大尺寸像素电荷转移的优化方法

Charge Transfer Optimization Method of the Large Size Pixel

为了提高CMOS图像传感器大尺寸像素的电荷转移效率,消除图像拖尾,通过对像素内电荷转移的RC模型分析,提出一种优化电荷转移的方法。从工艺和版图两方面进行优化,工艺方面是在N埋层的形成步骤中增加一步P型杂质注入,使光电二极管内存在电场,增强电荷转移;版图方面是优化光电二极管的版图为U型,使传输栅伸进光电二极管内尽量长,减少RC模型的传输级数,提高电荷转移效率。与传统像素相比,工艺和版图的优化使电荷转移效率分别提高了2倍和3.3倍,转移时间也分别缩短到传统像素结构的26%和30%左右。对传统像素结构进行工艺和版图同时优化则使电荷转移效率提高了9.5倍。

In order to improve the charge transfer efficiency of the large size pixel in CMOS image sensor and eliminate the image lag, an optimized method of charge transfer was proposed by analyzing the RC model of the charge transfer in pixel, optimizing the pixel in both the process and layout. One is adding a P-type implant during the process of forming the N buried layer, which leads to an electric field within the photodiode, thus the charge transfer is enhanced. The other is to optimize the photodiode layout as U-shaped to improve the charge transfer efficiency of pixel,which makes the transfer gate extend into the photodiode as deep as possible and reduce the transmission series of RC model. Compared with the traditional pixel, the charge transfer efficiency of the above two optimized methods were increased by 2 times and 3.3 times respectively. And the transfer time is also shortened by 26% and 30% re- spectively. The charge transfer efficiency was increased by 9.5 times both in the process and layout optimization.