qt - computer applications - leclair_public_talk

8/22/2019 QT - Computer Applications - Leclair_public_talk

http://slidepdf.com/reader/full/qt-computer-applications-leclairpublictalk 1/36

Electron tunnelingfrom quantum weirdness to your hard disk

Patrick LeClair



tunneling?



THE UNIVERSITY OF ALABAMACENTER FOR MATERIALS FOR INFORMATION TECHNOLOGY

An NSF Science and Engineering Center

a particle can pass through a “forbidden” region

analogy:

I could run right through the whiteboardclassically :

impossible!I am just “reflected”

quantum physics: there is a chance any weird thing can happen.it may not be a good chance!

example:

an electric current flowing across an insulator

quantum tunneling?

X

classical

quantum





light waves: colored glass

a very thick piece is not transparent a very thin piece is

light decays, but some makes it throughCDs are coated with metal

electron waves: behave similarly to light electrons can go through an insulator, if it is thin enough!this is “quantum tunneling”

based on probability ...

only possible for tiny, light particles on the nanoscale

an everyday analogy of sorts





electron tunneling?

a current flows between two metalsseparated by an insulator

electrons can appear across the barrier!

insulator must be very thin

10,000 times thinner than a hair

normal electronics - negligibleonly in specially designed structures





total internalreflection

scattered light

acrylic plane L E D

air

optical analogies

total internal reflection

used in the iPhonetouch screen ...


http://slidepdf.com/reader/full/qt-computer-applications-leclairpublictalk 7/36THE UNIVERSITY OF ALABAMA

CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center

IBM 350 RAMAC, the first hard disk

it stored about 4.4Mb

wikipedia.org - “RAMAC”

Toshiba’s 0.85-inch hard disk drive

the smallest HDD in the world.

capacity: 4 GB

What uses quantum tunneling? Your hard disk!





the need for hard disks (tech)volatility of semiconductor memories!

lose their memory when the power goes outneed some sort of nonvolatile storage necessarywhy not just battery backup of RAM?

cost per GB

RAM + batteries is too expensive!still has an easy failure mechanism ...

size & throughputhigher latency

bandwidth is hugeenormous capacity

endurance“unlimited” cycling

punched cards are nonvolatile





the need for mass storage (human)

soundseveral MB per minute / lossy (MP3)tens of MB per minute / “lossless”

pictures

several MB per image

video~ 1 MB per secseveral GB per movie

with lossy compression!

data miningenormous databases

apple.com





how do hard disks work, more or less?

spinning part holds data. (~104 rpm)sliding part reads and writes data. (~150 ft/sec)

wikipedia.org - “Hard_Disk”





160 Gbit 2.5” perpendicular drive for laptops

hard disk drives

images from M. Coey






Magnetic medium

hard disk drives

images from M. Coey






Read-write head

Magnetic medium

hard disk drives

images from M. Coey






Voice-coil actuator

Read-write head

Magnetic medium

hard disk drives

images from M. Coey






Spindle motor

Voice-coil actuator

Read-write head

Magnetic medium

hard disk drives

images from M. Coey





8 Gbit 1” drive forcameras 160 Gbit 2.5” perpendicular drive for laptops

Spindle motor

Voice-coil actuator

Read-write head

Magnetic medium

hard disk drives

images from M. Coey





media basics

Hard disctiny magnetized regionsdirection (N or S) stores bitmagnetic sensor reads bits

LP recordstiny bumps store bitsneedle moves up and down

CDspits store bitsoptical reflectivity





reading and writing basics Jimmy Zhu, Materials Today , July/Aug 2003

tiny electromagnet changes bits from N⇄ S

magnet sensor reads direction of bits





positioning basics

www.pcguide.com/ref/hdd/op/actActuator-c.html

• current powers a voice coil†

• field generated moves head L or R• more precise than stepper motors

† this is the same way a speaker cone moves

http://www.pcguide.com/ref/hdd/op/actActuator-c.html







positioning basics

www.pcguide.com/ref/hdd/op/actActuator-c.html

• current powers a voice coil†

• field generated moves head L or R• more precise than stepper motorsIBM 62PC "Piccolo" HDD, ~1979 - an early 8" disk

wikipedia.org - “Hard_Disk”

† this is the same way a speaker cone moves








The incredible shrinking bit!Predicted relative sizes of storage bits

2004

2002

2006

20082010

2012: 4.4 nm x 4.4 nm

50 nm

400 nm

(assumes areal densities continue to double yearly)

(one hair: ~50,000 nm ... 100 times smaller)

1 terabit per in2 = 1 trillion bits per in2 ... maybe within a few years!





