Sub-30ps ECL circuits using high-fT Si and SiGe epitaxial base SEEW transistors
Abstract
A high-performance bipolar technology is presented which involves Si and SiGe epitaxial base formation in a selective epitaxy emitter window (SEEW) structure. Si transistors have cut-off frequencies (fT) of 35-53 GHz while the fT of SiGe devices ranges from 45 GHz to 63 GHz. The SEEW structure allowed emitter width reduction to 0.35 μm using optical lithography with 0.8 μm minimum linewidth to operate the device at high current density near maximum fT. The ECL (emitter coupled logic) gate delay is examined as function of the trade-off between fT and intrinsic base resistance and of the main device parasitics, i.e., base resistance and collector-base capacitance. A minimum ECL gate delay of 24.3 ps was realized in an unloaded ECL ring oscillator.