Radiation-Induced Leakage Current and Electric Field Enhancement in CMOS Image Sensor Sense Node Floating Diffusions

Abstract

This paper investigates the leakage currents as well as the leakage current Random Telegraph Signals (RTSs) sources in sense node floating diffusions (FDs) and their consequences on imaging performances specifically after exposure to high-energy particle radiation. Atomic displacement damage and ionization effects are separately studied thanks to neutron and X-ray irradiations. Proton irradiations have been performed to simultaneously study displacement damage dose (DDD) and total ionizing dose (TID) effects while being more representative of the space environment. The studied DDD ranges from $500\,\,\text {TeV}\cdot \text {g}^{-1}$ to $40\,\,\text {GeV}\cdot \text {g}^{-1}$ , and the TID ranges from 24 krad(SiO2) to 72 krad(SiO2). High-magnitude electric field effects, such as transfer-gate-induced leakage current, are investigated to further understand the phenomena involved in FDs while giving new insights into the Electric Field Enhancement of the charge generation mechanisms. This paper shows that FDs are very sensitive to ionizing radiation because of the presence of depleted Si/SiO2 interface with high-magnitude electric fields around the junction. On the other hand, displacement damage in the FDs is a major source of high amplitude leakage current RTSs and leakage current nonuniformity. Such radiation-induced degradations can prevent the use of CMOS image sensor with long FD retention time (e.g., global shutter operating mode or burst imagers) in radiation environments.