Temperature dependence of 1/f noise in polysilicon-emitter bipolar transistors

1/f noise was measured on polysilicon-emitter bipolar n-p-n and p-n-p transistors over a temperature range of 173KIB was extracted for different temperatures and bias conditions. Based on the temperature dependence of the 1/f noise magnitude, we divide the temperature range into two regions, where the dominant noise mechanism is different. This transition temperature was 298 K and 238 K, respectively, for the n-p-n and p-n-p transistors. Using the extracted surface recombination current I_S, we find S_IB of the n-p-n transistor to have a weak 1/T dependence in the low-temperature area. A tunneling-assisted trapping model is suggested for the low-temperature area, which indicates that the noise originates from the dynamic trapping-detrapping of the carriers by the slow states located in the spacer oxide at the periphery of the emitter-base junction. The thermal activation energy extracted from the noise in the high-temperature region is 0.15 eV, representing stronger temperature dependence. The electron random walk model is proposed for this temperature range. Using this model, the same thermal activation energy 0.15 eV is calculated from the dc characteristics of the n-p-n transistor. The electron random walk model suggests that the 1/f noise arises from the slow interface states directly situated at the Si/SiO₂ interface in the space charge region.