BIO-INSPIRED NANOSTRUCTURES FOR IMPLEMENTING

VERTICAL PN-JUNCTIONS

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

[0001] This invention relates to pn-junction devices and more particularly relates to bio-inspired photosensors nanostructures for implementing pn-junctions. Particular embodiments in photodetection and energy harvesting are presented.

DESCRIPTION OF THE RELATED ART

[0002] Typical image sensing devices are planar, formed on the surface of a substrate. For example, a typical image sensor may include embedded p-type doped regions and n-type doped regions embedded in a surface of a silicon substrate. Unfortunately, the sensitivity of the photodetector is limited by the relatively small surface area available for an incoming photon to strike (hereafter called active area) as well as the short depletion region it passes through where the generated photo-charges will be collected. As resolution requirements for photodetectors increases, the capability of each sensor to detect photons is reduced, because the active area for collecting the photon is reduced.

[0003] A similar problem exists in the field of photovoltaics. However, the major problem in this field, among others, is the short depletion region path incident photon passes by before getting detected in a planar PN -junction; thus causing the photo-conversion efficiency of photo-voltaic to be often limited.

[0004] Additionally, certain low-light applications of photodetection, including fluorescence microscopy, require highly sensitive photodetectors. These types of applications also require relatively high resolution because of the extremely small size of the object to be imaged. Common planar photodetectors are typically not sufficiently sensitive nor with enough resolution power for such applications. In common systems, only Avalanche Photodiodes (AVD) are typically sensitive enough to capture enough light to perform this type of low-light application. The disadvantage of AVDs include cost and the need for cryogenic temperatures and complex control circuitry.

[0005] The referenced shortcomings of the art are not intended to be exhaustive, but rather are among many that tend to impair the effectiveness of previously known techniques in semiconductor sensors; however, those mentioned here are sufficient to demonstrate that the methodologies appearing in the art have not been satisfactory and that a significant need exists for the techniques described and claimed in this disclosure.

SUMMARY OF THE INVENTION

[0006] One embodiment of an apparatus is presented. The described embodiment includes a substrate, a first doped structure, and a second doped structure. In one embodiment, the first doped structure has a first doping type. The first doped structure may be formed above the substrate and extend outwardly from an upper surface of the substrate. In one embodiment, the second doped structure has a second doping type. The second doped structure may be formed above the substrate and in contact with the first doped structure. Additionally, the second doped structure may extend outwardly from the upper surface of the substrate.

[0007] In a further embodiment, the apparatus includes a first diffused layer formed between the substrate and the first doped structure, the first diffused layer having a third doping type. Additionally, the apparatus may include a second diffused layer formed between the substrate and the second doped structure, the second diffused layer having a fourth doping type. Also, the apparatus may include a first contact formed between the substrate and the first doped structure, and a second contact formed between the substrate and the second doped structure. In one embodiment, the first contact and the second contact comprise metal.

[0008] In another embodiment, the apparatus may include a first contact formed between the substrate and the first diffused layer; and a second contact formed between the substrate and the second diffused layer. [0009] In one embodiment, the first doped structure includes a rod-like structure. In such an embodiment, the second doped structure maybe deposited over a surface of the first doped structure. The first doped structure may have a substantially circular cross section. Alternatively, the first doped structure may have a substantially square cross section. In one embodiment, the second doped structure is substantially conical.

[0010] In one embodiment, the first doping type may be an n- typed doping, and the second doping type may be a p-type doping. Also, the third doping type may be an n ⁺ -typed doping, and the fourth doping type may be an p ⁺ -type doping.

[0011] In one embodiment, the apparatus may include a plurality of annular diffusion structures disposed within the second doped structure, but separated from each other by an insulator, the annular diffusion structures having the fourth doping type. In such an embodiment, the apparatus may also include a plurality of contacts, each contact coupled to one of the plurality of annular diffusion structures.

[0012] In one embodiment, the substrate may be flexible. In a particular embodiment, the substrate may be curved. In certain embodiments, the apparatus may also include an insulator layer formed between the substrate and the first and second doped structures.

[0013] In a further embodiment, the apparatus may include a transparent passivation layer formed above the substrate. In particular, the transparent passivation layer may include silicon glass.

[0014] In certain embodiments, the apparatus may include an interconnection layer, the first doped structure and the second doped structure being formed above the interconnection layer according to a hybrid process. In another embodiment, the first doped structure and the second doped structure may be formed within the interconnection layer according to a monolithic process. In certain embodiments, the apparatus may include structures formed both above and below the interconnection layer according to both hybrid and monolithic processes respectively. For example, such an apparatus may be configured to simultaneously harvest energy for operation of circuitry embedded in the monolithic design to sense photo signals or not. [0015] In a further embodiment, the apparatus may include one or more contact pads in electrical communication with the first doped structure and the second doped structure, the contact pads communicating signals from the first doped structure and the second doped structure to an external device.

[0016] One embodiment of a system is also presented. The system may include a substrate and a pn-junction structure. The pn-junction structure may include a first doped structure having a first doping type, the first doped structure formed above the substrate and extending outwardly from an upper surface of the substrate. Additionally, the pn-junction structure may include a second doped structure having a second doping type, the second doped structure formed above the substrate and in contact with the first doped structure, the second doped structure extending outwardly from the upper surface of the substrate.

