MOSFET - ECE 4130/6130: Advance VLSI Systems Fall 2009...

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1 ECE ECE 4130/6130 4130/6130 : Advance VLSI Systems : Advance VLSI Systems Fall Fall 2009 2009 MOSFET: A Circuit Designer MOSFET: A Circuit Designer s s Perspective Perspective Prof. Saibal Mukhopadhyay School of Electrical & Computer Engineering Georgia Institute of Technology
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2 Goals of this lecture Goals of this lecture ± Intuitive understanding of device operation ± Introduction of basic device equations ± Capacitive behavior of MOSFET ± Physical understanding of important deep-submicron effects ² Subthreshold conduction ² Short-channel effect ² Velocity saturation
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3 Purpose of this lecture Purpose of this lecture ± This is not a lecture on MOSFET physics ± We will not study in this lecture/course: ² Detail physics of MOSFET operation ² Detail derivation of MOSFET equations Threshold voltage equation Current equations Capacitance equations ± But, we need to understand the basic principles and know the equations to use them for circuit analysis and design. If you want to know the physics in more detail, please, consult a book on device physics or ask the instructor in office hours
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4 Reading Materials Reading Materials ± Chapter 6: Introduction to VLSI Circuits and Systems , Uyemura, ± Chapter 3: Digital Integrated Circuits: A Design Perspectives, J. M. Rabaey, A. Chandrakasan, B. Nikolic ± Lecture notes (posted in T-square, under “Resources/Lecture Slides”)
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5 What is a Transistor? What is a Transistor? V GS V T R on S D A Switch! |V GS | An MOS Transistor
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6 The MOS Transistor: Structure and Symbols The MOS Transistor: Structure and Symbols Polysilicon Aluminum D S G G S D NMOS Enhancement PMOS Enhancement B B
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7 Uyemura Uyemura , Figure 6.1 , Figure 6.1 nFET nFET current and voltages. current and voltages.
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8 MOSFET Device: MOSFET Device: A circuit designer A circuit designer s perspective s perspective ± It’s a switch: ² What is the controlling voltage? – Answer: Primarily, gate-to-source (Vgs) voltage ² How much control voltage is necessary to turn the switch on? – Answer: Threshold voltage (Vth or Vt or V T ) ² What and how much current flows through the switch when it is on? – Answer: the drain-to-source (Ids) current, it’s value depends on Vgs and Vds (drain-to-source volatge).
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9 Concept of Threshold Voltage Concept of Threshold Voltage ± Initially, n-type source and drain is separated by p- type body which inhibits electron flow. ± A positive voltage at the gate reduces the hole and increases the electron concentration at the surface ± Vth is the minimum voltage required to obtain an electron conc. original hole conc. (~doping density) in the surface. ± This creates a channel (n-type) for electrons to flow from source to drain.
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10 Computation of Threshold Voltage Computation of Threshold Voltage N N N N 2 ox B th ms f ox ox gate silicon bulk potential workfunction oxide depletion charge difference charge Q Q V CC φ + + + () 10 ln ; , .
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This note was uploaded on 12/14/2009 for the course ECE 6130 taught by Professor Staff during the Fall '08 term at Georgia Tech.

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MOSFET - ECE 4130/6130: Advance VLSI Systems Fall 2009...

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