U.S. patent application number 13/092827 was filed with the patent office on 2011-08-18 for method and apparatus for lighting a display device.
This patent application is currently assigned to QUALCOMM MEMS Technologies, Inc.. Invention is credited to Surya Prakash Ganti, Ming-Hau Tung, Chun-Ming Wang.
Application Number | 20110199667 13/092827 |
Document ID | / |
Family ID | 38428254 |
Filed Date | 2011-08-18 |
United States Patent
Application |
20110199667 |
Kind Code |
A1 |
Wang; Chun-Ming ; et
al. |
August 18, 2011 |
METHOD AND APPARATUS FOR LIGHTING A DISPLAY DEVICE
Abstract
Methods and apparatus for providing lighting in a display are
provided. In one embodiment, a microelectromechanical system (MEMS)
is provided that includes a transparent substrate and a plurality
of interferometric modulators. The interferometric modulators
include an optical stack coupled to the transparent substrate, a
reflective layer over the optical stack, and one or more posts to
support the reflective layer and to provide a path for light from a
backlight for lighting the display.
Inventors: |
Wang; Chun-Ming; (San Jose,
CA) ; Tung; Ming-Hau; (San Jose, CA) ; Ganti;
Surya Prakash; (San Jose, CA) |
Assignee: |
QUALCOMM MEMS Technologies,
Inc.
San Diego
CA
|
Family ID: |
38428254 |
Appl. No.: |
13/092827 |
Filed: |
April 22, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
12544184 |
Aug 19, 2009 |
7933475 |
|
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13092827 |
|
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|
11357702 |
Feb 17, 2006 |
7603001 |
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12544184 |
|
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Current U.S.
Class: |
359/290 ;
362/97.1 |
Current CPC
Class: |
G02B 26/001
20130101 |
Class at
Publication: |
359/290 ;
362/97.1 |
International
Class: |
G02B 26/02 20060101
G02B026/02; G02F 1/13357 20060101 G02F001/13357 |
Claims
1. A display comprising: a plurality of display elements having a
viewing side; a backlight positioned on a side of the plurality of
display elements opposite the viewing side; and one or more
waveguides positioned between the display elements, the one or more
waveguides configured to provide a path for light emitted by the
backlight to illuminate the display elements.
2. The display of claim 1, wherein the one or more waveguides
comprises one or more posts configured to support at least a
portion of the display elements.
3. The display of claim 1, wherein the one or more waveguides are
configured to direct the light emitted by the backlight to the
viewing side of the display elements.
4. The display of claim 1, wherein the display elements are
reflective display elements.
5. The display of claim 1, where in the display elements are micro
electromechanical display elements.
6. The display of claim 5, wherein the display elements comprise
interferometric modulators.
7. The display of claim 6, wherein the interferometric modulators
comprise: an optical stack coupled to a transparent substrate; a
reflective layer over the optical stack; and one or more posts to
support the reflective layer, the one or more posts comprising the
one or more waveguides.
8. The display of claim 1, further comprising a plurality of light
scatterers or reflectors configured to redirect the light passing
through the one or more waveguides to the display elements.
9. The display of claim 8, further comprising one or more
reflecting surfaces arranged to direct light emitted by the one or
more waveguides to the plurality of light scatterers or
reflectors.
10. The display of claim 8, further comprising a glass layer on the
viewing side of the display elements, the glass layer including the
plurality of light scatterers or reflectors.
11. The display of claim 1, further comprising: a processor in
electrical communication with the display elements, the processor
configured to process image data; and a memory device in electrical
communication with the processor.
12. A display comprising: a plurality of means for modulating
light, the plurality of light modulating means having a viewing
side; a means for emitting light positioned on a side of the
plurality of light modulating means opposite the viewing side; and
one or more means for guiding light positioned between the
plurality of light modulating means, the one or more light guiding
means configured to provide a path for light emitted by the light
emitting means to illuminate the plurality of light modulating
means.
13. The display of claim 12, wherein the one or more light guiding
means comprise one or more means for supporting at least a portion
of the light modulating means.
14. The display of claim 12, wherein the one or more light guiding
means are configured to direct the light emitted by the light
emitting means to the viewing side of the plurality of light
modulating means.
15. The display of claim 12, wherein the plurality of light
modulating means comprise: an first means for reflecting coupled to
a transparent substrate means; a second means for reflecting, said
second reflecting means being movable and positioned over the first
reflecting means; and means for supporting the second reflecting
means, wherein the supporting means comprises the light guiding
means.
16. The display of claim 12, further comprising a plurality of
means for scattering or reflecting light configured to redirect the
light passing through the light guiding means to the light
modulating means.
17. The display of claim 16, further comprising a third means for
reflecting arranged to direct light from the light guiding means to
the plurality of light scattering or reflecting means.
18. The display of claim 12, wherein the plurality of light
modulating means comprises a plurality of display elements, or
wherein the light emitting means comprises a backlight, or wherein
the one or more light guiding means comprises one or more light
guides.
19. A method for providing a display, the method comprising:
providing a plurality of display elements having a viewing side;
positioning a backlight on a side of the plurality of display
elements opposite the viewing side; and forming one or more
waveguides between the display elements, wherein the one or more
waveguides are configured to provide a path for light emitted by
the backlight to illuminate the display elements.