[0017] Additionally, the system may include a Readout Integrated Circuit (ROIC) coupled to the pn-junction structure, the ROIC configured to receive signals from the pn-junction structure. One embodiment of the system may also include an Alternating Current ("AC") to Direct Current ("DC") converter circuit coupled to the ROIC. In certain embodiments, the system may also include an energy storage device coupled to the ROIC. Also, the system may include one or more contact pads coupled to the ROIC, the contact pads configured to communicate signals from the ROIC to an external device.

[0018] A wide-angle photodetector is also presented. In one embodiment, the wide-angle photodetector may include a curved substrate and a plurality of photodetectors disposed above the surface of the curved substrate. The photodetectors may include a first doped structure having a first doping type, the first doped structure formed above the substrate and extending outwardly from an upper surface of the substrate, and a second doped structure having a second doping type, the second doped structure formed above the substrate and in contact with the first doped structure, the second doped structure extending outwardly from the upper surface of the substrate.

[0019] In a further embodiment, the wide-angle photodetector may include a Readout Integrated Circuit (ROIC) coupled to the plurality of photodetectors. In a particular embodiment, the curved substrate is convex and can be concave in which case it can be supported by optical mirror, all of these to realize a wide view image sensor system.

[0020] An opto-fluidic microscope detector is also presented. In one embodiment, the opto- fluidic microscope detector includes an annular substrate having an interior surface and an exterior surface, and a plurality of a plurality of photodetectors disposed within the interior portion of the annular substrate. In such an embodiment, the photodetectors include a first doped structure having a first doping type, the first doped structure formed above the interior surface of the substrate and extending inwardly from the interior surface of the substrate, and a second doped structure having a second doping type, the second doped structure formed above the interior surface of the substrate and in contact with the first doped structure, the second doped structure extending inwardly from the interior surface of the substrate. In a further embodiment, the opto-fluidic microscope detector may include a Readout Integrated Circuit (ROIC) coupled to the plurality of 3D photodetectors.

[0021] One embodiment of a method is also presented. The method may include providing a substrate, forming a first doped structure, having a first doping type, above the substrate and extending outwardly from an upper surface of the substrate, and forming a second doped structure, having a second doping type, above the substrate and in contact with the first doped structure, the second doped structure extending outwardly from the upper surface of the substrate.

[0022] The method may also include forming a first diffused layer formed between the substrate and the first doped structure, the first diffused layer having a third doping type, and forming a second diffused layer formed between the substrate and the second doped structure, the second diffused layer having a fourth doping type. Also, the method may include forming a first contact between the substrate and the first doped structure, and forming a second contact between the substrate and the second doped structure. In a particular embodiment, the first contact and the second contact comprise metal.

[0023] In one embodiment, the method includes forming a first contact between the substrate and the first diffused layer, and forming a second contact between the substrate and the second diffused layer. [0024] In a particular embodiment, the first doped structure is a rod-like structure. The method may include depositing the second doped structure over a surface of the first doped structure. The first doped structure may have a substantially circular cross section. Alternatively, the first doped structure may have a substantially square cross section. In one embodiment, the second doped structure may be substantially conical.

[0025] In one embodiment, the first doping type comprises an n-typed doping, and the second doping type comprises a p-type doping. Additionally, the third doping type may include a n ⁺ -typed doping, and the fourth doping type may include an p ⁺ -type doping.

[0026] In a further embodiment, the method may include forming a plurality of annular diffusion structures disposed within the second doped structure but all annular diffusion structures separated from each other by an insulator. The annular diffusion structures may have the fourth doping type. Additionally, the method may include forming a plurality of contacts. Each contact may be coupled to one of the plurality of annular diffusion structures.

[0027] In one embodiment, the substrate may be flexible. In a further embodiment, the substrate may be curved. In still a further embodiment, the method may include forming an insulator layer between the substrate and the first and second doped structures.

[0028] In one embodiment, the method may include forming a transparent passivation layer above the substrate. The transparent passivation layer may include silicon glass. Also, the method may include forming the first doped structure and the second doped structure above an interconnection layer according to a hybrid process. In another embodiment, the method may include forming the first doped structure and the second doped structure within an interconnection layer according to a monolithic process.

[0029] The method may also include forming one or more contact pads in electrical communication with the first doped structure and the second doped structure, the contact pads communicating signals from the first doped structure and the second doped structure to an external device. [0030] The present embodiments may further describe the photosensitivity analysis and show how the geometry of the photodiode impacts it. Additionally, a semi-empirical analysis of the NPR based photodiode sensitivity and responsivity will be presented. The resulting dependence of the NPR photo-detection sensitivity on its height is proven and supporting examples from biological photocells are discussed. Also, some simulation results which have been carried out using Sentaurus tools from Synopsys are discussed.

[0031] The term "coupled" is defined as connected, although not necessarily directly, and not necessarily mechanically.

[0032] The terms "a" and "an" are defined as one or more unless this disclosure explicitly requires otherwise.

