Budapest University of Technology and Economics Department of Electron Devices Microelectronics, BSc course Bipolar transistors 1

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET Structure of bipolar transistors ► Cross-sectional diagram, ► Layout photographs ► The inner transistor

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET Structure of bipolar transistors Two PN junctions in close proximity (few  m-s) Two options: npn or pnp structure Identical operation, we shall discuss npn devices only … This is the planar transistor BJT bipolar junction transistor emitter base collector

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET Structure of bipolar transistors In principle symmetrical, practically not… w BM "metallurgical" base width emitter base collector emitterbase collector n-type diffusion p-type diffusion base concentration

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET Structure of bipolar transistors E B emitter base collector

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET Structure of bipolar transistors Low power transistor Chip size: ~ 0.5  0.5  0.3 mm

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET Structure of bipolar transistors Medium power transistor B E

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET BJT structure for IC-s burried layer collector n type island p-Si substrate base contact emitter base collector contact

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET BJT in an integrated circuit E E B B C C burried layer collector n type island p-Si substrate

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET "Inner transistor" and parasitics "Inner": where the 3 layers (n,p,n) are in front of each other inner transistor

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET 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.

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET Operation of the bipolar transistor ► The transistor effect ► Currents in a bipolar transistor

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET The transistor effect A BJT is more than just two diodes!

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET The transistor effect The symbol of the BJT Emitter Base Collector 1949

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET Currents in a BJT Normal active operation: EB junction open, CB closed A = current gain (common base, steady-state, normal active) recombination

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET Currents in a BJT Injection efficiency: Transport efficiency: recombination

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET Currents in a BJT Charge in the base. Homogeneous & inhomogeneous base Q B base charge: charge of the minority carriers injected from the emitter inhomogeneous base: “built-in” electrical field Drift transistor open closed built-in field sink CB junction as a sink Diffusion charge

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET Potentials Effective base width Base width modulation U B – built-in potential of the base

Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 1 © András Poppe & Vladimír Székely, BME-EET Potentials