U.S. patent application number 14/929890 was filed with the patent office on 2016-03-10 for array of nanowires in a single cavity with anti-reflective coating on substrate.
The applicant listed for this patent is ZENA TECHNOLOGIES, INC.. Invention is credited to Munib Wober.
Application Number | 20160071898 14/929890 |
Document ID | / |
Family ID | 43298029 |
Filed Date | 2016-03-10 |
United States Patent
Application |
20160071898 |
Kind Code |
A1 |
Wober; Munib |
March 10, 2016 |
ARRAY OF NANOWIRES IN A SINGLE CAVITY WITH ANTI-REFLECTIVE COATING
ON SUBSTRATE
Abstract
An embodiment relates to image sensor comprising one or more
nanowires on a substrate of a cavity, the nanowire being configured
to transmit a first portion of an electromagnetic radiation beam
incident on the sensor, and the substrate that absorbs a second
portion of the electromagnetic radiation beam incident on the
sensor, wherein the first portion is substantially different from
the second portion. The substrate could have a anti-reflective
material. The ratio of a diameter of the cavity to a diameter of
the nanowire could be at less than about 10.
Inventors: |
Wober; Munib; (Topsfield,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ZENA TECHNOLOGIES, INC. |
Cambridge |
MA |
US |
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|
Family ID: |
43298029 |
Appl. No.: |
14/929890 |
Filed: |
November 2, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14021672 |
Sep 9, 2013 |
9177985 |
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14929890 |
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12478598 |
Jun 4, 2009 |
8546742 |
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14021672 |
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Current U.S.
Class: |
257/432 |
Current CPC
Class: |
B82Y 20/00 20130101;
B82Y 15/00 20130101; H01L 27/14629 20130101; H01L 27/14685
20130101; H01L 31/0304 20130101; H01L 27/14649 20130101; H01L
27/14625 20130101; H01L 27/14627 20130101; B82Y 99/00 20130101;
H01L 27/14621 20130101; H01L 27/1462 20130101 |
International
Class: |
H01L 27/146 20060101
H01L027/146; H01L 31/0304 20060101 H01L031/0304 |
Claims
1. An image sensor comprising one or more upstanding nanowires on a
substrate, wherein the nanowires are configured to transmit a first
portion of an electromagnetic radiation incident on the sensor but
not to transmit a second portion of the electromagnetic radiation
incident on the sensor; wherein the substrate is configured to
absorb the second portion of the electromagnetic radiation beam
incident on the sensor, wherein the first portion has frequencies
higher than a cutoff frequency and the second portion has
frequencies lower than the cutoff frequency.
2. The sensor of claim 1, wherein the second portion comprises at
least a portion of electromagnetic radiation that comes out from
the nanowire.
3. The sensor of claim 1, wherein the substrate comprises an
anti-reflective material on a front side of the substrate that is
exposed to the electromagnetic radiation beam incident on the
sensor.
4. The sensor of claim 1, wherein at least one of the one or more
upstanding nanowires has a diameter above 100 nm.
5. The sensor of claim 1, wherein the nanowire is configured to
separate wavelengths of the electromagnetic radiation beam incident
on the nanowire at a selective wavelength.
6. The sensor of claim 1, wherein at least one of the one or more
upstanding nanowires comprises GaAs.
7. The sensor of claim 1, wherein the substrate comprises GaAs.
8. The sensor of claim 1, wherein the sensor comprises a plurality
of nanowires and is configured to have a substantially minor change
in an optical response of the nanowire with a 10.degree. change in
a direction of the electromagnetic radiation beam incident on the
sensor.
9. The sensor of claim 1, wherein each of the nanowires is
configured to separate wavelengths of the electromagnetic radiation
beam incident on the nanowire through at a selective wavelength,
the sensor further comprising a pair of photosensitive elements
comprising a central photosensitive element and a peripheral
photosensitive element, wherein the central photosensitive element
is operably coupled to the nanowire and the peripheral
photosensitive element is operably coupled to the substrate around
the nanowire.
10. The sensor of claim 1, wherein the nanowires are active
elements configured to detect wavelengths of electromagnetic
radiation transmitted through the nanowires.
11. The sensor of claim 10, wherein the active element is a
photodiode.
12. A device comprising the sensor of claim 1, wherein the device
is an image sensor.
13. The device of claim 1, wherein the nanowires comprise a
waveguide.
14. The device of claim 13, further comprising a passivation layer
around the waveguide.
15. The device of claim 13, further comprising a metal layer around
the waveguide.
16. The device of claim 12, wherein the device comprises a filter
that cuts off visible light and passes IR light.
17. The device of claim 12, further comprising a cladding
surrounding the nanowires, wherein the nanowires have a nanowire
index of refraction (n.sub.1), and the cladding has a cladding
index of refraction (n.sub.2), wherein n.sub.1>n.sub.2, or
n.sub.1=n.sub.2.
18. The device of claim 13, wherein the selective wavelength is a
function of the diameter of the waveguide.
19. The device of claim 13, further comprising at least a pair of
metal contacts with at least one of the metal contacts being
contacted to the waveguide.
20. The sensor of claim 1, wherein the nanowires absorb the first
portion.
21. The sensor of claim 1, wherein the nanowires are configured to
store charge carriers generated by the first portion of the
electromagnetic radiation beam in the nanowires.
22. The device of claim 13, wherein the nanowires are configured to
store charge carriers generated by the first portion of the
electromagnetic radiation beam in the nanowires.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/021,672 filed Sep. 9, 2013, which is a
continuation of U.S. patent application Ser. No. 12/478,598 filed
Jun. 4, 2009 (now U.S. Pat. No. 8,546,742 issued Oct. 1, 2013).
This application is related to the disclosures of U.S. patent
application Ser. No. 12/204,686, filed Sep. 4, 2008 (now U.S. Pat.
No. 7,646,943, issued Jan. 12, 2010), Ser. No. 12/648,942, filed
Dec. 29, 2009 (now U.S. Pat. No. 8,229,255, issued Jul. 24, 2012),
Ser. No. 13/556,041, filed Jul. 23, 2012, Ser. No. 12/270,233,
filed Nov. 13, 2008 (now U.S. Pat. No. 8,274,039, issued Sep. 25,
2012), Ser. No. 13/925,429, filed Jun. 24, 2013, Ser. No.
13/570,027, filed Aug. 8, 2012 (now U.S. Pat. No. 8,471,190, issued
Jun. 25, 2013), Ser. No. 12/472,264, filed May 26, 2009 (now U.S.
Pat. No. 8,269,985, issued Sep. 18, 2012), Ser. No. 13/621,607,
filed Sep. 17, 2012 (now U.S. Pat. No. 8,514,411, issued Aug. 20,
2013), Ser. No. 13/971,523, filed Aug. 20, 2013 (now U.S. Pat. No.
8,810,808, issued Aug. 19, 2014), Ser. No. 14/459,398, filed Aug.
14, 2014, Ser. No. 12/472,271, filed May 26, 2009 (now abandoned),
Ser. No. 12/573,582, filed Oct. 5, 2009 (now U.S. Pat. No.
8,791,470, issued Jul. 29, 2014), Ser. No. 14/274,448, filed May 9,
2014, Ser. No. 12/575,221, filed Oct. 7, 2009 (now U.S. Pat. No.
8,384,007, issued Feb. 26, 2013), Ser. No. 12/633,323, filed Dec.
8, 2009 (now U.S. Pat. No. 8,735,797, issued May 27, 2014), Ser.
No. 14/068,864, filed Oct. 31, 2013, Ser. No. 14/281,108, filed May
19, 2014, Ser. No. 13/494,661, filed Jun. 12, 2012 (now U.S. Pat.
No. 8,754,359, issued Jun. 17, 2014), Ser. No. 12/633,318, filed
Dec. 8, 2009 (now U.S. Pat. No. 8,519,379, issued Aug. 27, 2013),
Ser. No. 13/975,553, filed Aug. 26, 2013 (now U.S. Pat. No.
8,710,488, issued Apr. 29, 2014), Ser. No. 12/633,313, filed Dec.
8, 2009, Ser. No. 12/633,305, filed Dec. 8, 2009 (now U.S. Pat. No.
8,299,472, issued Oct. 30, 2012), Ser. No. 13/543,556, filed Jul.
6, 2012 (now U.S. Pat. No. 8,766,272, issued Jul. 1, 2014), Ser.
No. 14/293,164, filed Jun. 2, 2014, Ser. No. 12/621,497, filed Nov.
19, 2009 (now abandoned), Ser. No. 12/633,297, filed Dec. 8, 2009
(now U.S. Pat. No. 8,889,455, issued Nov. 18, 2014), Ser. No.
14/501,983 filed Sep. 30, 2014, Ser. No. 12/982,269, filed Dec. 30,
2010, Ser. No. 12/966,573, filed Dec. 13, 2010 (now U.S. Pat. No.
8,866,065, issued Oct. 21, 2014), Ser. No. 14/503,598, filed Oct.
1, 2014, Ser. No. 12/967,880, filed Dec. 14, 2010 (now U.S. Pat.
No. 8,748,799, issued Jun. 10, 2014), Ser. No. 14/291,888, filed
May 30, 2014 Ser. No. 12/966,514, filed Dec. 13, 2010, Ser. No.
12/974,499, filed Dec. 21, 2010 (now U.S. Pat. No. 8,507,840,
issued Aug. 13, 2013), Ser. No. 12/966,535, filed Dec. 13, 2010
(now U.S. Pat. No. 8,890,271, issued Nov. 18, 2014), Ser. No.