20. The method of claim 19, wherein providing a plurality of
display elements comprises: providing a transparent substrate; and
forming a plurality of interferometric modulators including:
coupling an optical stack to the transparent substrate; forming a
reflective layer over the optical stack; and forming one or more
posts to support the reflective layer, the one or more posts
comprising the one or more waveguides.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
patent application Ser. No. 12/544,184, filed Aug. 19, 2009, and
titled METHOD AND APPARATUS FOR PROVIDING BACK-LIGHTING IN A
DISPLAY DEVICE, which is a continuation application of U.S.
application Ser. No. 11/357,702, filed Feb. 17, 2006, and titled
METHOD AND APPARATUS FOR PROVIDING BACK-LIGHTING IN AN
INTERFEROMETRIC MODULATOR DISPLAY DEVICE, each of which is hereby
incorporated by reference herein in its entirety.
BACKGROUND
[0002] 1. Field
[0003] The present invention relates generally to display devices,
and more particularly to interferometric modulator display
devices.
[0004] 2. Description of the Related Art
[0005] Microelectromechanical systems (MEMS) include
micromechanical elements, actuators, and electronics.
Micromechanical elements may be created using deposition, etching,
and/or other micromachining processes that etch away parts of
substrates and/or deposited material layers or that add layers to
form electrical and electromechanical devices. One type of MEMS
device is called an interferometric modulator. As used herein, the
term interferometric modulator or interferometric light modulator
refers to a device that selectively absorbs and/or reflects light
using the principles of optical interference. In certain
embodiments, an interferometric modulator may comprise a pair of
conductive plates, one or both of which may be transparent and/or
reflective in whole or part and capable of relative motion upon
application of an appropriate electrical signal. In a particular
embodiment, one plate may comprise a stationary layer deposited on
a substrate and the other plate may comprise a metallic membrane
separated from the stationary layer by a transparent medium (e.g.,
an air gap). As described herein in more detail, the position of
one plate in relation to the other plate can change the optical
interference of light incident on the interferometric modulator.
Such devices have a wide range of applications, and it would be
beneficial in the art to utilize and/or modify the characteristics
of these types of devices so that their features can be exploited
in improving existing products and creating new products that have
not yet been developed.
[0006] Conventional interferometric modulator display devices
typically implement front-lighting that provides light for viewing
images, for example, in the dark. The front-lighting is typically
provided by a light strip that surrounds the perimeter of an
interferometric modulator display. While such a front-lighting
scheme does provide light for viewing images in the dark, there is
generally an intrinsic (lighting) uniformity issue as the middle
portion of the interferometric modulator display remains darker
than the outer edges. As interferometric modulator displays
increase in size, this non-uniform effect of light caused by
front-lighting increases, which can lead to poor visibility of
images in the dark.
[0007] Accordingly, what is needed is an improved lighting scheme
for an interferometric display device to reduce non-uniformity of
light. The present invention addresses such a need.
SUMMARY
[0008] In general, in one aspect, this specification describes a
microelectromechanical system (MEMS) including a transparent
substrate, and a plurality of interferometric modulators. The
plurality of interferometric modulators include an optical stack
coupled to the transparent substrate, a reflective layer over the
optical stack, and one or more posts to support the reflective
layer and to provide a path for light from a backlight for lighting
the interferometric modulators.
[0009] Particular features can include one or more of the following
features. The MEMS can further include a glass layer between the
transparent substrate and the optical stack. The glass layer can
include a plurality of scatterers to disperse the light. The glass
layer can comprise first spin-on glass (SOG) including the
plurality of scatterers. The one or more posts can be composed of a
transparent polymer or second spin-on glass (SOG). Each of the one
or more posts can further be configured to direct the light to the
glass layer. The scatterers can be configured to disperse the light
to the interferometric modulators. Each of the one or more posts
can further comprise a mirror. The one or more posts can extend
from the optical stack through the reflective layer.
[0010] The MEMS, as a display device, can further include a display
including the MEMS, and a processor that is in electrical
communication with the display, the processor being configured to
process image data, and a memory device in electrical communication
with the processor. The display system can further include a
backlight coupled to the display for providing light to the
interferometric modulators. The display system can further include
a first controller configured to send at least one signal to the
display, and a second controller configured to send at least a
portion of the image data to the first controller. The display
system can further include an image source module configured to
send the image data to the processor. The image source module can
comprise at least one of a receiver, transceiver, and transmitter.
The display system can further include an input device configured
to receive input data and to communicate the input data to the
processor.
[0011] In general in another aspect, this specification describes a
micromechanical system (MEMS) including a transparent substrate
means, and a plurality of interferometric modulator means. The
plurality of interferometric modulator means includes an optical
stack means coupled to the transparent substrate means, a
reflective layer means over the optical stack means, and one or
more post means to support the reflective layer means and to
provide a path for light from a backlight means for lighting the
interferometric modulator means.
[0012] In general in another aspect, this specification describes a
method for providing light in a microelectromechanical system
(MEMS). The method includes providing a transparent substrate, and
forming a plurality of interferometric modulators. Forming a
plurality of interferometric modulators includes coupling an
optical stack to the transparent substrate, forming a reflective
layer over the optical stack, and forming one or more posts to
support the reflective layer and to provide a path for light from a
backlight for lighting the interferometric modulators.
