U.S. patent application number 12/975119 was filed with the patent office on 2011-04-21 for stiction mitigation with integrated mech micro-cantilevers through vertical stress gradient control.
This patent application is currently assigned to Qualcomm MEMS Technologies, Inc.. Invention is credited to Yeh-Jiun Tung.
Application Number | 20110090554 12/975119 |
Document ID | / |
Family ID | 41130483 |
Filed Date | 2011-04-21 |
United States Patent
Application |
20110090554 |
Kind Code |
A1 |
Tung; Yeh-Jiun |
April 21, 2011 |
STICTION MITIGATION WITH INTEGRATED MECH MICRO-CANTILEVERS THROUGH
VERTICAL STRESS GRADIENT CONTROL
Abstract
The present disclosure relates to the mitigation of stiction in
MEMS devices. In some embodiments, a MEMS device may be provided
with one or more restoration features that provide an assisting
mechanical force for mitigating stiction. The restoration feature
may be implemented as one or more deflectable elements, where the
deflectable elements may have various configurations or shapes,
such as a chevron, cross, and the like. For example, the
restoration feature can be a cantilever that deflects when at least
one component comes into contact or proximity with another
component. Multiple restoration features also may be employed and
placed strategically within the MEMS device to maximize their
effectiveness in mitigating stiction.
Inventors: |
Tung; Yeh-Jiun; (Sunnyvale,
CA) |
Assignee: |
Qualcomm MEMS Technologies,
Inc.
San Diego
CA
|
Family ID: |
41130483 |
Appl. No.: |
12/975119 |
Filed: |
December 21, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12275366 |
Nov 21, 2008 |
7859740 |
|
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12975119 |
|
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61080005 |
Jul 11, 2008 |
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Current U.S.
Class: |
359/290 |
Current CPC
Class: |
G02B 26/0841 20130101;
G02B 26/001 20130101; B81B 2201/047 20130101; B81B 3/0059 20130101;
B81B 3/0008 20130101 |
Class at
Publication: |
359/290 |
International
Class: |
G02B 26/00 20060101
G02B026/00 |
Claims
1. An electromechanical device comprising: a first component; a
second component movable relative to the first component in a first
direction; and at least one restoration feature, on the first
component, that applies a restoring force to the second component
in a second direction opposite to the first direction and comprises
at least one deflecting portion that surrounds an opening in the
first component and extends towards the second component when the
first component and the second components are apart from each
other.
2. The electromechanical device of claim 1, wherein the at least
one deflecting portion comprises a cantilever.
3. The electromechanical device of claim 1, wherein the at least
one deflecting portion comprises a plurality of leaves.
4. The electromechanical device of claim 1, wherein the opening in
the first component comprises a generally chevron-like shape.
5. The electromechanical device of claim 1, wherein the opening in
the first component comprises a generally cross-like shape.
6. The electromechanical device of claim 1, wherein the at least
one deflecting portion comprises a generally rectangular shape.
7. The electromechanical device of claim 1, wherein the at least
one restoration feature is positioned on a peripheral portion of
the first component.
8. The electromechanical device of claim 1, further comprising at
least one restoration feature, on the second component, that
applies a second restoring force to the second component in the
second direction.
9. The electromechanical device of claim 1, wherein the
micro-electromechanical (MEMS) device is an interferometric
modulator.
10. The electromechanical device of claim 9, wherein the first
component comprises a partially reflective layer and the second
component comprises a reflective layer.
11. The electromechanical device of claim 10, wherein the
reflective layer is deformable to move in the first direction.
12. The electromechanical device of claim 10, wherein the second
component further comprises a deformable layer coupled to the
reflective layer, the deformable layer configured to move in the
first direction.
13. The electromechanical device of claim 1, wherein the opening
comprises an etch hole through the first component.
14. The electromechanical device of claim 1, further comprising: a
display; a processor that is configured to communicate with the
display, the processor being configured to process image data; and
a memory device that is configured to communicate with the
processor.
15. The electromechanical device of claim 14, further comprising a
driver circuit configured to send at least one signal to the
display.
16. The electromechanical device of claim 15, further comprising a
controller configured to send at least a portion of the image data
to the driver circuit.
17. The electromechanical device of claim 14, further comprising an
image source module configured to send the image data to the
processor.
18. The electromechanical device of claim 17, wherein the image
source module comprises at least one of a receiver, transceiver,
and transmitter.
19. The electromechanical device of claim 14, further comprising an
input device configured to receive input data and to communicate
the input data to the processor.
20. An electromechanical apparatus comprising: means for partially
reflecting light; means for reflecting light, wherein the
reflecting means is movable in a first direction relative to the
partially reflecting means; and means for applying a restoring
force to the reflecting means, the restoring means on the partially
reflecting means, the restoring force in a second direction
opposite to the first direction, the restoring means surrounding an
opening in the partially reflecting means and extending towards the
reflecting means when the partially reflecting means and the
reflecting means are apart from each other.
21. The electromechanical apparatus of claim 20, wherein the
reflecting means comprises a reflective layer disposed on a
substrate.
22. The electromechanical apparatus of claim 20, wherein the
restoring means comprises a cantilever that curls towards the
reflecting means.
23. The electromechanical apparatus of claim 20, wherein the
restoring means comprises a plurality of cantilevers that curl
towards the reflecting means.
24. The electromechanical apparatus of claim 20, wherein the
restoring means minimizes stiction between the partially reflecting
means and the reflecting means.
