The threshold voltage
of a MOSFET is the gate-source voltage at which an inversion channel
forms, which can then conduct a high drain current.
This common qualitative notion of
indicates the physical
background of moderate inversion, i.e., the transition between weak and
strong inversion, between ON and OFF state.
Despite this rather simple-looking concept a precise and universal
definition of the threshold voltage does not exist. Worse yet, engineers and
scientists often exchange or demand
data without being aware of the
definitions used.
The following sections lay down all
definitions relevant for this
work and they should also clarify some misconceptions
about threshold voltage.