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Budapest University of Technology and Economics Department of Electron Devices Microelectronics, BSc course Bipolar transistors 1 http://www.eet.bme.hu/~poppe/miel/en/06-bipolar1.ppt http://www.eet.bme.hu Budapest University of Technology and Economics Department of Electron Devices Structure of bipolar transistors ► Cross-sectional diagram, ► Layout photographs ► The inner transistor 01-10-2012 Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 2 Budapest University of Technology and Economics Department of Electron Devices Structure of bipolar transistors Two PN junctions in close proximity (few m-s) emitter bipolar junction transistor base BJT collector This is the planar transistor Two options: npn or pnp structure Identical operation, we shall discuss npn devices only … 01-10-2012 Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 3 Budapest University of Technology and Economics Department of Electron Devices Structure of bipolar transistors emitter base n-type diffusion collector p-type diffusion base concentration In principle symmetrical, practically not… wBM "metallurgical" emitter 01-10-2012 base collector base width Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 4 Budapest University of Technology and Economics Department of Electron Devices Structure of bipolar transistors emitter base collector B 01-10-2012 E Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 5 Budapest University of Technology and Economics Department of Electron Devices Structure of bipolar transistors Low power transistor Chip size: ~ 0.50.50.3 mm 01-10-2012 Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 6 Budapest University of Technology and Economics Department of Electron Devices Structure of bipolar transistors Medium power transistor B E 01-10-2012 Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 7 Budapest University of Technology and Economics Department of Electron Devices BJT structure for IC-s base contact emitter base collector contact collector burried layer n type island p-Si substrate 01-10-2012 Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 8 Budapest University of Technology and Economics Department of Electron Devices BJT in an integrated circuit B E B E C collector burried layer n type island p-Si substrate C 01-10-2012 Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 9 Budapest University of Technology and Economics Department of Electron Devices "Inner transistor" and parasitics inner transistor "Inner": where the 3 layers (n,p,n) are in front of each other 01-10-2012 Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 10 Budapest University of Technology and Economics Department of Electron Devices Conditions of transistor operation 1. At least one layer (on one side) is more heavily doped than the middle layer. 2. The middle layer (base) is much thinner than the diffusion length of the minority carriers. 01-10-2012 Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 11 Budapest University of Technology and Economics Department of Electron Devices Operation of the bipolar transistor ► The transistor effect ► Currents in a bipolar transistor 01-10-2012 Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 12 Budapest University of Technology and Economics Department of Electron Devices The transistor effect A BJT is more than just two diodes! 01-10-2012 Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 13 Budapest University of Technology and Economics Department of Electron Devices The transistor effect The symbol of the BJT 1949 Emitter Base Collector 01-10-2012 Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 14 Budapest University of Technology and Economics Department of Electron Devices Currents in a BJT Normal active operation: EB junction open, CB closed recombination I C A I E I CB 0 01-10-2012 A = current gain (common base, steady-state, normal active) Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 15 Budapest University of Technology and Economics Department of Electron Devices Currents in a BJT I C A I E I CB 0 recombination Injection efficiency: Transport efficiency: 01-10-2012 I En e IE I Cn tr I En A e tr Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 16 Budapest University of Technology and Economics Department of Electron Devices Currents in a BJT Charge in the base. Homogeneous & inhomogeneous base built-in field open closed open closed CB junction as a sink sink Diffusion charge QB base charge: charge of the minority carriers injected from the emitter 01-10-2012 inhomogeneous base: “built-in” electrical field Drift transistor Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 17 Budapest University of Technology and Economics Department of Electron Devices Potentials Effective base width wB wBM S S ' E ' C SC' ~ U Dc U BC wB f (U CB ) Base width modulation UB – built-in potential of the base 01-10-2012 Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 18 Budapest University of Technology and Economics Department of Electron Devices Potentials 01-10-2012 Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 2008-2012 19
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