U.S. patent application number 12/155645 was filed with the patent office on 2008-10-02 for microelectronic imagers with curved image sensors and methods for manufacturing microelectronic imagers.
Invention is credited to Ulrich C. Boettiger, Jin Li, Steven D. Oliver.
Application Number | 20080237443 12/155645 |
Document ID | / |
Family ID | 35908818 |
Filed Date | 2008-10-02 |
United States Patent
Application |
20080237443 |
Kind Code |
A1 |
Oliver; Steven D. ; et
al. |
October 2, 2008 |
Microelectronic imagers with curved image sensors and methods for
manufacturing microelectronic imagers
Abstract
Microelectronic imagers with curved image sensors and methods
for manufacturing curved image sensors. In one embodiment, a
microelectronic imager device comprises an imager die having a
substrate, a curved microelectronic image sensor having a face with
a convex and/or concave portion at one side of the substrate, and
integrated circuitry in the substrate operatively coupled to the
image sensor. The imager die can further include external contacts
electrically coupled to the integrated circuitry and a cover over
the curved image sensor.
Inventors: |
Oliver; Steven D.; (Boise,
ID) ; Li; Jin; (Boise, ID) ; Boettiger; Ulrich
C.; (Boise, ID) |
Correspondence
Address: |
DICKSTEIN SHAPIRO LLP
1825 EYE STREET NW
Washington
DC
20006-5403
US
|
Family ID: |
35908818 |
Appl. No.: |
12/155645 |
Filed: |
June 6, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11488848 |
Jul 19, 2006 |
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12155645 |
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10922177 |
Aug 19, 2004 |
7397066 |
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11488848 |
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Current U.S.
Class: |
250/200 |
Current CPC
Class: |
H01L 27/14625 20130101;
H01L 2924/00 20130101; H01L 2924/0002 20130101; H01L 27/14636
20130101; H01L 27/1464 20130101; H01L 27/14634 20130101; H01L
27/14618 20130101; H01L 2924/0002 20130101 |
Class at
Publication: |
250/200 |
International
Class: |
G01J 1/20 20060101
G01J001/20 |
Claims
1-32. (canceled)
33. A microelectronic imager die comprising: a substrate; a
microelectronic image sensor at one side of the substrate, the
microelectronic image sensor having a face for receiving radiation;
integrated circuitry electronically coupled to the image sensor;
and a flexor unit that bends a portion of the substrate and the
image sensor.
34. The imager die of claim 33 wherein the flexor unit further
comprises: a first element attached to a backside of the substrate
under a central portion of the image sensor; and a spacer attached
to the backside of the substrate outward of the first element.
35. The imager die of claim 34 -wherein the first element has a
first coefficient of thermal expansion and the spacer has a
different second coefficient of thermal expansion.
36. The imager die of claim 34 wherein the first element is a first
compliant material and the spacer is a second compliant
material.
37. The imager die of claim 33 wherein the flexor unit comprises a
compartment attached to the backside of the substrate and a fluid
in the compartment at a pressure that causes the substrate to
bow.
38. The imager die of claim 33 wherein the flexor unit comprises a
sealed compartment over the image sensor and fluid in the
compartment at a pressure that causes the substrate to bow.
39. The imager die of claim 33 wherein the flexor unit comprises a
material attached to the backside of the substrate that induces a
force that bends the substrate.
40. The image die of claim 39 wherein the material comprises a
bimetallic plate, a shape memory metal, and/or an epoxy.
41. The imager of claim 33 wherein the flexor unit comprises an
actuator attached to the backside of the substrate, and wherein the
actuator moves to flex the substrate and bend the image sensor.
42. A microelectronic workpiece, comprising: a substrate having a
plurality of imager dies, wherein individual imager dies include an
image sensor having a curved face and integrated circuitry
operatively coupled to the image sensor; and a cover over the
substrate.
43. The microelectronic workpiece of claim 42, further comprising a
plurality of backside flexor units attached to a backside of the
substrate under the image sensors, and wherein individual flexor
units comprise: a first element, a spacer, and a plate, wherein at
least the first element changes to bend the substrate under a
corresponding image sensor.
