TAILIEUCHUNG - Field-E ect (FET) transistors

In a field-effect transistor (FET), the width of a conducting channel in a semiconductor and, therefore, its current-carrying capability, is varied by the application of an electric field (thus, the name field-effect transistor). As such, a FET is a “voltage-controlled” device. The most widely used FETs are Metal-Oxide-Semiconductor FETs (or MOSFET). MOSFET can be manufactured as enhancement-type or depletion-type MOSFETs. Another type of FET is the Junction Field-Effect Transistors (JFET) which is not based on metal-oxide fabrication technique. FETs in each of these three categories can be fabricated either as a n-channel device or a p-channel device. As transistors in. | Field-Effect FET transistors References Hayes Horowitz pp 142-162 and 244-266 Rizzoni chapters 8 9 In a field-effect transistor FET the width of a conducting channel in a semiconductor and therefore its current-carrying capability is varied by the application of an electric field thus the name field-effect transistor . As such a FET is a voltage-controlled device. The most widely used FETs are Metal-Oxide-Semiconductor FETs or MOSFET . MOSFET can be manufactured as enhancement-type or depletion-type MOSFETs. Another type of FET is the Junction Field-Effect Transistors JFET which is not based on metal-oxide fabrication technique. FETs in each of these three categories can be fabricated either as a n-channel device or a p-channel device. As transistors in these 6 FET categories behave in a very similar fashion we will focus below on the operation of enhancement MOSFETs that are the most popular. n-Channel Enhancement-Type MOSFET NMOS The physical structure of a n-Channel Enhancement-Type MOSFET NMOS is shown. The device is fabricated on a p-type substrate or Body . Two heavily doped n-type regions Source and Drain are created in the substrate. A thin fraction of micron layer of SiO2 which is an excellent electrical insulator is deposited between source and drain region. Metal is deposited on the insulator to form the Gate of the device thus metal-oxide semiconductor . Metal contacts are also made to the source drain and body region. To see the operation of a NMOS let s ground the source and the body and apply a voltage vGS between the gate and the source as is shown above. This voltage repels the holes in the p-type substrate near the gate region lowering the concentration of the holes. As vGS increases hole concentration decreases and the region near gate behaves progressively more like intrinsic semiconductor material excess hole concentration zero and then finally like ECE60L Lecture Notes Spring 2002 61 a n-type material as electrons from n electrodes source and

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