454Lec04_MOSFET1

454Lec04_MOSFET1 - ECEN 454 Digital Integrated Circuit...

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ECEN 454 Lecture 4 1 ECEN 454 Digital Integrated Circuit Design Lecture 4 MOS Transistor I
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ECEN 454 Lecture 4 2 Silicon Lattice Transistors are built on a silicon substrate Silicon is a Group IV material Forms crystal lattice with bonds to four neighbors Si Si Si Si Si Si Si Si Si
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ECEN 454 Lecture 4 3 Dopants Silicon is a semiconductor Pure silicon has no free carriers and conducts poorly Adding dopants increases the conductivity Group V: extra electron (n-type) Group III: missing electron, called hole (p-type) As Si Si Si Si Si Si Si Si BS i Si Si Si Si Si Si Si - + + -
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ECEN 454 Lecture 4 4 Extrinsic Silicon P-type: Majority carriers – holes Minority carries – electrons N-type: Majority carriers – electrons Minority carries – holes
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ECEN 454 Lecture 4 5 Mass Action Law (1) The product of carrier concentrations in equilibrium is always constant: Intrinsic silicon: Extrinsic silicon: ± Charge neutrality (assume donors and acceptors are all ionized) 2 i n p n = Intrinsic carrier concentration @T = 300K 3 10 10 45 . 1 × cm i n p n = = D A N p N n + = + Acceptor concentration Donor concentration N tot P tot
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ECEN 454 Lecture 4 6 Mass Action Law (2) P-type doped silicon N-type doped silicon A i N n n / 2 0 , , = >> D A i A N N p n N D i N n p / 2 0 , , = >> A D i D N N n n N
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ECEN 454 Lecture 4 7 Energy Band Diagram (1) Energy bands – solid-state physics: ± Quantum states cluster in bands leaving band-gaps in between ± Band-gaps are regions w/o allowed states
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ECEN 454 Lecture 4 8 Energy Band Diagram (2) Carries ± Conduction band electrons and valence band holes can move freely -- carries
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454Lec04_MOSFET1 - ECEN 454 Digital Integrated Circuit...

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