Nanowire-Based Sensors

Abstract

The nanowire-based sensor may include an array of nanowires attached to a substrate. The nanowires may have a cladding and be configured to selectively direct incident light toward the substrate to interact with surface plasmons in a metal layer on the surface of the substrate. The nanowire-based sensor may include an array of nanowires coupled to nearest neighboring nanowires. The nanowires may be arranged in spiral, half coil, or full coil configurations, in order of increasing radius.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure is related to U.S. Provisional Application No. 63 / 379,495, filed October 14, 2022, U.S. Provisional Application No. 63 / 380,747, filed October 24, 2022, U.S. Provisional Application No. 63 / 382,175, filed November 3, 2022, U.S. Provisional Application No. 63 / 490,414, filed March 15, 2023, and U.S. Provisional Application No. 63 / 502,494, filed May 16, 2023. The entire disclosure of each of these provisional applications is incorporated by reference. [Background technology]

[0002] Surface plasmon resonance (SPR) can be used for multiplexed detection of biomolecules and real-time monitoring of interactions of multiplexed chemical and biological analytes (e.g., interactions between RNA, DNA, or proteins and a wide variety of ligands or cofactors).

[0003] SPR is the generation of charge density oscillations at the interface between two media with opposite dielectric constants, such as a dielectric (e.g., buffer solution, air, or water) and a metal (e.g., silver or gold), upon interaction with plane-polarized light. This process changes the refractive index of the dielectric medium. The change in the refractive index of the dielectric medium alters the propagation constant of the surface plasmon, changing the resonance conditions between the interacting light wave and the surface plasmon. SPR-based biosensors can be prism-coupled, including a metal (e.g., gold) film, a prism (e.g., glass), a light source, and a detector with the metal film positioned at the interface between two dielectric media. One dielectric medium is a prism with a high refractive index, and the other is air or a liquid sample with a low refractive index. A laser beam passes through the prism, generating surface plasmons. The light reflected from the surface of the metal film is measured by a detector to generate an SPR spectrum. Gold can be a suitable material for metal films due to its high density of conduction band electrons, its combination of light wavelength and reflection angle, its immobility under physiological buffer conditions, and its easy functionalization with thiolated biomolecules.

[0004] Conventional color imaging devices, such as digital cameras, use a pixelated monochrome image sensor, such as a charge-coupled device (CCD), in combination with three different color filters to generate a color image. Conventional imaging devices include a lens, a filter, and a photodetector. The three different color filters typically transmit broadband portions of the visible spectrum centered around red, green, and blue wavelengths, e.g., 650 nm, 532 nm, and 473 nm, respectively. Each filter is sufficiently broadband so that the three filters cover the entire visible spectrum. Each "pixel" in the image sensor is composed of three "subpixels," each of which detects the amount of light that passes through an associated one of the three color filters.

[0005] Conventional "multispectral imaging" extends the capabilities of the human eye by using three or more filters with narrower bandwidths than conventional RGB imaging. The portions of the electromagnetic spectrum covered by these filters extend into the ultraviolet and / or infrared, providing more information than can be captured by conventional visible spectrum imaging devices. Multispectral imaging has many applications in both military and civilian applications, including remote sensing, vegetation mapping, non-invasive biological imaging, facial recognition, and food quality control. Conventional multispectral imaging devices include devices that use motorized filter wheels, multiple image sensors, and / or multilayer dielectric interference filters. Summary of the Invention

[0006] The device disclosed herein comprises a substrate of a first dielectric material, a periodic array of nanowires attached to a first surface of the substrate, a first metal layer on the first surface, and a second metal layer on a second surface of the substrate opposite the first surface. At least one of the nanowires comprises a semiconductor core and a cladding of a second dielectric material, the cladding surrounding the core. The nanowire and the substrate are in direct physical contact.

[0007] In one embodiment, the first dielectric material is an oxide.

[0008] In one embodiment, the second dielectric material is an oxide.

[0009] In one embodiment, the core is cylindrical.

[0010] In one aspect, the cladding has a uniform thickness in the radial direction of the core.

[0011] In one embodiment, the nanowires extend in a direction perpendicular to the first surface.

[0012] In one aspect, the device is configured to receive light into the core and direct the light through the core into the substrate, where the light in the substrate interacts with surface plasmons of the first metal layer.

[0013] In one embodiment, the nanowires are attached to the first surface and the second surface.

[0014] In one embodiment, the first metal layer extends to the sidewalls of the cladding.

[0015] The device disclosed herein comprises a substrate having a recess in a first surface thereof, a nanowire in the recess and extending from a bottom of the recess, a conformal coating on the bottom of the recess, on sidewalls of the nanowire and on a top surface of the nanowire, and a light-blocking layer at the bottom of the recess between the nanowire and overlying the conformal coating, wherein the conformal coating and the nanowire form a pn junction at an interface between the conformal coating and the nanowire.

[0016] In one aspect, the nanowires are coextensive with the depth of the recesses.

[0017] In one embodiment, the pn junction is continuous and conformal to the nanowire.

[0018] In one aspect, the device further comprises a dielectric-filled isolation trench in the substrate, the dielectric-filled isolation trench configured to prevent crosstalk between nanowires.

[0019] In one embodiment, the nanowire lattice and the substrate lattice are continuous.

[0020] In one embodiment, the substrate is a semiconductor.

[0021] In one embodiment, the conformal coating is on the sidewalls of the recess.

[0022] In one aspect, the conformal coating is a dielectric material.

[0023] In one embodiment, the conformal coating is aluminum oxide.

[0024] In one aspect, the light blocking layer is absent on the sidewalls of the nanowires and on the top surface of the nanowires.

[0025] In one aspect, the device further comprises an electrical contact to the substrate.

[0026] In one embodiment, the electrical contact comprises molybdenum oxide.

[0027] In one embodiment, the device further comprises bump contacts corresponding to the nanowires on a second surface of the substrate opposite the first surface.

