ho Yin; (Hong Kong, HK) |
Family ID: |
45021911 |
Appl. No.: |
12/788065 |
Filed: |
May 26, 2010 |
Current U.S.
Class: |
359/199.4 |
Current CPC
Class: |
G02B 7/1821 20130101;
G02B 26/0841 20130101; G02B 26/105 20130101 |
Class at
Publication: |
359/199.4 |
International
Class: |
G02B 26/10 20060101
G02B026/10 |
Claims
1. A biaxial micro-electromechanical (MEMS) device comprising: a
gimbal rotatable about a gimbal axis of rotation; a pair of gimbal
torsion bars connected between the gimbal and a support, the gimbal
torsion bars extending along the gimbal axis of rotation; a mirror
plate rotatable about a mirror axis of rotation, the mirror axis of
rotation being substantially perpendicular to the gimbal axis of
rotation; a pair of mirror plate torsion bars connected between the
mirror plate and the gimbal and extending along the mirror plate
axis of rotation; one or more gimbal moment-of-inertia-altering
blocks for altering the moment of inertia of the gimbal, each of
the one or more gimbal moment-of-inertia-altering blocks having a
center of mass positioned substantially away from the gimbal axis
of rotation on a surface of the mirror plate; and one or more
mirror plate moment-of-inertia-altering blocks for altering the
moment of inertia of the mirror plate, each of the one or more
mirror plate moment-of-inertia-altering blocks having a center of
mass positioned substantially away from the mirror plate axis of
rotation on a surface of the mirror plate, wherein a distance of
the mirror plate moment-of-inertia-altering blocks from the mirror
plate axis determines a resonant frequency of the biaxial MEMS
device.
2. The biaxial micro-electromechanical (MEMS) device of claim 1,
wherein the gimbal moment-of-inertia-altering blocks are aligned
along the mirror axis.
3. The biaxial micro-electromechanical (MEMS) device of claim 1,
wherein the mirror plate moment-of-inertia-altering blocks are
aligned along the gimbal axis.
4. The biaxial micro-electromechanical (MEMS) device of claim 1,
wherein the gimbal moment-of-inertia-altering blocks are not
aligned along the mirror axis and are center-symmetric.
5. The biaxial micro-electromechanical (MEMS) device of claim 1,
wherein the gimbal moment-of-inertia-altering blocks are not
aligned along the mirror axis and are center-asymmetric.
6. The biaxial micro-electromechanical (MEMS) device of claim 1,
wherein the mirror plate moment-of-inertia-altering blocks are not
aligned along the gimbal axis and are center-symmetric.
7. The biaxial micro-electromechanical (MEMS) device of claim 1,
wherein the mirror plate moment-of-inertia-altering blocks are not
aligned along the gimbal axis and are center-asymmetric.
8. The biaxial micro-electromechanical (MEMS) device of claim 1,
wherein the mirror plate and the gimbal include comb structures for
electrostatic activation.
9. The biaxial micro-electromechanical (MEMS) device of claim 1,
wherein at least one block has a parallelepiped shape.
10. The biaxial micro-electromechanical (MEMS) device of claim 1,
wherein at least one block has an arc-shape in cross-section.
11. The biaxial micro-electromechanical (MEMS) device of claim 1,
wherein the at least one mirror moment-of-inertia-altering blocks
and the at least one gimbal moment-of-inertia altering blocks
together form a cross-shaped structure.
12. The biaxial micro-electromechanical (MEMS) device of claim 1,
wherein the at least one mirror moment-of-inertia-altering blocks
and the at least one gimbal moment-of-inertia altering blocks are
positioned on a rear surface of the mirror plate.
13. The biaxial micro-electromechanical (MEMS) device of claim 1,
wherein the at least one mirror moment-of-inertia-altering blocks
and the at least one gimbal moment-of-inertia altering blocks
together form a ring-shaped structure.
14. A scanning system including the biaxial micro-electromechanical
(MEMS) device of claim 1.
