U.S. patent application number 13/372169 was filed with the patent office on 2012-06-07 for method and system for packaging a device.
This patent application is currently assigned to QUALCOMM MEMS TECHNOLOGIES, INC.. Invention is credited to Mark W. Miles, Jeffrey B. Sampsell.
Application Number | 20120140312 13/372169 |
Document ID | / |
Family ID | 35478377 |
Filed Date | 2012-06-07 |
United States Patent
Application |
20120140312 |
Kind Code |
A1 |
Miles; Mark W. ; et
al. |
June 7, 2012 |
METHOD AND SYSTEM FOR PACKAGING A DEVICE
Abstract
A MEMS-based display device is described, wherein an array of
interferometric modulators are configured to reflect light through
a transparent substrate. The transparent substrate is sealed to a
backplate and the backplate can contain electronic circuitry for
controlling the array of interferometric modulators. The backplate
can provide physical support for device components, such as
electronic components which can be used to control the state of the
display. The backplate can also be utilized as a primary structural
support for the device.
Inventors: |
Miles; Mark W.; (Atlanta,
GA) ; Sampsell; Jeffrey B.; (Pueblo West,
CO) |
Assignee: |
QUALCOMM MEMS TECHNOLOGIES,
INC.
San Diego
CA
|
Family ID: |
35478377 |
Appl. No.: |
13/372169 |
Filed: |
February 13, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12423531 |
Apr 14, 2009 |
8115983 |
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13372169 |
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11679134 |
Feb 26, 2007 |
7518775 |
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12423531 |
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|
11045800 |
Jan 28, 2005 |
7184202 |
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11679134 |
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60613275 |
Sep 27, 2004 |
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60613493 |
Sep 27, 2004 |
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60613477 |
Sep 27, 2004 |
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60613489 |
Sep 27, 2004 |
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Current U.S.
Class: |
359/291 ;
29/592.1 |
Current CPC
Class: |
Y10T 29/49002 20150115;
B81C 1/0023 20130101; G02B 26/001 20130101 |
Class at
Publication: |
359/291 ;
29/592.1 |
International
Class: |
G02B 26/00 20060101
G02B026/00; H05K 13/00 20060101 H05K013/00 |
Claims
1. A device, comprising: a substrate having a first surface; an
array of display elements formed on the first surface of the
substrate; a backplate, wherein the array of display elements is
located between the backplate and the substrate; and a seal between
the substrate and the backplate, wherein the seal includes
glass.
2. The device of claim 1, wherein the seal includes a
glass-frit.
3. The device of claim 1, wherein the seal is formed via a spin-on
process.
4. The device of claim 1, wherein the seal is a hermetic seal.
5. The device of claim 1, additionally comprising electronic
circuitry located on the backplane and in electrical communication
with the array of display elements.
6. The device of claim 5, wherein the electronic circuitry is
configured to control the state of the array of display
elements.
7. The device of claim 1, wherein the substrate is
light-transmissive.
8. The device of claim 1, wherein the substrate includes glass.
9. The device of claim 1, wherein the backplate includes glass.
10. The device of claim 1, wherein the display elements include an
array of interferometric modulators configured to reflect light
through the substrate.
11. The device of claim 1, wherein the seal includes a mechanical
extension of the backplate.
12. The device of claim 1, wherein the seal includes a mechanical
extension of the substrate.
13. A device, comprising: a substrate having a first surface; an
array of display elements formed on the first surface of the
substrate; a backplate sealed to the first surface of the substrate
via a seal extending around the array of interferometric
modulators, wherein the seal includes a glass frit.
14. The device of claim 13, additionally comprising electronic
circuitry located on the backplane and in electrical communication
with the array of interferometric modulators.
15. The device of claim 14, wherein the electronic circuitry is
configured to control the state of the array of interferometric
modulators.
16. A method of fabricating a device, comprising: providing a
substrate having an array of display elements formed on a first
surface of the substrate; and sealing a backplate to the first
surface of the substrate via a seal extending around the array of
display elements, wherein the seal includes glass.
17. The method of claim 16, wherein the seal includes a glass
frit.
18. The method of claim 16, wherein the array of display elements
includes an array of interferometric modulators.
19. The method of claim 16, wherein the backplate includes
electronic circuitry located thereon, the method additionally
comprising placing the electronic circuitry in electrical
communication with the array of interferometric modulators.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/423,531, filed on Apr. 14, 2009, and
scheduled to issue on Feb. 14, 2012 as U.S. Pat. No. 8,115,983,
which is a continuation of U.S. patent application Ser. No.
11/679,134, filed on Feb. 26, 2007, now issued as U.S. Pat. No.
7,518,775, which is a divisional of U.S. patent application Ser.
No. 11/045,800, filed on Jan. 28, 2005, now issued as U.S. Pat. No.
7,184,202, which claims priority under 35 U.S.C. .sctn.119(e) to
(1) U.S. Provisional Application No. 60/613,275, filed on Sep. 27,
2004, (2) U.S. Provisional Application No. 60/613,493, filed on
Sep. 27, 2004, (3) U.S. Provisional Application No. 60/613,477,
filed on Sep. 27, 2004, and (4) U.S. Provisional Application No.
60/613,489, filed on Sep. 27, 2004, each of which is hereby
incorporated by reference.
FIELD
[0002] The field of the invention relates to microelectromechanical
systems (MEMS). Embodiments of the invention relate to
micro-electro-mechanical systems (MEMS) and methods for packaging
such systems. More specifically, the invention relates to packaging
an interferometric modulator using a backplate that also holds
electronic circuitry connected to the modulator.
BACKGROUND
[0003] Consumers generally desire that electronic products be as
small and lightweight as possible. As flat panel displays grow in
capability and widespread application, it is not unusual for the
size of a product to be driven by the size of the display, with
great pressure to make the rest of the product fit within a minimal
volume. Two dimensions of that volume are frequently defined by the
2D footprint of the flat panel display. With the increasing
desirability of product "thinness," it becomes increasingly
desirable to make thinner layers, to combine layers, and/or to
eliminate layers from the product. Examples of product layers
include, but are not limited to, clear windows to protect the
display, airgaps between the protective window and the display,
frontlights in front of the display, touch screens, plastic films
with optical functionalities, the display front glass, the active
layers of the display, the display back glass, backlights behind
the display, PC boards, plastic films carrying interconnections,
and plastic and metal layers comprising the physical enclosure of
the product.
[0004] The predominant display used in manufacturing handheld
portable electronic devices is currently the Liquid Crystal Display
(LCD). The principal layers of the LCD include a front glass, a
back glass, and several plastic optical films. Due to the nature of
an LCD, both the front plate and the back plate of the LCD serve as
active or functional components of the LCD, placing limitations on
the degree to which layers can be combined, eliminated, and/or
replaced with a thinner layer in order to decrease the thickness of
the overall display. In addition, the active nature of both plates
of an LCD places limitations on the materials which can be used in
those plates, and therefore the strength and durability of the
plates. If additional strength and/or protection is required beyond
what can be provided using materials suitable for the LCD plates,
other layers of material may be required in addition to the LCD
plates, potentially adding to the thickness, weight, and cost of
the device.
[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. 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. One plate may comprise a stationary layer deposited on a
substrate, the other plate may comprise a metallic membrane
separated from the stationary layer by an air gap. 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] The system, method, 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.
