Bermel ECE 305 F16
ECE 305: Fall 2016
BJT Wrap-Up and Course Summary
Professor Peter BermelElectrical and Computer Engineering
Purdue University, West Lafayette, IN [email protected]
Pierret, Semiconductor Device Fundamentals (SDF)
Chapter 11 (pp. 389-426)
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Outline
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1) BJT Wrap-Up
2) Summary of ECE 305
3) Future directions for semiconductor
research
2
Recap: Doping for Gain
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2
,
2
,
i Bn E Edc
B p i E B
nD W N
W D n N
NE
NB
NC
Emitter doping: As high as possible without
band gap narrowing
Base doping: As low as possible, without
current crowding, Early effect
Collector doping: Lower than base doping
without Kirk Effect
Base Width: As thin as possible without
punch through
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4
HBT background
A heterojunction bipolar transistor
Shockley realized that HBT is possible, but Kroemer really provided the foundation of the field and worked out the details.
Kroemer
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collector breakdown
VBE
Common Emitter
(IE variable, IB fixed)
Common emitter breakdown voltage is smaller than common base breakdown voltage. Why?
Common Base
(IE fixed, IB variable)
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applications
1) optical fiber communications
-40Gb/s…….160Gb/s
2) Wideband, high-resolution DA/AD converters
and digital frequency synthesizers
-military radar and communications
3) Monolithic, millimeter-wave IC’s (MMIC’s)
-front ends for receivers and transmitters
future need for transistors with 1 THz power-gain cutoff freq.
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Bipolar Review Questions
Which transistor configuration would you use for high
current gain?
What is difference between single and double HBT
transistor? Was the first transistor single or double HBT?
Name one or two important differences between MOSFET
and Bipolar transistors.
Do you expect any gain for inverted active operation of
bipolar transistor? Why or why not?
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Summary of ECE 305
Semiconductor Devices
Fundamentals
Drift-diffusion model for semiconductors
15
D AD q p n N N
1
JP P P
pr g
t q
P P Pqp qD pJ E
1N N N
nr g
t q
J
N N Nqn qD nJ E
Band-diagram
Diffusion approximation,
Minority carrier transport,
Ambipolar transport
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Short-cut to Band-diagram
16
DN AN
… is equivalent to solving the Poisson equation
Vacuum level
EC
EV
EF
c2
c1
Neutral Neutral
Space
Charge
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Minority Carrier Diffusion
17
( )
( )
( 0 )
( 0 )
n i
p i
F Ei
F E
i
n x n e
p x n e
( )2 2 pn AqV
i i
F Fn e n enp
FpFn
q(Vbi-VA)
-VA
2
(0 ) Aqi
A
Vn eN
n
(0 ) Ap N
AN
0
2
(0 ) (0 ) (0 )
1
G G
A
V V
qVi
A
n n n
ne
N
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Small Signal AC Response
RS
G
CD
CJ
x
Δρ
x
Δρ
VA<
0
VA>
0
np
x
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Concepts for Device Analysis
19
Equilibrium DC Small signal
Large Signal
Diode Band-diagram diffusion dn/dt~jwn Charge-
control
Schottky Band-diagram TE Junction
capacitance
Majority
transport
BJT/HBT Band-diagram diffusion/TE dn/dt~jwn Charge-
control
MOSCAP
MOSFET
2D band-
diagram
Drift/TE MOS
capacitance
Charge-
control
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Major Questions for Semiconductor Researchers
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• Can we achieve computing power equivalent
to or greater than that of the human brain?
• Can we create and deploy sustainable energy
technologies to transition away from fossil
fuel usage?
• Can we integrate electronics with biology to
detect and fix debilitating diseases?
Grand Challenges in Electronics
21
1906-1950s 1947-1980s 1980-until now
Vacuum
TubesBipolar MOSFET
Spintronics
Bio Sensors
Displays ….
Now ??
?
1900 1920 1940 1960 1980 2000 2020
Te
mp
TubesBipolar MOS
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Emergence of Macroelectronics
Areasmall medium large
Perf
orm
ance
low
m
ed
ium
h
igh
mesoporous
NanoNetPoly-Si
Polymers
Flexible ElectronicsEnergy Biosensors
22
Thin Film Organic Transistors
23
www.faculty.iu-bremen.de/dknipp/group/research.htm
M.G. Kanatzidis, Nature, 428, 2004.
pentacene
Samsung flexible phone
Can you draw the band-diagram?
What type of transport theory would you use?
Would you be able to use numerical simulators
from nanohub.org to explore the TFT?
PV Simulations on nanoHUB.orga major resource for
computational nanotechnology
enabled by the HUBzero platform for
simulation, learning, and
collaboration
• 25 Hubs operating or under construction
• open source platform
• 6,144 dedicated cores with over 17,000 on standby
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Multijunction Photovoltaics
25
“ The NREL researchers improved the cell’s efficiency by enhancing the photon recycling in the lower, gallium-arsenide junction by using a gold back contact to reflect photons back into the cell, and by allowing a significant fraction of the luminescence from the upper, GaInP junction to couple into the GaAs junction. Both the open-circuit voltage and the short-circuit current were increased.”
—NREL News Release, June 24, 2013
• The new record obtain in June 2013, at 31.1%, is a significant jump from previous record cell by NREL at 29.5%.
• Enhanced photon recycling is believed to cause this improvement.
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Technology: Sequencing by Synthesis
Sanger method (1990s) Babbage computer (~1830s)
Intel Chip TodayIon-torrent system (2011)
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Technology: Sequencing by Synthesis
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Superhydrophobic coatings
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http://wyss.harvard.edu/viewpage/316
SLIPS Coatings ‘Waterproof’ circuit boards
http://www.cytonix.com/conformal-coating-s/1872.htm
Superhydrophobic coatings
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https://www.youtube.com/watch?v=16RcYoXOvRM
Anti-soiling coatings for photovoltaic modules
Artificial Skin
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M.L. Hammock et al., "25th Anniversary
Article: The Evolution of Electronic Skin
(E‐Skin): A Brief History, Design
Considerations, and Recent Progress.“
Advanced Materials 25, 5997-6038
(2013).
Artificial Skin
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Multiplex, flexible strain-gauge sensor based on the reversible interlocking of Pt-coated
polymer nanofibres. Image: Nature Materials (2012) http://dx.doi.org/10.1038/nmat3380
Developing New Ideas
32
“New ideas pass through three periods:
1) It can't be done.
2) It probably can be done, but it's not worth
doing.
3) I knew it was a good idea all along!”
“I don't pretend we have all the answers.
But the questions are certainly worth
thinking about.”
-- Sir Arthur C. Clarke
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