U.S. patent application number 10/927562 was filed with the patent office on 2006-03-09 for micromirrors and hinge structures for micromirror arrays in projection displays.
Invention is credited to Andrew Huibers, Satyadev Patel.
Application Number | 20060050353 10/927562 |
Document ID | / |
Family ID | 35995897 |
Filed Date | 2006-03-09 |
United States Patent
Application |
20060050353 |
Kind Code |
A1 |
Huibers; Andrew ; et
al. |
March 9, 2006 |
MICROMIRRORS AND HINGE STRUCTURES FOR MICROMIRROR ARRAYS IN
PROJECTION DISPLAYS
Abstract
The micromirror of the present invention comprises a mirror
plate having thereon a cavity allowing deformation of a hinge
attached to the mirror plate and deflection of the mirror plate in
operation.
Inventors: |
Huibers; Andrew; (Palo Alto,
CA) ; Patel; Satyadev; (Sunnyvale, CA) |
Correspondence
Address: |
REFLECTIVITY, INC.
350 POTRERO AVENUE
SUNNYVALE
CA
94085
US
|
Family ID: |
35995897 |
Appl. No.: |
10/927562 |
Filed: |
August 25, 2004 |
Current U.S.
Class: |
359/238 ;
359/290; 359/291; 359/292 |
Current CPC
Class: |
G02B 26/0841
20130101 |
Class at
Publication: |
359/238 ;
359/290; 359/291; 359/292 |
International
Class: |
G02B 26/00 20060101
G02B026/00; G02F 1/01 20060101 G02F001/01 |
Claims
1. A spatial light modulator, comprising: an array of micromirrors,
each micromirror comprising a deformable hinge and a deflectable
reflective mirror plate attached to the deformable hinge, wherein
the mirror plate comprises a cavity in a surface of the mirror
plate; wherein a portion of the deformable hinge is disposed within
the cavity at least during a rotation of the mirror plate.
2. The spatial light modulator of claim 1, wherein the micromirror
further comprises: a substrate; and a post by which the mirror
plate and the hinge of the micromirror is held on the
substrate.
3. The spatial light modulator of claim 2, wherein the substrate is
transmissive to visible light.
4. (canceled)
5. The spatial light modulator of claim 2, wherein the cavity is an
elongated trench; and wherein the portion of the hinge is disposed
within the trench when the mirror plate is not deflected.
6. The spatial light modulator of claim 2, wherein the hinge has a
surface that is aligned to the same plane as the reflective surface
of the mirror plate.
7. The spatial light modulator of claim 6, wherein the surface of
the hinge comprises a light blocking layer.
8. The spatial light modulator of claim 2, wherein the hinge is
exposed to a light that it directed to the reflective surface of
the mirror plate for being modulated.
9. The spatial light modulator of claim 8, wherein the hinge
projects a shadow on the reflective surface of the mirror plate in
the presence of the incident light.
10. The spatial light modulator of claim 2, wherein the hinge is
outside the cavity when the mirror plate is not deflected, but
inside the cavity when the mirror plate is deflected.
11. The spatial light modulator of claim 10, wherein the hinge is
exposed to a light beam directed to the reflective surface of the
mirror plate.
12. The spatial light modulator of claim 2, wherein the substrate
is glass or quartz.
13. The spatial light modulator of claim 2, wherein the mirror
plates is operable to switch between an ON state and an OFF state,
wherein the mirror plate is rotated to an ON state angle in the ON
state, and to an OFF state angle other than the ON state angle in
the OFF state.
14. The spatial light modulator of claim 13, wherein the ON state
angle is 10.degree. or more relative to the substrate.
15. The spatial light modulator of claim 13, wherein the ON state
angle is 12.degree. or more relative to the substrate.
16. The spatial light modulator of claim 13, wherein the ON state
angle is 14.degree. or more relative to the substrate.
17. The spatial light modulator of claim 2, wherein the mirror
plate is substantially square.
18. The spatial light modulator of claim 2, wherein the mirror
plate has a zigzagged edge.