[0007] In one embodiment, for example, a display is provided,
including a transparent substrate, an array of interferometric
modulators configured to reflect light through said transparent
substrate, a backplate sealed to the transparent substrate and
providing a cavity for said interferometric modulators, and
electronic circuitry located on the backplate and in electrical
connection with the array of interferometric modulators.
[0008] In another embodiment, a device having a display is
provided, including a transparent substrate, an array of
interferometric modulators configured to reflect light through the
transparent substrate, and a backplate sealed to the transparent
substrate and providing a cavity for the interferometric
modulators, wherein the backplate comprises electronic circuitry
configured to control the interferometric modulators. In further
embodiments, the backplane serves as a primary structural component
of the display, and provides physical support for additional
electronic circuitry configured to control the display.
[0009] In another embodiment, a method of manufacturing a display
device is provided, including providing a transparent substrate
comprising an array of interferometric modulators, providing a
backplate comprising electronic circuitry configured to control the
array of interferometric modulators, sealing the transparent
substrate to the backplate so that a cavity is formed above the
array of interferometric modulators, and wherein the electronic
circuitry is placed in electrical communication with the array of
interferometric modulators. In another embodiment, a device is
provided, the device being produced by the above method.
[0010] In another embodiment, a display is provided, including
means for modulating light and reflecting it towards a viewer, a
first means for supporting the modulating means, means for
controlling the state of the modulation means, a second means for
supporting the controlling means and providing a cavity for the
modulating means.
[0011] In another embodiment, a display for an electronic device is
provided, including a first transparent substrate, a first array of
interferometric modulators configured to reflect light through the
first transparent substrate and in a first direction, a backplate
sealed to the first transparent substrate and providing a cavity
for the first array of interferometric modulators, wherein the
backplate comprises electronic circuitry configured to control the
first array of interferometric modulators, and a second transparent
substrate sealed to the backplate, wherein the second transparent
substrate comprises a second array of interferometric modulators
configured to reflect light in a second direction, and wherein the
first direction and the second direction are opposite
directions.
[0012] In another embodiment, a display for an electronic device is
provided, including a first transparent substrate, a first array of
interferometric modulators configured to reflect light through the
first transparent substrate and in a first direction, a backplate
sealed to the first transparent substrate and providing a cavity
for the first array of interferometric modulators, wherein the
backplate comprises electronic circuitry configured to control the
first array of interferometric modulators, and a second transparent
substrate sealed to the first backplane, wherein the second
transparent substrate comprises a second array of interferometric
modulators configured to reflect light in a second direction, and
wherein the first direction and the second direction are opposite
directions.
[0013] In another embodiment, a device having a display is
provided, including a first transparent substrate, a first array of
interferometric modulators configured to reflect light through said
first transparent substrate, a second transparent substrate opposed
to the first transparent substrate, and a second array of
interferometric modulators configured to reflect light through the
second transparent substrate.
[0014] In another embodiment, a method of manufacturing a display
is provided, including providing a first transparent substrate
comprising a first array of interferometric modulators, providing a
second transparent substrate comprising a first array of
interferometric modulators, providing a backplate comprising
electronic circuitry configured to control the state of the first
and second arrays of interferometric modulators, sealing the first
transparent substrate to the backplate, sealing the second
transparent substrate to the backplate, and placing the electronic
circuitry in electrical connection with the first and second arrays
of interferometric modulators. In another embodiment, a display is
provided, the device being manufactured by the above method.
[0015] In another embodiment, a display is provided, the display
including a first means for modulating light and reflecting it
towards a viewer; a first means for supporting the first modulating
means; a second means for modulating light and reflecting it
towards a viewer; a second means for supporting the second
modulating means, means for controlling the state of said first and
second modulation means, and a third means for supporting said
controlling means.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] 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 released position and a movable reflective layer of a second
interferometric modulator is in an actuated position.
[0017] FIG. 2 is a system block diagram illustrating one embodiment
of an electronic device incorporating a 3.times.3 interferometric
modulator display.
[0018] FIG. 3 is a diagram of movable mirror position versus
applied voltage for one exemplary embodiment of an interferometric
modulator of FIG. 1.
[0019] FIG. 4 is an illustration of a set of row and column
voltages that may be used to drive an interferometric modulator
display.
[0020] 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.
3.
[0021] FIG. 6A is a cross section of the device of FIG. 1.
[0022] FIG. 6B is a cross section of an alternative embodiment of
an interferometric modulator.
[0023] FIG. 6C is a cross section of another alternative embodiment
of an interferometric modulator.
[0024] FIG. 7 is an exploded view of an embodiment of a display in
which a printed circuit carrier is bonded to a backplate.
[0025] FIG. 8A is an assembled view of an embodiment of a display
in which an interferometric modulator carrier serves as the
backplate and is connected to an array of interferometric
modulators on a substrate.
[0026] FIG. 8B is an assembled view of the embodiment of FIG.
8A.
[0027] FIG. 9A is a top view of the lower component of an
embodiment of a display in which an interferometric modulator
carrier serves as the backplate and is connected to an array of
interferometric modulators on a substrate.
[0028] FIG. 9B is a top view of the upper component of an
embodiment of a display in which an interferometric modulator
carrier serves as the backplate and is connected to an array of
interferometric modulators on a substrate.
[0029] FIG. 10A is an assembled view of an embodiment of a display
in which an interferometric modulator carrier serves as the
backplate and is internally connected to an array of
interferometric modulators on a substrate.
[0030] FIG. 10B is an exploded view of the embodiment of FIG.
10A.
[0031] FIG. 11 is an exploded view of an embodiment of a display in
which an interferometric modulator carrier serves as a backplate,
and electronic components are located on the same surface of the
substrate as the array of interferometric modulators.
[0032] FIG. 12 is a cross-sectional view of one embodiment of a
dual-screen display in which an interferometric modulator carrier
is disposed between two substrates.
[0033] FIG. 13 is a cross-sectional view of a dual-screen display
in which a substrate can perform some of the same functions as an
interferometric modulator carrier.
[0034] FIG. 14 is a cross-sectional view of a dual-screen display
having an annular interferometric modulator carrier.
[0035] FIG. 15 is a cross-sectional view of a dual-screen display
without an interferometric modulator carrier.
[0036] FIG. 16 is a cross-sectional view of a device in which the
interferometric modulator carrier of a display can serve as the
primary structural support for the device.
[0037] FIG. 17A is a perspective view of an embodiment of a display
in which a contoured interferometric modulator carrier serves as a
backplate.
[0038] FIG. 17B is a cross-sectional view of the embodiment of FIG.
17A.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0039] One embodiment of the invention is an interferometric
modulator-based display, as discussed in greater detail below,
wherein the backplate includes active components. Typically in an
interferometric modulator, the backplate serves a purely mechanical
function. Thus, fewer constraints are placed on the materials which
can be used in the backplate, and there is greater freedom for
layers to be combined, eliminated, and/or replaced with alternate
or thinner layers. In particular, in this embodiment the backplate
may be employed to hold electronic circuitry which controls the
state of the interferometric modulator. For example, integrated
circuits, such as display driver chips, may be mounted directly
onto the backplate and then electrically connected to the
interferometric modulator. The backplate can also be used to
provide structural support for a device enclosing the display. The
use of a backplate for multiple purposes advantageously permits the
construction of an interferometric modulator-based display which
may be thinner, stronger, easier to fabricate and/or less expensive
than displays based on other technologies.