12/910,664, filed Oct. 22, 2010 (now U.S. Pat. No. 9,000,353 issued
Apr. 7, 2015), Ser. No. 14/632,739, filed Feb. 26, 2015, Ser. No.
12/945,492, filed Nov. 12, 2010, Ser. No. 13/047,392, filed Mar.
14, 2011 (now U.S. Pat. No. 8,835,831, issued Sep. 16, 2014), Ser.
No. 14/450,812, filed Aug. 4, 2014, Ser. No. 13/048,635, filed Mar.
15, 2011 (now U.S. Pat. No. 8,835,905, issued Sep. 16, 2014), Ser.
No. 13/106,851, filed May 12, 2011, Ser. No. 13/288,131, filed Nov.
3, 2011, Ser. No. 14/334,848, filed Jul. 18, 2014, Ser. No.
14/032,166, filed Sep. 19, 2013, Ser. No. 13/543,307, filed Jul. 6,
2012, Ser. No. 13/963,847, filed Aug. 9, 2013, Ser. No. 13/693,207,
filed Dec. 4, 2012, 61/869,727, filed Aug. 25, 2013, Ser. No.
14/322,503, filed Jul. 2, 2014, and Ser. No. 14/311,954, filed Jun.
23, 2014, Ser. No. 14/563,781, filed Dec. 8, 2014, 61/968,816,
filed Mar. 21, 2014, Ser. No. 14/516,402, filed Oct. 16, 2014, Ser.
No. 14/516,162, filed Oct. 16, 2014, and 62/161,485, filed May 14,
2015 are each hereby incorporated by reference in their
entirety.
FIELD OF INVENTION
[0002] The embodiments relate to an integrated circuit manufacture,
more particularly, light detecting devices such as a photodiode
(PD) comprising of a nanowire.
BACKGROUND
[0003] An image sensor has a large number of identical sensor
elements (pixels), generally greater than 1 million, in a Cartesian
(square) grid. The distance between adjacent pixels is called the
pitch (p). The area of a pixel is p.sup.2. The area of the
photosensitive element, i.e., the area of the pixel that is
sensitive to light for conversion to an electrical signal, is
normally only about 20% to 30% of the surface area of the
pixel.
[0004] Conventional color image sensors are fabricated with colored
filters arranged in a Bayer configuration. An example of a
convention Bayer filter pattern has a color scheme including red,
green, and blue filters (RGB). The Bayer filter pattern is 50%
green, 25% red and 25% blue, hence is also referred to GRGB or
other permutation such as RGGB. Twice as many green elements as red
or blue are used to mimic the human eye's greater resolving power
with green light. Since each pixel is filtered to record only one
of three colors, the data from each pixel cannot fully determine
color on its own. To obtain a full-color image, various demosaicing
algorithms can be used to interpolate a set of complete red, green,
and blue values for each point in the sensed scene.
[0005] The challenge of a designer is to channel as much of the
light impinging on the pixel to the photosensitive element of the
pixel. There are a number of factors that diminish the amount of
light from reaching the photosensitive element. One factor is the
manner in which the image sensor is constructed.
[0006] The layers of a typical sensor are listed in Table I and
shown in FIG. 1.
TABLE-US-00001 TABLE I Typical Layer Description Thickness (.mu.m)
15 OVERCOAT 2.00 14 MICRO LENS 0.773 13 SPACER 1.40 12 COLOR FILTER
1.20 11 PLANARIZATION 1.40 10 PASS3 0.600 9 PASS2 0.150 8 PASS1
1.00 7 IMD5B 0.350 6 METAL3 31.18 5 IMD2B 0.200 4 METAL2 21.18 3
IMD1B 0.200 2 METAL1 1.18 1 ILD 0.750
[0007] In Table I, typically the first layer on a silicon substrate
is the ILD layer and the topmost layer is the overcoat. In Table I,
ILD refers to a inter-level dielectric layer, METAL1, METAL2 and
METAL3 refer to different metal layers, IMD1B, IMD2B and IMD5B
refer to different inter-metal dielectric layers which are spacer
layers, PASS1, PASS2 and PASS3 refer to different passivation
layers (typically dielectric layers).
[0008] The total thickness of the layers above the silicon
substrate of the image sensor is the stack height (s) of the image
sensor and is the sum of the thickness of the individual layers. In
the example of Table I, the sum of the thickness of the individual
layers is about 11.6 micrometers (.mu.m).
[0009] The space above the photosensitive element of a pixel must
be transparent to light to allow incident light from a full color
scene to impinge on the photosensitive element located in the
silicon substrate. Consequently, no metal layers are routed across
the photosensitive element of a pixel, leaving the layers directly
above the photosensitive element clear.
[0010] The pixel pitch to stack height ratio (p/s) determines the
cone of light (F number) that can be accepted by the pixel and
conveyed to the photosensitive element on the silicon. As pixels
become smaller and the stack height increases, this number
decreases, thereby lowering the efficiency of the pixel.
[0011] More importantly, the increased stack height with greater
number of metal layers obscure the light from being transmitted
through the stack to reach the photosensitive element, in
particular of the rays that impinge the sensor element at an angle.
One solution is to decrease the stack height by a significant
amount (i.e., >2 .mu.m). However, this solution is difficult to
achieve in a standard planar process.
[0012] Another issue, which possibly is the one that most limits
the performance of the conventional image sensors, is that less
than about one-third of the light impinging on the image sensor is
transmitted to the photosensitive element such as a photodiode. In
the conventional image sensors, in order to distinguish the three
components of light so that the colors from a full color scene can
be reproduced, two of the components of light are filtered out for
each pixel using a filter. For example, the red pixel has a filter
that absorbs green and blue light, only allowing red light to pass
to the sensor.
[0013] Yet another issue is that the efficiency of the image sensor
decreases dramatically with increasing departure of the angle of
incident light from normal incidence. In order for the incident
onto the image sensor to be detected, it must reach the sensing
element of the image sensor. Light that strikes the image sensor at
an angle of incidence away from the normal to the image sensor,
some of the light fails to reach the sensing element, resulting in
a decrease in the efficiency of the image sensor.
[0014] The development of nanoscale technology and in particular
the ability to produce nanowires has opened up possibilities of
designing structures and combining materials in ways not possible
in planar technology. There is a need to minimize the dependence of
the efficiency of an image sensor as a function of the angle of
incidence of the incident light.
DESCRIPTION OF THE FIGURES
[0015] FIG. 1 shows a cross sectional view of a conventional image
sensor.
[0016] FIG. 2 shows a cross sectional view of an embodiment of an
image sensor having a microlens.
[0017] FIG. 3 shows an embodiment of an array of nanowires within a
single cavity of the image sensor of an embodiment.
[0018] FIG. 4 shows a schematic of a top view of a device
containing image sensors of the embodiments disclosed herein, each
image sensor having two outputs representing the complementary
colors.
[0019] FIG. 5 shows a response of the single wire of diameter 65 nm
in a 1200 nm cavity as a function of wavelength with illumination
incident at 0 and 10 degrees from the vertical.
[0020] FIG. 6 shows a response of an array of 5 wires of diameter
60 nm in a 1200 nm cavity as a function of wavelength with
illumination incident at 0 and 10 degrees from the vertical.
[0021] FIG. 7 shows a response of the single wire of diameter 65 nm
in a 600 nm cavity as a function of wavelength with illumination
incident at 0 and 10 degrees from the vertical.
DETAILED DESCRIPTION
[0022] In the following detailed description, reference is made to
the accompanying drawings, which form a part hereof. In the
drawings, similar symbols typically identify similar components,
unless context dictates otherwise. The illustrative embodiments
described in the detailed description, drawings, and claims are not
meant to be limiting. Other embodiments may be utilized, and other
changes may be made, without departing from the spirit or scope of
the subject matter presented here.
[0023] The term nanowire refers to a structure that has a thickness
or diameter of the order of nanometers, for example, 100 nanometers
or less and an unconstrained length. Nanowires could include
metallic (e.g., Ni, Pt, Au), semiconducting (e.g., Si, InP, GaN,
etc.), and insulating (e.g., SiO.sub.2,TiO.sub.2) materials.
Molecular nanowires are composed of repeating molecular units
either organic or inorganic. Nanowires could exhibit aspect ratios
(length-to-width ratio) of 1000 or more. As such they could be
referred to as 1-dimensional materials. Nanowires could have many
interesting properties that are not seen in bulk or 3-D materials.
This is because electrons in nanowires could be quantum confined
laterally and thus occupy energy levels that could be different
from the traditional continuum of energy levels or bands found in
bulk materials. As a result, nanowires could have discrete values
of electrical and optical conductance. Examples of nanowires
include inorganic molecular nanowires (Mo.sub.6S.sub.9-xI.sub.x,
Li.sub.2Mo.sub.6Se.sub.6), which could have a diameter of 0.9 nm,
and can be hundreds of micrometers long. Other important examples
are based on semiconductors such as InP, Si, GaN, etc., dielectrics
(e.g. SiO.sub.2,TiO.sub.2), or metals (e.g. Ni, Pt).
[0024] The term excitons refer to electron hole pairs.
[0025] An active element is any type of circuit component with the
ability to electrically control electron and/or hole flow
(electricity controlling electricity or light, or vice versa).