[0028] In one embodiment, the bump contacts comprise LiF.

[0029] In one embodiment, the nanowires are arranged in an array of unit cells.

[0030] In one embodiment, the nanowires of different unit cells are not connected.

[0031] In one aspect, the nanowires of the same unit cell are not connected.

[0032] In one embodiment, at least one of the unit cells includes a first nanowire of radius R1, a second nanowire of radius R2, a third nanowire of radius R3, and a fourth nanowire of radius R4, where R4>R3>R2>R1, and the first nanowire, the second nanowire, the third nanowire, and the fourth nanowire are arranged at the vertices of a rectangle.

[0033] In one embodiment, (1) the first nanowire is closest to the second nanowire and the fourth nanowire, but not closest to the third nanowire; (2) the second nanowire is closest to the first nanowire and the third nanowire, but not closest to the fourth nanowire; (3) the third nanowire is closest to the second nanowire and the fourth nanowire, but not closest to the first nanowire; and (4) the fourth nanowire is closest to the first nanowire and the third nanowire, but not closest to the second nanowire.

[0034] In one embodiment, (R2-R1)=(R3-R2).

[0035] In one embodiment, R1=10 nm, R2=15 nm, R3=20 nm, and R4=25 nm.

[0036] In one embodiment, R1=30 nm, R2=45 nm, R3=50 nm, and R4=70 nm.

[0037] In one embodiment, R1=10 nm, R2=12.5 nm, R3=14 nm, and R4=20 nm.

[0038] In one embodiment, at least one of the unit cells includes nine nanowires, a first nanowire of radius R1, a second nanowire of radius R2, a third nanowire of radius R3, a fourth nanowire of radius R4, a fifth nanowire of radius R5, a sixth nanowire of radius R6, a seventh nanowire of radius R7, an eighth nanowire of radius R8, and a ninth nanowire of radius R9, where R9>R8>R7>R6>R5>R4>R3>R2>R1, and the first nanowire, the second nanowire, the third nanowire, the fourth nanowire, the fifth nanowire, the sixth nanowire, the seventh nanowire, the eighth nanowire, and the ninth nanowire are in a 3x3 square grid.

[0039] In one embodiment, (1) the first nanowire is closest to the second and sixth nanowires but not the other nanowires of the nine nanowires, (2) the second nanowire is closest to the first, third, and fifth nanowires but not the other nanowires of the nine nanowires, (3) the third nanowire is closest to the second and fourth nanowires but not the other nanowires of the nine nanowires, (4) the fourth nanowire is closest to the third, fifth, and ninth nanowires but not the other nanowires of the nine nanowires, and (5) the fifth nanowire is closest to the second, fourth, sixth, and eighth nanowires. (5) the sixth nanowire is closest to the first, fifth, and seventh nanowires but not the other nanowires of the nine nanowires; (6) the sixth nanowire is closest to the first, fifth, and seventh nanowires but not the other nanowires of the nine nanowires; (7) the seventh nanowire is closest to the sixth and eighth nanowires but not the other nanowires of the nine nanowires; (8) the eighth nanowire is closest to the fifth, seventh, and ninth nanowires but not the other nanowires of the nine nanowires; and (9) the ninth nanowire is closest to the sixth and eighth nanowires but not the other nanowires of the nine nanowires.

[0040] In one embodiment, (1) the first nanowire is closest to the second and eighth nanowires but not to any other nanowires of the nine nanowires, (2) the second nanowire is closest to the first, third, and ninth nanowires but not to any other nanowires of the nine nanowires, (3) the third nanowire is closest to the second and fourth nanowires but not to any other nanowires of the nine nanowires, (4) the fourth nanowire is closest to the third, fifth, and ninth nanowires but not to any other nanowires of the nine nanowires, and (5) the fifth nanowire is closest to the fourth and sixth nanowires but not to any other nanowires of the nine nanowires. , but not the other nanowires of the nine nanowires; (6) the sixth nanowire is closest to the fifth, seventh, and ninth nanowires but not the other nanowires of the nine nanowires; (7) the seventh nanowire is closest to the sixth and eighth nanowires but not the other nanowires of the nine nanowires; (8) the eighth nanowire is closest to the first, seventh, and ninth nanowires but not the other nanowires of the nine nanowires; and (9) the ninth nanowire is closest to the second, fourth, sixth, and eighth nanowires but not the other nanowires of the nine nanowires.

[0041] In one aspect, (R2-R1) = (R3-R2) = (R4-R3) = (R5-R4) = (R6-R5) = (R7-R6) = (R8-R7).

[0042] In one embodiment, R1 = 30 nm, R2 = 35 nm, R3 = 40 nm, R4 = 45 nm, R5 = 50 nm, R6 = 55 nm, R7 = 60 nm, R8 = 65 nm, and R9 = 70 nm. [Brief explanation of the drawings]

[0043] [Figure 1] FIG. 1 shows a schematic cross-sectional view of the device.

[0044] [Figure 2] FIG. 2 shows a schematic perspective view of the device of FIG.

[0045] [Figure 3] FIG. 3 shows a schematic cross-sectional view of the device.

[0046] [Figure 4] FIG. 4 shows a schematic perspective view of the device of FIG.

[0047] [Figure 5] FIG. 5 shows the electric field components along the z-axis within the substrate of the device of FIG.

[0048] [Figure 6] FIG. 6 shows the electric field component along the y-axis within the substrate of the device of FIG.

[0049] [Figure 7] FIG. 7 shows the output spectrum from the substrate of the device of FIG.

[0050] [Figure 8] FIG. 8 shows a schematic cross-sectional view of the device.

[0051] [Figure 9] FIG. 9 shows the electric field component along the y-axis within the substrate of the device of FIG.

[0052] [Figure 10] FIG. 10 shows a schematic representation of the absorption spectrum of an uncoupled nanowire and an absorbance spectrum of a coupled nanowire.