19. The spatial light modulator of claim 1, further comprising: an
array of electrodes and circuitry with each electrode and circuitry
being associated with a micromirror of the micromirror array for
deflecting the mirror plate of the micromirror.
20. The spatial light modulator of claim 19, wherein the electrodes
and circuitry are formed on a separate substrate than a substrate
on which the micromirrors are formed.
21. The spatial light modulator of claim 19, wherein the electrodes
and circuitry are formed on a substrate on which the micromirrors
are formed.
22. The spatial light modulator of claim 1, wherein the cavity is
located in a reflecting surface of the mirror plate.
23. The spatial light modulator of claim 1, wherein the cavity is
located in a surface opposite to a reflecting surface of the mirror
plate.
24. The spatial light modulator of claim 1, wherein the hinge
extends the cavity.
25. The spatial light modulator of claim 23, wherein the reflecting
surface has no cavity and is substantially flat.
27. The spatial light modulator of claim 1, wherein the hinge is a
torsion hinge and is operable to rotate proximate to or within the
cavity.
28. The spatial light modulator of claim 1, wherein the cavity is
disposed such that the cavity faces an electrode provide for
rotating said mirror plate.
29. A projection system, comprising: an illumination system
providing a light beam; a spatial light modulator of claim 1; an
optical element for directing the light onto or from the spatial
light modulator; and a display target.
30. The system of claim 29, wherein the illumination system further
comprises: a light source; a lightpipe; and a color filter.
31. The system of claim 30, wherein the color filter is positioned
between the light source and lightpipe.
32. The system of claim 30, wherein the color filter is positioned
after lightpipe and the light source along a propagation path of
light from the light source.
33. A spatial light modulator, comprising: an array of
micromirrors, each of which comprises a deformable hinge; and
deflectable mirror plate attached to the deformable hinge, wherein
the mirror plate has a reflective surface that is substantially
that without a dent, and another surface having a cavity.
34. The spatial light modulator of claim 33, wherein the
micromirror further comprises: a substrate; and a non-deflectable
post directly connecting the mirror plate to the substrate.
35. The spatial light modulator of claim 33, wherein at least a
portion of the deformable hinge is disposed in the cavity.
36. The spatial light modulator of claim 33, wherein the deformable
hinge is connected to a portion of the cavity via a contact.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention is related generally to spatial light
modulators, and, more particularly, to spatial light modulators
with micromirror arrays and hinge structures and methods of making
the same.
BACKGROUND OF THE INVENTION
[0002] Spatial light modulators (SLMs) are transducers that
modulate an incident beam of light in a spatial pattern in response
to an optical or electrical input. The incident light beam may be
modulated in phase, intensity, polarization, or direction. This
modulation may be accomplished through the use of a variety of
materials exhibiting magneto-optic, electro-optic, or elastic
properties. SLMs have many applications, including optical
information processing, display systems, and electrostatic
printing.
[0003] The present invention relates to SLMs having reflective
micromirrors that are provided within a micromirror array for,
e.g., projection-type displays (or for steering light beams,
maskless lithography and maskless micro array production). A
simplified such display system is illustrated in FIG. 1. In its
very basic configuration, display system 100 comprises light source
102, optical devices (e.g. light pipe 104, condensing lens 106 and
projection lens 108), display target 112 and spatial light
modulator 110 that further comprises a plurality of micromirror
devices (e.g. an array of micromirror devices). Light source 102
(e.g. an arc lamp) emits light through the light integrator/pipe
104 and condensing lens 106 and onto spatial light modulator 110.
The micromirrors of the spatial light modulator 110 are selectively
actuated 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 108, resulting in an image on display target 112
(screen, a viewer's eyes, a photosensitive material, etc.).
Generally, more complex optical systems, such as systems employing
more than three spatial light modulators (each being designated for
modulating one of the three primary colors--red, green, and red)
are often used, especially in displaying applications for color
images.
