Gate-controlled gain tuning of fully depleted silicon-on-insulator-based 1 T pixel for in-sensor white balance

Abstract

White balance (WB) is a critical back-end processing function in image sensor to keep color constancy under various lighting conditions by adjusting RGB color channel gain values. In this work, we proposed a novel gate-controlled gain tuning method for Fully-Depleted Silicon-on-Insulator (FDSOI) one-transistor (1T) pixel to achieve WB inside sensor. Based on the pixel structure of p-well under BOX for sensing and nMOSFET on the top for readout, the 1T pixel output gain is modulated by MOSFET gate according to transistor transfer characteristic. About 5x gain modulation range in RGB spectrums photoresponse (nonlinearity<3%) is experimentally demonstrated in the devices fabricated by 22nm FDSOI-based technology. The scheme for in-sensor WB demonstration is provided with a novel 1T pixel array design, and the evaluation result shows in-sensor WB achieving almost equivalent performance (Delta-E deviation<1) compared with using conventional back-end WB.