A novel superjunction collector design for improving breakdown voltage in high-speed SiGe HBTs

Abstract

We present a novel collector design for silicon-germanium heterojunction bipolar transistors (SiGe HBTs). The design improves the well-known speed / breakdown voltage trade-off in SiGe HBTs for radio-frequency (RF) and millimeter-wave applications. Applying multiple alternating p and n-type layers (a superjunction) deep in the collector-base (CB) space charge region (SCR) alters the electric field and electron temperature in the CB junction. Consequently impact ionization is suppressed while the width of CB SCR is not increased, and therefore, the breakdown voltages (BVCEO and BVCBO) are increased with no degradation in the device speed and RF or mm-wave performance. For a fixed ac performance, the BVCEO is improved by 0.33 V, producing a SiGe HBT with fT = 101 GHz, fmax = 351 GHz, and BVCEO = 3.0 V in DESSIS TCAD simulations. The proposed structure is also contrasted with other approaches in the literature.