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BACKGROUND OF THE INVENTION
This invention relates generally to micro-machined three-dimensional
structures, and in particular to micro-machined mirrors for use in optical
readers, such as bar code readers or scanners.
Conventional bar code scanners are used to scan a surface with a laser
beam. Conventional bar code scanners further typically utilize mirrors
that are oscillated to permit the laser beam to scan. Conventional mirrors
for bar code scanners are relatively large and imprecise.
In order to manufacture smaller and more precise bar code mirrors,
micro-machining processes have been used in which a silicon substrate is
micro-machined to produce a mirror. However, conventional micro-machined
mirrors and their manufacturing processes suffer from a number of
limitations. Prior art micro-machined mirrors do not provide appropriate
compliance in all directions of the movement of the mirror. Such mirrors
typically are not sufficiently shock resistant or able to operate over
wide ranges of temperature over extended use.
Various known devices include a dual axis mode of operation whereby a
mirror is rotated about a primary and a secondary axis. The typical
device, however, requires a dual gimbaled structure having a gimbaled
mirror coupled to a gimbaled support structure. The use of multiple gimbal
couplings suffers from high cost and complex manufacturing. Typical
devices attempting dual axis operation utilizing typical single point
gimbal would suffer from component fatigue due to high material stress
associated with the gimbal bending movements that result from rotational
movement of the mirror about a secondary axis. Also, these single-gimbal
dual axis devices typically suffer from compromised performance in terms
of limited degree of rotational angle about the secondary axis per unit of
driving force (e.g. electrostatic or magnetic).
The present invention provides micro-machined mirror devices which overcome
one or more limitations of the existing micro-machined devices.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a mirror assembly is
provided that includes a mass having having a first axis and a second
axis, a pair of T-shaped hinges attached to a support structure supporting
said mass, each T-shaped hinge having a first leg member attached to the
mass and a T-member attached to the leg and to the support structure at
opposite ends of the T-member, said T-member and leg member capable of
torsional and translational movement, and at least two devices operatively
associated with the mass and located to apply force to the mass, the
capable of rotating the mass about the to rotate the mass about the first
and second axes.
According to another aspect of the present invention, a method is provided
for supporting a mass. The method includes supporting the mass with a pair
of T-shaped hinges attached to a support structure, each T-shaped hinge
having a first leg member attached to the mass and a T-member attached to
the leg and to the support structure at opposite ends of the T-member,
said T-member and leg member capable of torsional and translational
movement, oscillating the mass about a first axis with at least two
devices capable of applying force to the mass, and oscillating the mass
about a second axis with the at least two devices.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross section view of a laser scanning device according to the
present invention.
FIG. 2 is a schematic side view of a preferred embodiment of the mirror
assembly of FIG. 1.
FIG. 3 is a top view of the top cap of the mirror assembly of FIG. 2.
FIG. 4 is a cross-sectional view of the top cap of FIG. 3.
FIG. 5 is a cross-sectional view of the top cap of FIG. 3.
FIG. 6 is a top view of the mirror of the mirror assembly of FIG. 2.
FIG. 6A is a top view of an alternative embodiment of the hinge of the
mirror assembly of FIG. 2.
FIG. 6B is a top view of an alternative embodiment of the hinge of the
mirror assembly of FIG. 2.
FIG. 6C is a top view of an alternative embodiment of the hinge of the
mirror assembly of FIG. 2.
FIG. 6D is a top view of an alternative embodiment of the mirror of the
mirror assembly of FIG. 2.
FIG. 7 is a cross-sectional view of the mirror of FIG. 6.
FIG. 8 is a cross-sectional view of the mirror of FIG. 6.
FIG. 9 is a bottom view of the mirror of FIG. 6.
FIG. 10 is a top view of the bottom cap of the mirror assembly of FIG. 2.
FIG. 11 is a cross-sectional view of the bottom cap of FIG. 10.
FIG. 12 is a cross-sectional view of the bottom cap of FIG. 10.
