Gamma-Ray Irradiation Effects on CMOS Image Sensors in Deep Sub-Micron Technology

INTRODUCTION CMOS Active Pixel Sensors (APS) excel in domains that include low power operation and on-chip integration of analog and digital circuitry. Since these sensors are utilized for applications involving the detection of signals as low as a few electrons, radiation tolerance of such devices is of primary concern. All possible radiation effects are usually grouped into three basic types: transient effects (not dealt in this study), ionization damage and displacement damages [1], [2], [6]. Ionization damage has been considered to be the dominant mechanism when energetic photons (γ and X-rays) interact with solid-state matter. The major concerns due to this damage are charge build-up in the gate dielectric and radiation induced interface states. The introduction of discrete energy levels at the Si-Si02 interface leads to increased generation rates and thus higher surface leakage currents. Similarly, displacement of lattice atoms in the bulk leads to modified minority carrier lifetimes and increased bulk-generated leakage currents [2], [3], [4], [5].