First demonstration of sub-0.25/spl mu/m-width emitter InP-DHBTs with > 400 GHz f/sub t/ and > 400 GHz f/sub max/

We report performance of sub-0.25/spl mu/m 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-0.25/spl mu/m emitter-width DHBT and among the fastest for any DHBTs. With the peak f/sub t/ and f/sub max/ performance occurring at I/sub c/ = 8mA (V/sub ce/ /spl sim/ 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 /spl mu/m and the width of the emitter at the emitter-base junction is less than 0.25 /spl mu/m owing to undercutting of the underlying emitter semiconductor. When comparing with 0.4 /spl mu/m emitter width DHBTs, we find that 0.4 /spl mu/m device has the higher measured f/sub t/, /spl sim/ 420GHz, due to the lower emitter resistance for that emitter layout. F/sub max/ was highest for the 0.25/spl mu/m emitter devices due to lower base-collector mesa capacitance, C/sub 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.