FIG. 13 is a top view of the base member of the mirror assembly of FIG. 2.
FIG. 14 is a cross-sectional view of the base member of FIG. 13.
FIG. 15 is a cross-sectional view of the base member of FIG. 13.
FIG. 16 is a top view of the top cap and mirror of the mirror assembly of
FIG. 2.
FIG. 17 is a top view of the bottom cap and base member of the mirror
assembly FIG. 2.
FIG 18 is a cross-sectional view of the mirror assembly of FIG. 16
illustrating the oscillation of the mirror collection plate.
FIG. 19 is a view of the mirror assembly of FIG. 18 illustrating the use of
tapered surfaces to minimize clipping of the laser light.
FIGS. 20A-20B show embodiments of the present invention capable of dual
axis operation.
FIGS. 21A-21C are schematic representations of a mirror in dual axis
operation.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A mirror assembly for use in a bar code reader is provided. The mirror
assembly preferably includes a micro-machined three-dimensional mirror
supported generally by a pair of "T" shaped hinges in a support structure.
The mirror assembly further preferably includes one or more travel stops
for limiting the movement of the mirror. The mirror assembly further
preferably includes one or more tapered edge surfaces and cut-outs for
minimizing clipping of incident and reflected laser beams.
FIG. 1 is a cross section view of a laser scanning device such as a bar
code scanner 100 having a light beam 115 that emanates from the device to
strike a target 120. The light beam is reflected or scattered by the
target 120. The bar code scanner 100 includes a laser beam source 105 and
a mirror assembly 110. During the operation of the bar code scanner 100,
the optically reflective portion 111 of the mirror assembly 110 is
preferably oscillated to permit the laser beam 115 to scan a surface, such
as a bar code symbol 120, by reflecting the laser beam 115 off of the
optically reflective portion 111 of the mirror assembly 110. The reflected
light 125 enters the bar code scanner 100 through a window 165 and is
detected by a light detector 160. The laser beam source 105 may comprise
any number of conventional commercially available devices to generate the
laser beam 115.
The bar code scanner 100 may include additional features for user
interface, control and data processing. These features may comprise a
processor 130 and memory device 135 as part of a central processing unit
140, a controller 145 for generating voltage used to oscillate the mirror
110, a data entry device such as a keypad 150 and a data display device
such as a liquid crystal display 155. The mirror assembly 110 made
according to the present invention is described below in reference to
FIGS. 2-19.
Referring to FIG. 2, in a preferred embodiment, the mirror assembly 110
includes a top cap 205, a mirror 210, a bottom cap 215, and a base member
220. The top cap 205 includes an opening that permits the laser beam 115
to reflect off of the mirror 210. In this manner, the mirror 210 is
surrounded and protected by the top cap 205 and the bottom cap 215. The
sub-assembly that includes the top cap 205, mirror 210 and bottom cap 215
is formed and then mounted onto the base member 220.
The top cap 205 and bottom cap 215 may be fabricated from any number of
conventional commercially available materials such as, for example,
silicon glass, ceramic or plastic. In a preferred embodiment, the top cap
205 is fabricated by micro-machining a silicon wafer.
FIGS. 3-5 show various views of a preferred embodiment of the top cap 205
which has a frame 301 that includes a top, bottom, left and right support
members 305, 315, 325 and 335. Top and bottom travel stop members 310 and
320 are coupled respectively to the top and bottom support members 305 and
315. The left and right support members 325 and 335 include corresponding
left and right rim cutouts 330 and 340 for minimizing clipping of the
incident light.
The top cap frame 301 provides an overall support structure for the top cap
205. The thickness of the frame 301 may range, for example, from about 400
to 600 microns with a preferred thickness ranging from about 390 to 400
microns in order to provide a compact structure having a low mass.