44. The microelectronic workpiece of claim 43 wherein the first
elements have a first coefficient of thermal expansion and the
spacers have a different second coefficient of thermal
expansion.
45. The microelectronic workpiece of claim 43 wherein the first
elements are composed of a first compliant material and the spacers
are composed of a second compliant material.
46. The microelectronic workpiece of claim 42, further comprising a
plurality of compartments attached to the backside of the substrate
at corresponding imager dies, and wherein the compartments contain
a fluid at a pressure that causes the substrate to flex under the
image sensors.
47. The microelectronic workpiece of claim 46 wherein the fluid in
the compartments is at a lower pressure than an ambient
pressure.
48. The microelectronic workpiece of claim 46 wherein the fluid in
the compartments is at a higher pressure than an ambient
pressure.
49. The microelectronic workpiece of claim 42, further comprising a
material attached to the backside of the substrate under
corresponding image sensors that bends the substrate locally under
the image sensors.
50. The microelectronic workpiece of claim 49 wherein the material
comprises an epoxy.
51. The microelectronic workpiece of claim 49 wherein the material
comprises bimetallic plates and/or members made from a shape memory
alloy.
52. The microelectronic workpiece of claim 42, further comprising a
standoffs between the cover and the substrate, sealed compartments
over the image sensors, and a fluid in the compartments at a
pressure that causes the substrate to bow locally at the image
sensors.
53. The microelectronic workpiece of claim 51 wherein the fluid in
the compartments is at a lower pressure than an ambient
pressure.
54. The microelectronic workpiece of claim 51 wherein the fluid in
the compartments is at a higher pressure than an ambient
pressure.
55. The microelectronic workpiece of claim 42, wherein the cover
has a higher coefficient of thermal expansion from the
substrate.
56. The microelectronic workpiece of claim 42, further comprising a
plurality of actuators attached to the backside of the substrate at
the imager dies, wherein the actuators move local regions of the
substrate to bow the substrate locally and flex the image
sensors.
57. The microelectronic workpiece of claim 42, further comprising a
plurality of vacuum cups attached to the backside of the substrate,
the individual vacuum cups having a curved interior surface adhered
to the backside under a corresponding image sensor.
58-76. (canceled)
77. A microelectronic imager die comprising: a substrate having a
front side and a back side; a microelectronic image sensor having a
face for receiving radiation at the front side of the substrate;
integrated circuitry in the substrate electrically connected to the
image sensor; and a curved flexor unit having a curved surface,
wherein the backside of the substrate in the region of the image
sensor is attached to the curved surface of the flexor unit such
that the substrate in the region of the image sensor at least
generally conforms to the curved surface.
78. The die of claim 77, wherein the curved flexor unit comprises a
vacuum cup having an opening through which a vacuum can be
drawn.
79. The die of claim 77, wherein the curved flexor unit comprises a
vacuum cup having an opening through which a vacuum can be drawn,
and wherein the backside of the substrate is adhered to the curved
surface of the vacuum cup.
80. The die of claim 77, wherein the curved flexor unit comprises a
vacuum cup having the curved surface and interconnects, and wherein
the substrate further comprises backside interconnects electrically
coupled to interconnects of the curved flexor unit and the
integrated circuitry.
Description
TECHNICAL FIELD
[0001] The present invention generally relates to microelectronic
imagers with curved image sensors and methods for forming curved
image sensors for use in such microelectronic imagers.
BACKGROUND
[0002] Microelectronic imagers are used in digital cameras,
wireless devices with picture capabilities, and many other
applications. Cell phones and Personal Digital Assistants (PDAs),
for example, incorporate microelectronic imagers for capturing and
sending pictures. The growth rate of microelectronic imagers has
been steadily increasing as they become smaller and produce better
images with more pixels.
[0003] Microelectronic imagers include image sensors that use
Charged Coupled Device (CCD) systems, Complementary Metal-Oxide
Semiconductor (CMOS) systems, or other solid-state systems. CCD
image sensors have been widely used in digital cameras and other
applications. CMOS image sensors are also quickly becoming very
popular because they are expected to have low production costs,
high yields, and small sizes. CMOS image sensors can provide these
advantages because they are manufactured using technology and
equipment developed for fabricating semiconductor devices. CMOS
image sensors, as well as CCD image sensors, are accordingly
"packaged" to protect delicate components and to provide external
electrical contacts.
