Infrared image sensors based on high density rectangular planar arrays of nano tunnel junctions have been proposed. These sensors would differ fundamentally from prior infrared sensors based, variously, on bolometry or conventional semiconductor photodetection.
Infrared image sensors based on conventional semiconductor photodetection must typically be cooled to cryogenic temperatures to reduce noise to acceptably low levels. Some bolometer type infrared sensors can be operated at room temperature, but they exhibit low detectivities and long response times, which limit their utility. The proposed infrared image sensors could be operated at room temperature without incurring excessive noise, and would exhibit high detectivities and short response times. Other advantages would include low power demand, high resolution, and tailorability of spectral response. Neither bolometers nor conventional semiconductor photodetectors, the basic detector units as proposed would partly resemble rectennas. Nanometer-scale tunnel junctions would be created by crossing of nanowires with quantum mechanical-barrier layers in the form of thin layers of electrically insulating material between them (see figure). A microscopic dipole antenna sized and shaped to respond maximally in the infrared wavelength range that one seeks to detect would be formed integrally with the nanowires at each junction. An incident signal in that wavelength range would become coupled into the antenna and, through the antenna, to the junction. At the junction, the flow of electrons between the crossing wires would be dominated by quantum-mechanical tunneling rather than thermionic emission. Relative to thermionic emission, quantum- mechanical tunneling is a fast process. As described below, the quantum- mechanical tunneling would be exploited to rectify the infrared-frequency alternating signal delivered to the junction from the antenna.
Each nanojunction would be asymmetrical in that the crossing nanowires would be made of two different materials: for example, two different metals, a metal and semiconductor, or the same semiconductor doped at two different levels. The resulting asymmetry and nonlinearity of the tunneling current as a function of voltage across the junction could be exploited to effect rectification of the signal. Because the asymmetry would be present even in the absence of bias, the device could be operated at low or zero bias and, therefore, would demand very little power.
Other advantages of the proposed sensors would include the following:
- High spatial resolution would be achieved by virtue of the density of nanowires and, consequently, of nanojunctions.
- The barriers are expected to keep dark currents very small, leading to high signal-to-noise ratios.
- Different nanojunctions within the same sensor could be fabricated with antennas tailored for different wavelengths, enabling multispectral imaging.
This work was done by Kyung-Ah Son of Caltech; Jeong S. Moon of HRL, LLC; and Nicholas Prokopuk of Naval Air Warfare Center for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free online at www.techbriefs.com/tsp under the Electronics/Computers category. In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Innovative Technology Assets Management
JPL
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109-8099
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Refer to NPO-42587, volume and number of this NASA Tech Briefs issue, and the page number.
This Brief includes a Technical Support Package (TSP).
Arrays of Nano Tunnel Junctions as Infrared Image Sensors
(reference NPO-42587) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory, detailing the fabrication schemes and applications of nano tunnel junctions (NTJs) as infrared image sensors. It is part of the NASA Tech Briefs series, specifically referenced as NPO-42587, and aims to disseminate aerospace-related technological advancements with broader scientific and commercial implications.
The primary focus is on the fabrication processes of nano tunnel junctions, which are critical components in infrared imaging systems. Two distinct fabrication schemes are outlined:
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Scheme 1 involves the growth of a dielectric film (e.g., SiO2) on a silicon substrate, followed by e-beam lithography to pattern the film. The process includes reactive ion etching, metal deposition, and lift-off techniques to create the nano tunnel junctions. This method allows for the use of two different metals to form crossing nanowires, although it also mentions the possibility of using a single metal or a semiconductor with varying doping levels.
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Scheme 2 utilizes a silicon-on-insulator (SOI) surface, where e-beam lithography is again employed to pattern the silicon. The process includes reactive ion etching, thermal oxidation, and further e-beam lithography for metal deposition and lift-off. In this scheme, a highly doped silicon and a metal are used, with SiO2 serving as the barrier layer.
The document emphasizes the significance of these nano tunnel junctions in the development of room temperature infrared imagers, which have potential applications in various fields, including aerospace, environmental monitoring, and security. The use of NTJs allows for improved sensitivity and performance in infrared detection, making them suitable for advanced imaging systems.
Additionally, the document provides information on accessing further resources through NASA's Scientific and Technical Information (STI) Program Office, encouraging collaboration and innovation in the field. It also includes a disclaimer regarding the proprietary nature of the information and the absence of liability from the U.S. government for the use of the information contained within.
Overall, this Technical Support Package serves as a valuable resource for researchers and engineers interested in the fabrication and application of nano tunnel junctions in infrared imaging technologies, highlighting NASA's commitment to advancing aerospace-related developments.