25. An electromechanical device comprising: a first component; a
second component spaced from the first component and configured to
move in a first direction between an undriven position and a driven
position, the driven position located closer to the first component
than the undriven position; and at least one restoration feature,
on the second component, that applies a restoring force to the
second component in a second direction opposite to the first
direction and comprises at least one deflecting portion that
surrounds an opening in the second component and extends towards
the first component when the second component is in the undriven
position.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending U.S. patent
application Ser. No. 12/275,366, filed Nov. 21, 2008, which claims
the benefit of U.S. Provisional Patent Application No. 61/080,005
filed on Jul. 11, 2008, entitled "STICTION MITIGATION WITH
INTEGRATED MECH MICRO-CANTILEVERS THROUGH VERTICAL STRESS GRADIENT
CONTROL," by Yeh-Jiun Tung. The disclosures of all the
above-referenced prior applications, publications, and patents are
considered part of the disclosure of this application, and are
incorporated by reference herein in their entirety.
BACKGROUND
[0002] 1. Field
[0003] The present disclosure relates to micro-electromechanical
systems. More particularly, some embodiments relate to systems and
methods for improving the micro-electromechanical operation of
interferometric modulators.
[0004] 2. Description of the Related Technology
[0005] Micro-electromechanical systems (MEMS) include micro
mechanical 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.
[0006] An interferometric modulator or interferometric light
modulator refers to a device that selectively absorbs and/or
reflects light using the principles of optical interference. 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.
[0007] 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 an air gap. The position of
one plate in relation to another 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.
SUMMARY
[0008] In one embodiment, a micro-electromechanical (MEMS) device
comprises a first component, a second component, and at least one
restoration feature. The second component is movable relative to
the first component in a first direction. The at least one
restoration feature may be on the second component and can apply a
restoring force to the second component in a second direction
opposite to the first direction. The at least one restoration
feature comprises at least one deflecting portion that borders an
opening through the second component and extends towards the first
component when the first and second components are apart from each
other.
[0009] In an embodiment, a micro-electromechanical (MEMS) apparatus
comprises: means for partially reflecting light; means for
reflecting light, wherein the reflecting means is movable in a
first direction relative to the partially reflecting means; and
means for applying a restoring force to the reflecting means, the
restoring means on the reflecting means, the restoring force in a
second direction opposite to the first direction, the restoring
means bordering an opening through the reflecting means and
extending towards the partially reflecting means when the partially
reflecting means and the reflecting means are apart from each
other.
[0010] In another embodiment, a method of fabricating a
microelectromechanical systems (MEMS) device comprises: forming an
electrode layer over a substrate; depositing a sacrificial layer
over the electrode layer; depositing a reflective layer over the
sacrificial layer; forming a plurality of support structures, said
support structures extending through the sacrificial layer;
depositing a mechanical layer over the plurality of support
structures; and patterning the mechanical layer to form at least
one restoration feature from etch holes in the mechanical
layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] 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.
[0012] FIG. 2 is a system block diagram illustrating one embodiment
of an electronic device incorporating a 3.times.3 interferometric
modulator display.
[0013] FIG. 3 is a diagram of movable mirror position versus
applied voltage for one exemplary embodiment of an interferometric
modulator of FIG. 1.
[0014] FIG. 4 is an illustration of a set of row and column
voltages that may be used to drive an interferometric modulator
display.
[0015] FIG. 5A illustrates one exemplary frame of display data in
the 3.times.3 interferometric modulator display of FIG. 2.
[0016] FIG. 5B illustrates one exemplary timing diagram for row and
column signals that may be used to write the frame of FIG. 5A.
[0017] FIGS. 6A and 6B are system block diagrams illustrating an
embodiment of a visual display device comprising a plurality of
interferometric modulators.
[0018] FIG. 7A is a cross section of the device of FIG. 1.
[0019] FIG. 7B is a cross section of an alternative embodiment of
an interferometric modulator.
[0020] FIG. 7C is a cross section of another alternative embodiment
of an interferometric modulator.
[0021] FIG. 7D is a cross section of yet another alternative
embodiment of an interferometric modulator.
[0022] FIG. 7E is a cross section of an additional alternative
embodiment of an interferometric modulator.
[0023] FIG. 8A is a side cross-sectional view of an embodiment of
the interferometric modulator including restoration features with
the modulator shown in the undriven state.
[0024] FIG. 8B is a side cross-sectional view of the embodiment of
FIG. 9A in the driven state.
[0025] FIGS. 8C-F show side cross-sectional views of various
embodiments of the interferometric modulator including restoration
features with the modulator shown in the undriven state.
[0026] FIGS. 8G-J show top cross-sectional views of various
embodiments of the restoration features.
[0027] FIG. 8K illustrates a perspective view of a generally
circular restoration feature in accordance with certain embodiments
described herein.
[0028] FIGS. 9A-H are schematic cross-sections depicting certain
steps in the fabrication of an array of MEMS devices.
[0029] FIGS. 10A-D show exemplary simulation models of a portion of
the restoration features in the driven and undriven state.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] The present disclosure relates to the mitigation of stiction
in MEMS devices. In MEMS devices, stiction can cause a movable
component in a device to stick temporarily or permanently, and
thus, may cause the device to fail or operate improperly.
[0031] In certain embodiments described herein, a MEMS device may
be provided with one or more restoration features that provide an
assisting mechanical force for mitigating stiction. For example, in
some embodiments, the restoration feature is a cantilever that
deflects when at least one component comes into contact or
proximity with another component. This deflection of the
restoration feature results in a restoration force that is applied
in a direction generally opposite to the direction of movement of
the at least one component.