[0040] Another embodiment of the invention is an interferometric
modulator-based display that has two opposed screens. The backplate
of one display is used to form an interferometric modulator that
faces in the opposite direction. This can be used, for example, in
a cellular telephone that includes displays on opposite sides of
the telephone. The use of the backplate to perform these functions
advantageously permits the creation of dual-screen displays which
are thinner, more rugged, and/or have a smaller footprint than
other dual-screen displays.
[0041] 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 invention 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 invention 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.
[0042] 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.
[0043] 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 released state, the
movable layer is positioned at a relatively large distance from a
fixed partially reflective layer. In the second position, the
movable 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.
[0044] 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 and highly
reflective layer 14a is illustrated in a released position at a
predetermined distance from a fixed partially reflective layer 16a.
In the interferometric modulator 12b on the right, the movable
highly reflective layer 14b is illustrated in an actuated position
adjacent to the fixed partially reflective layer 16b.
[0045] The fixed layers 16a, 16b are electrically conductive,
partially transparent and partially reflective, and may be
fabricated, for example, by depositing one or more layers each of
chromium and indium-tin-oxide onto a transparent substrate 20. The
layers are patterned into parallel strips, and may form row
electrodes in a display device as described further below. The
movable layers 14a, 14b may be formed as a series of parallel
strips of a deposited metal layer or layers (orthogonal to the row
electrodes 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 deformable metal
layers are separated from the fixed metal layers by a defined air
gap 19. A highly conductive and reflective material such as
aluminum may be used for the deformable layers, and these strips
may form column electrodes in a display device.
[0046] With no applied voltage, the cavity 19 remains between the
layers 14a, 16a and the deformable layer is 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 layer is deformed and is forced against
the fixed layer (a dielectric material which is not illustrated in
this Figure may be deposited on the fixed layer to prevent shorting
and control the separation distance) as illustrated by the 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.
[0047] FIGS. 2 through 5 illustrate one exemplary process and
system for using an array of interferometric modulators in a
display application. FIG. 2 is a system block diagram illustrating
one embodiment of an electronic device that may incorporate aspects
of the invention. In the exemplary embodiment, the electronic
device includes a processor 21 which may be any general purpose
single- or multi-chip microprocessor such as an ARM, Pentium.RTM.,
Pentium II.RTM., Pentium III.RTM., Pentium IV.RTM., Pentium.RTM.
Pro, an 8051, a MIPS.RTM., a Power PC.RTM., an ALPHA.RTM., or any
special purpose microprocessor such as a digital signal processor,
microcontroller, or a programmable gate array. As is conventional
in the art, the processor 21 may be configured to execute one or
more software modules. In addition to executing an operating
system, the processor may be configured to execute one or more
software applications, including a web browser, a telephone
application, an email program, or any other software
application.
[0048] In one embodiment, the processor 21 is also configured to
communicate with an array controller 22. In one embodiment, the
array controller 22 includes a row driver circuit 24 and a column
driver circuit 26 that provide signals to a pixel array 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 released 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
release 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 released 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 released 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 released pre-existing state. Since each pixel of the
interferometric modulator, whether in the actuated or released
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.
[0049] 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.
[0050] 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 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. 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.
[0051] 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 released states.
[0052] 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 releases 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 release 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 present invention.
[0053] The details of the structure of interferometric modulators
that operate in accordance with the principles set forth above may
vary widely. For example, FIGS. 6A-6C illustrate three different
embodiments of the moving mirror structure. FIG. 6A is a cross
section of the embodiment of FIG. 1, where a strip of metal
material 14 is deposited on orthogonally extending supports 18. In
FIG. 6B, the moveable reflective material 14 is attached to
supports at the corners only, on tethers 32. In FIG. 6C, the
moveable reflective material 14 is suspended from a deformable
layer 34. This embodiment has benefits because the structural
design and materials used for the reflective material 14 can be
optimized with respect to the optical properties, and the
structural design and materials used for the deformable layer 34
can be optimized with respect to desired mechanical properties. The
production of various types of interferometric devices is described
in a variety of published documents, including, for example, U.S.
Published Application 2004/0051929. A wide variety of well known
techniques may be used to produce the above described structures
involving a series of material deposition, patterning, and etching
steps.
[0054] The lifetime of an interferometric modulator of the type
discussed above can be greatly extended by protecting the
interferometric modulator from mechanical interference, excessive
moisture, and other potentially damaging substances. Embodiments of
interferometric modulator-based displays utilize a backplate (also
referred to as a backplane) to provide this protection. For
example, the edge of a backplate can be attached with adhesive near
the edge of the transparent substrate to prevent mechanical
interference from reaching and potentially damaging the
interferometric modulator elements fabricated on the backside of
the display glass. Additionally, the backplate together with its
adhesive attachment to the transparent substrate prevents moisture
and other potentially detrimental gases, liquids and solids from
reaching the interferometric modulator elements. Accordingly, the
backplate can be transparent or opaque, conductive or insulating,
essentially two-dimensional or projecting appreciably into a third
dimension. In one embodiment, the backplate can be made of material
completely unsuitable for use as a transparent display substrate,
such as an opaque metal.
[0055] It can be seen in embodiments of interferometric-based
displays, the backplate need not serve any role as an active or
functional component of the display. Thus, a minimal set of
requirements and specifications related to the functionality of the
display are placed on the backplate. Consequently, there is
significant freedom available in the backplate design to address
other system needs and functions. Configurations in which the
backplate is employed for multiple, non-packaging-related purposes
are well suited for use in display-centric products which
incorporate MEMS-based displays and associated ancillary
components.
[0056] The backplate itself can be part of the display's lighting
system. Any number of RF-related functions including but not
limited to shielding, passive components, and antennas can be
integrated into the backplate. As described herein, the backplate
can be a PC board, an electronics layer, an electrical connection
component, a battery, or merely a mechanical component to support
or hold other components that serve various purposes in a device.
The backplate can be used to implement any suitable function of the
electronic product. The capabilities described above are possible
since the nature of the interferometric modulator display imposes
only a limited set of requirements on the backplate.
[0057] The backplate can be employed to hold electronics, and the
footprint of the back plate can be expanded well beyond the active
display area formed by the interferometric modulator so that the
backplate essentially becomes a "backbone" for and the principal
structural element of the device which contains the display. In
some embodiments this is desirable because the display can be made
much stronger than conventional displays that require glass
materials for a backplate.
[0058] Accordingly, it is desirable to employ the backplate to
perform various device functions or to impart desirable attributes
to the devices. For example, the backplate can reduce the amount of
volume consumed by components and parts in a portable electronic
device by providing a means for integrating such components
directly onto the backplate. By using backplate materials of
increased durability the display will have increased resistance to
damage by mechanical shock or other means. Also, the component
integration can improve portability, reduce weight, improve
handling, and increase ruggedness of the device. Cost savings in
the manufacturing process can be achieved by increasing the degree
of integration within the device (e.g., by having components or
sub-assemblies perform a greater number of functions), thereby
reducing the overall number of parts in the device.