[0013] Implementations may provide one or more of the following
advantages. An interferometric modulator display that has an
improved lighting scheme for an interferometric display device to
having a higher lighting uniformity relative to conventional
interferometric modulator displays devices that implement a
front-lighting scheme. In one embodiment, uniform lighting is
provided through posts (or rails) that are integrated within the
interferometric display device. Such a design may be more
power-efficient relative to conventional techniques in illuminating
a central area of an interferometric display. Moreover, the
brightness of an interferometric display may be enhanced even with
ambient light.
[0014] The details of one or more implementations are set forth in
the accompanying drawings and the description below. Other features
and advantages will be apparent from the description and drawings,
and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is an isometric view depicting a portion of one
embodiment of an interferometric modulator display in which a
movable reflective layer of a first interferometric modulator is in
a relaxed position and a movable reflective layer of a second
interferometric modulator is in an actuated position.
[0016] FIG. 2 is a system block diagram illustrating one embodiment
of an electronic device incorporating a 3.times.3 interferometric
modulator display.
[0017] FIG. 3 is a diagram of movable mirror position versus
applied voltage for one exemplary embodiment of an interferometric
modulator of FIG. 1.
[0018] FIG. 4 is an illustration of a set of row and column
voltages that may be used to drive an interferometric modulator
display.
[0019] FIGS. 5A and 5B illustrate one exemplary timing diagram for
row and column signals that may be used to write a frame of display
data to the 3.times.3 interferometric modulator display of FIG.
2.
[0020] FIG. 6A is a cross section of an interferometric modulator
of FIG. 1. FIGS. 6B-E are alternative embodiments of an
interferometric modulator.
[0021] FIGS. 7A-7B illustrate cross-sectional views of an
interferometric modulator display.
[0022] FIGS. 8A-8B illustrate a flow diagram illustrating a process
for manufacturing an interferometric modulator display according to
one embodiment.
[0023] FIGS. 9A-9N illustrate the process of manufacturing an
interferometric modulator display according to the process of FIGS.
8A-8B.
[0024] FIGS. 10A and 10B are system block diagrams illustrating an
embodiment of a visual display device comprising a plurality of
interferometric modulators.
[0025] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0026] The following detailed description is directed to certain
specific embodiments of the invention. However, the invention can
be embodied in a multitude of different ways. In this description,
reference is made to the drawings wherein like parts are designated
with like numerals throughout. As will be apparent from the
following description, the embodiments may be implemented in any
device that is configured to display an image, whether in motion
(e.g., video) or stationary (e.g., still image), and whether
textual or pictorial. More particularly, it is contemplated that
the embodiments may be implemented in or associated with a variety
of electronic devices such as, but not limited to, mobile
telephones, wireless devices, personal data assistants (PDAs),
hand-held or portable computers, GPS receivers/navigators, cameras,
MP3 players, camcorders, game consoles, wrist watches, clocks,
calculators, television monitors, flat panel displays, computer
monitors, auto displays (e.g., odometer display, etc.), cockpit
controls and/or displays, display of camera views (e.g., display of
a rear view camera in a vehicle), electronic photographs,
electronic billboards or signs, projectors, architectural
structures, packaging, and aesthetic structures (e.g., display of
images on a piece of jewelry). MEMS devices of similar structure to
those described herein can also be used in non-display applications
such as in electronic switching devices.
[0027] As discussed above, conventional interferometric modulator
display devices typically implement front-lighting that provides
light for viewing images, for example, in the dark. While such a
front-lighting scheme does provide light for viewing images in the
dark, there is generally an intrinsic lighting uniformity issue as
the middle portion of the interferometric modulator display remains
darker than the outer edges. As interferometric modulator displays
increase in size, this non-uniform effect of light caused by
front-lighting increases, which can lead to poor visibility of
images in the dark. Accordingly, this specification describes an
improved lighting scheme for an interferometric display device to
reduce non-uniformity of light. In one embodiment, an
interferometric modulator display is provided that includes a
transparent substrate, and an optical stack is formed on the
transparent substrate. A reflective layer is formed over the
optical stack, and one or more posts to support the reflective
layer are formed over the optical stack. The one or more posts
provide a path for light from a backlight for lighting the
interferometric modulator display.
[0028] One interferometric modulator display embodiment comprising
an interferometric MEMS display element is illustrated in FIG. 1.
In these devices, the pixels are in either a bright or dark state.
In the bright ("on" or "open") state, the display element reflects
a large portion of incident visible light to a user. When in the
dark ("off" or "closed") state, the display element reflects little
incident visible light to the user. Depending on the embodiment,
the light reflectance properties of the "on" and "off" states may
be reversed. MEMS pixels can be configured to reflect predominantly
at selected colors, allowing for a color display in addition to
black and white.
[0029] FIG. 1 is an isometric view depicting two adjacent pixels in
a series of pixels of a visual display, wherein each pixel
comprises a MEMS interferometric modulator. In some embodiments, an
interferometric modulator display comprises a row/column array of
these interferometric modulators. Each interferometric modulator
includes a pair of reflective layers positioned at a variable and
controllable distance from each other to form a resonant optical
cavity with at least one variable dimension. In one embodiment, one
of the reflective layers may be moved between two positions. In the
first position, referred to herein as the relaxed position, the
movable reflective layer is positioned at a relatively large
distance from a fixed partially reflective layer. In the second
position, referred to herein as the actuated position, the movable
reflective layer is positioned more closely adjacent to the fixed
partially reflective layer. Incident light that reflects from the
two layers interferes constructively or destructively depending on
the position of the movable reflective layer, producing either an
overall reflective or non-reflective state for each pixel.
