Effect of uniaxial strain on characteristic frequency of scaled SiGe HBT with embedded stress raiser

Abstract

In order to further improve the high-frequency characteristics of highly scaled SiGe HBT and consider the compatibility with the mature CMOS technology, a new SiGe HBT structure is proposed by introducing an embedded Si1−yGey stress raiser to produce additional uniaxial stress in the bulk collector region. The energy-band configuration of multi-layered emitter has been investigated by the estimation of the strain effect, and then the influence of stress raiser on the electrical properties and frequency response has been studied by employing the SILVACO TCAD tools. The results show that the device performance has been enhanced to different degrees by altering the Ge fraction (y) in the stress raiser. At y = 0.3, the current gain is increased by approximately 6% compared to the case without stress in the collector region (y = 0). For the case of a uniform Si0.75Ge0.25 base, the cut-off frequency (fT) and the maximum oscillating frequency (fmax) are, respectively, peaked at 507.7 GHz and 730.7 GHz. Approximately 29.1% improvement in fT and 71.5% improvement in fmax have been achieved for the proposed HBT device in comparison with an equivalent traditional SiGe HBT. At y = 0.1, the frequency characteristic is considered the best due to the maximum of fT × fmax product.