[0004] Currently, varieties of MEMS-based SLMs for use in display
systems have been developed. Regardless of the differences, a
common basic configuration of the MEMS-based SLMs comprises a hinge
and a micromirror plate that is attached to the hinge for rotating
relative to the substrate by the hinge. And the mechanism of the
MEMS-based SLMs for display is based on rotating the micromirror
plate of individual micromirrors along the hinge at different
angles, thus reflecting incident light onto or away from a display
target at the different angles. In this regard, mechanical
properties of the hinge, the micromirror plate and the attachment
of the two are critical factors to the overall performance of the
micromirrors and the quality of the displayed images.
[0005] Therefore, what is needed is a spatial light modulator
having micromirrors devices with robust mechanical properties for
use in display systems.
SUMMARY OF THE INVENTION
[0006] Disclosed herein is a micromirror device having a
deflectable and reflective mirror plate and a deformable hinge,
wherein the mirror plate has a cavity in a surface other than the
reflective surface provided for reflecting incident light. The
deformable hinge, such as a torsion hinge can be disposed within
the cavity of the mirror plate. The objects and advantages of the
present invention will be obvious, and in part appear hereafter,
and are accomplished by the present invention that provides a
method and apparatus for operating pixels of spatial light
modulators in display systems. Such objects of the invention are
achieved in the features of the independent claims attached hereto.
Preferred embodiments are characterized in the dependent claims. 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.
BRIEF DESCRIPTION OF DRAWINGS
[0007] 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:
[0008] FIG. 1 diagrammatically illustrates an exemplary display
system employing a spatial light modulator in which embodiments of
the invention can be implemented;
[0009] FIG. 2 is a perspective view of a portion of the spatial
light modulator having a set of micromirrors according to an
embodiment of the invention;
[0010] FIG. 3A is a cross-sectional view of a micromirror in FIG.
2;
[0011] FIG. 3B is another cross-sectional view of a micromirror in
FIG. 2;
[0012] FIG. 4 is a cross-sectional view of the micromirror
according to an embodiment of the invention;
[0013] FIG. 5 is a perspective view of a portion of the spatial
light modulator having a set of micromirrors in FIG. 4;
[0014] FIG. 6 is a cross-sectional view of the micromirror
according another embodiment of the invention;
[0015] FIG. 7 illustrates a perspective view of a portion of the
spatial light modulator having a set of micromirrors in FIG. 6;
[0016] FIG. 8 is a cross-sectional view of the micromirror
according to yet another embodiment of the invention;
[0017] FIG. 9 illustrates a perspective view of a portion of the
spatial light modulator having a set of micromirrors in FIG. 8;
[0018] FIG. 10 is a cross-sectional view of the micromirror
according to yet another embodiment of the invention;
[0019] FIG. 11 illustrates a perspective view of a portion of the
spatial light modulator having a set of micromirrors in FIG.
10;
[0020] FIG. 12 is a cross-sectional view of the micromirror
according to yet another embodiment of the invention;
[0021] FIG. 13 illustrates a perspective view of a portion of the
spatial light modulator having a set of micromirrors in FIG.
12;
[0022] FIG. 14A and FIG. 14B are cross-section views of the
micromirror in FIG. 3A and FIG. 3B during an exemplary fabrication
process.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0023] The micromirror of the present invention comprises a
reflective deflectable mirror plate attached to a deformable hinge
that is held on a substrate. For holding the deformable hinge in a
way such that the mirror plate and the deformable hinge are in the
same plane when the mirror plate is not deflected, the mirror plate
has a cavity within with the hinge is located and connected to the
mirror plate. The hinge can be aligned to a surface of the mirror
plate, while the surface may or may not be the reflective surface.
When the hinge is align with the reflective surface, the hinge is
exposed to the light beam incident to the mirror plate, and a
portion of the mirror plate is shaded by the hinge from the
incident light. As another example of the invention, the mirror
plate is directly held by and connected to a substrate via a
non-deflectable post. In this instance, the mirror plate has a
deformable portion within the mirror plate.
