But first, enough electrons must be attracted near the gate to counter the dopant ions added to the body of the FET this forms a region with no mobile carriers called a depletion region, and the voltage at which this occurs is the threshold voltage of the FET. The positive voltage attracts free-floating electrons within the body towards the gate, forming a conductive channel. In n-channel enhancement-mode devices, a conductive channel does not exist naturally within the transistor, and a positive gate-to-source voltage is necessary to create one such. Unlike pinch off, the term threshold voltage is unambiguous and refers to the same concept in any field-effect transistor. This is somewhat confusing since pinch off applied to insulated-gate field-effect transistor (IGFET) refers to the channel pinching that leads to current saturation behaviour under high source–drain bias, even though the current is never off. When referring to a junction field-effect transistor (JFET), the threshold voltage is often called pinch-off voltage instead. It is an important scaling factor to maintain power efficiency. The threshold voltage, commonly abbreviated as V th or V GS(th), of a field-effect transistor (FET) is the minimum gate-to-source voltage (V GS) that is needed to create a conducting path between the source and drain terminals. Note that the y-axis is logarithmic, showing that only extremely small amounts of current pass below the threshold voltage (around 0.45 V) when the conducting channel connects. Simulation result for formation of inversion channel (electron density) and attainment of threshold voltage (IV) in a nanowire MOSFET.
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