WORKSHOP PAPER
Evaluation of X-ray Induced Degradation of Light Response and Dark Current in BSI CMOS Image Sensors with Backside Deep Trench Isolation
Abstract
Radiation degradation of image sensors is well investigated for medical and space applications with X-ray dose ranging from a few kGy to GGy. This paper reports X-ray degradation that was observed with a prototype 4.6 μm backside illuminated (BSI) digital pixel sensor (DPS) fabricated in a 45nm / 65nm stacked process (Chip A) [1] after 0.1Gy to 50 Gy X-ray irradiation. While the issue of X-ray degradation has been solved in the latest fabrication lots, the findings through this investigation should be worth sharing with the imaging community. Especially, it is suggested that dark signal increase comes from interface states of the shallow-trench isolation (STI), dark signal increase and light responsivity degradation come from those of the pyramid surface for diffraction (PSD) structure for near infrared (NIR) sensitivity enhancement and backside deep-trench isolation (BDTI) structure.Keywords
X-ray induced degradation, BSI CMOS image sensors, backside deep trench isolation, dark current, light response,References
[1]) R. Ikeno et al., "A 4.6-μm, 127-dB dynamic range, ultra-low power stacked digital pixel sensor with overlapped triple Quantization", IEEE Trans Electron Devices, 2022. https://doi.org/10.1109/ted.2021.3121352
[2]) Jiaming Tan et al., "Analyzing the radiation degradation of 4-transistor deep submicron technology CMOS image sensors", Sensors, 2012. https://doi.org/10.1109/jsen.2012.2186287
[3]) V. Goiffon et al., "Overview of ionizing radiation effects in image sensors fabricated in a deep-submicrometer CMOS imaging technology", IEEE Trans. Electron Devices, 2009. https://doi.org/10.1109/ted.2009.2030623