Drift Field Implementation in Large Pinned Photodiodes for Improved Charge Transfer Speed

Abstract

We present a methodology for generating built-in drift fields in large photodiodes. With the aid of TCAD we demonstrate how non-uniform doping profiles can be implemented in a standard CMOS process using a single additional mask and controlled using the implant conditions and mask geometry. We demonstrate that the resulting doping profile creates a built-in drift field and simulates the effect of the drift field on the charge transfer speed. We show that implementing a drift field can improve charge transfer characteristics of the photodiode.

Keywords

• CMOS image sensors
• pinned photodiodes
• charge transfer
• large photodiodes