[0033] The term "substantially" and its variations are defined as being largely but not necessarily wholly what is specified as understood by one of ordinary skill in the art, and in one non-limiting embodiment "substantially" refers to ranges within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5% of what is specified.

[0034] The terms "comprise" (and any form of comprise, such as "comprises" and "comprising"), "have" (and any form of have, such as "has" and "having"), "include" (and any form of include, such as "includes" and "including") and "contain" (and any form of contain, such as "contains" and "containing") are open-ended linking verbs. As a result, a method or device that "comprises," "has," "includes" or "contains" one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more elements. Likewise, a step of a method or an element of a device that "comprises," "has," "includes" or "contains" one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed.

[0035] Other features and associated advantages will become apparent with reference to the following detailed description of specific embodiments in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein.

[0037] FIG. 1A is a perspective view diagram illustrating one embodiment of a pn-junction structure.

[0038] FIG. 1 B is a cross-section diagram illustrating one embodiment of a pn-junction structure.

[0039] FIG. 1 C is a bottom view diagram illustrating one embodiment of a pn-junction structure.

[0040] FIG. 2A is a perspective view diagram illustrating another embodiment of a pn-junction structure.

[0041] FIG. 2B is a bottom view diagram illustrating the pn-junction structure of FIG. 2A.

[0042] FIG. 3 A is a perspective view diagram illustrating one embodiment of a color sensing pn- junction structure.

[0043] FIG. 3B is a lateral cross-section view diagram illustrating the color sensing pn-junction structure of FIG. 3 A.

[0044] FIG. 3C is a lateral cross-section view diagram illustrating one embodiment of a color sensing pn-junction structure.

[0045] FIG. 4A is a perspective view diagram illustrating another embodiment of a pn-junction structure.

[0046] FIG. 4B is a front view diagram illustrating another embodiment of a pn-junction structure.

[0047] FIG. 4C is a front view cross-section diagram illustrating one embodiment of a color sensing pn-junction structure. [0048] FIG. 4D is a front view cross-section diagram illustrating another embodiment of a color sensing pn-junction structure having multiple cathode contacts.

[0049] FIG. 5A is a lateral cross-section diagram illustrating one embodiment of a system having a pn-junction structure formed according to a monolithic process.

[0050] FIG. 5B is a lateral cross-section diagram illustrating another embodiment of a system having a pn-junction structure formed according to a hybrid process.

[0051] FIG. 6 is a lateral cross-section diagram illustrating another embodiment of a system having a pn-junction structure having a portion formed according to a monolithic process and a portion formed according to a hybrid process.

[0052] FIG. 7 is a lateral cross-section diagram illustrating one embodiment of a wide-angle photodetector.

[0053] FIG. 8 is a lateral cross-section diagram illustrating one embodiment of a system having an insulator layer.

[0054] FIG. 9A is a lateral cross-section diagram illustrating one embodiment of an opto-fluidic microscope detector.

[0055] FIG. 9B is a perspective view diagram illustrating the opto-fluidic microscope detector of FIG. 9A.

[0056] FIG. 10 is a schematic flowchart diagram illustrating one embodiment of a method for manufacturing a pn-junction structure according to the present embodiments.

[0057] FIG. 11 A is a front cross-section view diagram illustrating one embodiment of a color sensing pn-junction structure having contacts arranged along a single plane.

[0058] FIG. 1 IB is a front cross-section view diagram illustrating one embodiment of a color sensing pn-junction structure having contacts arranged along a single plane, and having a first doped structure comprising multiple substructures, each with its own contact formed along the plane. [0059] FIG. 12 is a schematic of the NPR test implementation and shows an SEM picture of the fabricated NPR photodiode to be soon tested.

[0060] FIG. 13 is the responsivity of NPR photodiode versus its height.

[0061] FIG. 14 is the SEM of a fabricated NPR using liftoff and deep ICPRIE.

DETAILED DESCRIPTION

[0062] Various features and advantageous details are explained more fully with reference to the nonlimiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well known starting materials, processing techniques, components, and equipment are omitted so as not to unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the invention, are given by way of illustration only, and not by way of limitation. Various substitutions, modifications, additions, and/or rearrangements within the spirit and/or scope of the underlying inventive concept will become apparent to those skilled in the art from this disclosure.

[0063] The present embodiments may revolutionize semiconductor electronic imaging technology by providing three-dimensional pn-junction structures. PN-junction structures are the building blocks of several types of semiconductor sensor devices, particularly in the fields of optics and photonics. The present embodiments describe a variety of rod-like nanostructures which maybe implemented in a variety of, e.g., sensing and energy harvesting applications.

[0064] FIGs. 1A-1C illustrate one embodiment of an apparatus 100 that includes a three- dimensional (3D) pn-junction. The described embodiment includes a first doped structure 102, and a second doped structure 104. As shown in FIGs. 5A-6, the apparatus 100 may include a substrate 502. In one embodiment, the first doped structure 102 has a first doping type. The first doped structure 102 may be formed above the substrate 502 and extend outwardly from an upper surface of the substrate 502. In one embodiment, the second doped structure 104 has a second doping type. The second doped structure 104 may be formed above the substrate 502 and in contact with the first doped structure 102. Additionally, the second doped structure 104 may extend outwardly from the upper surface of the substrate 502.

