U.S. patent application number 13/215138 was filed with the patent office on 2012-02-23 for reduced capacitance display element.
This patent application is currently assigned to QUALCOMM MEMS Technologies, Inc.. Invention is credited to William J. Cummings, Brian J. Gally.
Application Number | 20120044563 13/215138 |
Document ID | / |
Family ID | 36144731 |
Filed Date | 2012-02-23 |
United States Patent
Application |
20120044563 |
Kind Code |
A1 |
Cummings; William J. ; et
al. |
February 23, 2012 |
REDUCED CAPACITANCE DISPLAY ELEMENT
Abstract
A display element, such as an interferometric modulator,
includes a transparent conductor configured as a first electrode
and a movable minor configured as a second electrode.
Advantageously, the partial reflector is positioned between the
transparent conductor and the movable mirror. Because the
transparent conductor serves as an electrode, the partial reflector
does not need to be conductive. Accordingly, a greater range of
materials may be used for the partial reflector. In addition, a
transparent insulative material, such as a dielectric, may be
positioned between the transparent conductor and the partial
reflector, for example, in order to decrease a capacitance of the
display element without changing a gap distance between the partial
reflector and the movable minor. Thus, a capacitance of the display
element may be reduced without changing the optical characteristics
of the display element.
Inventors: |
Cummings; William J.;
(Clinton, WA) ; Gally; Brian J.; (Los Gatos,
CA) |
Assignee: |
QUALCOMM MEMS Technologies,
Inc.
San Diego
CA
|
Family ID: |
36144731 |
Appl. No.: |
13/215138 |
Filed: |
August 22, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11155939 |
Jun 17, 2005 |
8004504 |
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13215138 |
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60613542 |
Sep 27, 2004 |
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60613488 |
Sep 27, 2004 |
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Current U.S.
Class: |
359/292 ;
359/290; 427/162 |
Current CPC
Class: |
G02B 26/001
20130101 |
Class at
Publication: |
359/292 ;
359/290; 427/162 |
International
Class: |
G02B 26/00 20060101
G02B026/00; B05D 1/36 20060101 B05D001/36; B05D 5/06 20060101
B05D005/06 |
Claims
1-28. (canceled)
29. A display element comprising: a substantially transparent
conductive layer; a partially reflective insulator having a
thickness of between about 40 and 150 Angstroms; a moveable
reflective layer, the partially reflective insulator being
positioned between the conductive layer and the moveable reflective
layer, wherein a voltage applied between the conductive layer and
the moveable reflective layer induces movement of the moveable
reflective layer; and a first dielectric layer positioned between
the conductive layer and the partially reflective insulator.
30. The display element of claim 29, wherein when the voltage is
applied between the conductive layer and the moveable reflective
layer, at least a portion of the moveable reflective layer moves so
that the at least a portion of the moveable reflective layer
physically contacts the partially reflective insulator.
31. The display element of claim 29, further comprising a second
dielectric layer positioned between the partially reflective
insulator and the moveable reflective layer.
32. The display element of claim 29, wherein the first dielectric
layer includes a material selected from the group consisting of
SiO.sub.2, Al.sub.2O.sub.3, and Silicon Nitride.
33. The display element of claim 29, wherein the partially
reflective insulator includes a material selected from the group
consisting of Silicon Nitride, CrO.sub.2, CrO.sub.3,
Cr.sub.2O.sub.3, Cr.sub.2O, and CrOCN.
34. The display element of claim 29, further comprising a circuit
configured to drive the moveable reflective layer such that light
reflected by the moveable reflective layer and the partially
reflective insulator can be modulated so as to form part of a
viewable image.
35. The display element of claim 34, wherein the display element
includes a display element in a reflective display.
36. The display element of claim 29, wherein the display element is
included with a plurality of other display elements to form an
image by selectively modulating incident light.
37. The display element of claim 29, wherein the moveable
reflective layer includes a metal.
38. A method of forming a display element, the method comprising:
forming a substantially transparent conductive layer; forming a
moveable reflective layer; forming a partially reflective insulator
having a thickness of between about 40 and 150 Angstroms, the
partially reflective insulator being formed between the conductive
layer and the moveable reflective layer, wherein a voltage applied
between the conductive layer and the moveable reflective layer
induces movement of the moveable reflective layer; and forming a
first dielectric layer between the conductive layer and the
partially reflective insulator.
