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N_FET_N14 - MOS Field-Effect Transistors(MOSFETs(14 1 Field...

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MOS Field-Effect Transistors (MOSFETs) (14) 1
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Field Effect Transistors (FET) 2 Figure 5.6 Cross-section of an npn BJT. Before looking at structure of an FET, let us look at the structure (one view) of the BJT.
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Field Effect Transistors (FET) This is the other major type of transistor, known as the Field Effect Transistor or (FET). In this case also, voltage between the two terminals of the device (FET) is used to control the current through the third terminal. Current control is based on an electric field established by the voltage applied to the control terminal, known as ‘Gate’. Current is conducted by only one type of carrier (electrons or holes) depending upon the type of FET (n-channel or p-channel) ------- because of this FET is also known as ‘The unipolar Transistor’. There are different type of FETs; the type, in general, is relevant to the material used in the fabrication process. A few of the types are: MOSFET ==> NMOS, PMOS and CMOS Enhancement Type Depletion Type 3
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Field Effect Transistors (FET) There are different type of FETs; the type, in general, is relevant to the material used in the fabrication process. A few of the types are: MOSFET ==> NMOS, PMOS and CMOS Enhancement Type Depletion Type IGFET : Insulated Gate FET MOSFET ==> Metal Oxide Semiconductor FET NMOS ==> N-Channel MOSFET PMOS ==> P-Channel MOSFET CMOS ==> Complementary MOSFET : A couple of MOSFETs are fabricated side by side; one is NMOS & other PMOS 4
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Field Effect Transistors (FET) IGFET ==> Insulated Gate FET : instead of Metal, certain type of Silicon called polysilicon is used to form the gate electrode. It is same as MOSFET, except the difference in the Gate-electrode material Compared to BJTs MOSFETs occupy much smaller space on the Silicon Chip / or substrate. The manufacturing process is much simpler. Digital logic and memory function can be implemented even without the use of resistors or diodes etc. ------- therefore suitable for fabrication of ‘Very large scale Integrated’ (VLSI) Ics. e.g. microprocessors, memory chips. There are many types of FET variants, however, it shall suffice to discuss enhancement-type MOSFET, which is the most significant device. 5
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Field Effect Transistors (FET) Figure 4.1 (a) shows Structure of Enhancement-type MOSFET 6
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Field Effect Transistors (FET) Structure of Enhancement-type MOSFET 7 Figure 4.1 Physical structure of the enhancement-type NMOS transistor: (a) perspective view; (b) cross-section. Typically L = 0.1 to 3 μm, W = 0.2 to 100 μm, and the thickness of the oxide layer (t ox ) is in the range of 2 to 50 nm.
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Field Effect Transistors (FET) § 4.1 .1 Device Structure & Physical Operation The n-channel MOSFET is fabricated on a p-type substrate. Two heavily doped n-type regions, indicated in the figure as the n + source and the n+ drain regions, are created in the substrate.
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