[0059] The configurations of the embodiments herein can be suitable
for use in display-centric products, such as cell phones, laptop
computers, digital cameras, and GPS units. Such devices are
display-centric in the sense that each relies on a flat panel
display as a primary means of providing information. The display
can also participate in input functions. Accordingly, the display
can have an impact on the mechanical, electrical, system, and
aesthetic design aspects of the product that often exceeds the
contributions from the other components in the product. The display
is often constructed from a material, such as glass, which tends to
be more fragile than the rest of the materials comprising the
product. As a result, the mechanical and product design process
tends to be centered on the capabilities and characteristics of the
display, instead of, e.g., the processor or the battery. Many
components within handheld products share similar footprints. These
include PC boards, light sources, keyboards, batteries, integrated
circuits, supplementary or alternative flat panel displays, and
others. Because they are generally planar, the design tools from
which they derive produce a similar output, usually in the form of
one or more photolithographic masks or other phototools. Thus,
there are opportunities for increased integration and increased
efficiency in the design process which can be significantly enabled
by incorporating functions into the backplate.
[0060] In one embodiment, the packaging of a MEMS component, such
as an interferometric modulator-based display, enables mechanical
support for a wide range of components, including but not limited
to drivers, processors, memory, interconnect arrays, vapor
barriers, the product housing, and the like. The backplate of the
interferometric modulator matrix, in its simplest form, serves to
provide a barrier to particles and gasses that can interfere with
the functioning of the array. By further imbuing the
interferometric modulator backplate, or carrier, with a
functionality of one or more of the remaining product components, a
higher degree of integration and design efficiency can be
achieved.
[0061] Embodiments of the invention provide a means for reducing
the form-factor and number of components required in a MEMS-centric
product without affecting the number of functions performed. In one
embodiment, where the MEMS is an interferometric modulator display,
this is achieved as a result of the nature of the interferometric
modulator array, which is monolithically fabricated on a single
substrate.
[0062] FIG. 7 depicts an embodiment of an interferometric modulator
display device 600, shown in an exploded view. The device 600
includes a transparent substrate 602, which includes an array 604
of interferometric modulators configured to reflect light that has
entered through substrate 602 back through substrate 602 and onward
to a viewer. An array of interferometric elements such as array 604
provides a means for modulating light and reflecting it towards a
viewer. The transparent substrate 602 may comprise a layer of
glass. In an alternate embodiment, the transparent substrate 602
may advantageously comprise a layer of transparent polymeric
material, or any other suitable sufficiently transparent material.
The transparent substrate 602 thus provides a means for supporting
array 604. In certain embodiments, the transparent substrate 602
can be from about 0.7 to 0.5 mm, depending on the nature of the
manufacturing process and product. The device 600 also includes
driver chip 612, located on the same side of substrate 602 as array
604, and placed in electrical connection with array 604 through
trace leads 616a, to which driver chip 612 is directly bonded. This
approach to chip placement is known as chip on glass (COG). The
driver chip 612 can be placed in electrical connection with
external circuitry (not shown) through trace leads 616b which
connect with a mounting point 624 (e.g. for a flex cable).
[0063] Located on substrate 602, and surrounding the array 604, is
a seal 606, depicted here as an annular seal, under which the trace
leads 616a and 616c run. The seal 606 may be referred to as a seal
ring, as in various embodiments, the seal 606 completely encircles
the array 604. The seal 606 may be a semi-hermetic seal, such as a
conventional epoxy-based adhesive. In other embodiments, the seal
606 may be a PIB, o-ring(s), polyurethane, liquid spin-on glass,
solder, polymers, or plastics, among other types of seals. In still
other embodiments, the seal 606 may be a hermetic seal, such as a
thin film metal weld or a glass frit. In alternate embodiments, the
seal ring may comprise an extension of either one or both of the
backplate or transparent substrate. For example, the seal ring may
comprise a mechanical extension (not shown) of a backplate 608. In
still other embodiments, the seal ring may comprise a separate
member, such as an annular member.
[0064] Still with respect to FIG. 7, the backplate 608, together
with at least the seal 606 and transparent substrate 602, forms a
protective cavity enclosing the array 604 of interferometric
modulators. Although not shown, a desiccant may be provided within
the protective cavity, in order to prevent moisture buildup over
the lifetime of the device. The backplate 608 may be made of any
suitable material, whether transparent or opaque, conductive or
insulating. Suitable materials for the backplate 608 include, but
are not limited to, glass (e.g. float, 1737, soda lime), plastic,
ceramics, polymers, laminates, and metals and metal foils (e.g.
stainless steel (SS302, SS410), Kovar, plated Kovar). In contrast
to an LCD, which would require electrode arrays on both substrates,
the array 604 resides on only one substrate, enabling backplate 608
to be made of a material which is thinner and/or completely
different from the material used in transparent substrate 602. In
one embodiment, the backplate 608 is adapted to prevent moisture
from entering the protective cavity and damaging the array 604.
Thus, a component such as backplate 608 provides a means for
protecting the array 604 from moisture and other environmental
contaminants.
[0065] The use of materials other than glass in construction of the
backplate can provide several advantages. Backplates formed from
alternate materials which are thinner and lighter than backplates
formed of glass, such as stamped metal backplates, permit the
creation of thinner, lighter displays. Reducing the weight of the
backplate has particular advantages with respect to portable
display-centric devices, as those devices are frequently dropped.
If the backplate is lighter, less force will be transferred to the
frontplate upon impact with the ground. In addition, stamped metal
backplates may be less expensive to produce in large quantities
than glass backplates.
[0066] The display also includes a printed circuit (PC) carrier
610, located on the opposite side of backplate 608 as the
transparent substrate 602. The PC carrier 610 may be a PC
carrier/component stack-up for a display product such as a personal
digital assistant (PDA) or a cellular phone. The PC carrier 610 may
be fabricated separately from the backplate 608, and then bonded to
the backplate.
[0067] An alternate placement is shown for driver chip 614, which
is located on the upper side of PC carrier 610, and is in
electrical connection with array 604 by means of trace leads 616c
and 616d and flex cable 618. The flex cable 618 is mounted to PC
carrier 610 and transparent substrate 602 in order to provide
electrical communication between the devices on the PC carrier 610
and the transparent substrate 602. Driver chip 614 can be placed in
electrical connection with external circuitry through trace leads
616e and external interconnect pins 622. An alternate approach to
COG is known as chip on flex (COF), or tape automated bonding
(TAB). Although not depicted in FIG. 7, a driver chip could be
bonded directly to a flex connector such as flex connector 618, and
placed in electrical connection with the array 604 by trace leads
running to the point on the substrate on which the flex connector
is mounted. PC carrier 610 also provides physical support for
additional electronic components 620 (e.g. ICs and passives)which
can be connected to external circuitry via external interconnect
pins 622 and trace leads 616f, or in connection with driver chip
614 via trace leads 616g. Certain of these electronic components,
such as driver chips 612 and 614, provide a means for controlling
the state modulators within the array 604.
[0068] PC carrier 610 can be a single or multilayer conductor
polymer laminate which can be fabricated using any suitable
technique. It can comprise one or more polymeric layers which
provide structural support and/or insulation for one or more layers
of interconnections comprising patterned or non-patterned
conductors. The conductors provide electrical connections between
the different components mounted on the surface. Because PC carrier
610 can be a multilayer conductor polymer laminate, the
interconnections are not limited to trace leads on a surface of the
carrier as depicted in the FIG. 7, but may also include alternate
interconnections such as leads located within the carrier 610.