39. The method of claim 38, wherein when the voltage is applied
between the conductive layer and the moveable reflective layer, at
least a portion of the moveable reflective layer moves so that the
at least a portion of the moveable reflective layer physically
contacts the partially reflective insulator.
40. The method of claim 38, further comprising forming a second
dielectric layer between the partially reflective insulator and the
moveable reflective layer.
41. The method of claim 38, wherein the first dielectric layer
includes a material selected from the group consisting of
SiO.sub.2, Al.sub.2O.sub.3, and Silicon Nitride.
42. The method of claim 38, wherein the partially reflective
insulator includes a material selected from the group consisting of
Silicon Nitride, CrO.sub.2, CrO.sub.3, Cr.sub.2O.sub.3, Cr.sub.2O,
and CrOCN.
43. The method of claim 38, wherein the display element includes a
display element in a reflective display.
44. The method of claim 38, wherein the moveable reflective layer
includes a metal.
45. A display element comprising: means for transmitting light and
conducting electricity; means for partially reflecting light, the
partially reflecting means having a thickness of between about 40
and 150 Angstroms, and the partially reflecting means including an
insulator; moveable means for reflecting light, the partially
reflecting means being positioned between the transmitting means
and the movable reflecting means, wherein a voltage applied between
the transmitting means and the movable reflecting means induces
movement of the movable reflecting means; and means for insulating
positioned between the transmitting means and the partially
reflecting means.
46. The display element of claim 45, wherein the transmitting means
includes a substantially transparent conductive layer, the
partially reflecting means includes a partially reflective
insulator layer, the movable reflecting means includes a moveable
reflective layer, and the insulating means includes a first
dielectric layer.
47. The display element of claim 46, wherein when the voltage is
applied between the conductive layer and the moveable reflective
layer, at least a portion of the moveable reflective layer moves so
that the at least a portion of the moveable reflective layer
physically contacts the partially reflective insulator.
48. The display element of claim 46, further comprising a second
dielectric layer positioned between the partially reflective
insulator and the moveable reflective layer.
49. The display element of claim 46, wherein the first dielectric
layer includes a material selected from the group consisting of
SiO.sub.2, Al.sub.2O.sub.3, and Silicon Nitride.
50. The display element of claim 46, wherein the partially
reflective insulator includes a material selected from the group
consisting of Silicon Nitride, CrO.sub.2, CrO.sub.3,
Cr.sub.2O.sub.3, Cr.sub.2O, and CrOCN.
51. The display element of claim 46, further comprising a circuit
configured to drive the moveable reflective layer such that light
reflected by the moveable reflective layer and the partially
reflective insulator can be modulated so as to form part of a
viewable image.
52. The display element of claim 51, wherein the display element
includes a display element in a reflective display.
53. The display element of claim 46, wherein the display element is
included with a plurality of other display elements to form an
image by selectively modulating incident light.
54. The display element of claim 46, wherein the moveable
reflective layer includes a metal.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/155,939, filed Jun. 17, 2005, which claims
priority under 35 U.S.C. .sctn.119(e) to U.S. Provisional
Application Ser. No. 60/613,542, filed on Sep. 27, 2004, both of
which are hereby expressly incorporated by reference herein in
their entirety. In addition, this application claims priority under
35 U.S.C. .sctn.119(e) to U.S. Provisional Application Ser. No.
60/613,488, filed on Sep. 27, 2004.
FIELD OF THE INVENTION
[0002] The field of the invention relates to microelectromechanical
systems (MEMS).
DESCRIPTION OF THE RELATED TECHNOLOGY
[0003] 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 OF CERTAIN EMBODIMENTS
[0004] The systems, methods, and devices of the invention each have
several aspects, no single one of which is solely responsible for
its desirable attributes. Without limiting the scope of this
invention, its more prominent features will now be discussed
briefly. After considering this discussion, and particularly after
reading the section entitled "Detailed Description of Certain
Embodiments" one will understand how the features of this invention
provide advantages over other display devices.
[0005] In some embodiments, a display element comprises: a
substantially transparent conductive layer; a partially reflective
insulator having a thickness of between about 40 and 150 Angstroms;
a moveable reflective layer, the partially reflective insulator
being positioned between the conductive layer and the moveable
reflective layer, wherein a voltage applied between the conductive
layer and the moveable reflective layer induces movement of the
moveable reflective layer; and a first dielectric layer positioned
between the conductive layer and the partially reflective
insulator.