[0053] [Figure 11] FIG. 11 shows examples of triangular lattice arrangements of nanowires with a radius of 30 nm, nanowires with a radius of 40 nm, and nanowires with a radius of 50 nm.

[0054] [Figure 12] FIG. 12 shows the absorption spectrum of the nanowires in the arrangement of FIG.

[0055] [Figure 13] FIG. 13 shows the absorption spectra of nanowires in another triangular lattice that is the same as the triangular lattice in FIG. 11, except that the nanowire radii are 40 nm, 45 nm, and 50 nm.

[0056] [Figure 14] FIG. 14 shows examples of square lattice arrays of nanowires with a radius of 30 nm, nanowires with a radius of 40 nm, and nanowires with a radius of 50 nm.

[0057] [Figure 15A] FIG. 15A shows examples of square lattice arrays of nanowires with a radius of 30 nm, nanowires with a radius of 40 nm, nanowires with a radius of 50 nm, nanowires with a radius of 60 nm, and nanowires with a radius of 70 nm.

[0058] [Figure 15B] FIG. 15B shows another example of a square lattice arrangement 220 of nanowires 221 with a radius of 30 nm, nanowires 222 with a radius of 40 nm, nanowires 223 with a radius of 50 nm, nanowires 224 with a radius of 60 nm, and nanowires 225 with a radius of 70 nm.

[0059] [Figure 16] FIG. 16 shows a schematic cross section of a portion of the device.

[0060] [Figure 17] FIG. 17 shows that the device of FIG. 16 may be connected to signal processing circuitry using interconnects.

[0061] [Figure 18] FIG. 18 shows that the device of FIG. 16 may be connected to an array of pixel transistors and signal processing circuitry.

[0062] [Figure 19] FIG. 19 shows a top view of a unit cell in one embodiment.

[0063] [Figure 20] FIG. 20 shows the absorption spectra of nanowires with 10 nm and 15 nm radii in the unit cell of FIG.

[0064] [Figure 21] FIG. 21 shows a top view of a unit cell in one embodiment.

[0065] [Figure 22] FIG. 22 shows the absorption spectra of nanowires with 30 nm, 40 nm, and 50 nm radii in the unit cell of FIG.

[0066] [Figure 23] FIG. 23 shows a top view of a unit cell in one embodiment.

[0067] [Figure 24] FIG. 24 shows the absorption spectra of nanowires with radii of 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, and 55 nm in the unit cell of FIG.

[0068] [Figure 25] FIG. 25 shows a top view of a unit cell in one embodiment.

[0069] [Figure 26] FIG. 26 shows a top view of a unit cell in one embodiment.

[0070] [Figure 27] FIG. 27 shows the absorption spectra of nanowires with radii of 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, and 100 nm in the unit cell of FIG.

[0071] [Figure 28] FIG. 28 shows a top view of a unit cell in one embodiment.

[0072] [Figure 29A] FIG. 29A shows the absorption spectrum of a Si nanowire with a radius of 50 nm.

[0073] [Figure 29B] FIG. 29B shows the absorption spectrum of a 20 nm radius Si nanowire. DETAILED DESCRIPTION OF THE INVENTION

[0074] FIG. 1 schematically illustrates a cross section of a portion of a device 100. FIG. 2 schematically illustrates a perspective view of the device 100 of FIG. 1. The device 100 includes a substrate 140. The substrate 140 is made of a dielectric material such as an oxide (e.g., SiO2). Nanowires are attached to at least one surface of the substrate 140. The nanowires are periodically arranged. At least one nanowire includes a core 120 and a cladding 110 surrounding the core 120. The core 120 may be cylindrical. The core 120 is a semiconductor (e.g., Si). The cladding 110 is a dielectric material such as an oxide (e.g., SiO2). The materials of the cladding 110 and the substrate 140 may or may not be the same. The cladding 110 may have a uniform thickness in the radial direction of the core 120. For convenience, a coordinate system is defined as follows: the plane of FIG. 1 is the xz plane. The y-axis extends in the plane of Figure 1. The x-, y-, and z-axes are mutually orthogonal. The z-axis is perpendicular to the substrate 140. The x-axis is parallel to the substrate 140. In this coordinate system, the core 120 extends along the z-axis.

[0075] On the surface of the substrate from which the nanowires extend is a metal layer 130A. Metal layer 130A does not extend between the nanowires and the substrate 140; that is, core 120 and cladding 110 are in direct physical contact with substrate 140. On the surface of the substrate opposite metal layer 130A is another metal layer 130B.

[0076] The device 100 is configured to receive light 199 along the z-axis. This does not mean that the light 199 must propagate exactly along the z-axis. The light 199 may instead propagate along one or more directions, not limited to the x-y plane. The light 199 is not limited to visible light. The light 199 may be infrared, ultraviolet, or other electromagnetic radiation in general, such as other wavelength ranges. The light 199 may be "broadband" light, i.e., have a wide range of wavelengths. For example, the light 199 may be white light. The device 100 may have substances 150 (e.g., biomolecules) present on the metal layer 130A, the metal layer 130B, or both. The output light 188 from the device 100 may be detected from a sidewall of the substrate 140.

[0077] According to Maxwell's equations, when light 199 is exactly incident on the nanowire along the z-axis, the electric field vector of the light 199 has only E and E components along the x and y axes, respectively. The nanowire acts as an absorption waveguide, filtering and confining the light 199 as it propagates along the nanowire. When the light 199 reaches the substrate 140, which has a lower refractive index than the core 120, the light 199 diffracts and diverges within the substrate 140, resulting in light components propagating within the substrate 140 along the x and y axes.

[0078] The component of light propagating along the x-axis has electric field components Ey and Ez, which are along the y-axis and z-axis, respectively. The component of light propagating along the y-axis has electric field components Ex and Ez, which are along the x-axis and z-axis, respectively.

[0079] Light components propagating along the x-axis or y-axis interact with the surface plasmons of metal layer 130A and metal layer 130B, while light components propagating along the z-axis do not interact with the surface plasmons of metal layer 130A and metal layer 130B.

