The Reset Switch Charge Decay Effect in JWST/MIRI Observations

Blocked impurity band arsenic-doped silicon detectors such as those used in the James Webb Space Telescope’s Mid-Infrared Instrument were invented in the 1980s to overcome many of the unwanted second-order effects found in the photoconductor detectors of that era. However, simply by virtue of operating the detectors at deep cryogenic temperatures (< 10 K), non-ideal effects become inevitable, especially in the silicon readout integrated circuits that are hybridized with these detectors. Here, we describe a non-linearity we have dubbed the Reset Switch Charge Decay (RSCD) effect. We discuss the physical origin and show the impact on both laboratory and flight data. Initial mitigation strategies show promise but are complicated by the fact that the magnitude of the effect depends on both the fluence and the flux of the incident signal, and the decay time appears to be readout speed dependent.