U.S. patent application number 13/327675 was filed with the patent office on 2012-04-12 for analog interferometric modulator device with electrostatic actuation and release.
This patent application is currently assigned to QUALCOMM MEMS TECHNOLOGIES, INC.. Invention is credited to Lior Kogut, Manish Kothari, Jeffrey B. Sampsell.
Application Number | 20120088027 13/327675 |
Document ID | / |
Family ID | 38789755 |
Filed Date | 2012-04-12 |
United States Patent
Application |
20120088027 |
Kind Code |
A1 |
Kothari; Manish ; et
al. |
April 12, 2012 |
ANALOG INTERFEROMETRIC MODULATOR DEVICE WITH ELECTROSTATIC
ACTUATION AND RELEASE
Abstract
Examples of methods of manufacturing a microelectromechanical
system (MEMS) device can include forming a first reflective layer
on a substrate, forming a sacrificial layer over the first
reflective layer, removing a portion of the sacrificial layer to
form an opening, and filling the opening with a dielectric material
to form a post. Some methods further include forming a second
reflective layer over the sacrificial layer, removing a portion of
the second reflective layer and a portion of the post to form a
hole, filling the hole with a conductive material to form an
electrode, and removing the sacrificial layer.
Inventors: |
Kothari; Manish; (Cupertino,
CA) ; Kogut; Lior; (Haifa, IL) ; Sampsell;
Jeffrey B.; (Pueblo West, CO) |
Assignee: |
QUALCOMM MEMS TECHNOLOGIES,
INC.
San Diego
CA
|
Family ID: |
38789755 |
Appl. No.: |
13/327675 |
Filed: |
December 15, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12687850 |
Jan 14, 2010 |
8098416 |
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13327675 |
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|
11444567 |
Jun 1, 2006 |
7649671 |
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12687850 |
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Current U.S.
Class: |
427/105 |
Current CPC
Class: |
G02B 26/001
20130101 |
Class at
Publication: |
427/105 |
International
Class: |
B05D 5/12 20060101
B05D005/12 |
Claims
1. A method of manufacturing an electromechanical systems (EMS)
device, comprising: forming an optical stack over a substrate,
wherein the optical stack is partially transparent or translucent
and at least partially reflective of light, and includes a first
electrode; forming a sacrificial layer over the optical stack;
forming a reflective element over the sacrificial layer, wherein
the reflective element includes a second electrode; forming a
support structure between the first electrode and the second
electrode; forming a third electrode in a portion of the support
structure between the first electrode and the second electrode; and
removing the sacrificial layer to form a cavity between the optical
stack and the reflective element, wherein after removing the
sacrificial layer, the reflective element is movable between a
first position and a second position upon application of a voltage
between the first electrode and the second electrode.
2. The method of claim 1, wherein forming the optical stack
includes: forming a partially reflective layer; forming an
electrically conductive layer, the first electrode including a
portion of the electrically conductive layer; and forming an
electrically nonconductive layer over the electrically conductive
layer.
3. The method of claim 1, wherein forming the reflective element
includes forming an electrically conductive layer over the
sacrificial layer, the second electrode including a portion of the
electrically conductive layer.
4. The method of claim 3, wherein the reflective element includes a
lower surface of the electrically conductive layer.
5. The method of claim 1, wherein forming the support structure
includes: removing a portion of the sacrificial layer to form an
opening; and filling the opening with an electrically nonconductive
material to form a post.
6. The method of claim 5, wherein forming the third electrode
includes: removing a portion of the post to form a hole in the
post; and filling the hole in the post with an electrically
conductive material to form the third electrode.
7. The method of claim 1, wherein forming the reflective element
includes: forming a first layer; and forming a second layer over
the first layer.
8. The method of claim 7, wherein the first layer is more flexible
than the second layer.
9. The method of claim 7, wherein the first layer is thinner than
the second layer.
10. The method of claim 7, wherein at least one of the first layer
or the second layer is electrically conductive, the second
electrode including a portion of the electrically conductive
layer.
11. The method of claim 1, wherein forming the reflective element
further includes forming one or more extensions above an upper
surface of the reflective element.
12. The method of claim 1, wherein at least a portion of the third
electrode is lower than the reflective element when the reflective
element is in the second position, and wherein at least a portion
of the third electrode is higher than the reflective element when
the reflective element is in the first position.
13. The method of claim 1, wherein the cavity includes an
interferometric optical cavity.
14. The method of claim 1, wherein the reflective element in
contact with a portion of the optical stack when in the first
position and not in contact with the portion of the optical stack
when in the second position.
15. A method of manufacturing an electromechanical systems (EMS)
device, the method comprising: forming a first electrode over a
substrate; forming an electrically nonconductive layer over the
first electrode; forming a sacrificial layer over the electrically
nonconductive layer; forming a second electrode over the
sacrificial layer; forming a reflective element over the
sacrificial layer; forming a support structure between the first
electrode and the second electrode; forming a third electrode in a
portion of the support structure between the first electrode and
the second electrode; and removing the sacrificial layer, wherein
after removing the sacrificial layer, the reflective element is
movable between a first position and a second position, wherein at
least a portion of the third electrode is lower than the reflective
element when the reflective element is in the second position, and
wherein at least a portion of the third electrode is higher than
the reflective element when the reflective element is in the first
position.
16. The method of claim 15, wherein the reflective element includes
a lower surface of the second electrode.
17. The method of claim 15, wherein forming the support structure
includes: removing a portion of the sacrificial layer to form an
opening; and filling the opening with an electrically nonconductive
material to form a post.
18. The method of claim 17, wherein forming the third electrode
includes: removing a portion of the post to form a hole in the
post; and filling the hole in the post with an electrically
conductive material to form the third electrode.
19. The method of claim 15, wherein forming the reflective element
includes: forming a first layer; and forming a second layer over
the first layer.
20. The method of claim 19, wherein the first layer is more
flexible than the second layer.
21. The method of claim 19, wherein the first layer is thinner than
the second layer.
22. The method of claim 19, wherein at least one of the first layer
or the second layer is electrically conductive, the second
electrode including a portion of the electrically conductive
layer.
23. The method of claim 15, wherein forming the reflective element
further includes forming one or more extensions above an upper
surface of the reflective element.
24. The method of claim 15, wherein the reflective element is in
contact with a portion of the electrically nonconductive layer when
in the first position and not in contact with the portion of the
electrically nonconductive layer when in the second position.
25. The method of claim 15, wherein removing the sacrificial layer
forms an interferometric optical cavity between the reflective
element and the electrically nonconductive layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/687,850, filed Jan. 14, 2010, entitled
"ANALOG INTERFEROMETRIC MODULATOR DEVICE WITH ELECTROSTATIC
ACTUATION AND RELEASE," which is a continuation of U.S. patent
application Ser. No. 11/444,567, filed Jun. 1, 2006, now U.S. Pat.
No. 7,649,671, entitled "ANALOG INTERFEROMETRIC MODULATOR DEVICE
WITH ELECTROSTATIC ACTUATION AND RELEASE," each of which is hereby
incorporated by reference herein in its entirety.
BACKGROUND
[0002] 1. Field
[0003] The invention relates to microelectromechanical system
devices and in particular to analog, digital, and/or optical
devices utilizing a microelectromechanical system.
[0004] 2. Description of the Related Art
[0005] Microelectromechanical 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. 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 an air gap. As described herein in more detail,
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
[0006] One embodiment of a microelectromechanical system (MEMS)
device comprises a first electrode, a second electrode electrically
insulated from the first electrode, and a third electrode
electrically insulated from the first electrode and the second
electrode. The MEMS device also comprises a support structure which
separates the first electrode from the second electrode. The MEMS
device further comprises a reflective element located and movable
between a first position and a second position. The reflective
element is in contact with a portion of the device when in the
first position and is not in contact with the portion of the device
when in the second position. An adhesive force is generated between
the reflective element and the portion when the reflective element
is in the first position. Voltages applied to the first electrode,
the second electrode, and the third electrode at least partially
reduce or counteract the adhesive force.
[0007] Another embodiment of a microelectromechanical system (MEMS)
device comprises a first means for conducting electricity, a second
means for conducting electricity, the second conducting means
electrically insulated from the first conducting means, and a third
means for conducting electricity, the third conducting means
electrically insulated from the first conducting means and the
second conducting means. The MEMS device further comprises means
for separating the first conducting means from the second
conducting means. The MEMS device further comprises means for
reflecting light, the reflecting means located and movable between
a first position and a second position. The reflecting means is in
contact with a portion of the device when in the first position and
is not in contact with the portion of the device when in the second
position. An adhesive force is generated between the reflecting
means and the portion when the reflecting means is in the first
position. Voltages applied to the first conducting means, the
second conducting means, and the third conducting means at least
partially reduce or counteract the adhesive force.
