NMOS

Overview

The NMOS transistor (N-type Metal-Oxide-Semiconductor Field-Effect Transistor) is the most basic building block of almost all modern digital circuits, including the FinFET you asked about previously.

How an NMOS Transistor Works

An NMOS transistor acts as an electronically controlled switch.

  1. Structure: It has three main terminals on a silicon substrate:
    • Source
    • Drain
    • Gate (separated from the silicon by a thin layer of oxide)
  2. OFF State (Switch Open):
    • When the Gate voltage (Vth) is zero (or low), there is a high-resistance barrier between the Source and the Drain.
    • No significant current flows; the switch is OFF.
  3. ON State (Switch Closed):
    • When a sufficiently positive voltage, greater than the threshold voltage (Vth), is applied to the Gate (i.e. VG > Vth), the electric field pulls negatively charged electrons into the region beneath the gate oxide.
    • This creates a conductive path (called the channel) between the Source and the Drain.
    • Current (composed of these electrons) can now flow from the Drain to the Source; the switch is ON.

In digital logic (like a computer processor), the ON state represents a logical '1' or 'True', and the OFF state represents a logical '0' or 'False'.

Examples of electronic transistors.