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Project Still I Rise Summer STEM Camp:
Materials Science
Outline
• Introduction
• What is a semiconductor and how does it work?
• “From sand to product”
• What is materials science?
– Electrical Properties
– Magnetic Properties
– Mechanical Properties
3
Conductors and Insulators
• Conductors – Materials that allow current
to flow through and provide electricity to the items which require power to operate
– Metallic objects can serve as a conductor
– Can you think of some conductors?
• Insulators – Materials that DO NOT allow
current to flow through and provide electricity
– Rubber, plastic, and paper objects can serve as an insulator
– Can you think of some insulators?
4
What is a Semiconductor?
• Semiconducting materials are the core of most electronics in use today – They are found in: computers, cell phones, and many other
devices such as transistors, solar cells, diodes, and digital and analog integrated circuits
• Semiconductors are materials with electrical conductivity caused by the flow of electrons – Without electrons and external stimulation, semiconductors
are insulators – With electrons and external stimulation, semiconductors are
conductors
• To introduce electrons, a technique called ‘doping’ is required
Si
Si Si Si
Si
Si
Si Si
Si Si
Si
Si
Si
Si
Si
Si
Si
Si Si
Si Si
Si
Si
Si
Si
Silicon atoms share valence electrons to form insulator-like bonds
Covalent Bonds in Silicon Crystal
5
Donor atoms provide excess electrons to form N-type silicon.
Si
Si
Si
Si
Si Si
Si
Si
Si
Si Si
Si
Si
Si
Si
Si
Si
Si
Si Si
Si
Si
Si
Si
Si
Phosphorus atom serves as N-type dopant
Excess electron (-)
P
P
P
Free Electrons in N-type Silicon
6
Acceptor atoms provide a deficiency of electrons to form P-type silicon.
Hole (+)
Boron atom serves as P-type dopant
Si
Si Si
Si
Si
Si
Si Si
Si
Si
Si
Si
Si
Si
Si Si
Si
Si Si
Si
Si
Si Si
Si
Si
B
B
B
Holes in P-type Silicon
7
Valence electron freed from copper atom
Negative terminal from voltage supply
Positive terminal from voltage supply
e -
e -
e -
e -
Flow of Electrons in Copper Wire
8
Free electrons flow toward positive charge
Positive terminal from voltage supply
Negative terminal from voltage supply
e -
e -
e -
e -
Flow of Free Electrons in N-type Silicon
9
Positive terminal from voltage supply
Negative terminal from voltage supply
+Holes flow toward negative terminal
-Electrons are supplied by the voltage source
e -
e -
e -
Flow of +Holes in P-type Silicon
10
1
Semiconductor Industry Overview
11
The silicon ingot is grown and individual
wafers are sliced.
Wafer Preparation
12
Wafer Fab
Wafers undergo a series of steps in the manufacture of
integrated circuits. The steps include layering, patterning,
etching and doping.
Layering Patterning
Etching Doping
13
Electrical Test Probe
Individual integrated circuits are tested to distinguish good die from bad ones.
Defective IC
14
Assembly
Good chips are attached
to a lead frame package.
15
Die Attach and Wire Bonding
lead frame
bonding pad
connecting pin
gold wire
16
Final Test
Chips are electrically tested under
varying environmental conditions.
17
How Computer Chips are Made
• Globalfoundries "sand to silicon" video:
• http://www.youtube.com/watch?v=UvluuAIiA50
What is Materials Science?
Basically, it is the study of “stuff”!
What is Materials Science?
Basically, it is the study of “stuff”!
• Electrical Properties • Magnetic Properties • Mechanical Properties
Electrical Properties
How a material responds to an applied electric field. - How easily can electricity (current) pass through a material? - What can we do to tune the conductivity of a material? (additives, “doping”)
Experiment 1
Why are electrical properties important?
Processors for next-gen devices..
Biosensors
Solar Panels
Valence electron freed from copper atom
Negative terminal from voltage supply
Positive terminal from voltage supply
e -
e -
e -
e -
Flow of Electrons in Copper Wire
23
Copper is a Widely-used Electrical Conductor
- +
Zap
Battery
e-
e-
e-
e-
24
Conductor
Testing Materials for Conductivity
- +
Zap
Battery
25
Experiment 1
Does water conduct electricity?
Conduction through water is limited due to lack of free current carriers.
+ -
Zap
Battery
Is Water a Good Electrical Conductor?
27
Experiment 1
What about salt water?
Na+ Cl-
Ocean
sid
e
Sa
lt
Table salt is a compound of sodium (Na) and chlorine (Cl). Salt dissolves in water; thus breaking the ionic bonds that hold Na+ and Cl- together.
Electrically-charged ions
Impurities added to a Stable Substance Help Improve Conductivity
29
Sodium and chlorine ions provide electrical path for current flow in water.
+ -
Zap
Battery Na+ Cl-
Transforming Insulating Water into a Conductive Substance
30
Magnetic Properties
Magnetism – Phenomenon by which materials exert an attractive or repulsive force or influence on other materials. - Can we make a material magnetic? - Why is a material magnetic?
Magnetic Properties
How does magnetism work?
Experiment 2
Can we make a magnet with a nail and a copper wire?
Experiment 2
How does it work?
Passing a current through a wire produces a magnetic field around the
wire. More Coils = More Magnetic
Experiment 2
Why are magnetic properties important?
Random Access Memory (RAM) Computer Hard Drives
Magnetic Trains
Mechanical Properties
The mechanical behavior of a material reflects the relationship between its response or deformation to an applied load or force. Key mechanical design properties: stiffness, strength, hardness, ductility, and toughness.
Experiment 3
How does temperature affect mechanical properties?
Experiment 3
Why does this happen?
Temperature of Liquid Nitrogen is -321 oF!
Materials are ductile because their atoms and/or molecules can “slip” past each other without damaging the material. However, when a material is extremely cold, the molecules almost literally “freeze” in place. The material can no longer bend or stretch, and breaks into pieces as a result.
Mechanical Properties Why are mechanical properties important?
Infrastructure Transportation
Flexible Screens
Acknowledgement
• This work is partially funded by NSF UNITE US/Ireland R&D Partnership for support under award NSF-ECCS–1407765
• The presenters would also like to thank Julian Serda for some discussions and ideas/resources used in this presentation
Thank You!
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