[0080] 3 shows a variation of device 100 in which nanowires are attached to substrate 140 on both sides of substrate 140. Metal layer 130B does not extend between the nanowires and substrate 140. FIG. 2 shows a schematic perspective view of device 100 of FIG. 1. The nanowires on both sides of substrate 140 are not necessarily aligned. As shown in FIG. 3, the nanowires on both sides of substrate 140 are not aligned.

[0081] 5 shows the electric field component along the z-axis (i.e., Ez) in a cross section of the y-z plane of substrate 140 for light components propagating along the y-axis. The maxima and minima of Ez for metal layers 130A and 130B indicate that Ez can support plasmonic waves because metals cannot support electric fields in the longitudinal direction (aligned along the surface or tangent). The single maximum and minimum of Ez indicates the relationship between the nanowire pitch and the propagation mode of output light 188.

[0082] 6 shows the electric field component along the y-axis (i.e., Ey) for a light component propagating along the x-axis in a cross section of the yz plane of substrate 140. The zero Ey for metal layer 130A and metal layer 130B indicates that the metal cannot support an electric field in the longitudinal direction (aligned along the surface or tangent), and therefore cannot support plasmonic waves.

[0083] A substance 150 (e.g., a biomolecule) present on metal layer 130A, metal layer 130B, or both, may alter the resonance condition of E. Output light 188 may be filtered to maintain E and attenuate Ex and E. Output light 188 may be used to detect substance 150.

[0084] 7 shows an example spectrum of output light 188 from substrate 140. Here, substrate 140 is 100 microns thick, and light 199 does not have a distinct peak. Despite the absence of a distinct peak in light 199, the spectrum of output light 188 does have a distinct peak. The position of the peak depends on the diameter and pitch of the nanowire. The position of the peak is sensitive to plasmonic charge oscillations within metal layers 130A and 130B, and can therefore be used to detect material 150 on metal layers 130A and 130B.

[0085] The device 100 may be used as an optical coupler to a slab waveguide resonator. The nanowires may be placed at any position on the slab waveguide (as the substrate 140) and may cover only a portion of the slab waveguide. The nanowires may couple broadband input light from the slab waveguide to obtain desired output light with a narrow spectrum. The nanowires may also be used as confinement waveguides to feed doped oxide slab waveguide lasers. In this embodiment, the sidewall surfaces of the substrate 140 may be partially or fully mirrored (i.e., coated with a partially or fully reflective film).

[0086] 8 shows a variation of device 100 in which metal layer 130A extends to the sidewalls of cladding 110. In other words, metal layer 130A surrounds cladding 110 rather than just being on the surface of substrate 140. Metal layer 130A may or may not cover the entire sidewall of cladding 110. Metal layer 130B may extend to the sidewall of cladding 110 of any nanowires that extend from the surface to substrate 140. The surface of the nanowire that receives light 199 is preferably free of metal layer 130A, but may have a thin metal layer.

[0087] FIG. 9 shows the electric field component (i.e., Ey) along the y-axis in a cross section of the yz plane of the substrate 140 of the light component propagating along the x-axis in the variation shown in FIG. 8. While Ey does not support plasmonic waves in FIG. 6, in FIG. 9, Ey supports plasmonic waves in the portion of the metal layer 130A parallel to the z-axis. The high-contrast bands in FIG. 9 indicate plasmonic waves propagating in the portion of the metal layer 130A parallel to the z-axis. The variation in FIG. 9 increases the utilization of light 199 compared to the variations in FIGS. 1 and 3.

[0088] Semiconductor nanowires (e.g., Si nanowires) can selectively filter broadband illumination into narrow bands. The filtering effect depends on the radius of the nanowire. This effect is due to the high dispersion properties of semiconductors (the complex refractive index strongly depends on the wavelength of the incident light). Light in a semiconductor nanowire is a strongly guided wave surrounded by an evanescent field that exponentially decays outside the physical boundary of the semiconductor nanowire. When a nanowire is not coupled to other nanowires (i.e., the evanescent field of a nanowire does not overlap with the evanescent field of other nanowires), there can be a linear relationship between the radius of the nanowire and the position of its absorption peak.

[0089] As the spacing between the nanowires decreases and the evanescent fields begin to overlap, the behavior of the nanowires begins to deviate from that of uncoupled nanowires. Nanowire coupling may be used to control the width of the nanowire absorption peak.

[0090] The exponential decay of the evanescent field results in strong coupling between nanowires at spacings shorter than the wavelength of the absorption peak. Figure 11 shows a schematic of the absorption spectrum of a 45 nm radius, 1 micron long silicon nanowire array. As the pitch decreases, coupling increases. With increased coupling, the absorption peak tends to become higher (i.e., absorption becomes stronger), the absorption peak tends to shift toward shorter wavelengths, and the absorption peak tends to broaden at shorter wavelengths (i.e., the absorption peak profile changes from narrowband to low-pass filter).

[0091] When multiple nanowires of the same radius are in their evanescent fields, their absorption broadens, as shown in Figure 10. Placing multiple nanowires with similar radii (i.e., closely spaced absorption peaks) adjacent to each other results in a narrower absorption peak. This is because nanowires with overlapping evanescent fields share the incident light, and each nanowire absorbs the wavelengths at which it resonates, determined by its singleton bandwidth. By exploiting this effect, multispectral image sensors can be designed with low light waste and very high external quantum efficiency. When a set of nanowires with different radii is appropriately selected and positioned so that their closest radii are within each other's evanescent fields, all available light is shared and absorbed. In other words, the response of each nanowire significantly diagonals itself compared to its neighbors.

[0092] To demonstrate this effect, Figure 11 shows an example array 200 of nanowires 201 with a radius of 30 nm, nanowires 202 with a radius of 40 nm, and nanowires 203 with a radius of 50 nm. Nanowires 201, 202, and 203 are arranged in a triangular lattice as shown, with a center-to-center distance between nearest nanowires of 400 nm. The choice of these three radius values ​​of 30 nm, 40 nm, and 50 nm is not coincidental. Their absorption spectra are consistent with the CIE tristimulus ocular response curve.

