Small pixel pitch MCT P on N MWIR photodiodes at DEFIR: towards 7.5um and beyond with very high image quality

Abstract

MCT p-on-n photodiodes manufactured at Lynred and CEA-LETI have demonstrated state of the art performances for HOT applications. On blue and red mid infrared bands on 15μm pixel pitch, respectively 150 and 130K operating temperatures have been obtained, due to diffusion limited dark current and low defectivity. To achieve equivalent results on smaller pixel, the p-on-n technology at DEFIR, joint laboratory between Lynred and CEA-LETI, has been improved. The technological process was modified to ensure a proper diode formation and to efficiently passivate the interface between MCT and encapsulation layers, especially in the vicinity of the space charge region. The manufactured arrays with a 5.3μm cutoff wavelength have been hybridized on a digital output SXGA (1280×1024) direct injection ROIC with a pixel pitch of 7.5 μm. This paper present the measured current, blackbody responsivity and RMS noise on FPAs with F/4 numerical aperture. We will also discuss spectral response, quantum efficiency, shot-noise limited photodiodes and noise histograms shapes and their distribution tails at 130K. The very low number of defective pixel allow to address higher operating temperature and measurements have been performed at 140K and even 150K with very limited performance degradation. Pixel pitch of 5 μm has been characterized on test chips and present I-V curves with low dispersion and long bias plateau. As for larger pixel sizes, these photodiodes are shot-noise limited. Modulation transfer function has been measured by electron beam induced current and presents high value, up to 56%.

A 14-Bit Hybrid Analog-to-Digital Converter for Infrared Focal Plane Array Digital Readout Integrated Circuit

“…This setup allows the 7-bit SAR ADC to perform coarse quantization in the first phase with only 7 SAR clock cycles. In the second phase, a 7-bit SS ADC conducts fine quantization using 2 7 SS clock cycles.…”

“…This setup allows the 7-bit SAR ADC to perform coarse quantization in the first phase with only 7 SAR clock cycles. In the second phase, a 7-bit SS ADC conducts fine quantization using 2 7 SS clock cycles. The value of the unit capacitor, Cu, is a compromise considering thermal noise, the process capacitance error, parasitic capacitance, and the switching mode of the capacitor array.…”

“…In [ 7 , 8 , 9 ], small-pixel digital sensors provide advantages in reducing the size, weight, and power (SWaP), improving noise immunity, simplifying interfacing requirements, and lessening susceptibility to electromagnetic interference (EMI). DROIC, which is based on pixel-level ADC, directly accomplishes analog-to-digital conversion in a pixel array [ 10 , 11 , 12 , 13 ].…”