Low frequency noise in polysilicon-emitter bipolar junction transistors

This paper describes experimental results on low frequency noise in several types of polysilicon-emitter NPN bipolar junction transistors. The experimental data were modelled using a combination of 1/f noise, generation-recombination noise (g-r), and shot noise, and good agreement between model calculations and experimental measurements were obtained. Observed differences in the experimental low frequency noise spectra of devices with similar geometry and under similar biasing conditions could be explained by the differences in the generation-recombination (g-r) noise contributions. Experiments were performed on devices with emitter areas varying from 1.6 to 144 μm2, and it was found that the magnitude of the flicker noise contribution KF varied inversely with emitter area AE or emitter perimeter PE. The fact that KF∼A−1E or KF∼P−1E is explained by the observation that AE∼PE within fabrication errors/tolerances. Using a set of 3.2 μm2 BJTs with pronounced g-r noise, input current noise was measured at different temperatures and from a deconvolution of the noise spectra, a trap at ∼400 meV and with a capture cross section of ∼4×10−17 cm2 was identified. Finally, the effect of different base implant and rapid thermal annealing conditions, polysilicon emitter thicknesses, and surface etching conditions on the noise magnitude were studied, and these results are also reported.