[0093] 12 shows the absorption spectra of nanowire 201, nanowire 202 and nanowire 203. The absorption peaks of these nanowires are narrowed due to the bonds between these nanowires.

[0094] FIG. 13 shows the absorption spectra of nanowires in another triangular lattice, which is the same as the triangular lattice in FIG. 11, except that the nanowire radii are 40 nm (instead of 30 nm), 45 nm (instead of 40 nm), and 50 nm, respectively.

[0095] There may be nanowires of more than two radii in the lattice, and in one example, each nanowire has an adjacent nanowire with a radius one above or one below the respective nanowire.

[0096] 14 shows an example of a square lattice arrangement 210 of nanowires 211 with a radius of 30 nm, nanowires 212 with a radius of 40 nm, and nanowires 213 with a radius of 50 nm. Each nanowire's nearest neighbors have radii that are one increment (10 nm in this example) larger or smaller. For example, the nearest neighbor to one of nanowires 213 is not one of nanowires 211 because their radii differ by more than one increment. The absorption spectrum of the nanowires in this example shows three distinct, narrowed absorption peaks, similar to FIG. 12.

[0097] 15A shows an example of a square lattice arrangement 220 of nanowires 221 with a radius of 30 nm, nanowires 222 with a radius of 40 nm, nanowires 223 with a radius of 50 nm, nanowires 224 with a radius of 60 nm, and nanowires 225 with a radius of 70 nm. Each nanowire's nearest neighbors have radii that are one increment (10 nm in this example) larger or smaller. For example, the nearest neighbor of one of nanowires 223 is not one of nanowires 221 or one of nanowires 225 because their radii differ by more than one increment. The absorption spectrum of the nanowires in this example shows five distinct, narrowed absorption peaks.

[0098] 15B shows another example of a square lattice arrangement 220 of nanowires 221 with a radius of 30 nm, nanowires 222 with a radius of 40 nm, nanowires 223 with a radius of 50 nm, nanowires 224 with a radius of 60 nm, and nanowires 225 with a radius of 70 nm. Each nanowire's nearest neighbors have radii that are one increment (10 nm in this example) larger or smaller. For example, the nearest neighbor of one of nanowires 223 is not one of nanowires 221 or one of nanowires 225 because their radii differ by more than one increment. The absorption spectrum of the nanowires in this example shows five distinct, narrowed absorption peaks.

[0099] In some scenarios, it is not necessary to read the signal from each individual nanowire. Instead, signals from nanowires of the same radius are summed. The diagonal arrows represent the summing and sum reading paths.

[0100] By engineering the spacing, radius, and spatial arrangement of the nanowires, the absorption peak width of the nanowires may be tailored for various applications, such as three-color digital cameras, multispectral sensors, and solar-blind image sensors (e.g., with nanowires spaced approximately 200 nm apart, with an absorption peak at approximately 200-300 nm).

[0101] The nanowires do not require anti-reflective coatings, microlenses or color filters and can be fabricated using standard CMOS fabrication processes.

[0102] 16 shows a schematic cross-section of a portion of device 300. Device 300 includes substrate 340 having recesses 390 in its surface. Nanowires 320 are located within recesses 390 and extend from the bottom of recesses 390. In one embodiment, the lattice of nanowires 320 and that of substrate 340 are continuous (i.e., nanowires 320 and substrate 340 are composed of the same single crystal). Device 300 includes conformal coating 310 on the bottom of recesses 390, the sidewalls of nanowires 320, the top surface of nanowires 320, and optionally the sidewalls of recesses 390. Device 300 includes light-blocking layer 330 covering conformal coating 310 at the bottom of recesses 390 between nanowires 320. In other words, light-blocking layer 330 is separated from substrate 340 by conformal coating 310. Preferably, light-blocking layer 330 is not present on the sidewalls or top surface of nanowire 320, although this is not a requirement. Device 300 includes electrical contact 360 to substrate 340. Electrical contact 360 may serve as a common electrode for nanowire 320. Device 300 includes bump contact 370 corresponding to nanowire 320 and located on the surface of substrate 340 opposite recess 390. Device 300 does not require microlenses or color filters. Thus, in one embodiment, device 300 does not include microlenses or color filters. Conformal coating 310 and nanowire 320 form a p-n junction at the interface between conformal coating 310 and nanowire 320. In FIG. 16 , the p-n junction is continuous and conformal (i.e., the angle and shape are preserved) to nanowire 320. Device 300 may optionally include a dielectric-filled isolation trench 345 in substrate 340. Optional dielectric-filled isolation trenches 345 help separate charge carriers from different nanowires 320 to prevent crosstalk.

[0103] The substrate 340 may be doped silicon (e.g., n-Si), Ge, InAs, or other suitable semiconductor material. The conformal coating 310 may be a dielectric material (e.g., aluminum oxide, which may be dopant-free aluminum oxide formed by atomic layer deposition). The nanowires 320 may be formed by etching the substrate 340. The nanowires may extend to a distance equal to or less than the depth of the recess 390. The light-shielding layer 330 may be a metal layer, such as an aluminum layer. The electrical contact 360 may include a layer of molybdenum oxide in direct contact with the substrate 340 and a layer of metal (e.g., aluminum) on the molybdenum oxide layer. The electrical contact 360 may function as a hole collector. The bump contact 370 may be a layer of LiF and a layer of metal on the LiF layer. The recess 390 may be formed by etching the substrate 340.