[0030] The depicted portion of the pixel array in FIG. 1 includes
two adjacent interferometric modulators 12a and 12b. In the
interferometric modulator 12a on the left, a movable reflective
layer 14a is illustrated in a relaxed position at a predetermined
distance from an optical stack 16a, which includes a partially
reflective layer. In the interferometric modulator 12b on the
right, the movable reflective layer 14b is illustrated in an
actuated position adjacent to the optical stack 16b.
[0031] The optical stacks 16a and 16b (collectively referred to as
optical stack 16), as referenced herein, typically comprise of
several fused layers, which can include an electrode layer, such as
indium tin oxide (ITO), a partially reflective layer, such as
chromium, and a transparent dielectric. The optical stack 16 is
thus electrically conductive, partially transparent and partially
reflective, and may be fabricated, for example, by depositing one
or more of the above layers onto a transparent substrate 20. The
partially reflective layer can be formed from a variety of
materials that are partially reflective such as various metals,
semiconductors, and dielectrics. The partially reflective layer can
be formed of one or more layers of materials, and each of the
layers can be formed of a single material or a combination of
materials.
[0032] In some embodiments, the layers of the optical stack 16 are
patterned into parallel strips, and may form row electrodes in a
display device as described further below. The movable reflective
layers 14a, 14b may be formed as a series of parallel strips of a
deposited metal layer or layers (orthogonal to the row electrodes
of 16a, 16b) deposited on top of posts 18 and an intervening
sacrificial material deposited between the posts 18. When the
sacrificial material is etched away, the movable reflective layers
14a, 14b are separated from the optical stacks 16a, 16b by a
defined gap 19. A highly conductive and reflective material such as
aluminum may be used for the reflective layers 14, and these strips
may form column electrodes in a display device.
[0033] With no applied voltage, the cavity 19 remains between the
movable reflective layer 14a and optical stack 16a, with the
movable reflective layer 14a in a mechanically relaxed state, as
illustrated by the pixel 12a in FIG. 1. However, when a potential
difference is applied to a selected row and column, the capacitor
formed at the intersection of the row and column electrodes at the
corresponding pixel becomes charged, and electrostatic forces pull
the electrodes together. If the voltage is high enough, the movable
reflective layer 14 is deformed and is forced against the optical
stack 16. A dielectric layer (not shown) within the optical stack
16 may prevent shorting and control the separation distance between
layers 14 and 16, as illustrated by pixel 12b on the right in FIG.
1. The behavior is the same regardless of the polarity of the
applied potential difference. In this way, row/column actuation
that can control the reflective vs. non-reflective pixel states is
analogous in many ways to that used in conventional LCD and other
display technologies.
[0034] FIGS. 2 through 5 illustrate one exemplary process and
system for using an array of interferometric modulators in a
display application.
[0035] FIG. 2 is a system block diagram illustrating one embodiment
of an electronic device that may incorporate aspects of the
invention. In the exemplary embodiment, the electronic device
includes a processor 21 which may be any general purpose
single-chip or multi-chip microprocessor such as an ARM (Advanced
RISC Machine), Pentium.RTM., Pentium II.RTM., Pentium III.RTM.,
Pentium IV.RTM., Pentium.RTM. Pro, an 8051, a MIPS.RTM., a Power
PC.RTM., an ALPHA.RTM., or any special purpose microprocessor such
as a digital signal processor, microcontroller, or a programmable
gate array. As is conventional in the art, the processor 21 may be
configured to execute one or more software modules. In addition to
executing an operating system, the processor may be configured to
execute one or more software applications, including a web browser,
a telephone application, an email program, or any other software
application.
[0036] In one embodiment, the processor 21 is also configured to
communicate with an array driver 22. In one embodiment, the array
driver 22 includes a row driver circuit 24 and a column driver
circuit 26 that provide signals to a display array or panel 30. The
cross section of the array illustrated in FIG. 1 is shown by the
lines 1-1 in FIG. 2. For MEMS interferometric modulators, the
row/column actuation protocol may take advantage of a hysteresis
property of these devices illustrated in FIG. 3. It may require,
for example, a 10 volt potential difference to cause a movable
layer to deform from the relaxed state to the actuated state.
However, when the voltage is reduced from that value, the movable
layer maintains its state as the voltage drops back below 10 volts.
In the exemplary embodiment of FIG. 3, the movable layer does not
relax completely until the voltage drops below 2 volts. There is
thus a range of voltage, about 3 to 7 V in the example illustrated
in FIG. 3, where there exists a window of applied voltage within
which the device is stable in either the relaxed or actuated state.
This is referred to herein as the "hysteresis window" or "stability
window."