[0006] In some embodiments, a method of forming a display element
comprises: forming a substantially transparent conductive layer;
forming a moveable reflective layer; forming a partially reflective
insulator having a thickness of between about 40 and 150 Angstroms,
the partially reflective insulator being formed between the
conductive layer and the moveable reflective layer, wherein a
voltage applied between the conductive layer and the moveable
reflective layer induces movement of the moveable reflective layer;
and forming a first dielectric layer between the conductive layer
and the partially reflective insulator.
[0007] In some embodiments, a display element comprises: first
means for transmitting light and conducting electricity; second
means for partially reflecting light and insulating, the second
means having a thickness of between about 40 and 150 Angstroms;
third moveable means for reflecting light, the second means being
positioned between the first means and the third means, wherein a
voltage applied between the first means and the third means induces
movement of the third means; and fourth dielectric means positioned
between the first means and the second means.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] 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.
[0009] FIG. 2 is a system block diagram illustrating one embodiment
of an electronic device incorporating a 3.times.3 interferometric
modulator display.
[0010] FIG. 3 is a diagram of movable minor position versus applied
voltage for one exemplary embodiment of an interferometric
modulator of FIG. 1.
[0011] FIG. 4 is an illustration of a set of row and column
voltages that may be used to drive an interferometric modulator
display.
[0012] FIGS. 5A and 5B illustrate one exemplary timing diagram for
row and column signals that may be used to write a frame of display
data to the 3.times.3 interferometric modulator display of FIG.
2.
[0013] FIGS. 6A and 6B are system block diagrams illustrating an
embodiment of a visual display device comprising a plurality of
interferometric modulators.
[0014] FIG. 7A is a cross section of the device of FIG. 1.
[0015] FIG. 7B is a cross section of an alternative embodiment of
an interferometric modulator.
[0016] FIG. 7C is a cross section of another alternative embodiment
of an interferometric modulator.
[0017] FIG. 7D is a cross section of yet another alternative
embodiment of an interferometric modulator.
[0018] FIG. 7E is a cross section of an additional alternative
embodiment of an interferometric modulator.
[0019] FIG. 8 is a cross-section of an exemplary interferometric
modulator having a transparent conductor.
[0020] FIG. 9 is a cross-sectional view of an exemplary reduced
capacitance interferometric modulator.
[0021] FIG. 10 is a cross-sectional view of another exemplary
reduced capacitance interferometric modulator.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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. In
some embodiments, the layers 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.
[0027] 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.
[0028] FIGS. 2 through 5 illustrate one exemplary process and
system for using an array of interferometric modulators in a
display application.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] FIGS. 4 and 5 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. 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] The display device 40 includes a housing 41, a display 30,
an antenna 43, a speaker 44, an input device 48, and a microphone
46. The housing 41 is generally formed from any of a variety of
manufacturing processes as are well known to those of skill in the
art, including injection molding, and vacuum forming. In addition,
the housing 41 may be made from any of a variety of materials,
including but not limited to plastic, metal, glass, rubber, and
ceramic, or a combination thereof. In one embodiment the housing 41
includes removable portions (not shown) that may be interchanged
with other removable portions of different color, or containing
different logos, pictures, or symbols.
[0037] 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.
[0038] 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.
[0039] The network interface 27 includes the antenna 43 and the
transceiver 47 so that the exemplary display device 40 can
communicate with one ore 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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).
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] FIG. 8 is a cross-section of an exemplary interferometric
modulator 100. The interferometric modulator 100 comprises a
substrate 120, a transparent conductor 140, a partial reflector
116, a dielectric 112, a movable mirror 114, and supports 118. In
the embodiment of FIG. 8, the supports 118 support moveable minor
114 and define an air gap 119 between the dielectric layer 112 and
the moveable minor. In an advantageous embodiment, the air gap 119
is sized according to the desired optical characteristics of the
interferometric modulator. For example, the air gap 119 may be
sized in order to reflect a desired color from the interferometric
modulator.