[0069] Although the backplate 608 can provide a vapor transmission
barrier sufficient to protect array 604 in the embodiment of FIG.
7, in alternative embodiments discussed below with respect to other
figures the functions of the backplate 608 are performed by the
carrier. In such embodiments, the carrier may advantageously
comprise materials which minimize or prevent vapor transmission.
The skilled artisan will appreciate that PC carriers formed of FR4
will transmit water vapor at a relatively high rate. In some
alternative embodiments, the PC carrier 610 may be formed of or
include gold plated thin film metals to enhance the water vapor
transmission barrier of the carrier. Other suitable materials for
the carrier 610 include, but are not limited to, ceramics, aluminum
nitride, beryllium oxide, and alumina. The PC carrier 610 may be
formed of a board or a flexible sheet.
[0070] The PC carrier 610 serves to support the components which
are associated with the display operation. The PC carrier 610 can
be connected to additional PC carriers which carry components
relevant to the overall operation of the product, or provide
physical and electrical support to these components as well.
Therefore, a component such as PC carrier 610 provides a means for
supporting these electronic components. The PC carrier 610 may
include electronic interfaces for use with radio-frequency (RF)
signals. The skilled artisan will understand that the PC carrier
610 may serve not only as protection for circuitry that is
integrated into the backplane but may also enhance RF circuit
needs. For example, metal caps may be included for RF enhancement
or protection. Antenna properties may also be incorporated into the
PC carrier 610 or the interferometric modulator array 604,
including, but not limited to, the use of a metal backplane or a
metal cap as an antenna for a cell phone.
[0071] Although for simplicity only six trace leads 616a,c are
shown connecting the driver chips 612 and 614 with array 604, it
will be understood that many more trace leads may be necessary for
the driver chips to control the state of the array 604, depending
on the size of the array. Similarly, although only three trace
leads 616b,e are depicted as connecting the driver chips with
external circuitry, certain embodiments may require different
numbers of input trace leads. Similarly, although for simplicity no
trace leads are depicted in this figure as running to the top or
bottom (with respect to the figure) of array 604, it will be
understood that embodiments of the present invention can utilize
the configurations discussed with respect to this and following
figures to provide an electrical connection with any portion of the
array 604 (e.g. to provide both row and column signals from driver
circuitry).
[0072] The trace leads 616a,c (alternately and interchangeably
referred to as conductive busses or electrical traces) may comprise
electrical traces formed from conductive material. These traces
616a,c may be between about 25 micrometers (.mu.m) and 1 millimeter
(mm) wide, e.g., about 50 micrometers across, and may be between
about 0.1 micrometers (.mu.m) to 1 micrometers (.mu.m) thick.
Larger or smaller sizes, however, are possible. The trace leads
616a,c may comprise metal in some embodiments. Photolithographic,
electroplating, as well as electroless techniques may be employed
to form the trace leads. In certain embodiments, a metal based
slurry or silver paste may be employed. Other methods and materials
may also be used to form the trace leads.
[0073] In an alternate embodiment, the backplate 608 (FIG. 7) is
eliminated and the PC carrier itself makes up the backplate. FIGS.
8A and 8B depict such a display device 650. As can be seen in FIG.
8A, which depicts device 650 in an assembled state, carrier 652
provides physical support for driver chips 652a and 652b, which are
in electrical connection with electronic components 656a and 656b
and external interconnect pins 658 via trace leads 660a, which may
be located on or within carrier 652. Driver chips 654a,b are also
in electrical connection with electrical feedthroughs 662 via trace
leads 660b.
[0074] As can be seen in FIG. 8B, which depicts device 650 in an
exploded view, electrical feedthroughs 662 extend from the upper
surface of carrier 652 to the lower surface. When assembled,
anisotropic conducting film ledge 664 provides an electrical
connection between feedthroughs 662 and trace leads 660c located on
the upper surface of transparent substrate 666. Trace leads 660c
are in electrical contact with array 668 of interferometric
modulators located on the upper surface of transparent substrate
666, enabling an electrical connection between driver chips 654a,b
and array 668. When device 650 is assembled, seal ring 670 forms,
along with transparent substrate 666 and carrier 652, a protective
cavity around array 668. Thus, a carrier such as carrier 652
provides a means for supporting electronic circuitry, such as
driver circuitry, and for protecting the array 668.
[0075] ACF materials are conveniently employed for providing
electrical interconnects between components, and they are often
used to connect the flex connector of TAB drivers to display
substrates. However, other connection methods can be employed,
including but not limited to zebra connectors, flex cables, bump
bonds, and micromechanical pressure conductors (e.g. MEMS springs),
which are described in greater detail with respect to FIG. 10B.
[0076] In certain embodiments in which the interferometric
modulator carrier 652 is formed from materials through which vapor
can permeate into the protective cavity, the interior side of
interferometric modulator carrier 652 may be advantageously coated
with a vapor barrier 672. In addition to, or in place of, vapor
barrier 672, desiccant 674 may be provided within the protective
cavity. In FIG. 8B, a layer of desiccant 674 is shown below the
vapor barrier 672. In embodiments in which the interferometric
modulator carrier 652 is made of a substrate that is sufficiently
vapor resistant, no vapor barrier 672 is required.
[0077] FIGS. 9A and 9B depict a top view of two components, 700 and
702 that come together to make a display device similar to the
device 650 shown in FIG. 8. FIG. 9A depicts the lower portion 700
of the two components which come together to make the display
device. A transparent lower substrate 704 includes an
interferometric modulator array 706 which is configured to reflect
light through the substrate 704. Surrounding the outer edges of the
substrate 704 and circumscribing a seal ring 708 is an ACF ledge
710 which provides electrical connections to the array 706 via
trace leads 712a located on substrate 704.
[0078] FIG. 9B depicts a top view of the upper portion 702 which is
configured to mate with the lower portion 700 and come together to
make the display device. A corresponding interconnect ledge 714,
located along the edge of this interferometric modulator carrier
716, circumscribes a set of electronic components 718a-d (e.g.
driver chips, ICs, passives, etc.), at least some of which (718a,b
in this embodiment) are electrically connected to interconnect
ledge 714 via trace leads 712b. Some of electronic components
718a-d are connected to each other via trace leads 712c, and
connections between some electronic components 718 and external
circuitry can be made via trace leads 712 and external interconnect
pins 720. When the two modules are brought together, the connection
between interconnect ledge 714 and ACF ledge 710 places electronic
components 718a,b in electrical connection with the array 706
located on substrate 704.
[0079] FIGS. 10A and 10B depict a reduced footprint display device
750. As will be apparent from the following discussion, the reduced
footprint of device 750 is due to the elimination of ledges, such
as those seen in FIGS. 7 and 8, on which components such as driver
chips and connections were located, exterior to the protective
cavity formed by the seal rings. FIG. 10A shows the device 750 in
an assembled state, and FIG. 10B shows the device 750 in an
exploded view. Referring to FIG. 10A the device 750 includes a
transparent substrate 754 which is sealed to an interferometric
modulator carrier 770 through a seal ring 764. In this embodiment,
the carrier 770 acts as a backplate for the device 750.