[0008] An embodiment of a method of operating a
microelectromechanical system (MEMS) device comprises providing a
MEMS device that comprises a first electrode, a second electrode
electrically insulated from the first electrode, and a third
electrode electrically insulated from the first electrode and the
second electrode. The MEMS device further comprises a support
structure which separates the first electrode from the second
electrode. The MEMS device further comprises a reflective element
located and movable between a first position and a second position.
The reflective element is in contact with a portion of the device
when in the first position and is not in contact with the portion
of the device when in the second position. An adhesive force is
generated between the reflective element and the portion when the
reflective element is in the first position. The method further
comprises applying voltages to the first electrode, the second
electrode, and the third electrode to at least partially reduce or
counteract the adhesive force.
[0009] An embodiment of a method of manufacturing a
microelectromechanical system (MEMS) device comprises forming a
first reflective layer on a substrate, forming a sacrificial layer
over the first reflective layer, removing a portion of the
sacrificial layer to form an opening, and filling the opening with
a dielectric material to form a post. The method further comprises
forming a second reflective layer over the sacrificial layer,
removing a portion of the second reflective layer and a portion of
the post to form a hole, filling the hole with a conductive
material to form an electrode, and removing the sacrificial
layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] 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.
[0011] FIG. 2 is a system block diagram illustrating one embodiment
of an electronic device incorporating a 3.times.3 interferometric
modulator display.
[0012] FIG. 3 is a diagram of movable mirror position versus
applied voltage for one exemplary embodiment of an interferometric
modulator of FIG. 1.
[0013] FIG. 4 is an illustration of a set of row and column
voltages that may be used to drive an interferometric modulator
display.
[0014] FIG. 5A illustrates one exemplary frame of display data in
the 3.times.3 interferometric modulator display of FIG. 2.
[0015] FIG. 5B illustrates one exemplary timing diagram for row and
column signals that may be used to write the frame of FIG. 5A.
[0016] FIGS. 6A and 6B are system block diagrams illustrating an
embodiment of a visual display device comprising a plurality of
interferometric modulators.
[0017] FIG. 7A is a cross section of the device of FIG. 1.
[0018] FIG. 7B is a cross section of an alternative embodiment of
an interferometric modulator.
[0019] FIG. 7C is a cross section of another alternative embodiment
of an interferometric modulator.
[0020] FIG. 7D is a cross section of yet another alternative
embodiment of an interferometric modulator.
[0021] FIG. 7E is a cross section of an additional alternative
embodiment of an interferometric modulator.
[0022] FIG. 8A is a side cross-sectional view of an embodiment of a
MEMS device in a relaxed or unactuated state.
[0023] FIG. 8B is a side cross-sectional view of the MEMS device
shown in FIG. 8A in an actuated or driven state.
[0024] FIG. 9A is a side cross-sectional view of another embodiment
of a MEMS device in a relaxed or unactuated state.
[0025] FIG. 9B is a side cross-sectional view of the MEMS device
shown in FIG. 9A in an actuated or driven state.
[0026] FIG. 10A is a side cross-sectional view of an additional
embodiment of a MEMS device in a relaxed or unactuated state.
[0027] FIG. 10B is a side cross-sectional view of the MEMS device
shown in FIG. 10A in an actuated or driven state.
[0028] FIG. 11A is a side cross-sectional view of a portion of an
embodiment of a MEMS device in the actuated or driven state before
a voltage is applied to a third electrode.
[0029] FIG. 11B is a close-up, side cross-sectional view of the
portion of the MEMS device shown in FIG. 11A after the voltage is
applied to the third electrode.
[0030] FIGS. 12A-12D are side cross-sectional views of different
embodiments of a reflective element in a MEMS device.
[0031] FIGS. 13A-13D are side cross-sectional views of additional
embodiments of MEMS devices in the relaxed state.
[0032] FIG. 14 is a side cross-sectional view of an embodiment of a
MEMS device in the actuated or driven state.
DETAILED DESCRIPTION OF EMBODIMENTS
[0033] 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.
[0034] Some embodiments of a MEMS device may comprise a movable
element, such as a mirror or a deformable mechanical layer, which
moves between a first position in which the moveable element is in
contact with a portion of the device and a second position in which
the moveable element is not in contact with the portion of the
device. While in the first position, an adhesive force (e.g.,
stiction) may be generated between the movable element and the
contact portion. Accordingly, it may be advantageous to provide
MEMS devices and methods of operation in which the adhesive force
may be at least partially reduced or counteracted while the
moveable element is in the first position. In certain embodiments,
the MEMS device comprises one or more electrodes configured to at
least partially reduce or counteract the adhesive force on the
movable element. In one embodiment, voltages may be applied to the
one or more electrodes to provide an electrostatic force that at
least partially counteracts the adhesive force. In other
embodiments, a time-varying voltage may be used to elastically
deform or oscillate the movable element so as to reduce the contact
area over which the adhesive force is generated. In certain
embodiments, the time-varying voltage may cause the movable element
to vibrate or resonate such that the adhesive force is reduced.
[0035] 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.
[0036] 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
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.
[0037] 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.
[0038] 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.
[0039] In some embodiments, the layers of the optical stack 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.
[0040] 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 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.
[0041] FIGS. 2 through 5B illustrate one exemplary process and
system for using an array of interferometric modulators in a
display application.
[0042] 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.
[0043] 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." 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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).
[0059] 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.
[0060] 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.
[0061] In some implementations 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.
[0062] 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 cavity,
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.
[0063] 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.
[0064] An embodiment of a MEMS device that incorporates some of the
aspects of the present invention is now discussed with reference to
FIGS. 8A and 8B. The MEMS device 100 comprises a first electrode
101, a second electrode 102 that is electrically insulated from the
first electrode 101, and a third electrode 103 that is electrically
insulated from the first electrode 101 and the second electrode
102. The MEMS device 100 further comprises a support structure 105
which separates the first electrode 101 from the second electrode
102. The MEMS device 100 further comprises a reflective element 107
which is located and movable between a first position (as
schematically illustrated by FIG. 8B) and a second position (which
is schematically illustrated by FIG. 8A). In the first position,
the reflective element 107 is in contact with a portion 113 of the
device 100. In the second position, the reflective element 107 is
not in contact with the portion 113 of the device 100. When the
reflective element 107 is in the first position, an adhesive force
is generated between the reflective element 107 and the portion 113
of the device 100. Voltages applied to the first electrode 101, the
second electrode 102, and the third electrode 103 at least
partially reduce or counteract the adhesive force.
[0065] FIG. 8A illustrates a side cross-sectional view of an
embodiment of a MEMS device 100 in a relaxed or unactuated state.
FIG. 8B illustrates a side cross-sectional view of the MEMS device
100 in an actuated or "driven" state. The MEMS device 100 may be
formed on a transparent or translucent substrate layer 120, which
in one embodiment may comprise glass. An optical layer 124 may be
deposited on the substrate layer 120. The optical layer 124 may be
partially transparent or translucent and partially reflective to
light and may be fabricated, for example, by depositing one or more
layers each of chromium and indium-tin-oxide onto the substrate
120. In some embodiments, at least a portion of the optical layer
124 is electrically conductive and comprises the first electrode
101 of the MEMS device 100. The optical layer 124 may be patterned
into substantially parallel strips and may form row electrodes in a
display device as described herein. In some embodiments, a
dielectric layer 128 may be formed over the optical layer 124 and
may comprise various transparent or translucent materials such as
oxides.
[0066] In certain embodiments, a support structure 105 is disposed
over the dielectric layer 128. The support structure 105 may
comprise a mechanical layer 132 and one or more support posts 136a,
136b. As schematically illustrated in FIGS. 8A and 8B, in certain
embodiments the mechanical layer 132 comprises the reflective
element 107, and the support structure 105 is configured so that
the reflective element 107 faces the dielectric layer 128 in a
substantially plane parallel and spaced arrangement. The reflective
element 107 and the dielectric layer 128 define a cavity 144
therebetween.
[0067] In some embodiments, at least a portion of the mechanical
layer 132 is electrically conductive and comprises the second
electrode 102 in the MEMS device 100. The mechanical layer 132 may
be patterned into substantially parallel strips and may form column
electrodes in a display device as described herein. The mechanical
layer 132 may be fabricated from a deformable and highly conductive
and reflective material such as a metal, which in some embodiments
may be aluminum. In some embodiments, portions of the support posts
136a, 136b are electrically nonconductive and insulate the
mechanical layer 132 from other portions of the device 100 (e.g.,
the optical layer 124). The nonconductive portions of the support
posts 136a, 136b may comprise a dielectric material such as, for
example, aluminum oxide. The dielectric layer 128 also serves to
electrically insulate the mechanical layer 132 from the optical
layer 124.
