Modulation transfer function measurements of Type-II mid- wavelength and long-wavelength infrared superlattice focal plane arrays

Abstract Mid-wavelength Infrared (MWIR) and long-wavelength infrared (LWIR) Barrier Infrared Detector (BIRD) based on Antimonides Type-II superlattice detector array material are hybridized to 640 × 512, 1024 × 1024 and 1344 × 784 pixels format read out integrated circuits. The focal plane arrays (FPAs) Noise Equivalent Temperature Difference (NEΔT), Quantum Efficiency (η), Dark Current Density (J D ), and Modulation Transfer Function (MTF) performance were measured at operating temperatures. High performance 640 × 512 array format MWIR High Operating Temperature (HOT) FPA has typical NEΔT ∼ 19 mK, J D  ∼ 6.2 × 10 −7  A/cm 2 , and η ∼ 53% using 3–5 μm band pass filter at 115 K operating temperatures. Best performance 640 × 512 array format LWIR FPA has NEΔT ∼ 25 mK, J D  ∼ 2.5 × 10 −5  A/cm 2 and η ∼ 41% using 8–9.4 μm band pass filter at 60 K operating temperatures. For MTF investigation, a novel direct one-to-one image approach of Line Spread Function (LSF) and Edge Spread Function (ESF) are patterned onto substrate-removed FPAs. The direct LSF and ESF image are produced by 1000 A° thick gold layer deposition. The direct image horizontal and vertical MTFs are compared with projected knife-edge ESF-derived MTFs and results indicate that direct image MTFs have higher values compared to projected knife-edge ESF-derived MTFs at a Nyquist frequency. However, direct image MTF requires no lens MTF correction. The only relevant requirement for the direct image MTF is for the deposited pattern and substrate to be extremely thinned in which the HOT-BIRD FPAs fulfilled for this investigation.