The top travel stop 310 preferably limits the motion of the reflective
portion of the mirror 210 in the direction normal to the plane of the
reflective portion of the mirror 210 (the Z-direction). The top travel
stop 310 preferably extends in substantially orthogonal direction from the
top support member 305. In a preferred embodiment, the top travel stop 310
is positioned within the plane of the top support member 305. The
thickness of the top travel stop 310 may range, for example, from about
340 to 580 microns. In a preferred embodiment, the thickness of the top
travel stop 310 ranges from about 350 to 380 microns in order to provide
optimum shock protection, freedom of motion, and a compact structure
having a low mass.
Referring to FIG. 4, in a particularly preferred embodiment, the bottom
surface 310b of the top travel stop 310 is recessed below the level of the
bottom surface 305b of the top support member 305. In this manner, the
bottom surface 310b of the top travel stop 310 is preferably positioned
above the level of the reflective surface of the mirror 210. The length of
the top travel stop member 310 may range, for example, from about 800 to
2800 microns. In a preferred embodiment, the length of the top travel stop
member 310 ranges from about 2000 to 2500 microns. In a particularly
preferred embodiment, the length of the top travel stop member 310 is
selected to overlap with the mirror collection plate 610 of the mirror by
about 300 microns.
The bottom travel stop 320 extends in a substantially orthogonal direction
from the bottom support member 315 and is substantially identical to the
top travel stop 310. An opening 345 permits light to reflect off of the
reflective surface of the mirror 210. The opening 345 preferably includes
a left rim cut out 330 and a right rim cut out 340. The left and right rim
cut outs, 330 and 340, are preferably positioned on opposite sides in
surrounding relation to the reflective surface of the mirror 210. In this
manner, the left and right rim cut-outs, 330 and 340, provide optical
access to the reflective surface of the mirror 210.
In a preferred embodiment, the top cap frame 301, travel stops 310 and 320,
rim cut outs 330 and 340, and the opening 345 all include tapered edges,
350A and 350B, to facilitate optical access to the reflective surface of
the mirror 210 (FIG. 5). The taper angle of the tapered edges, 350A and
350B, preferably ranges from about 50 to 60 degrees in order to optimally
facilitate the reflection of laser light transmitted at an angle towards
the edge portions of the reflective surface of the mirror 210.
FIG. 6 shows a top view of a mirror or mirror assembly 210 made according
to one embodiment of the present invention. The mirror 210 includes a
frame or mirror support structure 600 having support members 602, 604, 606
and 608. The mirror 210 further comprises a mirror collection plate 610
with a reflective surface 628, a top T-shaped hinge 612, a bottom T-shaped
hinge 614, a top left travel stop finger 616, a top right travel stop
finger 618, a bottom left travel stop finger 620, a bottom right travel
stop finger 622, an opening 624, a conductive layer 626, and a reflective
surface 628.
The mirror frame 600 provides the overall support structure for the mirror
210. The thickness of the frame 600 may range, for example, from about 400
to 600 microns with a preferred thickness ranging from about 400 to 450
microns in order to provide a compact structure having a low mass. In a
preferred embodiment, the support members 602, 604, 606, and 608 provide
effective beam lengths ranging from about 500-2500 microns and cross
sections of about 8,000 microns.sup.2 to 160,000 microns.sup.2 in order to
optimally absorb shock loads of about 2000g/0.5 mS half sine wave input.
The mirror collection plate 610 is coupled to the top T-shaped hinge 612
and the bottom T-shaped hinge 614. In this manner, the mirror collection
plate 610 rotates about the axis 630 i.e. has torsional movement about
such axis. In a preferred embodiment, the axis 630 is positioned
substantially along the centerline of the mirror collection plate 610 and
is coincident with the center of the T-shaped hinges, 612 and 614, thereby
providing a common axis of rotation for the springs. The reflective
surface 628 is coupled to the top 632 of the mirror collection plate 610.
In this manner, rotation of the mirror collection plate 610 about the axis
630 causes laser light from a stationary laser to reflect off of the
reflective surface 628 in a plurality of directions.