Components incapable of controlling current by means of another
electrical signal are called passive elements. Resistors,
capacitors, inductors, transformers, and even diodes are all
considered passive elements. Active elements include in embodiments
disclosed herein, but are not limited to, an active waveguide,
transistors, silicon-controlled rectifiers (SCRs), light emitting
diodes, and photodiodes. A waveguide is a system or material
designed to confine and direct electromagnetic radiation of
selective wavelengths in a direction determined by its physical
boundaries. Preferably, the selective wavelength is a function of
the diameter of the waveguide. An active waveguide is a waveguide
that has the ability to electrically control electron and/or hole
flow (electricity controlling electricity or light, or vice versa).
This ability of the active waveguide, for example, is one reason
why the active waveguide could be considered to be "active" and
within the genus of an active element.
[0026] An optical pipe is an element to confine and transmit an
electromagnetic radiation that impinges on the optical pipe. The
optical pipe can include a core and a cladding. The core could be a
nanowire. The optical pipe could be configured to separate
wavelengths of an electromagnetic radiation beam incident on the
optical pipe at a selective wavelength through the core and the
cladding, wherein the core is configured to be both a channel to
transmit the wavelengths up to the selective wavelength and an
active element to detect the wavelengths up to the selective
wavelength transmitted through the core. A core and a cladding are
generally complimentary components of the optical pipe and are
configured to separate wavelengths of an electromagnetic radiation
beam incident on the optical pipe at a selective wavelength through
the core and cladding.
[0027] An embodiment relates to an image sensor comprising one or
more nanowires on a substrate of a cavity, the nanowire being
configured to transmit a first portion of an electromagnetic
radiation beam incident on the sensor, and the substrate comprising
an anti-reflective material that absorbs a second portion of the
electromagnetic radiation beam incident on the sensor, wherein the
first portion is substantially different from the second portion,
wherein the anti-reflective material absorbs at least 68 percent of
optical light incident on the anti-reflective material, and wherein
the anti-reflective material does not disrupt an electronic surface
properties of epitaxial silicon to cause surface current leakage or
provide sites for recombination of carriers generated by photons
when the anti-reflective material is contacted with epitaxial
silicon.
[0028] Preferably, the second portion comprises at least a portion
of electromagnetic radiation that comes out from the nanowire.
[0029] Preferably, the anti-reflective material is in an
anti-reflective layer on a front side of the substrate that is
exposed to the electromagnetic radiation beam incident on the
sensor.
[0030] Preferably, the sensor comprises a plurality of nanowires in
each of the cavity.
[0031] Preferably, the nanowire is configured to separate
wavelengths of the electromagnetic radiation beam incident on the
nanowire at a selective wavelength.
[0032] Preferably, the first portion comprises electromagnetic
radiation of wavelengths of light of a certain color and the second
portion comprises electromagnetic radiation of wavelengths of light
of a complementary color.
[0033] Preferably, the sensor is configured to have an array
optical response that substantially resembles a human eye optical
response.
[0034] Preferably, the sensor comprises a plurality of nanowires
and is configured to have a substantially minor change in an array
optical response with a 10.degree. change in a direction of the
electromagnetic radiation beam incident on the sensor.
[0035] Preferably, the anti-reflective layer comprises a plurality
of anti-reflective films configured to absorb electromagnetic
radiation of a plurality of wavelengths.
[0036] Preferably, each of the nanowires is configured to separate
wavelengths of the electromagnetic radiation beam incident on the
nanowire through at a selective wavelength, the sensor further
comprising a pair of photosensitive elements comprising a central
photosensitive element and a peripheral photosensitive element,
wherein the central photosensitive element is operably coupled to
the nanowire and the peripheral photosensitive element is operably
coupled to the substrate around the nanowire.
[0037] Preferably, the nanowire is configured to be an active
element to detect wavelengths of electromagnetic radiation
transmitted through the nanowire.
[0038] Preferably, the active element is configured to be a
photodiode, a charge storage capacitor, or combinations
thereof.
[0039] Preferably, the anti-reflective material absorbs at least
about 90 percent of optical light incident on the anti-reflective
material.
[0040] Preferably, the anti-reflective material reduces a surface
leakage current.
[0041] Preferably, the plurality of nanowires are located so as to
create a regular or semi-regular tessellation wherein a shape is
repeated over a plane without any gaps or overlaps. A regular
tessellation means a tessellation made up of congruent regular
polygons. Regular means that the sides of the polygon are all the
same length. Congruent means that the polygons are all the same
size and shape. A regular polygon has 3 or 4 or 5 or more sides and
angles, all equal. A semi-regular tessellation has two properties:
(1) it is formed by regular polygons; and (2) the arrangement of
polygons at every vertex point is identical.
[0042] Preferably, the tessellation is a regular tessellation such
as a triangular tessellation, a square tessellation, a hexagonal
tessellation or combinations thereof.
[0043] Another embodiment relates to a device comprising the sensor
having a plurality of nanowires in each of the cavity, with each of
the nanowires configured to separate wavelengths of the
electromagnetic radiation beam incident on the nanowire through at
a selective wavelength, the sensor further comprising a pair of
photosensitive elements comprising a central photosensitive element
and a peripheral photosensitive element, wherein the central
photosensitive element is operably coupled to the nanowire and the
peripheral photosensitive element is operably coupled to the
substrate around the nanowire. The device could be an image
sensor.
[0044] Preferably, the nanowire comprises a waveguide.
[0045] The device could further comprise a passivation layer around
the waveguide.
[0046] The device could further comprise a metal layer around the
waveguide.
[0047] Preferably, the device comprises no color or IR filter.
[0048] Preferably, the nanowire has a nanowire index of refraction
(n.sub.1), and a cladding surrounding the nanowire has a cladding
index of refraction (n.sub.2), wherein n.sub.1>n.sub.2,
n.sub.1=n.sub.2, or n.sub.1<n.sub.2.
[0049] Preferably, the selective wavelength is a function of the
diameter of the waveguide.
[0050] The device could further comprise at least a pair of metal
contacts with at least one of the metal contacts being contacted to
the waveguide.
[0051] Another embodiment relates to a device comprising the sensor
having the nanowire configured to be an active element to detect
wavelengths of electromagnetic radiation transmitted through the
nanowire. The device could be an image sensor.
[0052] Preferably, the waveguide is configured to convert energy of
the electromagnetic radiation transmitted through the waveguide and
to generate excitons.
[0053] Preferably, the waveguide comprises a PIN junction that is
configured to detect the excitons generated in the waveguide.
[0054] The device could further comprise an insulator layer around
the waveguide and a metal layer around the insulator layer to form
a capacitor that is configured to collect the excitons generated in
the waveguide and store charge in the capacitor.
[0055] The device could further comprise metal contacts that
connect to the metal layer and waveguide to control and detect the
charge stored in the capacitor.
[0056] The device could further comprise a cladding around the
nanowire, and the substrate comprises a peripheral photosensitive
element, wherein the peripheral photosensitive element is operably
coupled to the cladding.
[0057] Preferably, the substrate comprises an electronic
circuit.
[0058] The device could further comprise a lens structure or an
optical coupler over the nanowire, wherein the lens structure or
the optical coupler is operably coupled to the nanowire.
[0059] The device could further comprise a stack surrounding the
nanowire, the stack comprising metallic layers embedded in
dielectric layers.
[0060] Preferably, a surface of the stack comprises a reflective
surface.
[0061] Preferably, the anti-reflective material is not located on
the nanowire or on a back-side of the substrate opposite to a front
side of the substrate that is exposed to the electromagnetic
radiation beam incident on the sensor.
[0062] Preferably, a wall surface of the cavity has a reflective
surface.
[0063] Preferably, a wall surface of the nanowire has a reflective
surface.
[0064] Preferably, a wall surface of the of the nanowire has
reflective surface.
[0065] Another embodiment relates to an image sensor comprising a
plurality of nanowires on a substrate of a cavity, the nanowire
being configured to transmit a first portion of an electromagnetic
radiation beam incident on the sensor, the substrate absorbs a
second portion of the electromagnetic radiation beam incident on
the sensor, wherein the first portion is substantially different
from the second portion.
[0066] Yet another embodiment relates to an image sensor comprising
a nanowire on a substrate of a cavity, the nanowire being
configured to transmit a first portion of an electromagnetic
radiation beam incident on the sensor, the substrate absorbs a
second portion of the electromagnetic radiation beam incident on
the sensor, wherein the first portion is substantially different
from the second portion, and the ratio of a diameter of the cavity
to a diameter of the nanowire is at less than about 10.
[0067] In yet other embodiments, a plurality of nanowires are
arranged on a regular tessellation.
[0068] In yet other embodiments, as shown in FIG. 2, a coupler that
may take the shape of a micro lens efficiently could be located on
the optical pipe to collect and guide the electromagnetic radiation
into the optical pipe. As shown in FIG. 2, the optical pipe
comprises of a nanowire core of refractive index n.sub.1 surrounded
by a cladding of refractive index n.sub.2.
[0069] In the configuration of the optical pipe of FIG. 2, it is
possible to eliminate pigmented color filters that absorb about 2/3
of the light that impinges on the image sensor. The core functions
as an active waveguide and the cladding of the optical pipe could
function as a passive waveguide with a peripheral photosensitive
element surrounding the core to detect the electromagnetic
radiation transmitted through the passive waveguide of the
cladding. Passive waveguides do not absorb light like color
filters, but can be designed to selectively transmit selected
wavelengths.
