lecture23

lecture23 - 6.720J/3.43J - Integrated Microelectronic...

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Unformatted text preview: 6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 23-1 Lecture 23 - The Si surface and the Metal-Oxide-Semiconductor Structure (cont.) April 4, 2007 Contents: 1. Ideal MOS structure under bias (cont.) 2. Dynamics of the MOS structure Reading assignment: del Alamo, Ch. 8, 8.3 (8.3.5), 8.4 (8.4.1, 8.4.2) 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 23-2 Key questions How sharply does the inversion layer turn on and off with the gate voltage? How do the capacitance-voltage characteristics of the MOS struc- ture look like? How do the C-V characteristics of a MOS structure depend on the frequency of the small signal? 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 23-3 1. MOS structure under bias (cont.) Subthreshold regime In MOSFETs interested in current with the device nominally OFF, that is, for V < V th : Subthreshold current MOS structure in depletion but finite electron concentration at sur- face: 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]. Courtesy of S. Mertens, MIT. Used with permission. 6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 23-4 Compute Q e in depletion: 2 kT n q s N A q s exp Q e q N i A 2 2 s kT This key dependence seen in exact solution: 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]. Courtesy of S. Mertens, MIT. Used with permission. 6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 23-5 Express Q e in terms ov V by expanding s around sth : kT q s N A q ( V V th ) exp Q e q 4 f nkT with: dV n = d s | th 1 + 2 2 f Note: n > 1 Key characteristic of subthreshold regime is inverse subthreshold slope : kT S = n ln 10 q At best, if n = 1, S = 60 mV/dec at room temperature....
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lecture23 - 6.720J/3.43J - Integrated Microelectronic...

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