[0004] FIG. 1 is a schematic side cross-sectional view of a
conventional microelectronic imaging unit 1 including an imaging
die 10, a chip carrier 30 carrying the die 10, and a cover 40
attached to the chip carrier 30 and positioned over the die 10. The
imaging die 10 includes an image sensor 12 and a plurality of
bond-pads 16 operably coupled to the image sensor 12. The chip
carrier 30 has a base 32, sidewalls 34 projecting from the base 32,
and a recess defined by the base 32 and sidewalls 34. The die 10 is
received within the recess and attached to the base 32. The chip
carrier 30 further includes an array of terminals 18 on the base
32, an array of contacts 24 on an external surface 38, and a
plurality of traces 22 electrically connecting the terminals 18 to
corresponding external contacts 24. The terminals 18 are positioned
between the die 10 and the sidewalls 34 so that wire-bonds 20 can
electrically couple the terminals 18 to corresponding bond-pads 16
on the die 10.
[0005] One problem with the microelectronic imaging unit 1
illustrated in FIG. 1 is that the die 10 must fit within the recess
of the chip carrier 30. Dies having different shapes and/or sizes
accordingly require chip carriers configured to house those
specific types of dies. As such, manufacturing imaging units with
dies having different sizes requires fabricating various
configurations of chip carriers and significantly retooling the
manufacturing process.
[0006] Another problem with conventional microelectronic imaging
units is that they have relatively large footprints. For example,
the footprint of the imaging unit 1 in FIG. 1 is the surface area
of the base 32 of the chip carrier 30, which is significantly
larger than the surface area of the die 10. Accordingly, the
footprint of conventional microelectronic imaging units can be a
limiting factor in the design and marketability of picture cell
phones or PDAs because these devices are continually being made
smaller in order to be more portable. Therefore, there is a need to
provide microelectronic imaging units with smaller footprints.
[0007] The imager 1 shown in FIG. 1 also has an optics unit
including a support 50 attached to the chip carrier 30 and a lens
system with a plurality of lenses 70 (identified individually by
reference numbers 70a-c). Traditional lens systems include a
plurality of lenses for focusing the image at the image sensor 12.
Traditional lens systems accordingly flatten the field of the image
at the image sensor 12 so that the image is focused across the face
of the image sensor 12. In the embodiment shown in FIG. 1, for
example, the lens 70c may flatten the image "I" across the face of
the image sensor 12. In other conventional systems, one or more of
the lenses 70a-c can be combined into a single aspherical lens that
can focus and flatten an image.
[0008] Another problem with conventional microelectronic imaging
units that lens systems with multiple lenses or more complex
aspherical lenses are relatively tall and complex. Conventional
lens systems accordingly have high profiles, can be expensive to
manufacture, and may be difficult to assemble. Therefore, it would
be desirable to reduce the demands and complexity of lens systems
in the manufacturing of microelectronic imagers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic side cross-sectional view of a
packaged microelectronic imager in accordance with the prior
art.
[0010] FIG. 2 is a cross-sectional view illustrating one stage of
fabricating a plurality of microelectronic imagers at the wafer
level in accordance with an embodiment of the invention.
[0011] FIG. 3 is a cross-sectional view illustrating a subsequent
stage of fabricating a plurality of microelectronic imagers at the
wafer level in accordance with an embodiment of the invention.
[0012] FIGS. 4A and 4B are schematic side cross-sectional views
illustrating alternative embodiments of microelectronic imagers
fabricated in accordance with an embodiment of the invention.
[0013] FIG. 5 is a cross-sectional view illustrating an embodiment
for forming curved image sensors in microelectronic imagers in
accordance with an embodiment of the invention.
[0014] FIG. 6 is a cross-sectional view illustrating an embodiment
for forming curved image sensors in microelectronic imagers in
accordance with another embodiment of the invention.
