Deep Cooling Technology For Image Sensor Based On Thermoelectric Cooling

Scientific research camera have a wide range of applications in areas such as low-light imaging and astronomical observation.The detection capability limit depends on the overall noise level.Deep cooling can effectively suppress the thermal dark current,which greatly improves the signal-to-noise ratio of the camera.Nowadays,deep cooled scientific research camera which are cooled by thermoelectric cooler has matured for foreign,but there is no high-performance deep cooled scientific research camera product available in China.This is not only cause of great difficulty camera electronics systems,but there are reasons for domestic long life vacuum packaging and deep cooling technology immature.Under the background that the image sensor such as EMCCD,CCD,CMOS has been initially implemented,the self-controllable of deep cooling technology which is one of the key technologies of scientific camera is urgently needed.Firstly,in all visible light image sensors,taking EMCCD which need deeper cooling temperature as an example,through the analysis of the influence of cooling temperature on its performance,it is determined that it needs to be cooled to about-90°C to effectively suppress its thermal dark current.Then the four key aspects of deep cooling,including cold-end efficient thermal insulation,Dewar vacuum packaging,thermoelectric cooler（TEC）performance optimization and hot-end heat dissipation are studyed.On this basis,the first domestic deep cooled system based on thermoelectric cooling with a cooling temperature of-90°C and a theoretical vacuum life of 10 years is developed.The cold end thermal insulation design aims to reduce the thermal load of the TEC to achieve a lower cooling temperature.First,according to the influence of the leakage heat on the cooling temperature,the target heat leakage is determined.Then,the three heat leakage paths of heat conduction,convection and radiation are theoretically analyzed and numerically simulated.According to the analysis of the influence of each variable in the heat leakage,the thermal insulation design of Dewar is carried out.Analysis shows that in order to effectively suppress the cold end heat leakage,the Dewar pressure should be<0.1Pa,therefore,the Dewar must be vacuum packaged.Vacuum packaging is an effective method to suppress the heat leakage caused by conduction and convection in Dewar.Through theoretical analysis of deflation,leakage,and penetration.Among the total gas leakage,the material deflation is the largest,and the leakage and penetration are relatively small.In addition,the analysis of the leakage shows that in order to maintain the vacuum holding time for 10 years,due to the leakage of Argon gas,the Dewar leak rate should also be<5.9e^-8PaL/s.Accordingly,effective sealing measures are selected to ensure low leakage rate.Finally,the theoretical calculation of the permeation is carried out.The goal of TEC performance optimization is to design an optimal TEC for a given operating condition.Due to the large error of the performance curve provided by the manufacturer,and not providing the thermoelectric material parameters which are necessary for performance calculation,in this paper,two methods for extracting parameters of thermoelectric materials are proposed.The performance of another different structure TEC is calculated by the extracted parameters,and then compared with the experiment.It is verified that the extracted parameters can effectively characterize the performance of thermoelectric materials.The error of cooling temperature and voltage calculated by the parameters extracted by the first method that based on basic formula of thermoelectric effect is<4.11%and<6.80%,respectively,which is<3%for the second method that based on numerical analysis method.Based on the material parameters extracted by the second method,a 5-stage TEC is optimized and customized by genetic algorithm.Effective heat dissipation at the hot end is another important factor in ensuring that TEC can achieve deep cooling.In this paper,for different application requirements,air cooling and water cooling are used.The requirements for heat dissipation resistance in the two modes are calculated and analyzed separately,and an air-cooled and water-cooled integrated radiator is designed accordingly.The thermal resistance of the two modes of the heat sink is theoretically analyzed.At the end of the project,the preliminary experimental verification of the vacuum packaging performance of Dewar is carried out,including the leak rate test at each sealing part,the deflation rate test of the components,and the feasibility of maintaining the Dewar vacuum by the getter.The final assembly of the cooling system is then carried out and its performance is tested,including tests for cooling temperature and heat dissipation at the hot end.The system is a universal cooling system that can be used for deep cooling of image sensors with heat less than 1W.