6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 35-1 Lecture 35 - Bipolar Junction Transistor (cont.) May 3, 2007 Contents: 1. Current-voltage characteristics of ideal BJT (cont.) Reading materi al: del Alamo, Ch. 11, §11.2 (11.2.1) Cite as: Jesús del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.720J/3.43J - Integrated Microelectro nic Devices - Spring 2007 Lecture 35-2 Key ques tions • How does the BJT operate in other regimes? • How does a complete model f o r the ideal BJT look like? Cite as: Jesús del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.720J/3.43J - Integrated Microelectro nic Devices - Spring 2007 Lecture 35-3 1. Current-voltage ch aracteristics of ideal BJT (cont.) � Forward-active regime (VBE > 0, VBC < 0 ) Summary of key results: WB << LB n-Emitter p-Base n-Collector IE<0 IB>0 IC>0 VBE > 0 VBC < 0 qVBE IC = IS exp kT IS qVBE IB = (exp − 1) βF kT qVBE IS qVBE IE = −IC − IB = −IS exp − (exp − 1) kT βF kT Cite as: Jesús del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.720J/3.43J - Integrated Microelectro nic Devices - Spring 2007 Lecture 35-4 • Current gain 2ni DBICNB WB NEDBWEβF � � 2 = IBni DE NBDEWB NE WE To maximize βF: • NE � NB • WE � WB (for manufacturing reasons, WE � WB) • want npn, rather than pnp because this way DB > DE βF hard to control ⇒ if βF is high enough (> 50), circuit techniques effectively compensate for this. Cite as: Jesús del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.720J/3.43J - Integrated Microelectro nic Devices - Spring 2007 Lecture 35-5 Cite as: Jesús del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.720J/3.43J - Integrated Microelectro nic Devices - Spring 2007 Lecture 35-6 • Equivalent circuit model C E qVBEIS expB kT IS (exp qVBE -1)βF kT qVBE IC = IS exp kT IS qVBE IB = (exp − 1) βF kT qVBE IS qVBE IE = −IC − IB = −IS exp − (exp − 1) kT βF kT Cite as: Jesús del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.720J/3.43J - Integrated Microelectro nic Devices - Spring 2007 Lecture 35-7 • Energy band diagram E(n) B(p) C(n) EC EV EFthermal� equilibrium EC forward� active EV Efe Efh qVBE qVBC • Summary of minority carrier profiles (not to scale) nBpE pC nBopEo pCo 0 WB WB+xBC-WE-xBE -xBE WB+xBC+WC � x Cite as: Jesús del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.720J/3.43J - Integrated Microelectro nic Devices - Spring 2007 Lecture 35-8 � Reverse regime (VBE < 0 , VBC > 0) IE: electron injection from C to B, collection into E IB: hole injection from B to C, recombination in C n-Emitter p-Base n-Collector IE>0 IB>0 IC<0 VBE < 0 VBC > 0 Minority carrier profiles (not to scale): 0 WB-xBE WB+xBC-WE-xBE WB+xBC+WC pE nB pC pEo nBo pCo� x Cite as: Jesús del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.720J/3.43J - Integrated Microelectro nic Devices - Spring 2007 Lecture 35-9 Current eq uations (just like FAR, b ut role o f collector and emitter reversed): IE = IS exp qVBC kT IB = IS βR (expqVBC kT − 1) IC = −IE − IB = −IS exp qVBC kT − IS βR (expqVBC kT − 1) Equival ent-circuit model representation: C IS (exp qVBC -1)βR kT qVBCB IS exp kT E Cite as: Jesús del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].Prefactor in IE expression is IS: emitter current scales with 6.720J/3.43J - Integrated Microelectro nic Devices - Spring 2007 Lecture 35-10 AE.IB AC EB B IE AE EB B CC But, IB scales roughly as AC: • downward component scales as AC • upward component scales as AC − AE � AC Hence, βR � 0.1 − 5 � βF. Cite as: Jesús del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 18-8Forward-active Gummel plot (VCE=3V ):Reverse Gummel (VEC=3V ):Cite as: Jesús del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.720J/3.43J - Integrated Microelectro nic Devices - Spring 2007 Lecture 35-11 Energy b a nd diagram: E(n) B(p) C(n) EC EFthermal� equilibrium EV reverse EC EV Efe Efh qVBE qVBC Cite as: Jesús del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.720J/3.43J - Integrated Microelectro nic Devices - Spring 2007 Lecture 35-12 � Cut-off regime (VBE < 0 , VBC < 0) IE: hole generation in E, extraction into B IC: hole generation in C, extraction into B n-Emitter p-Base n-Collector IE>0 IB<0 IC>0 VBE < 0 VBC < 0 Minority carrier profiles (not to scale): 0 WB-xBE WB+xBC-WE-xBE WB+xBC+WC pE nB pC pEo nBo pCo� x