[0015] FIG. 7 is a cross-sectional view illustrating an embodiment
for forming curved image sensors in microelectronic imagers in
accordance with another embodiment of the invention.
[0016] FIG. 8 is a cross-sectional view illustrating a process for
bending a substrate to fabricate curved microelectronic imagers in
accordance with a specific embodiment of the method shown in FIG.
7.
[0017] FIG. 9 is a cross-sectional view illustrating another
embodiment for fabricating curved image sensors in accordance with
the invention.
[0018] FIG. 10 is a cross-sectional view illustrating a device and
method for fabricating curved image sensors in accordance with
still another embodiment of the invention.
[0019] FIG. 11 is a cross-sectional view illustrating a device and
method for fabricating curved image sensors in accordance with yet
another embodiment of the invention.
[0020] FIGS. 12A and 12B are cross-sectional views illustrating a
device and a process for fabricating curved image sensors in
accordance with an embodiment of the invention.
DETAILED DESCRIPTION
A. Overview
[0021] The following disclosure describes several embodiments of
microelectronic imagers having curved image sensors and methods for
fabricating such microelectronic imagers at the wafer level and at
the individual die level. In one embodiment, a microelectronic
imager device comprises an imager die having a substrate, a curved
microelectronic image sensor having a convex and/or concave face at
one side of the substrate, and integrated circuitry in the
substrate operatively coupled to the image sensor. The imager die
can further include external contacts electrically coupled to the
integrated circuitry and a cover over the curved image sensor.
[0022] The curved microelectronic image sensor can have a convex
and/or concave face with a desired radius of curvature. For
example, the curved image sensor can have a face with a single
radius of curvature, a plurality of curves with different radii,
and/or flat portions in combination with one or more curves. The
curved face of the image sensor is expected to receive a generally
spherical image field such that the lens assembly does not need to
significantly flatten the field to compensate for a planar sensor
array.
[0023] In an alternative embodiment, a microelectronic imager
device includes an imager die having a substrate with a bowed
portion, a microelectronic image sensor having a curved face at the
bowed portion of the substrate, and integrated circuitry
electrically coupled to the image sensor. The imager device can
further include a flexor unit that exerts a force against the
substrate to bend or otherwise flex the substrate to form the bowed
portion under the image sensor. The flexor unit, for example, can
include a first element attached to a first region of the substrate
under an image sensor, a spacer attached to the substrate outwardly
of the first element, and a plate attached to the first element and
the spacer. The first element expands or contracts more or less
than the spacer to flex the substrate. The flexor unit can
alternatively comprise a compartment at the front side and/or the
backside of the substrate and a fluid in the compartment at a
pressure that causes the substrate to bow. Another embodiment of
the flexor unit can comprise a material attached to the backside of
the substrate that bends the substrate into a desired curvature.
The flexor unit can alternatively comprise an actuator attached to
the backside of the substrate to flex the substrate and bend the
image sensor into a desired curvature.
[0024] Another aspect of the invention is a method for
manufacturing microelectronic imager devices. In one embodiment, a
such method includes constructing an imager die having a substrate,
integrated circuitry in the substrate, and an image sensor having a
curved face at one side of the substrate. This method can further
include positioning a cover over the substrate and/or bending the
substrate to flex the image sensor.
[0025] Several details of specific embodiments of the invention are
described below with reference to CMOS imagers to provide a
thorough understanding of these embodiments. CCD imagers or other
types of sensors, however, can be used instead of CMOS imagers in
other embodiments of the invention. Several details describing well
known structures often associated with microelectronic devices may
not be set forth in the following description for the purposes of
brevity. Moreover, other embodiments of the invention can have
different configurations or different components than those
described and shown in this section. As such, other embodiments of
the invention may have additional elements or may not include all
the elements shown and described below with reference to FIGS.
2-12B.
B. Microelectronic Imagers with Curved Image Sensors
[0026] FIG. 2 is a side cross-sectional view illustrating an imager
unit assembly 200 having a plurality of microelectronic imager
units 202 at one stage of a method for packaging imagers in
accordance with an embodiment of the invention. The assembly 200
illustrated in FIG. 2 includes an imager workpiece 210, standoffs
230 projecting from the imager workpiece 210, and a cover 240
attached to the standoffs 230. A plurality of optics units (not
shown) are typically mounted to the cover 240 either before or
after forming curved image sensors on the imager workpiece 210 to
fabricate microelectronic imagers.
