A Simulation Study of Electric Field Engineering with Multi-Level Pinned Photodiodes for Fast and Complete Charge Transfer

TL;DR

This paper introduces a multi-level pinned photodiode design for CMOS sensors, demonstrating through simulation that it enables faster and more complete charge transfer compared to conventional designs, without extra manufacturing steps.

Contribution

A novel multi-level PPD structure is proposed and analyzed via simulation, offering improved charge transfer speed and completeness without additional fabrication complexity.

Findings

Achieves 31% reduction in charge transfer time

Enables fast, complete charge transfer without extra masks

Provides a simulation-based analysis method for pinning process

Abstract

In a CMOS image sensor pixel, fast and complete charge transfer from pinned photodiode (PPD) is desired and necessary in some applications. In special cases such as time-of-flight imaging or large pinned photodiodes, the PPD potential well shape highly affects the charge transfer performance and should be engineered carefully. In the present work, a PPD structure named multi-level PPD is introduced and examined through simulation study. Moreover, a fast and effective way to analyze the pinning process for a lag-free design is introduced. It is concluded that the proposed PPD achieves fast and complete charge transfer without additional implementation masks or process steps. The proposed PPD is compared with a similar conventional rectangular pixel and 31% reduction in the charge transfer time is observed.