[0080] The carrier 770 includes a first display circuit 756 which
connects through a trace lead 762a to an electrical feedthrough
766. The electrical feedthrough 766 is used as a connection to the
interior components of the device 750 as will be explained in more
detail with reference to FIG. 10B. The display circuit 756 is also
in electrical connection with a set of external interconnect pins
760 for connecting the display device 750 to external devices. In
addition, a set of interconnect leads 762b connect the display
circuit 756 to a flex cable 772 which provide an electrical
connection to the interior components of the device 750.
[0081] Referring now to FIG. 10B, the interior components of the
reduced footprint display device 750 can be seen. As shown, the
transparent substrate 754 includes an interferometric modulator
array 752 that is configured to reflect light through the substrate
754. Interior to the interferometric modulator array 752 are a set
of conducting posts 768 which are adapted to provide an electrical
connection to a matching set of conducting pads 767a on the lower
surface of the carrier 770. As will be imagined, the conducting
pads 767a are in communication with the electrical feedthroughs 766
so as to provide an electrical link to the display circuit 756
(FIG. 10A).
[0082] Of course it should be realized that the display circuit 756
can be connected to the conducting pads 767 through the flex cable
772. As shown, the flex cable 772 mounts to the lower surface of
the carrier 770 and is in electrical connection with the conducting
pads 767b, which then connect to the interferometric modulator 752
through the conducting posts 768. This configuration does not
require feedthroughs to be present in the carrier 770 and thus can
reduce the chance that water vapor may traverse the carrier 770 and
come in contact with the interferometric modulator 752.
[0083] Also shown is a desiccant 774 on the lower surface of the
carrier 770 which acts to absorb any moisture that may enter the
protective cavity of the device.
[0084] Because contacts between the conducting posts 768 and the
conducting pads 767a,b are internal to the device 750, the material
characteristics of the bonds can present issues. ACF materials,
which outgas during curing, can produce substances that interfere
with the operation of the array. Alternatives to ACF materials
include low temperature solders, micromechanical pressure
connectors, bump bonds, and other affixing materials which are
neutral from a chemical and outgassing standpoint. In some
embodiments, such as those employing vacuum packaging, the
electrical feedthroughs can act as both interconnects and
mechanical standoffs, or just mechanical standoffs. As mechanical
standoffs, they maintain a distance between the interferometric
modulator array and the interferometric modulator backplate to
protect against the force of external mechanical or atmospheric
pressures.
[0085] Of course, while only a relatively few conducting posts are
illustrated in this embodiment, it should be realized that tens,
hundreds, or thousands of such posts can be fabricated within the
array 752. Similarly, tens, hundreds or thousands of matching
conducting pads can be formed on the lower surface of the carrier
770. This allows complex electronic circuits, such as driver
circuits to be connected to the array 752.
[0086] While FIG. 10 depicts an embodiment using conducting support
posts, a variety of structures can be utilized to place the array
752 in electrical connection with the interferometric modulator
carrier 770. For instance, micromechanical pressure connectors can
be used. Micromechanical pressure connectors come in a variety of
forms, and include conductive metallic structures that extend above
the plane of the substrate because of inherent mechanical stresses.
They can be fingers or coils which when deposited and patterned
reside partially on a sacrificial layer and partially on the
substrate or on one or more films or structures without an
intervening sacrificial layer between it and the structure. In this
embodiment, during the final MEMS fabrication step (the release
step where the sacrificial layer is removed), the stresses in the
connector cause it to displace vertically away from the substrate.
If aligned properly with conducting features on an opposing
substrate or interferometric modulator carrier, they can provide an
electrical interconnect which does not outgas.
[0087] It should also be understood that some or all of the driver
chips could be placed on the lower surface of the carrier 770 and
thereby inside of the sealed cavity formed by the carrier 770, the
transparent substrate 754 and the seal ring 764. In this alternate
embodiment, as illustrated in FIG. 10B, a circuit chip 758 is
mounted on the lower surface of the carrier 770. The chip 758 is in
electrical communication with the flex cable 772 via traces 762c
and the conducting pads 767b via traces 762d. This allows the chip
758 to communicate with the interferometric modulator array 752 and
to the display circuit 756 which is on the upper surface of the
carrier 770.
[0088] FIG. 11 depicts an embodiment of a display module 800 in
which driver chips 802a and 802b are located on a transparent
substrate 804, and are electrically connected via trace leads 810a
to an interferometric modulator array 806, so that the driver chips
802a,b can control the state of the array 806. The driver chips
802a,b are located within a protective cavity formed when the
substrate 804 is bonded to interferometric modulator carrier 814 by
seal ring 816. The driver chips 802a,b are electrically connected
to external interconnect pins 808 via trace leads 810b and 810c, as
well as flex cable 812. A configuration in which the driver chips
802a,b are located on the same surface as the array 806 may
advantageously reduce the number of connections to be made with the
interferometric modulator carrier 814, as a driver chip suitable
for use in this display may have significantly more outputs than
inputs.
[0089] Although not depicted, a vapor barrier and/or desiccant can
be used on the interior of the protective cavity formed by at least
seal ring 816, carrier 814, and substrate 804. Additional
components (not shown), including but not limited to those
components previously discussed with respect to other embodiments,
can be incorporated into display module 800, either on the
transparent substrate 804 or on interferometric modulator carrier
814. These components can be internal or external to the protective
cavity formed by substrate 804, carrier 814, and seal ring 816, and
connections with and between these components can be made using any
of the methods discussed above with respect to previous
embodiments.
Dual Sided Displays
[0090] A class of electronic products employs two displays
integrated opposite each other so that there are two viewable
surfaces on opposing sides. This class includes "clamshell" phones,
which can have a main display which acts as the primary information
interface and is revealed only when the product is opened, and a
sub-display, which resides on the exterior of the product and
provides status information at all times. These phones make
aggressive demands on product integration and display module
thinness.
[0091] FIG. 12 illustrates dual-sided interferometric modulator
based sub-display/main-display module 850. As shown,
interferometric modulator array 852 resides on transparent
substrate 854 and is bonded via seal ring 856 to interferometric
modulator carrier 858. The carrier, 858, is subsequently bonded via
seal ring 860 to transparent substrate 862, upon which
interferometric modulator array 864 resides. In this particular
configuration, the thickness of the overall module 850 is reduced
because the two displays share the same carrier 858, which can
perform one or more of the functions previously described.
Therefore, in certain embodiments, the carrier 858 provides a means
for supporting electronic circuitry configured to control the state
of array 864.
[0092] Although the carrier 858 and each of the substrates 854 or
862 are depicted in FIG. 12 as being the same size, the carrier
and/or either of the substrates can extend beyond either of seal
rings 856 and 860, and additional components may be located on
either of these surfaces external to the seal rings. Thus, the
surface area of any one of the carrier 858 or substrates 854 or 862
may be greater than the surface areas of the others. Connections
between the interferometric modulators 852 and 864 and the carrier
858, as well as connections through the carrier, can be made via
any method or combination of methods discussed previously,
including but not limited to flex cables, electrical feedthroughs,
trace leads, conductive support posts, or micromechanical pressure
connectors.
[0093] Another embodiment of a dual sided display 900 is shown in
FIG. 13. In this embodiment the interferometric modulator carrier
has been eliminated. An upper transparent substrate 902, bearing an
upper interferometric modulator array 906 is bonded via a seal ring
910 to a lower transparent substrate 908 on its opposing side.
