GaN Electronics: RF Reliability and Degradation Mechanisms

AlGaN/GaN高电子迁移率晶体管（HEMT）是未来高效率军用和民用微波系统的关键使能技术。该提案的目的是提供对导致GaN RF功率放大器（PA）退化的潜在物理过程的变革性见解。鉴于英国强大的RF电子基础，这对英国具有战略重要性，因为GaN RF功率电子器件通过高达40 W/mm的功率密度和超过300 GHz的频率在系统能力方面实现了颠覆性的飞跃。英国在这一领域拥有国际领先的学术研究团体，包括布里斯托和卡迪夫。该提案中解决的关键问题是，RF应力下的器件退化与DC应力下的器件退化明显不同，通常会导致源极电阻大幅增加，这在DC应力下从未发生过，并且无法用传统模型解释。这一观察结果表明，射频操作中的器械会施加电压/电流应力，这在静态条件下无法实现，因此必须了解射频操作模式与退化机制之间的相互作用。布里斯托为了解直流GaN晶体管退化的国际努力做出了开创性贡献，其中包括GaN晶体管中与氧相关的反应和扩散过程以及与位错相关的击穿。这包括用于检测泄漏途径的电致发光成像，用于检测捕获状态的动态分析和瞬态分析，以及脉冲操作对体陷阱和表面陷阱的影响的模拟。在过去的15年里，卡迪夫在RF PA设计和测量方面建立了世界领先的能力。具体地，波形工程系统使得RF电流/电压波形不仅能够被直接测量，而且能够几乎随意地被操纵。波形的这种操纵使得卡迪夫对理解高效率RF PA操作做出了开创性的贡献。在本项目中，将使用“调谐”RF操作至定义非常明确的状态以实现“受控”RF应力的独特功能，以了解RF器械退化的阶跃变化。将使用失效器械的逆向工程、射频应力之前/之后和期间的电气和电光测量以及物理器械模拟来确定射频特定退化机制。这种预测、设计和测量RF波形的能力是了解PA工作期间器件所承受RF应力的关键，也是确定和指定HEMT安全工作区域的关键。该项目利用与德国和美国最先进的铸造厂的合作关系，使该项目能够使用生产质量的设备，这对工作的相关性至关重要。将通过与Selex的指导和互动（针对系统级问题）以及与IQE的互动（针对材料），在相关性方面对该项目进行指导。布里斯托和卡迪夫的关键协同作用将解决一个至关重要的问题，为吸收这种破坏性的技术，射频退化机制的识别。这将使不同模式的射频操作的影响被预测，并开发一种新的强大的射频可靠性测试方法，从而提供了巨大的英国利益和国际影响。

AlGaN/GaN high electron mobility transistors (HEMT) are a key enabling technology for future high efficiency military and civilian microwave systems. The aim of this proposal is to provide transformative insight into the underlying physical processes that cause degradation in GaN RF power amplifiers (PA). This is of strategic importance for the UK given its strong RF electronics base, due to the fact that GaN RF power electronics delivers a disruptive step change in systems capability through power densities as high as 40W/mm and frequencies exceeding 300GHz. The UK has internationally leading academic research groups in this field, including Bristol and Cardiff. The key issue addressed in this proposal is that device degradation under RF stress is distinctly different than under DC stress, often resulting in a large increase in source resistance, something that never occurs under DC stress and is not explicable by conventional models. This observation implies that a device in RF operation applies voltage/current stresses, which are inaccessible under static conditions, making it imperative to understand the interaction between the RF operating mode and the degradation mechanism. Bristol has provided seminal contributions to the international effort to understand DC GaN transistor degradation, where an understanding is slowly emerging that includes oxygen related reactions and diffusion processes, and dislocation linked breakdown in GaN transistors. This includes electroluminescence imaging for detection of leakage pathways, dynamic transconductance and transient analysis to detect trapping states, and the simulation of the effect of pulsed operation on bulk and surface traps. Over the last 15 years, Cardiff has established a world leading capability in RF PA design and measurement. In particular waveform engineering systems enable RF current/voltage waveforms to not only be measured directly but also to be manipulated almost at will. This manipulation of the waveform has allowed Cardiff to make seminal contributions to the understanding of high efficiency RF PA operation. In this project, the unique capability to 'tune' RF operation into extremely well defined states to enable 'controlled' RF stressing will be used to gain the step change understanding of RF device degradation. Reverse engineering of failed devices, electrical and electro-optical measurement before/after and during the RF stress, combined with physical device simulation, will be used to determine the RF specific degradation mechanisms. This capability to predict, engineer and measure the RF waveforms is key to achieving an understanding of the RF stresses that devices undergo during PA operation, and then to determine and specify the safe-operating-area for HEMTs. This project utilises a partnership with state-of-the-art foundries in Germany and the USA, allowing the project to use production quality devices, essential for the relevance of the work. The project will be guided in terms of its relevance through guidance and interaction with Selex for systems level issues and IQE for the materials. The key synergy of Bristol and Cardiff will address a vitally important issue for the uptake of this disruptive technology, the identification of the RF degradation mechanisms. This will enable the impact of different modes of RF operation to be predicted, and a novel robust RF reliability test methodology to be developed, thus delivering large UK benefit and international impact.