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Advanced

Semiconductor

Devices

Lecture 6

Advanced

Semiconductor

Devices

Lecture 6

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Lecture outline

Review

Basic two-terminal MOS structure

Regions of operation

Solution for charges and potentials

Approximations for regions of operation

Surface potential model in moderate inversion

MOS Capacitor

MOS Capacitor in moderate inversion

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Voltage and charge balance

Total charge in semiconductor body

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Electron charge density

Surface electron charge density

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Charge inversion

Inversion charge basis of current transport

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Flatband

Accumulation

Depletion and inversion

Regions of operation

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Charge density and Poisson equation

Solution for semiconductor

charge

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Charge density and Poisson equation

Charge density as a

function of distance

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Solution of Poisson equation

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Solution of Poisson equation

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Solution for surface electric field

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Solution for semiconductor charge

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Semiconductor charges andpotentials

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Solution for gate voltage

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Depletion

Condition for depletion

Approximation for gate voltage in depletion

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Inversion

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Gate voltage and surface potential ininversion

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Weak inversion

On the border of moderate inversion

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Weak inversion

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Strong inversion

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Moderate inversion

Need a simple solution for semiconductor charges and

potentials in moderate inversion !!!

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Moderate inversion

Need a simple solution for semiconductor charges and

potentials in moderate inversion !!!

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Moderate inversion

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MOS Capacitor

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MOS C it i l ti

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MOS Capacitor in accumulation

Semiconductor charge capacitance exponentially increasing

for large negative surface potential

Therefore, in accumulation

MOS Capacitor in depletion and

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MOS Capacitor in depletion andweak inversion

MOS Capacitor in depletion and

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MOS Capacitor in depletion andweak inversion

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MOS C it i d t d

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Obtained MOS capacitor model in all regions of operation

Can obtain model parameters from experimental

measurements of gate capacitance

MOS Capacitor in moderate andstrong inversion