[0027] The imager workpiece 210 includes a substrate 212 having a
front side 214, a backside 216, and an initial thickness To to
between the front side 214 and backside 216. The imager workpiece
210 further includes a plurality of imaging dies 220 formed on
and/or in the substrate 212. Individual imaging dies 220 can
include an image sensor 221, integrated circuitry 222 operatively
coupled to the image sensor 221, and terminals 223 (e.g.,
bond-pads) electrically coupled to the integrated circuitry 222.
The image sensors 221 can be CMOS devices, CCD image sensors, or
other solid state devices for capturing pictures in the visible
spectrum or sensing radiation in other spectrums (e.g., IR or UV
ranges). As explained in more detail below, the terminals 223 can
be connected to through-wafer interconnects formed according to the
processes disclosed in U.S. patent application Ser. No. 10/713,878
entitled "Microelectronic Devices, Methods for Forming Vias in
Microelectronic Devices, and Methods for Packaging Microelectronic
Devices," filed on Nov. 13, 2003, which is incorporated by
reference herein in its entirety. Other embodiments of external
contacts can include terminals that are at an intermediate depth
within the first substrate 212 instead of being at the front side
214.
[0028] The embodiment of the imager unit assembly 200 illustrated
in FIG. 2 is fabricated at the wafer level such that several
imaging units 202 are packaged before singulating (e.g., cutting)
the first substrate 212, the spacers 230 and the cover 240 along
lines A-A. One aspect of wafer-level packaging is using automated
equipment to further process the assembly 200 to form curved image
sensors and to install optics units (not shown) onto the cover 240.
FIGS. 3-4B illustrate several aspects of forming curved image
sensors and embodiments of assemblies having curved image
sensors.
[0029] FIG. 3 illustrates the imager unit assembly 200 at a
subsequent stage of a process for forming curved image sensors on
the imaging dies 220. At this stage of the process, the substrate
212 has been thinned from the initial thickness T.sub.0 to a
thickness T.sub.1 so that the portions of the substrate 212 between
the standoffs 230 are at least relatively flexible. In several
embodiments, the substrate 212 can be thinned using a back grinding
process, a chemical-mechanical planarization process, and/or an
etching procedure known in the art to form a new backside 216. The
final thickness T.sub.1 between the front side 214 and the backside
216 can be in the range of approximately 20-200 .mu.m depending
upon the type of material. When the substrate 212 is composed of
silicon, the thickness T.sub.1 is generally less than approximately
150 .mu.m and can be in the range of approximately 20-80 .mu.m. The
very thin portions of the substrate 212 between the standoffs 230
acts much like a flexible membrane, and as such the portions of the
substrate 212 under the image sensors 221 can be flexed to bend the
image sensors 221. After thinning the substrate, the assembly 200
illustrated in FIG. 3 can be further processed to construct the
through-wafer interconnects 224 through the substrate 212 to
provide electrical contacts on the backside 216 of the substrate
212. Additional suitable processes for forming such interconnects
are disclosed in U.S. application Ser. No. 10/879,838, which is
herein incorporated by reference.
[0030] FIG. 4A is a cross-sectional view illustrating one
embodiment of the imager unit assembly 200 after bending the
substrate 212 to form curved image sensors 221. In this embodiment,
the substrate 212 has curved portions 250 in the areas aligned with
the image sensors 221. The curved portions 250 are generally
discrete bowed regions of the substrate 212 that form projecting
bumps on the backside 216. In one embodiment, the curved portions
250 have a shape of a portion of a sphere with a radius of
curvature R. The curved portions 250 are not limited to a spherical
configuration and can have other configurations with one or more
curves and/or flat portions depending upon the particular
application.
[0031] The image sensors 221 flex as the curved portions 250 of the
substrate 212 are formed such that the image sensors 221 have
curved faces 260. The curvature of each curved face 260 is
configured so that the array on the curved face 260 is at a desired
focal distance for the image. In the embodiment illustrated in FIG.