[0037] For a display array having the hysteresis characteristics of
FIG. 3, the row/column actuation protocol can be designed such that
during row strobing, pixels in the strobed row that are to be
actuated are exposed to a voltage difference of about 10 volts, and
pixels that are to be relaxed are exposed to a voltage difference
of close to zero volts. After the strobe, the pixels are exposed to
a steady state voltage difference of about 5 volts such that they
remain in whatever state the row strobe put them in. After being
written, each pixel sees a potential difference within the
"stability window" of 3-7 volts in this example. This feature makes
the pixel design illustrated in FIG. 1 stable under the same
applied voltage conditions in either an actuated or relaxed
pre-existing state. Since each pixel of the interferometric
modulator, whether in the actuated or relaxed state, is essentially
a capacitor formed by the fixed and moving reflective layers, this
stable state can be held at a voltage within the hysteresis window
with almost no power dissipation. Essentially no current flows into
the pixel if the applied potential is fixed.
[0038] In typical applications, a display frame may be created by
asserting the set of column electrodes in accordance with the
desired set of actuated pixels in the first row. A row pulse is
then applied to the row 1 electrode, actuating the pixels
corresponding to the asserted column lines. The asserted set of
column electrodes is then changed to correspond to the desired set
of actuated pixels in the second row. A pulse is then applied to
the row 2 electrode, actuating the appropriate pixels in row 2 in
accordance with the asserted column electrodes. The row 1 pixels
are unaffected by the row 2 pulse, and remain in the state they
were set to during the row 1 pulse. This may be repeated for the
entire series of rows in a sequential fashion to produce the frame.
Generally, the frames are refreshed and/or updated with new display
data by continually repeating this process at some desired number
of frames per second. A wide variety of protocols for driving row
and column electrodes of pixel arrays to produce display frames are
also well known and may be used in conjunction with the present
invention.
[0039] FIGS. 4 and 5A-5B illustrate one possible actuation protocol
for creating a display frame on the 3.times.3 array of FIG. 2. FIG.
4 illustrates a possible set of column and row voltage levels that
may be used for pixels exhibiting the hysteresis curves of FIG. 3.
In the embodiment shown in FIG. 4, actuating a pixel involves
setting the appropriate column to -V.sub.bias, and the appropriate
row to +.DELTA.V, which may correspond to -5 volts and +5 volts,
respectively. Relaxing the pixel is accomplished by setting the
appropriate column to +V.sub.bias, and the appropriate row to the
same +.DELTA.V, producing a zero volt potential difference across
the pixel. In those rows where the row voltage is held at zero
volts, the pixels are stable in whatever state they were originally
in, regardless of whether the column is at +V.sub.bias, or
-V.sub.bias. As is also illustrated in FIG. 4, it will be
appreciated that voltages of opposite polarity than those described
above can be used, e.g., actuating a pixel can involve setting the
appropriate column to +V.sub.bias, and the appropriate row to
-.DELTA.V. In this embodiment, releasing the pixel is accomplished
by setting the appropriate column to -V.sub.bias, and the
appropriate row to the same -.DELTA.V, producing a zero volt
potential difference across the pixel.
[0040] FIG. 5B is a timing diagram showing a series of row and
column signals applied to the 3.times.3 array of FIG. 2 which will
result in the display arrangement illustrated in FIG. 5A, where
actuated pixels are non-reflective. Prior to writing the frame
illustrated in FIG. 5A, the pixels can be in any state, and in this
example, all the rows are at 0 volts, and all the columns are at +5
volts. With these applied voltages, all pixels are stable in their
existing actuated or relaxed states.
[0041] In the frame shown in FIG. 5A, pixels (1,1), (1,2), (2,2),
(3,2) and (3,3) are actuated. To accomplish this, during a "line
time" for row 1, columns 1 and 2 are set to -5 volts, and column 3
is set to +5 volts. This does not change the state of any pixels,
because all the pixels remain in the 3-7 volt stability window. Row
1 is then strobed with a pulse that goes from 0, up to 5 volts, and
back to zero. This actuates the (1,1) and (1,2) pixels and relaxes
the (1,3) pixel. No other pixels in the array are affected. To set
row 2 as desired, column 2 is set to -5 volts, and columns 1 and 3
are set to +5 volts. The same strobe applied to row 2 will then
actuate pixel (2,2) and relax pixels (2,1) and (2,3). Again, no
other pixels of the array are affected. Row 3 is similarly set by
setting columns 2 and 3 to -5 volts, and column 1 to +5 volts. The
row 3 strobe sets the row 3 pixels as shown in FIG. 5A. After
writing the frame, the row potentials are zero, and the column
potentials can remain at either +5 or -5 volts, and the display is
then stable in the arrangement of FIG. 5A. It will be appreciated
that the same procedure can be employed for arrays of dozens or
hundreds of rows and columns. It will also be appreciated that the
timing, sequence, and levels of voltages used to perform row and
column actuation can be varied widely within the general principles
outlined above, and the above example is exemplary only, and any
actuation voltage method can be used with the systems and methods
described herein.
[0042] FIG. 6A is a cross section of the embodiment of FIG. 1,
where a strip of metal material 14 is deposited on orthogonally
extending supports 18. In FIG. 6B, the moveable reflective layer 14
is attached to supports at the corners only, on tethers 32. In FIG.
