First demonstration of sub-0.25μm-width emitter InP-DHBTs with > 400 GHz ft and > 400 GHz fmax

We report performance of sub-0.25μm emitter-width InP/InGaAs/InP DHBTs. These are the smallest emitter-width III-V devices reported to date. Measured ft/fmax performance of 406GHz/423GHz is the first ever reported for a sub-0.25μm emitter-width DHBT and among the fastest for any DHBTs. With the peak f_t and f_max performance occurring at I_c = 8mA (V_ce ∼ 1.25V), this is the lowest power consumption DHBT ever reported with state of the art cutoff frequencies. The as-patterned emitter contact metal width for these devices was 0.25 μm and the width of the emitter at the emitter-base junction is less than 0.25 μm owing to undercutting of the underlying emitter semiconductor. When comparing with 0.4 μm emitter width DHBTs, we find that 0.4 μm device has the higher measured f_t, ∼ 420GHz, due to the lower emitter resistance for that emitter layout. F_max was highest for the 0.25μm emitter devices due to lower base-collector mesa capacitance, C_bc, which results from the reduced mesa width. We find this behavior to be consistent with scaling tradeoffs in the design of ultra-fast DHBTs.