The thickness of the mirror collection plate 610 may range, for example,
from about 100 to 600 microns with a preferred thickness ranging from
about 100 to 250 microns to provide a low mass and maximize the effective
natural frequency of the mirror 210.
The reflective surface 628 may be comprised of any number of conventional
commercially available optically reflective surfaces such as, for example,
gold, silver or aluminum. In a preferred embodiment, the reflective
surface 628 comprises gold in order to optimize the amount of optical
energy that is reflected. In a preferred embodiment, the surface roughness
of the reflective surface 628 is less than about 0.1 wavelengths of the
reflected light in order to optimize the amount of optical energy that is
reflected.
The FIGS. 7 and 8 show cross-sectional views of the mirror of FIG. 6 and
FIG. 9 shows a bottom view of the mirror of FIG. 6. As illustrated in
FIGS. 7-9, in a preferred embodiment, the bottom 634 of the mirror
collection plate 610 includes a top travel stop 710, a bottom travel stop
715, and a cavity 720. The top travel stop 710 extends from the bottom 634
of the mirror collection plate 610. The top travel stop 710 preferably
limits movement of the mirror collection plate 610 in the z-direction. The
top travel stop 710 preferably extends from the bottom 634 of the mirror
collection plate 610 in a substantially orthogonal direction. The top
travel stop 710 may extend from the bottom 634 of the mirror collection
plate 610 for a distance ranging, for example, from about 200 to 400
microns with a preferred distance ranging from about 200 to 250 microns to
optimally limit movement of the mirror collection plate 610. In a
preferred embodiment, the top travel stop 710 is centered about the axis
630 and is positioned adjacent to and on one side of the cavity 720. The
bottom travel stop 715 is preferably identical to the top travel stop 710
described above.
The cavity 720 extends into the bottom of the mirror collection plate 610,
which reduces the mass of the mirror collection plate 610. In this manner,
the droop of the mirror 210 is reduced. In a preferred embodiment, the
depth and volume of the cavity 720 ranges from about 200 to 500 microns
and 8.times.10.sup.6 to 1.times.10.sup.9 microns..sup.3 In a preferred
embodiment, the cavity 720 is centrally positioned along the axis 630 and
within the back side 634 of the mirror collection plate 610.
For typical bar code scanner applications, the rotational accuracy of the
laser beam may be required to be within 1.3.degree. when the mirror
collection plate 610 is subjected to an across-the-hinge self-induced
gravity torque. Where torque T=mg*h/2, with mg=mirror collection plate
weight and h=mirror collection plate thickness. The mirror accuracy is a
function of the pointing accuracy and mirror droop. The torsional spring
constant K.sub.r of the T-shaped hinges, 612 and 614, is determined by the
resonant frequency F of the mirror collection plate 610 and the size and
mass of the mirror collection plate 610. The mirror tilt angle .theta. due
to a gravity torque is determined by the relation, .theta.=T/K.sub.r.
Consequently, the thickness and mass of the mirror collection plate 610,
are preferably selected to provide a mirror tilt angle less than
1.3.degree.. In a preferred embodiment, the thickness and mass of the
mirror collection plate 610 are reduced by reducing the thickness of the
mirror collection plate 610 and by providing one or more cavities in the
mirror collection plate 610.
