U.S. patent application number 10/969300 was filed with the patent office on 2006-04-20 for asymmetric spatial light modulator in a package.
Invention is credited to Regis Grasser, Andrew Huibers.
Application Number | 20060082860 10/969300 |
Document ID | / |
Family ID | 36180447 |
Filed Date | 2006-04-20 |
United States Patent
Application |
20060082860 |
Kind Code |
A1 |
Huibers; Andrew ; et
al. |
April 20, 2006 |
ASYMMETRIC SPATIAL LIGHT MODULATOR IN A PACKAGE
Abstract
Disclosed herein is a micromirror package having a micromirror
being attached to a supporting surface of a package substrate, and
sealed between the package substrate and a package cover, whereas
the micromirror array is placed offset the center of the supporting
surface.
Inventors: |
Huibers; Andrew; (Palo Alto,
CA) ; Grasser; Regis; (Mountain View, CA) |
Correspondence
Address: |
REFLECTIVITY, INC.
350 POTRERO AVENUE
SUNNYVALE
CA
94085
US
|
Family ID: |
36180447 |
Appl. No.: |
10/969300 |
Filed: |
October 19, 2004 |
Current U.S.
Class: |
359/291 |
Current CPC
Class: |
G02B 26/0833 20130101;
Y10S 359/904 20130101 |
Class at
Publication: |
359/291 |
International
Class: |
G02B 26/00 20060101
G02B026/00 |
Claims
1. A package of a spatial light modulator having an array of
pixels, comprising: a window transmissive to the incident light to
be modulated; and a package substrate on which the pixel array is
positioned, wherein the geometric center of the micromirror array
is offset from the geometric center of the window when viewed from
the top of the window.
2. The package of claim 1, wherein each pixel of the pixel array
comprises a reflective and deflectable micromirror.
3. The package of claim 2, wherein the window is defined by a light
blocking mask on a package cover of the package.
4. The package of claim 2, wherein an in-plane symmetric axis of
the micromirror array is offset from but parallel to an in-plane
symmetric axis of the window.
5. The package of claim 4, wherein a diagonal of the micromirror
array is offset form but parallel to a diagonal of the window.
6. The package of claim 2, wherein the micromirror array has no
diagonal that is parallel to a diagonal of the window.
7. The package of claim 2, wherein the offset comprises 1.5% or
more of the total number of columns of the micromirror array.
8. The package of claim 7, wherein the offset comprises 1.5% or
more of the total number of rows and/or columns of the micromirror
array.
9. The package of claim 2, wherein the offset comprises 5% or more
of the total number of columns of the micromirror array.
10. The package of claim 2, wherein the offset comprises 10% or
more of the total number of columns of the micromirror array.
11. The package of claim 2, wherein the offset comprises 50 or more
of the columns of the micromirror array.
12. The package of claim 11, wherein the offset comprises 50 or
more of the rows of the micromirror array.
13. The package of claim 2, wherein the offset comprises 100 or
more of the columns of the micromirror array.
14. The package of claim 2, wherein the offset comprises 150 or
more of the columns of the micromirror array.
15. The package of claim 2, wherein the package substrate comprises
a cavity having a supporting surface on which the micromirror array
device is positioned; and wherein the geometric center of the
micromirror array is offset from the geometric center of the
supporting surface.
16. The package of claim 15, wherein no major edges of the
micromirror array is parallel to a major edge of the supporting
surface.
17. The package of claim 2, wherein the micromirror array comprises
a number of active micromirrors and a number of inactive
micromirrors; wherein each active micromirror is operated according
image data of a desired image; and each inactive micromirror is
operated irrelevant to the image data; and wherein an inactive area
having the inactive micromirrors is offset from an active area
having the active micromirrors.
18. The package of claim 17, wherein the geometric center of the
active area is offset from the geometric center of the entire
micromirror array.
19. The package of claim 18, wherein the geometric center of the
active area is offset form the geometric center of the package
cover.
20. The package of claim 18, wherein the geometric center of the
active area is offset form the geometric center of the window.
21. The package of claim 3, wherein the geometric center of the
window is offset from the geometric center of the package
cover.
22. The package of claim 17, wherein the active area has an aspect
ratio of 4:3.
23. The package of claim 17, wherein the active area has an aspect
ratio of 16:9.
