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lecture24 - 6.720J/3.43J Integrated Microelectronic Devices...

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6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 24-1 Lecture 24 - The Si surface and the Metal-Oxide-Semiconductor Structure (cont.) The ”Long” Metal-Oxide-Semiconductor Field-Effect Transistor April 6, 2007 Contents: 1. Dynamics of the MOS structure (cont.) 2. Three-terminal MOS structure 3. Introduction to MOSFET Reading assignment: del Alamo, Ch. 8, §§ 8.5-8.6; Ch. 9, § 9.1 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].
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6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 24-2 Key questions What happens to the C-V characteristics of a MOS structure if the bias is switched abruptly? What happens to the electrostatics of the MOS structure if we contact the inversion layer and we apply a bias to it? How does a MOSFET look like and how does it work (roughly)? 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].
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6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 24-3 1. Dynamics of the MOS structure (cont.) Deep depletion Consider what happens after the application of a voltage step from depletion towards inversion. On top of step, put HF small signal to measure C V + A + + + + + + V th 0 + ++ + + 0 t B + + + + + + + + + + C A C HF C - - - - - - - - - - - - - - - - - - - - + + + - + + C + + + + + + + - - - - - - - - - - - - - - - C dd 0 t B - - - - - - - - - - equilibrium - - - - - - - - - - - - - - - - - - - - - - - - - deep depletion� (t<< τ g ) x d >x dmax inversion�± (t>> τ g x dmax Immediately after the onset of the step (after an RC delay), inversion layer does not have a chance to grow (electrons must be generated) MOS remains in depletion (” deep depletion ”) x d grows beyond x dmax C smaller than C HF 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].
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6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 24-4 Even though V > V th , capacitance in deep depletion described by expression derived for depletion regime: C ox C dd 1 + 4 V γ V 2 F B C-V characteristics: C ox C low frequency high frequency deep depletion A B C Cite as: Jesús del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007.
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