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Focal Plane Array for Passive Standoff Chemical Detection Based on Colloidal Quantum Dot Technology


OBJECTIVE: Develop methods that enable the production of low cost long wavelength infrared (LWIR) focal plane array technology specialized for use with chemical imaging sensors using colloidal quantum dot technology. DESCRIPTION: The Chemical/Biological Defense community has a need for passive standoff systems that detect and classify areas contaminated with chemical and biological vapors, aerosols, liquids and solids. Recently, hyperspectral imaging systems have shown great promise for the detection, identification, and real time display of chemical vapor and aerosol clouds. However, deployment of hyperspectral technology is limited by the cost, yield, and reliability of the infrared focal plane technology used in these sensors. The infrared focal plane array technology required for passive standoff detection of chemical and biological signatures is significantly different from the technology optimized for thermal imaging. The subdivision of far field spectral radiance into discrete spectral bands requires array technology with higher sensitivity, shorter integration times, and lower noise figures than is typically achieved with un-cooled technology. Similarly, the need for spectral response cutoff ranges in the 10 to 12 micron wavelength range to access important CB and toxic industrial material signatures exceeds the requirements for cooled thermal imaging devices while placing an additional burden on the cryocoolers needed to achieve requisite noise levels. The present topic addresses the need to develop and mature new infrared focal-plane-array technologies, to minimize/eliminate the requirement for cryogenic cooling, and to reduce costs. II-VI semiconductors have been successfully used for long wavelength infrared (LWIR) hyper spectral imaging within the Chemical/Biological defense community for some time. In particular HgCdTe photodetectors have been used successfully over a large range of wavelengths for chemical sensing. HgCdTe is a mature technology that has seen wide usage. However, HgCdTe fabrication still remains plagued with very low yields and high costs for device quality HgCdTe material. Also, HgCdTe requires cryogenic cooling at LWIR wavelengths. The high cost of HgCdTe and the need for cryogenic cooling have severely limited its application. Recently II-VI materials have been developed in colloidal quantum dot form. These materials have seen successful application in areas such as LED"s and solar cells. Colloidal quantum dot technology has the advantage of low cost and does not require apitaxial growth on expensive substrates. To date most colloidal quantum dot devices are based on cadmium or zinc chalcogenides and have been used for telecommunications type applications. The goal of this effort is to extend the utility of colloidal quantum dot devices to longer wavelengths in the infrared. This will require the use of II-VI materials with a lower bandgap. Candidates include PbS, PbSe, HgS, and HgTe. Recently infrared photodetectors have been demonstrated with cutoffs at 7 microns using HgTe colloidal quantum dots. It should be possible to extend this technology to the 8 to 12 micron spectral region for chemical/biological sensing applications. PHASE I: Examine methods for producing infrared focal plane arrays that are designed for use in standoff chemical and biological sensors based on colloidal quantum dots. Develop reliable fabrication methods for the production colloidal quantum dots. Characterize the new quantum dots and identify a path for practical realization of low-cost, high-performance LWIR focal plane arrays based on this technology. Conduct a study to define the spectral response range, pixel size and format, and noise requirements for focal plane array technology to be used across a range of standoff hyperspectral imaging system technologies. Examine methods to extend the capabilities of II-VI colloidal quantum dot photodetectors into the long wave infrared region (8 to 12 microns). Examine focal plane array (FPA) design constraints and imaging requirements to achieve designs that improve yield and quality while meeting cost and performance targets. Develop a manufacturing improvement plan for the production of the technology that identifies further research and development needed for this effort. PHASE II: Fabricate prototype focal plane arrays and assess FPA performance at the device level. Explore pathways to manufacture the IR FPA material and devices. Manufacturing development will require safe and reproducible production of large quantities of device quality quantum dots along with subsequent procedures to fabricate and characterize FPAs. Examine FPA formats of interest the chemical biological defense community and develop appropriate manufacturing methods. Develop and implement readout electronics designs required to effectively utilize the focal plane array technology. Explore the packaging of focal plane arrays into an integrated detector assembly for use with a hyperspectral imager and assess the performance of the system. Determine and document improvements in the system. PHASE III: Further research and development during Phase III efforts will be directed towards refining a final deployable design, incorporating design modifications based on results from tests conducted during Phase II, and improving engineering/form-factors, equipment hardening, and manufacturability designs to meet U.S. Army CONOPS and end-user requirements. The primary barrier to the broader use of hyperspectral technology for remote sensing of hazardous materials has been the technology cost, which is primarily driven by the cost of the focal plane technology. First responders such as civilian support teams, fire departments, and military post-blast reconnaissance teams have a critical need for a rugged and versatile and low cost sensor that can be transported to the field to test for possible CB contamination. This effort will facilitate the transition of the technology to those applications. REFERENCES: 1. D.A. Scribner, M.R. Kruer, and J.M. Killiany,"Infrared focal plane array technology", Proceedings of the IEEE, volume 79, issue 1, pages 66-85 (1991). 2. Werner Gross, Thomas Hierl, and Max Schulz,"Correctability and long-term stability of infrared focal plane arrays", Optical Engineering, volume 38, issue 5, pages 862-869 (1999). 3. M. R. Kruer, D. A. Scribner, and J. M. Killiany,"Infrared focal plane array technology development for Navy applications", Optical Engineering, volume 26, pages 182-190 (March 1987). 4. Sean Keuleyan, Emmanuel Lhuillier, and Philippe Guyot-Sionnest,"Synthesis of Colloidal HgTe Quantum Dots for Narrow Mid-IR Emission and Detection", Journal of the American Chemical Society, volume 133, pages 16422-16424 (2011). 5. Sean Keuleyan, Emmanuel Lhuillier, Vuk Brajuskovic and Philippe Guyot-Sionnest,"Mid-infrared HgTe colloidal quantum dot photodetectors", Nature Photonics, volume 5, pages 489-493 (2011).
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