Pinned Photodiode CMOS Image Sensor TCAD Simulation: In-Depth Analysis of in-Pixel Pinning Voltage Measurement for a Diagnostic Tool
TCAD simulations are conducted on a pinned photodiode (PPD), with the aim to reproduce the pinning voltage measurement developed by Tan et al. A thermionic model is proposed and detailed in order to explain the exponential injection occurring at an injection voltage higher than the pinning voltage, and the correct method to extract the transfer gate inversion voltage is given. Then, various nonidealities are simulated, such as doping variations or doping layer shifts, the goal being to get a PPD diagnostic tool based on the pinning voltage measurement. Finally, the PPD is simulated in a real reading mode, and a charge partition mechanism is demonstrated in specific conditions.