[0052] As described above with respect to FIGS. 7A, 7B, and 7C,
typically a voltage difference is placed across the movable mirror
14 and the partial reflector 16 in order to actuate the
interferometric modulator. Thus, in the embodiment of FIGS. 7A, 7B,
and 7C, for example, the movable mirror 14 and the partial
reflector 16 are at least partially conductive so that they may be
connected to the row and column lines of the display device. In
exemplary embodiments where the partial reflector 16 is also an
electrode of the interferometric modulator (FIGS. 7A, 7B, and 7C,
for example), the partial reflector may comprise chromium,
titanium, and/or molybdenum.
[0053] In the exemplary interferometric modulator 100, the
transparent conductor 140 is shown positioned between the partial
reflector 116 and the substrate 120. In this embodiment, the
transparent conductor 140 is configured as an electrode of the
interferometric modulator and, thus, the interferometric modulator
100 may be actuated by placing an appropriate voltage difference,
e.g., 10 volts, between the moveable minor 114 and the transparent
conductor 140. In an exemplary embodiment, the transparent
conductor 140 comprises Indium Tin Oxide (ITO), Zinc Oxide, Florine
doped Zinc Oxide, Cadmium Tin Oxide, Aluminum doped Zinc Oxide,
Florine doped Tin Oxide, and/or Zinc Oxide doped with Gallium,
Boron or Indium. In this embodiment, the partial reflector 116 is
not required to be conductive and, thus, the partial reflector 116
may comprise any suitable partially reflective material, either
conductive or nonconductive.
[0054] In certain embodiments of interferometric modulator, a
reflectivity of the partial reflector 116 is within the range of
about 30-36%. For example, in one embodiment the reflectivity of
the partial reflector 116 is about 31%. In other embodiments, other
reflectivities are usable in connection with the systems and
methods described herein. In other embodiments, the reflectivity of
the partial reflector 116 may be set to other levels according to
the desired output criteria for the interferometric modulator 100.
In a typical interferometric modulator, as a thickness of the
partial reflector increases, the reflectivity of the partial
reflector also increases, thus reducing the effectiveness of a dark
state and limiting the contrast of the interferometric modulator.
Therefore, in order to achieve a desired reflectivity of the
partial reflector, in many embodiments reduction of a thickness of
a partial reflector is desired.
[0055] In the embodiment of FIG. 8, the partial reflector 116 may
advantageously be thinner due to the fact that the transparent
conductor 140 serves as the electrode. Thus, the partial reflector
does not need to be conductive, because the transparent conductor
serves as the electrode. Accordingly, in embodiments including a
transparent conductor, such as transparent conductor 140, a
thickness of a partial reflector may be reduced in order to achieve
a desired reflectivity. In one embodiment, the partial reflector
116 has a thickness of about 75 Angstoms. In another embodiment,
the partial reflector 116 has a thickness in the range of about
60-100 Angstroms. In yet another embodiment, the partial reflector
116 has a thickness in the range of about 40-150 Angstroms.
[0056] In one embodiment, the partial reflector comprises silicon
nitride, which is a non-conductive, partially reflective material.
In other embodiments, oxides of chromium are used, including, but
not limited to, CrO.sub.2, CrO.sub.3, Cr.sub.2O.sub.3, Cr.sub.2O,
and CrOCN. In some embodiments, low conductivity dielectric
materials are used as the partial reflector. These low conductivity
dielectric materials are generally referred to as "high-k
dielectrics", where "high-k dielectrics" refers to materials having
a dielectric constant greater than or equal to about 3.9. High-k
dielectrics may include, for example, SiO.sub.2, Si.sub.3N.sub.4,
Al.sub.2O.sub.3, Y.sub.2O.sub.3, La.sub.2O.sub.3, Ta.sub.2O.sub.5,
TiO.sub.2, HfO.sub.2, and ZrO.sub.2, for example.