[0032] The restoration feature may be implemented as one or more
deflectable elements, where the deflectable elements may have
various configurations or shapes, such as a chevron, cross, and the
like. Multiple restoration features also may be employed and placed
strategically within the MEMS device to maximize their
effectiveness in mitigating stiction.
[0033] Furthermore, the restoration feature may have benefits
beyond mitigating stiction. For example, holes or slots formed in
the at least one component to create the restoration feature can
provide a conduit for etchant and the removal of a sacrificial
layer during fabrication. As such, the restoration feature may
provide a combination of functions not limited to mitigating
stiction. For example, the restoration features may be useful to
reduce snap in and to modify hysteretic behavior. This may be
useful for characteristics such as providing additional control of
the displayed color of a device. As another example, the
restoration feature may provide a mechanism for reducing or
increasing response time by inhibiting actuation and enhancing
release of the device.
[0034] In some embodiments, one or more restoration features may be
fabricated into one or more components of a MEMS device using
various techniques. For example, the restoration feature may be
fabricated by including a stress gradient in a direction generally
perpendicular to the component and selectively patterning release
structures (e.g., holes or slots) in the component, such that a
portion of the elements of the restoration feature deflect in a
direction generally perpendicular to the component. Different
layers of materials to obtain desired restoration forces and shapes
may be employed. For illustrative purposes, certain embodiments of
these restoration features may be described in applications for an
optical interferometric modulator (IMOD) MEMS device.
[0035] The following detailed description is directed to certain
specific embodiments. However, the teachings of the present
disclosure can be implemented in a multitude of different ways. In
this description, reference is made to the drawings wherein like
parts are designated with like numerals throughout. 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.
[0036] The figures are provided to illustrate various embodiments.
In particular, FIGS. 1-7 illustrate various aspects of an
interferometric modulator display and display system. FIGS. 8A-8K
are then provided to illustrate various embodiments of one or more
restoration features that may be employed in various
interferometric modulators. FIGS. 9A-9H illustrate a fabrication
process of the interferometric modulator including the restoration
features. These figures will now be further described below.
[0037] Referring now to FIG. 1, an interferometric modulator
display embodiment comprising an interferometric MEMS display
element is illustrated. 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.
[0038] 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
gap 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
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.
[0039] 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.
[0040] The optical stacks 16a and 16b (collectively referred to as
optical stack 16), as referenced herein, typically comprise 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.
[0041] 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.
[0042] With no applied voltage, the gap 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 illustrated in this Figure)
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.
[0043] FIGS. 2 through 5B illustrate one exemplary process and
system for using an array of interferometric modulators in a
display application. 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- or multi-chip microprocessor such as an ARM, 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.
[0044] 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. Thus, there
exists a window of applied voltage, about 3 to 7 V in the example
illustrated in FIG. 3, 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. 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.
[0045] 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.
[0046] FIGS. 4, 5A, and 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 FIG. 4 embodiment, 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.
[0047] 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.
[0048] In the FIG. 5A frame, 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.
[0049] FIGS. 6A and 6B 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.
[0050] The display device 40 includes a housing 41, a display 30,
an antenna 43, a speaker 45, 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.
[0051] 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.
[0052] The components of one embodiment of exemplary display device
40 are schematically illustrated in FIG. 6B. 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] 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). 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).
[0060] 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, or 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.
[0061] 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.
[0062] 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
embodiments, control programmability resides in the array driver
22. Those of skill in the art will recognize that the
above-described optimizations may be implemented in any number of
hardware and/or software components and in various
configurations.
[0063] The details of the structure of interferometric modulators
that operate in accordance with the principles set forth above may
vary widely. For example, FIGS. 7A-7E illustrate five different
embodiments of the movable reflective layer 14 and its supporting
structures. FIG. 7A 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. 7B, the moveable reflective layer 14
is attached to supports at the corners only, on tethers 32. In FIG.
7C, 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 herein
referred to as support posts. The embodiment illustrated in FIG. 7D
has support post plugs 42 upon which the deformable layer 34 rests.
The movable reflective layer 14 remains suspended over the gap, as
in FIGS. 7A-7C, 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. 7E is based on the
embodiment shown in FIG. 7D, but may also be adapted to work with
any of the embodiments illustrated in FIGS. 7A-7C, as well as
additional embodiments not shown. In the embodiment shown in FIG.
7E, 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.
[0064] In embodiments such as those shown in FIG. 7, the
interferometric modulators function as direct-view devices, in
which images are viewed from the front side of the transparent
substrate 20, the side opposite to that upon which the modulator is
arranged. In these embodiments, the reflective layer 14 optically
shields the portions of the interferometric modulator on the side
of the reflective layer opposite the substrate 20, including the
deformable layer 34. This allows the shielded areas to be
configured and operated upon without negatively affecting the image
quality. Such shielding allows the bus structure 44 in FIG. 7E,
which provides the ability to separate the optical properties of
the modulator from the electromechanical properties of the
modulator, such as addressing and the movements that result from
that addressing. This separable modulator architecture allows the
structural design and materials used for the electromechanical
aspects and the optical aspects of the modulator to be selected and
to function independently of each other. Moreover, the embodiments
shown in FIGS. 7C-7E have additional benefits deriving from the
decoupling of the optical properties of the reflective layer 14
from its mechanical properties, which are carried out by the
deformable layer 34. This allows the structural design and
materials used for the reflective layer 14 to be optimized with
respect to the optical properties, and the structural design and
materials used for the deformable layer 34 to be optimized with
respect to desired mechanical properties.