[0024] The micromirror of the present invention has many
applications, one of which is spatial light modulators of display
systems as shown in FIG. 1. Referring to FIG. 1, an exemplary
display system having a spatial light modulator composed of an
array of micromirrors is illustrated therein. In its basic
configuration, display system 100 comprises illumination system
101, optical elements 108 and 109, spatial light modulator 110, and
display target 112.
[0025] The illumination system provides primary color light that
are sequentially applied to the spatial light modulator. In an
exemplary configuration, the illumination system 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. In this particular configuration,
the color wheel is positioned after the light source and lightpipe
on the propagation path of the illumination light from the light
source. Of course, other optical configurations can also be used,
such as placing the color wheel between the light source and the
lightpipe. Optical element 108, which can be a condensing lens,
directs the primary color light onto the spatial light modulator in
which the primary color light is reflected either into or away from
projection lens 109 so as to generate a desired image pattern in
the display target. The set of primary colors can comprise any set
of three or more colors used to render the output image.
[0026] In a number of embodiments of the invention, the micromirror
array of the spatial light modulator micromirror array has millions
of micromirrors depending upon the desired resolution of the
display system. For example, the spatial light modulator may have a
resolution of 1024.times.768 or higher, or 1280.times.1024 or
higher, or 1640.times.1280 or higher. Of course, the micromirror
array device may have a fewer number of micromirrors than in
display, or other applications, such as optical switching.
[0027] The micromirror array, especially used for display systems,
can be constructed having a pitch (the center-to-center distance
between adjacent micromirrors) of 25 micrometers or less, or 10.16
micrometers or less, or from 4.38 to 10.16 micrometers. The gap
between adjacent micromirrors is approximately of 0.5 micrometers
or less, or from 0.1 to 0.5 micrometer. And the mirror plate of the
micromirror has a dimension of from 20 micrometers to 10
micrometers.
[0028] FIG. 2 illustrates a perspective view of a portion of an
exemplary spatial light modulator in FIG. 1. For simplicity
purposes, only 4.times.4 micromirrors are presented. The
micromirrors are formed on substrate 230, which can be a light
transmissive substrate, such as glass or quartz. Alternatively, the
micromirrors can be formed on a semiconductor wafer having thereon
circuitry, such as memory cells and electrodes. In another
embodiment of the invention, the micromirrors can be formed on a
micromirror plate that is formed on a transfer substrate that is
light transmissive. Specifically, the micromirror plate can be
formed on the transfer substrate and then the micromirror substrate
along with the transfer substrate is attached to another substrate
such as a light transmissive substrate followed by removal of the
transfer substrate and patterning of the micromirror substrate to
form the micromirror.
[0029] In accordance with an embodiment of the invention, the
micromirror array comprises at least a micromirror whose hinge and
mirror plate are in the same plane. For example, micromirror 210
comprises a mirror plate that is attached to a hinge. The mirror
plate has a reflective surface for reflecting light incident
thereon. In response to an electrostatic force (e.g. derived from
an electrostatic field established between the mirror plate and an
electrode (not shown in the figure)), the mirror plate is operable
to rotates relative to the substrate. The hinge of the micromirror
is positioned on the same plane as the mirror plate. In particular,
the hinge is located within a trench of the mirror plate.
Alternatively, the hinge and the surfaces of the mirror plate can
be disposed in separate planes.
[0030] The trench can be made on the reflecting surface of the
mirror plate--resulting exposure of the hinge to the incident
light; and a portion of the mirror plate (e.g. the portion of the
mirror plate underneath the hinge in relation to the propagation
direction of the incident light) is shaded by the hinge.
Alternatively, the trench can be made on the opposite surface of
the mirror plate to the reflecting surface, resulting in hiding the
hinge from the incident light. In accordance with yet another
embodiment of the invention, the cavity can be made in the mirror
plate such that the cavity faces an electrode that is disposed for
deflecting the mirror plate having the cavity. This configuration
is more preferred since undesired light scattering from the hinge
can be avoided.
[0031] The hinge within the trench can be positioned as desired.
For example, the hinge can be positioned such that a surface of the
hinge is aligned with a surface of the mirror plate. In particular,
for simplifying the fabrication, an example of which will be
discussed in detail afterwards, the surface exposed to the incident
light of the hinge is aligned to the reflecting surface of the
mirror plate.