15. A biaxial micro-electromechanical (MEMS) device comprising: a
gimbal rotatable about a gimbal axis of rotation; a pair of gimbal
torsion bars connected between the gimbal and a support, the gimbal
torsion bars extending along the gimbal axis of rotation; a mirror
plate rotatable about a mirror axis of rotation, the mirror axis of
rotation being substantially perpendicular to the gimbal axis of
rotation; a pair of mirror plate torsion bars connected between the
mirror plate and the gimbal and extending along the mirror plate
axis of rotation; one or more moment-of-inertia-altering blocks for
altering the moment of inertia of both the gimbal and the mirror
plate, each of the one or more gimbal moment-of-inertia-altering
blocks having a center of mass positioned substantially away from
the gimbal axis of rotation and substantially away from the mirror
axis of rotation on a surface of at least one of the mirror plate
or the gimbal, wherein a distance of the one or more
moment-of-inertia-altering blocks from the mirror plate axis and
from the gimbal axis determines a resonant frequency of the biaxial
MEMS device.
16. The biaxial micro-electromechanical (MEMS) device of claim 15,
wherein the one or more moment-of-inertia-altering blocks are
positioned on a gimbal surface.
17. The biaxial micro-electromechanical (MEMS) device of claim 15,
wherein the one or more moment-of-inertia-altering blocks is a
single moment-of-inertia-altering block positioned on a gimbal
surface.
18. The biaxial micro-electromechanical (MEMS) device of claim 17,
wherein the single moment-of-inertia-altering block is positioned
on a rear gimbal surface.
19. The biaxial micro-electromechanical (MEMS) device of claim 15,
wherein the one or more moment-of-inertia-altering blocks is a
single moment-of-inertia-altering block positioned on a mirror
plate surface.
20. A scanning system including the biaxial micro-electromechanical
(MEMS) device of claim 15.
Description
FIELD OF THE INVENTION
[0001] The invention relates to micro-electromechanical systems
(MEMS) in general, and, more particularly, to adjustment of the
resonant frequency of MEMS systems.
BACKGROUND OF THE INVENTION
[0002] MEMS scanning devices find application in a wide variety of
electrical, mechanical, and optical systems. A non-exhaustive list
of applications includes scanners, displays, projectors, switches,
printers, barcode readers, retinal displays, resonators, and
sensors. MEMS scanning devices may be driven by, for example,
electrostatic actuation, electromagnetic actuation, a combination
of electrostatic and electromagnetic actuation, and piezoelectric
actuation.
[0003] In scanning applications, MEMS devices are typically driven
at their resonant frequencies to produce the desired scanning angle
and scanning speed. When using a MEMS device as a mirror in a
scanning device, the mirror size affects the resulting resonant
frequency. If a large mirror size is used, it is difficult to
obtain a high resonant frequency. If the mirror size or mass is
decreased, the resonant frequency increases.
[0004] Various approaches have been used to alter the resonant
frequency of MEMS devices. U.S. Pat. No. 6,256,131 describes a MEMS
mirror including selectively removable tabs. The resonant frequency
is measured and tabs are removed via laser trimming to reduce the
mass of the mirror body to increase the resonant frequency to a
desired frequency.
[0005] U.S. Pat. No. 7,034,370 uses a voltage differential between
electrodes to tune the natural frequency of a MEMS structure and
thereby increase the manufacturing yield.
[0006] U.S. Pat. No. 6,753,639 discloses a MEMS microbeam
oscillator which has material added to or decreased from its
surface to tune the oscillator. The material is ablated via a laser
following measurement of the resonant frequency of the oscillator.
Similarly, material may be deposited onto the upper surface of the
microbeam oscillator to tune the device.
[0007] U.S. Pat. No. 7,187,488 uses laser or ion beam trimming of a
MEMS mirror in a sacrificial portion to fine tune the natural
frequency of the device. U.S. Patent Application Publication
2010/0002284 describes a method of modulating the resonant
frequency of a torsional MEMS device. The resonant frequency of a
MEMS device is measured and if it is greater than a standard
resonant frequency, a mass increaser is bonded to the back surface
of the MEMS device. As shown in the figures, these mass increasers
are positioned along the single torsional axis of the MEMS
device.
[0008] There remains a need in the art for improved techniques for
altering the resonant frequency of MEMS devices, particularly for
reducing the resonant frequency of MEMS devices.
SUMMARY OF THE INVENTION
[0009] The present invention relates to biaxial MEMS devices in
which the resonant frequency may be altered through the addition of
moment-of-inertia-altering blocks to the device.
[0010] As discussed above, a MEMS biaxial scanning mirror is
typically driven at its resonant frequency to achieve a large
scanning angle. However, there are many applications for MEMS
scanning mirrors which require different resonant frequencies.
