Neutron Displacement Damage in Bipolar Junction Transistors Isolated from an Integrated Circuit

We have studied the neutron displacement damage effect in bipolar junction transistors (BJTs) isolated from an integrated circuit (IC) through experiment and modeling. Both vertical npn and lateral pnp BJTs were isolated from a LM741 linear bipolar integrated circuit and underwent 14-MeV neutron irradiation. Measured Gummel curves reveal that, in addition to the expected increase in base currents with increasing neutron fluence, the ideality factors of the Gummel curves increase with fluence for the npn, but decrease with fluence for pnp. To understand this response, detailed TCAD simulations were performed. Simulation results not only reproduce the measured Gummel curves, but more importantly they reveal that the total recombination ratio between the emitter-base (EB) depletion region (DR) and the neutral base (NB) appears to be responsible for the changing of ideality factor with neutron fluence. Specifically, for vertical npn, recombination in the EB DR is much more dominant than that in the NB for all the fluences considered, which leads to increasing ideality factor with increasing fluence. On the contrary, for lateral pnp, recombination in the DR is the strongest for the lowest fluence and its contribution becomes smaller with increasing fluence than the recombination in the NB, which leads to decreasing ideality factor with increasing fluence.