[0032] In accordance with another embodiment of the invention,
though less preferred, the hinge can be positioned within the
trench such that the surface of the hinge exposed to the incident
light is below the reflecting surface of the mirror plate when
viewed along the incident light. And the reflecting surface is
preferably flat without cavity.
[0033] In accordance with yet another embodiment of the invention,
the trench can be made on a surface of the mirror plate not exposed
to the incident light. Specifically, the trench can be made in a
surface opposite to the reflecting surface exposed to the incident
light. In this way, the hinge formed within the trench will be
hidden from the incident light, which is not shown in the figure.
The hinge can be positioned within the trench such that a surface
of the hinge is aligned with a surface of the mirror plate. And the
hinge can extends across the cavity, special across the length of
the trench in the particular example as shown in the figure.
[0034] For enabling the deflection of the mirror plate, the mirror
plate can be attached to the hinge via a hinge contact that is
positioned within the trench and between the hinge and a surface of
the trench.
[0035] When the micromirror is constructed such that the hinge is
positioned with the trench but exposed to the incident light (e.g.
when the trench is made in the reflecting surface of the mirror
plate), light scattering may occur, resulting in quality
degradation of the displayed images, especially reduction in
contrast ratio. This problem can be alleviated by depositing a
light blocking/absorbing film on the portion of the hinge exposed
to the incident light. Moreover, the trench in the mirror plate can
also be coated with a light blocking/absorbing material for
reducing unexpected light scattering therefrom.
[0036] For better illustrating the relative geometric positions of
the mirror plate and the hinge, a cross-section view taken along
line AA as shown in FIG. 2 is presented in FIG. 3A. Referring to
FIG. 3A, hinge 230 is held on substrate 230 by posts. Attached to
the hinge via the hinge contact is mirror plate 211. The incident
light propagates from "the bottom," travels through substrate 230,
and impinges hinge 203 and the reflective surface of mirror plate
211.
[0037] FIG. 3B is another cross-section view taken along line BB in
FIG. 2. It clearly shows that hinge 203 is positioned within trench
201 of mirror plate 211 and connected to the mirror plate via hinge
contact 205. The trench is in the reflecting surface of the mirror
plate, and thus exposed to the incident light.
[0038] Alternative to the trench in the mirror plate for the hinge
to be positioned, a cavity within the mirror plate can be made for
the same purposes, as shown in FIG. 4. Referring to FIG. 4, mirror
plate 203 is formed on substrate 230, and held on the substrate by
post 207. For enabling the rotation of the mirror plate above the
substrate, elastic strip 208 is attached to the mirror plate; and
cavity 201 is formed within the mirror plate. The cavity is at a
location such that a portion of the elastic strip can move freely
into the cavity during the deflection of the mirror plate. In this
particular example, the mirror plate is held by the post, and the
post is preferably positioned offset from the geometric center of
the mirror plate such that the mirror plate can rotate
asymmetrically--that is, the mirror plate can rotate to a larger
angle in one direction than in another. Accordingly, the cavity
within the mirror plate is centered at a location offset from the
geometric center of the mirror plate, but centered proximately the
post. Alternatively, the post can be positioned around the
geometric center.
[0039] Substrate 230 in this particular example can be a light
transmissive substrate, such as glass or quartz. The cavity is made
in the reflective surface of the mirror plate. In operation, the
incident light propagates through the substrate and impinges the
elastic strip and the mirror plate. The cavity is exposed to the
incident light. For reducing unexpected light scattering, the
elastic strip, as well as the portion of the mirror plate
underneath the hinge can be coated with a light blocking/absorbing
material.
[0040] In another embodiment of the invention, the cavity can be
made in a surface not exposed to the incident light, such as the
surface opposite to the reflection surface of the mirror plate,
which is not shown in the figure. In this instance, one or more
posts can be provided to hold the elastic strip and the mirror
plate on the substrate; and the elastic strip is hidden from the
incident light and thus not exposed to the incident light.
