Vertical scaling of type I InP HBT with f/sub T/ > 500 GHz

We have fabricated the high-speed InP/InGaAs-based single heterojunction bipolar transistors (SHBTs) with current gain cutoff frequency, f/sub T/ from 166GHz to over 500GHz by the approach of vertical scaling. Collector thickness is reduced from 3000/spl Aring/ to 750/spl Aring/ and the peak current density is increased up to 1300kA/cm/sup 2/. In this paper, device RF performance has been compared with respect to materials with different vertical dimensions. The scaling limitation is also studied by analytical approach. The extracted physical parameters suggest that the parasitic emitter resistance is the major limit on further enhancing ultra-scaled HBT intrinsic speed due to the associated RECBC delay. The cut-off frequency of a 500/spl Aring/ collector SHBT has been measured and the results indicate a dramatic drop on f/sub T/, supporting the conclusion projected by model analysis. It is also commented that for deeply downscaled HBTs, impact ionization could be another degrading mechanism limits device bandwidth.