6C, the moveable reflective layer 14 is suspended from a deformable
layer 34, which may comprise a flexible metal. The deformable layer
34 connects, directly or indirectly, to the substrate 20 around the
perimeter of the deformable layer 34. These connections are
referred to herein as support posts. The embodiment illustrated in
FIG. 6D has support post plugs 42 upon which the deformable layer
34 rests. The movable reflective layer 14 remains suspended over
the cavity, as in FIGS. 6A-6C, but the deformable layer 34 does not
form the support posts by filling holes between the deformable
layer 34 and the optical stack 16. Rather, the support posts are
formed of a planarization material, which is used to form support
post plugs 42. The embodiment illustrated in FIG. 6E is based on
the embodiment shown in FIG. 6D, but may also be adapted to work
with any of the embodiments illustrated in FIGS. 6A-6C as well as
additional embodiments not shown. In the embodiment shown in FIG.
6E, an extra layer of metal or other conductive material has been
used to form a bus structure 44. This allows signal routing along
the back of the interferometric modulators, eliminating a number of
electrodes that may otherwise have had to be formed on the
substrate 20.
[0043] FIG. 7A and FIG. 7B respectively illustrate cross-section
and an exploded view of an embodiment of an interferometric
modulator display 700. Referring to FIG. 7A, the interferometric
modulator display 700 includes a substrate 702, and an
interferometric modulator array comprising a plurality of
interferometric modulators 704. The interferometric modulator
display 700 further includes a mechanical layer 706 and a plurality
of support posts 708 to support the mechanical layer 706. In
accordance with the present invention, the plurality of support
posts 708 are also operable to act as a waveguide (e.g., to provide
a path) to propagate light 710 from a backlight (not shown) through
the mechanical layer 706 to the substrate 702. Accordingly, the
light 710 can be uniformly dispersed across a viewable area of the
interferometric modulator display 700.
[0044] FIG. 7B shows an exploded view of the interferometric
modulator display 700 according to one embodiment. As shown in FIG.
7B, in one embodiment, the substrate 702 comprises two layers--a
first substrate layer 712 and a second substrate layer 714. In one
embodiment, both the first substrate layer 712 and the second
substrate layer are substantially transparent and/or translucent.
For example, the first substrate layer 712 can be glass, silica,
and/or alumina, and the second substrate layer 714 can comprise
spin-on glass (SOG). In one embodiment, the second substrate layer
714 includes scatterers (or reflectors) 716 to further disperse
light 710 (from a backlight (not shown)) more uniformly through the
substrate 702. Although scatterers 716 are illustrated as circular,
one of skill in the art will recognize that any shape or surface
suitable for reflecting, directing or scattering light may be used
in the invention, including prisms and thin-film layers for
redirecting light. The interferometric modulator display 700
further includes an optical stack 718. In one embodiment, the
optical stack 718 comprises several fused layers, including an
electrode layer (e.g., indium tin oxide (ITO)), a partially
reflective layer (e.g., chromium), and a transparent dielectric.
The partially reflective layer can be formed from a variety of
materials that are partially reflective such as various metals,
semiconductors, and dielectrics. The partially reflective layer can
be formed of one or more layers of materials, and each of the
layers can be formed of a single material or a combination of
materials.
[0045] As shown in FIG. 7B, the support posts 708 support the
mechanical layer 706 over the optical stack 718 such that the
mechanical layer 706 is separated from the optical stack by a
transparent medium 720 (e.g., an air gap). In addition, as
discussed above, the support posts 708 also provide a path for
light 710 from a backlight (not shown) to pass through the
mechanical layer 706 and the optical stack 718 to the substrate
702. In one embodiment, a mirror 722 (e.g., an aluminum mirror)
deflects the light 710 throughout the substrate 702. The mirror 722
may include a light pipe or any other optical pathway for directing
light. Thus, unlike a conventional interferometric modulator
display that may have poor lighting uniformity due to a
front-lighting scheme, the interferometric modulator display 700
implements a backlighting scheme to more uniformly distribute light
across an interferometric modulator display.
[0046] FIGS. 8A-8B illustrates a process 800 of fabricating an
interferometric modulator display (e.g., interferometric modulator
700) in accordance with one embodiment.
[0047] Referring first to FIG. 8A, the process 800 begins with
providing a substrate (step 802). Referring to the example of FIG.
9A, a substrate 902 is provided. The substrate 902 can be
transparent or not transparent. In one embodiment, the substrate
1102 comprises glass. A glass layer is deposited (step 804). As
shown in FIG. 9B, a glass layer 904 is deposited over the substrate
902. In one embodiment, the glass layer 904 includes a plurality of
scatterers (or reflectors) 906 for dispersing light, as discussed
in greater detail above. The glass layer 904 can comprise spin-on
glass (SOG) or any other transparent dielectric material. A
conductive layer is formed (step 806). As shown in FIG. 9C, a
conductive layer 908 is formed over the glass layer 904. In one
embodiment the conductive layer 908 comprises one or more layers
and/or films. For example, in one embodiment the conductive layer
908 comprises a conductive layer (e.g., indium tin oxide (ITO)) and
a partially reflective layer (e.g., chromium). An oxide layer is
deposited (step 808). As shown in FIG. 9D, an oxide layer 910 is
deposited over the conductive layer 908. In one embodiment, the
oxide layer 910 comprises a silicon oxide compound
(Si.sub.XO.sub.Y). A sacrificial layer is deposited (step 810).
Referring to FIG. 9E, a sacrificial layer 912 is deposited over the
oxide layer 910. In one embodiment, the sacrificial layer 912
comprises molybdenum. In one embodiment, the height of the
sacrificial layer 912 determines the amount of spacing between the
first conductive layer 908 (or conductive plate) and a second
conductive plate (e.g., a mechanical layer discussed below). In one
embodiment, the height of the sacrificial layer 912 is
substantially (1800 .ANG.-2100 .ANG.).
