The Design And Optimization Of The Pixel Of Indirect Time-Of-Flight Range Imagers

Over the past few years,Range imaging systems for three-dimensional vision have become one of the most popular research directions in Smart CMOS Image Sensors.Especially after Apple released the i Phone X with Structured Light for 3D face modeling and unlocking,range imagers have attracted rising attention.Indirect Time-Of-Flight is one of the most favorable methods for range imaging,which uses CCD/CMOS image sensor with periodic modulation laser for detection,accompanied by the rapid development and improvement of CMOS image sensor technology.Comparing with other methods,such as Stereo Vision,Structured Light and Direct Time-Of-Flight,Indirect Time-Of-Flight provides better performances in terms of strong background light rejection,more effective feature points,compatibility and no baseline requirement.There is a huge market demand for I-TOF Range Imagers in mobile phone,automotive,factory automation,security,and VR.Since the pixel structure of I-TOF is different from that of 2D imaging CMOS sensor,the pixel quality of I-TOF Range Imagers will dramatically affect the accuary of depth measurement,therefore it is necessary to optimize the pixel by continuously improving process and iterative design.The thesis presents the design and optimization of the pixel of I-TOF Range Imagers with the simulation platform based on Sentaurus TCAD.The propose pixel structure has been emulated from process to device successfully.The design has been fabricated using 130 nm CIS process.We have successfully captured depth images from the test chip.The experimental results of the chip demonstrate that the proposed pixel works smoothly in the condition of using the method of I-TOF.In this work,we discussed the following three points,aiming to improve the performance of the pixel by reducing the deficiency of the pixels under the current standard process.(1)Implementing Double N buried layer in order to improve Photo-electronabsorption efficiency.(2)Designing non-uniform channel doping and optimizing the channel doping concentration so as to improve DC and Charge Transfer Efficiency.(3)Reducing IR crosstalk by Deep Trench Isolation(DTI).The simulation result shows that the Photo-electron absorption efficiency of I-TOF pixel effectively increased by 10% at long wavelength bands and the IR DC increased to 26.09% at the 40 MHz frequency of 850 nm demodulation light.Moreover,the IR crosstalk have declined 43.34% with 4um DTI.The simulation methods of the pixel of I-TOF Range Images in this work can be a guideline of pixel design which promises to further improve those performance.And the proposed I-TOF pixel structure has verified its functionality through tape-out.So we are ready for the next tape-out design whose pixel would be optimized on process.