[0065] The restoration features 513 can provide, among other
things, additional force to separate the deformable layer 506 from
the stationary layer 502, and this additional force can mitigate or
overcome the adhesion forces. As will be described below in detail,
the restoration features 513 are provided to help the recovery of
the deformable layer 506 from its driven state to the undriven
state by applying an additional force onto the deformable layer 506
in the direction away from the stationary layer 502.
[0066] For example, in the illustrated embodiment shown in FIG. 8A,
in the undriven state, a portion of the restoration features 513
may curl or curve toward the stationary layer 502 and thus extend
into the air gap between the deformable layer 506 and the
stationary layer 502. As will be described more fully below, this
portion may result from a stress gradient that can be fabricated
into at least the portion of the deformable layer 506 and/or the
stationary layer 502, which comprise the deflecting portions
515.
[0067] When undriven, the deformable layer 506 may be apart from
the stationary layer 502 and the deflecting portions 515 of
restoration features 513 may extend towards the stationary layer
502 (e.g., into the region between stationary layer 502 and
deformable layer 506). When driven, the deformable layer 506
deforms into the driven state illustrated in FIG. 8B. The
deflecting portions of 515 of restoration features 513 deform by
contact of the deformable layer 506 and thus conform to shape of
the stationary layer 502 that comes in contact with restoration
features 513. For example, in certain embodiments, the restoration
features 513 may deflect into the substantially flat configuration
shown in FIG. 8B. In certain embodiments, the restoration features
513 may deflect into other configurations, such as curved or bowed
shapes depending on the contact area of deformable layer 506. In
their deflected state, the restoration features 513 may provide a
potential assisting force that can mitigate or prevent
stiction.
[0068] In certain embodiments, the deflecting portions 515 do not
completely close the openings 517 when the deformable layer 506 is
in the driven state. In other embodiments, the deflecting portions
515 are deformed to nearly close or completely close the openings
517 when the deformable layer 506 is in the driven state.
[0069] The restoration features 513 deflected, even in a flat
configuration, will have a tendency to return to their normal
deflected configuration, e.g., having a portion that tends to
extend back into the interferometric cavity as shown in FIG. 8A.
This tendency can produce a force that tends to assist the
deformable layer 506 to return to its undriven state. Therefore,
when the deformed layer 506 begins to move from the deformed state
back to its undriven state, the force of the restoration features
513 can help mitigate stiction and/or speed of the recovery of the
deformable layer 506.
[0070] The restoration features 513 may be configured with various
sizes. For example, as shown in the figures, the deflecting
portions 515 may be a cantilever having a length that partially
spans the gap between deformable layer 506 and the stationary layer
502. In other embodiments, the deflecting portions 515 may be
cantilevers that are long enough to contact or come into near
contact with the stationary layer 502 even in their undriven state.
These different sizes of the deflecting portions 515 can be useful
to reduce snap in and to control the hysteretic behavior of the
device. Alternatively, different lengths of deflecting portions 515
may be utilized in order to modify the actuation and release times
of the device during operation. In order to minimize impact on
optical or color performance, various restoration features 513 may
be located in regions that are not within the viewable area of the
device.
[0071] One skilled in the art will recognize that the restoration
features 513 may not have the exact configuration as illustrated in
FIGS. 8A-8K. Many different types of structures may be employed as
the restoration features 513. Additionally, different materials can
also be employed.
[0072] For the sake of convenience, the term restoration feature
can refer to any and all mechanisms having the function of exerting
a restoration force that assists the deformed layer 506 in
returning to its undriven state. Although two restoration features
513 are illustrated in FIGS. 8A-8D, a single restoration feature
(such as in FIGS. 8E-8F) or any number of restoration features may
be employed. For example, multiple restoration features 513 can be
arranged across various areas of the deformable layer 506. In
particular, the restoration features 513 may be placed in a
specific area on the deformable layer 506, or may be placed to
provide relatively even restoration forces over a wide area on the
deformable layer 506.
[0073] In addition, the restoration features 513 can be configured
to provide different strengths of restoration forces depending on
their location on the deformable layer 506. The size, placement and
strength of the restoration features 513 can all be varied
according to the desired characteristics of the interferometric
modulator 501. In certain embodiments the initial voltage input may
be adjusted in order to drive the interferometric modulators 501 to
their fully driven state, as the restoration features 513 may
create an increased amount of resistance against the driven state
of modulators 501.
[0074] In addition, the restoration features 513 may include one or
more layers coated by an anti-stiction polymer coating, which can
reduce the degree of adhesion between the deformable layer 506 and
the stationary layer 502 when in contact with each other. The
restoration features 513 may also be textured or have a roughened
surface to reduce contact area, and thus, the amount of adhesion
between the deformable layer 506 and the stationary layer 502 when
in contact.
[0075] In order to illustrate various embodiments of the
restoration features 513, FIGS. 8A-K will now be further described.
FIGS. 8A and 8B illustrate an embodiment of the interferometric
modulator 501, which includes the restoration features 513. The
restoration features 513 may extend from the deformable layer 506.
Accordingly, when the interferometric modulator 501 is driven from
its undriven state (FIG. 8A) to the driven state (FIG. 8B), the
restoration features 513 are deflected from their normal
configuration to a relatively flat configuration. In some
embodiments, the restoration features 513 may be configured to
deflect only partially (rather than completely flat), and thus,
define a gap or minimum distance (not shown) between the stationary
layer 502 and the portions of the deformable layer 506 not
contacting the stationary layer 502 when the interferometric
modulator 501 is in the driven state.
