Correlated noise and gain in unfilled and epoxy-underfilled hybridized HgCdTe detectors

Spatially correlated noise in focal plane arrays ( FPAs) affects the photometric signal- to- noise ratio and can lead to overestimation of conversion gain ( detector nodal capacitance). Capacitive coupling leads to charge sharing between neighboring pixels and correlates the measured pixel signal. This correlation can lead to image degradation, in particular for undersampled large survey telescopes. We present new comparative measurements of the interpixel coupling of 1.7 and 2.5 mu m cutoff HgCdTe FPAs. Rockwell Scientific FPAs with epoxy underfill exhibit correlations that result in a 16% - 20% systematic overestimation of the conversion gain. Results for a Raytheon Vision Systems 1.7 mu m cutoff HgCdTe detector tested both before and after epoxy underfill show increased coupling in the presence of the epoxy, but the coupling is not spatially symmetric. We speculate that the difference in the observed correlation for each vendor is related to multiplexer geometry and pixel nodal capacitance.