ChapterIII-partI-EE477-SNAZ-Spring09

ChapterIII-partI-EE477-SNAZ-Spring09 - University of...

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MOS VLSI Circuit Design: MOS Transistor Nazarian EE477L – Spring 2009 University of Southern California University of Southern California
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2 USC/EE477L/Spring 2009 MOSFET M etal O xide S emiconductor F ield E ffect T ransistor (MOSFET) is a unipolar: single carrier-type device The dominant dc current is carried by only one type: electrons (in nMOS) and holes (in pMOS) By contrast, a BJT ( B ipolar J unction T ransistor) depend on both electrons and holes (but it is a minority carrier device) Because its output current is carried by injected minority carriers which pass through a thin base junction in the output MOS occupies smaller silicon area than BJT and with fewer fabrication steps
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3 USC/EE477L/Spring 2009 Two-Terminal MOS Structure Under thermal equilibrium (Mass Action Law) If substrate is uniformly doped @ NA (Typically 10 15 to 10 16 ) ) 10 45 . 1 ( 3 10 2 cm n n np i i A i p A p N n n N p 2 0 0
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4 USC/EE477L/Spring 2009 NMOS – Accumulation
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5 USC/EE477L/Spring 2009 NMOS – Depletion
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6 USC/EE477L/Spring 2009 NMOS – Inversion
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7 USC/EE477L/Spring 2009 Band Theory – Background I Valence band : The band made up of the occupied molecular orbitals and is lower in energy than conduction band. It is generally completely full in semi- conductors. When heated, electrons from this band jump out across the band gap and into the conduction band, making the material conductive Conduction band : The band of orbitals that are high in energy and generally empty. In semiconductors, it is the band that accepts electrons from the valence band
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8 USC/EE477L/Spring 2009 Band Theory – Background II Band gap : For insulators and semiconductors, the band gap generally refers to the energy difference btn the top of the valence band and the bottom of the conduction band; it is the amount of energy required to free an outer shell electron from its orbit about the nucleus to the conduction band A material with a small, positive band gap (< 3 eV) is referred to as a semiconductor. A material with a large band gap is called an insulator
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9 USC/EE477L/Spring 2009
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This note was uploaded on 07/21/2010 for the course EE 477L taught by Professor Parker during the Spring '08 term at USC.

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ChapterIII-partI-EE477-SNAZ-Spring09 - University of...

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