Research on non-uniform emitter spacing technology to improve thermal stability of multi-finger SiGe HBT under High-Power

An electro-thermal feedback model for multi-finger power SiGe heterojunction bipolar transistor (HBT) was presented in this paper. Based on the model, the influence of the change of emitter finger spacing on the surface temperature distribution of SiGe HBT was investigated. It is found that under the same bias conditions, with the increase of emitter finger spacing, the peak junction temperature drops while the temperature difference among emitter fingers decreases, but the non-uniform temperature distribution still exists. Based on this conclusion, an optimization method for non-uniform emitter finger spacing (NUSE )was proposed without increasing the chip area. In order to thoroughly study the improvement effect of NUSE, the surface temperature distribution of novel SiGe HBT with NUSE under various bias conditions is simulated. The results show that under different bias conditions, the peak junction temperature of the novel device fall obviously, and the uniformity of temperature distribution on emitter fingers was significantly improved, which can not be achieved for SiGe HBT with traditional uniform emitter finger spacing (UES) structure. The superiority of NUSE technology is exhibited.