[MUSIC] Let's look at the Venn diagram of MOSFET in different perspective. This is the 3D Venn diagram of MOSFET. So here, source and drain and, you lay down the MOSFET and here's the gate. And underneath gate, there's a gate dielectric and p-type silicon. Here, the m+ and the source and drain region go on to the end of the silicon. And then there's the entirely p-type semiconductor. So we're drawing a Venn diagram, only the silicon semiconductor and then gate dielectrics located at gate and dielectric located here. So gate voltage is 0 and drain voltage is 0. So this region is the Ec is here. And then Fermi energy very close to the ec means that there are a lot of majority electron, I mean, the m+ electron is located in source region. Same thing for the drain region, Fermi energy across Ec, huge carrier concentration in drain region. And then here, m+ to p, so that's a pn junction. So Fermi energy is constant under equilibrium. And then here, Fermi energy is close to the Ev because here's the p-type semiconductor, And here's the pn junction again. Now, you applying gate voltage above threshold voltage and Vd = 0, no current flowing. If you make gate voltage above threshold voltage, inversion charges form only at ten nanometer below the silicon oxide layer. So at the below surface of oxide layer, then this bending, so Fermi energy is above the Ei, means inversion charge is formed. Those inversion charge only occurs at, Ten nanometer, just below the gate dielectric. Underneath the inversion layer, let's say that there's one micrometer much less, but the one micrometer of depletion charge, where is it, here. In here, depletion charge is formed. And then underneath depletion charge, there will be just the p-type semiconductor, so that the Fermi energy is close to the Ev. So inversion charge only occurs under the silicon oxide layer ten nanometers region. Now, you're applying drain voltage above the Vg minus Vth. Then a positive drain voltage in drain lowers the potential of the drain. And then current starting to flowing, electron moves source to drain, then, Channel region, Fermi energy is above the Ei, which is the surface potential, above the 2 pi f. Therefore, inversion charges form, but the region, depleted the region, the Fermi energy go below the Ei. Which means that this is the depleted region where the now minority electron is existing. However, huge number of minority inversion charge at the channel and source region will be swept down to the drain region by the high diverse electric fill of the pn junction. So let's understand MOSFET as a water flow. Because the current flowing in our MOSFET device is exactly the same as the water flowing potential energy. So this is the MOSFET and then this is the pn junction. And then pn junction has a p-type semiconductor and n-type semiconductor. There is a built-in potential between the pn junction, This direction. And then in this direction, mp junction, MOSFET device, Venn diagram forming like this. So what is the built-in potential in our np junction? That's the built-in potential, right? So those built-in potential blocking the current flowing from the source to drain when gate voltage is 0. So when gate voltage is 0, there is the built-in potential of the pi bi, therefore water can now flow from the source to drain. Now, you applying gate voltage above the threshold voltage. Then, gate voltage above the threshold voltage makes the minority electron inversion charge. Channel is formed because the surface potential is above the 2 pi f, and then lowers the barrier of the channel. So electron water channel is formed. However, current is not flowing because you didn't apply drain voltage. Current is 0, channel is formed, but the current is not flowing, you didn't apply drain voltage. Now you applying drain voltage with the VD1, then you lower the potential of the drain region. Then water are starting to flow in from the source to drain. And then those voltage in drain region doesn't influencing the channel of electron. Therefore, current are linearly increasing. At more higher drain voltage, compared to the previous one, lowers more potential of the drain region. And more current flowing, but they are starting to saturating because the drain potential, Drain potential in drain region influencing the channel of the water by reducing the water channels. So starting to reducing the electron channel, and the water is starting to saturate it because of the narrow channel in drain region. At a pinch off, where the Vg minus, Vd = Vg -Vth, then pinch off is formed, and current is after that current is saturate, because there is no channel at the drain region and current are, after that, saturating. So further evolve the pinch off saturation drain voltage, then huge electric field or potential difference occur at the pinch off region, and current are swept down to the channel to the drain region. But there is no inversion, therefore currents are saturated.