Therefore, it is a desirable feature to have a flexible design for
the MEMS scanning mirror to create devices with different resonant
frequencies. For example, a scanning mirror for a touch panel
application requires a low resonant frequency. Low resonant
frequencies can be realized by large moments of inertia, typically
via a large-area mirror plate. However, it is not easy to achieve a
large amplitude/scanning angle for a large-area mirror plate MEMS
device since the mirror plate suffers greater damping force during
rotation. Further, large-area mirror plates increase the cost of
MEMS devices.
[0011] In a biaxial scanning mirror design, the mechanical
properties of the mirror plate are usually coupled to those of the
gimbal structure. Any adjustment to the resonant frequency of
mirror plate typically causes a corresponding change for to the
gimbal resonant frequency. Therefore, techniques are needed to
reduce the unwanted resonant frequency change or to adjust one
component to a desired resonant frequency value while adjusting the
resonant frequency of another component.
[0012] The present embodiments describe a biaxial MEMS device that
includes a gimbal rotatable about a gimbal axis of rotation. A pair
of gimbal torsion bars connects the gimbal to a support along the
gimbal rotation axis. A mirror plate is rotatable about a mirror
axis of rotation, the mirror plate rotation axis being
substantially perpendicular to the gimbal rotation axis. A pair of
mirror plate torsion bars connects the mirror plate to the gimbal
along the mirror plate axis of rotation. One or more gimbal
moment-of-inertia-altering blocks are positioned on a rear surface
of the mirror plate away from the gimbal axis of rotation.
Additionally, one or more mirror plate moment-of-inertia-altering
blocks are positioned on a rear surface of the mirror plate away
from the mirror plate rotation axis such that the distance from the
mirror plate axis determines a resonant frequency of the biaxial
MEMS device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 shows simplified perspective views of a biaxial MEMS
structure; FIG. 1A is a top view and FIG. 1B is a bottom view.
[0014] FIGS. 2A, 2B, and 2C demonstrate techniques for altering
mirror plate and gimbal moments of inertia.
[0015] FIG. 3 depicts a biaxial MEMS structure having a
moment-of-inertia-altering structure in the form of a cross.
[0016] FIG. 4 depicts a biaxial MEMS structure having
moment-of-inertia-altering blocks rotated away from the axes of
rotation to other angles.
[0017] FIG. 5 shows a biaxial MEMS structure with a single pair of
moment-of-inertia-altering blocks.
[0018] FIGS. 6A-6C shows methods for adjusting the blocks of the
MEMS structure of FIG. 5.
[0019] FIG. 7 shows a biaxial MEMS structure with a single block
for altering the moment of inertia.
[0020] FIG. 8 shows a method for adjusting the blocks of the MEMS
structure of FIG. 5.
[0021] FIG. 9 shows a biaxial MEMS structure using a ring-shaped
block to adjust the moment of inertia.
[0022] FIGS. 10A-10D depict methods for altering the moment of
inertia using the ring-shaped block of FIG. 9.
[0023] FIGS. 11A-11B show a biaxial MEMS structure using a single
pair of moment-of-inertia-altering blocks.
[0024] FIGS. 12A-12B show a biaxial MEMS structure using a single
moment-of-inertia-altering block.
[0025] FIGS. 13A-13G depict an exemplary manufacturing process for
the MEMS structures.
[0026] FIG. 14 shows a biaxial MEMS structure with comb structures
for electrostatic actuation.
[0027] FIG. 15 schematically depicts a scanner incorporating a
biaxial MEMS structure.
DETAILED DESCRIPTION
[0028] Turning now to the drawings in detail, FIGS. 1A and 1B show
an embodiment of a biaxial MEMS structure. The principal features
of the MEMS structure are gimbal 10, gimbal torsional bars 20,
mirror plate 30, and mirror plate torsional bars 40. Gimbal 10 is
rotated by gimbal torsional bars 20 about a gimbal axis of rotation
50. Similarly, mirror plate 20 is rotated by mirror plate torsional
bars 40 about a mirror plate axis of rotation 60.
[0029] One or more blocks 70 and one or more blocks 80 are
positioned underneath the mirror plate in order to affect the
moment of inertia and, thereby, the resonant frequency of the
mirror plate. Note that in the exemplary embodiments the blocks are
positioned on the rear surfaces of the mirror plate and/or gimbal;
however, the blocks may optionally be positioned on the front
surfaces of the mirror plate and/or gimbal with the same effect.