24. A display system, comprising: a light source providing
illumination light for the system; a spatial light modulator having
a package of a pixel array in claim 1 for modulating the
illumination light so as to produce a desired image; a plurality of
optical elements for directing the illumination light onto and away
from the spatial light modulator; and a display target on which the
desired image is produced.
25. The display system of claim 24, further comprising: a color
filter for producing sequential illumination light beams of primary
colors.
26. The display system of claim 25, further comprising: a light
integrator that is placed between the light source and the color
filter.
27. The display system of claim 25, further comprising: a light
integrator that is placed after the light source and the color
filter at a propagation path of the illumination light.
28. A spatial light modulator, comprising: a pixel array,
comprising an active area that includes an array of active pixels
whose operation states are associated with image data of a desired
image, wherein the geometric center of the active area is offset
from the geometric center of the entire micromirror array when
viewed from the top of the micromirror array.
29. The spatial light modulator of claim 28, wherein a pixel of the
pixel array comprises a reflective and deflectable micromirror.
30. The spatial light modulator of claim 29, wherein the offset is
characterized by 1.5% or more of the total number of columns and/or
rows of the micromirror.
31. The spatial light modulator of claim 29, wherein the offset is
characterized by 1.5% or more of the total number of rows of the
micromirror.
32. The spatial light modulator of claim 29, wherein the offset is
characterized by 5% or more of the total number of columns of the
micromirror.
33. The spatial light modulator of claim 29, wherein the offset is
characterized by 10% or more of the total number of columns of the
micromirror.
34. The spatial light modulator of claim 29, wherein the offset is
characterized by 50 columns or more of the columns of the
micromirror.
35. The spatial light modulator of claim 34, wherein the offset is
characterized by 50 columns or more of the rows of the
micromirror.
36. The spatial light modulator of claim 29, wherein the offset is
characterized by 100 columns or more of the columns of the
micromirror.
37. The spatial light modulator of claim 29, wherein the offset is
characterized by 150 columns or more of the columns of the
micromirror.
38. The spatial light modulator of claim 29, further comprising: a
package substrate having a supporting surface on which the
micromirror array is positioned; a package cover having a window
transmissive to an incident light to be modulated; and wherein the
geometric center of the active area is offset from the geometric
center of the window.
39. The spatial light modulator of claim 38, wherein the geometric
center of the active area is offset from the geometric center of
the package cover.
40. The spatial light modulator of claim 38, wherein the supporting
surface is a surface of a cavity in the package substrate; and
wherein the package cover is bonded to the package substrate.
41. A package of a spatial light modulator, comprising: a pixel
array, comprising an active area that includes an array of active
pixels whose operation states are associated with image data of a
desired image; a package substrate having a supporting surface on
which the pixel array is positioned; a package cover having a
window transmissive to the incident light to be modulated; wherein
the geometric center of the active area is offset from the
geometric center of the window when viewed from the top of the
window.
42. The package of claim 41, wherein each pixel of the pixel array
comprises a deflectable reflective micromirror.
43. The spatial light modulator of claim 42, wherein the offset is
characterized by 1.5% or more of the total number of columns and/or
rows of the micromirror.
44. The spatial light modulator of claim 42, wherein the offset is
characterized by 1.5% or more of the total number of rows of the
micromirror.
45. The spatial light modulator of claim 42, wherein the offset is
characterized by 5% or more of the total number of columns of the
micromirror.
46. The spatial light modulator of claim 42, wherein the offset is
characterized by 10% or more of the total number of columns of the
micromirror.
47. The spatial light modulator of claim 42, wherein the offset is
characterized by 50 columns or more of the columns of the
micromirror.
48. The spatial light modulator of claim 47, wherein the offset is
characterized by 50 columns or more of the rows of the
micromirror.
49. The spatial light modulator of claim 42, wherein the offset is
characterized by 100 columns or more of the columns of the
micromirror.
50. The spatial light modulator of claim 42, wherein the offset is
characterized by 150 columns or more of the columns of the
micromirror.
51. The spatial light modulator of claim 42, wherein the geometric
center of the active area is offset from the geometric center of
the package cover.
52. The spatial light modulator of claim 42, wherein the geometric
center of the active area is offset form the geometric center of
the entire micromirror array.
53. A package, comprising: a package substrate having a supporting
surface on which a pixel array is positioned; and a package cover
having a window transmissive to light to be modulated, wherein the
geometric center of the window is offset from the geometric center
of the package cover.
