Threshold voltage extraction in Tunnel FETs

• Standard threshold voltage extraction methods are shown to be unreliable for TFETs.
• Two alternative methods based on differentiation and integration are proposed.
• Both methods were successfully tested on experimental Fin-type TFETs.
• The integration based method is recommended to reduce measurement noise.

This article proposes two possible extrapolation-type methods to extract the threshold voltage of Tunnel Field Effect Transistors (TFETs). The first one, which we call the “CTR method,” makes use of the drain Current-to-Transconductance Ratio function. As this method requires differentiating the drain current with respect to the gate voltage, it is blurred by the amplified effect of measurement noise when applied to real device transfer characteristics. To avoid this effect, a second method is also proposed that uses integration of the drain current with respect to gate voltage instead of differentiation. This second method, which was named “H1 method” when it was originally applied to non-crystalline inversion mode MOSFETs, produces comparable results to those obtained from the CTR method, but it has the advantage of inherently reducing the effect of measurement noise by virtue of the low-pass filtering capacity of integration. Both methods are based on defining threshold voltage as the gate voltage axis intercept of the linearly extrapolated strong conduction behavior of either CRT or H1 functions. This is made possible by approximating the drain current in the strong conduction region of the TFET’s transfer characteristics by a monomial function of the gate voltage. Both methods are illustrated and compared by applying them to measured transfer characteristics of experimental Fin-type TFETs.