U.S. patent application number 12/103333 was filed with the patent office on 2008-09-11 for method of repairing micromirrors in spatial light modulators.
This patent application is currently assigned to TEXAS INSTRUMENTS INCORPORATED. Invention is credited to Michel Combes, James Dumphy, Satyadev Patel, Peter Richards.
Application Number | 20080218842 12/103333 |
Document ID | / |
Family ID | 36931713 |
Filed Date | 2008-09-11 |
United States Patent
Application |
20080218842 |
Kind Code |
A1 |
Patel; Satyadev ; et
al. |
September 11, 2008 |
Method of Repairing Micromirrors in Spatial Light Modulators
Abstract
Disclosed herein is method of operating a device that comprises
an array of micromirrors. The method comprises a process usable for
repairing stuck micromirrors of the micromirror array during the
operation. The reparation process applies, at the ON state, two
consecutive refresh voltages to the mirror plates of the
micromirrors in the array with the pulses being separated in time
longer than the characteristic oscillation time of the
micromirrors. The reparation process can be applied independently
to the micromirrors. Alternatively, the reparation process can be
incorporated with a bias inversion process.
Inventors: |
Patel; Satyadev; (Sunnyvale,
CA) ; Dumphy; James; (San Jose, CA) ;
Richards; Peter; (San Francisco, CA) ; Combes;
Michel; (Dallas, TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
US
|
Assignee: |
TEXAS INSTRUMENTS
INCORPORATED
Dallas
TX
|
Family ID: |
36931713 |
Appl. No.: |
12/103333 |
Filed: |
April 15, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11069408 |
Feb 28, 2005 |
7375873 |
|
|
12103333 |
|
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Current U.S.
Class: |
359/291 |
Current CPC
Class: |
G02B 26/0841
20130101 |
Class at
Publication: |
359/291 |
International
Class: |
G02B 26/08 20060101
G02B026/08 |
Claims
1-20. (canceled)
21. A method of operating a device comprising an array of
micromirrors each comprising a deflectable mirror plate and an
addressing electrode, the method comprising: applying a bias
voltage to the mirror plates and a set of voltages to the
addressing electrodes during a sequence of color field periods; and
applying first refresh voltage pulse to the mirror plates during a
spoke period intervening two adjacent color field periods.
22. The method of claim 21, further comprising: applying the bias
voltage to the mirror plate and a voltage to the addressing
electrode associated with said mirror plate such that the mirror
plate is rotated to an ON state angle of 10.degree. degrees or more
from a non-deflected state, wherein the difference between said two
voltages is 30 volts or more.
23-26. (canceled)
27. The method of claim 21, further comprising: performing a
reparation process that comprises the first and a second refresh
voltage following the first voltage pulses for the micromirrors,
wherein the first and second refresh voltage pulses are spaced in
time longer than the intrinsic oscillation time of the
micromirror.
28. The method of claim 27, wherein the reparation process further
comprises: adjusting the bias voltage and the voltages on the
addressing electrodes such that the micromirrors are expected to be
in the OFF state; and applying the first and second refresh voltage
pulses to repair a stuck micromirror in the ON state.
29. The method of claim 28, wherein the reparation process is
performed at most once during each frame period of a sequence of
frames.
30. The method of claim 27, wherein the reparation process is
performed either during selected frames of the sequence of frames
or during a spoke time period intervening two of a sequence of
color field period.
31-33. (canceled)
34. The method of claim 21, wherein the polarization of the first
refresh voltage pulse is opposite to the polarity of the bias
voltage.
35. The method of claim 21, wherein the mirror plate comprises a
metallic reflecting layer and a non-metallic layer, and each mirror
plate is attached to a deformable hinge that comprises an electric
conductive layer and a non-metallic layer; and wherein the
deformable hinge deforms under the refresh voltage pulses so as to
produce a restoration energy when the mirror plate is at the OFF
state.
36. (canceled)
37. The method of claim 21, further comprising: changing the bias
voltage from first value to second value, wherein the micromirror
is expected to be at the OFF state with the second value of the
bias voltage; maintaining the bias voltage at the second value for
a transition time period where the mirror plates at the ON state
are expected to be at the OFF state; and performing the reparation
process during said transition time period.
38. The method of claim 27, wherein the reparation process lasts
for a time period selected from the group consisting of 10
microseconds or less and 1 microsecond or less.
39. (canceled)
40. A method of operating a device comprising an array of
micromirrors each comprising a deflectable mirror plate and an
addressing electrode, the method comprising: switching the
micromirrors between an ON and OFF state with first bias voltage
and a set of voltages on the addressing electrodes; and applying
first and second refresh voltage pulses to the micromirrors,
wherein the first and second refresh voltage pulses are spaced in
time longer than the intrinsic oscillation time of the
micromirrors.
41. The method of claim 40, wherein the step of switching the
micromirrors between the ON and OFF states further comprises:
applying a bias voltage to the mirror plates of the micromirrors
and a set of voltages to the addressing electrodes, wherein the
voltages on the addressing electrodes are determined according to a
set of image data produced from an image using a
pulse-width-modulation technique.
42. The method of claim 41, further comprising: applying the bias
voltage to the mirror plate and a voltage to the addressing
electrode associated with said mirror plate such that the mirror
plate is rotated to an ON state angle of 10.degree. degrees or more
from a non-deflected state, wherein the difference between said two
voltages is 30 volts or more.
43. The method of claim 42, wherein the ON state angle is
12.degree. degrees or more relative to the non-deflected state.
44. The method of claim 42, further comprising: adjusting at least
one of the applied bias voltage and the voltage on the addressing
electrode such that the voltage difference between the mirror plate
and addressing electrode is 17 volts or less.
45. The method of claim 42, wherein the voltage on the addressing
electrode changes 10 volts or more when the mirror plate switches
between the ON and OFF states.
46. The method of claim 45, wherein the change of the voltage on
the addressing electrode is from 13 to 25 volts when the mirror
plate switches between the ON and OFF states.
47. The method of claim 40, wherein the step of applying a set of
refresh voltage pulses further comprises: performing a reparation
process that comprises first and second refresh voltage pulses for
the micromirrors, wherein the first and second refresh voltage
pulses are spaced in time longer than the intrinsic oscillation
time of the micromirror.
48. The method of claim 47, wherein the reparation process further
comprises: adjusting the bias voltage and the voltages on the
addressing electrodes such that the micromirrors are expected to be
in the OFF state; and applying the first and second refresh voltage
pulses to repair a stuck micromirror in the ON state.
49-79. (canceled)
80. A computer readable medium comprising computer executable
instructions for performing the method of claim 21.
81. A computer readable medium comprising computer executable
instructions for performing the method of claim 40.
82. (canceled)
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention is related generally to the art of
spatial light modulators having micromirror arrays, and more
particularly, to a method and an apparatus for operating the
micromirror array of the spatial light modulator in producing
videos.
BACKGROUND OF THE INVENTION
[0002] Microstructures, such as micromirror devices, have found
many applications in basic signal transduction. For example, a
spatial light modulator based on micromirror device steers light in
response to electrical or optical signals. Such a modulator can be
a part of a communication device or an information display.
[0003] A major factor that limits the reliability and widespread
use of micromirror devices is adhesion. Adhesion is a result of the
dominance of surface and interfacial forces, such as capillary,
chemical bonding, electrostatic, and van der Waals forces, over
mechanical forces which tend to separate micromirror device
components. When mechanical restoring forces cannot overcome
adhesive forces, the micromirror devices are said to suffer from
stiction. Stiction failures in contacting micromirror devices, can
occur after the first contacting event (often referred to as
initial stiction), or as a result of repeated contacting events
(often referred to as in-use stiction). Initial stiction is often
associated with surface contamination (e.g., residues of bonding
materials or photoresist), or with high energy of contacting
surfaces (e.g., clean oxidized silicon or metallic surfaces). For
the case of in-use stiction, each time one part of the micromirror
(e.g. mirror plate of a micromirror device) touches the other (e.g.
stopping mechanism) or the substrate, the contact force grows and
ultimately becomes too large for the restoring force to overcome.