[0070] A waveguide, whether passive or active, has a cutoff
wavelength that is the lowest frequency that the waveguide can
propagate. The diameter of the semiconductor nanowire of the core
serves as the control parameter for the cutoff wavelength of the
nanowire.
[0071] The nanowire could also serve as a photodiode by absorbing
the confined light and generating electron hole pairs
(excitons).
Excitons so generated can be detected by using at least one of the
following two designs: (1) A core is made up of a three layers,
semiconductor, insulator and metal thus forming a capacitor to
collect the charge generated by the light induced carriers.
Contacts are made to the metal and to the semiconductor to control
and detect the stored charge. The core could be formed by growing a
nanowire and depositing an insulator layer and a metal layer
surrounding the nanowire. (2) A core having a PIN junction that
induces a potential gradient in the core wire. The PIN junction in
the core could be formed by growing a nanowire and doping the
nanowire core while it is growing as a PIN junction and contacting
it at the appropriate points using the various metal layers that
are part of any device.
[0072] The photosensitive elements of the embodiments typically
comprise a photodiode, although not limited to only a photodiode.
Typically, the photodiode is doped to a concentration from about
1.times.10.sup.16 to about 1.times.10.sup.18 dopant atoms per cubic
centimeter, while using an appropriate dopant.
[0073] The layers 1-11 in FIG. 2 illustrate different stacking
layers similar to layers 1-11 of FIG. 1. The stacking layers
comprise dielectric material-containing and metal-containing
layers. The dielectric materials include as but not limited to
oxides, nitrides and oxynitrides of silicon having a dielectric
constant from about 4 to about 20, measured in vacuum. Also
included, and also not limiting, are generally higher dielectric
constant gate dielectric materials having a dielectric constant
from about 20 to at least about 100. These higher dielectric
constant dielectric materials may include, but are not limited to
hafnium oxides, hafnium silicates, titanium oxides,
barium-strontium titanates (BSTs) and lead-zirconate titanates
(PZTs).
[0074] The dielectric material-containing layers may be formed
using methods appropriate to their materials of composition.
Non-limiting examples of methods include thermal or plasma
oxidation or nitridation methods, chemical vapor deposition methods
(including atomic layer chemical vapor deposition methods) and
physical vapor deposition methods.
[0075] The metal-containing layers could function as electrodes.
Non-limiting examples include certain metals, metal alloys, metal
silicides and metal nitrides, as well as doped polysilicon
materials (i.e., having a dopant concentration from about
1.times.10.sup.18 to about 1.times.10.sup.22 dopant atoms per cubic
centimeter) and polycide (i.e., doped polysilicon/metal silicide
stack) materials. The metal-containing layers may be deposited
using any of several methods. Non-limiting examples include
chemical vapor deposition methods (also including atomic layer
chemical vapor deposition methods) and physical vapor deposition
methods. The metal-containing layers could comprise a doped
polysilicon material (having a thickness typically in the range
1000 to 1500 Angstrom
[0076] The dielectric and metallization stack layer comprises a
series of dielectric passivation layers. Also embedded within the
stack layer are interconnected metallization layers. Components for
the pair of interconnected metallization layers include, but are
not limited to contact studs, interconnection layers,
interconnection studs.
[0077] The individual metallization interconnection studs and
metallization interconnection layers that could be used within the
interconnected metallization layers may comprise any of several
metallization materials that are conventional in the semiconductor
fabrication art. Non-limiting examples include certain metals,
metal alloys, metal nitrides and metal silicides. Most common are
aluminum metallization materials and copper metallization
materials, either of which often includes a barrier metallization
material, as discussed in greater detail below. Types of
metallization materials may differ as a function of size and
location within a semiconductor structure. Smaller and lower-lying
metallization features typically comprise copper containing
conductor materials. Larger and upper-lying metallization features
typically comprise aluminum containing conductor materials.
[0078] The series of dielectric passivation layers may also
comprise any of several dielectric materials that are conventional
in the semiconductor fabrication art. Included are generally higher
dielectric constant dielectric materials having a dielectric
constant from 4 to about 20. Non-limiting examples that are
included within this group are oxides, nitrides and oxynitrides of
silicon. For example, the series of dielectric layers may also
comprise generally lower dielectric constant dielectric materials
having a dielectric constant from about 2 to about 4. Included but
not limiting within this group are hydrogels such as silicon
hydrogel, aerogels like silicon Al, or carbon aerogel,
silsesquioxane spin-on-glass dielectric materials, fluorinated
glass materials, organic polymer materials, and other low
dielectric constant materials such as doped silicon dioxide (e.g.,
doped with carbon, fluorine), and porous silicon dioxide.
[0079] Typically, the dielectric and metallization stack layer
comprises interconnected metallization layers and discrete
metallization layers comprising at least one of copper
metallization materials and aluminum metallization materials. The
dielectric and metallization stack layer also comprises dielectric
passivation layers that also comprise at least one of the generally
lower dielectric constant dielectric materials disclosed above. The
dielectric and metallization stack layer could have an overall
thickness from about 1 to about 4 microns. It may comprise from
about 2 to about 4 discrete horizontal dielectric and metallization
component layers within a stack.
[0080] The layers of the stack layer could be patterned to form
patterned dielectric and metallization stack layer using methods
and materials that are conventional in the semiconductor
fabrication art, and appropriate to the materials from which are
formed the series of dielectric passivation layers. The dielectric
and metallization stack layer may not be patterned at a location
that includes a metallization feature located completely therein.
The dielectric and metallization stack layer may be patterned using
wet chemical etch methods, dry plasma etch methods or aggregate
methods thereof. Dry plasma etch methods as well as e-beam etching
if the dimension needs to be very small, are generally preferred
insofar as they provide enhanced sidewall profile control when
forming the series of patterned dielectric and metallization stack
layer.
[0081] The planarizing layer 11 may comprise any of several
optically transparent planarizing materials. Non-limiting examples
include spin-on-glass planarizing materials and organic polymer
planarizing materials. The planarizing layer 11 could extend above
the optical pipe such that the planarizing layer 11 would have a
thickness sufficient to at least planarize the opening of the
optical pipe, thus providing a planar surface for fabrication of
additional structures within the CMOS image sensor. The planarizing
layer could be patterned to form the patterned planarizing
layer.
[0082] Optionally, there could be a series of color filter layers
12 located upon the patterned planarizing layer 11. The series of
color filter layers, if present, would typically include either the
primary colors of red, green and blue, or the complementary colors
of yellow, cyan and magenta. The series of color filter layers
would typically comprise a series of dyed or pigmented patterned
photoresist layers that are intrinsically imaged to form the series
of color filter layers. Alternatively, the series of color filter
layers may comprise dyed or pigmented organic polymer materials
that are otherwise optically transparent, but extrinsically imaged
while using an appropriate mask layer. Alternative color filter
materials may also be used. The filter could also be filter for a
black and white, or IR sensors wherein the filter cuts off visible
and pass IR predominantly.
[0083] The spacer layer (13) could be one or more layers made of
any material that physically, but not optically, separates the
stacking layers from the micro lens (14). The spacer layer could be
formed of a dielectric spacer material or a laminate of dielectric
spacer materials, although spacer layers formed of conductor
materials are also known. Oxides, nitrides and oxynitrides of
silicon are commonly used as dielectric spacer materials. Oxides,
nitrides and oxynitrides of other elements are not excluded. The
dielectric spacer materials may be deposited using methods
analogous, equivalent or identical to the methods described above.
The spacer layer could be formed using a blanket layer deposition
and etchback method that provides the spacer layer with the
characteristic inward pointed shape.
[0084] The micro lens (14) may comprise any of several optically
transparent lens materials that are known in the art. Non-limiting
examples include optically transparent inorganic materials,
optically transparent organic materials and optically transparent
composite materials. Most common are optically transparent organic
materials. Typically the lens layers could be formed incident to
patterning and reflow of an organic polymer material that has a
glass transition temperature lower than the series of color filter
layers 12, if present, or the patterned planarizing layer 11.
[0085] In the optical pipe of FIG. 2, the high index material in
the core could, for example, be silicon nitride having a refractive
index of about 2.0. The lower index cladding layer material could,
for example, be a glass, for example a material selected from Table
II, having a refractive index about 1.5.
TABLE-US-00002 TABLE II Typical Material Index of Refraction Micro
Lens (Polymer) 1.583 Spacer 1.512 Color Filter 1.541 Planarization
1.512 PESiN 2.00 PESiO 1.46 SiO 1.46
In Table II, PESiN refers to plasma enhanced SiN and PESiO refers
to plasma enhanced SiO.
[0086] Optionally, a micro lens could be located on the optical
pipe near the incident electromagnetic radiation beam receiving end
of the image sensor. The function of the micro lens or in more
general terms is to be a coupler, i.e., to couple the incident
electromagnetic radiation beam into the optical pipe. If one were
to choose a micro lens as the coupler in this embodiment, its
distance from the optical pipe would be much shorter than to the
photosensitive element, so the constraints on its curvature are
much less stringent, thereby making it implementable with existing
fabrication technology.
[0087] The shape of the optical pipe could be different for
different embodiments. In one configuration, the optical pipe could
cylindrical, that is, the diameter of the pipe remains the
substantially the same throughout the length of the optical pipe.