4A, the curved image sensors 221 have concave curved faces 260
relative to the direction of the radiation to accommodate
non-planar image fields.
[0032] The curved image sensors 221 with the curved faces 260 are
expected to (a) reduce the complexity of fabricating lens systems
and (b) increase the options of lens systems that can be used with
the imagers. For example, because the image sensors 221 have curved
faces 260, the image field does not need to be flattened using
optics to the same extent as image fields need to be flattened for
planar image sensors. This is expected to eliminate the need for
field flattening lenses in the optics units that are attached to
the cover 240, or at least reduce the complexity of fields
flattening lenses. Therefore, the imaging dies 220 illustrated in
FIG. 4A reduce the constraints on lens designs such that fewer
lenses or less complex lenses can be used to reduce the cost of
fabricating microelectronic imagers.
[0033] The curved image sensors 221 illustrated in FIG. 4A are also
advantageous because they are particularly well-suited for
miniature camera applications that require a wide-angle field of
view and/or have a short focal distance. One problem with miniature
cameras is that it is difficult to adequately flatten the image
field because the focal distance between the lenses and the image
sensors 221 is extremely short. As a result, images from
conventional miniature cameras are typically focused at the center
but out of focus at the periphery. The curved image sensors 221
mitigate this problem because the periphery of the image sensors
221 is at, or at least closer to, the desired focal distance of the
image field. The curved image sensors 221 are also expected to be
very useful for megapixel wide-angle applications that have longer
focal distances for the same reason. Therefore, the curved image
sensors 221 are further expected to provide better quality images
for miniature cameras or other applications that have a wide-angle
field of view.
[0034] FIG. 4B is a cross-sectional view illustrating another
embodiment of the imager unit assembly 200 having a plurality of
imaging dies 220 with curved image sensors 221. In this embodiment,
the curved portions 250 of the substrate 212 project into the
cavity between the cover 240 and the substrate 212. The curved
portions 250 accordingly form small discrete dimples on the
backside 216 of the substrate 212 such that the image sensors 221
have convex curved faces 260 relative to the direction of the
radiation. As described above, the curved portions 250 can have the
shape of a portion of a sphere having a radius of curvature R, but
other configurations may also be suitable.
C. Methods and Devices for Forming Curved Image Sensors
[0035] FIG. 5 is a cross-sectional view of an embodiment of
fabricating curved image sensors using a plurality of flexor units
500 attached to the backside 216 of the substrate 212. The flexor
units 500 can be positioned at each imaging die 220 or only at
known-good imaging dies 220 depending upon the particular
application. The individual flexor units 500 include a first
element 510 attached to the backside 216 of the substrate 212 under
a corresponding image sensor 221. The first elements 510, for
example, can be expansion/contraction members attached to the
substrate 212 at areas aligned with the central regions of the
corresponding image sensors 221. The individual flexor units 500
can further include a spacer 520 arranged outwardly from the first
element 510 and a plate 530 attached to the first element 510 and
the spacer 520. In one embodiment, the first elements 510 are made
from a material having a first coefficient of thermal expansion,
and the spacers 520 are made from a material having a second
coefficient of thermal expansion less than that of the first
elements 510. In other embodiments, the first elements 510 can be a
shape memory metal, such as Nitinol, and the spacers 520 can be a
substantially incompressible material.
[0036] The flexor units 500 operate by expanding/contracting the
first elements 510 either more or less than the spacers 520 to bend
the substrate 212 in the local regions under corresponding image
sensors 221. For example, the flexor units 500 can be attached to
the substrate 212 at an elevated temperature, and then the assembly
can be cooled such that the first elements 510 exert local forces
(arrows F) that bend the substrate 212 into the concave curved
portions 250 (shown in dashed lines) similar to those shown in FIG.
4A. The spacers 520 in this example contract less than the first
elements 510 as they cool. Alternatively, the first elements 510
can have a lower coefficient of thermal expansion than the spacers
520 such that the first element 510 exerts a force in the opposite
direction to form convex curved portions similar to those
illustrated in FIG. 4B.