[0068] As shown in FIG. 8A, in certain embodiments, at least one of
the support posts 136a comprises the third electrode 103. The third
electrode 103 may be fabricated from an electrically conductive
material such as, for example, aluminum, nickel, indium-tin-oxide,
or molybdenum. Electrically nonconductive portions of the support
post 136a may insulate the third electrode 103 from the first
electrode 101 and the second electrode 102. The electrically
nonconductive portions of the support post 136a may comprise a
dielectric material.
[0069] In certain embodiments, as shown in FIGS. 8A and 8B, the
mechanical layer 132 comprises a mechanically deformable material.
As discussed herein with reference to FIG. 1, the mechanical layer
132 may be moved from the relaxed state to the driven state by
applying a voltage difference between the first electrode 101
(e.g., the optical layer 124) and the second electrode 102 (e.g.,
the mechanical layer 132). If the voltage difference exceeds a
threshold value, an electrostatic force causes the mechanical layer
132 to deform and move into contact with the dielectric layer 128,
as shown in FIG. 8B. The dielectric layer 128 prevents shorting
between the optical layer 124 and the mechanical layer 132 in the
driven state and may prevent damage to the optical layer 124 and
mechanical layer 132 from contact during the driven state.
Additionally, the thickness of the dielectric layer 128 may be used
to control the distance the mechanical layer 132 moves between the
relaxed and driven states.
[0070] In some embodiments, a portion of the mechanical layer 132
may be configured to comprise the reflective element 107. For
example, a portion of the lower surface 148 of the mechanical layer
132 may be made highly reflective. The reflective element 107 is
configured to move between at least the second position of the
relaxed state (FIG. 8A) and the first position of the driven state
(FIG. 8B). In the driven state of certain embodiments, the
reflective element 107 is in contact with the portion 113 of the
device 100 as shown in FIG. 8B.
[0071] As further described herein in reference to FIG. 1, the
device 100 may act as an "interferometric modulator." In the
undriven state, light incident on a surface 152 of the substrate
layer 120 is transmitted into the cavity 144. Depending on the
height of the cavity 144, determined by the position of the
mechanical layer 132, interference within the cavity 144 causes
light of certain wavelengths to be reflected and light of other
wavelengths to be absorbed. If the reflected light is in the
visible portion of the electromagnetic spectrum, the surface 152 of
the substrate will display a color corresponding to the reflected
wavelength. In contrast, in the driven state, the height of the
cavity 144 is much smaller (e.g., the reflective element 107
contacts the dielectric layer 128) than in the undriven state, and
the device 100 absorbs substantially all of the incident light, or
at least substantially all of the incident visible light. In the
driven state, the surface 152 of the substrate will display black.
By suitably configuring the size and height of the cavity 144, the
device 100 may be used to form pixels in an image display
device.
[0072] In the driven state, the reflective element 107 is in
contact with the portion 113 of the device 100, thereby generating
an adhesive force between the reflective element 107 and the
portion 113. For example, in the embodiment shown in FIG. 8B, the
adhesive force tends to adhere the deformed portion of the
mechanical layer 132 to the dielectric layer 128.
[0073] The adhesive force may be caused by forces such as, for
example, capillary, electrostatic, or van der Waals forces, or
other intermolecular forces. The adhesive force depends on a range
of factors including, for example, the materials used, the shape,
orientation, and configuration of structures in the device 100, the
roughness of the contact surfaces, and ambient humidity and
pressure. The adhesive force may depend on the manner in which the
structures within the device 100 are operated, for example, through
impulsive motions involving large accelerations or through more
gentle quasi-static motions. "Stiction" is a commonly used term
that may include some of the adhesive effects discussed herein.
[0074] The process of actuating and deactuating the device 100 is
described herein with reference to FIG. 3. A voltage difference may
be applied between the mechanical layer 132 and the optical layer
124. As shown in FIG. 3, as the voltage difference increases above
a first threshold value, an electrostatic force causes the
mechanical layer 132 to deform from the relaxed state (FIG. 8A) to
the driven state (FIG. 8B). As the voltage difference is reduced,
the device 100 remains in the driven state until the voltage
difference drops below a second threshold value. At the second
threshold, the electrostatic force of attraction between the
mechanical layer 132 and the optical layer 124 becomes smaller than
mechanical restoring forces tending to return the mechanical layer
132 to the relaxed state. Accordingly, as the voltage drops below
the second threshold, the reflective element 107 "releases" from
the portion 113 with which it was in contact. In the sample
embodiment of FIG. 3, the first threshold voltage is about 8 volts,
and the second threshold voltage is about 2 volts. FIG. 4 shows one
embodiment of an "actuation protocol" that is used to drive the
MEMS device 100 through this actuation and release cycle.
[0075] The adhesive force may alter the nature of this actuation
and release cycle. In some embodiments of the MEMS device 100, the
adhesive force between the reflective element 107 and the portion
113 of the device 100 in contact with the reflective element 107
may be sufficiently large that adhesion inhibits, or in some cases
prevents, the release of the reflective element 107 as the voltage
difference drops below the second threshold. Accordingly, it is
advantageous to provide architectures that at least partially
reduce or counteract the adhesive force.
[0076] In certain embodiments of the MEMS device 100, voltages
applied to the first electrode 101, the second electrode 102, and
the third electrode 103 at least partially reduce or counteract the
adhesive force while the reflective element 107 is in contact with
the portion 113 of the device 100 (e.g., the first position shown
in FIG. 8B). In the embodiment shown in FIGS. 8A and 8B, the
support post 136a comprises the third electrode 103. The third
electrode 103 is electrically insulated from the first electrode
101 (the optical layer 124 in FIGS. 8A and 8B) and the second
electrode 102 (the mechanical layer 132 in FIGS. 8A and 8B). In
certain such embodiments, a voltage applied to the third electrode
103 generates an electrostatic force 156 on the second electrode
102 (e.g., a force that attracts the mechanical layer 132 toward
the third electrode 103). The electrostatic force 156 may at least
partially counteract the adhesive force between the reflective
element 107 and the portion 113 when the device 100 is in the first
position (shown in FIG. 8B).
[0077] As illustrated in FIG. 8B, the electrostatic force 156 can
be decomposed into a parallel force component 160 and a
perpendicular force component 164. As used herein, the term
"parallel force component" or "parallel component" refers to a
component of the electrostatic force 156 that is generally parallel
to the plane that includes the portion 113 of the device 100 in
contact with the reflective element 107 while in the first
position. The term "parallel direction" or "parallel" refers to the
direction of the parallel force component 160. As used herein, the
term "perpendicular force component" or "perpendicular component"
refers to a component of the electrostatic force 156 that is
generally perpendicular to the plane that includes the portion 113
of the device 100 in contact with the reflective element 107 while
in the first position. The term "perpendicular direction" or
"perpendicular" refers to the direction of the perpendicular force
component 164. The perpendicular direction is at an angle of ninety
degrees to the parallel direction.
[0078] Without subscribing to any particular theory, the
electrostatic force 156 may at least partially reduce or counteract
the adhesive force for at least several reasons. For example, in
some embodiments of the device 100, the parallel force component
160 will urge the mechanical layer 132 in a direction indicated by
arrow 168. This urging may reduce or break intermolecular bonds or
forces responsible at least in part for the adhesive force between
the reflective element 107 and the portion 113 of the device 100.
In these or other embodiments, the perpendicular force component
164 similarly will urge a region of the mechanical layer 132 in a
direction indicated by arrow 172, which also may reduce or break
intermolecular bonds or forces responsible at least in part for the
adhesive force. In some embodiments, the parallel force component
160 will cause at least a portion of the mechanical layer 132 to
slide in the direction of the arrow 168, which may reduce the
adhesive force and permit movement of the mechanical layer 132 in
the direction of the arrow 172. In addition, in certain
embodiments, the perpendicular force component 164 will cause one
or more regions of the reflective element 107 to be displaced in
the direction of the arrow 172. The displaced or "pulled-off"
regions will lose contact with the portion 113 of the device 100,
which will at least partially reduce the adhesive force. In other
embodiments, the perpendicular force component 172 will cause an
elastic deformation of the mechanical layer 132, which may reduce
an area in which the reflective element 107 is in contact with the
portion 113. In general, the adhesive force will be reduced in
proportion to the reduction in contact area. In yet other
embodiments, the adhesive force will be reduced or counteracted by
a combination of any one or more of the aforementioned physical
effects. It is appreciated that in other embodiments, the
electrostatic force 156 may reduce or counteract the adhesive force
for additional reasons presently known or to be discovered, and the
scope of the claimed invention is not to be limited by the reasons
set forth herein.
