An Adjusted Constant-Current Method to Determine Saturated and Linear Mode Threshold Voltage of MOSFETs

The constant-current (CC) method uses a current criterion to determine the threshold voltage (
V
_TH
) of metal-oxide-semiconductor (MOS) field-effect transistors. We show that using the same current criterion in both saturation and linear modes leads to inconsistent results and incorrect interpretation of effects, such as drain-induced barrier lowering in advanced CMOS halo-implanted devices. The generalized adjusted CC method is based on the theory of the charge-based MOS transistor model. It introduces an adjusted current criterion, depending on
V
_DS
, allowing to coherently determine
V
_TH
for the entire range of
V
_DS
from linear operation to saturation. The method uses commonly available
I
_D
versus
V
_G
data with focus on moderate inversion. The method is validated with respect to the ideal surface potential model, and its suitability is demonstrated with technology-computer-aided-design data from a 65-nm CMOS technology and measured data from a 90-nm CMOS technology. Comparison with other widely used threshold voltage extraction methods is provided.