[0048] A mechanical layer is formed (step 812). Referring to the
example of FIG. 9F, a mechanical layer 914 is formed over the
sacrificial layer 912. In one embodiment, the mechanical layer 914
comprises a movable reflective layer as discussed above. In one
embodiment, the mechanical layer 914 comprises aluminum/nickel, and
has a height substantially in the range of 1100 .ANG.-1300 .ANG..
After formation of the mechanical layer, the process of forming the
support posts for the mechanical layer begins. Accordingly, the
mechanical layer is etched (step 812). Referring to the example of
FIG. 9G, the mechanical layer 914 is etched at locations where
support posts are desired. The sacrificial layer is etched (step
816). As shown in FIG. 9H, (in one embodiment) a greater portion of
the sacrificial layer 912 is etched relative to the portion of the
mechanical layer 914 that was etched (or removed). In this
embodiment, the sacrificial layer 912 is etched a distance d of
approximately 0.5-1 .mu.m greater than the mechanical layer 914.
The oxide layer is etched (step 818). As shown in FIG. 9I, the
oxide layer 910 is etched. The conductive layer is etched (step
820). Referring to FIG. 9J, the conductive layer 908 is etched. The
glass layer is etched (step 822). As shown in FIG. 9K, the glass
layer 904 is etched to reveal the substrate 902.
[0049] A mirror is formed (step 824). As shown in FIG. 9L, a mirror
916 is formed on the substrate 902. In one embodiment, the mirror
916 is formed by deposition of a (thin) metal layer 918 over the
mechanical layer 914. In one embodiment, a thickness (or height) of
the metal layer 918 is substantially in the range of 50-150 .ANG..
The deposition of the thin metal layer 918 can be implemented
through sputtering to achieve a pyramid-like structure for the
mirror 916 so that the mirror 916 can deflect a light from a
backlight throughout the glass layer 904 and the substrate 902. In
one embodiment, the mirror 916 comprises aluminum or other
reflective material. A plurality of posts are formed (step 826). As
shown by FIG. 9M, posts 920 are formed within the etched portions
of the layers of the interferometric modulator display. In one
embodiment, the posts 920 are formed using a planarization
technique followed by photolithography to remove unwanted portions
of the material that comprise the posts 920. The posts 920 can
comprise spin-on glass (SOG) or a transparent polymer. The
sacrificial layer is released (step 828). Referring to FIG. 9N, the
sacrificial layer 912 is released to form an air gap 922 between
the mechanical layer 914 and the oxide layer 910. The sacrificial
layer 912 can be released through one or more etch holes formed
through the metal layer 918 and the mechanical layer 914. The one
or more etch holes can be created after formation of the posts
920.
[0050] FIGS. 10A and 10B are system block diagrams illustrating an
embodiment of a display device 40. The display device 40 can be,
for example, a cellular or mobile telephone. However, the same
components of display device 40 or slight variations thereof are
also illustrative of various types of display devices such as
televisions and portable media players.
[0051] The display device 40 includes a housing 41, a display 30,
an antenna 43, a speaker 44, an input device 48, and a microphone
46. The housing 41 is generally formed from any of a variety of
manufacturing processes as are well known to those of skill in the
art, including injection molding, and vacuum forming. In addition,
the housing 41 may be made from any of a variety of materials,
including but not limited to plastic, metal, glass, rubber, and
ceramic, or a combination thereof. In one embodiment the housing 41
includes removable portions (not shown) that may be interchanged
with other removable portions of different color, or containing
different logos, pictures, or symbols.
[0052] The display 30 of exemplary display device 40 may be any of
a variety of displays, including a bi-stable display, as described
herein. In other embodiments, the display 30 includes a flat-panel
display, such as plasma, EL, OLED, STN LCD, or TFT LCD as described
above, or a non-flat-panel display, such as a CRT or other tube
device, as is well known to those of skill in the art. However, for
purposes of describing the present embodiment, the display 30
includes an interferometric modulator display, as described
herein.
[0053] The components of one embodiment of exemplary display device
40 are schematically illustrated in FIG. 10B. The illustrated
exemplary display device 40 includes a housing 41 and can include
additional components at least partially enclosed therein. For
example, in one embodiment, the exemplary display device 40
includes a network interface 27 that includes an antenna 43 which
is coupled to a transceiver 47. The transceiver 47 is connected to
a processor 21, which is connected to conditioning hardware 52. The
conditioning hardware 52 may be configured to condition a signal
(e.g. filter a signal). The conditioning hardware 52 is connected
to a speaker 45 and a microphone 46. The processor 21 is also
connected to an input device 48 and a driver controller 29. The
driver controller 29 is coupled to a frame buffer 28, and to an
array driver 22, which in turn is coupled to a display array 30. A
power supply 50 provides power to all components as required by the
particular exemplary display device 40 design.