[0065] In one embodiment, the substrate 502 is a silicon substrate. Those of skill in the art will appreciate that other suitable substrates 502, such as quartz or graphene and the like, may be substituted for silicon. The first doped structure 102 maybe grown or deposited above the substrate 502. In a particular embodiment, the first doped structure 102 may be grown or deposited directly on an upper surface of the substrate 502. Alternatively, one or more intermediary layers may be formed between the first doped structure 102 and the second doped structure. Various techniques may be used to grow or deposit the first doped structure 102, including, but not limited to Vapor Liquid Solid (VLS) techniques known in the art. The second doped structure 104 may be formed on the first doped structure 102 using, for example, Chemical Vapor Deposition (CVD), Atomic Layer Deposition (ALD) or the like.

[0066] In a further embodiment, the apparatus 100 includes a first diffused layer 108 formed between the substrate 502 and the first doped structure 102, the first diffused layer 108 having a third doping type. Additionally, the apparatus 100 may include a second diffused layer 106 formed between the substrate 502 and the second doped structure 104, the second diffused layer 106 having a fourth doping type. Also, the apparatus 100 may include a first contact 1 12 formed between the substrate 502 and the first doped structure 102, and a second contact 110 formed between the substrate 502 and the second doped structure 104. In one embodiment, the first contact 112 and the second contact 1 10 comprise metal.

[0067] In one embodiment, the first diffused layer 108 and the second diffused layer 106 may be formed using an ion implantation or bombardment technique. For example, a layer of p-type material may be deposited. Then, the layer of p-type material may be bombarded with p ⁺ ions to form the first diffused second diffused layer 106. Those of skill in the art will recognize a variety of operations suitable for forming an impurity diffused layer.

[0068] In another embodiment, the apparatus 100 may include a first contact 112 formed between the substrate 502 and the first diffused layer 108; and a second contact 1 10 formed between the substrate 502 and the second diffused layer 106. In one embodiment, the first contact 1 12 and the second contact 110 may be formed using, e.g., a metal sputtering technique. Alternatively electroplating, or other techniques may be used.

[0069] In one embodiment, the first doped structure 102 includes a rod-like structure. In such an embodiment, the second doped structure 104 may be deposited over a surface of the first doped structure 102. The first doped structure 102 may have a substantially circular cross section as shown in FIGs. 2A-2B. Alternatively, the first doped structure 102 may have a substantially square cross section as shown in FIGs 1 A-1C. In one embodiment, the second doped structure 104 is substantially conical as shown in FIGs 4A-4B. Indeed, one of skill in the art will recognize that the second doped structure 104 may have other geometric shapes, depending upon fabrication constraints or performance. For example, the second doped structure 104 may have a rectangular cross-section, an oval cross-section, or the like.

[0070] In one embodiment, the first doping type may be an n-type doping, and the second doping type may be a p-type doping. Also, the third doping type may be an n ⁺ -typed doping, and the fourth doping type may be an p ⁺ -type doping.

[0071] As illustrated in FIG. 3, another embodiment of the apparatus 300 may include a plurality of annular diffusion structures 302 disposed within the second doped structure 104 and separated by an insulating material 310 between each annular diffusion structure. Alternatively, the annular diffusion structures 302 may be disposed between a plurality of segments of the second doped structure 104 and/or insulating layers 310. In a particular embodiment, the annular diffusion structures 302 may have the fourth doping type. In a specific embodiment, the annular diffusion structures 302 are p ⁺ -type doped. In such embodiments, the apparatus 100 may also include a plurality of contacts 304 -308. Each contact 304-308 may be coupled to one of the plurality of annular diffusion structures 302. In a particular embodiment, the each contact 304-308 pay provide a signal corresponding to a color of detected light. For example, the first contact 304 may be configured to provide a signal corresponding to a level of blue- frequency light detected by the apparatus 300. In such an embodiment, the second contact 306 and the third contact 308 may provide signals corresponding to green- frequency light levels and red-frequency light levels respectively. [0072] In a particular embodiment, the apparatus 300 described in FIGs. 3 A-3B maybe enhanced using chromatic Nano-Photo-Rod technology to improve color sensing resolution. In certain applications, the cathode voltage sharing between three reverse-biased color photodiodes may become an issue. In such situation, only a single annular structure may be used at one time, but at the corresponding color height. In such an embodiment, the apparatus 300 may comprise three Chromatic Nano-Photo-Rods (CNPRs) per chromatic pixel.

[0073] In a further embodiment, the first doped structure 102 may include a plurality of doped substructures 312-316 as illustrated in FIG. 3 C. In a particular embodiment, the plurality of doped substructures 312-316 may be separated by an insulator layer 310. In particular, the plurality of doped substructures 312-316 may comprise three co-centric substructures 312-316, each insulated from the others. In particular, each of the co-centric substructures 312-316 may extend as high as their anode contacts respectively. These co-centric substructures 312-316 may comprise cathodes. In a particular embodiment, the co-centric substructures 312-316 may not share the same voltage potential at their bases. In such an embodiment, the contact 1 12 may be replaced with a plurality of contact structures 112 as illustrated. In one embodiment, the contact structures 1 12 may be electrically isolated from each other. In such an embodiment, the problem of voltage sharing between the three reverse-biased color photodiodes may be resolved by using only one color cone at a time corresponding to the color height. In such an embodiment, three CNPCs per chromatic pixel is achievable.