[0057] In other embodiments, the partial reflector 116 comprises a
dielectric stack having alternating layers of dielectrics with
different indices of refraction. As those of skill in the art will
recognize, the output characteristics of the interferometric
modulator 100, e.g., the color of light that is reflected from the
interferometric modulator 100, are affected by the reflectivity of
the partial reflector 116. Accordingly, tuning of the reflectivity
of the partial reflector 116 may be performed in order to achieve
desired output characteristics. In one embodiment, the index of
refraction of the partial reflector 116 can be fine-tuned by using
a partial reflector 116 comprising a combination of dielectric
materials in a stack structure. For example, in one embodiment, the
partial reflector 116 may comprise a layer of SiO.sub.2 and a layer
of CrOCN. In an exemplary embodiment of an interferometric
modulator having a partial reflector comprising a dielectric stack,
the material layers above substrate 120 include a layer of ITO that
is about 500 Angstroms thick, a layer of SiO.sub.2 that is about
1000 Angstroms thick, a layer of CrOCN that is about 110 Angstroms
thick, a layer of SiO.sub.2 that is about 275 Angstroms thick, an
air gap that is about 2000 Angstroms thick, and an Al reflector.
Thus, in this exemplary embodiment, the partial reflector comprises
a layer of SiO.sub.2 that is about 1000 Angstroms thick and a layer
of CrOCN that is about 110 Angstroms thick. Those of skill in the
art will recognize that there are many other suitable conductive or
non-conductive materials that may be used alone, or in combination
with other materials, as part of the partial reflector 116. Use of
these materials in combination with the systems and methods
described herein is expressly contemplated.
[0058] In a typical display, as a capacitance of the individual
display elements, e.g., interferometric modulators, increases, a
power required to change voltages across the display elements also
increases. For example, as a capacitance of any actuated display
elements in an interferometric modulator display increases, the
current required to change voltage levels on the columns of the
display also increases. Accordingly, display elements with reduced
capacitance are desired. The display elements of FIGS. 9 and 10 are
exemplary embodiments of display elements having reduced
capacitance.
[0059] FIG. 9 is a cross-sectional view of a reduced capacitance
interferometric modulator 200. The interferometric modulator 200 of
FIG. 9 comprises the substrate 120, the transparent conductor 140,
a dielectric 130, the partial reflector 116, the dielectric 112,
movable minor 114, supports 118, and air gap 119. In an exemplary
embodiment, the relative thicknesses of these layers are selected
so that a thickness of the air gap 119 is larger than a combined
thickness of the partial reflector 116, the dielectric 112, and the
dielectric 130. In the embodiment of FIG. 9, a lower capacitance is
achieved by de-coupling the partial reflector 116 from the
transparent conductor 140, thus increasing a distance between
electrodes (e.g., moveable minor 114 and transparent conductor 140)
of the interferometric modulator. More particularly, in the
embodiment of FIG. 9, the additional dielectric 130 is positioned
between the transparent conductor 140 and the partial reflector
116. The addition of the dielectric 130 does not change a distance
between the partial reflector 116 and the movable mirror 114, but
does, however, increase the distance between the transparent
conductor 140 and the movable minor 114. In one embodiment, the
dielectric 130 has a thickness of about 1,000 Angstroms. In other
embodiments, the dielectric 130 may have a thickness in the range
of about 800-3,000 Angstroms.
[0060] As described above with respect to FIG. 8, for example,
interferometric modulator embodiments including a transparent
conductor 140 may be actuated by placing a voltage between the
transparent conductor 140 and the movable minor 114. In the
exemplary embodiment of FIG. 9, when the movable mirror 114
collapses against dielectric layer 112, the resulting distance
between the movable minor 114 and the energized transparent
conductor 140 is increased by the thickness of dielectric layer
130. Because capacitance varies inversely to a distance separating
capacitive electrodes, by increasing a distance between the
electrodes of the interferometric modulator 200, a capacitance of
the interferometric modulator 200 is correspondingly decreased.
Thus, the addition of the dielectric 130 does not significantly
affect the optical characteristics of the interferometric modulator
200, but does decrease a capacitance between the electrodes, e.g.,
the movable minor 114 and the transparent conductor 140.