54. The package of claim 53, wherein the pixel comprises a
deflectable and reflective micromirror.
55. The package of claim 54, wherein the offset comprises 1.5% or
more of the length and/or the width of the package cover.
56. The package of claim 55, wherein the offset comprises 1.5% or
more of the width of the package cover.
57. The package of claim 54, wherein the offset comprises 5% or
more of the length of the package cover.
58. The package of claim 54, wherein the offset comprises 10% or
more of the length of the package cover.
59. The package of claim 54, wherein the geometric center of the
pixel array is offset from the geometric center of the package
cover.
60. The package of claim 54, wherein the geometric center of the
pixel array is offset from the geometric center of the window.
61. The package of claim 54, wherein the geometric center of the
pixel array comprises an active area having an array of active
pixels whose operation states are associated with image data of a
desired image, wherein the geometric center of the active area is
offset from the package cover.
62. The package of claim 54, wherein the geometric center of the
pixel array comprises an active area having an array of active
pixels whose operation states are associated with image data of a
desired image, wherein the geometric center of the active area is
offset from the window.
63. The package of claim 54, wherein the geometric center of the
pixel array comprises an active area having an array of active
pixels whose operation states are associated with image data of a
desired image, wherein the geometric center of the active area is
offset from the entire pixel array.
64. A package, comprising: a package substrate having a supporting
surface on which a pixel array is positioned, wherein the pixel
array comprises an active area having an array of active pixels
whose operation states are associated with image data of a desired
image; a package cover having a window transmissive to light to be
modulated; and wherein the geometric center of the active area is
offset from the geometric center of the window.
65. The package of claim 64, wherein the pixel comprises a
deflectable and reflective micromirror.
66. The package of claim 65, wherein the offset comprises 1.5% or
more of the length of the window.
67. The package of claim 66, wherein the offset comprises 1.5% or
more of the width of the window.
68. The package of claim 65, wherein the offset comprises 5% or
more of the length of the window.
69. The package of claim 65, wherein the offset comprises 10% or
more of the length of the window.
70. The package of claim 65, wherein the geometric center of the
pixel array is offset from the geometric center of the package
cover.
71. A projection system, comprising: an illumination system
providing illumination light for the system; a spatial light
modulator of claim 28 for modulating the illumination light so as
to produce an image; and a display target on which the produced
image is displayed.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention is generally related to the art of
microelectromechanical devices, and more particularly, to
micromirror array devices for use in display systems.
BACKGROUND OF THE INVENTION
[0002] Projection display systems employing spatial light
modulators require an exact direction of light so as to obtain a
clear and undistorted image. Undesired light, such as light
scattered by the components of the spatial light modulator, that
reaches the display target of the display system will negatively
effect the displayed image, distorting the object being viewed. An
approach to solve this problem is to include a light-blocking
device, such as a black mask or inactive area, inside the spatial
light modulator.
[0003] Micromirrors are key components of microelectromechanical
system (MEMS)-based spatial light modulators. A typical MEMS-based
spatial light modulator usually comprises an array of miniature
micromirrors. These micromirrors are selectively deflected, for
example, in response to an electrostatic force, which in turn
selectively reflect incident light to produce digital images.
Therefore, undesired light can be prevented from reaching the
target by turning the mirrors in the border areas to their inactive
state. An inactive state is a state that is not associated with the
image data of the image to be displayed in the display system. For
this and other reasons, micromirror array devices, as well as other
image engines such as liquid crystal devices or the like may
include inactive areas in borders on all sides to avoid undesired
light scattering.
[0004] In current spatial light modulators, the micromirror array
devices are sealed within spaces between package covers and package
substrates for protection purposes. The package covers either
themselves are transmissive to the incident light, or comprise
inlay windows that are transmissive to the incident light. In
either configuration, the micromirror device array is aligned to
the center of the package cover or the center of the inlay window
of the package cover. In the presence of a light blocking mask,
when the illumination light is incident at an angle to the surface
of the micromirror array in the spatial light modulator, a group of
micromirrors in the array will not be illuminated, and the
modulated light from another group of micromirrors in the array
will not be able to escape the package. As a result, the desired
image will not be properly produced in the display target.