The effect of the blocks on the moment of inertia is explained as
follows. In a rotation dynamic, the moment of inertia plays a role
similar to the role of a mass in a linear dynamic. The moment of
inertia determines the relationship between angular momentum and
angular velocity, torque, and angular acceleration. It is a measure
of an object's resistance to change in its rotation rate. The
moment of inertia J of a point mass rotating about a known axis is
defined by:
J=mr.sup.2 (1)
where m is mass and r is the perpendicular distance to the axis of
rotation.
[0030] The resonant frequency of the object in rotation is given
by:
f = 1 2 .pi. k J ( 2 ) ##EQU00001##
where f is the resonant frequency and k is the effective rotation
stiffness. From this equation it can be seen that the parameter
that governs the resonant frequency is moment of inertia, which
includes the mass m and the distance r. A large moment of inertia
will reduce an object's resonant frequency and create a low
resonant frequency device. However, as seen from equation (1), a
large moment of inertia results not only from mass, but also from
the perpendicular distance of the mass to the rotation axis.
[0031] Accordingly, the present embodiment increases the moment of
inertia without significantly increasing the mass. Regarding
equation (1), moment of inertia J increases proportionally with m,
but increases proportionally with the second power of r. Therefore,
by locating the center of mass of the block(s) substantially away
from the axis of rotation, a minor adjustment of the perpendicular
distance r will cause a significant change in the moment of inertia
J. Rather than enlarging the mirror plate 30 in the XY plane, the
block(s) 70 and 80 are fabricated underneath the mirror plate
(opposite to the mirror surface) as seen in FIGS. 1A and 1B. One
advantage of maintaining the area of mirror plate 30 is that the
drag force (the damping) on the mirror plate remains unchanged. If
the damping is not increased by increasing the moment of inertia
through increasing the mirror plate area, there will be no extra
driving torque required to compensate for damping. Low driving
torque results in low power consumption. Without significantly
changing the mirror plate's mass, the block(s) adjust the moment of
inertia efficiently, hence adjusting the resonant frequency of a
scanning mirror incorporating the MEMS structure.
[0032] According to the techniques of the present embodiment, the
resonant frequency of a scanning mirror can be precisely controlled
through the size and location of blocks 70 and 80. For a biaxial
scanning mirror with perpendicular rotation directions (that is,
gimbal rotation axis 50 and mirror rotation axis 60), the mirror
plate 30 and the gimbal 10 usually have different resonant
frequencies. Suppose a point mass m is close to the rotation axis
of a mirror plate with a perpendicular distance from the mirror
plate rotation axis r.sub.m, but substantially away from the gimbal
axis of rotation with a perpendicular distance from the gimbal axis
of rotation, r.sub.g, which is substantially greater than r.sub.m,
that is: r.sub.g>>r.sub.m. So the moment of inertia with
respect to the mirror axis and the gimbal axis are:
J.sub.m=mr.sub.m.sup.2 (3)
J.sub.g=mr.sub.g.sup.2 (4)
respectively. If the mass m increases as m+.DELTA.m, the change in
moment of inertia .DELTA.J.sub.g=.DELTA.mr.sub.g.sup.2 will be
larger than that of .DELTA.J.sub.m=.DELTA.mr.sub.m.sup.2 since
r.sub.g>>r.sub.m. If the distance r.sub.g changes to
r.sub.g+.DELTA.r.sub.g while keeping r.sub.m unchanged, J.sub.g
will increase substantially while J.sub.m will remain
unchanged.
[0033] If the ratio of r.sub.g/r.sub.m is precisely designed, a
desirable ratio of J.sub.g/J.sub.m can be created. Using this
technique, the present embodiment is able to adjust the resonant
frequency of the mirror plate and gimbal independently.
[0034] In the exemplary embodiment of FIGS. 1A and 1B, there are
four blocks under the mirror plate 30. A pair of blocks 70 for
altering the moment of inertia with respect to the gimbal axis 50
is located adjacent the edge of mirror plate 30 and aligned with
mirror rotation axis 60. A second pair of blocks 80 for altering
the moment of inertia with respect to mirror axis 60 is also
located adjacent the edge of mirror plate 30 but is aligned with
gimbal rotation axis 50. For the block pair 80 aligned along gimbal
rotation axis 50, length and/or position adjustment in the radial
direction (towards or away from mirror axis 60), as seen in FIG.
