Comparison of low frequency noise and high frequency performances of double and simple polysilicon Bi-CMOS BJT

The issue of this paper concerns 0.35 μm Bi-CMOS double polysilicon bipolar transistors and 0.5 μm Bi-CMOS simple polysilicon bipolar transistors. Low-frequency noise measurements are performed. Noise spectral densities are analysed versus bias and geometry. From these noise measurements, base and emitter series resistances are extracted. A comparison of both technologies is done. Though double polysilicon transistors have a more complex structure than the simple polysilicon ones, they exhibit similar or even better performances. Indeed, DC characteristics and noise levels are equivalent for both technologies. Double polysilicon transistors exhibit a reduction of the base resistance and a significant improvement of the transition frequency f_T is obtained.