SUMMARY OF THE INVENTION
[0005] In view of the foregoing, the present invention discloses a
spatial light modulator having an array of micromirror devices. The
micromirror array is positioned within a space between a package
cover and package substrate of a device package. The package cover
comprises a light absorbing mask defining a window through which
the illumination light passes and is incident to the
micromirrors.
[0006] In an example of the invention, the light absorbing mask is
asymmetric with the opening window being offset from the center of
the mask. The micromirror array is positioned with its center
offset from the window defined by the mask. In particular, the
micromirror array is aligned to the front of the illumination light
to be modulated by the micromirror array.
[0007] In another example, the micromirror is positioned such that
the active area of the micromirror array is offset from the window,
but aligned to the front of the illumination light to be modulated.
The active area, however, may not be located at the center of the
micromirror array. Instead, the active area can be offset from the
center of the micromirror array.
[0008] The objects and advantages of the present invention will be
obvious, and in part appear hereafter and are accomplished by the
present invention. Such objects of the invention are achieved in
the features of the independent claims attached hereto. Preferred
embodiments are characterized in the dependent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The accompanying drawings are illustrative and are not to
scale. In addition, some elements are omitted from the drawings to
more clearly illustrate the embodiments. 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, in which:
[0010] FIG. 1 is a diagram that schematically illustrates an
exemplary display system employing a spatial light modulator having
an array of micromirrors in a package in which embodiments of the
invention can be implemented;
[0011] FIG. 2 illustrates therein another display system employing
multiple spatial light modulators each having an array of
micromirrors in a package in which embodiments of the invention can
be implemented;
[0012] FIG. 3 is a cross-section view of a portion of an exemplary
micromirror array in the spatial light modulators of FIGS. 1 and
2;
[0013] FIG. 4 is a perspective view of a portion of an exemplary
micromirror array device;
[0014] FIG. 5 illustrates components of an exemplary micromirror
array device package in which embodiments of the invention can be
implemented;
[0015] FIG. 6 illustrates a top view of the asymmetric light
absorbing mask in FIG. 5;
[0016] FIG. 7 is a cross-section view of the package in FIG. 5;
[0017] FIG. 8 is a top view of the micromirror array and the
opening window defined by the mask in FIG. 5 according to an
embodiment of the invention;
[0018] FIG. 9 is a top view of the micromirror array and the
opening window defined by the mask in FIG. 5 according to another
embodiment of the invention;
[0019] FIG. 10 is a top view of the micromirror array and the
opening window defined by the mask in FIG. 5 according to yet
another embodiment of the invention;
[0020] FIG. 11 is a top view of the micromirror array and the
opening window defined by the mask in FIG. 5 according to yet
another embodiment of the invention;
[0021] FIG. 12 is a top view of the micromirror array having an
inactive area and an active area that is not aligned to the center
of the micromirror array according to an embodiment of the
invention;
[0022] FIG. 13 is a top view of the micromirror array having an
inactive area and an active area that is not aligned to the center
of the micromirror array according to another embodiment of the
invention; and
[0023] FIG. 14 is a top view of the micromirror array having an
inactive area and an active area that is not aligned to the center
of the micromirror array according to yet another embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0024] Turning to the drawings, FIG. 1 presents an exemplary
display system that employs a spatial light modulator comprising an
array of micromirrors. In its basic configuration, display system
100 comprises light source 110, optical devices (e.g. light pipe
112, condensing lens 113 and projection lens 115), display target
116 and spatial light modulator 114 that further comprises a
plurality of micromirror devices (e.g. an array of micromirrors).
Light source 110 (e.g. an arc lamp) emits light through the color
wheel 111, the light integrator/pipe 112, and condensing lens 113
and onto spatial light modulator 114. Though the color wheel is
positioned before the light pipe in this example, the color wheel
may be positioned after the light pipe as well. The micromirrors of
the spatial light modulator 114 are actuated selectively by a
controller (e.g. as disclosed in U.S. Pat. No. 6,388,661 issued May
14, 2002, incorporated herein by reference) so as to reflect--when
in their "ON" position--the incident light into projection optics
415, resulting in an image on display target 416 (screen, a
viewer's eyes, a photosensitive material, etc.). Generally, more
complex optical systems are often used, especially in displaying
applications for color images.
[0025] A display system may use multiple spatial light modulators,
an exemplary such display system is illustrated in FIG. 2.
