On the gm/ID-based approaches for threshold voltage extraction in advanced MOSFETs and their application to ultra-thin body SOI MOSFETs

In this paper, we investigate the transconductance-to-current ratio (gm/ID) methods for the threshold voltage extraction using two popular threshold voltage criteria applicable to advanced bulk and SOI MOSFETs, namely: the condition of the maximum of the second derivative of the inversion charge and of the equality of the drift and diffusion drain current components. Using analytical modeling, we derive the first-order electrical parameters matching these two physical conditions and show that in the ideal MOSFET they do not coincide. The first corresponds to the point on the gm/ID versus gate voltage (Vg) curve where d(gm/ID)/dVG exhibits a minimum and where the ratio of gm/ID to its maximum value is equal to 2/3, whereas the second is met at the point where this ratio equals 1/2. The gm/ID methods for the VTH extraction using the above two criteria and their correlation with other methods are discussed. Since our modeling is based on the unified charge control model, its predictions are expected to be valid for both bulk and SOI MOSFETs. Experimental and simulation results for advanced SOI MOSFETs are used to validate modeling derivations and clarify practical applicability and limitations of the gm/ID methods.