MOSFET Usage

• Metal (Gate)
• Oxide (SiO2, insulator)
• Semiconductor (Si wafer)
• Field
• Effect
• Transistor

NMOS

Also known as N-FET, N-type MOSFET or N-channel MOSFET. This refers to the fact that these use electrons as the charge carrier. Electrons come from source, which is the most negative voltage.

This functions as a switch that is normally open and closes when $V_{GS}>V_t$. When this happens, we get a drain current $I_D$.

For example, we could have a microcontroller connected to the pin.

• When it outputs $0\text{ V}$, the LED remains off.
• When it outputs $5\text{ V}$, the LED turns on.

A series resistor may be included to limit in rush current.

PMOS

A PMOS uses P-type carriers, which are holes. These $h^{+}$ carriers come from the source, which is the most positive voltage. In this case, we technically have $V_{SG}$, but we can just think of it in terms of the difference between the two terminals and use $|V_{GS}|$ instead.

When $|V_{GS}|$ is more than the threshold, the drain current $I_D$ activates. The PMOS acts opposite to the NMOS, such that it’s normally ON and turns off when $|V_{GS}|>V_t$. Thus, we would have:

• $0\text{ V}$ = ON
• $5\text{ V}$ = OFF

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