[0041] FIG. 5 illustrates a spatial light modulator having an array
of micromirrors in FIG. 4. Though illustrated as rectangular or
square in shape, the cavity of the individual micromirror can be in
any desired shapes, such as circle or even an irregular shape, as
long as the formed cavity provides a space enabling the deflection
of the mirror plate.
[0042] Referring to FIG. 6, another exemplary micromirror according
to an embodiment of the invention is illustrated therein. Mirror
plate 203 has cavity 254 formed on a reflective surface of the
mirror plate. Elastic strip 250 is attached to the reflective
surface and connected to substrate 230 via post 252. The post is
positioned such that the portion of the elastic strip around the
post deflects during operation, and the deflected portion can enter
into the cavity such that the mirror plate can rotate.
[0043] FIG. 7 illustrates a perspective view of a portion of an
array of micromirrors in FIG. 6. It can be seen in the drawing
that, the elastic strips of individual micromirrors can be
connected together to form a strip across the micromirrors of an
entire row of the micromirror array. This configuration simplifies
the electronic setup for the system. For example, all the mirror
plates of the micromirrors can be provided with a uniform voltage
via the connected frames in operation. Electrostatic forces between
the mirror plates and electrodes for deflecting the mirror plates
can be simply manipulated through the voltages applied to
individual electrodes.
[0044] Referring to FIG. 8, a cross-section view of another
exemplary micromirror according to an embodiment of the invention
is illustrated therein. The micromirror comprises mirror plate 203
and elastic strip 208 that is attached to the reflective surface of
the mirror plate. The elastic strip has a flexible portion 256 that
is connected to the light transmissive substrate. In order for
enabling rotation of the mirror plate relative to the light
transmissive substrate, the mirror plate has a cavity that is
located around the flexible portion of the elastic strip. With is
configuration, the cavity in the mirror plate, the elastic strip
and the mirror contact in combination enables the mirror plate to
rotate relative to the light transmissive substrate.
[0045] FIG. 9 illustrates a perspective view of a portion of an
array of micromirrors in FIG. 8. As an aspect of the embodiment of
the invention, the elastic strip of the adjacent micromirrors can
be connected together as shown in the figure.
[0046] In the presence of the flexible portion (e.g. flexible
portion 256 in FIG. 8), the cavity may not be necessary according
to another embodiment of the invention, as shown in FIG. 10. In
this instance, the flexible portion extends a particular distance
from the reflecting surface of the mirror plate to the light
transmissive substrate--defining the particular distance between
the mirror plate and the substrate. As a result, the mirror plate
is able to be deflected. FIG. 11 illustrates a perspective view of
a portion of an array of micromirrors of FIG. 10. As an aspect of
the embodiment, the elastic strips of adjacent micromirrors can be
connected together.
[0047] In the above examples, the elastic strips of the
micromirrors are provided for enabling the rotation of the mirror
plate. In yet another embodiment of the invention, a non-deformable
post can be provided, not only for holding the mirror plate above
the substrate, but also for enabling the mirror plate to rotate
relative to the substrate, as shown in FIG. 12.
[0048] Referring to FIG. 12, reflective mirror plate 203 is
attached to and held by post 212 that is non-deformable and formed
on the light transmissive substrate 230. In operation, an
electrostatic force is exerted to the mirror plate for rotating the
mirror plate relative to the substrate. The mirror plate has a
reflective surface for reflecting incident light. The reflective
surface, however is perfectly flat without a dent like those in the
art unavoidably formed during the fabrication.
[0049] The mirror plates of the micromirrors as described above may
take any desired shapes, though preferably four-sided or
substantially four-sided shapes. The mirror plate may also have
zigzagged edges. Because the mirror plate is responsible for
reflecting the incident light, the mirror plate is desired to have
a reflective surface with high reflectance, such as reflecting 90%
or more, or 99% or more incident light. In accordance with the
operation mechanism of the micromirror plate and the constructional
design, it is desired that the posts comprise materials that are
insusceptible to elastic deformation (e.g. fatigue, creep,
dislocation motion) during the operation of the device. It is also
preferred that such materials have large elastic modulus and
exhibits high stiffness. Opposite to that of the posts, the
materials of the hinge are expected to be more compliant because
the hinge deforms while the micromirror plate pivots. Moreover, the
hinge is desired to be electrically conducting such that the
micromirror plate can be held at a particular voltage level.
