Dependence of MOSFET noise parameters in n-channel MOSFETs on oxide thickness

Abstract

The expression for the 1 f noise resistance R n of a MOSFET at low drain bias contains the factor I d 2/[ g m ( V g - V T )] 2, which is unity in the elementary MOSFET theory but can be considerably larger than unity in practical units. The number fluctuation model characterizes R n further by the parameter [ N T ( E f )] eff/ ϵ and the mobility flucuation model introduces Hooge's parameter α. Measurements show that [ N T ( E f )] eff/ ϵ varies as t −2, α as t −1 and the mobility μ varies as t, where t is the oxide thickness. The dependence of R n upon T is chiefly determined by the t-dependence of the factor I d 2/[ g m ( V g - V T )] 2. Since the drain noise spectrum S I d ( f) is practically independent of t, it is a very useful parameter for characterizing the noise. All data are now mutually consistent.