Photo-generated Charge Transfer Efficiency Of CMOS Image Sensor Simulation And Research

With constant upgrades in CMOS process technology and design level,CMOS image sensor has developed rapidly,overcoming the deficiency of sensitivity,fill factor,dark current and noise.CMOS image sensor is a most typical solid-state imaging device,depending on the advantage of lower cost,lower power consumption,easy integration and simple manufacturing process which is compatible with CMOS process,CMOS image sensor has replaced CCD image sensor in many fields gradually and now has been widely used in digital video,monitoring system,medical electronics and aerospace industry,etc.The technology of CMOS image sensor is constantly improving and evolving in various market fields and will have a wider prospect.The pinned 4T active pixel sensor is the most popular CMOS image sensor.The introduced pinned P-type layer in photodiode,allowing greater absorption of blue light and reducing the dark current generated from the pixel interface effectively.The reset noise has also been eliminated validly due to correlated double sampling which has largely improved the imaging performance.For the large size of pinned 4T active pixel unit,owing to the flat electric potential in PPD,potential barrier and potential pocket existed in transfer transistor(TG)channel,there is a reduction in the photo-generated charge transfer efficiency and will lead to image lag.Therefore,the study of pinned 4T active pixel unit is of great significance.Numerous optimizations based on PPD structure and potential distribution of TG channel are put forward and simulated aiming at existing problems by Sentaurus TCAD software in this dissertation.Firstly,combining the manufacturing process of pixel,the process simulation and device simulation of the 4T active pixel unit has been accomplished.On the basic of the formed pinned 4T active pixel unit by process,a novel PPD structure used four layers of ion implantation has been proposed,which achieves a potential gradient in PPD,contributing to the photo-generated charge transfer efficiency.On aspect of optimization of the TG channel during the charge transfer,the non-uniform doped channel,beveled oxide layer of TG and P~+N~+type doped grid have been utilized,the feasibility of three optimization schemes are also verified and the simulated results of schemes are analyzed comparatively in the end.