[0074] Similarly, as illustrated in FIGs. 4C-4D, the second doped structure 104 may include a plurality of substructures 402, 406, 408. In a particular embodiment, each of the substructures 402, 406, and 408 may be separated by an insulator layer 404, 408, respectively. In still a further embodiment, each of the plurality of substructures 402, 406, 408 may be coupled to a separate contact 412-416 respectively. This embodiment may further enhance color sensing resolution.

[0075] If the cathode voltage sharing between the 3 reverse-biased color photodiode becomes an issue, one embodiment may use only one color cone at a time at the corresponding color height. Such an embodiment may yield three chromatic CNPCs per chromatic pixel. In a particular embodiment, three co-centric (insulated from each other) cathode may be used as high as their anode conic contacts. These co-centric cathodes will not share the same voltage potential at their bases. This embodiment is illustrated in FIG. 4D.

[0076] FIGs. 1 1A-1 1B illustrate an alternative embodiment of a color sensing PN-junction structure. In this embodiment, the contacts may be formed along a single plane. For example, the contacts may be formed over a substrate in a plane that is parallel to a surface of the substrate 502.

[0077] In a further embodiment, the apparatus 100 may include a transparent passivation layer 552 formed above the substrate 502. In particular, the transparent passivation layer 552 may include silicon glass.

[0078] In certain embodiments, the apparatus 100 may include an interconnection layer 506, the first doped structure 102 and the second doped structure 104 being formed above the interconnection layer 506 according to a hybrid process. In another embodiment, the first doped structure 102 and the second doped structure 104 may be formed within the interconnection layer 506 according to a monolithic process.

[0079] The advantages of a monolithic process may include ( 1 ) fewer extra-processing steps, (2) the device may be integrated within standard CMOS processes, (3) less optical-cross talk may result, (4) no need for micro-lens due to large active areas, (5) the surrounding metal interconnection can be used as "focusing" devices similar to micro-lenses used in CMOS imagers, and (6) zero-cross pixel cross-talk both electrically and optically. These advantages make monolithic processes good for manufacturing image sensors. The disadvantages of monolithic processes include (1) the process may be limited to deep trench etching design rules, (2) parasitic capacitance from the surrounding metal routing interconnections may need to put metal routing clearance around the NPR structure, and (3) depending on fabrication limitations, NPR length may be limited to a certain range.

[0080] The advantages of the hybrid process include ( 1 ) a variety of nano fabrication techniques can be used to manufacture the required NPR structure, and (2) higher photo-collection. These advantages make hybrid processes good for manufacturing energy harvesting devices. The disadvantages of the hybrid approach include (1 ) The semiconductor material used to build the NPR may not be epitaxial leading to amorphous structure the cause of large dark currents and noise, (2) large RC delay and large parasitic capacitance may limit the NPR photo-sensitivity, and (3) due to top-metal layer requirements NPR distribution density might be reduced.

[0081] In certain embodiments, the apparatus 100 may include structures formed both above and below the interconnection layer 506 according to both hybrid and monolithic processes respectively. The embodiment of FIG. 6 is useful in biomedical and spatial imaging where extended-imaging-time and very-limited-power supply requirements are needed. Advantageously, the apparatus of FIG. 6 may have multiple simultaneous uses because of the dual use of the smart-NPR structure. For example, such an apparatus 100 may be configured to simultaneously harvest energy for operation of circuitry and sense photo signals.

[0082] In a further embodiment, the apparatus 100 may include one or more contact pads 508 in electrical communication with the first doped structure 102 and the second doped structure 104, the contact pads 508 communicating signals from the first doped structure 102 and the second doped structure 104 to an external device.

[0083] In one embodiment, the substrate 502, 702 may be flexible. Also, as illustrated in FIG. 7, the substrate 702 maybe curved. As illustrated in FIG. 8, another embodiment of the apparatus 800, may also include an insulator layer 802 formed between the substrate 502 and the first and second doped structures 104. In one embodiment, the insulator layer 802 may include a buried oxide layer used in Silicon-On-Insulator CMOS chips. Such an embodiment maybe used in harsh environments, for example in spacecraft applications.

[0084] FIG. 5 A illustrates one embodiment of a system 500. The system may include a substrate 502 and a pn-junction structure 510. The pn-junction structure 510 may include a first doped structure 102 having a first doping type, the first doped structure 102 formed above the substrate 502 and extending outwardly from an upper surface of the substrate 502. Additionally, the pn-junction structure 510 may include a second doped structure 104 having a second doping type, the second doped structure 104 formed above the substrate 502 and in contact with the first doped structure 102, the second doped structure 104 extending outwardly from the upper surface of the substrate 502. In a particular embodiment, the pn-junction structure 510 may comprise a photodetector. [0085] Additionally, the system 500 may include a Readout Integrated Circuit (ROIC) 504 coupled to the pn-junction structure 510, the ROIC 504 configured to receive signals from the pn- j unction structure 510.

