lectures_2013_2014_a analog
TRANSCRIPT
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Course:
Analog Circuit Design
Time schedule:Mo 11.00-13.00We 14.00-16.00
Th 14.00-16.00
Office hours:Th 16.00-18.00
Exams:Feb. (2), Jun.-Jul. (2), Sep. (2)Oral examination
Additional course material:ftp://ftp.dii.unisi.it/pub/users/vignoli/Analog_Circuit_Design
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References:
F. MalobertiAnalog Design for CMOS VLSI SystemsKluwer 2001
J. Millman, C. HalkiasIntegrated Electronics: Analog and Digital Circuit and SystemsMcGraw-Hill 1972
R. Spencer, M. Ghausi
Introduction to Electronic Circuit DesignPrentice Hall 2003
P. Gray, R MeyerAnalysis and Design of Analog Integrated Circuits (3rd ed.)Wiley 1993
M.S. TyagiIntroduction to Semiconductor Material and Devices
Wiley 1991
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MATERIALS: electric behavior
semiconductor Insulator conductor
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In semiconductors EF is in the Band-Gap
SEMICONDUCTORS: electric behavior
kTEE F
eEf
+
=
1
1)(
Fermi-Dirac distribution: occupation probability for the energy level E
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NC is the number of available states (per cm-3) in the conduction band
kT
EE
CkT
EE
deii
FcFc
eNekThmdEEfENpn
=
==
2/3
2'
241)()(
where Ne(E) is Energetic State Density function in the material.
Intrinsic Semiconductors: free carriers
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DOPING
The Fermi energy
moves with doping
EF n-type
EF p-type
T effect
ACCEPTORDONOR
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Also PVD
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Single crystal silicon SCS Anisotropic crystal Semiconductor, great heat conductor
Silicon dioxide is created by interaction between silicon and oxygenor water vapor Si + O
2= SiO
2or Si + 2H
2O = SiO
2+ 2H
2 Excellent thermal and electrical insulator protects surface from contaminants forms insulating layer between conductors
forms barrier to dopants during diffusion or ion implantation grows above and into silicon surface
Thermal oxide, LTO, PSG: different names for different depositionconditions and methods
Polycrystalline silicon polysilicon Mostly isotropic material Semiconductor also a conductor, but with much more resistance than metal or diffused layers created when silicon is epitaxially grown on SiO2 commonly used (heavily doped) for gate connections in most MOS processes
Silicon nitride Si3N4 Excellent electrical insulator
Aluminum Al Metal excellent thermal and electrical conductor
Materials
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PHOTOLITOGRAPHY
Photoresist
spin.-coating
Thick film: 1 mm
EXPOSITION:The mask is transferred to
the photoresist
Uv - X-ray
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The photoresist chemically reacts and dissolves in thedeveloping solution, only on the parts that were notmasked during exposure (positive method).
Development is performed with an alkalinedeveloping solution.
After the development, photoresist is left on the
wafer surface in the shape of the mask pattern.Masked photoresist
solvents remove exposed (unexposed) resistEtching removes material from wafer surface where resist has beenremoved
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Wet etching
Dry etching
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EFFECT OF FLATBAND VOLTAGE VFB (VFB < 0)
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VGB = 0
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GATEPolisilicon
OXIDESiO2
SUBSTRATEP-type Si
SUBSTRATE CONTACTPolisilicon
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Space charge regions
x-tOX 0 xD
x-tOX 0 xD
PotentialVGB-VFB
-VFB
VGB
VOX
s(0)
+
VOX
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STRONG INVERSION CONDITION
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SMALL SIGNAL EQUIVALENT CIRCUIT OF A MOS TRANSISTOR