In this case, the device remains in one state indefinitely. This
phenomenon can arise from a variety of underlying mechanisms, such
as contact area growth, creation of high-energy surface by
micro-wear, surface charge separation etc.
[0004] The stiction of the micromirrors often exhibits dynamic
characters. For example, the stiction in a micromirror can vary
over time, and the restoration force necessary to overcome the
stiction in the same micromirror may also vary over time. In a
micromirror array device, such as a micromirror-based spatial light
modulator, the stiction may occur in different micromirrors at
different times in operation. Such stiction in individual
micromirrors may also vary over time.
[0005] Therefore, what is needed is a method and apparatus for
repairing the stuck micromirrors.
SUMMARY OF THE INVENTION
[0006] In view of the foregoing, the present invention provides a
method and apparatus for repairing the stuck micromirrors with
refresh voltage pulses. The reparation can be performed dynamically
during operation of the micromirrors. Alternatively, it can be
performed when the micromirrors are not in operation. Such objects
of the invention are achieved in the features of the independent
claims attached hereto. Preferred embodiments are characterized in
the dependent claims.
[0007] In an embodiment of the invention, a method of operating an
array of micromirrors in displaying a video comprising a set of
frames, wherein each micromirror comprises a deflectable mirror
plate and an addressing electrode associated with the mirror plate
is disclosed. The method comprises: switching the micromirrors
between an ON and OFF state during a sequence of frame periods
corresponding to the frames; and performing a reparation process
within a frame period of the sequence of frame periods, wherein the
reparation process comprises: turning the micromirrors of the array
to the OFF state; and applying first and second refresh voltage
pulses to the mirror plates of the micromirrors in the array,
wherein the refresh voltage pulses are separated in time longer
than a characteristic oscillation time of the micromirrors.
[0008] In another embodiment of the invention, a method is
disclosed. The method comprises: illuminating an array of
micromirrors with an illumination light, wherein each micromirror
comprises a reflective deflectable mirror plate and an addressing
electrode associated with the mirror plate for deflecting the
mirror plate; operating the micromirrors according to the method of
claim 100; and projecting the reflected illumination light from the
deflected micromirrors onto a display target so as to produce the
desired video.
BRIEF DESCRIPTION OF DRAWINGS
[0009] While the appended claims set forth the features of the
present invention with particularity, the invention, together with
its objects and advantages, may be best understood from the
following detailed description taken in conjunction with the
accompanying drawings of which:
[0010] FIG. 1 illustrates an exemplary display system employing a
spatial light modulator having an array of micromirrors in which
embodiments of the invention can be implemented;
[0011] FIG. 2 illustrates a cross-section of a portion of the
spatial light modulator in FIG. 1;
[0012] FIG. 3 illustrates a exploded cross-sectional view of a
micromirror device in FIG. 2;
[0013] FIG. 4a diagrammatically plots voltages used in operating
the micromirror device according to an embodiment of the
invention;
[0014] FIG. 4b diagrammatically plots voltages used in operating
the micromirror device according to another embodiment of the
invention;
[0015] FIG. 5a illustrates, in cross-section view, the micromirror
with the voltages as plotted in FIG. 4;
[0016] FIG. 5b schematically illustrates the status of the
deformable hinge of the micromirror before and after the
application of the refresh voltage pulse;
[0017] FIG. 6 diagrammatically plots voltages used in operating the
micromirror device according to yet another embodiment of the
invention;
[0018] FIG. 7a diagrammatically plots first refresh pulse used in
repairing the stuck micromirrors according to an embodiment of the
invention;
[0019] FIG. 7b diagrammatically plots second refresh pulse
following the first refresh pulse in FIG. 7a used in repairing the
stuck micromirrors according to the embodiment of the
invention;
[0020] FIG. 8 diagrammatically plots voltages used in operating the
micromirror device according to yet another embodiment of the
invention;
[0021] FIG. 9 is a perspective view of an exemplary micromirror
device useable in the spatial light modulator of FIG. 1;
[0022] FIG. 10 schematically illustrates a top view of the
deflectable mirror plate of the micromirror device of FIG. 9;
[0023] FIG. 11 is a perspective view of another exemplary
micromirror device useable in the spatial light modulator of FIG.
1; and
[0024] FIG. 12 schematically illustrates a top view of the
deflectable mirror plate of the micromirror device of FIG. 1.
[0025] FIG. 13 is a perspective view of an exemplary spatial light
modulator of FIG. 1;
[0026] FIG. 14 is a top view of another exemplary spatial light
modulator of FIG. 1;
[0027] FIG. 15 schematically shows an exemplary circuitry array
that is connected to an array of electrodes for deflecting the
micromirrors of the spatial light modulators;
[0028] FIG. 16 schematically shows a top view of another exemplary
micromirror array;
[0029] FIG. 17 schematically shows a top view of yet another
exemplary micromirror array;
[0030] FIGS. 18a to 19 schematically show a top view of another
exemplary micromirror array device comprising an array of
electrodes and circuitry and micromirrors;
[0031] FIG. 20 schematically illustrates circuits in which
embodiments of the invention can be implemented; and
[0032] FIG. 21 illustrates an exemplar circuits for controlling the
voltages applied to the micromirrors.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0033] In order to repair the stuck micromirrors, refresh pulses
are applied to the micromirrors so as to produce additional
mechanical restoration forces in the micromirrors. The additional
mechanical restoration force is added to the restoration force in
the micromirrors so as to enhance the restoration force.
[0034] In the instance of operating an array of micromirrors,
reparation procedures are initiated according to a predetermined
schedule. In each reparation procedure, voltages of the
micromirrors of the array are set to values such that the
micromirrors are expected to be at the OFF state. Refresh voltage
pulses are then applied to the micromirrors of the array. In the
presence and after the application of the refresh voltage pulse,
the micromirrors at the OFF state are not affected, and maintain
their positions at the OFF state. However, the stuck micromirrors
due to the in-site stiction are further deflected so as to produce
additional deformation, under which additional mechanical
restoration energy can be derived. The additional restoration
energy is added to the stored restoration energy in the
micromirrors and thus, helping to drive these stuck micromirrors to
the OFF state.
[0035] For liberating all stuck micromirrors, the refresh voltage
pulses applied each time preferably comprise two consecutive pulses
with the time interval therebetween is longer than the intrinsic
time period of the micromirrors, such as the reciprocal of the
resonant frequency of the micromirrors. Of course, the time
interval between the two consecutive refresh voltage pulses can be
shorter than the intrinsic time period of the micromirrors. The
reparation procedure can be carried out during each frame period.
Alternatively, it can be performed at any predetermined time
period.
[0036] The reparation procedure can be incorporated with other
procedures, such as bias inversion that is performed primarily for
eliminating static charge accumulation. For example, the polarity
of the bias voltage (the voltage of the deflectable mirror plate)
can be inversed at predetermined times during operation so as to
dynamically eliminate accumulated static charge in the micromirror.
During the course of the bias voltage inversion, first refresh
voltage pulse can be applied so as to liberate the stuck
micromirrors from stiction followed by the application of the
second refresh voltage pulse. The two refresh voltage pulses
preferably have opposite polarities, and have a time interval
therebetween of longer than the intrinsic time (e.g. the reciprocal
of the resonant frequency) of the micromirrors but shorter than the
time to complete the inversion.
