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Array Detectors S W McKnight and C A DiMarzio Focal Plane Arrays Imaging Systems H R Runciman, Thermal Imaging, CRC Press Scanning vs. Staring Arrays • Scanning Systems – – – – – Point detector or linear array with scanning optics Less complicated detector Calibration easier Scanning system expensive, fragile Fast detector • Staring Arrays – – – – Multiple detectors elements to capture pixels of image Less complicated optics (lighter, smaller, no moving parts) Longer integration time to increase sensitivity Need multiplexer for signal read-out • Charge-Coupled Devices (CCD’s) – Charge transfer and collection – Easier processing, less interconnects • CMOS – Individually addressed and processed pixels – Less power – No loss in tranfer N-Channel FET Structure S, Source G, Gate n+ D, Drain n+ SiO2 Insulator 20-100mm Channel: 2 to 500 mm into page P-Type Material NMOS Metal-Oxide-Semiconductor B, Body Channel Length 1 to 10 mm Energy Band Picture of MOSFET (No Bias—Flatband) E Ec Ef Ev Metal (Al or Poly-Si) Oxide (SiO2) Semiconductor (p-Si) z Energy Band Picture of MOSFET (Positive Gate Bias) E Фb2 Ec Ef Va Фb1 Metal (Al or Poly-Si) Oxide (SiO2) Ev Semiconductor (p-Si) z MOSFET Carrier Reconfiguration (Depletion Bias) E Фb2 Va Ec Ef Фb1 Depletion Region Oxide Metal (SiO2) (Al or Poly-Si) Ev Semiconductor (p-Si) z Creation of Depletion Layer and Inversion Channel • Depletion layer forms within 1μs after bias is applied • Inversion channel created by thermally generated carriers in ~ 1 s • For times short compared to 1 s, nonequilibrium situation with depletion region and empty channel. • Carriers created by optical absorption or external injection can be stored in well for many ms. Carrier Injection Optical Injection E Ec Current Injection Vo-Vi Ef Va>Vt Depletion Region Ev Ef Oxide Metal (SiO2) (Al or Poly-Si) Semiconductor (p-Si) z Charge-Coupled Device (CCD) S G B Channel Length 1 to 10 mm D S D B ~10 mm X nRows Charge Transfer in CCD J Allison, Electronic Engineering Semiconductors and Devices, McGraw-Hill Streetman & Banerjee, Solid State Electronic Devices, Prentice-Hall Focal Plane Arrays • Monolithic Technology – – – – – Detector and read-out CCD on same chip Parallel processing (lower cost) Improved ruggedness Lower performance Lower yield • Hybrid Technology – – – – Detector and read-out fabricated separately and bonded Single-device processing (more expensive) Thermal mismatch Choice of material for better performance • HgCdTe for IR detector • Silicon for CCD Hybrid Technology H R Runciman, Thermal Imaging, CRC Press Hybrid Focal Plane Array J L Miller, Principles of Infrared Technology, Van Norstrand Reinhold Array Interconnects J L Miller, Principles of Infrared Technology, Van Norstrand Reinhold Platinum-Silicide Schottky Detectors EB~0.22 eV ↔ λ=5.6 μ PtSi Si hν Streetman & Banerjee, Solid State Electronic Devices, Prentice-Hall PtSi Array Detectors • • • • • Low quantum efficiency (~1%) Mid-Wave IR detection (1-5μ) Long integration time (~1/60 s) Good sensitivity ~0.05o C Compatible with Si technology Infrared Night Imaging Sierra Pacific Infrared, Inc. Infrared Night Imaging (2:15 AM) Sierra Pacific Infrared, Inc. Infrared Imaging—Circuit Hot Spot Sierra Pacific Infrared, Inc. Infrared Imaging—Water Damage in Ceiling Sierra Pacific Infrared, Inc. Infrared Imaging—Tank Fluid Level Sierra Pacific Infrared, Inc. Infrared Imaging--- Building Energy Efficiency Sierra Pacific Infrared, Inc. Infrared Imaging—Building Energy Efficiency Sierra Pacific Infrared, Inc. Infrared Imaging—Biology Sierra Pacific Infrared, Inc. Infrared Imaging—Power Line Faults Sierra Pacific Infrared, Inc. Infrared Medical Imaging—Patient Recovering from Spinal Surgery Sierra Pacific Infrared, Inc.