4T Complementary Metal Oxide Semiconductor Image Sensor Charge Transfer Efficiency Optimization

Abstract

4T CMOS image sensors are widely used in various imaging fields by virtue of low noise, high integration and low cost, but their pixel cells are manufactured with non-ideal effects causing trap energy levels and potential deviations, resulting in incomplete charge transfer of photogenerated signals, thus producing image trailing and affecting the imaging effect. Traditionally, the improvement of charge transfer efficiency is only limited to the optimization of one or two parameters or the optimization of the working state. In this paper, we propose a more systematic research method to optimize the charge transfer efficiency through five aspects: TG channel threshold voltage injection adjustment, PPD N-type impurity injection dose and injection angle, as well as TG operating voltage and FD reset voltage, respectively. The optimal process state and operating conditions are obtained: TG channel injection dose of 8.0 e12 cm−2, PPD N-type impurity injection dose of 3.0 e12 cm−2, injection angle of −4°, TG operating voltage of 2.7 V and FD reset voltage of 3.9 V, where the residual charge in the signal transfer path is minimal, and the design method in this paper has some guidance for the design of CIS pixels.