Low frequency noise in heavily doped polysilicon thin film resistors

Abstract

Low frequency noise and current–voltage measurements in several heavily doped polysilicon resistors of varying geometry and both p and n type, and over a limited range of temperatures from −60 to 50 °C were conducted for the first time. We found that the noise in p-type polysilicon was independent of temperature, but not the n-type polysilicon. For the p-type resistors, linear current–voltage characteristics were observed, and the relative noise spectral density was independent of bias and inversely proportional to frequency. For the n-type resistors, linear current–voltage characteristics were observed, and the relative noise spectral density was independent of bias. Finally, the normalized noise level in the linear n-type resistors was almost an order of magnitude lower than for the p-type resistors. We believe that this difference is because n-type dopants segregate to the grain boundaries, thus passivating some of the traps there. Boron (p-type dopant), on the other hand, does not segregate to the grain boundaries, leaving more unpassivated grain-boundary traps which capture and emit more carriers, resulting in more low frequency noise.