[0050] In the embodiments as discussed above, the cavity can be
made in any suitable shapes. In particular, the depth of the cavity
is determined based on the deflection of the mirror plate. In an
embodiment of the invention, the depth of the cavity is selected
such that the mirror plate can be deflected. Specifically, the
portion of the elastic strip in direct contact with the post (e.g.
as shown in FIG. 4) can move into the cavity freely. In another
embodiment of the invention, the interior surface of the cavity
acts as a contacting surface for limiting the deflection of the
mirror plate. Accordingly, the depth of the cavity is selected such
that deflection of the mirror plate is stopped when a portion of
the elastic strip contact against the interior surface of the
cavity.
[0051] There is a variety of ways to construct the micromirror
devices described above. An exemplary process will be discussed in
the following with references to FIG. 14A and FIG for fabricating
the micromirror in FIG. 3A (and FIG. 3B). It should be appreciated
by those ordinary skills in the art that the exemplary processes
are for demonstration purposes only and should not be interpreted
as a limitation.
[0052] For better illustrates the exemplary fabrication process,
FIG. 14A and FIG. 14B respectively illustrates the micromirror in
cross-section views of FIGS. 3A and 3B in the fabrication process.
Referring to FIG. 14A, substrate 230 is provided. First sacrificial
layer 232 is deposited on the substrate following by patterning of
the sacrificial layer so as to form post area 238 for the posts.
After pattering sacrificial layer 232, post layer 233 is deposited
and patterned so as to form the posts of the micromirror.
[0053] The substrate in this case is a light transmissive
substrate, such as glass or quartz. First sacrificial layer 232 may
be any suitable material, such as amorphous silicon, or could
alternatively be a polymer or polyimide, or even polysilicon,
silicon nitride, silicon dioxide, etc. depending upon the choice of
sacrificial materials, and the etchant selected. If the first
sacrificial layer is amorphous silicon, it can be deposited at
300-350.degree. C. The thickness of the first sacrificial layer can
be wide ranging depending upon the micromirror size and desired
title angle of the micro-micromirror, though a thickness of from
500 .ANG. to 50,000 .ANG., preferably around 10,000 .ANG., is
preferred. The first sacrificial layer may be deposited on the
substrate using any suitable method, such as LPCVD or PECVD.
[0054] As an optional feature of the embodiment, an anti-reflection
layer (not shown in the figure) may be deposited on the surface of
the substrate. The anti-reflection layer can be deposited for
reducing the reflection of the incident light from the surface of
the substrate. Alternatively, other optical enhancing layers may be
deposited on either surface of the glass substrate as desired. As
another aspect of the embodiment of the invention, a light blocking
material can be deposited on the light transmissive substrate. The
light blocking material can be deposited as a light blocking frame,
or light blocking strips, or light blocking grid on a surface of
the light transmissive substrate, or can be formed on the edges of
the light transmissive substrate.
[0055] After patterning the post layers, hinge layer 234 is
deposited and patterned to form the designed hinge. After
completion of the hinge, a portion of the mirror plate 241 as
better illustrated in FIG. 14B is formed. Mirror plate portion 241
has the sane thickness as the hinge on the first sacrificial layer.
For this purpose, second sacrificial layer 236 is deposited and
patterned such that, after patterning, the formed hinge is covered
by the second sacrificial material. Then a portion of the mirror
plate 241 is deposited and patterned. The mirror portion 241 has
substantially the same thickness as hinge 234. On the formed mirror
plate portion 241, third sacrificial layer 237 is deposited and
patterned followed by depositing and patterning of mirror contact
240 and mirror portion 242, as better illustrated in FIG. 14B.
