Ultra-scaled SiGeC HBTs beyond the existing roadmap - A simulation based study

硅锗（SiGe）异质结双极晶体管（HBT）由于与CMOS的共集成而在高频（HF）应用中得到了广泛的应用，例如通信和汽车雷达。这允许在单个芯片上将高速数据传输与数字信号处理相结合。截止频率高达700 GHz的SiGeHBT的制作已经得到证实，最近的模拟预测截止频率高达2 THz的物理极限。凭借这样的性能，SiGe BiCMOS技术正在成为快速兴起的毫米波和THz电子学领域的推动者，其应用领域包括，健康、安全和科学。上述HF性能极限的预测是基于（半）经典传输模拟工具的层次结构。器件优化导致SiGe基极层厚度为5nm，其对应于约36个原子层。在溶解度极限处的峰值硼浓度下，在5 nm的晶格晶胞堆叠中统计上仅存在0.36个掺杂原子<100>。在基地，用于防止硼外扩散制造的HBT中的碳的影响，被考虑到只有现象。此外，材料成分和掺杂原子在这种薄层中的随机排列导致了目前未知的电学性质的统计波动。很明显，到目前为止在半经典模拟中所做的假设是有问题的，需要在原子水平上进行更详细的研究。这种研究目前缺乏SiGeC HBT，其中垂直（面外）的载流子输运的表面是占主导地位的机制。这项研究建议解决载流子传输和由此产生的HF性能在高度规模的SiGeC HBT与硼掺杂的基层，第一次，通过应用原子模拟方法。由于完整的HBT结构不能模拟原子，多尺度建模方法将追求评估HF特性。首先，基于原子模拟，将针对组成和掺杂原子排列的很大变化来确定极其缩放的基层中与输运相关的材料性质。将开发方法提取相关的材料参数纳入玻尔兹曼输运模拟和校准经典漂移扩散输运模型。后者需要结构优化和生成紧凑模型所需的数据，这反过来又能够获得实际HBT结构和电路的真实HF特性。最后，能够弥合材料科学和电气工程之间的差距，随机原子排列的电特性和进一步缩放的垂直HBT结构的影响将被探索。调查将支持专门制造的SiGeC HBT的测量。

Silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) have found widespread use in high-frequency (HF) applications, such as communications and automotive radar, due to their co-integration with CMOS. This allows combining high-rate data transfer with digital signal processing on a single chip. So far, the fabrication of SiGeHBTs with cut-off frequencies up to 700 GHz has been demonstrated, and recent simulations predict cut-off frequencies up to 2 THz as physical limit. With such performance, SiGe BiCMOS technology is becoming the enabler for the rapidly emerging field of millimeter-wave and THz electronics with applications in the fields of, e.g., health,security and science. The prediction of the HF performance limit mentioned above was based on a hierarchy of (semi-)classical transport simulation tools. The device optimization resulted in a SiGe base layer thickness of 5 nm, which corresponds to about 36 atom layers. With a peak boron concentration at the solubility limit, thereare statistically just 0.36 doping atoms in a 5 nm stack of <100> lattice unit cells. The impact of carbon in the base, used to prevent boron outdiffusion in fabricated HBTs, was taken into account only phenomenologically. Also, the random arrangement of the material composition and doping atoms in such thin layers leads to presentlyunknown statistical fluctuations of the electrical properties. It is obvious that the assumptions made so far in semi-classical simulations are questionable, and a more detailed investigation is required at the atomistic level. Such studies are currently lacking for SiGeC HBTs, in which carrier transport perpendicular (out-of-plane) tothe surface is the dominant mechanism. This research proposal addresses carrier transport and the resulting HF performance in highly scaled SiGeC HBTs with a boron doped base layer, for the first time, by applying atomistic simulation approaches. Since the complete HBT structure cannot be simulated atomistically, a multiscalemodeling approach will be pursued to assess HF characteristics. First, based on atomistic simulations, the transport related material properties in extremely scaled base layers will be determined for a large variation of compositional and doping atomarrangements. Methods will be developed for extracting the material parameters relevant for incorporation into Boltzmann transport simulations and for calibrating classical drift-diffusion transport models. The latter are needed for structural optimization and generating the data needed for compact models, which in turn enable obtaining the realistic HF characteristics of actual HBT structures and circuits. Finally, being able to bridge the gap between material science and electrical engineering, the impact of random atomic arrangement on the electrical characteristics and further scaling of the vertical HBT structure will be explored. The investigations will be supported by measurements of specially fabricated SiGeC HBTs.