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Budapest University of Technology and Economics Department of Electron Devices Microelectronics, BSc course Field effect transistors.

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Presentation on theme: "Budapest University of Technology and Economics Department of Electron Devices Microelectronics, BSc course Field effect transistors."— Presentation transcript:

1 Budapest University of Technology and Economics Department of Electron Devices Microelectronics, BSc course Field effect transistors 1: The JFET

2 Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, The JFETs © András Poppe & Vladimír Székely, BME-EET The abstraction level of our study: SYSTEM MODULE + GATE CIRCUIT n+ SD G DEVICE V out V in

3 Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, The JFETs © András Poppe & Vladimír Székely, BME-EET The JFET ► FET = Field Effect Transistor – the flow of charge carriers is influenced by electric field transversal field is used to control Channel JUNCTION FET: depletion layers of pn- junctions close the channel ► Unipolar device: current is conducted by majority carriers ► Power needed for controlling the device  0 Most important parameter: U 0 pinch-off voltage Flow depletion layer

4 Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, The JFETs © András Poppe & Vladimír Székely, BME-EET The JFET – possible realization: The width of the closed PN junction controls the conductivity of the channel PN junction  junction FET depletion layer channel n type epi-layer

5 Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, The JFETs © András Poppe & Vladimír Székely, BME-EET The JFET – a "normally on" device ► Symbols: ► Characteristics: controlled resistor (see later the triode region of MOSFETs) pinch off voltage n channel p channel no saturation saturation

6 Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, The JFETs © András Poppe & Vladimír Székely, BME-EET Calculation of the pinch off voltage d h (x) 0 L x S width of depl. layer d geom. width of channel W U(x) Pinch off: d geom. width = 2 x width of depletion layer

7 Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, The JFETs © András Poppe & Vladimír Székely, BME-EET Problem Determine the pinch off voltage of a Si JFET, if the channel width is d = 4  m and the doping is N d = /cm 3 !

8 Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, The JFETs © András Poppe & Vladimír Székely, BME-EET The characteristic geom. width of channel width of depletion layer

9 Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, The JFETs © András Poppe & Vladimír Székely, BME-EET The characteristic geom. width of channel width of depletion layer

10 Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, The JFETs © András Poppe & Vladimír Székely, BME-EET The characteristic Channel conductivity

11 Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, The JFETs © András Poppe & Vladimír Székely, BME-EET The characteristic Current constant For the triode region!

12 Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, The JFETs © András Poppe & Vladimír Székely, BME-EET The characteristic For all regions! Only in saturation:

13 Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, The JFETs © András Poppe & Vladimír Székely, BME-EET Small signal parameters, equivalent Slope / transconductance Output conductance Voltage gain In Out


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