[0104] FIG. 17 shows that device 300 may be connected to signal processing circuitry 399 using interconnect 398. Signal processing circuitry 399 may be any existing or to-be-developed circuitry capable of processing signals read from nanowire 320. For example, signal processing circuitry 399 may be a circuit fabricated using CMOS technology. Device 300, interconnect 398, and signal processing circuitry 399 may be connected by wafer bonding or other suitable techniques. FIG. 18 shows that device 300 may be connected to an array of pixel transistors 396 and signal processing circuitry 397. Device 300, array of pixel transistors 396, and signal processing circuitry 397 may be connected by wafer bonding or other suitable techniques. Alternatively, device 300 may be fabricated after interconnect 398 and signal processing circuitry 399, or array of pixel transistors 396 and signal processing circuitry 397, are attached to substrate 340.

[0105] The radius and placement of the nanowires 320 may be designed to achieve a desired response to incident light. In one embodiment, the nanowires 320 are arranged in an array of unit cells. Nanowires 320 of different unit cells are not bonded. Nanowires 320 of the same unit cell are bonded.

[0106] Figure 19 shows a top view of a unit cell in one embodiment. The unit cell has four nanowires 320 arranged in a "half coil" configuration, as indicated by the arrows indicating the direction of increasing radius of the nanowires within the unit cell. The four nanowires are silicon nanowires. The four nanowires are arranged at the vertices of a square. The length of the four nanowires may be several microns (e.g., 3 microns). That is, the four nanowires have radii of 10 nm, 15 nm, 20 nm, and 25 nm, respectively, and are arranged so that (1) the 10 nm nanowire is closest to the 15 nm and 25 nm nanowires but not to the 20 nm nanowire, (2) the 15 nm nanowire is closest to the 10 nm and 20 nm nanowires but not to the 25 nm nanowire, (3) the 20 nm nanowire is closest to the 15 nm and 25 nm nanowires but not to the 10 nm nanowire, and (4) the 25 nm nanowire is closest to the 10 nm and 20 nm nanowires but not to the 15 nm nanowire. The pitch of the four nanowires within the unit cell (i.e., the closest distance between nearest neighbors) is 200 nm. The device 300 with the arrangement of Figure 19 may be used as a solar-blind UV image sensor. That is, the device 300 with the arrangement of Figure 19 can form images using ultraviolet radiation at wavelengths that are completely absorbed by the Earth's ozone layer. Such wavelengths are from about 200 nm to about 300 nm.

[0107] Figure 20 shows the absorption spectra of 10 nm and 15 nm radius nanowires in the unit cell of Figure 19. The 20 nm and 25 nm radius nanowires serve to limit the long wavelength absorption of the 10 nm and 15 nm radius nanowires.

[0108] Figure 21 shows a top view of a unit cell in one embodiment. The unit cell has four nanowires 320 arranged in a "half coil" configuration, as indicated by the arrows indicating the direction of increasing radius of the nanowires within the unit cell. The four nanowires are silicon nanowires. The four nanowires are arranged at the vertices of a square. The length of the four nanowires may be several microns (e.g., 3 microns). That is, the four nanowires have radii of 30 nm, 40 nm, 50 nm, and 70 nm, respectively, and are arranged so that (1) the 30 nm nanowire is closest to the 40 nm and 70 nm nanowires but not to the 50 nm nanowire, (2) the 40 nm nanowire is closest to the 30 nm and 50 nm nanowires but not to the 70 nm nanowire, (3) the 50 nm nanowire is closest to the 40 nm and 70 nm nanowires but not to the 30 nm nanowire, and (4) the 70 nm nanowire is closest to the 30 nm and 50 nm nanowires but not to the 40 nm nanowire. The pitch of the four nanowires within the unit cell (i.e., the closest distance between nearest neighbors) is 400 nm. 21 may be used as an image sensor that detects red, green, and blue light (i.e., an RGB image sensor). Specifically, nanowires with radii of 30 nm, 40 nm, and 50 nm absorb blue, green, and red light, respectively. The 70 nm nanowire serves to avoid absorbing infrared light that is avoided by the 50 nm nanowire.

[0109] FIG. 22 shows the absorption spectra of nanowires with 30 nm, 40 nm, and 50 nm radii within the unit cell of FIG.

[0110] Figure 23 shows a top view of a unit cell in one embodiment. This unit cell has nine nanowires 320 arranged in a "full coil," as indicated by the arrows showing the direction of increasing radius of the nanowires within the unit cell. These nine nanowires are silicon nanowires. These nine nanowires are arranged at the vertices of a square, the midpoints of the sides of the square, and the center of the square. That is, the nine nanowires are in a 3x3 square grid. The length of these nine nanowires may be several microns (e.g., 3 microns).That is, the nine nanowires have radii of 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, and 70 nm, respectively. (1) The nanowire with a radius of 30 nm is closest to the nanowires with radii of 35 nm and 55 nm, but not to any other nanowires among the nine nanowires. (2) The nanowire with a radius of 35 nm is closest to the nanowires with radii of 30 nm, 40 nm, and 50 nm, but not to any other nanowires among the nine nanowires. (3) The nanowire with a radius of 40 nm is closest to the nanowires with radii of 35 nm and 45 nm, but not to any other nanowires among the nine nanowires. (4) The nanowire with a radius of 45 nm is closest to the nanowires with radii of 40 nm, 50 nm, and 70 nm, but not to any other nanowires among the nine nanowires. (5) The nanowire with a radius of 50 nm is closest to the nanowires with radii of 35 nm, 45 nm, 55 nm, and 65 nm, but not to any other nanowires of the nine nanowires; (6) the nanowire with a radius of 55 nm is closest to the nanowires with radii of 30 nm, 50 nm, and 60 nm, but not to any other nanowires of the nine nanowires; (7) the nanowire with a radius of 60 nm is closest to the nanowires with radii of 55 nm and 65 nm, but not to any other nanowires of the nine nanowires; (8) the nanowire with a radius of 65 nm is closest to the nanowires with radii of 50 nm, 60 nm, and 70 nm, but not to any other nanowires of the nine nanowires; and (9) the nanowire with a radius of 70 nm is closest to the nanowires with radii of 45 nm and 65 nm, but not to any other nanowires of the nine nanowires. The pitch of the nine nanowires in the unit cell (i.e., the closest distance between nearest neighbors) is 400 nm. A device 300 with the array of Figure 23 may be used as a multispectral image sensor.