[0037] In the following, embodiments of the present invention will
be illustrated with particular examples wherein the micromirrors
are members of spatial light modulators in display systems.
However, it will be immediately understood by those skilled in the
art that the following examples are for demonstration purposes
only, and it will not be interpreted as a limitation. Instead, any
variations without departing from the spirit of the invention are
also applicable. For example, the present invention can also be
applied to other type of microelectromechanical devices in which
in-site stiction may occur, such as micromirrors in optical
switches.
[0038] Turning to the drawings, an exemplary micromirror based
display system is illustrated in FIG. 1. In its basic
configuration, display system 100 comprises illumination system 116
for producing sequential color light, spatial light modulator 110,
optical element 108 for directing illumination light from the
illumination system onto the spatial light modulator, and optical
element 112 that projects the reflected illumination light onto
display target 114.
[0039] Illumination system 116 further comprises light source 102,
which can be an arc lamp, lightpipe 104 that can be any suitable
integrator of light or light beam shape changer, and color filter
106, which can be a color wheel. The filter in this particular
example is positioned after light pipe 104 at the propagation path
of the illumination light. In another example, the color filter can
be positioned between the light source and light pipe 104, which is
not shown in the figure.
[0040] The present invention is also applicable to other
micromirror based display systems, such as a display system
employing more than one spatial light modulator of micromirrors.
For example, a display system may employ three separate micromirror
based spatial light modulators with each being designated for
modulating a primary color. The modulated primary colors are then
combined together to produce full color image or video.
[0041] FIG. 2 illustrates a cross-section view of an exemplary
spatial light modulator in FIG. 1. For simplicity purposes, only
eight micromirror devices are illustrated therein. In general, the
micromirror array of a spatial light modulator consists of
thousands or millions of micromirrors, the total number of which
determines the resolution of the displayed images. For example, the
micromirror array of the spatial light modulator may have
1024.times.768, 1280.times.720, 1400.times.1050, 1600.times.1200,
1920.times.1080 or even larger number of micromirrors. In other
applications, the micromirror array may have less number of
micromirrors.
[0042] In this example, the array of deflectable reflective mirror
plates (e.g. 124) is disposed between light transmissive substrate
120 and semiconductor substrate 122 having formed thereon an array
of addressing electrodes (e.g. addressing electrode 126) each of
which is associated with a mirror plate for electrostatically
deflecting the mirror plate. In operation, the illumination light
passes through the light transmissive substrate and illuminates the
reflective surfaces of the mirror plates, from which the
illumination light is modulated. The reflected illumination light
from the mirror plates at the ON state is collected by the
projection lens (e.g. projection lens 112 in FIG. 1) so as to
generate a "bright" pixel in the display target (e.g. display
target 114 in FIG. 1). The reflected illumination from the mirror
plates at the OFF state travels away from the projection lens,
resulting in the corresponding pixels in the display target to be
"dark."
[0043] In an alternative configuration, the deflectable reflective
mirror plates can be formed on the semiconductor substrate having
the addressing electrode, in which instance, the light transmissive
substrate may not be provided, which is not shown in the
figure.
[0044] The micromirrors in the array can be arranged in many
suitable ways. For example, the micromirrors can be arranged such
that the center-to-center distance between the adjacent mirror
plates can be 10.16 microns or less, such as 4.38 to 10.16 microns.
The nearest distance between the edges of the mirror plate can be
from 0.1 to 1.5 microns, such as from 0.15 to 0.45 micron, as set
forth in U.S. patent application Ser. No. 10/627,302, Ser. No.
10/627,155, and Ser. No. 10/627,303, both to Patel, filed Jul. 24,
2003, the subject matter of each being incorporated herein by
reference.
[0045] As a way of example, an exemplary micromirror in FIG. 2 is
schematically illustrated in a cross-section view in FIG. 3.
Referring to FIG. 3, micromirror 118 comprises deflectable mirror
plate 124 having a reflective surface for reflecting the
illumination light to be modulated. The mirror plate is attached to
deformable hinge 129 (e.g. a torsion hinge) via hinge contact 128
with the deformable hinge being held and supported by post 133 on
substrate 120 such that the mirror plate can be deflected (rotated)
relative to the substrate. The deflection of the mirror plate is
achieved by electrostatic field established between the mirror
plate and addressing electrode 126. In accordance with an
embodiment of the invention, only one addressing electrode is
provided for the micromirror. Alternatively, multiple addressing
electrodes can be provided for each micromirror. Stopper 130 is
provided to limit the rotation of the mirror plate in accordance
with the operation states, such as the ON state when the
micromirror is operated in a binary mode including the ON and OFF
state. The stopper 130 can be formed in many alternative ways, such
as those set forth in U.S. patent application Ser. No. 10/437,776
filed Apr. 13, 2003 and Ser. No. 10/613,379 filed Jul. 3, 2003,
Ser. No. 10/703,678 filed Nov. 7, 2003, the subject matter of each
being incorporated herein by reference.
[0046] In operation, the mirror plate rotates towards the ON state
position with the electrostatic field established between the
mirror plate and addressing electrode. The rotation of the mirror
plate is stopped by the stopper when the mirror plate arrives at
the ON state angle, in which situation the mirror plate abuts
against the stopper. During the rotation of the mirror plate to the
ON state angle, the hinge is deformed, and restoration energy due
to such deformation is stored in the hinge. When the OFF state is
desired, the voltages of the mirror plate and the addressing
electrode are reduced such that the resulted electrostatic field
cannot balance the restoration energy stored in the deformable
hinge. Therefore, the mirror plate departs from the ON position and
returns to the OFF state.
[0047] However, the mirror plate may not be able to depart from the
ON state when the restoration force can not overcome the surface
force between the contact surfaces of the mirror plate and the
stopper, even through the electrostatic field between the mirror
plate and the addressing electrode is reduced to zero, in which
situation the in-use stiction occurs. In order to liberate the
stuck mirror plate from stiction, reparation process comprising
refresh voltage pulses are performed with the voltage pulses being
applied to the mirror plate so as to produce additional restoration
energy. Specifically, refresh voltage pulses force the mirror plate
to move towards the addressing electrode and thus, producing
additional deformation in the deformable hinge. The additional
deformation results in additional mechanical restoration energy
that is added to and thus, enhancing the stored restoration energy
in the hinge.
[0048] The refresh voltage pulse can be applied in many ways. As a
way of example in a video display application wherein the video
comprises a sequence of frames, one single refresh voltage pulse is
applied in one frame period, as illustrated in FIG. 4a.
[0049] Referring to FIG. 4a, during frame period (0, T), bias
voltage V.sub.bias is applied to the mirror plate. Voltage V.sub.e
on the addressing electrode (e.g. electrode 126 in FIG. 3) varies
over time according to the image data (e.g. image data generated
according to a pulse-width-modulation algorithm) so as to switch
the mirror plate between the ON and OFF states. On or around the
termination of the frame period T, refresh voltage pulse
V.sub.refresh, represented by the thick line, is added to the bias
voltage V.sub.bias. The peak value of the refresh pulse can be the
same as, and is preferably 1.5 times or more, such as 2 times or
more, 3 times or more, or 5 times or more, or 10 times or more of
the amplitude of the bias voltage V.sub.bias before application of
the refresh voltage. The duration of the refresh pulse can be 5
microseconds or less, such as 2 microseconds or less and 1
microsecond or less. The polarity of the refresh voltage pulse may
or may not be the same as the polarity of the bias voltage
immediately before the refresh pulse.
[0050] In accordance with another embodiment of the invention, the
reparation process comprising the refresh pulses can be applied
during color fields, as shown in FIG. 4b. Referring to FIG. 4b, the
frame has multiple color fields. The color fields are defined by
the configuration of the color wheel as shown in FIG. 1, as set
forth in U.S. patent application Ser. No. 10/899,635 filed Jul. 26,
2004, Ser. No. 10/899,637 filed Jul. 26, 2004, Ser. No. 10/771,231
filed Feb. 3, 2003, the subject matter of each being incorporated
herein by reference.