The top T-shaped hinge 612 is coupled to the left support member 606, the
right support member 608, and the top portion of the mirror collection
plate 610. The top T-shaped hinge 612 preferably includes a vertical
support member 644 (beam or leg) and a second or horizontal support member
646 (T-member). The horizontal support member 646 preferably is supported
at opposite ends by the left support member 606 and the right support
member 608. In a preferred embodiment, the horizontal support member 646
is substantially orthogonal to both the left support member 606 and the
right support member 608. The vertical support member 644 is coupled to
the horizontal support member 646. In a preferred embodiment, the vertical
support member 644 is substantially orthogonal to the horizontal support
member 646. The vertical support member 644 is coupled to the mid-point of
the horizontal support member 646. The vertical support member 644 is
positioned along the axis 630. The length, width and thickness of the
vertical support member 644 may range, for example, from about 100 to 2500
microns, 2 to 100 microns and 2 to 100 microns, respectively. In a
preferred embodiment, the length, width and thickness of the vertical
support member 644 range from about 800 to 1000 microns, 8 to 15 microns
and 8 to 15 microns, respectively. The torsional spring constant of the
vertical support member 644 may range, for example, from about
2.times.10.sup.-9 to 10.times.10.sup.-7 lbf-ft/radian. In a preferred
embodiment, the torsional spring constant of the vertical support member
644 ranges from about 2.times.10.sup.-8 to 10.times.10.sup.-8
lbf-ft/radian. The length, width and thickness of the horizontal support
member 646 may range, for example, from about 500 to 4500 microns, 6 to
100 microns and 6 to 100 microns, respectively. In a preferred embodiment,
the length, width and thickness of the horizontal support member 646 range
from about 2200 to 2500 microns, 15 to 25 microns and 15 to 25 microns,
respectively.
The bottom T-shaped hinge 614 is coupled to the left support member 606,
the right support member 608, and the bottom portion of the mirror
collection plate 610. The bottom T-shaped hinge 614 has the same structure
as the top T-shaped hinge 612.
Other embodiments of a T-shaped hinge according to the present invention,
as illustrated in FIGS. 6A-6C, provide enhanced sensitivity for sensing
acceleration loading conditions. In FIG. 6A, a T-shaped hinge 612A
includes a vertical support member 644A having a serpentine shape and a
horizontal support member 646A having a substantially linear shape. In
FIG. 6B, an alternative embodiment of a T-shaped hinge 612B includes a
vertical support member 644B coupled to a horizontal support member 646B
at location that is off-center. In FIG. 6C, one or both of the T-shaped
hinges 612 and 614 are modified to include a T-shaped hinge 612C having a
vertical support member 644C that intersects a horizontal support member
646C at an acute angle and is also coupled to the horizontal support
member 646C at location that is off-center.
The top left travel stop 616 extends from and is coupled to the top left
portion of the mirror collection plate 610. The top left travel stop 616
preferably limits the motion of the mirror collection plate 610 in the
x-direction. The top left travel stop 616 preferably is positioned in the
plane of the mirror collection plate 610. In a preferred embodiment, the
top left travel stop 616 extends from the mirror collection plate 610 in a
substantially orthogonal direction. The thickness of the top left travel
stop 616 may range, for example, from about 200 to 600 microns. In a
preferred embodiment, the thickness of the top left travel stop 616 ranges
from about 250 to 350 microns in order to optimally provide shock
protection, and a resilient compact structure having a low mass. The
length of the top left travel stop 616 may range, for example, from about
500 to 2000 microns. In a preferred embodiment, the length of the top left
travel stop 616 ranges from about 900 to 100 microns. In a particularly
preferred embodiment, the top surface of the top left travel stop 616 is
planar with the top surface of the mirror collection plate 610. In a
particularly preferred embodiment, the bottom surface of the top left
travel stop 616 is planar with the bottom surface of the mirror collection
plate 610.
The top right and bottom left and right travel stops 618, 620 and 622 are
substantially identical to the top left travel stop 616. These travel
stops are positioned in corresponding locations about the mirror
collection plate 610.
The travel stops, 616, 618, 620 and 622, preferably provide overswing and
x-axis shock protection for the mirror collection plate 610 during
manufacturing and operation. In a preferred embodiment, the travel stops
616, 618, 620, and 622 are formed as integral parts of the mirror
collection plate 610. In a preferred embodiment, the travel stops 616,
618, 620, and 622 provide effective beam lengths greater than about 500
microns and cross sections of about 40,000 microns.sup.2 to 240,000
microns.sup.2 in order to optimally absorb shock loads of about 2000g/0.5
mS half sine wave input.