[0054] The network interface 27 includes the antenna 43 and the
transceiver 47 so that the exemplary display device 40 can
communicate with one or more devices over a network. In one
embodiment the network interface 27 may also have some processing
capabilities to relieve requirements of the processor 21. The
antenna 43 is any antenna known to those of skill in the art for
transmitting and receiving signals. In one embodiment, the antenna
transmits and receives RF signals according to the IEEE 802.11
standard, including IEEE 802.11(a), (b), or (g). In another
embodiment, the antenna transmits and receives RF signals according
to the BLUETOOTH standard. In the case of a cellular telephone, the
antenna is designed to receive CDMA, GSM, AMPS or other known
signals that are used to communicate within a wireless cell phone
network. The transceiver 47 pre-processes the signals received from
the antenna 43 so that they may be received by and further
manipulated by the processor 21. The transceiver 47 also processes
signals received from the processor 21 so that they may be
transmitted from the exemplary display device 40 via the antenna
43.
[0055] In an alternative embodiment, the transceiver 47 can be
replaced by a receiver. In yet another alternative embodiment,
network interface 27 can be replaced by an image source, which can
store or generate image data to be sent to the processor 21. For
example, the image source can be a digital video disc (DVD) or a
hard-disc drive that contains image data, or a software module that
generates image data.
[0056] Processor 21 generally controls the overall operation of the
exemplary display device 40. The processor 21 receives data, such
as compressed image data from the network interface 27 or an image
source, and processes the data into raw image data or into a format
that is readily processed into raw image data. The processor 21
then sends the processed data to the driver controller 29 or to
frame buffer 28 for storage. Raw data typically refers to the
information that identifies the image characteristics at each
location within an image. For example, such image characteristics
can include color, saturation, and gray-scale level.
[0057] In one embodiment, the processor 21 includes a
microcontroller, CPU, or logic unit to control operation of the
exemplary display device 40. Conditioning hardware 52 generally
includes amplifiers and filters for transmitting signals to the
speaker 45, and for receiving signals from the microphone 46.
Conditioning hardware 52 may be discrete components within the
exemplary display device 40, or may be incorporated within the
processor 21 or other components.
[0058] The driver controller 29 takes the raw image data generated
by the processor 21 either directly from the processor 21 or from
the frame buffer 28 and reformats the raw image data appropriately
for high speed transmission to the array driver 22. Specifically,
the driver controller 29 reformats the raw image data into a data
flow having a raster-like format, such that it has a time order
suitable for scanning across the display array 30. Then the driver
controller 29 sends the formatted information to the array driver
22. Although a driver controller 29, such as a LCD controller, is
often associated with the system processor 21 as a stand-alone
Integrated Circuit (IC), such controllers may be implemented in
many ways. They may be embedded in the processor 21 as hardware,
embedded in the processor 21 as software, or fully integrated in
hardware with the array driver 22.
[0059] Typically, the array driver 22 receives the formatted
information from the driver controller 29 and reformats the video
data into a parallel set of waveforms that are applied many times
per second to the hundreds and sometimes thousands of leads coming
from the display's x-y matrix of pixels.
[0060] In one embodiment, the driver controller 29, array driver
22, and display array 30 are appropriate for any of the types of
displays described herein. For example, in one embodiment, driver
controller 29 is a conventional display controller or a bi-stable
display controller (e.g., an interferometric modulator controller).
In another embodiment, array driver 22 is a conventional driver or
a bi-stable display driver (e.g., an interferometric modulator
display driver). In one embodiment, a driver controller 29 is
integrated with the array driver 22. Such an embodiment is common
in highly integrated systems such as cellular phones, watches, and
other small area displays. In yet another embodiment, display array
30 is a typical display array or a bi-stable display array (e.g., a
display including an array of interferometric modulators).
[0061] The input device 48 allows a user to control the operation
of the exemplary display device 40. In one embodiment, input device
48 includes a keypad, such as a QWERTY keyboard or a telephone
keypad, a button, a switch, a touch-sensitive screen, a pressure-
or heat-sensitive membrane. In one embodiment, the microphone 46 is
an input device for the exemplary display device 40. When the
microphone 46 is used to input data to the device, voice commands
may be provided by a user for controlling operations of the
exemplary display device 40.
[0062] Power supply 50 can include a variety of energy storage
devices as are well known in the art. For example, in one
embodiment, power supply 50 is a rechargeable battery, such as a
nickel-cadmium battery or a lithium ion battery. In another
embodiment, power supply 50 is a renewable energy source, a
capacitor, or a solar cell, including a plastic solar cell, and
solar-cell paint. In another embodiment, power supply 50 is
configured to receive power from a wall outlet.
[0063] In some embodiments control programmability resides, as
described above, in a driver controller which can be located in
several places in the electronic display system. In some cases
control programmability resides in the array driver 22. Those of
skill in the art will recognize that the above-described
optimization may be implemented in any number of hardware and/or
software components and in various configurations.
[0064] Various implementations of an interferometric modulator
display have been described. Nevertheless, one of ordinary skill in
the art will readily recognize that there that various
modifications may be made to the implementations, and any variation
would be within the spirit and scope of the present invention. For
example, the process steps described above in connection with FIGS.
8A-8B may be performed in a different order and still achieve
desirable results. In addition, the substrate can be treated so
that scatterers are embedded within the substrate. Further,
processes for creating etch hole (e.g., to release a sacrificial
layer) are compatible with process steps discussed above.
Accordingly, many modifications may be made by one of ordinary
skill in the art without de parting from the spirit can scope of
the following claims.
* * * * *