advsemi_lec5 2013-04-13
TRANSCRIPT
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Advanced
Semiconductor
Devices
Lecture 5
Advanced
Semiconductor
Devices
Lecture 5
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2 V. Ariel 2013 Advanced Semiconductor Devices Lecture 5
Lecture outline
Review
Photodiode
Pixel Structure
MOS Transistor overview and fabrication
Basic two-terminal MOS structure
Regions of operation
Solution for charges and potentials
Approximations for regions of operation
All figures based on Tsividis, McAndrew, Operation ans Modeling of the
MOS Transistor Copyright Oxford University Press
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3 V. Ariel 2013 Advanced Semiconductor Devices Lecture 5
Photo-current generation
Practical pn-junction photodiode under reverse bias
x
Ap N;
nx0
cxp
x
W
( )LG xn+hn
hn
0,n px x W One-side junction D An N p N +
= =?
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4 V. Ariel 2013 Advanced Semiconductor Devices Lecture 5
Junction current
The total current is the sum of dark and photon generated currents
J
0J
AV
0 0 0
11
1
W nPH p
n n
DJ J J qF e qn
L L
a
a
- = + = - + +
0PHJ qF
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5 V. Ariel 2013 Advanced Semiconductor Devices Lecture 5
3T APS design
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6 V. Ariel 2013 Advanced Semiconductor Devices Lecture 5
MOS Transistor overview
Lilienfield patent from 1930
Basic MOS Transistor
structure
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MOS Transistor fabrication techniques
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MOS Transistor Crossection
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MOS Transistor SEM imsage
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Basic semiconductor equations
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Contact potentials
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Basic two-terminal MOS structure - capacitor
Gate
Insulator
Semiconductor Body
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Interface charge
Parasistic interface charges
Contact potential
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Flatband voltage
Assume
Need to apply external voltage in order to
straighten energy bands
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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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17 V. Ariel 2013 Advanced Semiconductor Devices Lecture 5
Charge inversion
Inversion charge basis of current transport
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18 V. Ariel 2013 Advanced Semiconductor Devices Lecture 5
Flatband
Accumulation
Depletion and inversion
Regions of operation
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19 V. Ariel 2013 Advanced Semiconductor Devices Lecture 5
Charge density and Poisson equation
Solution for semiconductor
charge
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20 V. Ariel 2013 Advanced Semiconductor Devices Lecture 5
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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Charge and potential balance
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Semiconductor charges andpotentials
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Solution for gate voltage
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Accumulation
Condition for charge accumulation
Approximate solution for charge accumulation
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Deep 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
W k i i
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Weak inversion
Since
Approximation for inversion charge
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Approximation for inversion chargein strong inversion
St i i
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Strong inversion
M d t i i
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Moderate inversion
No simple solution for semiconductor charges and
potentials in moderate inversion !!!