Referring to FIG. 2, the display system employs three spatial light
modulators 121, 124, and 127, each comprising an array of
micromirrors and being designated for respectively modulating the
multi-color (e.g. three primary color such as red, green, and blue,
or cyan, magenta, and yellow) light beams. A dichroic prism
assembly 101 is provided for splitting incident light into primary
colors. For this purpose, the dichroic prism assembly comprises
prisms 123a, 123b, 123c, 123d, 123e and 123f.
Totally-internally-reflection (TIR) surfaces, i.e. TIR surfaces
120a, 120b, and 120c, are defined at the prism surfaces that face
air gaps. The surfaces 122a and 122b of prisms 123c and 123e are
coated with dichroic films, yielding dichroic surfaces. In
particular, dichroic surface 122a reflects green light and
transmits other light. Dichroic surface 122b reflects red light and
transmits other light. The three spatial light modulators, 121, 124
and 127, each having a micromirror array device, are arranged
around the prism assembly.
[0026] In operation, incident white light 126 from light source 110
enters into prism 123b and is directed towards TIR surface 120a at
an angle larger than the critical TIR angle of TIR surface 120a.
TIR surface 120a totally internally reflects the incident white
light towards spatial light modulator 124, which is designated for
modulating the blue light component of the incident white light. At
the dichroic surface 122a, the green light component of the totally
internally reflected light from TIR surface 120a is separated
therefrom and reflected towards spatial light modulator 121, which
is designated for modulating green light. As seen, the separated
green light may experience TIR by TIR surface 120b in order to
illuminate spatial light modulator 121 at a desired angle. This can
be accomplished by arranging the incident angle of the separated
green light onto TIR surface 120b larger than the critical TIR
angle of TIR surface 120b. The rest of the light components, other
than the green light, of the reflected light from the TIR surface
120a pass through dichroic surface 122a and are reflected at
dichroic surface 122b. Because dichroic surface 122b is designated
for reflecting red light component, the red light component of the
incident light onto dichroic surface 122b is thus separated and
reflected onto spatial light modulator 127, which is designated for
modulating red light. Finally, the blue component of the white
incident light (white light 126) reaches spatial light modulator
124 and is modulated thereby. By collaborating operations of the
three spatial light modulators, red, green and blue lights can be
properly modulated. The modulated red, green, and blue lights are
recollected and delivered onto display target 116 through optic
elements, such as projection lens 115, if necessary.
[0027] FIG. 3 illustrates a cross-section view of a simplified
spatial light modulator in FIGS. 1 and 2. For simplicity and
demonstration purposes, only 8 micromirror devices are presented
therein. In this particular example, spatial light modulator 114
comprises an array of deflectable and reflective mirror plates such
as mirror plate 136. The micromirrors are formed on substrate 130,
which can be a light transmissive substrate, such as glass or
quartz. For deflecting the micromirrors, an array of addressing
electrodes (e.g. addressing electrode 134) is formed on
semiconductor substrate 132, which is placed proximate to the
micromirror array such that the mirror plates of the micromirrors
can be deflected in response to electrostatic forces derived from
electrostatic fields that are established between the mirror plates
and addressing electrodes. The addressing electrode is connected to
a voltage output node of a memory cell, such as a DRAM or a
charge-pump memory cell such that the electrical potential, thus
the voltage between the mirror plate and electrode if the electric
potential of the mirror plate is fixed, can be uniquely determined
and controlled by the data stored in the memory cell. A charge-pump
memory cell comprises a transistor and a capacitor, wherein the
first plate of the capacitor is connected to the drain of the
transistor forming a voltage output node, and the second plate of
the capacitor is connected to a pumping signal whose voltage varies
over time during operation. The gate of the transistor is connected
to a wordline, and the source of the transistor is connected to a
bitline, 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. Operations of the memory
cells using pulse-width-modulation technique is set forth in U.S.
Pat. No. 6,388,661 issued May 14, 2002, and U.S. patent application
Ser. No. 10/607,687 filed May 27, 2003, and U.S. patent application
Ser. No. 10/865,993 filed May 11, 2004, both to Richards, the
subject matter of each being incorporated herein by reference. In
operation, the data in the memory cell are updated according to the
image data, such as the bit plane data of the image produced by the
pulse-width-modulation. Such data in the memory cell reflects in
the voltage on the addressing electrode, and in turn, determines
the ON and OFF state of the mirror plate to which the electrode is
associated. At the ON/or OFF state, the mirror plate reflects
illumination light 138 either onto (e.g. 140) or away (e.g. 142)
from the display target, producing a dark or bright image pixel in
the display target.
