常开型SiC JFET功率器件的热可靠性研究

发布时间：2018-04-14 16:10

本文选题：SiC + JFET　；参考：《西安电子科技大学》2015年硕士论文

【摘要】：SiC JFET功率器件凭借其优良的材料特性及结构优势,成为目前最有发展前景的高温器件,但其工作时存在的热可靠性问题仍然限制着目前SiC JFET器件的工作温度。针对这个问题,本论文着重研究了SiC JFET器件在静态工作时的温度特性和动态雪崩模式工作下的热可靠性。通过分析SiC JFET的热稳定性发现,当器件的产生功率等于相应条件下的耗散功率时,器件达到热平衡状态。器件只有处在稳定的平衡点时,才能可靠的工作,一旦跳到非稳定平衡点,器件则极有可能发生热失效。器件在工作时存在自热效应,且内部温度分布不均,高温主要分布在沟道区域。仿真发现,自热效应会使器件结温升高,从而出现热可靠性问题,并且结温升高会引起载流子迁移率下降,从而导致器件电流发生退化,严重时退化程度达30%以上。此外,随着器件偏压的增大,电流密度会达到一个最大值,对应的工作点称为临界点,器件在高于临界电压的偏压下工作,不会得到任何性能上的改善,因此器件工作时压降应保持在临界电压以内。仿真分析发现,增大栅压,器件的电流能力提高,并且临界电压和临界结温也会相应降低,器件热可靠性得到改善。而环境温度升高及散热条件变差时,会导致相同偏压下器件的电特性和热稳定性变差。因此,对于给定的器件,在高温工作时,其性能和热稳定性难免发生退化,但可以通过合理地提高栅偏置和改善散热来弥补性能的退化和提升器件的热可靠性。本文还重点研究了两个结构参数对SiC JFET器件的正向特性及结温的影响,分析得出,合理的增大沟道宽度和降低漂移层宽度,一方面能够在较小的偏压下显著地提高器件的电流密度,从而成倍地减小器件面积,降低成本,另一方面在保持相同的电流密度下,可以减小器件的正向压降,降低器件的结温,从而降低器件的功耗和提升器件的热可靠性。分析温度对阈值电压的影响发现,SiC JFET器件阈值电压随温度的增大线性降低,变化率约为1.8~2mV/K,但通过合理的设计,可以使温度对SiC JFET器件阈值电压的影响忽略不计,从而避免器件因温度升高引起的误导通现象。通过对不同条件下器件的雪崩仿真发现,负载电感的增大和初始雪崩电流的增大都会明显增大器件的雪崩持续时间,并且会一定程度上增大器件的雪崩电压,从而引起器件瞬时功率和雪崩能量的增大,导致器件结温上升更严重,从而引起可靠性问题。当电感或初始雪崩电流增大到一定程度时,器件会发生热失效。仿真分析得到1500K为器件材料所能承受的理论极限温度,而实验发现,实际器件的热可靠性还与其电极及封装材料的热稳定性密切相关。因此,器件在使用时,应注意相应条件下电感负载和雪崩初始电流的最大限制,以保证器件安全可靠的度过雪崩工作模式。本论文的研究无论是对给定器件的使用,还是新器件的设计,均具有重要的指导意义。
[Abstract]:SiC JFET power device with its excellent material properties and structural advantages, become the most promising high temperature devices, but the thermal reliability problems existing in the work of the current SiC JFET devices still limit working temperature. To solve this problem, this paper focuses on the thermal reliability of temperature characteristic and dynamic avalanche mode SiC JFET in the static working device. Through the analysis of thermal stability of SiC JFET found that when the device has power dissipation power is equal to the corresponding conditions, the device thermal balance. Balance device only in a stable, can work reliably, jump to unstable equilibrium point, there is a great device possible thermal failure. Devices are self heating effect at work, and the internal temperature of the uneven distribution of temperature is mainly distributed in the channel region. Simulation shows that the self heating effect will cause the junction temperature Thus increased thermal reliability problems, and the increase of junction temperature will cause the carrier mobility decreases, resulting in device current degradation, severe degradation degree was more than 30%. In addition, with the increase of device bias, current density will reach a maximum value, the corresponding point is called the critical point, the device in bias higher than the threshold voltage, will not get any performance improvement, so the device pressure should be maintained at less than the critical voltage. The simulation results indicate that the increase of the gate voltage, increasing the current capacity of the device, and the threshold voltage and the critical temperature will be reduced accordingly, thermal reliability are improved. And the environmental temperature and heat dissipation conditional difference, cause the electrical properties and thermal stability of the device under the same bias variation. Therefore, for a given device, working under high temperature, the properties and thermal stability will inevitably happen retreat But, can increase the gate bias and improve heat dissipation to compensate the thermal reliability of lifting device degradation and performance. This paper also focuses on the effects of positive characteristics and the junction temperature of the two structural parameters on SiC JFET device analysis, a reasonable increase of the channel width and reduce the width of the drift layer, on the one hand can significantly improve the current density of the device in the smaller bias, thereby greatly reduce device area, reduce the cost, on the other hand, maintain the same current density, the device can reduce the forward voltage drop, reduce the junction temperature of the device, thereby reducing power consumption and improve the thermal reliability analysis of temperature influence on devices. The threshold voltage, the threshold voltage of SiC JFET device with increasing linear temperature decreased, the change rate is about 1.8~2mV/K, but through reasonable design, can make the temperature value of the threshold voltage on SiC JFET devices Effect is negligible, so as to avoid the device due to temperature rise caused by the misleading phenomenon. Through the simulation of different conditions by an avalanche device that increases the load inductance and the increase of the initial avalanche current will significantly increase the duration of avalanche device, and avalanche voltage of the device to a certain extent increase, causing an increase in the instantaneous power device and the avalanche energy, causing the junction temperature rise is more serious, causing reliability problems. When the inductance or initial avalanche current increases to a certain extent, the device will heat failure. The simulation results for the theoretical limit temperature of 1500K can withstand the device material, and the experiments showed that the thermal stability of practical device but also its reliability the electrode and the packaging materials are closely related. Therefore, the device is in use, should pay attention to the maximum limit under the corresponding conditions and initial avalanche current inductive load, In order to ensure safe and reliable avalanche work mode, the research of this paper has important guiding significance for both the use of given devices and the design of new devices.

【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN304.24;TN386

【参考文献】