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)

12/7/2016

Outline

12/7/2016 Bermel ECE 305 F16

1) BJT Wrap-Up

2) Summary of ECE 305

3) Future directions for semiconductor

research

2

Recap: Doping for Gain

Bermel ECE 305 F16

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

12/7/2016 3

Bermel ECE 305 F16

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

12/7/2016

Bermel ECE 305 F16

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)

12/7/2016

5

Bermel ECE 305 F16

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.

12/7/2016 6

Bermel ECE 305 F16

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?

12/7/2016 7

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

12/7/2016 Bermel ECE 305 F16

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

12/7/2016 Bermel ECE 305 F16

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

12/7/2016 Bermel ECE 305 F16

Small Signal AC Response

RS

G

CD

CJ

x

Δρ

x

Δρ

VA<

0

VA>

0

np

x

12/7/2016 Bermel ECE 305 F1617

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

12/7/2016 Bermel ECE 305 F16

Major Questions for Semiconductor Researchers

12/7/2016 Bermel ECE 305 F16 20

• 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

12/7/2016 Bermel ECE 305 F16

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

12/7/2016 Bermel ECE 305 F16 24

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.

12/7/2016 Bermel ECE 305 F16

Technology: Sequencing by Synthesis

Sanger method (1990s) Babbage computer (~1830s)

Intel Chip TodayIon-torrent system (2011)

12/7/2016 26

Technology: Sequencing by Synthesis

Bermel ECE 305 F16 27

Superhydrophobic coatings

12/7/2016 Bermel ECE 305 F16 28

http://wyss.harvard.edu/viewpage/316

SLIPS Coatings ‘Waterproof’ circuit boards

http://www.cytonix.com/conformal-coating-s/1872.htm

Superhydrophobic coatings

12/7/2016 Bermel ECE 305 F16 29

https://www.youtube.com/watch?v=16RcYoXOvRM

Anti-soiling coatings for photovoltaic modules

Artificial Skin

12/7/2016 30

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

12/7/2016 Bermel ECE 305 F16 31

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

12/7/2016 Bermel ECE 305 F16