[0061] FIG. 10 is a cross-sectional view of an exemplary reduced
capacitance interferometric modulator 300. The interferometric
modulator 300 of FIG. 10 comprises a substrate 312, a transparent
conductor 310, a dielectric 308, a partial reflector 306, a
dielectric 304, a movable minor 302, supports 318, and an air gap
303. In the embodiment of FIG. 10, the movable minor 302 and the
partial reflector 306 are separated by the dielectric layer 304 and
an air gap 303. In this embodiment, the air gap 303 and dielectric
308 are sized so that in the released state, e.g., the state shown
in FIG. 10, the interferometric modulator 300 absorb substantially
all light incident on the substrate 312 so that a viewer sees the
interferometric modulator 300 as black. When the interferometric
modulator 300 is actuated, e.g., the movable minor 302 is collapsed
so that it contacts the dielectric 304, the interferometric
modulator 300 reflects substantially all wavelengths of incident
light so that the interferometric modulator 300 appears white to a
viewer. In certain embodiments, reflection of substantially all
wavelengths of light provides white light that is referred to as
"broadband white." Due to the fact that the interferometric
modulator 300 operates in a reverse manner when compared to the
interferometric modulators 100 and 200 (e.g. the interferometric
modulator 300 produces color or white in the released state and
black in the actuated state), the interferometric modulator 300 is
referred to as a "reverse interferometric modulator."
[0062] In one embodiment, an optical gap (including the air gap 303
and the dielectric 306) of the reverse interferometric modulator
300 is much smaller than an optical gap of an interferometric
modulator that produces black in an actuated state and color or
white in a released state (e.g., FIG. 100). For example, the
dielectric 304 may have a thickness of less than about 150
Angstroms and the air gap 304 may have a thickness of about 1,400
Angstroms, while the interferometric modulator 100 may have a
dielectric thickness in the range of about 350 to 850 Angstroms and
an air gap in the range of about 2,000-3,000 Angstroms. Thus,
reverse interferometric modulators, such as the interferometric
modulator 300, have smaller optical gaps than regular
interferometric modulators and, accordingly, the electrodes of
reverse interferometric modulators are generally closer together.
In the exemplary embodiment of FIG. 10, the distance between the
moveable mirror 302 and the partial reflector 306 is in the range
of about 150 to 200 Angstroms when the interferometric modulator
300 is in a collapsed position. This distance comprises the
thickness of the dielectric 304 (about 150 Angstroms in the
embodiment of FIG. 10) and a small gap of about 0-50 Angstroms that
is present because the moveable mirror 302 and dielectric 304 may
not be intimately contacting one another in the collapsed position.
In other reverse interferometric modulators, the optical gap and
distance between electrodes may be greater or smaller than the
figures introduced above.
[0063] Due to the decreased distance between electrodes, the
capacitance of reverse interferometric modulators is generally
higher than regular interferometric modulators. Accordingly,
reverse interferometric modulators may consume additional power
when changing voltages across their row and/or column terminals. In
order to reduce the capacitance of the reverse interferometric
modulator 300, the dielectric layer 308 is positioned between the
terminals of the interferometric modulator. For example, the
interferometric modulator 300 includes a dielectric 308 adjacent to
the transparent conductor 310. In the same manner as discussed
above with respect to FIG. 9, for example, addition of the
dielectric 308 does not affect a distance between the partial
reflector 306 and the movable minor 302, but does, however increase
the distance between the transparent conductor 310 and the movable
mirror 302, thus decreasing a capacitance of the interferometric
modulator 300. Accordingly, a capacitance of the reverse
interferometric modulator 300 may be significantly reduced with the
addition of the dielectric layer 308 between the electrodes of the
interferometric modulator.
[0064] The interferometric modulators 100, 200, and 300 each
include a movable minor (mirror 114 in FIGS. 8 and 9, and minor 302
in FIG. 10). These exemplary moveable minors are deformable so that
they collapse against the dielectric 112 (FIGS. 8 and 9), 304 (FIG.
10) when an appropriate voltage is present across the terminals of
the interferometric modulators. Those of skill in the art will
recognize, however, that the improvements described above with
respect to FIGS. 8, 9, and 10, may be implemented in other
embodiments of interferometric modulators having differently
configured movable mirrors. For example, the interferometric
modulators 100, 200, and 300, may be modified to have moveable
minors that are attached to supports at the corners only, such as
by tethers (e.g., FIG. 7B) or may have moveable minors suspended
from deformable layers (e.g., FIG. 7C). Use of the improved systems
and methods described with respect to FIGS. 7, 8, and 9, are
expressly contemplated with these other configurations of movable
minors.
[0065] Various embodiments of the invention have been described
above. Although this invention has been described with reference to
these specific embodiments, the descriptions are intended to be
illustrative of the invention and are not intended to be limiting.
Various modifications and applications may occur to those skilled
in the art without departing from the true spirit and scope of the
invention.
* * * * *