四管像素满阱容量影响因素研究

Research on the Full Well Capacity of Four-Transistor Pixel

在分析光电二极管电容、浮空节点电容以及电荷转移效果这三方面影响满阱容量的基础上,着重讨论了最重要的光电二极管电容对满阱容量的影响,建立了满阱容量的计算模型。将测试结果与模型公式进行拟合,可以预估像素的满阱容量,指导像素设计。为了提高四管像素的满阱容量,提出在钳位光电二极管与浮空节点之间增加P型注入层稳定阱容量的方法。增加P型注入层可以大幅减小积分时间内光电二极管中储存的光生电子向浮空节点方向的泄漏,从而有效稳定阱容量。测试结果表明,在多种工艺条件下,像素的满阱容量从基本可以忽略提升至十万个电子的量级。

The influences of floating node capacitance, charge transfer effects and the photodiode capacitance on full well capacity（FWC） are analyzed. Moreover, the effect of photodiode capacitance was discussed intensively and a computational model of the FWC is established. Experimental results were used for fitting the computational model, which is useful to estimate the FWC and instructive to pixel design. In order to increase the full well capacity of four-transistor pixel, a p-type injection layer is added between the pinned photo-diode and floating node to stabilize the FWC. Adding the p-type injection layer can significantly reduce the leakage of photo-generated electrons from the photodiode potential well to the floating node in the integration time. The test results show that FWC can be increased from almost zero to one hundred thousand electrons under different process conditions.