Development of an integrated optical E-Probe for GaN power transistor reliability analysis

AlGaN/GaN高电子迁移率晶体管（HEMT）是目前设想的未来雷达，卫星和通信应用的关键技术，范围从民用到军用。尽管目前AlGaN/GaN hemt的性能在2-10 GHz频率下达到高达40W/mm的功率水平，也就是说，这是一个惊人的性能，可以为许多系统应用带来颠覆性的变化，但AlGaN/GaN hemt的长期可靠性仍然是一个严重的问题，不仅在英国和欧洲，而且在美国和日本。影响AlGaN/GaN HEMT可靠性的几个关键因素导致了各种不同的失效机制，包括陷阱产生、金属迁移等。这些是由：(i)器件温度，（ii）局部应力/应变（反向压电和热），（iii）高电场加速的。了解这些参数对于可靠性测试至关重要，特别是对于加速寿命测试来预测平均故障时间（MTTF）。布里斯托尔的CDTR开发并开创了拉曼热成像技术，以亚微米空间和纳秒时间分辨率探测温度和应力/应变，在只有几微米大小的AlGaN/GaN hemt的有源器件区域，但目前还没有可用于实验量化电场强度及其横向分布的非侵入性探针，特别是在高压下操作器件时。因此，目前只能通过模拟来估计电场强度。本课题的主要目标是开发、测试和应用一种新型无创光学探针（E-probe）来量化AlGaN/GaN HEMT器件通道中的电场强度及其横向分布，并将其集成到拉曼热成像中，实现AlGaN/GaN HEMT的电场、温度和应力同步分析，为AlGaN/GaN HEMT可靠性研究开发一种独特而有益的分析技术。对器件进行退化/应力试验，以探测电场强度及其分布的变化，从而进行最先进的可靠性研究。在应力过程中产生的电荷载流子陷阱改变了电场强度，我们希望能够首次在这里直接探测。载波捕获时间从毫秒到秒不等。我们的目标是，这个项目的一个高风险组成部分，也发展探测电场中随时间变化的能力，在设备中进行载流子捕获/脱捕。

AlGaN/GaN high electron mobility transistors (HEMT) are a key technology currently envisioned for future radar, satellite and communication applications, ranging from civilian to military use. Although the performance of AlGaN/GaN HEMTs presently reaches power levels up to 40W/mm at frequencies as high as 2-10 GHz, i.e., a spectacular performance enabling disruptive changes for many system applications, long-term reliability of AlGaN/GaN HEMTs is still a serious issue, not only in the UK and Europe, but also in the USA and Japan. There are several key factors affecting AlGaN/GaN HEMT reliability resulting in a variety of different failure mechanisms, including trap generation, metal migration and others. These are accelerated by: (i) device temperature, (ii) local stresses / strains (converse piezo-electric and thermal), (iii) high electric fields. Knowledge of these parameters is essential for reliability testing, in particular, for accelerated lifetime testing to predict mean time to failure (MTTF). The CDTR in Bristol developed and pioneered Raman thermography, to probe temperature and stress/strain with sub-micron spatial and nano-second time resolution in the only a few micron size active device area of AlGaN/GaN HEMTs, but there is presently no non-invasive probe available for experimentally quantifying electric field strength and its lateral distribution in particular when operating devices at high voltages. Therefore presently only simulation can be used to estimate electric field strength. The key aim of this research project is to develop, test and employ a non-invasive novel optical probe (E-probe) to quantify electric field strength and its lateral distribution in the device channel of AlGaN/GaN HEMTs, and to integrate it into Raman thermography, to enable simultaneous electric field, temperature and stress analysis of AlGaN/GaN HEMTs, to develop a unique and highly beneficial analysis technique for AlGaN/GaN HEMT reliability research. Experiments on degrading / stressing of devices to probe the resulting changes in the electric field strength and its distribution will be performed for state-of-the-art reliability research. Charge carrier traps generated during stressing change electric field strength which we expect to be able to probe directly here for the first time. Carrier trapping times range from milliseconds to seconds. We aim, a higher-risk component of this project, to also developing the ability to probing time-dependent changes in the electric field with carrier trapping / detrapping in the devices.