[0028] In general, the micromirror array of a spatial light
modulator consists of hundreds of thousands or even 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 fewer numbers of micromirrors. FIG. 4
demonstratively illustrates a perspective view of an exemplary
spatial light modulator in FIG. 3. Referring to FIG. 4, an array of
micromirrors is formed on light transmissive substrate 130, while
an array of addressing electrodes is formed on silicon substrate
132 that is placed proximate to the micromirrors on substrate 130.
The two substrates are aligned (e.g. such that each mirror plate is
associated with an addressing electrode) and bonded together. The
distance between the substrates, thus the distance between the
mirror plates and addressing electrodes can be maintained by, for
example, posts deployed between the substrates and within the
micromirror array and/or the addressing electrode array.
Alternatively, the distance between the two substrates can be
maintained by pillars (e.g. spacer rings) between the substrates
and along the circumferences of the substrate, which is not shown
in the figure.
[0029] In the above example, the micromirrors are formed on light
transmissive substrate 130 separate from substrate 132 on which the
addressing electrodes are formed. Alternatively, the micromirrors
and the addressing electrodes can be formed on the same substrate,
preferably a semiconductor wafer, such as semiconductor substrate
132. In another embodiment of the invention, the micromirror
substrate can be bonded to a transfer substrate, and then the
micromirror substrate along with the transfer substrate is attached
to another substrate such as a silicon substrate having electrodes
and circuits formed thereon followed by removal of the transfer
substrate and patterning of the micromirror substrate to form the
micromirrors, other micromirror designs and methods are also
possible, which will not be discussed in detail.
[0030] The micromirror array device is often packaged for
protection purposes. An exemplary device package is illustrated in
FIG. 5, as set forth in U.S. patent application Ser. No. 10/443,318
to Tarn filed May 22, 2003, the subject matter being incorporated
herein by reference. Referring to FIG. 5, micromirror array device
114 is sealed within the space between package cover 148 and
package substrate 146 that is bonded to the package cover via
sealing medium 150. The package cover is transmissive to the
illumination light. Light blocking/absorbing mask 152 on the
package cover define a window (aperture) through which the
illumination light is incident onto the micromirrors and is
modulated thereby. In the embodiment of the invention, the light
absorbing block/absorbing mask is capable of blocking or absorbing
85% or more, or 95% or more, or more preferably 97% or more of the
illumination light incident thereto.
[0031] In this particular example, the package substrate comprises
a cavity in which the micromirror array device is positioned.
Alternatively, the package substrate can be a flat substrate, and
is bonded to the package cover via a spacer ring, which is not
illustrated.
[0032] In accordance with an embodiment of the invention, the light
absorbing mask is asymmetric, as shown in FIG. 6. Referring to FIG.
6, light absorbing/blocking strips 222, 224, 226, and 228 on the
borders of mask 152 have different widths, and the difference
preferably accords to the arrangement of the illumination light
beam that is incident at an angle to the micromirrors, thus an
angle to the plane of the window defined by the mask. For example,
strips 222 and 224 corresponding to the trailing and leading edges
of the illumination light beam 138 have different widths. Strips
226 and 228 whose lengths are along the illumination light beam may
or may not have the same width. Window 200 so defined by the strips
is offset from the center of mask 152. Specifically, the geometric
center of the window is offset form the geometric center of the
package cover. As a way of example, the offset comprises an offset
of 1.5% or more, such as 5% or more, or 10% or more of the length
of the package cover, or an offset of 1.5% or more, such as 5% or
more, or 10% or more of the width of the package cover, or a
combination thereof.
[0033] The micromirror array device (e.g. device 114) can be
positioned on the package substrate with its center aligned to the
center window 200. Because of the offset of the window to the
package cover (and the mask), the micromirror array device is
offset from the center of package cover 148. The micromirror array
device may also be offset from the center of the supporting surface
of the package substrate. The advantage of the asymmetric light
absorbing/blocking mask is better illustrated in FIG. 7.