[0079] In some embodiments, one or more of the voltages applied to
the first electrode 101, the second electrode 102, and the third
electrode 103 may include a time-varying voltage. The time-varying
voltage may cause the magnitude and/or direction of the
electrostatic force 156 also to be time-varying. The variation in
time of the electrostatic force 156 may facilitate the release of
the reflective element 107 from the portion 113 of the device 100
(FIG. 8B). In certain embodiments, the time-varying voltage
includes one or more voltage pulses of short temporal duration, for
example, one or more impulses. The impulse of certain embodiments
has a component generally parallel to the reflective element 107,
while in other embodiments, the impulse has a component generally
perpendicular to the reflective element 107. In certain such
embodiments, the one or more impulses may generate a sufficiently
large acceleration of the reflective element 107 that the adhesive
force is reduced, and the reflective element 107 is released from
the portion 113. In other embodiments, the one or more impulses may
cause a portion of the reflective element 107 to undergo an elastic
deformation, which as discussed above, may reduce the contact area
with the portion 113 and thereby reduce the adhesive force.
[0080] In other embodiments of the MEMS device 100 shown in FIGS.
8A and 8B, one or more of the voltages applied to the first
electrode 101, the second electrode 102, and the third electrode
103 includes a time-varying voltage having a frequency. For
example, in one embodiment, the time-varying voltage may include a
sinusoidal component that oscillates at the frequency. In other
embodiments, the time-varying voltage may include voltages
comprising a band of frequencies centered about the frequency. In
certain embodiments, the time-varying voltages will cause a portion
of the reflective element 107 to undergo an elastic oscillation,
which may at least partially reduce the adhesive force while the
reflective element is in the first position (FIG. 8B). In certain
such embodiments, the elastic oscillation will reduce an area of
the reflective element 107 that is in contact with the portion 113
of the device 100 and thereby reduce the adhesive force. In other
of these certain embodiments, the elastic oscillations of the
reflective element 107 will cause oscillatory accelerations of the
portion 113, which may in part reduce the intermolecular forces
responsible for the adhesive force.
[0081] As is well known, when a force that oscillates at a forcing
frequency is applied to a mechanical system, the mechanical system
will undergo elastic oscillations having an amplitude that is in
direct proportion to the magnitude of the force. The amplitude of
the elastic oscillations will be largest if the forcing frequency
is equal to a mechanical resonant frequency of the mechanical
system. In some embodiments of the MEMS device 100, the frequency
of the time-varying voltage applied to at least one of the
electrodes 101, 102, and 103, is selected to be substantially equal
to a mechanical resonant frequency of the reflective element 107.
In such embodiments, the time-varying voltage will induce elastic
oscillations or vibrations in the reflective element 107 that have
a substantial amplitude so as to reduce the adhesive force and to
facilitate the release of the reflective element 107 from the first
position shown in FIG. 8B. In other such embodiments, the frequency
of the time-varying voltage will be selected so that the reflective
element 107 undergoes an elastic oscillation with a sufficient
amplitude that is effective to reduce the adhesive force. In some
of these embodiments, the frequency that is effective at reducing
the adhesive force may be different from a mechanical resonant
frequency of the reflective element 107.
[0082] Voltages with various ranges of magnitudes and frequencies
can be applied to the first electrode 101, the second electrode
102, and/or the third electrode 103 to at least partially reduce or
counteract the adhesive force. A person of skill in the art will
recognize that suitable magnitudes and frequencies of the voltages
can be calculated for any configuration of the MEMS device 100. For
example, in certain embodiments the voltage applied to at least one
of the first electrode 101, the second electrode 102, and the third
electrode 103 has a magnitude in a range from about 10 Volts to
about 50 Volts, and a frequency in a range from about 100 Hz to
about 10 MHz. These example ranges are not intended to be
limitations on the possible ranges of suitable magnitudes and
frequencies, however, and in other embodiments different magnitudes
and frequencies are used.
[0083] The details of the voltages applied to the first electrode
101, the second electrode 102, and the third electrode 103 in MEMS
devices that operate in accordance with the principles set forth
herein may vary widely. The voltages applied to the electrodes 101,
102, and 103 may be different from the examples described herein,
which are intended to serve as examples and are not intended to
limit the scope of the claimed invention. For example, the
magnitudes, durations, frequencies, order of application, and other
characteristics of the applied voltages may differ widely. Many
other voltage combinations are possible in different embodiments of
the MEMS device 200.
[0084] FIGS. 9A and 9B illustrate a side cross-sectional view of
another embodiment of a MEMS device 200 in the relaxed state (FIG.
9A) and the driven state (FIG. 9B). The MEMS device 200 is
fabricated on a substrate layer 220 and comprises an optical layer
224, a dielectric layer 228, and a mechanical layer 232. The
substrate layer 220, the optical layer 224, and the dielectric
layer 228 have generally the same characteristics and features as
the respective layers 120, 124, and 128 in the MEMS device 100
described with reference to FIGS. 8A and 8B. The mechanical layer
232 comprises one or more support posts 236a, 236b and has
generally the same characteristics as the mechanical layer 132
except as specifically stated otherwise.
[0085] In the embodiment shown in FIGS. 9A and 9B, the reflective
element 107 comprises a mirror 275 disposed between the mechanical
layer 232 and the dielectric layer 228. In certain embodiments, the
mirror 275 is generally parallel to and spaced from the mechanical
layer 232. The reflective element 107 comprises a support
connection 277 that mechanically couples the mirror 275 to the
mechanical layer 232 and that provides an electrical connection to
the mirror 275. In the embodiment shown in FIGS. 9A and 9B, the
mirror 275 and the support connection 277 comprise an electrically
conductive material such as, for example, aluminum, nickel,
indium-tin-oxide, or molybdenum. A portion 279 of the mechanical
layer 232 comprises an electrically nonconductive material, which
is configured to provide electrical insulation between the mirror
275 and the mechanical layer 232. In this embodiment, the mirror
275 is mechanically coupled to, but electrically insulated from,
the mechanical layer 232.
[0086] In the embodiment of the MEMS device shown in FIGS. 9A and
9B, the mirror 275 comprises a reflective surface of the reflective
element 107, which is electrically conductive and highly reflective
and which may be fabricated from a highly conductive and reflective
metal such as, for example, aluminum. In this embodiment, a lower
surface of the mechanical layer 232 is not configured to be
reflective. In the embodiment of FIGS. 9A and 9B, the optical layer
224 comprises the first electrode 101. The support structure 105
comprises the mechanical layer 232 and the support posts 236a and
236b, and the mechanical layer 232 comprises the second electrode
102. The mirror 275 comprises the third electrode 103.
[0087] As described with reference to FIGS. 8A and 8B, a voltage
difference applied between the mechanical layer 232 and the optical
layer 224 can cause the mechanical layer 232 to deform from the
relaxed state (FIG. 9A) to the driven state (FIG. 9B). The
reflective element 107 moves from the second position when it is in
the relaxed state (FIG. 9A) to the first position when it is in the
driven state (FIG. 9B). In the driven state, the reflective element
107 is in contact with the portion 113 of the device 200, and an
adhesive force is generated therebetween.
[0088] In some embodiments of the MEMS device 200, voltages applied
to the first electrode 101, the second electrode 102, and the third
electrode 103 at least partially reduce or counteract the adhesive
force while the reflective element is in the first position (FIG.
9B). As further described with reference to FIGS. 8A and 8B, the
applied voltages may induce elastic deformations or elastic
oscillations in the reflective element 107 that at least partially
reduce the adhesive force. In certain embodiments of the MEMS
device 200, one or more of the voltages are time-varying. In some
of these embodiments, the time-varying voltage may include a
voltage comprising one or more frequencies. The frequency of the
time-varying voltage may be selected to be a mechanical resonant
frequency of the reflective element 107 or to increase an amplitude
of an elastic oscillation induced in the reflective element 107. In
other embodiments, one or more short duration voltage impulses may
be applied to at least one of the electrodes 101, 102, and 103. For
example, in one embodiment, one or more voltage impulses is applied
to the mirror 275 while in the first position so as to induce
oscillations, vibrations, or accelerations that facilitate the
release of the reflective element 107 from the portion 113 of the
device 200. In yet other embodiments, the voltages applied to the
electrodes 101, 102, and 103 may be selected to include a
combination of the aforementioned voltages. For example, in one
embodiment, an oscillatory voltage is applied to one of the
electrodes while one or more voltage impulses are applied to any or
all of the three electrodes. The voltages applied to the electrodes
101, 102, and 103 may be different from the examples described
herein and many other variations and combinations of are possible
in other embodiments of the MEMS device 200.
[0089] FIGS. 10A and 10B illustrate a side cross-sectional view of
another embodiment of a MEMS device 300 in the relaxed state (FIG.
