transistors at work

Transistors at Work

What a transistor is

How it works

How it’s put togetherSpecial Thanks to Elena Sipe, Patrick Kimball, and Steve Behbahany

Image courtesy http://www.yuanlei.com/hardware/specs1/i850e_chips.jpg

What is a Transistor?

The main components of microprocessors.

Microprocessors are vital to many of the

products we use in every day life:

Televisions

Cars

MOSFET Transistor, courtesy of

http://info.tuwien.ac.at/theochem/si-srtio3_interface/mosfet.jpg

http://vista.pca.org/yos/Porsche-911-Turbo.jpg

Radios

home appliances

computers

http://www.sonyericsson.com/cws/products/

mobilephones/overview/x1?cc=us&lc=en

How does it work?

Transistors are miniature electronic switches.

Transistors have two operating positions

On

Off

Binary functionality of transistors enables the processing of information in a computer or other system.

http://intel.com/education/transworks/flat1.htm

Image courtesy of http://www.anz.com/aus/promo/Switching/images/LightSwitch.jpg

Conductors, Insulators, and Semi-

conductors

Conductors - allow electrical current to flow

Insulators - do not allow electrical current to flow

Pure silicon, the base material of most transistors, is a Semiconductor - its conductivity can be modulated by the introduction of impurities.


http://www.intel.com/education/transworks/flat5.htm

The On/Off States of a Transistor

Step A

Transistors consist of

three terminals:

Source

Gate

Drain. http://intel.com/education/transworks/flat7.htm


Step B

n-type transistor - source and drain are negatively charged and sit on a positively charged well of p-silicon. http://intel.com/education/transworks/flat7.htm

A very small quantity of boron or gallium, which have one less valence electron than silicon, is implanted into the silicon base (creating p-type silicon).


Periodic table: http://www.dayah.com/periodic/Images/periodic%20table.png

A trace amount of phosphorous or arsenic, which contain one more valence electron than silicon, is implanted in the source and drain areas (creating n-type silicon).

Step C

When positive voltage

is applied to the gate,

positively charged

holes are repelled

from the gate which

forms an electron

channel between the

source and the drain,

allowing a clear path

for electricity to flow.



Step D

Electrons are able to

flow through the

transistor. This

completes the circuit;

the transistor is now

“on”.http://intel.com/education/transworks/flat7.htm


Step E

If the voltage at the

gate is removed,

holes are not repelled

from the area

between the source

and drain. The

pathway is broken

and the transistor is

turned off. http://intel.com/education/transworks/flat7.htm


How a Transistor Handles Information

The transistor's "on" state

is represented by a 1,

and the "off" state is

represented by a 0.

Specific sequences and

patterns of 1's and 0's

generated by multiple

transistors can represent

letters, numbers, colors,

and graphics. This is

known as binary notation.



On a wafer, billions of transistors are housed on a single square chip. One malfunctioning transistor could cause a chip to short-circuit, ruining the chip. Thus, the process of creating each microscopic transistor must be very precise.

Wafer image: http://upload.wikimedia.org/wikipedia/fr/thumb/2/2b/PICT0214.JPG/300px-PICT0214.JPG

Making Microprocessors

What size do you think an

individual transistor being

made today is?

Size of Transistors

Scaling of successive generations of MOSFETs into the nanoscale regime (from Intel).

One chip is made of millions or billions of transistors

packed into a length and width of less than half an

inch. Channel lengths in MOSFET transistors are

less than a tenth of a micrometer. Human hair is

approximately 100 micrometers in diameter.

Transistor: MOS

We will illustrate the process sequence of

creating a transistor with a Metal Oxide

Semiconductor(MOS) transistor.

p-Si

Insulatorconductor

n-Si

Source DrainGate

n-Si

½” to ¾“

Image courtesy: Pro. Milo Koretsky

Chemical Engineering Department at OSU

IC Manufacturing ProcessIC Processing consists of selectively

adding material (Conductor, insulator,

semiconductor) to, removing it from or

modifying it

Wafers

Deposition /

OxidationEtching / CMP

Loop

Photo/

Pattern

Transfer Cle

an

Cle

an Ion Implant /

Anneal

Graphics copy-write Pro. Milo Koretsky


(Note that these steps are not all the steps to create

a transistor. Some steps are skipped. This is purely to

show the various stages in the loop to create a transistor.)

Making a Transistor: Starting Silicon Wafer

Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

Si

Wafers



Clean substrate

Si

Polished Silicon Wafer



Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

Chemical Vapor Deposition: Si3N4

Si



Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

Spin Coating of Photoresist

Si

mask



Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

Develop Photoresist

Si



Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

Plasma Etch Si3N4

Si



Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

Plasma Etch: Strip Photoresist

Si



Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

Ion Implantation

Si

IONS IONSIONS

1.75 u

1/50th of a human hair



Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

Anneal

Si

HEAT HEATHEAT

Activate (& diffuse) the dopant

• Clean before anneal



Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

The Final Steps…a completed transistor

Gate: +

e- e-

Source - Drain: +

Si



Economy of Transistors

~$300 /chip

X ~200 chips/wafer

X 200 wafers/furnace

load =

$12 Million

per furnace

loadhttp://www.dvhardware.net/article16696.html

http://www.nitride.co.jp/english

/products/wafer.html

Additional helpful websites

http://micro.magnet.fsu.edu/electromag/jav

a/transistor/

http://jas.eng.buffalo.edu/education/fab/N

MOS/nmos.html

http://micro.magnet.fsu.edu/electromag/java/transistor/

http://micro.magnet.fsu.edu/electromag/java/transistor/

http://jas.eng.buffalo.edu/education/fab/NMOS/nmos.html

http://jas.eng.buffalo.edu/education/fab/NMOS/nmos.html

transistors at work

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