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In field-effect transistors (FETs), depletion mode and enhancement mode are two major transistor types, corresponding to whether the transistor is in an on state or an off state at zero gate–source voltage. Enhancement-mode MOSFETs (metal–oxide–semiconductor FETs) are the common switching elements in most integrated circuits.
However, at high frequencies or when switching rapidly, a MOSFET may require significant current to charge and discharge its gate capacitance. In an enhancement mode MOSFET, voltage applied to the gate terminal increases the conductivity of the device. In depletion mode transistors, voltage applied at the gate reduces the conductivity. [1]
A depletion-mode device with gate tied to the opposite supply rail is a much better load than an enhancement-mode device, acting somewhere between a resistor and a current source. The first depletion-load NMOS circuits were pioneered and made by the DRAM manufacturer Mostek , which made depletion-mode transistors available for the design of the ...
In n-channel enhancement-mode devices, a conductive channel does not exist naturally within the transistor. With no V GS, dopant ions added to the body of the FET form a region with no mobile carriers called a depletion region. A positive V GS attracts free-floating electrons within the body towards the gate. But enough electrons must be ...
For electronic semiconductor devices, a native transistor (or sometimes natural transistor) is a variety of the MOS field-effect transistor that is intermediate between enhancement and depletion modes. Most common is the n-channel native transistor.
PMOS uses p-channel (+) metal-oxide-semiconductor field effect transistors (MOSFETs) to implement logic gates and other digital circuits. PMOS transistors operate by creating an inversion layer in an n-type transistor body. This inversion layer, called the p-channel, can conduct holes between p-type "source" and "drain" terminals.
The VMOS was invented by Hitachi in 1969, [11] when they introduced the first vertical power MOSFET in Japan. [12] T. J. Rodgers, while he was a student at Stanford University, filed a US patent for a VMOS in 1973. [13] Siliconix commercially introduced a VMOS in 1975. [11] The VMOS later developed into what became known as the vertical DMOS . [14]
The main benefit of the power MOSFET compared to the BJT is that the MOSFET is a depletion channel device and so voltage, not current, is necessary to create a conduction path from drain to source. At low frequencies this greatly reduces gate current because it is only required to charge gate capacitance during switching, though as frequencies ...