[0076] In another embodiment as illustrated in FIG. 8C, the
restoration features 513 may be formed on the top surface of the
stationary layer 502. In another embodiment illustrated in FIG. 8D,
the restoration features 513 may be positioned on both the
deformable layer 506 and the stationary layer 502. Although not
illustrated, the restoration features 513 may extend from various
sub-layers, if any, of the deformable layer 506 or from various
sub-layers of the stationary layer 502 or substrate 500.
[0077] As shown in FIGS. 8E-F, the restoration features 513 may be
positioned in various positions, such as a central portion of
deformable layer 506 or stationary layer 502. For example, the
restoration features 513 may be positioned in the center portion of
the deformable layer 506 in some embodiments since the restoration
force in the deformed layer 506 may be at a minimum in the center
as compared to the restoration force nearer the edges of the
deformable layer 506 adjacent the posts 504. The restoration
features 513 can be positioned in a variety of locations on the
stationary layer 502, or the deformable layer 506, or both.
[0078] FIGS. 8G-J show top cross-sectional views of various
embodiments of the restoration features 513 and FIG. 8K shows a
perspective view of another embodiment. In the illustrated
embodiment of FIGS. 8G-J, the restoration features 513 are located
generally on the deformable layer 506 between the support posts 504
(only one post 504 is labeled on the figure for clarity) on a
portion of the deformable layer 506 which interacts with incident
light. For example, as shown in FIG. 8G, the restoration features
513 can be on a central portion of the deformable layer 506 between
the support posts 504. Optionally, the restoration features 513 can
positioned on other portions of the deformable layer 506 which do
not significantly interact with incident light, such that the
existence of the restoration features 513 does not affect the
optical characteristics of the interferometric modulator 501. For
example, the restoration features 513 can be on a peripheral
portion of the deformable layer 506 near the support posts 504. In
still another embodiment (not illustrated), the restoration
features 513 can be positioned on both the central and peripheral
portions of the deformable layer 506 with respect to the support
posts 504.
[0079] The surface of the restoration features 513 may be generally
smooth or planar, or the surface of the restoration features 513
may be rough, bumpy or embossed. In certain embodiments, the
restoration features 513 may be shaped to maintain a tilt or
rounded shape when deflected, and thus, the restoration features
513 in their driven state may not necessarily be flattened. In
certain embodiments, the restoration features 513 can be configured
to provide a reduced area of contact between the deformable layer
506 and the stationary layer 502.
[0080] In certain embodiments, the restoration features 513 can
comprise the same materials as either the deformable layer 506 or
the stationary layer 502 from which the restoration features 513
are formed. The restoration features 513 can be made from various
materials, including, but not limited to, a metal, an alloy, a
dielectric material, and an elastomeric material. For example, such
materials may include metals including aluminum, semiconductors,
oxides of metals or semiconductors, nitrides of metals or
semiconductors, and oxynitrides of metals or semiconductors.
Restoration features 513 can be any material that substantially do
not affect or only insignificantly affect the electrical or optical
characteristics of the MEMS device such as interferometric
modulator 501. In addition, various masking or color adjustments
can be made to areas below and around the restoration features 513
on the stationary layer 502. For example, portions of the
stationary layer 502 may be colored or darkened to help compensate
for any optical effects of the restoration features 513.
[0081] In one embodiment, the restoration features 513 are
optically transparent to the light modulated by the interferometric
modulator 501. For example, in certain embodiments, in which the
restoration features 513 are on the stationary layer 502 of the
interferometric modulator 501, the restoration features 513 can be
transparent to the light being modulated. Optionally, in the case
where the modulated light includes visible light, the transparent
material that can be used for the restoration features 513
includes, for example, oxides of metals or semiconductors, nitrides
of metals or semiconductors, and oxynitrides of metals or
semiconductors. In certain embodiments, the restoration features
513 generally operate like the materials from which it is formed.
For example, the restoration features on the deformable layer 506b
of the interferometric modulator 501 can be reflective to the light
being modulated. In certain embodiments in which the optical
properties of the restoration features 513 are disruptive or
otherwise interfere with the optical performance of the
interferometric modulator 501, the restoration features can be
configured or sized to have a minimal effect on the operation of
the interferometric modulator 501.
[0082] In another embodiment, the restoration features 513 may be
made of a material that absorbs the light modulated by the
interferometric modulator 501. In another embodiment, the
restoration features 513 may be covered with such a light absorbing
material. Optionally, in the case where the modulated light
includes visible light, the light absorbing material that can be
used for the restoration features 513 includes, for example,
polymeric materials or metals, such as chrome, nickel, titanium,
molybdenum, etc.
[0083] In still another embodiment, the restoration features 513
may be made of a material that reflects the light modulated by the
interferometric modulator 501. The restoration features 513 may be
covered with such a light reflecting material. Optionally, in the
case where the modulated light includes visible light, the light
reflecting material that can be used for the restoration features
513 includes, for example, polymeric materials or metals, such as
silver, aluminum, gold, platinum, etc.
[0084] Multiple restoration features 513 can be used. Thus, several
of the restoration features 513 can be fabricated to provide the
landing surfaces of the layers of the interferometric modulator
501. The multiple restoration features 513 may be arranged to be at
at least one location in order to minimize a probability of
stiction (e.g., between the deformable layer 506 and the stationary
layer 502). For example, the restoration features 513 may be spaced
as remote as possible from one another on the deformable layer 506
or can be positioned at least a threshold distance from one or more
of the support structures between the deformable layer 506 and the
stationary layer 502
[0085] The restoration features 513 may have any cross-sectional
shape. As shown in FIGS. 8G-K, the cross-sectional shape of the
restoration features 513 can have one or more shapes, examples of
which include but are not limited to: generally semi-triangular,
generally semi-chevron-like, generally semi-tabbed-like, generally
semi-circular, generally semi-oval, generally semi-rectangular,
generally semi-pentagonal, generally X-shaped, and so forth. FIG.