2A, adjusts the moment of inertia of mirror plate 30 efficiently,
but does not significantly affect the gimbal moment of inertia
based on equations (3) and (4). In contrast, for the block pair 70
aligned along mirror axis 60 length and/or position adjustment in
the radial direction (towards or away from gimbal axis 50), as seen
in FIG. 2B, adjusts the moment of inertia of gimbal 10 efficiently,
but does not significantly affect the mirror plate moment of
inertia. Since radial distance rather than mass is the primary
factor to adjust the moment of inertia, the selected mass can be
relatively small. Various positions in the radial direction can
efficiently and precisely adjust the moment of inertia. The ratio
of the radial distance in block pairs 70 and 80 can be finely tuned
to create the desired mirror plate resonant frequency and gimbal
resonant frequency.
[0035] Each of the blocks in block pairs 70 and 80 can be
independently sized and/or positioned with respect to the rotation
axis that the block pair will affect. Each block in a pair need not
be the same size as the other block of the block pair, as seen in
block pair 70 in FIG. 2C. In block pair 70, one block is selected
to have a greater width than the other blocks. Using this
combination of independent size and position selection, a given
combination can control the resonant frequencies of both the mirror
plate 30 and the gimbal 10. Further, although the blocks 70 and 80
are shown as having a parallelepiped shape, other block shapes may
be selected, some of which are described below; however, the shape
of the block can be arbitrarily selected based on the desired
resonant frequency response of the system.
[0036] In the exemplary embodiment of FIG. 3, the length adjustment
of the block pairs causes the blocks to merge with each other,
forming a cross-shaped structure 75. The biaxial structure can be
adjusted by the configuration/thickness of the blocks that form the
cross. In additional, the cross structure increases the mirror
plate stiffness and reduces its dynamic deformation during
scanning.
[0037] A further exemplary embodiment is depicted in FIG. 4. In the
configuration shown in FIG. 4, there are four blocks 72, 74, 76,
and 78; the block positions are rotated away from the axes of
rotation to other angles. The selection of the angle depends on the
size of the blocks, the distance from the axes of rotation and the
desired resonant frequency. The structure depicted in FIG. 4 is no
longer axis symmetric, but is still center symmetric. The same
equations govern the adjusting method as in the above
embodiments.
[0038] A further exemplary embodiment is shown in FIG. 5. A single
pair of blocks, 92 and 94 is positioned in alignment with the
mirror axis 60. The ratio of the resonant frequency adjustment
between mirror plate 30 and gimbal 10 can be designed by adjusting
the ratio between the length and width of blocks 92 and 94. Similar
to the above embodiments, there are three methods to adjust this
ratio. Method one is adjustment in radius direction, method two is
the adjustment perpendicular to the radius direction and method
three is a combination of methods one and two as depicted in FIGS.
6A-6C. Note that although FIGS. 5 and 6 depict a pair of blocks
aligned with the mirror axis, this embodiment may alternatively use
a pair of blocks aligned along the gimbal axis. Further, as shown
in FIG. 8, blocks 92 and 94 can be rotated from an axial alignment
to any angle.
[0039] In the embodiment of FIG. 7, a pair of blocks is merged to
form a single rectangular block 100. Adjusting block 100's length
and width independently causes different changes in mirror and
gimbal resonant frequencies.
[0040] Other shapes may be used as a mass to be positioned under
the mirror plate. As seen in FIG. 9, a ring-shaped block 110 is
used to adjust the resonant frequency. To adjust the resonant
frequency, several techniques can be used. One technique adjusts
the inner radius in the radial direction, shown in FIG. 10A.
Alternatively, the ring can be separated into multiple parts, 110a
and 110b as seen in FIG. 10B, or 110a, 110b, 110c, and 110d as seen
in FIGS. 10C and 10D. When separated into multiple parts, each part
has an arc-shaped cross-section. FIG. 10C is an axis-symmetric
positioning of the ring parts while FIG. 10D is a center-symmetric
positioning of the ring parts. By adjusting the length of every
arc, the resonant frequencies of the mirror and gimbal can be
adjusted independently. Another advantage of the ring-shaped block
is that it enhances the mirror plate's stiffness and reduces its
dynamic deformation during scanning.
