GaN Electronics: RF Reliability and Degradation Mechanisms

AlGaN/GaN高电子迁移率晶体管（HEMT）是未来高效军用和民用微波系统的关键使能技术。本提案的目的是为导致GaN射频功率放大器（PA）退化的潜在物理过程提供变革性的见解。鉴于英国强大的射频电子基础，这对英国具有战略意义，因为GaN射频功率电子通过高达40W/mm的功率密度和超过300GHz的频率，提供了系统能力的破坏性阶变。英国在这一领域拥有国际领先的学术研究团体，包括布里斯托尔和卡迪夫。本提案中解决的关键问题是，射频应力下的器件退化与直流应力下的器件退化明显不同，通常会导致源电阻大幅增加，这在直流应力下永远不会发生，并且无法用传统模型解释。这一观察结果表明，射频工作中的器件施加电压/电流应力，而这些应力在静态条件下是无法获得的，因此必须了解射频工作模式与退化机制之间的相互作用。布里斯托尔对国际上理解直流GaN晶体管降解的努力做出了开创性的贡献，其中包括氧相关反应和扩散过程，以及GaN晶体管中位错相关击穿的理解正在慢慢出现。这包括用于检测泄漏路径的电致发光成像，用于检测捕获状态的动态跨导和瞬态分析，以及脉冲操作对体和表面陷阱的影响的模拟。在过去的15年中，卡迪夫在射频放大器设计和测量方面建立了世界领先的能力。特别是波形工程系统使射频电流/电压波形不仅可以直接测量，而且几乎可以随意操纵。这种对波形的操纵使得卡迪夫对高效率射频PA操作的理解做出了开创性的贡献。在本项目中，将射频操作“调谐”到非常明确的状态以实现“控制”射频应力的独特能力将用于获得RF器件退化的阶跃变化理解。失效器件的逆向工程，射频应力前后和期间的电学和电光测量，结合物理器件仿真，将用于确定射频特定退化机制。这种预测、设计和测量射频波形的能力是了解器件在PA操作过程中所承受的射频应力的关键，然后确定和指定hemt的安全操作区域。该项目利用了与德国和美国最先进的铸造厂的合作关系，允许项目使用生产质量设备，这对工作的相关性至关重要。该项目将通过与Selex的系统级问题和IQE的材料的指导和互动来指导其相关性。布里斯托尔和卡迪夫的关键协同作用将解决这一颠覆性技术的采用至关重要的问题，即射频降解机制的识别。这将能够预测不同模式的射频操作的影响，并开发一种新的强大的射频可靠性测试方法，从而为英国带来巨大的利益和国际影响。

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.