Astrometric errors introduced by interpixel capacitive coupling in hybridized arrays

Abstract

Interpixel capacitance (IPC) between adjacent pixels in hybridized arrays gives rise to an electrostatic cross talk. This cross talk causes MTF degradation and blurring of images or spectra collected using these devices. As pixel size is driven down from the 18-μm pixel pitch of the H2RG read out circuits to the 10- or 15-μm H4RGs IPC is driven up resulting in greater cross talk, all else being equal. Mounting evidence indicates that IPC varies as a function of depletion state of the photo-active diodes. For single pixel events, increasing the event intensity corresponds to a decreasing fractional coupling. If left uncorrected, IPC can give rise to systematic errors in precision astrometric and photometric measurements, in particular when dealing with confused point sources or spatially extended structures for shape measurements as demonstrated through comparison of registered sources from ESO HAWK-I and HST ACS WFC datasets. Furthermore, these errors will be the most significant when operating near the sensitivity limit of these devices. Deconvolution-based correction methods are invalidated by this same signal dependence. Instead, a numerical method of successive approximation can be used to correct coupling due to a well-characterized IPC. Examination of single pixel reset data above flat fields could be used to characterize IPC’s functional relationship for neighboring pixels. This higher quality characterization can result in more accurate correction.