Simulation And Design Of Pixel Structure With Demodulation Function For Time Of Flight Method

In the fields of industrial control,virtual reality,automatic driving and biomedicine,the acquisition of 3D depth data has always played an important role.However,the limitations of high algorithm complexity,large equipment size and high power consumption restrict the development of traditional 3D sensors.In recent years,with the continuous development of CMOS technology,it is possible to obtain 3D data with low power consumption and small volume by the time of flight method.TOF is a three-dimensional imaging method that continuously sends light pulses to the target,then receives the light returned from the object with the sensor,and obtains the distance between the target and the object by detecting the flight time of the light pulses.The measurement accuracy and performance of the time of flight method are extremely dependent on the performance of pixel devices.Therefore,it is of great significance to develop a pixel device with excellent performance and matching with CMOS technology.Based on the principle of indirect time of flight ranging,the relationship between the ranging accuracy of indirect time of flight system and the performance of its pixel devices are analyzed.And the working principle,basic structure and performance indexes of various kinds of indirect time of flight pixel devices are compared.As well as,the design limitations of pixel devices with the development of technology are pointed out.Then the advantages and disadvantages of CAPD,PPD and Kinect are analyzed.After extracting the key points that need to be improved,three different pixel devices are designed based on standard CMOS technology and CIS technology.The main research work is as follows:1.Aiming at the CAPD,based on the surrounding structure and 0.18 um CMOS process,according to its principle and characteristics,a 10 um × 10 um CAPD with doping and reasonable structure area is designed with high resistance substrate.The problem of energy dissipation can be solved by using high resistance substrate.Finally,the simulation results show that the photogenerated charge transfer time of the designed CAPD device is less than 20 ns.2.For the demodulator based on PPD,the potential gradient in the sensitive region is difficult to form due to the existence of n-buried layer of this kind of device,and most electrons in the sensitive region rely on diffusion for transmission,which makes it difficult to achieve high demodulation contrast at high frequency.Based onthe principle that the potential relationship increases with the width of PN junction depletion region,GSMC 0.18 um CIS process is used to enhance the electric field in the two directions of electron transfer by using triangle PPD and guide gate respectively,and a demodulated structure with an area of 3um×6um photochargic charge transfer time less than 10 ns is obtained.3.For Kinect demodulator,STI is used as demodulator isolation structure and grating to increase quantum efficiency.Based on GSMC 0.18 um CIS process,a novel3 um×5 um demodulated pixel based on Kinect structure is designed by referring to the problems in PPD charge transfer process and the response methods adopted by CIS process.Among the three devices designed in this paper,the performance of this device is the best.Through simulation,the demodulation contrast can reach 87.39% at100 MHz demodulation frequency.