10A) and the driven state (FIG. 10B). The MEMS device 300 is
fabricated on a substrate layer 320 and comprises an optical layer
324, a dielectric layer 328, and a mechanical layer 332. The
substrate layer 320, the optical layer 324, and the dielectric
layer 328 have generally the same characteristics and features as
the respective layers 120, 124, and 128 in the MEMS device 100
described with reference to FIGS. 8A and 8B. The mechanical layer
332 comprises one or more support posts 336a and 336b and has
generally the same characteristics as the mechanical layer 132
except as specifically stated otherwise.
[0090] In the embodiment shown in FIGS. 10A and 10B, the reflective
element 107 comprises a mirror 375 disposed between the mechanical
layer 332 and the dielectric layer 328. In certain embodiments, the
mirror 375 is generally parallel to and spaced from the mechanical
layer 332. The reflective element 107 comprises a support
connection 377 that mechanically couples the mirror 375 to the
mechanical layer 332. In the embodiment shown in FIGS. 10A and 10B,
the mirror 375 and the support connection 377 comprise an
electrically conductive material such as, for example, aluminum,
nickel, indium-tin-oxide, or molybdenum. In contrast to the MEMS
device 200 (FIGS. 9A and 9B), the conductive support post 377
electrically couples the mirror 375 to the mechanical layer 332.
Thus, in this embodiment, the mirror 375 is both mechanically and
electrically coupled to the mechanical layer 332.
[0091] In this embodiment of the MEMS device, the mirror 375 is
electrically conductive and highly reflective and which may be
fabricated from a highly conductive and reflective metal such as,
for example, aluminum. In this embodiment, a lower surface of the
mechanical layer 332 is not configured to be reflective. In the
embodiment of FIGS. 10A and 10B, the optical layer 324 comprises
the first electrode 101. The support structure 105 comprises the
mechanical layer 332 and the support posts 336a and 336b. The
mechanical layer 332 and the mirror 375 comprise the second
electrode 102. As shown in FIGS. 10A and 10B, each of the support
posts 336a, 336b includes an electrically conductive portion. The
third electrode 103 of the device 300 comprises these electrically
conductive portions. In this embodiment, and in distinction to the
device 100 shown in FIGS. 8A and 8B, the conductive portions of the
support posts 336a, 336b are positioned substantially symmetrically
with respect to the mirror 375 to provide a third electrode 103
which is positioned substantially symmetrically with respect to the
reflective element 107.
[0092] As described above with reference to FIGS. 8A to 9B, a
voltage difference applied between the mechanical layer 332 and the
optical layer 224 can cause the mechanical layer 232 to deform from
the relaxed state (FIG. 10A) to the driven state (FIG. 10B). The
reflective element 107 moves from the second position when it is in
the relaxed state (FIG. 10A) to the first position when it is in
the driven state (FIG. 10B). In the driven state, the reflective
element 107 is in contact with the portion 113 of the device 200,
and an adhesive force is generated therebetween.
[0093] By applying voltages to the electrodes 101, 102, and 103,
the MEMS device 300 can at least partially reduce or counteract the
adhesive force between the reflective element 107 and the portion
113 of the device 300. The voltages may be applied to the device
300 in substantially the same manner as described for the MEMS
devices 100 and 200 so as to achieve a reduction in the adhesive
force.
[0094] FIG. 10B shows an embodiment of the MEMS device 300 in which
the conductive portions of the support posts 336a, 336b are
maintained at the same electric potential as one another. In this
embodiment, a pair of electrostatic forces 356a and 356b is
generated between the mirror 375 and the electrically conductive
portions of the support posts 336a and 336b, respectively. The
magnitude of the electrostatic force 356a is substantially equal to
the magnitude of the electrostatic force 356b due to the
substantially symmetrical placement of the electrically conductive
portions 336a, 336b and due to their being maintained at the same
electric potential. Each of the electrostatic forces 356a, 356b can
be decomposed into parallel force components 360a, 360b,
respectively, and perpendicular force components 364a, 364b,
respectively. The electrostatic forces 356a, 356b (or their
components 360a, 360b and 364a, 364b) can be added together
vectorally to produce a net force acting on the mirror 375. Because
the electrically conductive portions of the support posts 336a,
336b in the device 300 are maintained at the same potential and are
positioned substantially symmetrically relative to the mirror 375,
the parallel force components 360a and 360b are substantially equal
in magnitude but opposite in direction. Therefore, the net parallel
force component acting on the mirror 375 is substantially zero. In
this embodiment, the perpendicular force components 364a, 364b are
also substantially equal in magnitude, however, they are in the
same direction. Therefore, the net electrostatic force acting on
the reflective element 107 is substantially perpendicular to the
plane that includes the portion 113 of the device 300.
[0095] In some embodiments of the MEMS device 300, voltages are
applied to the electrodes 101, 102, and 103 so that the net
electrostatic force on the reflective element 107 causes at least a
partial reduction of the adhesive force between the reflective
element 107 and the portion 113 of the device 300. As described
herein with reference to FIGS. 8A to 9B, the applied voltages may
induce elastic deformations or elastic oscillations in the
reflective element 107 that at least partially reduce the adhesive
force. In certain embodiments of the MEMS device 300, one or more
of the voltages are time-varying and may include a voltage
comprising one or more frequencies. The frequency of the
time-varying voltage may be selected to be a mechanical resonant
frequency of the device 300 or to increase an amplitude of an
elastic oscillation induced in the device 300. In other
embodiments, one or more short duration voltage impulses may be
applied to at least one of the electrodes 101, 102, and 103. For
example, in one embodiment, one or more voltage impulses is applied
to the third electrode while the reflective element 107 is in the
first position (FIG. 10B) so as to induce oscillations or
accelerations that facilitate the release of the reflective element
107 from the portion 113 of the device 300. In another embodiment,
the voltages are applied so as to induce a vibration of the
reflective element 107 in the generally perpendicular direction
indicated by arrow 380. In yet other embodiments, the voltages
applied to the electrodes 101, 102, and 103 may be selected to
induce a combination of the aforementioned oscillations or
accelerations. For example, in one embodiment, an oscillatory
voltage is applied to one of the electrodes while one or more
voltage impulses are applied to any or all of the three electrodes.
The voltages applied to the electrodes 101, 102, and 103 may be
different from the examples described herein and many other
variations and combinations of are possible in different
embodiments of the MEMS device 300.
[0096] In other embodiments of the MEMS device 300, the
electrically conductive portion of the support post 336a may be
maintained at a different electric potential than the electrically
conductive portion of the support post 336b. In these embodiments,
the electrostatic forces 356a and 356b will not be of substantially
equal magnitude. Accordingly, the net electrostatic force on the
reflective element 107 will include a net parallel force component.
By appropriately selecting the values of the electric potentials
applied to each of the conductive portions of the support posts
336a, 336b, a net parallel force component can be generated in at
least one of the directions indicated by double-headed arrow 384.
Accordingly, the reflective element 107 may be induced to oscillate
or vibrate along the two directions of the arrow 384. The applied
voltages may have a time varying component with a frequency
selected to induce an elastic deformation or an elastic oscillation
of the reflective element 107. In some embodiments, the frequency
may be selected to substantially match a mechanical resonant
frequency of the reflective element 107 or to cause an increased
amplitude oscillation. In certain embodiments, voltages between the
electrically conductive portions of the support posts 336a and 336b
and the reflective element 107 are cycled so as to induce a
periodic displacement of the reflective element 107 in the two
directions of the double-headed arrow 384. The periodic
displacement may at least partially reduce the adhesive force and
assist the release of the reflective element 107 from the portion
113 of the device 300.
[0097] Although FIGS. 10A and 10B illustrate the third electrode
103 comprising electrically conductive portions of the two support
posts 336a and 336b, it is contemplated that in other embodiments
the third electrode 103 can comprise electrically conductive
portions of additional support posts (and/or other suitable
structural elements). In certain embodiments the third electrode
103 comprises electrically conductive portions of four support
posts disposed substantially symmetrically around the mirror 375,
e.g., the two support posts 336a and 336b and two substantially
similar support posts disposed in a plane that is perpendicular to
the plane of the cross-section shown in FIGS. 10A and 10B. Voltages
applied to electrically conductive portions of each of the support
posts can be used to induce displacements, oscillations, and/or
vibrations not only in the direction of the arrows 380 and 384 (as
described above) but also in a mutually perpendicular direction
(e.g., into or out of the plane of FIGS. 10A and 10B). A person of
skill in the art will recognize that by applying suitable voltages
as described herein (including time-varying and impulsive
voltages), the adhesive force can be at least partially reduced or
counteracted while the reflective element 107 is in the driven
state (e.g., FIG. 10B) so as to assist movement to the relaxed
state (e.g., FIG. 10A). Many variations in the configuration of,
and the voltages applied to, the third electrode 103 are possible,
and the example embodiments discussed herein are not intended as a
limitation on the scope of the claimed invention.
