Field-Effect Transistors


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This is a presentation about FETs, made for english class.

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Field-Effect Transistors

  1. 1. Field-Effect Transistors
  2. 2. Field-effect transistors <ul><li>General overview </li></ul><ul><li>Types of field-effect transistors </li></ul><ul><li>Uses </li></ul>
  3. 3. 1. General overview <ul><li>Field-effect transistors (FETs) follow an other principle than bipolar junction transistors </li></ul><ul><li>They rely on an electric field to control the shape and hence the conductivity of a „channel“ in a semiconductor material </li></ul><ul><li>FETs controlled by voltage (  BJTs controlled by current) </li></ul>
  4. 4. 1. General overview <ul><li>The concept of the field effect transistor predates the bipolar junction transistor (BJT) </li></ul><ul><li>Was not physically implemented until after BJTs, due to limitations of semiconductor materials and relative ease of manufacturing BJTs compared to FETs at that time. </li></ul>
  5. 5. 1. General overview <ul><li>Basic principle of FETs </li></ul><ul><li>The terminals of a FET refer to their function: Gate (G), Source (S), Drain (D) </li></ul>control terminal current channel of charge carriers for charge carriers control voltage
  6. 6. 1. General overview <ul><li>FETs are voltage-controlled by the voltage between gate and source terminal </li></ul><ul><li>Voltage effects the electric field of the transistor which enlarges or diminishes the channel </li></ul><ul><li> Effects the current stream through the FET </li></ul>
  7. 7. 2. Types of field-effect transistors <ul><li>Junction Field-Effect Transistors </li></ul><ul><li>JFETs </li></ul><ul><li>Simplest type of FET </li></ul><ul><li>Long channel semiconductor </li></ul><ul><li>Either p- or n-doped (  p-type, n-type) </li></ul><ul><li>A contact at each end  source and drain terminals </li></ul><ul><li>Gate terminal surrounds the channel and is doped opposite to the doping of the channel </li></ul>
  8. 8. 2. Types of field-effect transistors <ul><li>Junction Field-Effect Transistors </li></ul><ul><li>JFETs </li></ul><ul><li>N-channel types and P-channel types </li></ul>
  9. 9. 2. Types of field-effect transistors <ul><li>Metal-Oxide-Semiconductor FETs </li></ul><ul><li>MOS-FETs </li></ul><ul><li>Most common field-effect transistor </li></ul><ul><li>traditional metal–oxide–semiconductor (MOS) structure is obtained by depositing a layer of silicon dioxide and a layer of metal on top of a semiconductor die. As the silicon dioxide is a dielectric material its structure is equivalent to a planar capacitor, with one of the electrodes replaced by a semiconductor (substrate) </li></ul>
  10. 10. 2. Types of field-effect transistors <ul><li>Metal-Oxide-Semiconductor FETs </li></ul><ul><li>MOS-FETs </li></ul><ul><li>Metal electrode is used as the gate, the other forms the so called body/bulk/substrate terminal of a MOS-FET </li></ul><ul><li>Opposite doted semiconductors placed within the substrate form the drain and source terminals </li></ul><ul><li>Modulating the MOS-Capacitance forms a channel between source and drain terminals </li></ul><ul><li>This controls the current flow through the MOS-FET </li></ul>
  11. 11. 2. Types of field-effect transistors <ul><li>Metal-Oxide-Semiconductor FETs </li></ul><ul><li>MOS-FETs </li></ul>
  12. 12. 2. Types of field-effect transistors <ul><li>Metal-Oxide-Semiconductor FETs </li></ul><ul><li>MOS-FETs </li></ul>depletion-mode enhancement-mode P-Channel N-Channel
  13. 13. 3. Uses <ul><li>As well as BJTs, FETs can be used as switching and/or amplifying elements </li></ul><ul><li>JFETs are also often used as variable, controlable resistors </li></ul><ul><li>FETs, especially JFETs consumpt almost no current  high input impedance </li></ul><ul><li>Makes JFETs very suitable for pre-amplifiers </li></ul><ul><li>FETs behave like electron tubes from the old days </li></ul><ul><li>Integrated circuits (CMOS, other modern elements) use MOS-FETs as the switching element </li></ul><ul><li>Power-MOS-FETs are used in HiFi power amplifiers and produce a sound comparable to tube amplifiers </li></ul><ul><li>Many, many more uses… </li></ul>