[0051] For demonstration purposes only, FIG. 4b illustrates the
color fields produced by a color wheel having red, green, and blue
segments. The color wheel spins two rounds in a frame period.
Accordingly, the frame has red, green, blue, red, green, and blue
segments. The adjacent color fields have an intervening spoke filed
that is associated with the transition of the color fields in the
color wheel when the color is spinning. The frame period can be
split into two consecutive sub-frames each of which comprises a
red, green, and blue field, as shown in the figure. In the
embodiment of the invention, the reparation process can be
performed for each or selected color fields. Alternatively, the
reparation can be performed during each or only selected
sub-frames. The selections for the individual color fields or
sub-frames for performing the reparation can be made according to a
predefined criterion. For example, the selection can be every other
color fields (or sub-frames), or every certain number of color
fields (sub-frames), or random. In any situation, it is preferred
that the refresh voltage pulses of the reparation processes are
initiated and performed during the spoke periods so as to avoid
losing optical efficiency of the display system. This arises from
the fact that during the spoke periods, image data are not loaded
to the micromirrors, and the micromirrors are "blanked" during the
spoke periods.
[0052] In accordance with yet another embodiment of the invention,
the reparation process can be performed such that the ratio of the
total number switches of the micromirrors between the ON and OFF
(i.e. from the ON to OFF and from OFF to ON) to the total number
refresh voltage pulses applied to the micromirrors is greater than
1, such as greater than 2, or 3, or 4.
[0053] Referring to FIG. 5a, mirror plate 124 is at the ON state
with deformable hinge 132 at position F in the presence of the bias
voltage V.sub.bias before application of the refresh voltage
V.sub.refresh. When the refresh voltage pulse V.sub.refresh is
applied, the mirror plate rotates around the contact point of the
mirror plate to position and stopper 130 towards addressing
electrode 126 and to position B; and deformable hinge deforms from
position G to position F, resulting additional deformation (e.g.
displacement d) of the deformable hinge. The additional deformation
is better illustrated in FIG. 5b. As can be seen in FIG. 5b,
deformable hinge 132 has an additional deformation d from position
G to position F in the presence of the bias voltage having the
refresh voltage pulse. Such additional deformation d is added up to
the deformation of the deformable hinge established during the
rotation of the mirror plate to the ON state, and thereby,
increases the restoration energy with which the mirror plate
departs from the ON state towards the OFF state. After application
of the refresh voltage pulse and removal (or reduction in
amplitude) of the bias voltage, the mirror plate is released. The
mirror plate departs from the ON state under the enhanced
restoration force derived from the enhanced restoration energy.
[0054] The present invention is also applicable in operations of a
micromirror array device, such as the spatial light modulator in
FIG. 1 having an array of micromirrors. In operation, one or more
micromirrors of the array may be stuck due to in-site stiction. To
repair the stuck micromirrors, refresh voltage pulses can be
applied.
[0055] In accordance with an embodiment of the invention, a
reparation process is carried out according to a predetermined
schedule. For example, one reparation process can be performed
between two consecutive frames of a sequence of frame periods in
displaying a video. Alternatively, one reparation process is
performed in each frame period. For another example, the reparation
process can be performed in selected frame periods but preferably,
at most once for each frame period. Within a frame period, the
refresh process can be initiated at any time, such as at the
beginning, or at the end of the frame period.
[0056] The reparation process in the embodiment comprises two
consecutive refresh voltage pulses with opposite polarities and in
any order. Specifically, the first refresh voltage pulse may have
the polarity that is the same as or opposite to the polarity of the
bias voltage immediately prior to the refresh voltage pulses. The
time interval between the two consecutive voltage pulses is
preferably longer than the characteristic oscillation time (e.g.
the reciprocal of the resonant frequency) of the micromirror. If
the micromirrors of the array have different resonant frequency,
the time interval between the voltage pulses can be the reciprocal
of the average resonant frequency. For example, the time interval
between the two consecutive voltage pulses can be 5 times or more,
or 10 times or more, or 15 times or more of the characteristic
oscillation period of the micromirror.
[0057] The reparation process of the present invention can also be
incorporated in other operation processes, such as bias inversion
as set forth in U.S. patent application Ser. No. 10/607,687 filed
Jun. 27, 2003, the subject matter being incorporated herein by
reference. In operating the micromirror and devices having an array
of micromirrors, it is often advantages to invert the voltage
polarity so as to prevent static charge accumulation in micromirror
devices, for example. The bias inversion can be achieved by
inverting the polarity of the bias voltage on the deflectable
mirror plate. Alternatively, the inversion process can be
accomplished by inverting the polarity of the voltage difference
between the deflectable mirror plate and the associated addressing
electrode, as set forth in U.S. patent application Ser. No.
10/607,687 to Richards filed Jun. 27, 2003, the subject matter
being incorporated herein by reference. An exemplary reparation
process incorporated with bias inversion is demonstrated in FIG.
6.
[0058] Referring to FIG. 6, time is drawn in the horizontal axis;
and voltage is in the vertical axis. During time period from
T.sub.1 to T.sub.2, bias voltage V.sub.b+ having a positive
polarity is applied to the mirror plates of the micromirrors in the
micromirror array. Voltages on the addressing electrodes of the
electrode array associated with the micromirror array vary
individually between V.sub.e+ and V.sub.e- according to the image
data of the desired image. When the voltage of an addressing
electrode is V.sub.e+, the voltage difference between voltages of
the mirror plate V.sub.b+ and the addressing electrode V.sub.e+ is
not sufficient to rotate the mirror plate to the ON state, such as
the ON state in FIG. 3. When the voltage of an addressing electrode
is V.sub.e-, the mirror plate rotates to the ON state. The status
of the micromirrors in the micromirror array is demonstrated in the
dotted area in the figure.
[0059] At time T.sub.2, the bias voltage is changed to low negative
voltage V.sub.b0, and maintained at such low negative voltage
during the following transition time period from T.sub.2 to T.
During the transition period from T.sub.2 to T, the mirror plates
of the micromirrors in the array are expected to be at the OFF
state for both voltages V.sub.e- and V.sub.e+ with the low negative
bias voltage. However, some of the mirror plates of the
micromirrors in the micromirror array may experience in-site
stiction, thus can not be in the OFF state. The addressing
electrodes of the stuck micromirrors may be at different voltages,
i.e. V.sub.e+ and V.sub.e-. In order to repair these stuck
micromirrors, a refresh voltage pulse is applied to the
micromirrors of the micromirror array at time T.sub.p during the
transition period, as shown in the figure. The refresh voltage
pulse has amplitude V.sub.r and a negative polarity. Such refresh
voltage pulse drives the stuck mirror plates towards the addressing
electrodes associated with the stuck mirror plates, and causes
additional deflections in the stuck micromirrors. The additional
deflection, in turn, produces additional mechanical restoration
energy that is added to the restoration energy stored in the
deformable hinge, thus, reinforcing the total restoration energy
for moving the stuck mirror plates from the in-site stiction. After
application of the refresh voltage pulse, the reinforced
restoration energy is released, for example, from the deformed
hinge, so as to liberate the stuck mirror plate from the
stiction.
