Low-Frequency Noise in Polysilicon Emitter Bipolar Transistors

The low-frequency noise of polysilicon emitter transistors, having various emitter geometries and various properties of the oxide layer at the monosilicon-polysilicon interface, was investigated. The main 1/f noise source proved to be located in the oxide layer. This source causes 1/f noise both in the base current SIB and in the emitter series resistance Sre. The magnitude of the 1/f noise source depends on the oxide layer properties. The 1/f noise is ascribed to barrier height fluctuations of the oxide layer resulting in transparency fluctuations for both minority and majority carriers in the emitter giving rise to SIB and Sre, respectively. It is shown that the low transparency of the oxide layer also reduces the contribution of mobility fluctuations to SIB.