2017-11-10, Schäfer, Jan, Sigeneger, Florian, Šperka, Jiří, Rodenburg, Cornelia, Foest, Rüdiger

The self-organized discharge behaviour occurring in a non-thermal radio-frequency plasma jet in rare gases at atmospheric pressure was investigated. The frequency of the azimuthal rotation of filaments in the active plasma volume and their inclination were measured along with the gas temperature under varying discharge conditions. The gas flow and heating were described theoretically by a three-dimensional hydrodynamic model. The rotation frequencies obtained by both methods qualitatively agree. The results demonstrate that the plasma filaments forming an inclination angle α with the axial gas velocity uz are forced to a transversal movement with the velocity uφ=tan(α)*uz, which is oriented in the inclination direction. Variations of ${u}_{\phi }$ in the model reveal that the observed dynamics minimizes the energy loss due to convective heat transfer by the gas flow. The control of the self-organization regime motivates the application of the plasma jet for precise and reproducible material processing.

2018, Rücker, Holger, Heinemann, Bernd

This paper addresses fabrication aspects of SiGe heterojunction bipolar transistors which record high-speed performance. We previously reported fT values of 505 GHz, fMAX values of 720 GHz, and ring oscillator gate delays of 1.34 ps for these transistors. The impact of critical process steps on radio frequency performance is discussed. This includes millisecond annealing for enhanced dopant activation and optimization of the epitaxial growth process of the base layer. It is demonstrated that the use of a disilane precursor instead of silane can result in reduced base resistance and favorable device scalability.