Lower transparent substrate 904 bears a lower interferometric
modulator array 908 and is configured to reflect light through the
lower transparent substrate 904. Because the upper interferometric
modulator array 906 (which acts as the sub-display) is smaller in
size than the lower interferometric array 908, additional area
remains on the inner surface of upper transparent substrate 902
which may be used to support various functions that the
interferometric modulator carrier would typically support in other
embodiments. Thus, in certain embodiments, upper substrate 902
provides a means for supporting electronic circuitry configured to
control the state of array 906. In this embodiment, upper
transparent substrate 902 can be formed of a polymeric substance
which is less vapor resistant than glass. In order to prevent
moisture buildup over the lifetime of the device, vapor barrier 912
and desiccant 914 are provided on the inner surface of substrate
902.
[0094] In other embodiments of the display 900 depicted in FIG. 13,
wherein electronic components such as ICs are located within the
protective cavity formed by the upper and lower transparent
substrates, the vapor barrier 912 and/or desiccant 914 may be
applied directly or indirectly over the electronic components. This
application may be done by spray-coating or screen printing, for
example, or by any other suitable method.
[0095] FIG. 14 illustrates another embodiment of a dual sided
display 950, wherein an upper transparent substrate 952 and
interferometric modulator array 954 act as the sub-display. In this
embodiment, they are bonded and attached to an annular
interferometric modulator carrier 956. This assembly is then bonded
via a seal ring 958, to a transparent substrate 960 that is
configured to pass light to an interferometric modulator array 962.
As can be seen, the surface area of the substrate 952 is less than
the surface area of the substrate 960. When necessary (e.g. when
the annular carrier 956 comprises plastic, which is less vapor
resistant than glass), a vapor barrier 964 and desiccant 966 may be
provided.
[0096] While the module configuration shown in FIG. 14 may not be
as thin as that illustrated in FIG. 13, it provides a greater
degree of flexibility in the features that can be incorporated in
the sub-display carrier plane of the module. Because carrier 956
need not be transparent, the material used can be selected based on
other considerations, such as strength. Electrical feedthroughs can
be more easily provided through carrier 956 by passing them along
the juncture between the transparent substrate 952 and the PC
carrier 956. This enables placement of driver chips or other
components on the upper surface of the carrier 956. Because of the
height of the transparent substrate 952, components such as driver
chip 968 which have heights equal to or less than the height of the
substrate 952 will not add to the overall height of the device 950.
Trace leads 970 can run, for example, from the driver chip 968
located on the upper surface of the substrate 956 directly to the
array 954, without the need for flex cables, feedthroughs, or other
complex connections. Because carrier 956 can be a multilayer
conductor polymer laminate, as discussed previously, leads 970 can
run within the carrier 956, advantageously protecting the lead from
damage. Leads 970 may advantageously comprise two leads, one on or
within carrier 956 and placed in electrical contact with another
lead on the lower surface of upper substrate 952.
[0097] Still another embodiment of a dual sided display 1000 is
shown in FIG. 15. Components depicted in FIG. 15 include an upper
transparent substrate 1002 bearing an interferometric modulator
array 1006 configured to reflect light through the transparent
substrate 1002. The upper transparent substrate 1002 is bonded via
a sealing bead 1010 to a lower transparent substrate 1004, on which
interferometric modulator arrays 1008 is located.
[0098] FIG. 16 illustrates an embodiment of a device 1150 (e.g. a
cellular phone) comprising an interferometric modulator carrier
1152, which is bonded to a transparent substrate 1154 by means of a
seal ring 1156. As can be seen from FIG. 16, the surface area of
carrier 1152 is larger than the surface area of substrate 1154.
Driver chip 1158 is located on the upper side of carrier 1152, and
electrically connected via electrical feedthrough 1160 and
conducting post 1162 to an array 1164 of interferometric modulators
located on substrate 1154 and configured to reflect light through
substrate 1154. Located on the same side of the carrier 1152 as the
driver chip 1158 and in electrical connection with driver chip 1158
via trace leads 1166 are antenna 1168, device processor/memory
1170, battery 1172 and external interconnect hardware 1174. Located
on the opposite side of the carrier 1152 as the driver chip 1158
are the keyboard, keyboard lighting, and microphone hardware,
referenced collectively as 1176. Although not shown, the keyboard
and microphone hardware 1176 may be placed in electrical connection
with the driver chip 1158 on the opposite side of the carrier 1152
by any suitable method, including but not limited to electrical
feedthroughs, trace leads, and flex cables of the types discussed
above.
[0099] As illustrated in FIG. 16, carrier 1152 for the
interferometric modulator 1164 is the primary internal structural
component while also acting as the electrical interconnect means.
This entire assembly is encased in a shell 1166 which need not have
the structural rigidity of shells used in products which isolate
the display. The construction of this shell and its connection to
the interferometric modulator carrier minimize the amplitude of
mechanical shocks transmitted to the transparent substrate 1154 and
associate components, thereby increasing the product's overall
ruggedness. Carrier 1152 thus becomes the "backbone" of the
device.
[0100] In contrast with conventional display-centric device
assembly methods, in which the strength of the device comes from
the case encapsulating the device, the strength of the device can
come instead from the carrier 1152 located within the device, as
the carrier serves as the primary structural component of the
device. The increased strength of the carrier 1152 may be a result
of the materials which comprise the carrier. Alternately or in
addition to the choice of materials, the strength of the carrier
may be the result of the dimensions of the carrier. For instance,
increasing the thickness of the carrier 1152 or modifying the
cross-sectional shape of the carrier can provide the strength
necessary for the carrier to function as a primary structural
component of the device 1150. Many other configurations are
possible with this technique that increases both the physical and
structural role the interferometric modulator carrier plays in the
product.
Contoured Backplates
[0101] In yet another exemplary embodiment, the backplate comprises
a shaped printed circuit board or other shaped interferometric
modulator carrier. FIGS. 17A and 17B depict an embodiment of a
device 1200 comprising a shaped backplate 1228. As can be seen in
FIG. 17A, the backplate 1228 has a central region 1230 that is
domed. This domed central region 1230 is surrounded by a perimeter
region 1226 that is substantially flatter.
[0102] In the embodiment of FIGS. 17A and 17B, the backplate 1228
comprises a printed circuit board (PCB). This printed circuit board
is curved such that a cavity 1250 (see FIG. 17B) within the device
1200 is sufficiently large to accommodate an array 1210 of
modulators housed therein. In embodiments using a PCB for the
backplate 1228, the shaped cavity 1250 may be formed by stamping
the PCB backplate 1228 or any other suitable method for shaping or
cutting a PCB. In alternate embodiments, the backplate 1228 may
comprise glass or a glass compound, which is substantially
impermeable to moisture. If made of glass, the shaped central
region 1230 of the backplate may be formed by sandblasting or any
other suitable glass shaping or cutting method.
[0103] In the embodiment shown in FIG. 17A, an electrical component
1260 is mounted to the backplate 1228. A set of trace leads 1240
extend from holes 1234 in a perimeter region 1226 of the backplate
1228 and are electrically connected to the electrical component
1260. Leads 1262 from the electrical component 1260 may, for
example, be soldered to the trace leads 1240. As will be discussed
further with respect to FIG. 17B, the holes 1234 comprise vias 1242
which enable an electrical connection to be made between the upper
and lower surfaces of backplate 1228. In one exemplary embodiment,
the electrical component 1260 is a driver chip that is configured
to control the state of modulators in the array 1210. In other
embodiments, the electrical component could be any variety of
electrical components or devices, including but not limited to
other integrated circuits, other passive and active electrical
structures or components, or other surface-mounted electronics such
as transistors, capacitors, resistors, diodes, inductors, etc.