[0098] In yet other embodiments of the MEMS device 300, the
electrically conductive portions of the support posts 336a, 336b
are not positioned substantially symmetrically relative to the
reflective element. In these embodiments, the electrostatic forces
356a, 356b will not in general be substantially equal in magnitude
even if the conductive portions are maintained at the same electric
potential. In some embodiments, an asymmetric positioning is
provided by fabricating the device 300 such that one or more of the
conductive portions is not substantially centered within the
support posts 336a, 336b.
[0099] In certain preferred embodiments, the voltages applied to
the MEMS device 300 may be selected to induce displacements,
deformations, oscillations, or vibrations of the reflective element
107 in both the parallel and the perpendicular directions as
indicated by the arrows 384 and 380, respectively. In some of these
embodiments, the time-varying voltages may include voltages with
more than one frequency in order to induce resonant or increased
amplitude oscillations in both the parallel and perpendicular
directions. In other embodiments, a short duration voltage impulse
is applied to induce a displacement or acceleration in one
direction, while an oscillatory voltage is applied to induce an
oscillation or vibration in the other direction. In yet other
embodiments, the applied voltages are cycled to produce a
combination of these effects. Many other variations are
possible.
[0100] FIGS. 11A and 11B are side cross-sectional views of a
portion of one embodiment of a MEMS device 400 having an
elastically deformable reflective element 107 in the driven state.
The reflective element 107 is in the first position in which it is
in contact with the portion 113 of the device 400. In FIG. 11A, an
electric potential difference has not been applied between the
third electrode 103 and the reflective element 107. The mirror 475
of the reflective element 107 is oriented in a substantially flat
configuration that is substantially parallel to the portion 113 of
the device 400. As shown in FIG. 11A, the portion 113 of the device
that is in contact with the reflective element 107 defines a
contact area 413.
[0101] FIG. 11B shows a configuration of the MEMS device 400 of
FIG. 11A after an electrical potential difference has been
established between the third electrode 103 and the reflective
element 107. The electrostatic force between the third electrode
103 and the reflective element 107 causes an end portion 490 of the
reflective element 107 to deform elastically in a direction that is
generally perpendicular to the portion 113. The end portion 490 of
the reflective element 107 is no longer in contact with the portion
113 of the device. The contact area 413 between the reflective
element 107 and the portion 113 is reduced; therefore, the adhesive
force between the reflective element 107 and the portion 113 is
reduced. The reduction in the adhesive force facilitates the
release of the reflective element 107 from the portion 113 and
facilitates the operation of the device 400. After the reflective
element 107 has released from the portion 113 of the device in
which it was in contact, the potential difference between the third
electrode 103 and the reflective element 107 is reduced to zero in
certain embodiments of the device 400. After release from the
portion 113, the end portion 490 of the reflective element 107
generally returns to an orientation that is substantially parallel
to the plane that contains the optical layer 424 in order that the
cavity 444 provides suitable optical interference for light
incident on the device 400.
[0102] In other embodiments of MEMS device, in addition to or
instead of the deformation shown in FIG. 11B, the voltages applied
to the electrodes 101, 102, and 103 may cause elastic oscillations,
vibrations, resonances, or other types of displacement of the
reflective element 107 while it is in the first position as
described herein. These motions may generally be in the parallel
direction, the perpendicular direction, or a combination of both.
The motions induced by the voltages can at least partially reduce
the adhesive force between the reflective element 107 and the
portion 113, for example, by reducing the contact area between the
reflective element 107 and the portion 113, or by reducing the
magnitude of intermolecular forces responsible in part for the
adhesion, or for some other physical reason.
[0103] In certain embodiments, the third electrode 103 may be
positioned substantially symmetrically with respect to the
reflective element 107 (for example, as shown in FIGS. 10A and
10B), while in other embodiments, the third electrode 103 may be
positioned asymmetrically with respect to the reflective element
107 (for example, as shown in FIGS. 8A and 8B). Symmetrical
positions may be selected for embodiments of MEMS devices in which
it is advantageous to reduce displacements of the reflective
element 107 in the direction generally parallel to the portion 113.
Alternatively, asymmetrical positions may be selected for
embodiments in which it is advantageous to provide a parallel
displacement or vibration. The symmetrical or asymmetrical
positioning of the third electrode 103 can be achieved in a
different ways in various MEMS architectures. For example, in
embodiments in which the third electrode 103 comprises electrically
conductive portions of one or more support posts (e.g., the posts
336a, 336b in FIGS. 10A-10B), the positions of the support posts
can be selected to be symmetrical or asymmetrical with respect to
the reflective element 107. In other embodiments, the support posts
can be positioned symmetrically, but the locations of the
electrically conductive portions within the posts can be
asymmetric, for example, by disposing one or more conductive
portions away from a central axis of the support post.
[0104] In the embodiment schematically illustrated by FIGS.
11A-11B, the electrically conductive portion of the support post
436a is disposed substantially along a central axis of the post
436a. The conductive portion may be disposed away from the central
axis in other embodiments. As shown in FIGS. 11A-11B, the
conductive portion extends substantially the entire length of the
post 436a. In some embodiments, a top end 492 of the support post
436a extends beyond the mechanical layer 432. In the device 400
shown in FIGS. 11A and 11B, a lower end 494 of the conductive
portion of the third electrode 103 extends toward the dielectric
layer 428. A position of the lower end 494 may be different in
other embodiments. The position of the lower end 494 may be
selected to provide different magnitudes and/or directions of the
electrostatic force exerted on the reflective element 107 so as to
provide for different amounts of deformation of the reflective
element 107.
[0105] The third electrode 103 may be configured differently than
shown in FIGS. 8A-11B. For example, in different MEMS
architectures, the third electrode 103 may comprise one, two,
three, four, or more electrically conductive portions of the MEMS
device including, for example, portions of the support posts, the
mechanical layer, the mirror, or other portions of the device. In
some embodiments, the electrostatic force used to facilitate the
release of the reflective element 107 from the portion 113 may be
provided by electrodes 101, 102, and 103 as well as by other
electrodes. In one embodiment, for example, the third electrode 103
comprises a plurality of electrodes, each disposed near each side
of the reflective element 107. By suitably applying voltages to
these electrodes, the reflective element 107 can be induced to
oscillate or vibrate in multiple directions: a first direction that
is perpendicular to the portion 113 (indicated by the arrow 380 in
FIG. 10B) as well as second and third directions that are
substantially parallel to the portion 113 (e.g., a second direction
indicated by the arrow 384 in FIG. 10B and a third mutually
perpendicular direction that is into or out of the plane of FIG.
10B).
[0106] FIGS. 12A-12D are side cross-sectional views of various
configurations of the reflective element 107 in accordance with
various embodiments described herein. In certain embodiments, the
reflective element 107 comprises more than one layer. The
reflective element 107 shown in FIG. 12A comprises a second layer
514 disposed over a first layer 510. The layers may comprise
different materials and may have different mechanical and
electrical properties. In some embodiments, the first layer 510 is
configured to be a highly reflective portion of an interferometric
cavity, and the second layer 514 is configured to provide
structural rigidity to the reflective element 107. In these
embodiments, the first layer 510 comprises a highly reflective
metal such as aluminum, and the second layer 514 comprises a
dielectric material and/or a rigid material, such as an aluminum
alloy or nickel that may be deposited on at least a portion of the
first layer 510. In certain embodiments, at least a portion of one
or more of the layers may be electrically conductive. In certain
such embodiments, one or more of the electrodes 101, 102, and 103
may comprise at least a portion of the electrically conductive
portions of the layers. In some embodiments, the first layer 510
may be configured to have a different thickness than the second
layer 514. For example, as schematically shown in FIG. 12A, the
first layer 510 is thinner than the second layer 514. At least a
portion of the first layer 510 may be configured to be elastically
flexible. For example, end portions 590 of the first layer 510 of
the reflective element 107 in FIG. 12A may be configured to have
increased elastic flexibility as compared to the second layer 514.
The flexibility of the first layer 510 is advantageous in
embodiments such as, for example, the MEMS device 400 shown in
FIGS. 11A and 11B, wherein the electrostatic force causes an
elastic deformation of the end portions 590 of the reflective layer
107. In the embodiment shown in FIG. 12A, the thickness of the end
portions 590 of the first layer 510 is approximately equal to the
thickness of the second layer 514. In other embodiments, different
layer thicknesses may be used. In certain embodiments, the first
layer 510 is thinner than the second layer 514. In other
embodiments, at least the end portions 590 of the first layer 510
are thinner than the second layer 514. For example, in certain such
embodiments the thickness of the end portions 590 is in a range
from about 1/3 to about 1/2 the thickness of the central portions
of the reflective element 107.
