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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 USApbermel@purdue.edu

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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5

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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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