氮化镓基半导体电力电子器件击穿机理研究

发布时间：2018-08-17 17:57

【摘要】：氮化镓基电力电子器件在电力电子领域具有很大的应用潜力,其击穿电压的相关研究至关重要。目前GaN基电力电子器件的击穿电压距离其理论极限还有很大的距离,这就意味着其击穿特性还有很大的提升空间。为了充分提高GaN基电力电子器件的击穿特性,就需要对其击穿机理进行研究。本论文就是在此背景下对GaN基电力电子器件的击穿机理展开了广泛而深入的研究。本文的第二章对GaN基HEMT在工艺和仿真中存在的问题和需要注意的细节进行了讨论,然后讨论了测试中最大输出电流IDmax,阈值电压Vth,栅漏电Igleak,击穿电压VBR和特征导通电阻RON五个基本参数的判定标准。最后总结了三种击穿机制:局部高电场导致的雪崩击穿、泄漏电流与温度导致的热失控和栅漏间的空气击穿。这些基础问题的讨论,可以使得GaN基电力电子器件击穿机理的研究更加顺利。在第三章中,给出了与肖特基漏HEMT击穿特性相关的三个方面研究内容。首先,采用肖特基漏结构同时提高了AlGaN/GaN HEMT的正偏和反偏阻断电压,并且对两种阻断电压提高的机理进行了研究。通过采用肖特基漏,正偏和反偏阻断电压分别从72 V和-5 V提高到了149 V和-49 V,即肖特基漏可以同时提高这两个击穿电压。为了研究提高击穿电压的物理机理,对泄漏电流分量进行了分析,并用仿真进行了解释说明。其次,提出肖特基漏与漏场板相结合,可以提高反偏阻断电压的思想。漏场板可以缓解漏电极附近的电场峰值,通过采用漏场板反偏阻断电压从-67 V提高到-653 V。仿真结果表明,肖特基漏与漏场板相结合可以有效地提高器件的反偏阻断能力。最后,研究了漏场板对正偏阻断电压产生的影响。为了防止漏场板对正偏阻断电压产生负面影响,栅边缘和漏场板边缘的间距必须要大于某个特定值,该值要保证漏场板不会挤压正漏压产生的电势。作者在第四章中提出了一组耗尽电容模型,来解释AlGaN/GaN HEMT中高k钝化层提高击穿电压的机理。对于带有钝化层的HEMT,栅金属的侧壁和顶端会与GaN基异质结材料形成金属/绝缘体/半导体结构(MIS结构),这是高k钝化层调制电场的真正原因。基于提出的耗尽电容模型,第一次发现栅金属高度和场板厚度可以影响电场分布和击穿电压。较厚的栅金属可以提高器件的击穿电压,较厚的场板可以缓解场板处的电场峰值,也可以进一步改善器件的击穿特性。此外,结合提出的耗尽电容模型和高k钝化层强大的电场调制能力,作者设计了高特性AlGaN/GaN HEMT器件。设计的栅漏间距为7μm的HEMT,击穿电压为1310 V,功率品质因数高达3.67×109V2·?-1·cm-2,这一数值是所有GaN基HEMT的最高值。本文实现了三种高性能GaN基电力电子器件,即高压AlGaN沟道HEMT器件、增强型InAlN/GaN MISHEMT器件和高压环形AlGaN/GaN HEMT器件。对于栅漏间距为3μm的AlGa N沟道HEMT,击穿电压从144 V提高到了320 V。此外,国际上首次通过采用变频CV的方法对AlGaN沟道HEMT的陷阱态进行了表征,研究发现AlGa N沟道HEMT中的陷阱比Ga N沟道HEMT要深大约0.04 eV。采用栅介质与条件合理的F处理相结合的方法,同时提高了InAlN/GaN HEMT的阈值电压和击穿电压。通过F处理,阈值电压从-7.6 V正漂到了1.8 V。带负电荷的F离子调制导带,有效地降低了栅漏电和缓冲层漏电。栅漏间距为3μm,降低的缓冲层漏电将器件的击穿电压从80 V提高到了183 V。实验表明,栅介质与条件合理的F处理相结合可以同时提高阈值电压和击穿电压,是实现高压增强型InAlN/GaN HEMT的有效方法。栅漏间距为18.8μm的环形AlGaN/GaN HEMT,其击穿电压高达1812V。相对于常规长条形HEMT,通过采用环形结构,栅漏间平均击穿电场强度从0.42 MV/cm增加到了0.96 MV/cm。常规的场板是在二维空间对电场强度进行调制,从而提高击穿电压。作者制造的环形器件则是从第三个维度对电场强度进行了调制,使得器件的击穿特性有了很大的提升。这部分内容在第五章中重点介绍。在第六章中指出了常规三端击穿表征方法的局限性,并针对其在应用中出现的问题提出了一种改进的方法。对于常规击穿,作者总结了七种击穿曲线,但是发现常规击穿表征方法只能适用于其中的两种。对于其他的五种击穿曲线,一定漏压范围内,栅漏电的数值比漏电流的数值要大。此外,源电流也不能用来表征缓冲层漏电,它们的数值和符号是不一致的。出现这些问题的原因,是常规击穿表征方法在表征击穿特性时将栅源电流忽略掉了。这些问题表明,为了能够准确地表征器件的击穿机理,常规表征方法必须进行相应的改进。此外,关态应力击穿也出现了类似的问题。作者通过一种简单的方法,将缓冲层漏电和漏栅电流提取了出来,常规击穿表征方法也基于这两个泄漏电流进行了改进。通过采用改进的方法,常规击穿表征方法在应用中出现的问题得到了解决。实验与分析表明,改进的击穿表征方法对GaN基HEMT击穿机理的研究非常重要。
[Abstract]:The breakdown voltage of GaN-based power electronic devices is still far from its theoretical limit, which means that there is still much room to improve the breakdown characteristics of GaN-based power electronic devices. In this paper, the breakdown mechanism of GaN-based power electronic devices is studied extensively and deeply. In the second chapter of this paper, the problems in the process and Simulation of GaN-based HEMT and the details that need attention are discussed. The criteria for determining the five basic parameters are maximum output current IDmax, threshold voltage Vth, gate leakage Igleak, breakdown voltage VBR and characteristic on-resistance RON. Finally, three breakdown mechanisms are summarized: avalanche breakdown caused by local high electric field, thermal runaway caused by leakage current and temperature, and air breakdown between gate leakage. In the third chapter, three aspects related to the breakdown characteristics of Schottky leak HEMT are presented. Firstly, the Schottky leak structure is used to improve the forward bias and reverse bias blocking voltages of AlGaN/GaN HEMT, and the mechanism of increasing the two blocking voltages is discussed. By using Schottky leakage, the forward bias and reverse bias blocking voltages are increased from 72 V and - 5 V to 149 V and - 49 V respectively, which means that Schottky leakage can increase both breakdown voltages at the same time. The combination of Schottky leakage and leaky field plate can improve the idea of reverse bias blocking voltage. Leaky field plate can alleviate the peak value of electric field near the leaky electrode, and the reverse bias blocking voltage can be increased from - 67 V to - 653 V by using leaky field plate. The