[0060] At the stiction state, the addressing electrodes of some of
the stuck micromirrors are at voltage V.sub.e- and the others are
at V.sub.e+. For the given refresh voltage pulse with particular
amplitude and polarity, the voltage differences between the stuck
mirror plates and associated addressing electrodes, thus the
strengths of the produced additional mechanical restoration forces
(torques) are different. Specifically, the voltage difference
between the mirror plates and the addressing electrodes at V.sub.e+
is larger than that between the mirror plates and the associated
addressing electrodes at V.sub.e-. As a consequence, the produced
additional mechanical restoration forces, as well as the total
reinforced restoration energy are also different in stuck
micromirrors whose addressing electrodes are at V.sub.e+ and
V.sub.e-. The stuck micromirrors with larger reinforced restoration
energy can be liberated from the stiction; however, the
micromirrors with less reinforced restoration energy may not be
successfully repaired. For this reason, another refresh voltage
pulse at time T.sub.4 also during the transition period as shown in
the figure is added to the bias voltage applied to the mirror
plates so as to repair the remaining stuck micromirrors after
application of the previous refresh voltage pulse. The second
refresh voltage pulse at time T.sub.4 has amplitude of V.sub.r+ and
a positive opposite to that of the first refresh voltage pulse,
such as positive polarity. Such second refresh voltage pulse
results in a larger reinforced restoration energy in those stuck
micromirrors whose addressing electrodes are at V.sub.e- than the
reinforced restoration in those stuck micromirrors whose addressing
electrodes are at V.sub.e+. Therefore, the stuck micromirrors whose
addressing electrodes are at both V.sub.e+ and V.sub.e- are
repaired and secured to depart from the stiction.
[0061] The two consecutive refresh pulses as discussed above can be
configured and applied in many ways. For example, the first refresh
voltage pulse at time T.sub.p can be applied at the 1/3 of the
transition period, and the second refresh voltage pulse can be
applied at the 2/3 of the transition period. On general, the two
consecutive refresh voltage pulses are preferably separated in time
longer than the characteristic oscillation time (the reciprocal of
the resonant frequency) of the micromirrors. Specifically, the time
interval between the two consecutive voltage pulses can be 5 times
or more, or 10 times or more, or 15 times or more of the
characteristic oscillation period of the micromirror. The peak
value (amplitudes) of the refresh pulses are preferably 1.5 times
or more, such as 2 times or more, 3 times or more, or 5 times or
more, or 10 times or more of the amplitude of the bias voltage
V.sub.bias before application of the refresh voltage. The duration
of each of the two refresh pulses can be 5 microseconds or less,
such as 2 microseconds or less and 1 microsecond or less. The two
refresh pulses have opposite polarities, but can be applied to the
micromirrors in any order. For example, other than applying the
first pulse with the negative polarity prior to the pulse with the
positive polarity as shown in the figure, the pulse with positive
polarity can be applied prior to the pulse with the negative
polarity.
[0062] The two refresh voltage pulses are applied to the
micromirrors to repair the stuck micromirrors. However, the
non-stuck micromirrors (e.g. those micromirrors at the expected OFF
state during time period from T.sub.2 to T) are not affected. The
reparation process (i.e. application of the two consecutive refresh
voltage pulses) is preferably performed at most once in each frame
period of a sequence of frames. Alternatively, the reparation
process can be performed for selected frame periods of a sequence
of frames, while the selection can be made by the user.
[0063] At time T, the bias voltage is changed to V.sub.b- having a
negative polarity as opposed to the bias voltage before such
inversion (e.g. the bias voltage prior to T.sub.2 and during time
period from T.sub.1 to T.sub.2). During the following time period
from T to T.sub.5 in the following frame period, the micromirrors
switches between the ON and OFF states according to the image date
of the desired image. At time T.sub.5, another bias inversion
process, as well as the reparation process, may be initiated but
not required.
[0064] As a way of example, at time T.sub.5, another bias inversion
process incorporated with the reparation process is initiated, as
shown in then figure. First refresh voltage pulse within transition
period from T.sub.5 to 2T is applied. The first refresh voltage
pulse has a magnitude of V.sub.r+ and a positive polarity. At time
T.sub.7, second refresh voltage pulse is applied to the
micromirrors so as to secure that all stuck micromirrors whose
addressing electrodes are at V.sub.e- or V.sub.e+ are liberated
from stiction. At time 2T, the next frame period arrives. As a way
of example, table 1 lists exemplary values of the above
voltages.
TABLE-US-00001 TABLE 1 V.sub.e+ (Volt) V.sub.e- (Volt) V.sub.b+
(Volt) V.sub.b- (Volt) V.sub.r+ (Volt) V.sub.r- (Volt) V.sub.b0
(Volt) +3.3 to +5 -15 to -25 V +20 to +40 V -20 to -40 +40 to +150
+40 to +150 -4
[0065] In another example, the bias voltages, voltages on the
addressing electrodes for the ON and OFF states can be other
values. As a way of example, the ON state angle of the ON state for
the micromirror devices is 8.degree. degrees or more, such as
10.degree. degrees or more, or 12.degree. degrees or more, or
14.degree. degrees or more, or 16.degree. degrees or more. The OFF
state angle can be parallel to the substrate on which the mirror
plate is formed, or -2.degree. degrees or less, or -4.degree.
degrees or less. The voltage difference between the mirror plate
and the addressing electrode for the mirror plate at the ON state
can be 28 volts or more, such as 30 volts or more, 35 volts or more
or 40 volts or more. And such voltage difference can be maintained
for a time period corresponding to one least-significant-bit or
more defined based on a pulse-width-modulation algorithm for
producing a desired image. The voltage difference between the
mirror plate and the addressing electrode for the mirror plate at
the OFF state can be 17 volts or less.
[0066] The above voltage difference can be achieved in many
different ways by applying different voltages to the mirror plate
and the addressing electrode associated with the mirror plate. As
an aspect of the embodiment of the invention, the voltage applied
to the addressing electrode changes when the mirror plate switches
between the ON and OFF states. In particular, the voltage on the
addressing electrode may change polarity, for example, from
positive to negative and vice versa. Such voltage change whether
changing polarity or not, can be 10 volts or more, or 15 volts or
more, or 20 volts or more, and more preferably from 13 to 25
volts.
[0067] The time duration of the applied voltage to the addressing
electrode and mirror plate, may depend upon the image data of
desired images according to a PWM algorithm. As an example, the
duration of the applied voltages on the addressing electrode and
mirror plate, as well as the voltage differences between the mirror
plate and the addressing electrode (or the voltage difference
between the mirror plate and the conducting film on the substrate
if applicable) is 10 microseconds or more, such as 100 microseconds
or more, or 400 microseconds or more, or 600 microseconds or more,
or from 100 to 700 microseconds.
[0068] The voltage between the mirror plate and the addressing
electrode can be can be 25 Volts or less, or more preferably 20
volts or less, or more preferably 18 volts or less, such as from 5
to 18 volts, or from 10 to 15 volts. A low operation voltage has
many benefits, such as cost-effective and simplified design and
fabrication, as set forth in U.S. patent application Ser. No.
10/982,259 filed Nov. 5, 2004, and U.S. patent application Ser. No.
10/340,162 filed Jan. 10, 2003, the subject matter of each being
incorporate herein by reference.
[0069] The refresh voltage pulse as discussed above may be
configured in a variety of ways. As a way of example, FIG. 7a
illustrates the exploded view of an example of the refresh voltage
pulse at time T.sub.4 in FIG. 6. Referring to FIG. 7a, the refresh
voltage pulse starts from bias voltage V.sub.b0 during time
.DELTA.t.sub.1 with V.sub.b0 varying between V.sub.b0(min) and
V.sub.b0(max). During time .DELTA.t.sub.2 and the first half
.DELTA.t.sub.3 (.DELTA.t.sub.2+1/2.DELTA.t.sub.3), the refresh
voltage increases monotonically, and reaches peak value V.sub.r+
whose maximum and minimum values are represented by V.sub.r+(max)
and V.sub.r+(min) at half .DELTA.t.sub.3. In the following second
half of .DELTA.t.sub.3 and .DELTA.t.sub.4, the refresh voltage
pulse decreases monotonically and returns to the initial value of
V.sub.b0 at the beginning of period .DELTA.t.sub.5.
