Study On The Effective Thermophysical Properties And Cooling Performance Of Micro-thermoelectric Coolers

The continuous development of micro-electronic devices towards the direction of high integration and miniaturization,as well as the continuous increase of chip operation speed and power consumption,lead to extremely high heat flux density of electronic devices.The high heat flux tends to give rise to hotspot issues,while the excessive temperature will seriously affect the reliability and stability of electronic components.The ensuing thermal management problem has become one of the bottlenecks restricting the development and application of micro-electronic devices.Micro-thermoelectric coolers have great application potential in the thermal management of miniaturized,highly integrated and high-performance electronic device,especially the local cooling,due to its features of small to micro-nano scale,easy to package or integrate,high reliability and precise temperature control ability,as well as a high cooling heat flux density up to 1250W/cm~2.However,due to the influence of microscopic factors such as size effect and interfacial effects,the effective thermophysical properties and actual performance of micro-thermoelectric coolers are often lower than the theoretical performance.And at present,the theoretical research on the effective thermophysical properties and cooling performance of micro-thermoelectric coolers still need to be further explored,which is just the key and urgent problem to be solved for interpreting the thermal-electrical transport and conversion mechanism of micro-thermoelectric coolers,and to analyze and optimize the performance of micro-thermoelectric coolers.Therefore,this thesis aims to perfect the theoretical system of the effective thermophysical properties and cooling performance of micro-thermoelectric coolers,and explore the influencing factors of the cooling performance.Firstly,this thesis establishes a numerical model for characterizing the joint influence of size effect and interfacial effects on the effective thermophysical properties and cooling performance of micro-thermoelectric coolers based on the Boltzmann transport equation.The presented model is further verified by the comparison with experimental data.Then,the scale characteristic of the effective thermophysical properties are analyzed.Secondly,a numerical model to explore the influences of Thomson effect on the temperature characteristics and cooling performance of micro-thermoelectric coolers is further established.Then,the influences of Thomson effect on the performances of micro thermoelectric coolers of different sizes under different temperature and cold loads are discussed.Finally,the actual performance of micro-thermoelectric coolers for cooling high-power LED devices is explored.An embedded structure of micro-thermoelectric cooler cooling LED is designed according to the purchased LED device.The thermal performance,optical performance and comprehensive performance of LED integrated with micro-thermoelectric cooler are also investigated.The results show that the boundary effect can significantly reduce the effective Seebeck coefficient,effective thermal conductivity,effective figure of merit,and increase the effective electrical resistivity of the micro-thermoelectric cooler.And a smaller thickness of the thermoelectric elements corresponds to a greater influence of boundary effect.For example,when the thickness of the thermoelectric elements decrease from 20?m to 5?m,the effective figure of merit of the micro-thermoelectric cooler will decrease by 5%to18.1%compared to the intrinsic figure of merit of the thermoelectric material.Among the influencing factors on the effective thermophysical properties of the micro-thermoelectric cooler,the electrical boundary resistance has the greatest influence,followed by the phonon thermal boundary resistance.In addition,the boundary effect will reduce the cooling performance of the micro-thermoelectric cooler,and the greater the cold load,the greater the impact.The influences of Thomson effect on the temperature characteristic and cooling performance of the micro-thermoelectric cooler are closely related to its size and the heat flux density at the cold side.The results show that the Thomson effect can increase the cooling capacity of the micro-thermoelectric cooler,and the impact becomes more obvious with the increase of the current and the thickness of the thermoelectric element.In addition,for a micro-thermoelectric cooler with certain thermoelectric element thickness,the Thomson effect shows less influence on the maximum cooling temperature difference when the surface-length ratio increases gradually.And the performance improvement of micro-thermoelectric cooler caused by Thomson effect is even more obvious under higher heat flux condition.It indicates that the performance of thermoelectric coolers can be further improved by improving the temperature dependence of the Seebeck coefficient of the thermoelectric element,especially when micro-thermoelectric coolers are used for cooling electronic devices with high heat flux density.The embedded micro-thermoelectric cooler designed in this paper can significantly reduce the chip junction temperature and greatly improve the luminous efficacy and lifetime of the high power LED.For the high power LED integrated with micro-thermoelectric cooler,the maximum temperature drop of chip junction can reach12.3°C,which leads to an increase in luminous efficacy and lifetime of LED devices by12.3%and 50%,respectively.Although micro-thermoelectric cooler consumes additional electrical power,the comprehensive performance of LED device and micro-thermoelectric cooler can still be greatly improved.In addition,the study of the interfacial effects found that both the boundary effect and the contact effect increase the chip junction temperature,and the impact of contact effect is more significant.Compared with the thermal boundary resistance,the adverse impact of the electrical boundary resistance on the chip junction temperature plays a dominant role.However,the thermal contact resistance shows greater adverse influence than the electrical contact resistance.This finding indicates that when optimizing the boundary effect,it should mainly focus on the electrical boundary resistance,that is,the transport mechanism of electrons.And,the thermal contact resistance should be the main objective in the optimization of the contact effect.This thesis mainly interprets the microscopic factors and mechanisms that affect the effective thermophysical properties and performance of micro-thermoelectric coolers.And the proposed numerical method provides theoretical support for the study of the effective thermophysical properties and cooling performance of micro-thermoelectric coolers.Furthermore,the research content exhibits great reference value and guiding significance for the application,design and optimization of micro-thermoelectric coolers in the thermal management of electronic devices.