[0034] Referring to FIG. 7, a cross-sectional view of micromirror
array device package 144 in FIG. 5 is illustrated therein. The
illumination light is incident to the micromirror array device at
an angle and limited by the light absorbing mask. Specifically,
strips 222 and 224 of light absorbing mask 152 (as shown in FIG. 6)
respectively define leading edges 138a and trailing edge 138b of
the illumination light allowed for entering into the package and
shining on the micromirrors. The leading and trailing edges of the
illumination light present incident angles .alpha. and .beta. to
the window surface. The angles may or may not be the same. For
example, when the window is parallel to the micromirror array and
the illumination light is within a light cone, which often occurs
in practical operation, angles .alpha. and .beta. are
different.
[0035] For most efficiently utilizing the illumination light
entering into the package while allowing all reflected light from
the ON state of the micromirrors, the footprint of the illumination
light between leading edge 138a and effective trailing edge 138c on
the micromirror array substantially covers all micromirrors in the
micromirror array, and the micromirror array is illuminated by such
footprint in its entirety such that no illumination light is
wasted. The effective trailing edge 138c, which is different from
the trailing edge 138b, is such a boundary that the illumination
light within 138c and 138a can escape from the package after
reflection by the micromirrors in the ON state, while the
illumination light otherwise are blocked within the package after
reflection by the micromirrors in the ON state. As shown in the
figure, reflected light 156 of the incident illumination light
along effective trailing edge 138b is tangent to the edge of strip
224. Such configuration can be accomplished in many ways.
[0036] For example, the strips can be adjusted according to the
given position of the micromirror array device with in the package.
Alternatively, the position of the micromirror array device can be
adjusted according to the given window defined by the strips of the
light blocking/absorbing mask. Or the position of the micromirror
array device and the window can be both adjusted relatively. In any
situation, the micromirror array is offset from the window defined
by the light absorbing/blocking mask, as illustrate in FIGS. 8 to
11.
[0037] Referring to FIG. 8, micromirror array device 114 has an
in-plane symmetrical axis 172 that is offset from an in-plane
symmetrical axis 174 of window 200 defined by the mask as shown in
FIG. 6 when viewed from the top of the window. The two in-plane
symmetrical axes may or may not be parallel to each other. For
example, the micromirror array device can be rotated along an axis
parallel to its normal direction relative to the supporting surface
of the package substrate. The edges of the micromirror array device
are not parallel to the edges of the supporting surface.
[0038] In another example, micromirror array device 114 is
positioned such that its geometric center 176 is offset from center
178 of window 200 defined by the light absorbing/blocking mask, as
shown in FIG. 9. As an aspect of this embodiment, the micromirror
array device can also be positioned such that the micromirror array
device is rotated along an axis parallel to its normal direction
relative to window 200.
[0039] In yet another example, the micromirror array device is
positioned such that an diagonal of the micromirror array device is
offset but parallel to the corresponding diagonal of window 200
defined by the light absorbing/blocking mask, as shown in FIG. 10.
Specifically, diagonal 204 of micromirror array device 114 is
offset from diagonal 206 of window 200. The two diagonals can be
parallel to each other.
[0040] As a way of example, the offset of the in-plane asymmetric
axis 172 in relation to axis 174 in FIG. 8, or the offset of the
geometric center 176 in relation to center 178 in FIG. 9, or the
offset (distance) of diagonal 204 of the micromirror array relative
to diagonal 206 of window 200 in FIG. 10, can be 1.5% or more, or
5% or more, or 10% or more, or 20% or more of the total number of
columns in the micromirror array device. Alternatively, the offset
can be 50 columns or more, such as 100 columns, or 150 columns or
more of the micromirror array device.
[0041] In still yet another embodiment of the invention, the two
diagonals can be crossed, as shown in FIG. 11. Referring to FIG.
11, diagonal 208 of micromirror array 114 is not parallel to
diagonal 210 of window 200. The crossing of the two diagonals can
be within the micromirror array device as illustrated in the
figure, or can be outside the micromirror array device but within
window 200 when viewed from the top of the window, or can be
outside both of the window and micromirror array device, depending
upon the specific displacement scheme of the micromirror array
device in relation to the window.