[0107] In some embodiments, the thickness of the reflective element
107 is nonuniform. FIG. 12B is a side cross-sectional view of a
reflective element 107 in which the end portions 590 are configured
to be thinner than a central portion 591. As described above, the
thinner end portions 590 may facilitate the elastic deformation of
the reflective element 107. In some embodiments, the tapering of
the reflective element 107 from the center portion 591 to the end
portions 590 may be selected to provide a suitable mechanical
resonant frequency that can be excited by the voltages applied to
the electrodes 101, 102, and 103. In certain embodiments, the
thickness of the end portions 590 is in a range from about 1/3 to
about 1/2 the thickness of the central portions of the reflective
element 107; however, other thicknesses and other taperings can be
used.
[0108] FIG. 12C is a side cross-sectional view of a reflective
element 107 in which one or more extensions 592 are disposed on the
reflective element 107. As shown in FIG. 12C, the extensions 592
are disposed on or near the end portions 590 of the reflective
element 107, but in other embodiments, the extensions 592 may be
disposed at other locations. In some embodiments, the extensions
592 are electrically conductive and may provide an increased
electrostatic attraction to other portions of the MEMS device when
a voltage difference is applied between the extensions 592 and the
other portions (e.g., first or second electrodes 101, 102) of the
MEMS device. In some embodiments, the height of the extensions 592
above an upper surface of the reflective element 107 is in a range
from about 1/3 to about 1/2 of the thickness of the central
portions of the reflective element 107, although other heights may
be used.
[0109] FIG. 12D is a side cross-sectional view of a reflective
element 107 that comprises two layers 510 and 514 and the
extensions 592. In this embodiment, the extensions 592 are disposed
on the first layer 510, but they may be disposed on the second
layer 514 in other embodiments. The thicknesses of the layers 510
and 514 and the heights of the extensions 592 can be selected to
provide suitable electrical and/or structural properties that
assist in at least partially reducing the adhesive force.
[0110] The configurations and orientations shown in FIGS. 12A-12D
are not intended to be limitations. Other embodiments of the
reflective element 107 may combine one or more of the features
shown in FIGS. 12A-12D or may be configured differently. Many
variations are possible.
[0111] The details of the structure of interferometric modulators
that operate in accordance with the principles set forth herein may
vary widely. For example, FIGS. 13A-13C illustrate three different
embodiments of a MEMS device in the relaxed state. FIG. 13A shows a
MEMS device 600a that is fabricated on a substrate layer 620 and
that comprises an optical layer 624, a dielectric layer 628, and a
mechanical layer 632. The substrate layer 620, the optical layer
624, and the dielectric layer 628 have generally the same
characteristics and features as the respective layers 120, 124, and
128 in the MEMS device 100 described with reference to FIGS. 8A and
8B. The mechanical layer 632 comprises one or more support posts
636a and 636b and has generally the same characteristics as the
mechanical layer 132 (FIGS. 8A and 8B) except as specifically
stated otherwise.
[0112] In the embodiment shown in FIG. 13A, the reflective element
107 comprises a mirror 675 which is generally parallel to and
spaced from the mechanical layer 632 and the dielectric layer 628.
The reflective element 107 comprises a support connection 677 that
mechanically couples the mirror 675 to the mechanical layer 632. In
the embodiment shown in FIG. 13A, the mirror 675 and the support
connection 677 comprise an electrically conductive material such
as, for example, aluminum, nickel, indium-tin-oxide, or molybdenum.
A portion 679 of the mechanical layer 632 comprises an electrically
nonconductive material and is configured to provide electrical
insulation between the mirror 675 and the mechanical layer 632. In
this embodiment, the mirror 675 is mechanically coupled to, but
electrically insulated from, the mechanical layer 632.
[0113] In this embodiment of the MEMS device, the mirror 675 of the
reflective element 107 is electrically conductive and highly
reflective and may be fabricated from a highly conductive and
reflective metal such as, for example, aluminum. In this
embodiment, a lower surface 648 of the mechanical layer 632 is not
configured to be reflective. The optical layer 624 comprises the
first electrode 101. The support structure 105 comprises the
mechanical layer 632 and the support posts 636a and 636b. The
mechanical layer 632 comprises the second electrode 102. As shown
in FIG. 13A, the third electrode 103 of the device 600 comprises
electrically conductive portions of the support posts 636a,
636b.
[0114] In certain embodiments of the MEMS devices shown in FIGS.
13A-13D, the mirror 675 is electrically conductive and is connected
to an electric voltage or current source that is independent of the
three electrodes 101, 102, and 103. In these embodiments, different
voltages are applied to the optical layer 624, the mechanical layer
632, and the mirror 675 to provide a tunable interferometric cavity
644 in which the movement of the mirror surface (e.g., the
reflective element 107) has a tunable relationship to these applied
voltages. Further details regarding tunable MEMS architectures are
provided in U.S. patent application Ser. No. 11/144,546 titled
"ANALOG INTERFEROMETRIC MODULATOR DEVICE," filed Jun. 3, 2005,
which is hereby incorporated by reference herein in its
entirety.
[0115] By applying voltages to the electrodes 101, 102, and 103,
the MEMS device 600a can at least partially reduce or counteract
the adhesive force between the reflective element 107 and the
portion 113 of the device when in the first position. The voltages
may be applied to the device 600a in substantially the same manner
as described herein for the MEMS devices 100, 200, 300, and 400 so
as to achieve at least a partial reduction in the adhesive force
and to facilitate the release of the reflective element 107 from
the portion 113.
[0116] FIG. 13B is a side cross-sectional view of another
embodiment of a MEMS device 600b that is generally similar to the
device 600a shown in FIG. 13A except as described below. In this
embodiment, the reflective element 107 comprises one or more
extensions 692 extending toward the second electrode 102. The
extensions 692 may be disposed on an upper surface of the mirror
675. In some embodiments, the shape of the mirror 675 is generally
similar to the shapes illustrated in FIGS. 12C and 12D. The
extensions 692 protrude toward the second electrode 102 (e.g., the
mechanical layer 632). Because the extensions 692 are closer to the
second electrode 102, the electrostatic force exerted by the second
electrode 102 on the extensions 692 is larger than on other
portions of the mirror 675 and may facilitate the release of the
reflective element 107 when in the first position.
[0117] FIG. 13C is a side cross-sectional view of another
embodiment of a MEMS device 600c that is generally similar to the
devices 600a and 600b shown in FIGS. 13A and 13B except as
described below. In this embodiment, the second electrode 102 may
be configured to have one or more extensions 693 extending toward
the reflective element 107. In certain embodiments, the extensions
693 are disposed on the surface 648 of the mechanical layer 632.
Because the extensions 693 of the second electrode 102 are closer
to the reflective element 107, the electrostatic force exerted by
the second electrode 102 on the reflective element 107 is larger
and may facilitate the release of the reflective element 107 when
in the first position. In some embodiments, both the second
electrode 102 and the reflective element 107 are configured to
comprise the extensions 693 and 692, respectively.
[0118] In some embodiments of the devices 600b and 600c shown in
FIGS. 13B and 13C, the extensions 692 and/or 693 are coated with a
dielectric material so as to electrically insulate them from
contact with other portions of the devices 600b, 600c such as, for
example, the surface 648 of the mechanical layer 632.
[0119] FIG. 13D is a side cross-sectional view of another
embodiment of a MEMS device 600d that is generally similar to the
devices 600a, 600b, and 600c shown in FIGS. 13A-13C except as
described below. In the device 600d, the third electrode 103
comprises extensions that are disposed on the surface 648 of the
mechanical layer 632. The third electrode 103 is electrically
insulated from the second electrode 102 (e.g., the mechanical layer
632), for example, by providing a thin layer of nonconductive
material between the third electrode 103 and the second electrode
102. In these embodiments, the third electrode 103 protrudes more
closely to the reflective element 107, which may increase the
electrostatic force exerted by the third electrode 103 on the
reflective element 107 and may facilitate the release of the
reflective element 107 from the portion 113 when the reflective
element 107 is in the first position.
[0120] FIG. 14 illustrates a side cross-sectional view of another
embodiment of a MEMS device 700 shown in the driven or actuated
state. The MEMS device 700 is fabricated on a substrate layer 720
and comprises an optical layer 724, a dielectric layer 728, and a
mechanical layer 732. The substrate layer 720, the optical layer
724, and the dielectric layer 728 have generally the same
characteristics and features as the respective layers 120, 124, and
128 in the MEMS device 100 described with reference to FIGS. 8A and
8B. The mechanical layer 732 comprises one or more support posts
736a and 736b and has generally the same characteristics as the
mechanical layer 132 except as specifically stated otherwise.