[0041] Alternatively, the moment-of-inertia-altering block can be
positioned under gimbal 10 as seen in FIG. 11. FIG. 11A depicts
blocks 120 arranged symmetrically with respect to the mirror axis
60 while FIG. 11B depicts blocks 120 arranged in a center-symmetric
configuration. The length and width of the blocks can also be
altered to change the resonant frequency.
[0042] In the embodiment of FIG. 12, a single
asymmetrically-positioned block 130 may be positioned on or under
either mirror plate 30 (FIG. 12A) or gimbal 10 (FIG. 12B). The size
and position of the block 130 is selected in accordance with the
desired resonant frequency.
[0043] The MEMS structures of the present embodiments are typically
fabricated from silicon using a variety of known silicon-processing
techniques. An exemplary process is depicted in FIGS. 13A-13G; this
process can fabricate a variety of block shapes and
configurations.
[0044] In FIG. 13A a silicon wafer 200 acts as the base of the
structure; an alignment mark 210 is made on the backside of the
wafer. In FIG. 13B, block(s) 220 is (are) made on the front side of
the base wafer, the shape and the height of the block(s) can be
made according to a selected design to create a desired resonant
frequency. A top silicon wafer 300 which acts as the device wafer
is bonded to the base wafer by anodic bonding through silicon oxide
400, as seen in FIG. 13C.
[0045] To create the desired MEMS device thickness, top wafer 300
is thinned by grinding or chemical-mechanical polishing as shown in
FIG. 13D. In FIG. 13E the mirror 310 and gimbal 320 shapes are
patterned by aligning the alignment mark 210 from the base wafer
200. Following patterning, the base wafer is removed to leave only
the blocks 220 as seen in FIG. 13F. Finally, in 13G, the silicon
oxide 400 is removed (except where it bonds the blocks to the
mirror plate and gimbal) to release the MEMS structure, allowing
the mirror and gimbal to rotate.
[0046] In an electrostatically-actuated MEMS structure, interleaved
electrodes have a comb-shaped structure are typically employed.
Such a structure is depicted in FIG. 14. In this structure, gimbal
10 has two sets of comb-shaped structures, one which interfaces
with a support comb structure and the other which interfaces with a
mirror plate comb structure. As seen in FIG. 14, gimbal comb
structure 12 interfaces with support comb structure 5 to deflect
gimbal 10 about gimbal axis 50. Gimbal comb structure 14 interfaces
with mirror plate comb structure 32 to deflect mirror plate 30
about mirror plate axis 60. As seen in FIG. 14, mirror plate 30 is
located in the center and supported by a pair of torsional bars 40
having one end connected to gimbal 10; the gimbal 10 again is
supported by another pair of orthogonal torsional bars 20 having
one end connected to a fixed frame 2. Mirror 30 and gimbal 10 have
comb-drives in orthogonal orientations; therefore, rotational
motion in both the x- and y-directions can be actuated. Typically
the gimbal connects to ground. With electrical isolation, signals
with different voltage amplitudes and frequencies can be applied to
the mirror and fixed frame respectively to actuate the device.
[0047] FIG. 15 schematically depicts a bar-code scanning system 500
employing a MEMS device of the present embodiment. In the scanning
system 500 a light source 510 such as a laser or LED emits light
520 which passes through focusing optics 530 and is incident on
MEMS device 540. Motion of the mirror plate, as discussed above,
scans reflected light 520 onto an image to be scanned such as bar
code 550. Reflected light 560 is collected by light collector 570,
such as a photodiode to read the image. Although the MEMS device is
shown as separate from the light source, those skilled in the art
will appreciate that the light source, light collecting element,
and MEMS device can be integrated on the same substrate. Further,
although the scanning system depicted is a bar-code reader, it is
understood that scanning system could be used in a variety of
applications, including, but not limited to, displays, projectors,
switches, printers, retinal displays, resonators, and sensors which
may or may not include a photodiode as illustrated in the above
system.
[0048] While particular embodiments of the present invention have
been illustrated and described, it is understood that the invention
is not limited to the precise construction depicted herein and that
various modifications, changes, and variations are apparent from
the foregoing description. Such modifications, changes, and
variations are considered to be a part of the scope of the
invention as set forth in the following claims.
* * * * *