[0070] According to the invention, the duration of the refresh
pulse, that is the summation of .DELTA.t.sub.1, .DELTA.t.sub.2,
.DELTA.t.sub.3, .DELTA.t.sub.4, and .DELTA.t.sub.5, is preferably 5
microseconds or less, such as 2 microseconds or less and 1
microsecond or less. Of course, the duration of the refresh voltage
pulse may have other different values. As a way of example,
exemplary values of the parameters as discussed above are listed in
table 2 and table 3.
TABLE-US-00002 TABLE 2 .DELTA.t.sub.1 .DELTA.t.sub.2 .DELTA.t.sub.3
.DELTA.t.sub.4 .DELTA.t.sub.5 min (.mu.s) 0 0.2 0.5 0.2 2.0 max
(.mu.s) -- 0.5 1.0 0.5 --
TABLE-US-00003 TABLE 3 V.sub.b0 V.sub.b+ V.sub.b- V.sub.r+ V.sub.r-
min (V) -4 (20 to 40) - 0.1 (-20 to -40) + 0.1 (40 to 100) + 2.5
(-40 to -100) 5 max (V) -6 (20 to 40) + 0.1 (-20 to -40) - 0.1 (40
to 100) + 5 (40 to 100) + 2.5
[0071] The exploded view of the refresh voltage pulse with a
negative polarity is illustrated in FIG. 7b. Referring to FIG. 7b,
the refresh voltage starts from V.sub.b0 whose value lies within
the range between V.sub.b0(min) and V.sub.b0(max). During time
period .DELTA.t.sub.2 and the first half .DELTA.t.sub.3
(.DELTA.t.sub.2+1/2 .DELTA.t.sub.3), the refresh voltage decreases
monotonically, and reaches the negative peak value V.sub.r- whose
maximum and minimum values are represented by V.sub.r-(max) and
V.sub.r-(min) at half .DELTA.t.sub.3. In the following second half
of .DELTA.t.sub.3 and .DELTA.t.sub.4, the refresh voltage pulse
increases monotonically from the negative peak value and returns to
the initial value V.sub.b0 at the beginning of .DELTA.t.sub.5.
[0072] Alternative to the reparation process as discussed with
reference to FIG. 6 and FIGS. 7a and 7b where two consecutive
refresh voltage pulses are provided and are applied during the
transition period, the reparation process may have one single
refresh voltage pulse. Such refresh voltage may have the same
amplitude as any one of the above discussed two refresh voltage
pulses--the pulses at time T.sub.p and T.sub.4; and any
polarization. However, the reparation process with one single
refresh pulse may have disadvantages. As a way of example but
without losing the generality, assuming the reparation process
comprises one single refresh voltage pulse at time T.sub.p, such
single refresh voltage may only repair stick micromirrors
experiencing bias inversion during time from T.sub.2 to T.sub.p,
while can not repair the micromirrors experiencing inversion during
time from T.sub.p to T. Therefore, such reparation process may not
be efficient.
[0073] The reparation process with the single refresh voltage pulse
may be applied at time T when all micromirrors finish the bias
inversion. With this application scheme, the single refresh voltage
pulse can repair all stuck micromirrors with both of the V.sub.e+
and V.sub.e- voltages at the addressing electrodes, though this
reparation process is less preferred.
[0074] Alternatively to the reparation process where the two
consecutive refresh voltage pulses are applied during the
transition period, an alternative reparation process having two
refresh voltage pulses one of which is applied after the
termination of the transition period is also applicable, as shown
in FIG. 8, though less preferred.
[0075] Referring to FIG. 8, T.sub.2 to T.sub.3 is a transition time
where the bias voltage changes from V.sub.b+ to the low voltage
V.sub.b0. At time T.sub.3, the transition is expected to be
finished, wherein the addressing electrodes are at voltage V.sub.e-
and the mirror plates are at the bias voltage of V.sub.b0. During
the transition period, the first refresh voltage pulse is applied.
However, this first refresh voltage pulse is not able to repair the
stuck micromirrors experiencing the micromirrors experiencing
transition after the application of the first refresh voltage
pulse. For this reason, in the following period from T.sub.3 to T,
the micromirrors are "blanked", where no image data of the desired
image is fed into the micromirrors. During such blanking period,
the second refresh voltage pulse is applied to repair the remaining
stuck micromirrors after the application of the first refresh
voltage pulse. This reparation process is less favored because the
"blanking" period from T.sub.3 to T can result in degradation of
the brightness of the displayed image.
[0076] Alternative to the reparation process as discussed above
with reference to FIG. 8, the process may also have one single
refresh voltage pulse such as the refresh voltage pulse during the
transition period or the refresh voltage pulse during the
"blanking" period.
[0077] The refresh voltage pulse as discussed above can be applied
to different micromirrors having a deflectable mirror plate and a
stopping mechanism. The micromirror having a cross-section view of
FIG. 3 is one of many examples. Referring again to FIG. 3, the
mirror plate can be attached to the deformable hinge symmetrically
or asymmetrically. When the mirror plate is attached to the
deformable hinge with the attachment point substantially at or
around the geometric (or mass) center of the mirror plate, the
mirror plate rotates symmetrically--that is, the maximum angles
achievable by the mirror plate rotating in opposite directions are
substantially the same. Alternatively, when the attachment point is
offset from the geometric (or mass) center of the mirror plate, the
mirror plate rotates asymmetrically--that is the maximum angles
achievable by the mirror plate in opposite directions are
different. The asymmetric rotation of the mirror plate is more
advantageous in obtaining higher contrast ratio. The ON state angle
of the present invention is preferably 12.degree. degrees or more,
such as 14.degree. degrees or more, and 14.degree. degrees or more.
The OFF state can be a state where the mirror plate is parallel to
the substrate on which the mirror plates are formed, such as
substrate 120. The OFF state angle can be other values, such as
-1.degree. degree or less, such as -2.degree. degrees or less, and
-4.degree. degrees or less, wherein the minus sign "-" represents
the opposite rotation direction in relation to the ON state angle.
Such ON and OFF state angles can be achieved by attaching the
mirror plate asymmetrically to the deformable hinge. Specifically,
the hinge contact (128) contacts at the mirror plate at a location
away from the geometric or mass center of the mirror plate. As a
result, the deformable hinge, as well as the rotation axis is not
along a diagonal of a diagonal of the mirror plate when viewed from
the top of the mirror plate at the non-deflected state. Exemplary
micromirrors of asymmetric rotation will be better illustrated in
perspective views in FIGS. 8 to 11 afterwards.
[0078] In the cross-section view of FIG. 3, the deformable hinge
and the mirror plate are in different planes. Alternatively, the
mirror plate and the deformable hinge can be in the same plane. For
example, the mirror plate and the deformable hinge can be
fabricated or derived from a single flat substrate, such as a
single crystal (e.g. single crystal silicon). Alternatively, the
mirror plate and the deformable hinge can be derived from one
deposited film by patterning. The stopper (e.g. stopper 130) can be
in the same plane of the deformable hinge, but can also be in
different planes of the deformable hinge.
[0079] In addition to the addressing electrode whose operation
state (voltage) depends upon the image data of the desired image,
an additional electrode for rotating the mirror plate in the
direction opposite to that driven by the addressing electrode can
also be provided. For example, the additional electrode can be
formed on substrate 120 on which the mirror plate is formed.
Alternatively, the additional electrode can be formed on the
micromirror on a side opposite to the addressing electrode relative
to the rotation axis of the mirror plate.