The opening 624 preferably permits the mirror collection plate 610 to
rotate about the axis 630. The walls 636 of the opening 624 preferably
limit movement of the mirror collection plate 610 in the x-direction and
the y-directions. The opening 624 preferably includes a top section 638, a
middle section 640, and a bottom section 642. The top section 638 of the
opening 624 preferably contains the top T-shaped hinge 612 and the top
left and right travel stops, 616 and 618. The middle section 640 of the
opening 624 preferably contains the mirror collection plate 610. The
bottom section 642 of the opening 624 preferably contains the bottom
T-shaped hinge 614 and the bottom left and right travel stops, 620 and
622.
The walls of the middle section 640 of the opening 624 may be spaced apart
from the opposing edges of the mirror collection plate 610 by a distance
ranging, for example, from about 30 to 150 microns. In a preferred
embodiment, the walls of the middle section 640 of the opening 624 are
spaced apart from the opposing edges of the mirror collection plate 610 by
a distance ranging from about 60 to 100 microns in order to optimally
minimize movement of the mirror collection plate 610 in the x and y
directions. In a preferred embodiment, the gap in the x-direction is
different from the gap in the y-direction in order to optimally protect
the mirror collection plate 610 from shocks. In a preferred embodiment,
the gap between the mirror collection plate 610 and the middle section 640
of the opening 624 provides a spacing in the y-direction ranging from
about 15 to 45 microns and a spacing in the x-direction ranging from about
50 to 180 microns in order to optimally limit shock loads on the mirror
collection plate 610.
The conductive layer 626 is preferably coupled to the outer periphery of
the top surface of the mirror 210. The conductive surface 626 preferably
provides a conductive electrical path. The conductive layer 626 may be
fabricated from any number of conventional commercially available
materials such as, for example, gold, aluminum, or silver. In a preferred
embodiment, the conductive layer 626 is fabricated from gold. In a
preferred embodiment, the conductive layer 626 is bonded to the underlying
substrate by an intermediate layer of titanium.
The mirror 210 may be fabricated from any number of conventional
commercially available materials such as, for example, silicon, plated
metal or plastic. In a preferred embodiment, the mirror 210 is fabricated
by micro-machining a silicon wafer using any one, or combination, of the
known micro-machining processes.
In a preferred embodiment, the released and free-standing mirror collection
plate 610 is connected to the surrounding support frame, 600 by the
T-shaped hinges, 612 and 614. In a preferred embodiment, the travel stop
fingers, 616, 618, 620 and 622, provide overswing protection for the
mirror collection plate 610. In a preferred embodiment, a 200-micron deep
anisotropic deep reactive ion etching (DRIE) process is used to form very
precise, narrow gaps for X-axis shock protection and Y-axis shock
protection, where the mirror collection plate 610 is preferably completely
confined within the frame, 602, 604, 606 and 608, for X-axis and Y-axis
translational or planar motion i.e. in the planes of the mirrored surface.
Persons having ordinary skill in the art and the benefit of the present
disclosure will recognize that the term DRIE refers to deep reactive ion
etching of a substrate. In a preferred implementation, the DRIE process is
provided substantially as disclosed in U.S. Pat. Nos. 5,498,312 and
5,501,893, which are incorporated herein by reference. The T-shaped
hinges, 612 and 614, preferably provide the collection plate 610 with
optimal translational motion in X-axis and Y-axis directions, in which the
mirror collection plate 610 is shock-stopped by the frame, 602, 604, 606
and 608, while also simultaneously maintaining low stress levels within
the T-shaped hinges, 612 and 614, to avoid fracture. In a preferred
embodiment, the T-shape hinges, 612 and 614, are relatively compliant in
the X-axis and Y-axis directions, while they are sufficiently rigid for
rotational motion about the axis 630 for establishing the resonant
frequency of the mirror collection plate 610.