[0037] FIG. 6 is a cross-sectional view illustrating another
embodiment for fabricating curved image sensors in microelectronic
imagers using a plurality of flexor units 600 attached to the
backside 216 of the substrate 212 under corresponding imaging dies
220. In this embodiment, individual flexor units 600 include a
compartment 610 and a fluid in the compartment 610 at a pressure
that causes the substrate 212 to bow (not shown in FIG. 6) in a
manner that flexes a corresponding image sensor 221. In one
embodiment, the compartments 610 can be attached to the substrate
212 in a low pressure environment such that the pressure inside the
compartments 610 is less than the pressure in chambers 620 over the
corresponding image sensors 221. The pressure differential between
the compartments 610 and the chambers 620 exerts a force F.sub.1
that draws the portions of the substrate 212 under the image
sensors 221 into the compartments 610 to form curved portions (not
shown) similar to the concave curved portions 250 illustrated above
with respect to FIG. 4A. Alternatively, the compartments 610 can be
attached to the substrate 212 in a high pressure environment such
that the pressure in the compartments 610 is greater than the
pressure in the chambers 620. This second embodiment exerts a force
F.sub.2 against the substrate 212 to drive the portions of the
substrate 212 under the image sensors 221 into the chambers 620 to
form a convex curvature on the image sensors 221 as illustrated
above with respect to FIG. 4B. The pressure in the compartments 610
can also be set by vacuuming or pressurizing the compartments 610
using gas or fluid lines connected to the compartments 610.
[0038] FIG. 7 is a cross-sectional view illustrating yet another
embodiment for forming curved image sensors on the assembly 200
using flexor units 700 attached to the backside 216 of the
substrate 212 underneath corresponding image sensors 221. In this
embodiment, the flexor units 700 can be a material that expands or
contracts in a manner that bends the portions of the substrate 212
under the image sensors 221 into a concave and/or convex curvature.
The flexor units 700, for example, can be an epoxy deposited onto
the backside 216 of the substrate 212 and then cured in a manner
that causes the epoxy to contract. As the epoxy contracts, it is
expected to bend the substrate 212 to form convex curved portions
similar to those illustrated above with respect to FIG. 4B. The
epoxy can be deposited in many configurations, including a circle,
radial starburst pattern, or other suitable pattern. The flexor
units 700 can alternatively be small members of a shape memory
alloy that assumes a desired configuration when it is in an
operating temperature range. For example, the shape memory alloy
may be attached to the substrate 212 at a first temperature and
then expand, contract or otherwise flex as it reaches an operating
temperature range to bend the local regions of the substrate 212
under the image sensors 221 in a manner that forms concave and/or
convex portions similar to those illustrated above with respect to
FIG. 4A or 4B.
[0039] FIG. 8 is a cross-sectional view illustrating yet another
embodiment of a flexor unit 700 having a first material 710 and a
second material 720. The first material 710 typically has a higher
coefficient of thermal expansion than the second material 720. As
such, when the flexor 700 cools to an operating temperature range,
the first material 710 contracts by a greater extent (arrows
C.sub.1) than the second material 720 (arrows C.sub.2). The
difference in contraction is expected to cause the flexor unit 700
to exert a downward force against the substrate 212 to form a
concave curved face 260 (illustrated in dashed lines). In one
embodiment, the first layer 710 can be composed of aluminum and the
second layer 720 can be composed of Kovar to form a bimetallic
plate.
[0040] FIG. 9 illustrates another embodiment for bending the image
sensors 221 to have curved faces with a desired curvature. In this
embodiment, flexor units 900 are defined by sealed chambers over
the image sensors 221 and a fluid in the sealed chambers at a
pressure P. The pressure of the fluid causes the substrate 212 to
flex in the regions under the image sensors 221 as shown in FIGS.
