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!