![]() ![]() FETs appear in vast numbers in microprocessor chips and similar devices. Junction FETs have relatively slow switching speeds compared with MOSFETs and bipolar transistors, and are therefore not used in logic circuits. Deeply embedded in almost everything electronic, transistors have become the nerve cells of the Information Age. Unlike the bipolar transistor both types of FET require virtually no input current to the gate except a pulse to charge or discharge the gate capacitance. A voltage supply is connected across an N-channel MOSFETs drain and the source and gate to the source terminal are shorted as shown. In the MOSFET the gate is insulated from the source and drain regions and the channel forms when the gate voltage is applied. The gate-source/drain underlap, however, shows the different improved performances for the 4.6-nm monolayer SiC SBFET. In the junction FET the channel is a composite part of the structure. In contrast to bipolar transistors, FETs are unipolar devices the current flow is electrons (in n-channel devices) or holes (in p-channel devices). Applying voltage at the gate alters the width of the drain-source channel, which is the path along which charge carriers (electrons or holes) flow. Devices with p-type source, drain, and channel are called p-channel devices. If the source and drain regions are composed of n-type semiconductor the conduction channel is n-type these devices are known as n-channel devices. Current flow in a narrow conduction channel between drain and source is controlled by the voltage applied between gate and source, which can deplete the conduction channel of charge carriers. When the gate-source voltage of a MOSFET exceeds a certain voltage (threshold voltage, Vth), the drain-source resistance decreases, causing the MOSFET to. ![]() ![]() A semiconductor device having three terminals: source, gate, and drain. ![]()
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