Gate: Special connection in some semiconductor devices that upon receiving an appropriate signal (in the form of a voltage or pulse) allows controlling of the device, including turning it on and off. Source: (in semiconductors) One of the three terminals in a field effect transistor, comparable with the emitter in a junction transistor.ĭrain: One of the three terminals in a field effect transistor (FET) counterpart of the collector in a junction transistor. This is why a FET is a voltage-driven device. The channel size (effect size not the physical size) is governed by the voltage applied to the gate and not the current through the gate. This control action is carried out by the gate.
The channel is physically surrounded by the opposite type semiconductor material, which can influence the extent (effective size) of the channel, thus introducing less or more resistance for the flow of electrons. One side of the channel is called the source (counterpart of emitter) and the other side is called the drain (counterpart to collector). When a FET conducts, electrons move through the channel. The three elements of a field effect transistor have names different than those for BJT. In practice, a transistor is very small, and all its elements are made on a body that itself is a semiconductor and is part of the transistor elements. The strength of this field can control the flow of the electric carriers in the channel.Ī schematic of the active area of a FET and its three terminals are shown in Figure 1. The reason it is called field effect transistor is that the current through the channel is affected by an electrostatic field formed around the channel. If the channel material is made of N material, then the product is called N-channel FET, and if the channel is made of P-type semiconductor, the FET is called P-channel FET.Ī FET is a voltage-driven transistor, dissimilar to BJT, which is a current-driven device. In a field effect transistor, the main body can be N-type or P-type material in which a channel from the opposite type material is diffused. The structure and the manufacturing process of a FET are different from those of a bipolar junction transistor.
The flow of electrons can be controlled by adjusting the polarity and intensity of the field.Ī basic difference between a FET and a junction transistor is that a FET has only one P-N junction.
It has a channel or passage around which an electric field can be developed and through which electrons flow. The current, consequently, is much lower, which leads to much smaller power consumption in a circuit employing this category of the transistor.įield effect transistor (FET): Type of transistor, still made of semiconductor materials, based on a different structure and a different mechanism of operation than the junction transistor. Transistor circuit resistances for a field effect transistor are much larger than their counterparts in BJTs.
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