8G shows a top view of a plurality of restoring features 513
generally grouped in pairs in regions of the deformable layer 506
spaced away from the posts 504. The opening 517 (freely movable
portion with respect to the deformable layer 506) of each restoring
feature 513 is generally semi-chevron-like or V-shaped and the
deflecting portions 515a, 515b restoring features 513 are generally
semi-triangular-shaped.
[0086] While FIG. 8G shows the openings 517 of the restoring
features 513 being separated from one another by a portion 519 of
the deformable layer 506, other embodiments have two or more
deflecting portions 515 bordering the same opening 517. For
example, certain embodiments can have a generally X-shaped opening
517 (e.g., the openings 517 of FIG. 8G without the portions 519)
which is bounded by the two deflecting portions 515a, 515b.
[0087] In FIG. 8H, the opening 517 has a generally cross-like
shape, and four deflecting portions 515a, 515b, 515c, 515d border
the opening 517. In FIG. 8I, the restoring features 513 comprise
generally U-shaped openings 517 with generally rectangular-shaped
deflecting portions 515a, 515b. In certain other embodiments, the
opening 517 can be generally H-shaped, with the two deflecting
portions 515a, 515b bordering the opening 517. As noted, the
deflecting portions 515a, 515b may be configured with different
lengths that can span all or part of the gap between the deformable
layer 506 and the stationary layer 502. Accordingly, this variation
in length of the deflecting portions 515a, 515b may be useful in
configuring the amount of applied force and timing of when these
portions apply the force. Such variation in length may be useful
for modifying color control of the device and/or modifying
actuation and release time of the device during operation.
[0088] In FIG. 8J, the openings 517 have a generally curved shaped,
and the deflecting portions 515a, 515b have a curved edge (e.g.,
are generally semicircular-shaped). In FIG. 8K, the opening 517 has
a generally circular shape, and the deflecting portion 515 is a
generally circular region of the deformable layer 506 bordering the
opening 517. As described more fully below, upon forming the
opening 517 through the deformable layer 506, stress gradients in
the portion of the deformable layer 506 bordering the opening 517
are curled towards the stationary layer 502, thereby forming the
deflecting portion 515.
[0089] The restoration features 513 can be fabricated in various
configurations and made of various compounds as discussed above,
for example, by utilizing the presently existing techniques of
depositing and selectively etching a material. For example, the
restoration features 513 can also be created from deformations of
the layers of the interferometric modulator 301. In another
embodiment, the restoration features 513 can be created using
conventional semiconductor manufacturing techniques.
[0090] The restoration features 513 may be fabricated into one or
more components of a MEMS device using various techniques. In
general, the restoration features 513 may be fabricated based on a
stress gradient configured into at least the portions of the
deformable layer 506, which comprise the deflecting portions 515
and/or the stationary layer 502. In some embodiments, the
restoration features 513 may be formed by selectively patterning
release structures (e.g., holes or slots forming the opening 517)
in the deformable layer 506 and/or the stationary layer 502, such
that one or more deflecting portions 515 of the restoration feature
513 undergo a deflection having a component in a direction
generally away from the layer which contacts the restoration
features 513 (e.g., a direction generally perpendicular to the
layer in which the restoration feature 513 is formed). Different
layers of materials to obtain desired restoration forces and shapes
may be employed.
[0091] The restoration feature 513 may have benefits beyond
mitigating stiction. For example, holes or slots formed in the at
least one component (e.g., the deformable layer 506) to create the
restoration feature 513 can provide a conduit for etchant and the
removal of a sacrificial layer during fabrication. An embodiment of
a processing flow for a MEMS device will now be described with
reference to FIGS. 9A-9H.
[0092] Semiconductor manufacturing techniques may be used in the
fabrication processes, such as photolithography, deposition,
masking, etching (e.g., dry methods such as plasma etch and wet
methods), etc. Deposition includes dry methods such as chemical
vapor deposition (CVD, including plasma-enhanced CVD and thermal
CVD) and sputter coating, and wet methods such as spin coating.
[0093] In one embodiment, a method of manufacturing an
interferometric modulator, such as those described above, is
described with respect to FIGS. 9A-9H. In FIG. 9A, an electrode
layer 52 has been deposited on a substrate 50 and a partially
reflective layer 54 has been deposited over the electrode layer 52.
The partially reflective layer 54 and the electrode layer 52 are
then patterned and etched to form gaps 56 which may define strip
electrodes formed from the electrode layer 52. In addition, the gap
56 may comprise, as it does in the illustrated embodiment, an area
in which the electrode layer 52 and the partially reflective layer
54 have been removed from underneath the location where a support
structure will be formed. In other embodiments, the partially
reflective layer 54 and the electrode layer 52 are only patterned
and etched to form the strip electrodes, and the partially
reflective layer 54 and electrode layer 52 may thus extend
underneath some or all of the support structures. In one
embodiment, the electrode layer 52 comprises indium-tin-oxide
(ITO). In one embodiment, the partially reflective layer 54
comprises a layer of chromium (Cr). In other embodiments, the
placement of the layers 52 and 54 may be reversed, such that the
partially reflective layer 54 is located underneath the electrode
layer 52. In another embodiment, a single layer (not shown) may
serve as both the electrode layer and the partially reflective
layer. In other embodiments, only one of the electrode layer 52 or
the partially reflective layer 54 may be formed.