[0086] FIG. 6 illustrates another embodiment of a system 600. The system 600 include an Alternating Current to Direct Current ("AC/DC") converter circuit 606 coupled to the ROIC 504. In certain embodiments, the system may also include an energy storage device 608 coupled to the ROIC 504. Also, the system 600 may include one or more contact pads 508 coupled to the ROIC 504, the contact pads 508 configured to communicate signals from the ROIC 504 to an external device (not shown).

[0087] FIG. 7 illustrates one embodiment of a wide-angle photodetector 510. In one embodiment, the wide-angle photodetector 510 may include a curved substrate 702 and a plurality of photodetectors 510 disposed above the surface of the curved substrate 702. The photodetectors 510 may include a first doped structure 102 having a first doping type, the first doped structure 102 formed above the substrate 502 and extending outwardly from an upper surface of the substrate 502, and a second doped structure 104 having a second doping type, the second doped structure 104 formed above the substrate 502 and in contact with the first doped structure 102, the second doped structure 104 extending outwardly from the upper surface of the substrate 502.

[0088] In a further embodiment, the wide-angle photodetector 510 may include a Readout Integrated Circuit (ROIC) 504 coupled to the plurality of photodetectors 510. In a particular embodiment, the curved substrate 702 is convex, thus capturing photons 706 from a wide range of angels. Additionally, the apparatus 700 of FIG. 7 may include a transparent passivation layer 704 formed above the curved substrate 702.

[0089] FIGs. 9A-9B illustrate one embodiment of an opto-fluidic microscope detector 900. In one embodiment, the opto-fluidic microscope detector 900 includes an annular substrate 702 having an interior surface and an exterior surface, and a plurality of a plurality of photodetectors 510 disposed within the interior portion of the annular substrate 702. In such an embodiment, the photodetectors 510 include a first doped structure 102 having a first doping type, the first doped structure 102 formed above the interior surface of the substrate 502 and extending inwardly from the interior surface of the substrate 502, and a second doped structure 104 having a second doping type, the second doped structure 104 formed above the interior surface of the substrate 502 and in contact with the first doped structure 102, the second doped structure 104 extending inwardly from the interior surface of the substrate 502. In a further embodiment, the opto-fluidic microscope detector 900 may include a Readout Integrated Circuit (ROIC) 504 coupled to the plurality of 3D photodetectors 510.

[0090] In the embodiment of FIG. 9B, the light is tangent to the micro-fiuidic flow and a nano- holes metal sheet may be used as a light uniforming medium to be reflected by the flowing microorganisms bodies. Such an embodiment provides a 3D microscopic imaging that will benefit lab-on- chip biomedicine tremendously. Certain advantages of the embodiment in FIGs. 9A-9B include: (1) NPR high Low light sensitivity relaxes tangent light intensity requirement, (2) the NPR sensitivity geometry enables higher optical resolution and minimal cross talk, and (3) a fluorescent specimen may be used to have a 3D image of the object.

[0091 ] Indeed, the described embodiments may be used in a variety of applications, including but not limited to, CMOS imaging sensors, photovoltaics, biomedical imaging, space imaging, and night vision imaging. For example, the present embodiments may be advantageous in photovoltaics because the solar energy harvesting efficiency of the photovoltaic devices may be improved by expanding the total surface area that is capable of collecting a photon and converting the photon into usable energy. Specifically, in such an embodiment, the rod-like pn-junction structure may dramatically increase the probability of electron-hole pair generation (photo-electric effect) over the semiconductor active area, because the total surface area available to receive the photon is increased.

[0092] The schematic flow chart diagrams that follow are generally set forth as logical flow chart diagrams. As such, the depicted order and labeled steps are indicative of one embodiment of the presented method. Other steps and methods maybe conceived that are equivalent in function, logic, or effect to one or more steps, or portions thereof, of the illustrated method. Additionally, the format and symbols employed are provided to explain the logical steps of the method and are understood not to limit the scope of the method. Although various arrow types and line types may be employed in the flow chart diagrams, they are understood not to limit the scope of the corresponding method. Indeed, some arrows or other connectors may be used to indicate only the logical flow of the method. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of the depicted method. Additionally, the order in which a particular method occurs may or may not strictly adhere to the order of the corresponding steps shown.

[0093] FIG. 10 illustrates one embodiment of a method 1000 of forming a pn-junction structure 510. The method 1000 may include providing 1002 a substrate 502, forming 1004 a first doped structure 102, having a first doping type, above the substrate 502 and extending outwardly from an upper surface of the substrate 502, and forming 1006 a second doped structure 104, having a second doping type, above the substrate 502 and in contact with the first doped structure 102, the second doped structure 104 extending outwardly from the upper surface of the substrate 502.

