Lec_22 - EE143 F2010 Lecture 22 Electrical Characteristics...

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Professor N Cheung, U.C. Berkeley Lecture 22 EE143 F2010 1 Electrical Characteristics of MOS Devices The MOS Capacitor – Voltage components – Accumulation, Depletion, Inversion Modes – Effect of channel bias and substrate bias – Effect of gate oxide charges – Threshold-voltage adjustment by implantation – Capacitance vs. voltage characteristics MOS Field-Effect Transistor – I-V characteristics – Parameter extraction “metal” oxide semiconductor V G + x ox
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Professor N Cheung, U.C. Berkeley Lecture 22 EE143 F2010 2 2) Visit the Device Visualization Website http://jas.eng.buffalo.edu/ and run the visualization experiments of 1) Charge carriers and Fermi level, 2) pn junctions 3) MOS capacitors 4) MOSFETs 1) Reading Assignment Streetman: Section of Streetman Chap 8 on MOS
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Professor N Cheung, U.C. Berkeley Lecture 22 EE143 F2010 3 Work Function of Materials E o E V E C q SEMICONDUCTOR E f E o E f METAL Work function = q Vacuum energy level q M is determined by the metal material q S is determined by the semiconductor material, the dopant type , and doping concentration
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Professor N Cheung, U.C. Berkeley Lecture 22 EE143 F2010 4 Work Function (q M ) of MOS Gate Materials E o = vacuum energy level E f = Fermi level E C = bottom of conduction band E V = top of conduction band E f Examples: Al = 4.1 eV TiSi 2 = 4.6 eV E f E o q M E o q M E i E C E V 0.56eV q = 4.15eV 0.56eV q = 4.15eV (electron affinity) E o E i E C E V 0.56eV q = 4.15eV 0.56eV E f n+ poly-Si (E f = E C ) p+ poly-Si (E f = E V ) q M
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Professor N Cheung, U.C. Berkeley Lecture 22 EE143 F2010 5 Work Function of doped Si substrate q = 4.15eV E f E o q s Ei E C E V |q F | 0.56eV 0.56eV * Depends on substrate concentration N B E f E o q s Ei E C E V |q F | 0.56eV 0.56eV q = 4.15eV n-type Si p-type Si s (volts) = 4.15 +0.56 - | F | s (volts) = 4.15 +0.56 + | F | i B F n N q kT ln
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Professor N Cheung, U.C. Berkeley Lecture 22 EE143 F2010 6 The MOS Capacitor Si ox FB G V V V V x C [in Farads /cm 2 ] + _ V FB V ox (depends on V G ) V si (depends on V G ) + _ + _ “metal” oxide semiconductor V G + x ox Oxide capacitance/unit area
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Professor N Cheung, U.C. Berkeley Lecture 22 EE143 F2010 7 Flat Band Voltage V FB is the “built-in” voltage of the MOS: • Gate work function M : Al: 4.1 V; n+ poly-Si: 4.15 V; p+ poly-Si: 5.27 V • Semiconductor work function S : V ox = voltage drop across oxide ( depends on V G ) V Si = voltage drop in the silicon ( depends on V G ) S M FB V s (volts) = 4.15 +0.56 - | F | for n-Si s (volts) = 4.15 +0.56 + | F | for p-Si
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This note was uploaded on 03/03/2012 for the course EECS 142 taught by Professor Ee142 during the Spring '04 term at Berkeley.

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Lec_22 - EE143 F2010 Lecture 22 Electrical Characteristics...

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