In this paper, electrothermal consequences of down-scaling bipolar transistors, reducing the emitter resistance and implementing substrate modifications are examined by means of electrical measurements, numerical simulations and analytical calculations. A formulation is given for the optimum current density that can be run through the device and still maintain both sufficient transconductance and thermal stability. This expression sets a theoretical limit on the current density and therefore also on the speed of the given technology node. Particularly the lowering of the emitter resistivity is a trade-off between transconductance and thermal stability, and the optimum choice can be estimated from these results along with the maximum emitter area that will allow unconditional thermal stability.
- Bipolar transistors
- Emitter resistance
- High-frequency (HF) technologies
- Thermal instability