[0121] In the embodiment shown in FIG. 14, the reflective element
107 comprises a reflective portion of the mechanical layer 732, for
example, by making a portion of a lower surface 748 of the
mechanical layer 732 highly reflective. In this embodiment, the
first electrode 101 comprises the optical layer 724. The support
structure 105 comprises the mechanical layer 732 and the support
posts 736a and 736b. In some embodiments, at least a portion of the
mechanical layer 732 is electrically conductive and comprises the
second electrode in the MEMS device 700. In certain embodiments,
portions of the support posts 736a and 736b are electrically
nonconductive and insulate portions of the mechanical layer 732
from other portions of the device 700 (e.g., the optical layer
724).
[0122] The MEMS device 700 shown in FIG. 14 comprises electrodes
756a and 756b that are disposed above the support posts 736a and
736b and that are electrically insulated from other portions of the
device 700 by electrically nonconductive regions 758a and 758b. In
some embodiments, the electrically nonconductive regions 758a, 758b
comprise a dielectric material such as, for example, a dielectric
film. In the embodiment shown in FIG. 14, the third electrode 103
comprises the electrodes 756a and 756b. The electrodes 756a and
756b in other embodiments can have shapes and sizes that are
different than shown in FIG. 14. For example, the electrodes 756a
and 756b may be relatively short in some embodiments. It is
preferred, although not necessary, for at least a portion of each
of the electrodes 756a and 756b to be disposed above at least a
portion of the reflective element 107.
[0123] FIG. 14 schematically illustrates the MEMS device 700 when
the reflective element 107 is in a first position (the actuated or
driven state) in which the reflective element 107 is in contact
with a portion 113 of the device 700. As further described above,
the reflective element 107 can move to a second position (the
unactuated or relaxed state) in which it is not in contact with the
portion 113. For example, the mechanical layer 732 may be
fabricated from a mechanically deformable material such as a metal
(e.g., aluminum) that can move between the first and second
positions. When the device 700 is in the driven state, the
mechanical layer 732 is deformed and comprises bending regions 760a
and 760b, which are disposed between the portion 113 and the
support posts 736a and 736b, respectively. In certain embodiments,
the reflective element 107 (when in the driven state) is also
deformed and also comprises the bending regions 760a and 760b.
[0124] In some embodiments of the device 700, at least portions of
the electrodes 756a and 756b are disposed higher than the
reflective element 107 when the reflective element 107 is in the
first position. In certain embodiments, at least a portion of each
of the electrodes 756a and 756b protrudes away from the support
posts 736a and 736b, respectively, such that these portions are
disposed above (e.g., higher than) at least a portion of the
reflective element 107 when the reflective element 107 is in the
first position (FIG. 14). In certain preferred embodiments, the
electrodes 756a and 756b are configured so that at least a portion
of the electrodes 756a and 756b is disposed directly above at least
a portion of the bending regions 760a and 760b, respectively.
[0125] In some embodiments of the MEMS device 700, voltages are
applied to the electrodes 101, 102, and 103 so that a net
electrostatic force on the reflective element 107 at least
partially reduces or counteracts the adhesive force on the
reflective element 107 in the first position. As discussed further
above, the voltages may have various ranges of magnitudes and
frequencies and may be applied to induce displacements,
oscillations, and/or vibrations of the reflective element 107 to
assist in moving the reflective element 107 from the first position
to the second position. In certain embodiments, a voltage
difference is applied between the third electrode 103 (e.g., the
electrodes 756a, 756b) and the second electrode 102 (e.g., an
electrically conductive portion of the mechanical layer 732). The
voltage difference can have various ranges of magnitudes and
frequencies and can comprise one or more relatively short duration
impulses. In various embodiments, the third electrode 103 is
electrically connected to one or more voltage sources by traces or
wires that lead off of the display array 30 to the array driver 22
(see FIG. 2). In one embodiment of the device 700, the array driver
22 may use a driver circuit generally similar to the row and column
driver circuits 24 and 26 to communicate a suitable electrical
signal to the third electrode 103.
[0126] The voltage difference applied between the second and third
electrodes 102 and 103 causes net electrostatic forces indicated by
arrows 764a and 764b to act on the reflective element 107. In
certain preferred embodiments, portions of the electrodes 756a and
756b protrude directly above at least portions of the bending
regions 760a and 760b so that the net electrostatic forces 764a and
764b have reasonably large perpendicular components in the bending
regions 760a and 760b that tend to pull the reflective element 107
away from the portion 113. In certain such embodiments, the
electrostatic forces 764a and 764b may at least partially reduce or
counteract the adhesive force and may assist in moving the
reflective element 107 from the first position to the second
position. Without subscribing to any particular theory, the net
electrostatic force 764a applied in the bending region 760a may
induce crack opening at an edge of a contact interface between the
reflective element 107 and the portion 113. The crack may propagate
across the contact interface, assisting the reflective element 107
to peel away from the portion 113 and to move from the first
position to the second position. The net electrostatic force 764b
applied in the bending region 760b may act in a similar manner, and
in certain embodiments cracks may open at opposing edges of the
contact interface and propagate across the interface. Although it
is preferred that at least two electrodes 756a and 756b be used to
reduce or counteract the adhesive force on the reflective element
107, in other embodiments different configurations, orientations,
and numbers of electrodes (e.g., one) can be used, for example, to
initiate crack opening and facilitate release of the reflective
element 107.
[0127] Embodiments of the MEMS device 700 can provide certain
advantages. For example, the magnitudes of the electrostatic forces
764a, 764b at the bending regions 760a, 760b needed to facilitate
release from the driven to the undriven state typically are much
smaller than if the forces were applied to a central region of the
reflective element 107. Accordingly, smaller voltage differences
(e.g., between the second and third electrodes 102 and 103) can be
applied to the device 700. Moreover, in some embodiments, the
electrodes 756a and 756b reduce electrostatic instability and
collapse of the mechanical layer 732 onto the dielectric layer 728,
which can be a problem in some closing-gap devices. Further, in
certain embodiments, voltage impulses having a duration that is
shorter than a typical release time of the device 700 can be used
to facilitate movement of the reflective element 107 from the
driven state to the undriven state.
[0128] The MEMS devices disclosed herein may be fabricated using
suitable micromachining processes such as, for example, selective
deposition and etching as described in the heretofore incorporated
U.S. patent application Ser. No. 11/144,546. For example, certain
embodiments of a MEMS device, such as the device 100 shown in FIG.
8A, may be fabricated by depositing a partially reflective and
electrically conductive layer on a transparent or translucent
substrate 120 to provide the optical layer 124. A dielectric layer
128 is deposited over the optical layer 124. Then, a sacrificial
layer (not shown in FIG. 8A) is deposited over the dielectric layer
128. The sacrificial layer is selectively etched to form a
plurality of holes exposing the dielectric layer 128. The holes are
filled with a dielectric material such as, for example, aluminum
oxide, to form support posts 136a and 136b. Other suitable
dielectric materials include polymers and other organic or
inorganic compounds.
[0129] A conductive and reflective material such as, for example,
aluminum, is deposited over the support posts 136a, 136b and the
sacrificial layer to form a mechanical layer 132. To form an
electrically conductive portion of a third electrode 103, the
mechanical layer 132 is selectively etched in certain embodiments
to form an opening over the support post 136a. A portion of the
support post 136a is selectively etched to form a hole, which may
extend to the dielectric layer 128 in some embodiments. The hole is
filled with a conductive material such as, for example, aluminum,
nickel, indium-tin-oxide, or molybdenum, to form the electrically
conductive portion of the third electrode 103.
[0130] Thereafter, an etchant is applied to the sacrificial layer,
which reacts with and removes the sacrificial layer. As a result,
the space filled with the sacrificial material becomes the
interferometric cavity 144 and the MEMS device 100 of FIG. 8A is
formed. As is known in the MEMS device fabrication arts, additional
or different processing steps and materials may be used to
fabricate a MEMS device in accordance with the embodiments
disclosed herein.
[0131] Although certain preferred embodiments and examples are
discussed above, it is understood that the inventive subject matter
extends beyond the specifically disclosed embodiments to other
alternative embodiments and/or uses of the invention and obvious
modifications and equivalents thereof. It is intended that the
scope of the inventions disclosed herein should not be limited by
the particular disclosed embodiments. Thus, for example, in any
method or process disclosed herein, the acts or operations making
up the method/process may be performed in any suitable sequence and
are not necessarily limited to any particular disclosed sequence.
Various aspects and advantages of the embodiments have been
described where appropriate. It is to be understood that not
necessarily all such aspects or advantages may be achieved in
accordance with any particular embodiment. Thus, for example, it
should be recognized that the various embodiments may be carried
out in a manner that achieves or optimizes one advantage or group
of advantages as taught herein without necessarily achieving other
aspects or advantages as may be taught or suggested herein.
[0132] It is to be understood that persons of skill in the
appropriate arts may modify the invention herein described while
still achieving the favorable results of this invention.
Accordingly, the foregoing description is to be understood as being
a broad, teaching disclosure directed to persons of skill in the
appropriate arts and not as limiting upon the invention.
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