[0056] The materials of the structural layers, such as the hinge,
the mirror plate and other members if desired of the micromirror is
selected according to their designated functions, as well as the
etching method to be used for removing the sacrificial materials.
In particular, because the micromirror is designated for reflecting
incident light in the spectrum of interest (e.g. visible light
spectrum), it is preferred that the micromirror plate layer
comprises of one or more materials that exhibit high reflectivity
(preferably 90% or higher) to the incident light. According to one
embodiment of the invention, micromirror plate layer 300 is a
multi-layered structure. For example, the multilayered hinge may
comprise a reflection layer, a protection layer, and an enhancing
layer. The reflection layer may comprise one or more materials
exhibiting high light reflectivity. Examples of such materials are
Al, Ti, AlSiCu or TiAl. In the preferred embodiment of the
invention, layer 305 is aluminum with a thickness of 2500 .ANG..
This aluminum layer is preferred to be deposited at 150.degree. C.
or other temperatures preferably less than 400.degree. C. The
protection layer may be a SiO.sub.x layer with a preferred
thickness of 400 .ANG.. The enhancing layer may be comprised of
metal or metal alloy for enhancing the electric and mechanical
properties of the micromirror plate. An example of such enhancing
layer is titanium with a thickness of 80 .ANG.. Of course, other
suitable materials having high reflectivity to the incident light
of interest may also be adopted for the micromirror plate. In
depositing the micromirror plate layer, PVD is preferably used at
150.degree. C. The thickness of the micromirror plate layer can be
wide ranging depending upon the desired mechanical (e.g. elastic
module), the size of the micromirror, desired titled angle and
electronic (e.g. conductivity) properties of the micromirror plate
and the properties of the materials selected for forming the
micromirror plate. According to the invention, a thickness of from
500 .ANG. to 50,000 .ANG., preferably around 2500 .ANG., is
preferred. In patterning the mirror plate, the standard photoresist
patterning followed by etching using, for example CF4, Cl2, or
other suitable etchant depending upon the specific material of the
micromirror plate layer can be employed.
[0057] Because the hinge provides a rotation axis for the
micromirror plate, it is natural to expect that the hinge layer
comprises a material that is at least susceptible to plastic
deformation (e.g. fatigue, creep, and dislocation motion).
Furthermore, when the hinge layer is also used as electric contact
for the micromirror plate, it is desired that the material of the
hinge layer is electrically conductive. Examples of suitable
materials for the hinge layer are silicon nitride, silicon oxide,
silicon carbide, polysilicon, Al, Ir, titanium, titanium nitride,
titanium oxide(s), titanium carbide, CoSiN.sub.x, TiSiN.sub.x,
TaSiN.sub.x, or other ternary and higher compounds. When titanium
is selected for the hinge layer, it can be deposited at 1000C.
Alternatively, the hinge layer may comprise of multi-layers, such
as 100 .ANG. TiN.sub.x and 400 .ANG. SiN.sub.x. It should be noted
that hinge 326 can be a flexure, torsion or a combination
flexure-torsion hinge, and its thickness need not be the same as
that of micromirror 300. On the contrary, a reduced thickness
compared to the micromirror plate increases the flexibility of the
hinge, allowing the micromirror plate a greater pivoting angle
relative to the substrate.
[0058] In an embodiment of the invention, the micromirror plate
layer may comprise an aluminum layer, and the second sacrificial
layer is silicon. This design, however, can cause defects in the
hinge structure due to the diffusion of the aluminum and silicon at
the edges of the micromirror plate, wherein the aluminum is exposed
to the silicon. To solve this problem, a protection layer (not
shown) may be deposited on the patterned micromirror plate before
depositing the second sacrificial silicon layer such that the
aluminum layer can be isolated from the silicon sacrificial layer.
Then the protection layer is patterned according to the shape of
the micromirror plate.
[0059] It will be appreciated by those of skill in the art that a
new and useful spatial light modulator has been described herein.
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, 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 such embodiments as may come within the scope
of the following claims and equivalents thereof.
* * * * *