Thus, in a preferred embodiment of the present invention, the mirror
collection plate 610 is supported and suspended by a pair of hinges 612
and 614. These hinges permit torsional movement or rotation of the mirror
collection plate 610 about the common hinge axis 630 and movement of the
mirror collection in each of the x, y and z direction. The gap or space
648 between the mirror plate 610 and the frame 601 in the y-direction
permits movement of the mirror collection plate 610 in the y-direction
while the spacing 611 between the stops 616, 618, 620 and 621 and the
frame 601 permit movement in the x-direction. The gap 647 provides a hinge
compliance in the y-direction. The movements in the x and y directions are
sometimes referred to the planar or translational movements and the hinges
as springs. The beams 644 and 628 also permit the mirror collection plate
610 to move in the z-direction. The T-hinges provide the necessary
compliance to the mirror collection plate motion in the y-direction, which
improves the shock tolerance of the hinge to y-axis shock loads generated
by the mirror collection plate 610. Prior art typically utilizes a
straight-beam hinge, i.e. a beam connected to the frame without a
T-member, such as the member 646. Such straight-beam hinges tend to buckle
and fracture due to y-axis shock loads. Also, the beams or legs 644 and
648 of the T-hinges 612 and 614 move up in the z-direction due to shock
loads. The members 646 and 650 can torsionally rotate, which reduces the
stress induced in the 644 and 648 members of the hinges, which stress has
been found to be less than the stress induced in the straight-beam hinges.
The amount of stress reduction is a function of the "aspect ratio" of the
hinges 612 and 614, which is a ratio of the width/thickness.
As illustrated in FIGS. 7-9, the mirror 210 preferably includes portions,
602, 604, 606 and 608, that are full-wafer thickness (e.g., 400 microns),
and portions, 610, that are half-wafer thickness (e.g., 200 microns). The
cavity 720 in the center of the mirror collection plate 610 is preferably
etched 150-microns down from the bottom surface 634 of the mirror
collection plate 610, and the T-shape hinges, 612 and 614, are preferably
about 8-15 microns thick. The half-thickness mirror collection plate 610
reduces the amount of deep reactive ion etching (DRIE) and also improves
the position accuracy of the mirror collection plate 610. The cavity 720,
preferably etched in the center of the mirror collection plate 610, is
preferably primarily used to improve the position accuracy of the mirror
collection plate 610 and reduce the mass of the mirror collection plate
610 without substantially altering the resonant frequency.
The backside of the mirror collection plate 610 preferably includes the Z
travel-stops, 710 and 715, that preferably are full-wafer thickness (e.g.,
400-microns). Since the mirror collection plate 610, is preferably
200-microns thick, the thicker travel-stops, 710 and 715, optimally
maintain the 50-micron gap with the travel-stop fingers, 1010 and 1020, of
the bottom cap 215 and, therefore, help provide shock protection in the
Z-direction. A mirror collection plate 610 having minimum x-y plane
dimensions of about 3-mm.times.3-mm is preferred.
In an alternative embodiment, as illustrated in FIG. 6D, the left and right
support members, 606 and 608, of the mirror 210 further include cut-outs,
660A and 660B, positioned on opposite sides of the mirror collection plate
610. In this manner, the amount of viscous damping due to the resistance
to the passage of air between the mirror collection plate 610 and the left
and right support members, 606 and 608, is reduced. In this manner, the
frequency response characteristics of the mirror 210 are enhanced.
As illustrated in FIGS. 10-12, the bottom cap 215 includes a bottom cap
frame 1000 to provide support for the bottom cap. The frame 1000 includes
support members and top and bottom travel stop members as described above
for the top cap and shown in FIG. 3. The bottom cap further comprises an
upper left beam 1035, an upper right beam 1040, a lower left beam 1045, a
lower right beam 1050, a top conductive surface 1055, a bottom conductive
surface 1060, and an opening 1065.
The thickness of the bottom cap frame 1000 may range, for example, from
about 400 to 600 microns with preferred thickness ranging from about 400
to 450 microns to provide a compact structure having a low mass.
