Quantum Electronic Devices Group Playing pool with electrons Adam Micolich Quantum Electronic Devices Group School of Physics, The University of New South

Quantum ElectronicDevices Group

Playing pool with electronsPlaying pool with electronsAdam Micolich

Quantum Electronic Devices Group

School of Physics,The University of New South Wales

With support from:

www.tallpoppies.net.au


What is an electron?What is an electron?

• Electrons are the tiny negatively charged particles that orbit the nucleus in atoms.

• The electricity that comes out of your wall socket at home is basically a flow of these electrons, just like the water that comes out of your tap at home is a flow of water molecules.


Kill your computer (or playstation)!Kill your computer (or playstation)!

• If you smash your computer, somewhere inside you will find ~50 million or so transistors on a silicon chip

~50 million


The transistor is just a tap for electronsThe transistor is just a tap for electrons

• The voltage applied to the gate allows control of the current flowing in the channel.

GateGate

Insulator (oxide)

p-typesilicon substrate

n-Si

Interesting fact: the 1’s and 0’s that represent data in your computer are

just the on and off states of the transistors in the computer chips.

Gate

Insulator (oxide)


n-Si


• The number of transistors on a computer chip doubles roughly every 18 months, until…

Progress in electronicsProgress in electronics

1970 1975 1980 1985 1990 1995 2000 2005 2010103

104

105

106

107

108

109Transistors per chip

Year

80786PentiumPro

Pentium80486

8038680286

8086

80804004

?


• Everyone knows computers were really made for video games!

• This development even holds for video games, both for CPU and memory.

The same development happens for video gamesThe same development happens for video games


Fancy a snack?Fancy a snack?

Video: www.youtube.com


Computers are getting too hotComputers are getting too hot

• The heat problem has brought the usual speed increases to a grinding halt Core 2 Duo, etc.

• The current generation of computers really do produce enough heat to fry an egg!


Where does the heat come from?Where does the heat come from?

• The voltage applied to the gate allows control of the current flowing in the channel.

GateGate

Insulator (oxide)


n-Si

Interesting fact: the 1’s and 0’s that represent data in your computer are

just the on and off states of the transistors in the computer chips.

Gate

Insulator (oxide)


n-Si


Two Solutions…Two Solutions…

Better cooling, but it will only take you so far, and it doesn’t

help for laptops, etc.

We find a new way to do computing that doesn’t involve so much heat ‘spintronics’.

Spin-up (1) Spin-down (0)


How can we do this?How can we do this?

+

One way to make spintronics is to use magnetic materials, but this doesn’t work well when you want to put lots of tiny devices close together (imagine putting two fridge magnets together).

Another trick is to use a special property of some materials that makes the different spins bounce off walls in different ways – in a sense, we make a transistor that is basically a tiny pool table!


• We’re now reaching the point where transistors are becoming so small that the quantum mechanical properties of the electron become very important. Some strange things can happen when this occurs, but you might also be able to do some really useful things too!

What my research is aboutWhat my research is about

101 100 10-1102

104

106

108

Number of chip components

Feature size (microns)

1010

1012

1018

1014

1016

10-2 10-3

Classical Age

Historical Trend

SIA Roadmap

CMOS

19952000

2005

1970

1980

1990

4oK

Quantum Age

77oK

295oK

Quantum State Switch2010

?


How to make a real pool tableHow to make a real pool table

• There are some things we’ll need to make an electron pool table:

1. You need a flat table for the balls to roll on.

3. You need walls at the side for the balls to bounce off.

2. You need balls on the table.

4. You need pockets too.


How to make an electron pool tableHow to make an electron pool table

• Our electron pool table is really just a tiny transistor with some shape to it.

1. You need a flat table for the electrons to roll on (or in, as it turns out).

3. You need walls at the side for the electrons to bounce off.

2. You need balls (i.e., electrons) on the table.

4. You need pockets too (which as you’ll see serve many other important functions in our electron billiards).

1m

GaAs

Ti/Au


Some problems we need to deal withSome problems we need to deal with

If we want to

be able to do this…

We need to be able to stop this and get

this instead…

1. Impurities in the material. 2. Vibrating atoms in the material

• The electrons bounce off various things we don’t want them to. These include:


Incredibly tiny tablesIncredibly tiny tables

• Our devices are much smaller than the width of a human hair. Actually, the contain nanometer (billionth of a meter) scale features and are part of ‘nanotechnology’.