4A and 4B. In one embodiment, the cover 240 is assembled to the
standoffs 230 in an environment at a pressure higher than ambient
pressure such that the pressure in the sealed chambers drives the
portions of the substrate 212 under the image sensors 221 outwardly
to form the concave faces on the image sensors as illustrated in
FIG. 4A. In an alternative embodiment, the cover 240 is assembled
to the spacers 230 in an environment at a pressure lower than the
ambient temperature such that the substrate 212 is drawn into the
compartments to form convex curved faces on the image sensors as
illustrated in FIG. 4B.
[0041] FIG. 10 illustrates another embodiment for bending the image
sensors into a desired curvature in accordance with the invention
using a plurality of flexor units 1000 attached to the backside of
the substrate 212 under corresponding image sensors 221. In this
embodiment, the individual flexor units 1000 include a bracket 1002
attached to the backside 216 of the substrate 212 and an actuator
1010 attached to the bracket 1002. The actuator 1010 can have a
first end 1012 in contact with the backside 216 of the substrate
212 underneath a central portion of a corresponding image sensor
221. The actuator 1010 can further include a second end 1014
attached to the bracket 1002 and a line 1016 for transmitting
electrical signals or carrying fluids to control the actuator 1010.
In one embodiment, the actuator 1010 is a piezoelectric element and
the line 1016 is an electrically conductive wire that can be
coupled to a control unit. In a different embodiment, the actuator
can be a bladder or other type of structure that can be
expanded/contracted by adjusting a fluid pressure. In still another
embodiment, the actuator 1010 can be a pneumatic or hydraulic
cylinder. In operation, the actuator 1010 moves upwardly to form a
convex curved face on the image sensor 221 (see FIG. 4B) or
downwardly to form a concave curved face on the image sensor 221
(see FIG. 4A). The actuators 1010 can also be operated in real time
while using an imaging unit to provide fine adjustment of the focus
for wide-angle applications and other applications.
[0042] FIG. 11 illustrates still another embodiment for bending the
image sensors into a desired curvature. In this embodiment, a
flexor unit 1100 is defined by a transparent cover attached to the
standoff 230 at an elevated temperature. The transparent flexor
unit 1100 has a coefficient of thermal expansion greater than that
of the substrate 212 such that the flexor unit 1100 contracts more
than the substrate 212 as the assembly is cooled. The corresponding
contraction of the flexor unit 1100 causes the substrate 212 to
bend as shown by arrows B to form a concave curved face on the
image sensor 221 as shown above with respect to FIG. 4A.
[0043] FIGS. 12A and 12B are cross-sectional views that illustrate
still another embodiment for bending the image sensors into a
desired curvature in accordance with the invention using curved
flexor units 1200 attached to the backside of the substrate 212.
The flexor units 1200 are vacuum cups having an opening 1202 and an
interior surface 1204 with a curvature corresponding to the desired
curvature for the image sensors 221. FIG. 12A illustrates the
process before the substrate 212 is bent to form the curved face on
the image sensor 221. At this stage, there is a gap 1206 between
the backside 216 of the substrate 212 and the interior surface 1204
of the flexor unit 1200. To bend the substrate 212, a vacuum is
drawn through the opening 1202. Referring to FIG. 12B, the vacuum
drawn through the opening 1202 draws the backside 216 of the
substrate 212 against the interior surface 1204 of the flexor unit
1200. The backside 216 of the substrate 212 and/or the interior
surface 1204 of the flexor unit 1200 can be covered with an
adhesive that adheres the backside 216 of the substrate 212 to the
interior surface 1204 of the flexor unit 1200. The flexor unit 1200
can further include interconnects 1224 that contact the
interconnects 224 to carry the backside electrical contacts from
the substrate 212 to the exterior surface of the flexor unit
1200.
[0044] From the foregoing, it will be appreciated that specific
embodiments of the invention have been described herein for
purposes of illustration, but that various modifications may be
made without deviating from the spirit and scope of the invention.
For example, the substrate 212 can have patterns of trenches or
other voids etched on the front side 214 and/or the backside 216 to
preferentially direct the flexure of the substrate 212 using any of
the embodiments described above with respect to FIGS. 5-12B.
Similarly, ridges or other protrusions can be formed on the
substrate 212 in lieu of or in addition to voids to preferentially
direct the flexure of the substrate. Accordingly, the invention is
not limited except as by the appended claims.
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