In another configuration, the optical pipe could conical, where the
upper diameter of the cross sectional area of the optical pipe
could be greater or smaller than the lower diameter of the cross
sectional area of the optical pipe. The terms "upper" and "lower"
refer to the ends of the optical pipe located closer to the
incident electromagnetic radiation beam receiving and exiting ends
of the image sensor. Other shapes include a stack of conical
sections.
[0088] Table II lists several different glasses and their
refractive indices. These glasses could be used for the manufacture
of the optical pipe such that refractive index of the core is
higher than that of the cladding. The image sensors of the
embodiments could be fabricated using different transparent glasses
having different refractive indices without the use of pigmented
color filters.
[0089] By nesting optical pipes that function as waveguides and
using a micro lens coupler as shown in FIG. 2, an array of image
sensors could be configured to obtain complementary colors having
wavelengths of electromagnetic radiation separated at a cutoff
wavelength in the core and cladding of each optical pipe of every
image sensor. The complementary colors are generally two colors
when mixed in the proper proportion produce a neutral color (grey,
white, or black). This configuration also enables the capture and
guiding of most of the electromagnetic radiation incident beam
impinging on the micro lens to the photosensitive elements (i.e.,
photodiodes) located at the lower end of the optical pipe. Two
adjacent or substantially adjacent image sensors with different
color complementary separation can provide complete information to
reconstruct a full color scene according to embodiments described
herein. This technology of embodiments disclosed herein can further
supplant pigment based color reconstruction for image sensing which
suffers from the inefficiency of discarding (through absorption)
the non selected color for each pixel.
[0090] Each physical pixel of a device containing an image sensor
of the embodiments disclosed herein would have two outputs
representing the complementary colors, e.g., cyan (or red)
designated as output type 1 and yellow (or blue) designated as
output type 2. These outputs would be arranged as follows: [0091] 1
2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 . . . . [0092] 2 1 2 1 2 1 2 1 2 1 2
1 2 1 2 1 . . . . [0093] 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 . . . .
[0094] . . . .
[0095] Each physical pixel would have complete luminance
information obtained by combining its two complementary outputs. As
a result, the same image sensor can be used either as a full
resolution black and white or full color sensor.
[0096] In the embodiments of the image sensors disclosed herein,
the full spectrum of wavelengths of the incident electromagnetic
radiation beam (e.g., the full color information of the incident
light) could be obtained by the appropriate combination of two
adjacent pixels either horizontally or vertically as opposed to 4
pixels for the conventional Bayer pattern.
[0097] Depending on minimum transistor sizes, each pixel containing
an image sensor of the embodiments disclosed herein could be as
small as 1 micron or less in pitch and yet have sufficient
sensitivity. This could open the way for contact imaging of very
small structures such as biological systems.
[0098] The embodiments, which include a plurality of embodiments of
an image sensor, as well as methods for fabrication thereof, will
be described in further detail within the context of the following
description. The description is further understood within the
context of the drawings described above. The drawings are for
illustrative purposes and as such are not necessarily drawn to
scale.
[0099] An embodiment of a compound pixel comprises a system of two
pixels, each having a core of a different diameter such that cores
have diameters d.sub.1 and d.sub.2 for directing light of different
wavelengths (.lamda..sub.B and .lamda..sub.R). The two cores also
serve as photodiodes to capture light of wavelengths .lamda..sub.B
and .lamda..sub.R. The claddings of the two image sensors serve for
transmitting the light of wave length .lamda..sub.w-B and
.lamda..sub.w-R. The light of wave length .lamda..sub.w-B and
.lamda..sub.w-R transmitted through the cladding is detected by the
peripheral photosensitive elements surrounding the cores. Note that
(w) refers to the wavelength of white light. Signals from the 4
photodiodes (two located in the cores and two located in or on the
substrate surrounding the core) in the compound pixel are used to
construct color.
[0100] The embodiments include a nanostructured photodiode (PD)
according to the embodiments comprise a substrate and an upstanding
nanowire protruding from the substrate. A pn-junction giving an
active region to detect light may be present within the structure.
The nanowire, a part of the nanowire, or a structure in connection
with the nanowire, forms a waveguide directing and detecting at
least a portion of the light that impinges on the device. In
addition the waveguide doubles up as spectral filter that enables
the determination of the color range of the impinging light.
[0101] A nanostructured PD according to the embodiments comprises
of an upstanding nanowire. For the purpose of this application an
upstanding nanowire should be interpreted as a nanowire protruding
from the substrate in some angle, the upstanding nanowire for
example being grown from the substrate, preferably by as
vapor-liquid-solid (VLS) grown nanowires. The angle with the
substrate will typically be a result of the materials in the
substrate and the nanowire, the surface of the substrate and growth
conditions. By controlling these parameters it is possible to
produce nanowires pointing in only one direction, for example
vertical, or in a limited set of directions. For example nanowires
and substrates of zinc-blend and diamond semiconductors composed of
elements from columns III, V and IV of the periodic table, such
nanowires can be grown in the [111] directions and then be grown in
the normal direction to any {111} substrate surface. Other
directions given as the angle between normal to the surface and the
axial direction of the nanowire include 70,53.degree. {111},
54,73.degree. {100}, and 35,27.degree. and 90.degree., both to
{110}. Thus the nanowires define one, or a limited set, of
directions.
[0102] According to the embodiments, a part of the nanowire or
structure formed from the nanowire is used as a waveguide directing
and confining at least a portion of the light impinging on the
nanostructured PD in a direction given by the upstanding nanowire.
The waveguiding nanostructured PD structure could include a high
refractive index core with one or more surrounding cladding with
refractive indices less than that of the core. The structure is
either circular symmetrical or close to being circular symmetrical.
Light waveguiding in circular symmetrical structures are well know
for fiber-optic applications and many parallels can be made to the
area of rare-earth-doped fiber optic devices. However, one
difference is that fiber amplifier are optically pumped to enhance
the light guided through them while the described nanostructured PD
can be seen as an efficient light to electricity converter. One
well known figure of merit is the so called Numerical Aperture, NA.
The NA determines the angle of light captured by the waveguide. The
NA and angle of captured light is an important parameter in the
optimization of a new PD structure.
[0103] For a PD operating in IR and above IR, using GaAs is good,
but for a PD operating in the visible light region, silicon would
be preferable. For example to create circuits, Si and doped Si
materials are preferable. Similarly, for a PD working in the
visible range of light, one would prefer to use Si.
[0104] In one embodiment, the typical values of the refractive
indexes for III-V semiconductor core material are in the range from
2.5 to 5.5 when combined with glass type of cladding material (such
as SiO.sub.2 or Si.sub.3N.sub.4) having refractive indexes ranging
from 1.4 to 2.3. A larger angle of capture means light impinging at
larger angles can be coupled into the waveguide for better capture
efficiency.
[0105] One consideration in the optimization of light capture is to
provide a coupler into the nanowire structure to optimize light
capture into the structure. In general, it would be preferred to
have the NA be highest where the light collection takes place. This
would maximize the light captured and guided into the PD.
[0106] A nanostructured PD according to the embodiments could
comprise a substrate and a nanowire epitaxially grown from the
substrate in an defined angle .theta.. A portion of or all of the
nanowire could be arranged to act as a waveguiding portion
directing at least a portion of the impinging light in a direction
given by the elongated direction of the nanowire, and will be
referred to as a waveguide. In one possible implementation, a
pn-junction necessary for the diode functionality is formed by
varying the doping of the wire along its length while it is
growing. Two contact could be provided on the nanowire for example
one on top or in a wrapping configuration on the circumferential
outer surface and the other contact could be provided in the
substrate. The substrate and part of the upstanding structure may
be covered by a cover layer, for example as a thin film as
illustrated or as material filling the space surrounding the
nanostructured PD.
[0107] The nanowire could have a diameter in the order of 50 nm to
500 nm, The length of the nanowire could be of the order of 1 to 10
.mu.m. The pn-junction results in an active region arranged in the
nanowire. Impinging photons in the nanowire are converted to
electron hole pairs and in one implementation are subsequently
separated by the electric fields generated by the PN junction along
the length of the nanowire. The materials of the different members
of the nanostructured PD are chosen so that the nanowire will have
good waveguiding properties vis-a-vis the surrounding materials,
i.e. the refractive index of the material in the nanowire should
preferably be larger than the refractive indices of the surrounding
materials.
[0108] In addition, the nanowire may be provided with one or more
layers. A first layer, may be introduced to improve the surface
properties (i.e., reduce charge leakage) of the nanowire. Further
layers, for example an optical layer may be introduced specifically
to improve the waveguiding properties of the nanowire, in manners
similar to what is well established in the area of fiber optics.
The optical layer typically has a refractive index in between the
refractive index of the nanowire and the surrounding cladding
region material. Alternatively the intermediate layer has a graded
refractive index, which has been shown to improve light
transmission in certain cases. If an optical layer is utilized the
refractive index of the nanowire, n.sub.w, should define an
effective refractive index for both the nanowire and the
layers.
[0109] The ability to grow nanowires with well defined diameters,
as described above and exemplified below, could be to optimize the
waveguiding properties of the nanowire or at least the waveguide
with regards to the wavelength of the light confined and converted
by the nanostructured PD. The diameter of the nanowire is chosen so
as to have a favorable correspondence to the wavelength of the
desired light. Preferably the dimensions of the nanowire are such
that a uniform optical cavity, optimized for the specific
wavelength of the produced light, is provided along the nanowire.