~10000 mag

1m


NanotechnologyNanotechnology


NanotechnologyNanotechnology

1m

GaAs

Ti/Au


Coldest place in the universeColdest place in the universe

• Finally, the get rid of the vibrations, we need to make our samples really cold, less than a hundredth of a degree above absolute zero!

Hot! (50°C)

Really cold (273°C or ~0.01K)Cold (270°C or ~3K)


Electrons are waves not particlesElectrons are waves not particles

• Electrons are strange creatures – their wavelike properties mean that they can go around obstacles in a way that larger objects can’t…

Period 1/A

• And they can then interfere with themselves just like in Young’s double slit experiment.

• If we apply a magnetic field, we can change this interference from constructive to destructive and back again, and this allows us to ‘watch’ the electrons in the pool table!


Electron pool tables…Electron pool tables…

100

120

140

160

180

200

-0.4 -0.2 0 0.2 0.4

UpsweepDownsweepUpsweep >10 hrs later

Co

nd

uct

an

ce G

(S)

Magnetic field B (T)

125

130

-0.04 0 0.04

The little bumps are due to different possible paths

coming out of the exit hole. We’re

watching thousands of electrons per second going

through our billiard here!

1m


But in all seriousness…But in all seriousness…

• Our research is basically about finding out what happens at the outer limits of electronics, simply to see what happens.

With 50 years and a LOT of

work.Bardeen, Brattain and Shockley

discovered the first transistor in 1949.


The Moral of the StoryThe Moral of the Story

“But why, some say, the moon? Why choose this as our goal? And they may well ask why climb the highest mountain? Why, 35 years ago, fly the Atlantic? Why does Rice play Texas?

We choose to go to the moon. We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard, because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win, and the others, too.”

John F. Kennedy


A change of topic…A change of topic…


So how did I end up in physics?So how did I end up in physics?

Video: www.youtube.com


So how did I end up in physics?So how did I end up in physics?

• My parents were too worried I’d blow up the house or myself, so I wasn’t allowed to have a chemistry set.

• Little did they know that you can do far more damage if you know some physics!


Some of the perks of scienceSome of the perks of science

• You can get to play with expensive toys• The hours are flexible and the

environment is good (even if you do have to work hard)

• The travel is definitely a good part• You can have a job you really enjoy

with a lot of variety and challenges


So how did I do it?So how did I do it?

• Went to university and did a Bachelor of Science degree majoring in Physics. I wanted to do experiments mostly, so I took as many lab subjects as I could.

• I stayed on to do an honours year as part of my B.Sc. and took two projects on semiconductor physics, to start specialising.

• First up, I did my HSC. Lots of science subjects, in my case phys, chem and maths. Oh, and english, no point doing science if you can’t communicate!


So how did I do it?So how did I do it?

• Next up, I started my Ph.D., which took 3 years. During my Ph.D. I spent four months working, on exchange, at the University of Cambridge in the U.K.

• International experience is important these days, so after that I took off to work in the U.S. for a couple of years, doing physics research at the University of Oregon.

• Came back a few years ago, now I spend roughly 50% of my time teaching physics and the other 50% of my time on research, mostly supervising research students.


WHO should be doing physics research for a living?WHO should be doing physics research for a living?

Myth: You need to be “an Einstein” to be successful in

Physics

What you do need is the same for just about any job!

• Excellent communication skills(written and verbal)

• A good working knowledge of Physics

• Ability to work well in a team

•Ability to be resourceful (think on your feet)

• Lots of self-drive and tenacity

• Good management skills (esp. time management)

• A strong interest in answering the unanswered

Almost anyone can do it


Playing pool with electronsPlaying pool with electronsAdam Micolich

Quantum Electronic Devices Group

School of Physics,The University of New South Wales

With support from:

www.tallpoppies.net.au

Documents

Quantum Electronic Devices Group Playing pool with electrons Adam Micolich Quantum Electronic Devices Group School of Physics, The University of New South