[0080] In the example as shown in FIG. 3, the deflectable mirror
plates are formed on substrate 120 that is transmissive to the
illumination light to be modulated, such as glass and quartz when
the illumination light is visible light. The addressing electrodes
and circuitry are formed on substrate 122 that can be a standard
semiconductor substrate. In another embodiment of the invention,
the mirror plates can be directly derived from the light
transmissive substrate, such as by patterning the light
transmissive substrate so as to form the deflectable mirror plate.
In this instance, the deformable hinge can be single crystal or
deposited thin film, which will not be discussed in detail herein.
As another example, the mirror plates and the addressing electrodes
can be formed on the same substrate, such as semiconductor
substrate 122.
[0081] Addressing electrode 126 is preferably disposed such that
the edge of the addressing electrode extending beyond the mirror
plate, for example, beyond the furthest point of the mirror plate
measured from the deformable hinge, so as to maximize the
utilization efficiency of the electrostatic field, as set forth in
U.S. patent application Ser. No. 10/947,005 filed Sep. 21, 2004,
the subject matter being incorporated herein by reference. In an
embodiment of the invention, each mirror plate is addressed and
deflected by one single addressing electrode. In this instance, the
mirror plate is rotated to the ON state by an electrostatic force
derived from the electrostatic field established between the mirror
plate and the addressing electrode.
[0082] Referring to FIG. 9, a perspective view of an exemplary
micromirror device in which embodiments of the invention are
applicable is illustrated therein. Micromirror device 180 comprises
substrate 190 that is a light transmissive substrate such as glass
or quartz and semiconductor substrate 182. Deflectable and
reflective mirror plate 184 is spaced apart and attached to
deformable hinge 186 via a hinge contact. The deformable hinge is
affixed to and held by posts 188. The semiconductor substrate has
addressing electrode 192 for deflecting the mirror plate. In this
particular example, the light transmissive substrate operates as a
stopper for stopping the rotation of the mirror plate at the ON
state.
[0083] A top view of the micromirror in FIG. 9 is illustrated in
FIG. 9. As can be seen in FIG. 10, deformable hinge 186 is not
along but offset from the symmetrical axis OO' of the mirror plate
such that the mirror plate is operable to rotate asymmetrically.
The deformable hinge is located beneath the mirror plate in the
direction of the incident light. That is, the mirror plate is
located between the light transmissive substrate and the deformable
hinge such that the deformable hinge is not illuminated by the
incident light so as to prevent unexpected light scattering from
the deformable hinge, thereby, increasing the contrast ratio of the
produced image. The quality of the produced image is further
improved through reduction of the light scattering from the edges
of the mirror plate by forming the edges of the mirror plate into
zigzagged shape, as shown in the figure.
[0084] Another exemplary micromirror device having a
cross-sectional view of FIG. 3 is illustrated in its perspective
view in FIG. 11. Referring to FIG. 11, deflectable reflective
mirror plate 124 with a substantially square shape is formed on
light transmissive substrate 120, and is attached to deformable
hinge 132 via hinge contact 128. The deformable hinge is held by
hinge support 134, and the hinge support is affixed and held by
posts on the light transmissive substrate. For electrostatically
deflecting the mirror plate, an addressing electrode (not shown in
the figure for simplicity purposes) is fabricated in the
semiconductor substrate 122. For improving the electrical coupling
of the deflectable mirror plate to the electrostatic field,
extending metallic plate 136 can be formed on the mirror plate and
contacted to the mirror plate via post 138.
[0085] The mirror plate is preferably attached to the deformable
hinge asymmetrically such that the mirror plate can be rotated
asymmetrically in favor of high contrast ratio. The asymmetric
attachment is better illustrated in FIG. 12. Referring to FIG. 12,
mirror plate comprises diagonals BB and CC. Deformable hinge is
disposed with its length parallel to a diagonal (e.g. BB) of the
mirror plate. However, the length of the deformable is not along
any diagonal of the mirror plate in the top view when the mirror
plate is parallel to the light transmissive substrate. Of course,
the mirror plate can be attached to the deformable hinge
symmetrically by placing the attachment point around the geometric
or mass center of the mirror plate, which will not be discussed in
detail herein.
[0086] Similar to that in FIG. 9, the deformable hinge is
preferably formed beneath the deflectable mirror plate in the
direction of the incident light so as to avoid unexpected light
scattering by the deformable hinge. For reducing unexpected light
scattering of the mirror plate edge, the illumination light is
preferably incident onto the mirror plate along a corner of the
mirror plate.
[0087] Referring to FIG. 13, an exemplary spatial light modulator
having an array of micromirrors of FIG. 11 is illustrated therein.
For simplicity purposes, only 4.times.4 micromirrors are presented.
In this example, micromirror array 148 is formed on light
transmissive substrate 142; and addressing electrode and circuitry
array 146 is formed on semiconductor substrate 144 for deflecting
the micromirrors in the micromirror array. The deformable hinges of
the micromirrors, as well as the addressing electrodes are hidden
from the incident light.
[0088] The micromirrors in the micromirror array of the spatial
light modulator can be arranged in alternative ways, another one of
which is illustrated in FIG. 14. Referring to FIG. 14, each
micromirror is rotated around its geometric center an angle less
than 45.degree. degrees. The posts (e.g. 152 and 154) of each
micromirror (e.g. mirror 156) are then aligned to the opposite
edges of the mirror plate. No edges of the mirror plate are
parallel to an edge (e.g. edges 160 or 162) of the micromirror
array. The rotation axis (e.g. axis 158) of each mirror plate is
parallel to but offset from a diagonal of the mirror plate when
viewed from the top of the mirror plate at a non-deflected
state.
[0089] For driving the micromirrors, an array of addressing
electrodes are provided and disposed proximate to the mirror
plates. Each addressing electrode is connected to the voltage
output node of a circuitry, such as a memory cell such that the
voltage of the addressing electrode is controlled by the memory
cell. An exemplary circuitry of an array of memory cells according
to an embodiment of the invention is illustrated in FIG. 15. For
simplicity purposes, only 3.times.4 memory cells are presented. In
this example, each row of memory cells is connected to at least two
word-lines for actuating the memory cells in the row. The memory
cells can be connected to the wordlines in many different ways. For
example, the memory cells can be connected to the two wordlines
alternatively. With this configuration, the memory cells of each
row can be actuated separately and in different times, as set forth
in U.S. patent application Ser. No. 10/407,061 to Richards filed on
Apr. 2, 2003, the subject matter being incorporated herein by
reference. The memory cells of the memory cell array can be
standard RAM and DRAM. Alternatively, the memory cells can be
"charge-pump memory cells" as set forth in U.S. patent application
Ser. No. 10/340,162 to Richards filed Jan. 10, 2003, the subject
matter being incorporated herein by reference.
[0090] FIG. 16 illustrates the top view of another micromirror
array having an array of micromirrors of FIG. 9. In this example,
each micromirror is rotated 45.degree. degrees around its geometric
center. For addressing the micromirrors, the bitlines and wordlines
are deployed in a way such that each column of the array is
connected to a bitline but each wordline alternatively connects
micromirrors of adjacent rows. For example, bitlines b.sub.1,
b.sub.2, b.sub.3, b.sub.4, and b.sub.5 respectively connect
micromirrors groups of (a.sub.11, a.sub.16, and a.sub.21),
(a.sub.14 and a.sub.19), (a.sub.12, a.sub.17, and a.sub.22),
(a.sub.15 and a.sub.20), and (a.sub.13, a.sub.18, and a.sub.23).
Wordlines w.sub.1, w.sub.2, and w.sub.3 respectively connect
micromirror groups (a.sub.11, a.sub.14, a.sub.12, a.sub.15, and
a.sub.13), (a.sub.16, a.sub.19, a.sub.17, a.sub.20, and a.sub.18),
and (a.sub.21, a.sub.22, and a.sub.23). With this configuration,
the total number of wordlines is less the total number of
bitlines.