The core nanowire must be sufficiently wide to capture the desired
light. A rule of thumb would be that diameter must be larger than
.lamda./2n.sub.w, wherein .lamda. is the wavelength of the desired
light and n.sub.w is the refractive index of the nanowire. As an
example a diameter of about 60 nm may be appropriate to confine
blue light only and one 80 nm may be appropriate for to confine
both blue and green light only in a silicon nanowire.
[0110] In the infra-red and near infra-red a diameter above 100 nm
would be sufficient. An approximate preferred upper limit for the
diameter of the nanowire is given by the growth constrains, and is
in the order of 500 nm. The length of the nanowire is typically and
preferably in the order of 1-10 .mu.m, providing enough volume for
the light conversion region
[0111] A reflective layer is in one embodiment, provided on the
substrate and extending under the wire. The purpose of the
reflective layer is to reflect light that is guided by the wire but
has not been absorbed and converted to carriers in the
nanostructured PD. The reflective layer is preferably provided in
the form of a multilayered structure comprising repeated layers of
silicates for example, or as a metal film. If the diameter of the
nanowire is sufficiently smaller than the wavelength of the light a
large fraction of the directed light mode will extend outside the
waveguide, enabling efficient reflection by a reflective layer
surrounding the narrow the nanowire waveguide
[0112] An alternative approach to getting a reflection in the lower
end of the waveguide core is to arrange a reflective layer in the
substrate underneath the nanowire. Yet another alternative is to
introduce reflective means within the waveguide. Such reflective
means can be a multilayered structure provided during the growth
process of the nanowire, the multilayered structure comprising
repeated layers of for example SiN.sub.x/SiO.sub.x
(dielectric).
[0113] To form the pn-junction necessary for light detection at
least part of the nanostructure is preferably doped. This is done
by either changing dopants during the growth of the nanowire or
using a radial shallow implant method on the nanowire once it is
grown.
[0114] Considering systems where nanowire growth is locally
enhanced by a substance, as vapor-liquid-solid (VLS) grown
nanowires, the ability to alter between radial and axial growth by
altering growth conditions enables the procedure (nanowire growth,
mask formation, and subsequent selective growth) can be repeated to
form nanowire/3D-sequences of higher order. For systems where
nanowire growth and selective growth are not distinguished by
separate growth conditions it may be better to first grow the
nanowire along the length and by different selective growth steps
grow different types of 3D regions.
[0115] A fabrication method according to the present embodiments in
order to fabricate a light detecting pn-diode/array with active
nanowire region(s) formed of Si, comprises the steps of:
1. Defining of local catalyst/catalysts on a silicon substrate by
lithography. 2. Growing silicon nanowire from local catalyst. The
growth parameters adjusted for catalytic wire growth. 3. Radial
growing of other semiconductor, passivation, thin insulator or
metal concentric layer around the nanowire (cladding layer). 4.
Forming contacts on the PD nanwire and to the substrate and to
other metal layers in a CMOS circuit.
[0116] The growth process can be varied in known ways, for example,
to include heterostructures in the nanowires, provide reflective
layers etc.
[0117] Depending on the intended use of the nanostructured PD,
availability of suitable production processes, costs for materials
etc., a wide range of materials can be used for the different parts
of the structure. In addition, the nanowire based technology allows
for defect free combinations of materials that otherwise would be
impossible to combine. The III-V semiconductors are of particular
interest due to their properties facilitating high speed and low
power electronics. Suitable materials for the substrate include,
but is not limited to: Si, GaAs, GaP, GaP:Zn, GaAs, InAs, InP, GaN,
Al.sub.2O.sub.3, SiC, Ge, GaSb, ZnO, InSb, SOI
(silicon-on-insulator), CdS, ZnSe, CdTe. Suitable materials for the
nanowire 110 include, but is not limited to: Si, GaAs (p), InAs,
Ge, ZnO, InN, GaInN, GaNAlGaInN, BN, InP, InAsP, GaInP, InGaP:Si,
InGaP:Zn, GaInAs, AlInP, GaAlInP, GaAlInAsP, GaInSb, InSb. Possible
donor dopants for e.g. GaP, Te, Se, S, etc, and acceptor dopants
for the same material are Zn, Fe, Mg, Be, Cd, etc. It should be
noted that the nanowire technology makes it possible to use
nitrides such as SiN, GaN, InN and AlN, which facilitates
fabrication of PDs detecting light in wavelength regions not easily
accessible by conventional technique. Other combinations of
particular commercial interest include, but is not limited to GaAs,
GaInP, GaAlInP, GaP systems. Typical doping levels range from
10.sup.18 to 10.sup.20 A person skilled in the art is though
familiar with these and other materials and realizes that other
materials and material combinations are possible.
[0118] The appropriateness of low resistivity contact materials are
dependent on the material to be deposited on, but metal, metal
alloys as well as non-metal compounds like Al, AlSi, TiSi.sub.2,
TiN, W, MoSi.sub.2, PtSi, CoSi.sub.2, WSi.sub.2, In, AuGa, AuSb,
AuGe, PdGe, Ti/Pt/Au, Ti/Al/Ti/Au, Pd/Au, ITO (InSnO), etc. and
combinations of e.g. metal and ITO can be used.
[0119] The substrate is an integral part of the device, since it
also contains the photodiodes necessary to detect light that has
not been confined to the nanowire. The substrate in addition also
contains standard CMOS circuits to control the biasing,
amplification and readout of the PD as well as any other CMOS
circuit deemed necessary and useful. The substrate include
substrates having active devices therein. Suitable materials for
the substrates include silicon and silicon-containing materials.
Generally, each sensor element of the embodiments include a
nanostructured PD structure comprise a nanowire, a cladding
enclosing at least a portion of the nanowire, a coupler and two
contacts.
[0120] The fabrication of the nanostructured PDs on silicon is
possible to the degree that the nanowires are uniformly aligned the
(111) direction normal to the substrates and essentially no
nanowires are grown in the three declined (111) directions that
also extends out from the substrate. The well aligned growth of
III-V nanowires in predefined array structures on silicon
substrates, is preferred for successful large scale fabrication of
optical devices, as well as most other applications.
[0121] PD devices build on silicon nanowires are of high commercial
interest due to their ability to detect light of selected
wavelengths not possible with other material combinations. In
addition they allow the design of a compound photodiode that allows
the detection of most of the light that impinges on a image
sensor.
[0122] The silicon nanowire of the embodiments disclosed herein
could be made as follows. A substrate is provided which comprises
silicon having a silicon dioxide surface. The surface can be
modified with a surface treatment to promote adsorption of a gold
nanoparticle. Onto this modified surface, the gold nanoparticle can
be formed by deposition of a gold layer, followed by removal of the
gold layer over regions other than desired location of the gold
nanoparticle. The gold nanoparticle can be surface treated to
provide for steric stabilization. In other words, tethered,
sterically stabilized gold nanoparticles can be used as seeds for
further synthesis of nanowires, wherein the gold nanoparticles are
adsorbed to the modified silicon substrate. The degradation of
diphenyl silane (DPS) to forms silicon atoms. These silicon atoms
are introduced into the deep cavity in the stacking layers of the
IC. The silicon atoms attach to the gold nanoparticle and a silicon
nanowire crystallizes from the gold nanoparticle seed upon
saturation of the gold nanoparticle with silicon atoms.
[0123] The nanowire could have a PN or PIN junction that induces a
potential gradient in the nanowire. The PN or PIN junction could be
formed by growing a nanowire and doping the nanowire core while it
is growing as a PIN junction. For example, the doping of the
nanowire could have two levels of doping to form N and P, or in
other embodiments, the nanowire could comprise P, I and N regions
to form a PIN photodiode. Yet, another possibility is doping the
wire along its length in concentric circles to form P and N or P, I
and N regions to form a PN or PIN photodiode. The PN or PIN
junction nanowire (also referred to as a PN or PIN photodiode) is
contacted at the appropriate points along PN or PIN junction
nanowire using the various metal layers that are part of any device
to detect the charge generated by the light induced carriers in the
PN or PIN junction nanowire.
[0124] In other embodiments, there could be multiple nanowires in a
single deep cavity as shown in FIG. 3 wherein at the bottom is a
silicon substrate on which there is an array of nanowires over
which is a coupler (shown as an oval), and over the coupler is a
region (shown as rectangular box) through which light comes in to
the coupler.
[0125] The recognition of color and luminance by the embodiments of
the image sensors could be done by color reconstruction. Each
compound pixel has complete luminance information obtained by
combining its two complementary outputs. As a result, the same
image sensor can be used either as a full resolution black and
white or full color sensor.
[0126] The color reconstruction could be done to obtain full color
information by the appropriate combination of two adjacent pixels,
which could be one embodiment of a compound pixel, either
horizontally or vertically. The support over which color
information is obtained is less than the dimension of two pixels as
opposed to 4 for the Bayer pattern.
[0127] Each physical pixel of a device containing an image sensor
of the embodiments disclosed herein would have two outputs
representing the complementary colors, e.g., cyan, red (C, R)
designated as output type 1 or yellow, blue (Y, B) designated as
output type 2 as shown in FIG. 4. These four outputs of two pixels
of a compound pixel can be resolved to reconstruct a full color
scene of an image viewed by a device containing the image sensors
of the embodiments described herein.
