lecture28

lecture28 - 6.720J/3.43J - Integrated Microelectronic...

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Unformatted text preview: 6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 28-1 Lecture 28 - The Long Metal-Oxide-Semiconductor Field-Effect Transistor (cont.) April 18, 2007 Contents: 1. Second-order and non-ideal effects Reading assignment: del Alamo, Ch. 9, 9.7 Cite as: Jess 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 Microelectronic Devices - Spring 2007 Lecture 28-2 Key questions The potential of the inversion layer increases along the channel. This should change the local threshold voltage. Does this affect the I-V characteristics of the MOSFET? What happens to MOSFET I-V characteristics if we apply a bias to the body with respect to the source? Cite as: Jess 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 Microelectronic Devices - Spring 2007 Lecture 28-3 1. Second-order and non-ideal effects in MOSFETs Introduce four significant refinements to model: Body effect (impact of y-dependence of V T ) Back bias (impact of V BS ) Channel length modulation (impact of V DS > V DSsat ) Subthreshold regime (channel conduction for V GS < V T ) Cite as: Jess 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 Microelectronic Devices - Spring 2007 Lecture 28-4 Body effect In a MOSFET biased in linear or saturation regimes, channel voltage V ( y ) depends on position: voltage difference between channel and body V ( y ) V V T ( y ) (increases along y ) V DS V DS <V DSsat 0 V BS =0 V GS-V(y) V GS no body effect V T V GS-V(y) V GS with body effect V To Dependence of V T ( y ) further debiases transistor: I D lower than ideal V DSsat lower than ideal n + n + n + p S G D B V GS >V T I D y 0 L inversion layer depletion region 0 L y V DS 0 L y local gate overdrive V DS 0 L y V th (y) local gate overdrive Cite as: Jess del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007....
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lecture28 - 6.720J/3.43J - Integrated Microelectronic...

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