[0094] In FIG. 9B, a dielectric layer 58 has been deposited over
the patterned electrode layer 52 and partially reflective layer 54.
In one embodiment, the dielectric layer 58 may comprise SiO.sub.2.
In further embodiments, one or more etch stop layers (not shown)
may be deposited over the dielectric layer. These etch stop layers
may protect the dielectric layer during the patterning of overlying
layers. In one embodiment, a etch stop layer comprising
Al.sub.2O.sub.3 may be deposited over the dielectric layer 58. In a
further embodiment, an additional layer of SiO.sub.2 may be
deposited over the etch stop layer.
[0095] In FIG. 9C, a sacrificial layer 60 has been deposited over
the dielectric layer 58. In one embodiment, the sacrificial layer
60 comprises molybdenum (Mo) or silicon (Si), but other materials
may be appropriate. Advantageously, the sacrificial layer 60 is
selectively etchable with respect to the layers surrounding the
sacrificial layer 60. A movable layer 62, in the illustrated
embodiment of FIG. 9C, taking the form of a reflective layer 62,
has been deposited over the sacrificial layer 60 and is configured
to be movable relative to the partially reflective layer 54 once
the sacrificial layer 60 is removed. In certain embodiments, this
movable layer will comprise a conductive material. In the
illustrated embodiment, unlike the partially reflective layer 54,
the layer 62 need not transmit any light through the layer, and
thus advantageously comprises a material with high reflectivity. In
one embodiment, the layer 62 comprises aluminum (Al), as aluminum
has both very high reflectivity and acceptable mechanical
properties. In other embodiments, reflective materials such as
silver and gold may be used in the layer 62. In further
embodiments, particularly in non-optical MEMS devices in which the
layer 62 need not be reflective, other materials, such as nickel
and copper may be used in the layer 62.
[0096] In FIG. 9D, the sacrificial layer 60 and the layer 62 have
been patterned and etched to form apertures 64 which extend through
the sacrificial layer 62 and reflective layer 60. In the
illustrated embodiment, these apertures 64 are preferably tapered
to facilitate continuous and conformal deposition of overlying
layers.
[0097] With respect to FIG. 9E, a layer 70 can be deposited over
the patterned layer 62 and sacrificial layer 60. This layer 70 may
be used to form support posts located throughout an array of MEMS
devices. In embodiments in which the MEMS devices being fabricated
comprise interferometric modulator elements (such as modulator
elements 12a and 12b of FIG. 1), some of the support posts (such as
the support structures 18 of FIG. 1) will be located at the edges
of the upper movable electrodes (such as the movable reflective
layer 14 of FIG. 1) of those interferometric modulator elements. In
addition, these support posts may also be formed in the interior of
the resulting interferometric modulator elements, away from the
edges of the upper movable electrode, such that they support a
central or interior section of the upper movable electrode.
[0098] In FIG. 9F, the post layer 70 has been patterned and etched
to form a post structure 72. In addition, the illustrated post
structure 72 has a peripheral portion which extends horizontally
over the underlying layers; this horizontally-extending peripheral
portion will be referred to herein as a wing portion 74. As with
the patterning and etching of the sacrificial layer 60, the edges
75 of the post structure 72 are preferably tapered or beveled in
order to facilitate deposition of overlying layers.
[0099] Because the layer 62 was deposited prior to the deposition
of the post layer 70, the layer 62 may serve as an etch stop during
the etching process used to form the post structure 72, as the
portion of the post structure being etched is isolated from the
underlying sacrificial layer 60 by the layer 62, even though other
portions of the post layer 70 are in contact with the sacrificial
layer 60. Thus, an etch process can be used to form the post
structures 72 which would otherwise etch the sacrificial layer 60,
as well.
[0100] Variations to the above process may be made, as well. In one
embodiment, the layer 62 may be deposited after the patterning and
etching of the sacrificial layer 60, such that the post layer 70
may be completely isolated from the sacrificial layer 60, even
along the sloped sidewalls of the apertures in the sacrificial
layer 60. Such an embodiment provides an etch stop protecting the
post structure 72 during the release etch to remove the sacrificial
layer 60. In another embodiment, the post layer 70 may be deposited
over a patterned sacrificial layer 60 prior to the deposition of
the layer 62. Such an embodiment may be used if the sacrificial
layer 60 will not be excessively consumed during the etching of the
post structure 72, even without an etch stop.
[0101] In FIG. 9G, a mechanical layer 78 has been deposited over
the post structures 72 and the exposed portions of the layer 62. In
certain embodiments, in which the layer 62 provides the reflective
portion of the interferometric modulator element, the mechanical
layer 78 may advantageously be selected for its mechanical
properties, without regard for the reflectivity. In one embodiment,
the mechanical layer 78 advantageously comprises nickel (Ni),
although various other materials, such as Al, may be suitable. For
convenience, the combination of the mechanical layer 78 and the
layer 62 may be referred to collectively as the deformable
electrode or deformable reflective layer 80.
[0102] After deposition of the mechanical layer 78, the mechanical
layer 78 is patterned and etched to form desired structures. In
particular, the mechanical layer 78 may be patterned and etched to
form gaps which define electrodes which are strips of the
mechanical layer which are electrically isolated from one
another.