Example 1
Angle Dependence an Image Sensor Having a Single and Multiple
Nanowires
[0128] A nanowire capacitor-photodiode has the properties of
converting incoming light into charge stored in the capacitor. The
efficiency with which light is coupled into the nanowire, however,
is dependent on the angle of the incident light. Simulations
indicate that the efficiency decreases with increasing departure of
the angle from normal incidence. Light that fails to couple to the
nanowire could eventually end up either in the substrate or be
reflected out of the cavity altogether. With increasing departure
from normal incidence, the response of the nanowire decreases but
that of the substrate increases. This could lead to errors to in
scene color recognition and illumination, particularly for a non
telecentric lens.
[0129] A nanowire array capacitor-photodiode could display a
significantly reduced angular dependence in its response. In
addition to optical response, the optimal number of nanowires in a
single cavity could depend on the process and fabrication of the
nanowire capacitor-photodiode. Simulations indicate five nanowires
in a single cavity could dramatically reduce angular dependence as
shown in FIGS. 5 and 6. The units of the y axis are arbitrary as
the simulation results shown in FIGS. 5 and 6 is the show the
relative change in the response as a function of wavelength with
different angle of light incidence. The diameter of the cavity
containing the single or array of nanowires whose simulation
results are shown in FIGS. 5 and 6 was 1200 nm. Also, in arriving
at the simulations whose results are shown in FIGS. 5 and 6, it was
assumed that all light not absorbed by the nanowire would to be
absorbed in the substrate.
[0130] FIG. 5 shows a plot entitled "wire.sub.--65 nm_angle_plot"
simulating absorption in a 65 nm nanowire located concentrically in
a cavity of 1200 nm and by the substrate. The solid line is the
response of the single wire of diameter 65 nm as a function of
wavelength with illumination incident in a perpendicular direction
and the dashed line is the same response but for a wire illuminated
at 10 degrees from vertical. The dotted line is the response of the
substrate for vertical illumination and the dash dot line is the
same for illumination at 10 degrees. The term response refers to
the ability to absorb incident light.
[0131] FIG. 5 shows the following features of a single nanowire
capacitor-photodiode in a cavity: (1) the response of the single
nanowire has a maximum around 480 nm wavelength of light; (2) the
response of the single nanowire changes substantially with a change
in the angle of light incidence from perpendicular to the nanowire
to 10 degrees from the perpendicular axis; (3) the response of the
substrate has a maximum around 550 nm wavelength of light; and (4)
the response of the substrate is greater for the angle of light
incidence of 10 degrees from the perpendicular axis than for the
angle of light incidence perpendicular to the nanowire.
[0132] FIG. 6 shows a plot entitled "array.sub.--60 nm_angle_plot."
The solid line is the response of an array of 5 nanowires each of
diameter 60 nm as a function of wavelength with illumination
incident in a perpendicular direction and the dashed line is the
same response but for an array illuminated at 10 degrees from
vertical. The dotted line is the response of the substrate for
vertical illumination and the dash dot line is the same for
illumination at 10 degrees. The term response refers to the ability
to absorb incident light.
[0133] The 5 nanowires were arranged in a diamond with 4 nanowires
located at the four corners of the diamond and one nanowire located
at the center of the diamond, which was also the center of the
cavity of diameter 1200 nm. The distance between the central
nanowire and each of the four corner nanowires was 300 nm.
[0134] FIG. 6 shows the following features of a single nanowire
photodiode in a cavity: (1) the response of the single nanowire has
a maximum around 480 nm wavelength of light; (2) the response of
the single nanowire does not change substantially with a change in
the angle of light incidence from perpendicular to the nanowire to
10 degrees from the perpendicular axis; (3) the response of the
substrate has a maximum around 550 nm wavelength of light, but the
magnitude of the response of the substrate is substantially smaller
than that of the response of the substrate of a single nanowire
capacitor-photodiode in a cavity; and (4) the response of the
substrate is almost the same for the angle of light incidence of 10
degrees from the perpendicular axis as that for the angle of light
incidence perpendicular to the nanowire.
Example 2
An Array of Nanowires with Anti-Reflective Material on the
Substrate
[0135] In Example 1, the response of a single nanowire
capacitor-photodiode in a cavity clearly demonstrates that a
substantially portion of the light starting from about a wavelength
of 450 nm has to be absorbed by the surface in the cavity. In
short, an appropriate performance of the nanowire PD depends on all
light not absorbed by the nanowire to be absorbed in the
substrate.
[0136] Whenever a ray of light moves from one medium to another
(for example, when light enters a sheet of glass after travelling
through air), some portion of the light is reflected from the
surface (known as the interface) between the two media. The
strength of the reflection depends on the refractive indices of the
two media as well as the angle of the surface to the beam of light.
The exact value can be calculated using the Fresnel equations.
[0137] When the light meets the interface at normal incidence
(perpendicularly to the surface), the intensity of light reflected
is given by the reflection coefficient or reflectance, R:
R = ( n 0 - n S n 0 + n S ) 2 ##EQU00001##
where n.sub.0 and n.sub.S are the refractive indices of the first
and second media, respectively. The value of R varies from 0.0 (no
reflection) to 1.0 (all light reflected) and is usually quoted as a
percentage. Complementary to R is the transmission coefficient or
transmittance, T. If absorption and scattering are neglected, then
the value T is always 1-R. Thus if a beam of light with intensity I
is incident on the surface, a beam of intensity RI is reflected,
and a beam with intensity TI is transmitted into the medium.
[0138] Applying these principles to the embodiments of the
invention, in an example, if the index of refraction of Si for red
light is 4 and that of the cavity filled with SiO.sub.2 is about
1.5, R would then be equal to about 0.2. This means that 20% of the
incident power is reflected at the substrate and is not
detected.
[0139] According to the embodiments of the invention, strategies
for minimizing the reflection of incident light on the substrate of
the cavity is to provide an anti-reflective material in or on the
substrate of the cavity. An anti-reflective material could be in
the form of a coating and acts to reduce the reflection at the
surface, allowing a higher level of visible light transmission.
Anti-reflective or antireflection (AR) coatings are a type of
optical coating applied to the surface of optical devices to reduce
reflection. This improves the efficiency of the system since less
light is lost. The methods for implementing anti-reflective
coatings include the use of alternating layers of a low-index
material like silica and a higher-index material to obtain
reflectivity as low as 0.1% at a single wavelength or over a range
of wavelengths.
[0140] In one embodiment, the anti-reflective material could work
near a single light frequency. Other embodiments could use a green
antireflective coating, for example, on the substrate of the cavity
containing the blue absorbing nanowire, and a red anti-reflective
coating with a cyan absorbing nanowire.
[0141] Many AR coatings have transparent thin film structures with
alternating layers of contrasting refractive index. Layer
thicknesses are chosen to produce destructive interference in the
beams reflected from the interfaces, and constructive interference
in the corresponding transmitted beams. This makes the structure's
performance change with wavelength and incident angle, so that
color effects often appear at oblique angles. A wavelength range
must be specified when designing or ordering such coatings, but
good performance can often be achieved for a relatively wide range
of frequencies: usually a choice of IR, visible, or UV is
offered.
[0142] The simplest interference AR coating could be a single
quarter-wave layer of transparent material whose refractive index
is the square root of the substrate's refractive index. This
theoretically gives zero reflectance at the center wavelength and
decreased reflectance for wavelengths in a broad band around the
center. By using alternating layers of a low-index material like
silica and a higher-index material it is possible to obtain
reflectivities as low as 0.1% at a single wavelength.
[0143] One embodiment of the AR coating could be ultraviolet
anti-reflection (UAR) coating. This ultraviolet anti-reflection
coating could reduce surface reflection from quartz, fused silica,
semiconductor silicon substrates to less than 0.3% from 0.2 to 0.3
microns. UAR coatings are designed to promote effective
transmission of light in the ultraviolet wavelengths.
[0144] Anti-reflective coatings include several different
sub-layers comprising many different materials such as, but not
limited to, Al.sub.2O.sub.3, ZrO.sub.3, MgF.sub.2, SiO.sub.2,
cryolite, LiF. ThF.sub.4, CeF.sub.3, PbF.sub.2, ZnS, ZnSc, Si, Te,
MgO, Y.sub.2O.sub.3, Sc.sub.2O.sub.3, SiO, HfO.sub.2, ZrO.sub.2,
CeO.sub.2, Nb.sub.2O.sub.3, Ta.sub.2O.sub.5, and TiO.sub.2. The
thickness of each sublayer is often related to an even whole number
division of the wavelength of light that is most preferred to be
transmitted through the coated material.
[0145] Another embodiment of an anti-reflective coating could be a
treated silicon layer. An untreated silicon layer absorbs about
67.4 percent of light shone upon it--meaning that nearly one-third
of that light is reflected away. In the embodiments of the
invention, a silicon surface could be treated with a nanoengineered
reflective coating such that the material could absorb 90 or more
of the optical light directed onto the material. For example, the
nanoengineered anti-reflective material of Lin disclosed in
"Realization of a Near Perfect Antireflection Coating for Silicon
Solar Energy," published in November 2008 by the journal Optics
Letters, which is incorporated herein in its entirety by reference,
absorbed 96.21 percent of light shone upon it.
[0146] The new coating could also successfully tackle the tricky
challenge of angles. Typical antireflective coatings are engineered
to transmit light of one particular wavelength. The new coating
could stack multiple layers, for example seven layers, one on top
of the other, in such a way that each layer enhances the
antireflective properties of the layer below it. These additional
layers also help to bend the flow of light to an angle that
augments the coating's antireflective properties. This means that
each layer not only transmits light, it also helps to capture any
light that may have otherwise been reflected off of the layers
below it.
