High-field conduction mechanisms in polycrystalline-silicon resistors

Abstract
The non-linear I-V characteristics of polysilicon resistors at high electric fields have been extensively studied. The I-V measurements over a temperature range from -194° to 144°C were made on resistors fabricated in polysilicon films deposited by either LPCVD or APCVD method with boron or phosphorus as dopants having concentrations in the range from5 \times 10^{15}to5 \times 10^{19}cm-3. As doping level decreases below a critical doping concentration N*, I-V curves deviate asymmetrically from a hyperbolic-sine function. The number of grains ζNgalong the effective conduction path versus doping levels shows downward concavity with its maximum value near N*. ζNgis also a function of measurement temperatures. Such anomalous conduction phenomena cannot be explained by previous uniform grain-size models. This paper presents a new non-uniform grain-size model which effectively describes the high field conduction behavior of polysilicon resistors and shows that the non-uniform polycrystalline structure has a major effect on the non-linear I-V characteristics. The effects of these observed phenomena to the performance of inverters using polysilicon load resistors in high field regimes have also been investigated.

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