Modeling Heating Effects in Low-Power Multi-Gate SOI Devices and High-Power GaN HEMTs

由于高生产成本和器件可靠性问题，传统半导体器件的规模最终将达到极限，因此正在寻求传统金属氧化物半导体场效应晶体管（MOSFET）的替代品。有两种方法可以实现增强的器件性能：（1）通过使用诸如应变Si、SiGe、GaN等的替代材料;以及（2）通过使用替代的器件几何形状。全耗尽绝缘体上硅（SOI）、双栅极和FinFET器件是替代器件技术的示例。由于在这些结构中的有源硅膜被放置在掩埋绝缘体层的顶部上，因此消除了由于衬底漏电流引起的功率耗散。然而，掩埋氧化物层（其具有比体Si小约100倍的热导率）是热传导的巨大屏障，并且由于自加热效应而发生这些器件的沟道区中的载流子迁移率的劣化。除了绝缘体上硅低功率器件外，由于工作偏压大，加热也是高功率宽带隙GaN HEMT的一个问题。了解这些器件结构中的自加热现象也可以揭示它们的可靠性，即由于大电场和高晶格温度在沟道的栅漏端形成裂纹而导致的电流崩塌现象。因此，该项目的目的是开发复杂的基于粒子的设备仿真工具，同时考虑自通过求解电子和声子的玻尔兹曼输运方程（Boltzmann transfer equations，BTE），并考虑电子和声子的量子限制效应，计算了热效应。这样一个工具将是最复杂的模拟器，因为电子和声子输运是在同一物理水平内BTE。(1)对于低功率器件，它允许更好的器件设计，包括利用替代的掩埋绝缘体材料，这可能会导致更好的器件性能。这反过来又可以导致新一代的CMOS器件。(2)关于GaN HEMT，如果理解并防止电流崩溃的问题，那么这些器件将在寻求高功率、高温和高频器件的军事和汽车工业中得到应用。这个项目的另一个重要组成部分是参与该项目的学生将从事最先进的研究

Project SummarySince scaling of conventional semiconductor devices will ultimately reach its limits due to both high production cost and device reliability issues, alternatives to classical metal-oxide-semiconductor field effect transistors (MOSFETs) are being sought. There are two ways one can achieve enhanced device performance: (1) by using alternative materials such as strained-Si, SiGe, GaN, etc.; and (2) by using alternative device geometries.Fully-depleted silicon on insulator (SOI), dual gate and FinFET devices are examples of al-ternative device technologies. Since the active silicon film in these structures is placed on top of a buried insulator layer, the power dissipation due to the substrate leakage current is eliminated. However, the buried oxide layer (which has a thermal conductivity about 100 times smaller than bulk Si) is a tremendous barrier to heat conduction, and degradation of the carrier mobility in the channel region of these devices occurs due to self-heating effects. In addition to silicon on insula-tor low power devices, heating is also a problem in high power wide-bandgap GaN HEMTs due to the large operation biases. The understanding of self-heating in these device structures can also shed light on their reliability, namely the phenomenon of current collapse due to the formation of cracks at the gate-drain end of the channel due to large electric fields and high lattice tempera-tures.Therefore, the purpose of this project is to develop sophisticated particle-based device simu-lation tools that simultaneously take into account self-heating effects by solving the Boltzmann transport equations (BTEs) for both electrons and phonons, and considering quantum confine-ment effects for both the electrons and the phonons. Such a tool would be the most sophisticated simulator to date since electron and phonon transport is treated at the same physical level within the BTE.The impact of this project is two-fold. (1) For low-power devices it allows for better device de-signs including the utilization of alternative buried insulator materials that may lead to better de-vice performance. This in turn can lead to new generations of CMOS devices. (2) Regarding the GaN HEMTs, if the problem of current collapse is understood and prevented, then these devices will have applications in the military and the automotive industry where both high-power, high temperature and high-frequency devices are being sought. Yet another important component of this project is that the students involved in the project will work on the state of the art research