lecture26

lecture26 - 6.7205/3.435 - I ntegrated Microelectronic...

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6.7205/3.435 - Integrated Microelectronic Devices - Spring 2007 Lecture 26-1 Lecture 26 - The "Long" Metal-Oxide-Semiconductor Field-Effect Transistor (cont.) April 11, 2007 Contents: I. Current-voltage characteristics of ideal MOSFET 2. Charge-voltage characteristics of ideal MOSFET Reading assignment: del Alamo, Ch. 9, 559.4 (9.4.3-9.4.5): 9.5 Cite as: leslis del Alamo, course materials for 6.7201 Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month W]
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6.7205/3.435 - Integrated Microelectronic Devices - Spring 2007 Lecture 26-2 Key questions Why does the drain current in a MOSFET saturate at high VDs? What charges should we keep track of as we construct a model for the charge-voltage characteristics of the MOSFET? Cite as: leslis del Alamo, course materials for 6.7201 Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month W]
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6.7205/3.435 - Integrated Microelectronic Devices - Spring 2007 Lecture 26-3 1. I-V characteristics of ideal MOSFET (cont.) Problems with MOSFET current model for linear regime as VDs approaches VGS - VT. Problems centered around g = L: Local gate overdrive goes to zero + lQil 4 0. How can current be supported? Gradual-channel approximation becomes invalid. Sheet-charge approximation becomes invalid. Lateral field so large that linearity between field and velocity invalid. Model that can handle values all the way up to VGS- VT is rather complicated; but ... actually, don't need new model! Reason: when - VT, ID changes very little due to prominent debiasing on the drain side of the channel. Cite as: leslis del Alamo, course materials for 6.7201 Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month W]
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6.7205/3.435 - Integrated Microelectronic Devices - Spring 2007 Lecture 26-4
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lecture26 - 6.7205/3.435 - I ntegrated Microelectronic...

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