[0103] The underlying layer 62 may also be patterned and etched to
remove the exposed portions of the layer 62. In one embodiment,
this may be done via a single patterning and etching process. In
other embodiments, two different etches may be performed in
succession, although the same mask used to pattern and etch the
mechanical layer 78 may be left in place and used to selectively
etch the layer 62. In one particular embodiment, in which the
mechanical layer 78 comprises Ni and the layer 62 comprises Al, the
Ni may be etched by a Nickel Etch (which generally comprise nitric
acid, along with other components), and the Al may be etched by
either a phosphoric/acetic acid etch or a PAN
(phosphoric/acetic/nitric acid) etch. A PAN etch may be used to
etch Al in this embodiment, even though it may etch the underlying
sacrificial layer 60 as well, because the deformable reflective
layer 80 has already been formed over the sacrificial layer 60, and
the desired spacing between the deformable reflective layer 80 and
underlying layers has thus been obtained. Any extra etching of the
sacrificial layer 60 during this etch will not have a detrimental
effect on the finished interferometric modulator.
[0104] In FIG. 9H, it can be seen that the deformable electrode or
reflective layer 80, which comprises the mechanical layer 78 and
the layer 62, has also been patterned and etched to form etch holes
82. A release etch is then performed to selectively remove the
sacrificial layer 60, forming a cavity 84 which permits the
deformable reflective layer 80 to deform toward the electrode layer
52 upon application of appropriate voltage. In one embodiment, the
release etch comprises a XeF.sub.2 etch, which will selectively
remove sacrificial materials like Mo, W, or polysilicon without
significantly attacking surrounding materials such as Al,
SiO.sub.2, Ni, or Al.sub.2O.sub.3. The etch holes 82, along with
the gaps between the strip electrodes formed from the mechanical
layer 78, advantageously permit exposure of the sacrificial layer
60 to the release etch.
[0105] As noted above, restoration features 513 can be fabricated
by patterning etch holes 82 into suitable shapes and dimensions to
form openings 517 and deflecting portions 515, such as those shown
in FIGS. 8A-8K. Thus, in some embodiments, the restoration features
may be etched into the mechanical layer 78 and the etched portion
of the mechanical layer 78 can serve as etch holes that are used in
this fabrication process as part of the release etch.
[0106] The above-described modifications can help remove process
variability and lead to a more robust design and fabrication.
Additionally, while the above aspects have been described in terms
of selected embodiments of the interferometric modulator, one of
skill in the art will appreciate that many different embodiments of
interferometric modulators may benefit from the above aspects. Of
course, as will be appreciated by one of skill in the art,
additional alternative embodiments of the interferometric modulator
can also be employed. The various layers of interferometric
modulators can be made from a wide variety of conductive and
non-conductive materials that are generally well known in the art
of semi-conductor and electro-mechanical device fabrication.
[0107] Referring now to FIGS. 10A-D, these figures illustrate
exemplary simulation models of the restoration features 513 and
deformable layer 506. In the simulations shown, a quarter model of
the restoration features 513 and deformable layer 506 was used due
to the symmetry of a pixel. In the examples shown, the restoration
feature 513 has been modeled as an cross shaped or X-shaped feature
(e.g., similar to that shown in FIGS. 8G and 8H) having legs that
are approximately 6 microns long and the openings 517 may be
approximately 2 microns in width.
[0108] In FIGS. 10A-10B, a quarter of the restoration feature 513
is shown in its undriven, unactuated state. To help illustrate the
deflection of the restoration feature 513 in its undriven state,
FIGS. 10A-10B are shaded to indicate different vertical heights of
portions of the restoration feature 513. In FIG. 10A, the
simulation assumed that the deformable layer 506 did not include a
secondary local layer around the restoration feature 513. In FIG.
10B, the simulation assumed that the deformable layer 506 included
a secondary local layer, such as an oxide, patterned concentrically
around the restoration feature 513 thus causing the restoration
feature 513 to deform or deflect further in its undriven or
unactuated state in comparison to the simulation shown in FIG.
10A.
[0109] In FIGS. 10C-10D, the quarter of the restoration is shown in
its driven or actuated state. As noted, under actuation, strain
energy is induced in the restoration features 513. The magnitude of
strain energy is indicated in FIGS. 10C-10D by differences in
shading. The strain energy is stored in the restoration feature 513
and is released when the V.sub.bias voltage applied to the pixel is
reduced. When released, the strain energy may thus aid in the
restoration of the deformable layer 506 and the restoration feature
513 to the unactuated or undriven state. Accordingly, in some
embodiments, it may be desirable to maximize the strain energy in
certain areas of the deformable layer 506 and the restoration
feature 513 to increase the restoring force that is applied.
[0110] FIG. 10C shows the deformable layer 506 and the restoration
feature 513 from FIG. 10A, but in the actuated or driven state.
FIG. 10D, shows the deformable layer 506 and the restoration
feature 513 from FIG. 10B, but in the actuated or driven state. As
shown in FIG. 10D, the addition of a secondary oxide layer may
enhance the effect of the restoration feature, since the
deformation of the restoration feature is larger, thus resulting in
higher strain energy being stored. These models are merely
exemplary, and other configurations are within embodiments of the
present disclosure.
[0111] While the above detailed description has shown, described,
and pointed out novel features of the invention as applied to
various embodiments, it will be understood that various omissions,
substitutions, and changes in the form and details of the device or
process illustrated may be made by those skilled in the art without
departing from the spirit of the invention. As will be recognized,
the present invention may be embodied within a form that does not
provide all of the features and benefits set forth herein, as some
features may be used or practiced separately from others.
* * * * *