A new method for measuring the threshold voltage of small-geometry MOSFETs from subthreshold conduction

A new method for measuring the threshold voltage of small geometry MOS devices is presented. Based on the drain current equation in the subthreshold region, the threshold voltage (VTH), defined as the gate voltage required for a surface band-bending of 2φF, can be accurately determined experimentally by the Quasi-Constant-Current (QCC) method. Compared with some other commonly used methods, this technique has the advantages of better fitting accuracy in subthreshold region, extracting the VTH with a unique value, and being suitable for small geometry devices over a wide range of voltage biases, temperatures, and process parameter variations. It can be used either for circuit simulation like the MOS3 model in SPICE, or as a routine monitor of processing like channel doping profile, gate oxide thickness or source and drain junction depths.