[0094] The method 1000 may also include forming a first diffused layer 108 formed between the substrate 502 and the first doped structure 102, the first diffused layer 108 having a third doping type, and forming 1006 a second diffused layer 106 formed between the substrate 502 and the second doped structure 104, the second diffused layer 106 having a fourth doping type. Also, the method 1000 may include forming a first contact 1 12 between the substrate 502 and the first doped structure 102, and forming a second contact 110 between the substrate 502 and the second doped structure 104. In a particular embodiment, the first contact 1 12 and the second contact 110 comprise metal.

[0095] In one embodiment, the method 1000 includes forming a first contact 1 12 between the substrate 502 and the first diffused layer 108, and forming a second contact 110 between the substrate 502 and the second diffused layer 106. For example, such an embodiment may be used to manufacture a device for Silicon on Insulator (SOI) CMOS technology.

[0096] In a particular embodiment, the first doped structure 102 is a rod-like structure. The method 1000 may include depositing the second doped structure 104 over a surface of the first doped structure 102. The first doped structure 102 may have a substantially circular cross section. Alternatively, the first doped structure 102 may have a substantially square cross section. In one embodiment, the second doped structure 104 may be substantially conical.

[0097] In one embodiment, the first doping type comprises an n-typed doping, and the second doping type comprises a p-type doping. Additionally, the third doping type may include a n ⁺ -typed doping, and the fourth doping type may include an p ⁺ -type doping. [0098] In a further embodiment, the method 1000 may include forming a plurality of annular diffusion structures 302 disposed within the second doped structure 104. The annular diffusion structures 302 may have the fourth doping type. Additionally, the method 1000 may include forming a plurality of contacts 304. Each contact may be coupled to one of the plurality of annular diffusion structures 302.

[0099] In one embodiment, the substrate 502 may be flexible. In a further embodiment, the substrate 502 may be curved. In still a further embodiment, the method 1000 may include forming an insulator layer 802 between the substrate 502 and the first and second doped structures 104.

[0100] In one embodiment, the method 1000 may include forming a transparent passivation layer 552 above the substrate 502. The transparent passivation layer 552 may include silicon glass. Also, the method 1000 may include forming the first doped structure 102 and the second doped structure 104 above an interconnection layer 506 according to a hybrid process. In another embodiment, the method 1000 may include forming the first doped structure 102 and the second doped structure 104 within an interconnection layer 506 according to a monolithic process.

[0101] The method 1000 may also include forming one or more contact pads 508 in electrical communication with the first doped structure 102 and the second doped structure 104, the contact pads 508 communicating signals from the first doped structure 102 and the second doped structure 104 to an external device.

EXAMPLES

[0102] The present embodiments describe a nano-pho tonic rod (NPR) structure to replace the planar photodiode. It is a nano-photonic pillar of n-type (cathode) semiconductor covered by a p-type (anode) semiconductor as shown in FIGS. 1 A - 1C.

[0103] Embodiments of a NPR based pixel for electronic imaging may avoid the HRLL stringent requirements micro-lenses are used in the planar photodiodes to enhance the effective pixel fill factor especially, which becomes even harder with increasing resolution requirements. NPR structures, for example as illustrated in FIGs. 1 A- 1 C, may alleviate previous limitations of the art by eliminating the need for micro-lenses, thanks in part to its very high fill factor. Additionally, certain embodiments may boost the current imaging resolutions to higher levels, thus benefiting far more applications in biomedical imaging and communication systems.

Sensitivity Analysis

[0104] One of the features characterizing active pixel sensors is their photosensitivity that relates two factors, the conversion gain (CG) and the quantum efficiency (QE) as derived from the following:

where # , CG - qf C _D , where q is the electron charge and C _D is the photodiode capacitance at the integration node which can be written as: C _p ' _D = A'"' x C _pD , where A"" and C _P ^A _D are the area the integration node areal capacitance respectively. Therefore,

Vout— QE x (# ph) x CG (10),

(#ph) is the number of interacting photons which can be calculated as:

(# ph) = ^ ^{x A X T} (12),

nv where A ^gen is the generating area where the electron-hole pairs are photo-generated, Tint is the integration time, h is the Plank constant, v is the photon frequency and Φ _ίη is the incident light interacting flux. Therefore, r A ^gen Y T ^int

Vout = QE x — x CG (13).

hv

[0105] In one embodiment, the sensitivity is the derivation of the output voltage with respect to light intensity and integration time. This derivation may be taken in the linear region of the photon transfer curve of the pixel and this derivation can be replaced by the variation. The result is the following equation:

QE x A ^ge "

x CG (14).

inc x T" hv

On the other hand, the responsivity may be defined as:

R _e = Q ^{E x} - (15)·

hv

Therefore, the sensitivity can be derived from equations (14) and (15) as the following: n A gen j

S = ^x A ^ge " x CG = R x—- x -^- (16).

q Ά i^ _PD

[0106] Two cases, which differentiate two major types of APS sensors, follow from the above equation. W enA ^ge "≠l ^,nt , then the integration node is separated from the generation node; therefore, minimizing^'"' relative to A ^gen will enhance the sensitivity. This is the case of the 4T photogate APS sensor, where the floating diffusion, which plays the role of the integration node, is made as small the technology allows, while the photodiode is basically a large CCD MOS structure. In the other case, when A ^gen =A ^int , then the sensitivity S may be independent explicitly of the photodiode geometry and is only dependent on the device's physical characteristics. This case corresponds to the three- transistor (3T) APS configuration.