The top travel stop member 1010 preferably limits the motion of the
reflective portion of the mirror 210 in the z-direction. The top travel
stop member 1010 preferably extends in a substantially orthogonal
direction from the top support member 1005. In a preferred embodiment, the
top travel stop member 1010 is positioned within the plane of the top
support member 1005. The thickness of the top travel stop member 1010 may
range, for example, from about 350 to 550 microns. In a preferred
embodiment, the thickness of the top travel stop 1010 ranges from about
350 to 380 microns in order to provide a compact structure having a low
mass. In a particularly preferred embodiment, the top surface 1010A of the
top travel stop member 1010 is recessed below the level of the top surface
1005A of the top support member 1005. In this manner, the top surface
1010A of the top travel stop 1010 is preferably positioned below the level
of the mirror collection plate 610 of the mirror 210. The length of the
top travel stop member 1010 may range, for example, from about 1200 to
2800 microns. In a preferred embodiment, the length of the top travel stop
member 1010 ranges from about 2000 to 2500 microns. In a particularly
preferred embodiment, the length of the top travel stop member 1010 is
selected to overlap with the mirror collection plate 610 of the mirror by
about 300 microns.
The bottom travel stop member 1020 preferably extends in a substantially
orthogonal direction from the bottom support member 1015. The bottom
travel stop member 1020 is otherwise substantially identical to the
above-described top travel stop member 1010.
The upper left beam 1035 preferably provides support and limits the motion
of the mirror collection plate 610 of the mirror 210 in the z-direction
during the manufacturing process. In this manner, defective mirrors 210
are protected from shock, catastrophic failure and from falling into the
process equipment during the manufacturing process. The upper left beam
1035 preferably extends is a substantially orthogonal direction from the
left support member 1025. In a preferred embodiment, the upper left beam
1035 is positioned within the plane of the left support member 1025. The
thickness of the upper left beam 1035 may range, for example, from about
150 to 250 microns. In a preferred embodiment, the thickness of the upper
left beam 1035 ranges from about 200 to 220 microns in order to optimally
provide a compact structure having a low mass. In a particularly preferred
embodiment, the top surface of the upper left beam 1035 is recessed below
the level of the top surface 1025A of the left support member 1025. In
this manner, the top surface of the upper left beam 1035 is preferably
positioned below the level of the top left travel stop member 616 of the
mirror 210. The length of the upper left beam 1035 may range, for example,
from about 1500 to 2200 microns. In a preferred embodiment, the length of
the upper left beam 1035 is about 1800 microns.
The upper right and lower left and right beams 1040, 1045 and 1050 are
substantially identical to the upper left beam 1035. These beams are
positioned within the plane of corresponding support members.
The top conductive surface 1055 is preferably coupled to the outer
periphery of the top surface of the bottom cap 215. The top conductive
surface 1055 preferably provides a conductive electrical path. The top
conductive surface 1055 further preferably provides a bonding ring for
subsequent compression bonding of the bottom cap 215 to the mirror 210.
The top conductive surface 1055 may be fabricated from any number of
conventional commercially available materials such as, for example, gold,
aluminum, or silver. In a preferred embodiment, the top conductive surface
1055 is fabricated from gold. In a preferred embodiment, the top
conductive surface 1055 is bonded to the bottom cap 215 using an
intermediate layer of titanium. The bottom conductive surface 1060 is
preferably coupled to the outer periphery of the bottom surface of the
bottom cap 215 and is otherwise substantially identical to the top
conductive surface 1055.
In a preferred embodiment, the conductive surfaces 1055 and 1060
conformally coat all of the exposed surfaces of the bottom cap 215.
The opening 1065 preferably permits the drive pad electrodes, 1310 and
1315, of the base member 220 to electrostatically drive and capacitatively
sense the position of the mirror collection plate 610 of the mirror 210.
The opening 1065 preferably comprises a substantially rectangular opening
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