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

硅锗（SiGe）异质结双极晶体管（hbt）由于其与CMOS的协整，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结合高速率数据传输和数字信号处理。到目前为止，SiGeHBTs的截止频率高达700 GHz的制造已经被证明，最近的模拟预测截止频率高达2太赫兹作为物理极限。凭借这样的性能，SiGe BiCMOS技术正在成为快速崛起的毫米波和太赫兹电子领域的推动者，应用于健康、安全和科学等领域。上述高频性能极限的预测是基于（半）经典传输模拟工具的层次结构。器件优化使SiGe基层厚度达到5 nm，相当于约36个原子层。当硼浓度达到溶解度极限时，在小于100>的5 nm晶格单元电池中，统计上只有0.36个掺杂原子。碳在碱中的影响，用于防止硼在制备的HBTs中向外扩散，只考虑了现象。此外，材料组成和掺杂原子在如此薄的层中的随机排列导致了目前未知的电学性质的统计波动。显然，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。目前对SiGeC HBTs缺乏这样的研究，在SiGeC HBTs中，垂直于表面的载流子输运是主要机制。本研究计划首次应用原子模拟方法，研究了含硼基层的高尺度SiGeC HBTs中的载流子输运和由此产生的HF性能。由于完整的HBT结构不能原子地模拟，因此将采用多尺度建模方法来评估HF特性。首先，在原子模拟的基础上，将确定极大尺度基底层中与输运相关的材料性质，以适应组成和掺杂原子排列的大变化。将开发用于提取与纳入玻尔兹曼输运模拟和校准经典漂移扩散输运模型相关的材料参数的方法。后者用于结构优化和生成紧凑模型所需的数据，从而能够获得实际HBT结构和电路的真实高频特性。最后，为了能够弥合材料科学和电气工程之间的差距，将探索随机原子排列对垂直HBT结构的电学特性和进一步缩放的影响。这些研究将由特殊制造的SiGeC HBTs的测量来支持。

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.