02 Transistor IV - with Notes

02 Transistor IV - with Notes - EE115C Winter 2010 Digital...

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EE115C – Winter 2010 igital Electronic Circuits Digital Electronic Circuits Lecture 2: MOS Behavior
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Metal Oxide Semiconductor Field Effect Transistor Artist’s Rendition… Cross Sectional View rain Source Drain Body Gate Poly Si SiO SiO n+ n+ p+ p substrate 2 2 EE115C 2
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nMOS Cross-Section and Symbols Source Drain NMOS n+ n+ p+ Body Gate G D p substrate S Analog Representation D S G EE115C 3 Digital Representation
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pMOS Cross-Section and Symbols ource rain PMOS p+ p+ n+ Source Drain Body Gate n substrate S G G S D D EE115C 4 Analog Representation Digital Representation
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Which is Source, which is Drain ? 1.0 V 1.0 V 0.0 V 1.0 V 1.0 V 0.0 V ource ource rain rain Current flow Source Source Drain Drain EE115C 5 Carrier (electron) flow
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Long Channel Vs Short Channel Source Drain Body Gate NMOS nn p+ L ± Long channel transistors p substrate older technologies, long L’s ± hort channel transistors So t ca et as s t o s new, “deep submicron” technologies, short L’s operation more complicated EE115C 6 many 2 nd order effects become pronounced
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nMOSFET Basic Operation Volts Threshold Voltage, V T Source Drain Body Gate V s V g V d arrier (electron) flow Current flow n+ p+ substrate n+ Carrier (electron) flow ± Long Channel Devices p substrate Channel a.k.a. Inversion Layer ± Consider V s =V d and V g is increased ± Electron are stripped away from atoms in the source and drain region as well as deep in the substrate and attracted to the channel. Simultaneously, holes e pushed away from the surface and into the substrate EE115C 7 are pushed away from the surface and into the substrate A conducting channel of electrons is formed
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Linear (Triode) Operation n + n + D S G I D p -substrate x L B ± Channel is formed ± The application of a potential between the source and the drain causes current to flow ± The shape of the channel region changes it becomes more tapered N ( ) 2 DS DS n ox GS T DS WV IC V V V μ =− EE115C 8 ' 2 n k L ⎢⎥ ⎣⎦
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This note was uploaded on 04/18/2010 for the course EE 115C taught by Professor N/a during the Spring '10 term at UCLA.

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02 Transistor IV - with Notes - EE115C Winter 2010 Digital...

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