Threshold voltage VT of MOS field effect transistor (VDS=0)

MOS threshold voltage VT

The so-called ideal MOS tube is to assume that there is no positive charge in the gate oxide layer, and electrons cannot be exchanged between the metal gate and the semiconductor (that is, the contact potential difference between the metal and the semiconductor is not considered ). For the ideal n-channel MOS transistor shown in Figure 1.2-5 (the substrate is P-type silicon), when the voltage VGS is applied to the gate, A part of the voltage falls on the oxide layer, and another part of the voltage ф Landing on the surface of the semiconductor, there is:

MOS threshold voltage VT

From the previous discussion, we can see that to make the P-shaped surface a strong inversion, фMust meet:

MOS阈值电压VT

When the surface has just formed a strong inversion,，maximum thickness of depletion layer，the amount of charge per unit area in the depletion layerfor:

MOS阈值电压VT

Thus, the ideal threshold voltage of the n-channel MOS tube can be obtained MOS阈值电压VT ：

MOS阈值电压VT

Depend onandit can be seen from the expression that at a certain temperature, for a certain substrate material,andthe size is completely determined by the doping concentrationdecide. MOS threshold voltage VT. Doping concentrationbigger,bigger,Threshold voltage of ideal n-channel MOS tubebigger,