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
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4800 Oak Grove Drive
Pasadena, CA 91109-8099
Refer to NPO-42587, volume and number of this NASA Tech Briefs issue, and the page number.