[0111] FIG. 24 shows the absorption spectra of nanowires with radii of 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, and 55 nm within the unit cell of FIG.

[0112] Figure 25 shows a top view of a unit cell in one embodiment. This unit cell has nine nanowires 320 arranged in a "spiral," as indicated by the arrows indicating the direction of increasing radius of the nanowires within the unit cell. These nine nanowires are silicon nanowires. These nine nanowires are arranged at the vertices of a square, the midpoints of the sides of the square, and the center of the square. That is, the nine nanowires are in a 3x3 square grid. These nine nanowires may be several microns long (e.g., 3 microns). That is, the nine nanowires have radii of 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, and 70 nm, respectively. (1) The nanowire with a radius of 30 nm is closest to the nanowires with radii of 35 nm and 65 nm, but not to any other nanowires among the nine nanowires. (2) The nanowire with a radius of 35 nm is closest to the nanowires with radii of 30 nm, 40 nm, and 70 nm, but not to any other nanowires among the nine nanowires. (3) The nanowire with a radius of 40 nm is closest to the nanowires with radii of 35 nm and 45 nm, but not to any other nanowires among the nine nanowires. (4) The nanowire with a radius of 45 nm is closest to the nanowires with radii of 40 nm, 50 nm, and 70 nm, but not to any other nanowires among the nine nanowires. (5) the 50 nm radius nanowire is closest to the 45 nm and 55 nm radius nanowires but not to any other of the nine nanowires; (6) the 55 nm radius nanowire is closest to the 50 nm, 60 nm, and 70 nm radius nanowires but not to any other of the nine nanowires; (7) the 60 nm radius nanowire is closest to the 55 nm and 65 nm radius nanowires but not to any other of the nine nanowires; (8) the 65 nm radius nanowire is closest to the 30 nm, 60 nm, and 70 nm radius nanowires but not to any other of the nine nanowires; and (9) the 70 nm radius nanowire is closest to the 35 nm, 45 nm, 55 nm, and 65 nm radius nanowires.The pitch of the nine nanowires in the unit cell (i.e., the closest distance between nearest neighbors) is 400 nm. Device 300 with the array of Figure 25 may be used as a multispectral image sensor in the visible wavelength range.

[0113] Figure 26 shows a top view of a unit cell in one embodiment. The unit cell in Figure 26 is similar to the unit cell in Figure 23, except that the nanowires are Ge nanowires with radii of 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, and 130 nm, respectively, and are spaced at a 1 micron pitch. Device 300 with the array of Figure 26 may be used as a multispectral image sensor in the near-infrared wavelength range.

[0114] FIG. 27 shows the absorption spectra of nanowires with radii of 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, and 100 nm within the unit cell of FIG.

[0115] Figure 28 shows a top view of a unit cell in one embodiment. The unit cell in Figure 28 is similar to the unit cell in Figure 19, except that the nanowires have radii of 10 nm, 12.5 nm, 14 nm, and 20 nm, respectively, and a pitch of 200 nm. The device 300 with the array of Figure 28 may be used as a UV image sensor.

[0116] Device 300 may be used to detect ambient light. For example, device 300 may have nine absorption bands ranging from the ultraviolet A (UV-A) band (wavelengths 315-400 nm) to the near infrared.

[0117] The nanowires of device 300 may have higher-order absorption peaks, which are approximately half the wavelength of the main absorption peak. As shown in the example of FIG. 29A, a silicon nanowire with a 50 nm radius has a main absorption peak at approximately 600 nm and a higher-order absorption peak at approximately 380 nm. FIG. 29B shows a silicon nanowire with a 20 nm radius having a main absorption peak at approximately 380 nm. The higher-order peaks may be used to "skim off" unwanted absorption. For example, when a 50 nm silicon nanowire is combined with a 20 nm silicon nanowire, the 380 nm higher-order absorption peak of the 50 nm silicon nanowire is suppressed by the 380 nm main absorption peak of the 20 nm silicon nanowire.

[0118] While various aspects and embodiments are 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.

Claims

1. a substrate of a first dielectric material; a periodic array of nanowires attached to a first surface of the substrate; a first metal layer on the first surface; a second metal layer on a second surface of the substrate opposite the first surface; at least one of the nanowires comprises a semiconductor core and a cladding of a second dielectric material; the cladding surrounds the core; A device wherein the nanowires and the substrate are in direct physical contact.

2. The device of claim 1 , wherein the first dielectric material is an oxide.

3. The device of claim 1 , wherein the second dielectric material is an oxide.

4. The device of claim 1 , wherein the core is cylindrical.

5. The device of claim 1 , wherein the cladding has a uniform thickness radially about the core.

6. The device of claim 1 , wherein the nanowires extend in a direction perpendicular to the first surface.

7. The device of claim 1 configured to receive light into the core and direct the light through the core into the substrate, the light in the substrate interacting with surface plasmons of the first metal layer.

8. The device of claim 1 , wherein the nanowires are attached to the first surface and the second surface.

9. The device of claim 1 , wherein the first metal layer extends to the sidewalls of the cladding.

10. a substrate having a recess in a first surface of the substrate; a nanowire within the recess and extending from a bottom of the recess; a conformal coating on the bottom of the recess, the sidewalls of the nanowire, and the top surface of the nanowire; a light-blocking layer overlying the conformal coating at the bottom of the recesses between the nanowires; The conformal coating and the nanowire form a pn junction at an interface between the conformal coating and the nanowire.

11. The device of claim 10 , wherein the nanowire is coextensive with the depth of the recess.

12. The device of claim 10 , wherein the pn junction is continuous and conformal to the nanowire.

13. The device of claim 10 , further comprising a dielectric-filled isolation trench in the substrate, the dielectric-filled isolation trench configured to prevent crosstalk between nanowires.