[0104] Now with respect to FIG. 17B, it can be seen that attaching
the backplate 1228 to a substrate 1216 forms a cavity 1250 in the
package structure 1200. The array 1210 of modulators is housed in
this cavity 1250 between the backplate 1228 and the substrate 1216.
As described above, the backplate 1228 is domed. The curvature of
the domed central region 1230 also produces a recess 1252 where the
distance between the backplate 1228 and the substrate 1216 is
greater than in other parts of the cavity 1250. The cavity 1250 is
thus advantageously enlarged in the central region 1230 where the
array 1210 of modulators is disposed.
[0105] Room for unimpeded operation of the modulators the array
1210 is thereby provided. Although the central region 1230 of the
backplate 1228 is depicted as domed, numerous other shapes are also
within the scope of the invention. For example, the backplate 1228
may have a curved or recessed shape that is not necessarily limited
to the central region 1230 or may have other shapes such as a
ribbed design or a raised rectangular design. In one embodiment,
the edges of the backplate 1228 are beveled so that they provide a
lower profile. As long as at least a portion of the modulators in
the array 1210 are within an enlarged region or cavity of the
backplate 1228, then the desired room for unimpeded operation of
the that portion of the array 1210 is provided.
[0106] A plurality of through holes 1234 are formed in the
perimeter region 1226. The holes 1234 are staggered in the
embodiment shown in FIG. 17B. Separation between alternating holes
1234 may be between about 50 to 75 micrometers in some designs. In
other embodiments, wherein the holes 1234 are not staggered, the
pitch may also be between about 75 to 125 micrometers (.mu.m). The
backplate 1228 may have a thickness of between about 0.5 and 2.0
millimeters (mm) and thus the through holes will also be the same
depth so as to penetrate completely through the backplate 1228.
Values outside these ranges, however, are also within the scope of
the invention.
[0107] The number and configuration of holes 1234 can vary in
different embodiments of the invention. For example, in one
embodiment the holes 1234 may be in the domed or recessed central
region 1230 of the backplate 1228. Placement of the holes 1234 will
depend on the specific functionality desired. The exact position,
and combinations of positions, of the holes 1234, are within the
skill in the art. The holes 1234 may be formed by mechanically
drilling, laser drilling, or ultrasonic drilling, for example.
Other standard methods of forming the holes 1234 may also be
employed.
[0108] FIG. 17B also shows the electrical traces 1240 disposed on,
and traversing, the printed circuit board backplate 1228. An
electrical connection is formed between the backplate 1228 and the
spatial modulator, as described above (see FIG. 17A). For example,
in the embodiment shown, the electrical traces 1240 contact vias
1242 that pass through the printed circuit board backplate 1228.
The vias 1242 may be, for example, plated vias fabricated in any
manner well known in the printed circuit board field. Solder 1244
between the vias 1242 and a set of electrical pads 1246 on the
substrate 1216 provides a conductive pathway therebetween. As a
result of these electrical connections, the electrical traces 1240
on the PCB backplate 1228 are in electrical communication with the
electrodes in the array 1210 of modulators. As described above, a
wide variation in the designs of and processes for fabricating the
electrical connection between the PCB backplate 1228 the modulator
array 1210 are possible.
[0109] As illustrated in 17B, the PCB backplate 1228 may comprise a
multilayer structure. For example, a metallization layer 1264 can
be embedded in the printed circuit board backplate 1228. This
metallization layer 1264 is electrically connected to one of the
traces 1240 by a conducting plug 1266 as is conventional in
multilayer printed circuit boards. Other approaches to
manufacturing a multilayered backplane may be employed. Additional
conductive paths may be provided in this manner. For example, in
one exemplary embodiment (not depicted) the electrical traces may
be an integral part of the PCB backplate. In this embodiment, the
electrical traces may be embedded in the PCB backplate by
conventional multilayering of the PCB backplate 1228. These
electrical traces can be configured in many ways, including, but
not limited to, the electrical traces being in electrical
communication vias and/or the electrical pads. In addition, the
electrical traces 1240 can be in electrical communication with
individual modulators or in direct electrical communication with
the entire array or subportions thereof.
[0110] In the embodiment depicted in FIG. 17B, a desiccant 1254 is
positioned between the array 1210 of optical modulators and the
backplate 1228. The recessed portion of the backplate 1228 offers
increased clearance for the desiccant 1254 to be disposed in the
cavity 1250 without interfering with the operation of the array
1210.
[0111] The desiccant 1254 may have different shapes, forms, and
sizes and may be applied in different ways. In the embodiment shown
in FIG. 17B, this desiccant 1254 comprises a sheet that is mounted
to the backplate 1228 with adhesive. Specifically, the desiccant
1254 is adhered to the central region 1230 of the backplate 1228.
Advantageously, the recess created by the curvature of the front
side of the backplate 1228 provides space for the desiccant 1254
above the modulator array 1210.
[0112] The package structure 1200 enhances performance of the
modulators in multiple ways as well. Integration of electrical
busses 1240 on the outside of the package structure 1200 offer a
wide range of design possibilities that may enable enhancements of
the performance of the array 1210 or provide additional features.
For example, electrical busses can be arranged such that one end of
the bus connects to one end of a row or column electrode within the
array, and the other end of the bus connects to the other end of
the same row or column electrode. This connection adds a parallel
conduction path to the row or column, reducing the overall
resistance of the row or column.
[0113] Advantageously, the conductive busses 1240 provide a
relatively high conductivity connection to the array 1210 of
optical modulators. The conductive busses 1240 can be fabricated
with larger dimensions (e.g., width and thickness) than the
electrodes that connect the modulators in the array 1210. This
enhanced conductivity and, thus, reduced impedance, allows the
optical modulators in the array 1210 to be driven faster. In
addition, since the conductive busses 1240 are outside of the
package if they are mounted on the outer surface 1232 of the
package structure 1200, precious real estate within the cavity 1250
where the array 1210 of modulators is located, is not sacrificed.
Interference with the mechanical operation of the array 1210 of
interferometric modulators is also avoided. The package structure
1200 may also afford other advantages are not specifically recited
herein.
[0114] Other configurations of the conductive busses 1240 may be
utilized in other embodiments. For example, the conductive busses
1240 may follow different pathways and may be connected
differently. The specific geometry may be altered depending on the
designs or desired function. For example, in one exemplary
embodiment (not depicted), a portion of the holes 1234 are placed
on the domed region 1230 of the backplate 1228 and the conductive
busses 1240 are in electrical communication with at least a portion
of the modulators in the array 1210 that are below the respective
holes 1234. This embodiment may be useful for performing testing on
certain portions of the array 1210.
[0115] While the above detailed description has shown, described,
and pointed out novel features of the invention as applied to
various embodiments, it will be understood that various omissions,
substitutions, and changes in the form and details of the device or
process illustrated may be made by those skilled in the art without
departing from the spirit of the invention. As will be recognized,
the present invention may be embodied within a form that does not
provide all of the features and benefits set forth herein, as some
features may be used or practiced separately from others.
* * * * *