| Popis: |
In this paper, we investigate the emitter resistance R e in SiGe HBTs with speeds up to 280GHz, using a U-shaped polysilicon emitter. We observed that R e increased with lateral scaling, thereby degrading f T . Although a negligible component in the past, in this experiment R e * C cb transit time delay is playing a more significant role in limiting f T . R e was modeled to explain the increase due to lateral scaling, and was shown to result from the plugging of the emitter opening by the emitter polysilicon. Furthermore, process experiments were conducted to investigate the effect of emitter polysilicon thickness, sidewall height, and emitter i-layer thickness. |