14. The device of claim 10 , wherein the nanowire lattice and the substrate lattice are continuous.

15. The device of claim 10 , wherein the substrate is a semiconductor.

16. The device of claim 10 , wherein the conformal coating is on a sidewall of the recess.

17. The device of claim 10 , wherein the conformal coating is a dielectric material.

18. The device of claim 10 , wherein the conformal coating is aluminum oxide.

19. The device of claim 10 , wherein the light blocking layer is absent on the sidewalls of the nanowires and on the top surface of the nanowires.

20. The device of claim 10 further comprising an electrical contact to the substrate.

21. 21. The device of claim 20, wherein the electrical contact comprises molybdenum oxide.

22. The device of claim 10 further comprising bump contacts corresponding to the nanowires on a second surface of the substrate opposite the first surface.

23. 23. The device of claim 22, wherein the bump contacts comprise LiF.

24. The device of claim 10 , wherein the nanowires are arranged in an array of unit cells.

25. 25. The device of claim 24, wherein the nanowires of different unit cells are not connected.

26. 25. The device of claim 24, wherein the nanowires of the same unit cell are not connected.

27. At least one of the unit cells includes a first nanowire of radius R1, a second nanowire of radius R2, a third nanowire of radius R3, and a fourth nanowire of radius R4; Here, R4>R3>R2>R1, 25. The device of claim 24, wherein the first nanowire, the second nanowire, the third nanowire, and the fourth nanowire are arranged at the vertices of a square.

28. 28. The device of claim 27, wherein: (1) the first nanowire is closest to the second nanowire and the fourth nanowire, but not closest to the third nanowire; (2) the second nanowire is closest to the first nanowire and the third nanowire, but not closest to the fourth nanowire; (3) the third nanowire is closest to the second nanowire and the fourth nanowire, but not closest to the first nanowire; and (4) the fourth nanowire is closest to the first nanowire and the third nanowire, but not closest to the second nanowire.

29. 28. The device of claim 27, wherein (R2-R1)=(R3-R2).

30. 28. The device of claim 27, wherein R1 = 10 nm, R2 = 15 nm, R3 = 20 nm, and R4 = 25 nm.

31. 28. The device of claim 27, wherein R1 = 30 nm, R2 = 45 nm, R3 = 50 nm, and R4 = 70 nm.

32. 28. The device of claim 27, wherein R1 = 10 nm, R2 = 12.5 nm, R3 = 14 nm, and R4 = 20 nm.

33. At least one of the unit cells includes nine nanowires: a first nanowire of radius R1, a second nanowire of radius R2, a third nanowire of radius R3, a fourth nanowire of radius R4, a fifth nanowire of radius R5, a sixth nanowire of radius R6, a seventh nanowire of radius R7, an eighth nanowire of radius R8, and a ninth nanowire of radius R9; Here, R9>R8>R7>R6>R5>R4>R3>R2>R1, 25. The device of claim 24, wherein the first nanowire, the second nanowire, the third nanowire, the fourth nanowire, the fifth nanowire, the sixth nanowire, the seventh nanowire, the eighth nanowire, and the ninth nanowire are in a 3x3 square grid.

34. (1) the first nanowire is closest to the second and sixth nanowires but not to any other nanowires of the nine nanowires; (2) the second nanowire is closest to the first, third, and fifth nanowires but not to any other nanowires of the nine nanowires; (3) the third nanowire is closest to the second and fourth nanowires but not to any other nanowires of the nine nanowires; (4) the fourth nanowire is closest to the third, fifth, and ninth nanowires but not to any other nanowires of the nine nanowires; and (5) the fifth nanowire is closest to the second, fourth, sixth, and eighth nanowires.

34. The device of claim 33, wherein: (1) the sixth nanowire is closest to the first, fifth, and seventh nanowires but not the other nanowires of the nine nanowires; (2) the sixth nanowire is closest to the first, fifth, and seventh nanowires but not the other nanowires of the nine nanowires; (3) the seventh nanowire is closest to the sixth and eighth nanowires but not the other nanowires of the nine nanowires; (4) the eighth nanowire is closest to the fifth, seventh, and ninth nanowires but not the other nanowires of the nine nanowires; and (5) the ninth nanowire is closest to the sixth and eighth nanowires but not the other nanowires of the nine nanowires.

35. (1) the first nanowire is closest to the second and eighth nanowires but not the other nanowires of the nine nanowires; (2) the second nanowire is closest to the first, third, and ninth nanowires but not the other nanowires of the nine nanowires; (3) the third nanowire is closest to the second and fourth nanowires but not the other nanowires of the nine nanowires; (4) the fourth nanowire is closest to the third, fifth, and ninth nanowires but not the other nanowires of the nine nanowires; and (5) the fifth nanowire is closest to the fourth and sixth nanowires but not the other nanowires of the nine nanowires.

34. The device of claim 33, wherein: (1) the sixth nanowire is closest to the fifth, seventh, and ninth nanowires but not the other nanowires of the nine nanowires; (2) the sixth nanowire is closest to the fifth, seventh, and ninth nanowires but not the other nanowires of the nine nanowires; (3) the seventh nanowire is closest to the sixth and eighth nanowires but not the other nanowires of the nine nanowires; (4) the eighth nanowire is closest to the first, seventh, and ninth nanowires but not the other nanowires of the nine nanowires; and (5) the ninth nanowire is closest to the second, fourth, sixth, and eighth nanowires but not the other nanowires of the nine nanowires.

36. 34. The device of claim 33, wherein (R2-R1)=(R3-R2)=(R4-R3)=(R5-R4)=(R6-R5)=(R7-R6)=(R8-R7).

37. 34. The device of claim 33, wherein R1 = 30 nm, R2 = 35 nm, R3 = 40 nm, R4 = 45 nm, R5 = 50 nm, R6 = 55 nm, R7 = 60 nm, R8 = 65 nm, and R9 = 70 nm.

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