chapter2-device01 - CMOS VLSI Design 2.CMOS Transistor...

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Digital IC 2: Device Introduction CMOS VLSI Design 2.CMOS Transistor Theory Fu yuzhuo School of microelectronics,SJTU omar fadhil,Baghdad
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Digital IC 2: Device outline PN junction principle • CMOS transistor introduction • Ideal I-V characteristics under static conditions • Dynamic Characteristics • Non-ideal I-V effects 2/74
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Digital IC 2: Device PN junction diffusion • P-type hole concentration>>N-type hole concentration • N-type electron concentration>>P-type electron concentration Diffusion result • Build up space-charge region(depletion) • Stronger diffusion current, wider space-charge region Drift result • Opposite to the diffusion current • Resulting in a zero net flow Diffusion&Drift activity 3/74
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Digital IC 2: Device Depletion Region hole diffusion electron diffusion p n hole drift electron drift Charge Density Distance x + - Electrical x Field x Potential V x r W 2 -W 1 y 0 (a) Current flow. (b) Charge density. (c) Electric field. (d) Electrostatic potential. n p p n B A SiO 2 Al A B Al A B Cross-section of pn -junction in an IC process One-dimensional representation diode symbol 4/74
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Digital IC 2: Device PN junction energy band mV 600 ) n N N ln( 0.026 = ) n N N ln( q kT = Φ 2 i A D 2 i A D 0 势垒区 Example an abrupt junction has doping densities of N A =10 15 atoms/cm 3 , and N D =10 16 atoms/cm 3 , calculate the built-in potential at 300K, ni is the intrinsic carrier concentration in a pure sample of semi and equals approximately 1.5X10 10 atoms/cm 3 5/74
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Digital IC 2: Device Forward-bias Mode 6 Applied potential lowers the potential barrier Diffusion current dominates the drift component
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Digital IC 2: Device Reverse-bias mode Potential barrier is raised Drift current becomes dominant The number of minority carriers in the neutral regions is very small, so drift current component can almost be ignored 7/74
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Digital IC 2: Device Pn-juntion outline • PN junction analysis PN junction current • PN junction capacitance 8/74
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Digital IC 2: Device Diode static behavior Minority carrier concentration is supported by p-zone majority carrier concentration Minority carrier concentration in the neutral regions near the pn-junction under forward-bias conditions 9
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Digital IC 2: Device How to calculate diffusion current? N-region diffusion computing μ p / μ n are mobility of hole/electron Diffusion coefficiency 2 0 0 i A p D n n N n N p A / V n n N e p ) W ( p T D 0 2 2 n 2 0 n n 2 n 2 n 0 n 2 n n n p D n p , D W - W W p - W ) (W p x+ W - W p - ) (W p = (x) p dx dp D qA = dx dp T I s cm D s D p n / 13 , / 34 2 2 10
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Digital IC 2: Device How to calculate diffusion current? 1) (e T D 0 V 2 W W p D qA I n n p D D p (e T D 0 V 1 W W n D I p p n D D n 1) (e 1) (e ) ( T D T D 0 0 V V 2 1 S n n p p p n D D D D I W W p D W W n D qA I I I n p 11/74
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Digital IC 2: Device Diode static behavior Minority carrier concentration in the neutral regions near the pn-junction under reverse-bias conditions
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chapter2-device01 - CMOS VLSI Design 2.CMOS Transistor...

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