[0147] For example, the seven layers, each with a height of 50
nanometers to 100 nanometers, could be made up of silicon dioxide
and titanium dioxide nanorods positioned at an oblique angle such
that light is captured between the nanorods. The nanorods could be
attached to a silicon substrate via chemical vapor disposition. The
new coating could be affixed to nearly any photovoltaic materials,
including III-V multi-junction and cadmium telluride.
Example 3
Effect of Cavity Size on the Angle Dependence of a Single
Nanowire
[0148] A nanowire capacitor-photodiode in a smaller cavity could
display a significantly reduced angular dependence in its response
when the ratio of a diameter of the cavity to a diameter of the
nanowire is at less than about 10, preferably less than about 9,
more preferably less than 8, and most preferably less than 7.
[0149] Simulations indicate a nanowire of 65 nm in a single cavity
of 600 nm could dramatically reduce angular dependence as shown in
FIG. 7 as compared to the angular dependence of nanowire of 65 nm
in a single cavity of 1200 nm shown in FIG. 5. In arriving at the
simulations whose results are shown in FIGS. 5 and 7, it was
assumed that all light not absorbed by the nanowire would to be
absorbed in the substrate.
[0150] FIG. 7 shows a plot entitled "wire.sub.--65 nm_angle_plot"
simulating absorption in a 65 nm nanowire located concentrically in
a cavity of 600 nm and by the substrate. The solid line is the
response of the single wire of diameter 65 nm as a function of
wavelength with illumination incident in a perpendicular direction
and the dashed line is the same response but for a wire illuminated
at 10 degrees from vertical. The dotted line is the response of the
substrate for vertical illumination and the dash dot line is the
same for illumination at 10 degrees. The term response refers to
the ability to absorb incident light.
[0151] FIG. 7 shows the following features of a single nanowire
capacitor-photodiode in a cavity: (1) the response of the single
nanowire has a maximum around 480 nm wavelength of light; (2) the
response of the single nanowire does not change substantially with
a change in the angle of light incidence from perpendicular to the
nanowire to 10 degrees from the perpendicular axis; (3) the
response of the substrate has a maximum around 600 nm wavelength of
light; and (4) the response of the substrate is substantially the
same for the angle of light incidence of 10 degrees from the
perpendicular axis and for the angle of light incidence
perpendicular to the nanowire.
[0152] By comparing FIGS. 5 and 7, one notices that the scale is
different as there is less light (less photons) collected by the
narrower cavity of 600 nm versus a larger cavity of 1200 nm and
that the relative change between 0 degrees and 10 degrees is much
smaller.
[0153] The foregoing detailed description has set forth various
embodiments of the devices and/or processes via the use of
diagrams, flowcharts, and/or examples. Insofar as such diagrams,
flowcharts, and/or examples contain one or more functions and/or
operations, it will be understood by those within the art that each
function and/or operation within such diagrams, flowcharts, or
examples can be implemented, individually and/or collectively, by a
wide range of hardware, software, firmware, or virtually any
combination thereof. In one embodiment, several portions of the
subject matter described herein may be implemented via Application
Specific Integrated Circuits (ASICs), Field Programmable Gate
Arrays (FPGAs), digital signal processors (DSPs), or other
integrated formats. However, those skilled in the art will
recognize that some aspects of the embodiments disclosed herein, in
whole or in part, can be equivalently implemented in integrated
circuits, as one or more computer programs running on one or more
computers (e.g., as one or more programs running on one or more
computer systems), as one or more programs running on one or more
processors (e.g., as one or more programs running on one or more
microprocessors), as firmware, or as virtually any combination
thereof, and that designing the circuitry and/or writing the code
for the software and or firmware would be well within the skill of
one of skill in the art in light of this disclosure. In addition,
those skilled in the art will appreciate that the mechanisms of the
subject matter described herein are capable of being distributed as
a program product in a variety of forms, and that an illustrative
embodiment of the subject matter described herein applies
regardless of the particular type of signal bearing medium used to
actually carry out the distribution. Examples of a signal bearing
medium include, but are not limited to, the following: a recordable
type medium such as a floppy disk, a hard disk drive, a Compact
Disc (CD), a Digital Video Disk (DVD), a digital tape, a computer
memory, etc.; and a transmission type medium such as a digital
and/or an analog communication medium (e.g., a fiber optic cable, a
waveguide, a wired communications link, a wireless communication
link, etc.).
[0154] Those skilled in the art will recognize that it is common
within the art to describe devices and/or processes in the fashion
set forth herein, and thereafter use engineering practices to
integrate such described devices and/or processes into data
processing systems. That is, at least a portion of the devices
and/or processes described herein can be integrated into a data
processing system via a reasonable amount of experimentation. Those
having skill in the art will recognize that a typical data
processing system generally includes one or more of a system unit
housing, a video display device, a memory such as volatile and
non-volatile memory, processors such as microprocessors and digital
signal processors, computational entities such as operating
systems, drivers, graphical user interfaces, and applications
programs, one or more interaction devices, such as a touch pad or
screen, and/or control systems including feedback loops and control
motors (e.g., feedback for sensing position and/or velocity;
control motors for moving and/or adjusting components and/or
quantities). A typical data processing system may be implemented
utilizing any suitable commercially available components, such as
those typically found in data computing/communication and/or
network computing/communication systems.
[0155] The herein described subject matter sometimes illustrates
different components contained within, or connected with, different
other components. It is to be understood that such depicted
architectures are merely exemplary, and that in fact many other
architectures can be implemented which achieve the same
functionality. In a conceptual sense, any arrangement of components
to achieve the same functionality is effectively "associated" such
that the desired functionality is achieved. Hence, any two
components herein combined to achieve a particular functionality
can be seen as "associated with" each other such that the desired
functionality is achieved, irrespective of architectures or
intermedial components. Likewise, any two components so associated
can also be viewed as being "operably connected," or "operably
coupled," to each other to achieve the desired functionality, and
any two components capable of being so associated can also be
viewed as being "operably couplable," to each other to achieve the
desired functionality. Specific examples of operably couplable
include but are not limited to optical coupling to permit
transmission of optical light, for example via an optical pipe or
fiber, physically interacting components and/or wirelessly
interactable and/or wirelessly interacting components and/or
logically interacting and/or logically interactable components.
[0156] With respect to the use of substantially any plural and/or
singular terms herein, those having skill in the art can translate
from the plural to the singular and/or from the singular to the
plural as is appropriate to the context and/or application. The
various singular/plural permutations may be expressly set forth
herein for sake of clarity.
[0157] It will be understood by those within the art that, in
general, terms used herein, and especially in the appended claims
(e.g., bodies of the appended claims) are generally intended as
"open" terms (e.g., the term "including" should be interpreted as
"including but not limited to," the term "having" should be
interpreted as "having at least," the term "includes" should be
interpreted as "includes but is not limited to," etc.). It will be
further understood by those within the art that if a specific
number of an introduced claim recitation is intended, such an
intent will be explicitly recited in the claim, and in the absence
of such recitation no such intent is present. For example, as an
aid to understanding, the following appended claims may contain
usage of the introductory phrases "at least one" and "one or more"
to introduce claim recitations. However, the use of such phrases
should not be construed to imply that the introduction of a claim
recitation by the indefinite articles "a" or "an" limits any
particular claim containing such introduced claim recitation to
inventions containing only one such recitation, even when the same
claim includes the introductory phrases "one or more" or "at least
one" and indefinite articles such as "a" or "an" (e.g., "a" and/or
"an" should typically be interpreted to mean "at least one" or "one
or more"); the same holds true for the use of definite articles
used to introduce claim recitations. In addition, even if a
specific number of an introduced claim recitation is explicitly
recited, those skilled in the art will recognize that such
recitation should typically be interpreted to mean at least the
recited number (e.g., the bare recitation of "two recitations,"
without other modifiers, typically means at least two recitations,
or two or more recitations). Furthermore, in those instances where
a convention analogous to "at least one of A, B, and C, etc." is
used, in general such a construction is intended in the sense one
having skill in the art would understand the convention (e.g., "a
system having at least one of A, B, and C" would include but not be
limited to systems that have A alone, B alone, C alone, A and B
together, A and C together, B and C together, and/or A, B, and C
together, etc.). In those instances where a convention analogous to
"at least one of A, B, or C, etc." is used, in general such a
construction is intended in the sense one having skill in the art
would understand the convention (e.g., "a system having at least
one of A, B, or C" would include but not be limited to systems that
have A alone, B alone, C alone, A and B together, A and C together,
B and C together, and/or A, B, and C together, etc.). It will be
further understood by those within the art that virtually any
disjunctive word and/or phrase presenting two or more alternative
terms, whether in the description, claims, or drawings, should be
understood to contemplate the possibilities of including one of the
terms, either of the terms, or both terms. For example, the phrase
"A or B" will be understood to include the possibilities of "A" or
"B" or "A and B."
[0158] All references, including but not limited to patents, patent
applications, and non-patent literature are hereby incorporated by
reference herein in their entirety.
[0159] While various aspects and embodiments have been disclosed
herein, other aspects and embodiments will be apparent to those
skilled in the art. The various aspects and embodiments disclosed
herein are for purposes of illustration and are not intended to be
limiting, with the true scope and spirit being indicated by the
following claims.
* * * * *