[0042] In addition to the light absorbing/blocking mask, the
micromirror array device may comprise active and inactive
micromirrors. The operation states of the inactive micromirrors are
not related to the image data, such as the bitplane data derived
from applications of a pulse-width-modulation algorithm on the
desired image. In contrast, operations of the active micromirrors
are associated with the image data of the desired image. The
inactive micromirrors can be constantly at the OFF state, resulting
in black or dark areas in the display target so as to enhance the
viewing quality of the displayed image. Specifically when being
arranged around the circumference of the micromirror array and
surrounding the active micromirrors, the resulting black or dark
areas in the display target can be advantageous for achieving high
contrast ratio. The inactive micromirrors can be resulted from
displaying images of an aspect ratio different from the default
aspect ratio of the micromirror array device. For example, when a
micromirror array of a default aspect ratio (e.g. 4:3) is used to
display images of an irregular aspect ratio (e.g. 16:9), or vice
versa, not every micromirror in the micromirror array corresponds
to an image pixel of the desired image. These unassociated
micromirrors become inactive micromirrors in that particular
display application. The inactive micromirrors may also be a
consequence from manufacturing of the micromirror array. In
practical manufacturing, the micromirrors are often fabricated with
an aid of sacrificial materials, which were deposited during
formation of the structures of the micromirrors, and removed
afterwards. Removal of the sacrificial materials, such as through
vapor phase chemical etching with selected spontaneous vapor phase
etchants, is often accompanied by so-named "proximity etching
effect" wherein micromirrors in the vicinity of the edge of the
micromirror array are etched differently from the inner
micromirrors. As a result, the micromirrors around the
circumference of the micromirror array behave differently from the
inner micromirrors. For this and among other reasons, extra
micromirrors enclosing the desired micromirrors can be designed and
fabricated along with the desired micromirrors. These extra
micromirrors will be operated as inactive micromirrors.
[0043] In accordance with yet another embodiment of the invention,
the active region (a region having the active micromirrors) is not
at the center of the micromirror array, as shown in FIG. 12.
Referring to FIG. 12, micromirror array 114 comprises active area
194 and inactive areas 192. The active area is asymmetrically
disposed within the micromirror array. Specifically, the geometric
center A of the active area is offset from the geometric center I
of the inactive area. The inactive segments 180 and 184 have
different numbers of columns of inactive micromirrors. The inactive
segments 186 and 190 may have different numbers of rows of inactive
micromirrors as well.
[0044] As yet another example, the in-plane symmetrical axis 234 of
active area 194 can be offset from the in-plane symmetrical axis
230 of the entire micromirror array device 114 as illustrated in
FIG. 13. The two in-plane symmetrical axes may or may not be
parallel to each other.
[0045] As yet another example, a diagonal of the active area can be
offset from the corresponding diagonal of the entire micromirror
array device as shown in FIG. 14. Referring to FIG. 14, diagonal
236 of the active area is offset from and not parallel to diagonal
238 of micromirror array 114. Alternatively, the two diagonals can
be offset from but parallel to each other, which is not shown in
the figure.
[0046] In the above examples, the offset of the geometric center A
relative to geometric center I in FIG. 12, or the offset of the two
in-plane symmetrical axes in FIG. 13, or the offset of diagonals
236 and 238 in FIG. 14, may comprise an offset of 1.5% or more, or
5% or more, or 10% or more, or 20% or more of the total number of
columns in the micromirror array device, or an offset of 1.5% or
more, or 5% or more, or 10% or more, or 20% or more of the total
number of rows in the micromirror array device, or a combination
thereof. Alternatively, the offset may comprise an offset of 50
columns or more, such as 100 columns or more, or 150 columns or
more of the micromirror array device, or an offset of 50 rows or
more, such as 100 rows or more, or 150 rows or more of the
micromirror array device, or a combination thereof. The offset may
include offset along the rows and offset along the columns of the
micromirror array.
[0047] In addition to the offsets of the micromirror relative to
the package cover and/or the window and/or the supporting surface,
and the offsets of the active area relative to the inactive area,
and/or the entire micromirror array, other offsets may exist. For
example, the active area may be offset form the window; and the
mask may be offset from the package cover.
[0048] It will be appreciated by those skilled in the art that a
new micromirror package has been disclosed. In view of the 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, all of the disclosed methods are
applicable to a spatial light modulator that is comprised of liquid
crystal device (e.g. transmissive LCDs or reflective LCOS) instead
of a micromirror array. Therefore, the invention as described
herein contemplates all such embodiments as may come within the
scope of the following claims and equivalents thereof.
* * * * *