[0107] The geometry of the 3T APS photodiode may influence its sensitivity through the responsivity R _e , which depends on the depletion region width, besides other parameters. This width is the path length of the trajectory of the photon passing by the depletion region.

[0108] Four factors may have an impact on NPR photodiode sensitivity. First, the anode maybe fully depleted by lowering its doping concentration, thus expanding the depletion region width to the whole anode thickness. Consequently, the photodiode areal capacitance may be reduced and its responsivity R _e enhanced C . Second, by having the depletion region perpendicular to the photon pathway, the electron-hole pair EHP recombination in the depletion region maybe diminished. This effect may be due to the fact that as soon as EHP is created, electron and hole charges are separated by the junction internal electric field. Therefore, the number of collected charges increases, thus boosting the photodiode responsivity R _e. Third, the enhancement in the previous factor may be further improved because the depletion region volume is higher, compared to a similar photodiode, thanks to its high aspect ratio. The depletion region volume can be increased by widening the thickness of the anode, which in addition reduces the areal capacitance C as discussed in the first

PD

factor. Thus, increasing the anode thickness has double enhancing effect on the overall responsivity. Finally, in the case of full depletion, the effect of diffused dark current from the silicon dead area that is absent from the NPR photodiode structure may be minimal. A dark current can also be generated by the defects located in the depletion region. However, it is thought that their contribution may be minimal due to the built-in field.

[0109] The absence of a dead zone in the NPR, or in between NPR-photodiode-based pixels may cancel out photoelectrical crosstalk between pixels. This minimal crosstalk property may be absent in current CMOS imaging technology based on the planar photodiode. This is due, in part, to the relatively large volume of dead semiconductor area from which photo-thermal currents diffuse randomly to the adjacent pixels, thus increasing crosstalk.

Semi-Empirical Sensitivity Analysis

[0110] One widely accepted semi-empirical formula for the pixel photosensitivity can be rewritten as:

where C _\ and C ₂ are empirical fitting parameters, A and Tare the pixel active (z. e. A=NPR_base) and total areas, respectively. L and L^ff are the maximum and diffusion lengths of the photo-generated carriers respectively, and C _A and Cp are respectively the photodiode areal and peripheral capacitances. Finally, P and d are the photodiode perimeter and junction depth respectively, and fiA) is a function of the area accounting for the planar photodiode bottom area photo-charge contribution. The second term of the numerator considers the peripheral diffusion current contribution (lateral and bottom contributions). Assuming a negligible NPR photodiode footprint area, i. e. NPRJbase, and a minimal areal contribution _ ( ί)~(), the NPR sensitivity can be derived from equation (17) as:

which can be further simplified, knowing that the NPR diameter is much smaller than L _di ff , to the following equation:

S = ^- h (19).

C

[0111] Equation (19) may provide a mathematic relation between the NPR photodiode sensitivity S, on one hand, and its geometrical (A) and electrical properties (C ₂ and Cp) on the other. The parameters controlling the NPR photodiode sensitivity are its height h and its peripheral capacitance Cp. Therefore, enhancing NPR photodiode sensitivity may be achieved either by minimizing Cp or by enlarging NPR height h or both. The peripheral capacitance C _P can be reduced by fully depleting the NPR photodiode with a relatively thicker anode. The technique of enlarging NPR photodiode height h, however, may be biologically implemented by light-controlled height-extension in bio-photocells. This phenomenon has been observed in the biological photocells of mammalians such Bullfrogs. They adapt the length of their photocells (cones): elongating them in dim lights and shortening them in bright lights. A similar phenomenon is present in non-mammalian species such as Haplochromis burtoni (fish).

Fabrication and Simulation Analysis

[0112] The NPR structures may be fabricated based on N-doped wafer and using the lift-off masking technique to pattern various nanopillars in terms of diameter and pitch. The height may be determined by etching the non-masked area using Inductive-Coupling Plasma Reactive Ion Etching (ICPRIE). Next, the doping phase is realized by ion-implanting the surface of the nanorods with Boron to create P-doped anode layer. Finally, contact areas, to NPR cathode and anode layers, maybe created by heavily implanting these areas to make them ohmic. This will allows the probing and characterize the NPR structure. This fabrication technique is used merely for proof-of-concept and illustrative purposes, but is not intended to limit the scope of the claimed devices or methods in any way. Many sample arrays of NPR rods have been fabricated along with their probing contacts as depicted by FIG. 13.

[0113] Simulation carried out using Sentaurus work bench, a Synopsys TCAD tool, was performed on a single O^m-wide NPR photodiode to characterize its photo-electrical response versus various heights at a light wave length of 0.5μηι. FIG. 14 shows the dependence of the NPR photoresponsivity versus its height. The curve shows a linear trend of the NPR responsivity versus its height for size below 0.7|im.

[0114] All of the methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the apparatus and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. In addition, modifications may be made to the disclosed apparatus and components may be eliminated or substituted for the components described herein where the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope, and concept of the invention as defined by the appended claims.