• > 3.4 million high-resolution photos, or …

• 2,800 audio CDs, or…

• 1,600 hours of television, or …

10 TB per in2 on a quarter ?

(or, one bit for every $ of the national debt)





• > 3.4 million high-resolution photos, or …

• 2,800 audio CDs, or…

• 1,600 hours of television, or …

Library of Congress,Jefferson building

• the entire printedLibrary of Congress

10 TB per in2 on a quarter ?

(or, one bit for every $ of the national debt)

http://en.wikipedia.org/wiki/Image:LOC_-_Jefferson_building.jpg

http://en.wikipedia.org/wiki/Image:LOC_-_Jefferson_building.jpg





• we write with a tiny electromagnetthey actually work better when smaller

• tiny fringing fields to measure …• needs to be very fast …

• needs to be tiny …

this is where quantum tunneling comes in!

How to measure these small magnetic bits?





First, what is special about magnets?

N S

where does magnetism come from?

atoms = electrons + nucleus

electrons behave like little magnets, either N or S

non-magnetic materials have equal numbers of N & Spermanent magnets have more of one than the other!





tunneling between magnets

electrons are like little magnets: can be N or S

permanent magnets: more N than S!

electric currents coming from magnets: made up of more N than S

electrons do not like to tunnel into magnets pointing the wrong way!

N→ N or S→ S preferred!

Current between magnets depends on how they are aligned!

Same direction (both N) -- no problemOpposite direction (one N, one S) -- electrons do not want to go!





T M R

large flow of electrons

⇒ low resistance

small flow of electrons

⇒ large resistance

> 200%

topelectrode

bottomelectrode

filled

states

empty

states

“tunneling magnetoresistance”

amount of current tunneling between two magnets

depends on how they are aligned

quantum tunneling can sense the orientation of magnets!





putting it together

magnetic tunnel device reads

flies over bitsone magnet = FIXEDone magnet = FREE

fringing field changes free magnet

rotates direction slightly

changes current = reading!

quantum tunneling retrieves the data from your hard disk





“0”

“1”

Magnetic RAM

Hard disk sensor

tunneling devices are small & sensitive enough!





how does FLASH memory relate?

f





the basics of Flash

source drain

semiconductorchannel

storage layer

control gateinsulator

• electrons go between source and drain

• ‘control gate’ regulates how many

negative voltage stops electrons, positive helps

positive V - channel pinched

negative V - channel open

insulator





~12V~7V

storage layer

control gate

e- e- e- e-

e-

source drain

writing

• apply voltage to drain -- pull electrons through channel

• put a positive voltage on control gate

also pulls some electrons into storage layer, via tunneling!

• charge on storage layer = “0” .... we just wrote information

• electrons do not leak off until a voltage helps them tunnel out!





~ -9VOPEN

storage layer

control gate

e-

e-

~6V

source draine- e-

erasing

• negative voltage on controlpushes electrons away

blocks the channel• positive voltage on source

sucks out the electrons, only to the source

• no charge left on storage layer ... just erased our “0” and made “1”

reset all bits to “1”

X





~5V~1V

storage layer

control gate

e- e- e- e-

e-source drain

reading

• medium voltage on control, barely open

• if there is charge on the storage layer ...those electrons repel electrons going from S to Dchannel is pinched off = “0”

• no charge on storage layer,channel is open!

• presence of charge makes current high or low = readout

X





what’s so great about flash?

no mechanical limitations

lower latency

= attractive for speed, noise, power consumption, reliability.

++

--

cost/GB still significantly higher (but decreasing rapidly!)

finite number of erase/write (typically 106 cycles guaranteed)

it wears out eventually there are clever ways to prolong lifetime




summaryweird quantum physics is in use all around you

it takes some getting used to

but it gives us some neat toys!

contact:

[email protected]

bama.ua.edu/~physics

mailto:[email protected]

mailto:[email protected]

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