simulation results show that the combination of Schottky leakage and leaky field plate can effectively improve the reverse bias blocking ability of the device. In order to prevent the negative effect of the leaky field plate on the positive bias blocking voltage, the gap between the gate edge and the leaky field plate must be larger than a certain value, which ensures that the leaky field plate does not extrude the potential produced by the positive leakage voltage. To explain the mechanism of high K passivation layer increasing breakdown voltage in AlGaN/GaN HEMT, a metal/insulator/semiconductor structure (MIS) is formed between the side wall and the top of gate metal and GaN-based heterojunction material for HEMT with passivation layer, which is the real reason for modulating electric field in high K passivation layer. Thicker grid metal can increase the breakdown voltage of the device, thicker field plate can alleviate the peak value of electric field at the field plate, and can further improve the breakdown characteristics of the device. A high-performance AlGaN/GaN HEMT device with gate-to-drain spacing of 7 microns, breakdown voltage of 1310 V and power quality factor of 3.67 *109 V 2?-1.cm-2 is designed. This is the highest value of all GaN-based HEMTs. GaN MISHEMT devices and high voltage annular AlGaN/GaN HEMT devices. For AlGa N-channel HEMT with gate-to-drain spacing of 3 microns, the breakdown voltage increased from 144 V to 320 V. In addition, the trap states of AlGaN-channel HEMT were characterized by frequency conversion CV method for the first time in the world. It was found that the traps in AlGa N-channel HEMT were deeper than those in Ga N-channel HEMT. About 0.04 eV. The threshold voltage and breakdown voltage of InAlN/GaN HEMT are increased by combining gate dielectric with F-treatment under reasonable conditions. By F-treatment, the threshold voltage is drifted from - 7.6 V to 1.8 V. The negative charge F-ion modulated conductive band effectively reduces the gate leakage and buffer leakage. The gate-drain spacing is 3 micron and the buffer is reduced. Layer leakage increases the breakdown voltage of the device from 80 V to 183 V. The experimental results show that the threshold voltage and breakdown voltage can be increased simultaneously by combining gate dielectric with reasonable F treatment. It is an effective method to realize high voltage enhanced InAlN/GaN HEMT. The average breakdown electric field strength between the gate and drain is increased from 0.42 MV/cm to 0.96 MV/cm by using a circular structure in a regular strip HEMT. In Chapter 6, the limitation of conventional three-terminal breakdown characterization method is pointed out, and an improved method is proposed to solve the problems in its application. For conventional breakdown, seven breakdown curves are summarized, but the conventional breakdown characterization formulas are found. For the other five breakdown curves, the value of gate leakage current is larger than that of leakage current within a certain range of leakage voltage. In addition, the source current can not be used to characterize the buffer leakage, and their values and symbols are inconsistent. These problems show that the conventional characterization methods must be improved to accurately characterize the breakdown mechanism of the devices. Similar problems also occur in the off-state stress breakdown. The characterization method is also improved based on the two leakage currents. By using the improved method, the problems in the application of conventional breakdown characterization method are solved. The experiment and analysis show that the improved breakdown characterization method is very important for the study of the breakdown mechanism of GaN-based HEMT.
【学位授予单位】：西安电子科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TN386

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