An accurate method for predicting temperature-dependent current mismatch in weak inversion region of long and wide channel MOSFET without subthreshold hump

Abstract

We have found and verified that the current mismatch σ(ΔI/I) in the weak inversion region can be accurately predicted on the basis of the transconductance efficiency gm/I when a MOSFET does not have a subthreshold hump. We have also verified that, in a relatively long and wide channel MOSFET, the value of gate-voltage mismatch σ(ΔI/gm)(LW)1/2 in the weak inversion region converges to a constant value, regardless of the channel size and temperature. The constant value is determined by the MOSFET structure. In our method, both the convergence value of σ(ΔI/gm)(LW)1/2 in the weak inversion region and the gm/I behavior are used as input information of the σ(ΔI/I) prediction. It is possible to take this constant convergence value as an approximate value of σ(ΔI/gm)(LW)1/2, also in the moderate inversion region. Using this value, our method of σ(ΔI/I) prediction can be applied to the moderate inversion region with a reasonable degree of accuracy. In addition, a method for improving the accuracy of the predictions in the strong inversion region will be presented. We will discuss the mechanism that causes the value of σ(ΔI/gm)(LW)1/2 in the weak inversion region to become a constant value. On the other hand, when a MOSFET has a subthreshold hump, the constant value approximation of σ(ΔI/gm)(LW)1/2 in the weak inversion region cannot be used. The value of σ(ΔI/gm)(LW)1/2 in weak and moderate inversion regions increases with a decrease in current. This increase randomly fluctuates depending on the wafer or temperature. As a result, to predict the current mismatch σ(ΔI/I) accurately, it is necessary to remove the subthreshold hump of a MOSFET completely.