[0091] For the same micromirror array, the bitlines and wordlines
can be deployed in other ways, such as that shown in FIG. 17.
Referring to FIG. 17, each row of micromirrors is provided with one
wordline and one bitline. Specifically, bitlines b.sub.1, b.sub.2,
b.sub.3, b.sub.4 and b.sub.5 respectively connect column 1
(comprising micromirrors a.sub.11, a.sub.16, and a.sub.21), column
2 (comprising micromirrors a.sub.14 and a.sub.19), column 3
(comprising micromirrors a.sub.12, a.sub.17, and a.sub.22), column
4 (comprising micromirrors a.sub.15 and a.sub.20), and column 5
(comprising micromirrors a.sub.13, a.sub.18, and a.sub.23).
Wordlines WL.sub.1, WL.sub.2, WL.sub.3, WL.sub.4, and WL.sub.5
respectively connect row 1 (comprising micromirrors a.sub.11,
a.sub.12, and a.sub.13), row 2 (comprising micromirrors a.sub.14
and a.sub.15), row 3 (comprising micromirrors a.sub.16, a.sub.17,
and a.sub.18), row 4 (comprising micromirrors a.sub.19 and
a.sub.20) and row 5 (comprising micromirrors a.sub.21, a.sub.22,
and a.sub.23).
[0092] According to another embodiment of the invention, the mirror
plates of the micromirrors in the array can form a plurality of
pockets, in which posts can be formed, wherein the pockets are
covered by the extended areas of the addressing electrodes when
viewed from the top of the micromirror array device, as shown in
FIGS. 18a to 19.
[0093] Referring to FIG. 18a, a portion of an array of mirror
plates of the micromirrors is illustrated therein. The mirror
plates in the array form a plurality of pockets in between. For
example, pockets 172a and 172b are formed in which posts for
supporting and holding mirror plate 174 can be formed. For
individually addressing and deflecting the mirror plates in FIG.
18a, an array of addressing electrodes is provided, a portion of
which is illustrated in FIG. 18b.
[0094] Referring to FIG. 18b, each addressing electrode has an
extended portion, such as extended portion 178 of addressing
electrode 176. Without the extended portion, the addressing
electrode can be generally square, but having an area equal to or
smaller than the mirror plate.
[0095] FIG. 19 illustrates a top view of a micromirror array device
after the addressing electrodes in FIG. 17b and the mirror plates
in FIG. 18a being assembled together. It can be seen in the figure
that each addressing electrode is displaced a particular distance
along a diagonal of the mirror plate associated with the addressing
electrode. As a result, the pockets presented between the mirror
plates are covered by the addressing electrode, specifically by the
extended portions of the addressing electrodes. In this way, light
scattering otherwise occurred in the substrate having the
addressing electrodes can be removed. The quality, such as the
contrast ratio of the displayed images can be improved.
[0096] When used in a spatial light modulator of a display system
as shown in FIG. 1, the incident light beam is directed onto the
mirror plates in a direction along the displacement direction of
the addressing electrodes when viewed from the top of the
addressing electrodes as shown in the figure. For example, the
incident light has an angle .theta. to an edge of the addressing
electrode (or the mirror plate) when viewed from the top; and the
angle can be 135.degree. degrees.
[0097] The micromirrors in which embodiments of the invention can
be implemented may be composed of any suitable materials and
fabricated in many ways. According to the invention, the
deflectable mirror plate comprises reflective film, preferably
composed of a metallic material (e.g. aluminum, gold, silver)
having a high reflectivity, deposited on another non-metallic
material, such as SiO.sub.x, SiN.sub.x and TiN.sub.x for enhancing
the mechanical properties of the mirror plate. Alternatively, other
materials, such as a barrier layer for preventing diffusion between
the metallic reflecting layer and the mechanical enhancing layer,
can be deposited between the metallic reflecting layer and the
mechanical enhancing layer.
[0098] The deformable hinge preferably comprises an electrically
conductive layer. Examples of suitable materials for the hinge
layer are Al, Ir, titanium, titanium nitride, titanium oxide(s),
titanium carbide, TiSiN.sub.x, TaSiN.sub.x, or other ternary and
higher compounds.
[0099] The embodiments of the present invention can be implemented
in hardware devices, such as integrated circuits either analog or
digital, such as bias driver 206 of controller 202 in FIG. 20.
Referring to FIG. 20, controller 202, which further comprises
voltage controller 204, is a controlling unit that controls the
voltages on the mirror plates and electrodes. Specifically, the
controller selectively activates memory cells (e.g. memory cell
214) in response to activation signals and sets the selected memory
cells into desired voltage states. The electrodes connected to the
selected memory cells are accordingly set to desired voltages for
driving the mirror plate to rotate. Bias driver 206 controls
applications of the voltages to the mirror plates and electrodes.
In particular, bias driver 206 may perform the application of the
refresh voltage pulses of reparation processes and invention
process of inverting polarity of voltage differences across mirror
plates and electrodes in accordance with a predetermined
procedure.
[0100] As a way of example, FIG. 21 illustrates a circuit design
for the bias driver of FIG. 20. As can be seen from the figure, the
design is composed of transistors Q.sub.1, Q.sub.2, Q.sub.3 and
Q.sub.4, and resistors R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5
and R.sub.6. The source of transistor Q.sub.2 and one end of
resistor R.sub.4 form a voltage node V.sub.B+. The drain of
transistor Q.sub.4 and one end of resistor R.sub.6 form another
voltage node V.sub.B-. The gate of transistor Q.sub.1 is set to
voltage V.sub.DD. In this particular circuit design, the output
voltage V.sub.out from bias driver 206 depends upon the output
signal B from voltage controller 204. Specifically, the V.sub.out
of bias driver 160 is V.sub.B+ (larger than V.sub.DD) when the
output signal B of the voltage controller is set to 0. And the
output voltage V.sub.out is V.sub.B- (less than zero) when the
output signal B of the voltage controller is set to V.sub.DD. FIG.
21 shows an exemplary circuit design for the bias driver and the
controller of FIG. 20. In fact, the controller and the bias driver
can be any suitable circuit design as long as they provide electric
voltages to the mirror plate and/or the electrode and invert the
polarity of the voltage difference between the mirror plate and the
electrode.
[0101] Other than implementing the embodiments of the present
invention in controller 202, the embodiments of the present
invention may also be implemented in a microprocessor-based
programmable unit, and the like, using instructions, such as
program modules, that are executed by a processor. Generally,
program modules include routines, objects, components, data
structures and the like that perform particular tasks or implement
particular abstract data types. The term "program" includes one or
more program modules. When the embodiments of the present invention
are implemented in such a unit, it is preferred that the unit
communicates with the controller, takes corresponding actions to
signals, such as actuation signals from the controller, and inverts
polarity of the voltage differences.
[0102] It will be appreciated by those skilled in the art that a
new and useful method and apparatus for transposing pixel data
matrices into bitplane data matrices for use in display systems
having micromirror arrays have been described herein. In view of
many possible embodiments to which the principles of this invention
may be applied, however, it should be recognized that the
embodiments described herein with respect to the drawing figures
are meant to be illustrative only and should not be taken as
limiting the scope of invention. For example, those of skill in the
art will recognize that the illustrated embodiments can be modified
in arrangement and detail without departing from the spirit of the
invention. Therefore, the invention as described herein
contemplates all such embodiments as may come within the scope of
the following claims and equivalents thereof. In the claims, only
elements denoted by the words "means for" are intended to be
interpreted as means plus function claims under 35 U.S.C. .sctn.
112, the sixth paragraph.
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