The research of threshold voltage between theoretical computation and simulation

Power MOSFETs have been widely used in media power conversion topology as major switches. One of the important electrical parameters is threshold voltage (V
_th
) which is a key factor to drive circuit and control logic. A deviation of theoretical threshold voltage from simulation values has been usually observed. The theoretical computation of threshold voltage and the test method in real devices are analyzed to seek for primary cause to this phenomenon. The theory have been investigated a lot, which shows that computation results are independent of channel length. However, simulated results are closely relative to the channel length owing to the simulated method. Gate electrode bias (V
_GS
) is scanned from 0V to a certain value when the drain is shorted to the gate and the source is set as ground. Then V
_th
is deduced from the I-V characteristic curve at a given current I
_DS
. I
_DS
is always assigned a rated current of 250 μA which is commonly used in the real device test. This value always doesn't equal the current as the MOSFET is just turned on, which leads to a difference between the simulation and computation for the same device. In this paper a solution to restrain the deviation is presented. Precise I
_DS
is obtained by choosing the proper difference between V
_GS
and V
_th
in the current equation. And the solution has been verified by the simulation on the TCAD. The relation between V
_th
and channel length also has been revealed in the paper.