A Brief History

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Materials Science: 10 Things Every Engineer Should Know

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University of California, Davis

Materials Science: 10 Things Every Engineer Should Know

873 个评分

We explore “10 things” that range from the menu of materials available to engineers in their profession to the many mechanical and electrical properties of materials important to their use in various engineering fields. We also discuss the principles behind the manufacturing of those materials. By the end of the course, you will be able to: * Recognize the important aspects of the materials used in modern engineering applications, * Explain the underlying principle of materials science: “structure leads to properties,” * Identify the role of thermally activated processes in many of these important “things” – as illustrated by the Arrhenius relationship. * Relate each of these topics to issues that have arisen (or potentially could arise) in your life and work. If you would like to explore the topic in more depth you may purchase Dr. Shackelford's Textbook: J.F. Shackelford, Introduction to Materials Science for Engineers, Eighth Edition, Pearson Prentice-Hall, Upper Saddle River, NJ, 2015

从本节课中

Making Things Fast and Slow / A Brief History of Semiconductors

Welcome to week 5! In lesson nine we’ll deal with how to make things fast and slow. We’ll examine the lead-tin phase diagram and look at its practical applications as an example of making something slowly. Then we’ll evaluate the TTT diagram for eutectoid steel, and compare diffusional to diffusionless transformations with the TTT diagram, monitoring how we make things rapidly. Lesson ten is a brief history of semiconductors. Here, we discuss the role of semiconductor materials in the modern electronics industry. Our friend Arrhenius is back again, and this time we’re applying the Arrhenius Relationship to both intrinsic and extrinsic semiconductors. We’ll also look at combined intrinsic and extrinsic behavior.

A Brief History7:13

The Intrinsic Semiconductor4:31

The Extrinsic Semiconductor6:51

Combined Intrinsic and Extrinsic Behavior4:23

与讲师见面

James Shackelford
Distinguished Professor Emeritus
Department of Chemical Engineering and Materials Science

And welcome back to Kemper Hall here on the University of California,

Davis campus.

This time you see we're in a very different setting.

We're in a modern clean room.

And we're gonna talk about the role of semiconductor materials in

the modern electronic industry.

[MUSIC]

And so here we are at a modern clean room here on the Davis campus.

Specifically, this is the Center for Nano and

Micro Manufacturing here in Kemper Hall on the UC Davis campus.

It gives us a chance to reflect briefly on the history of the modern

electronics industry.

We've come to be familiar with these clean room backgrounds and various images.

In this case, we're reminded that the entity,

the electron, was really only discovered in the late 19th century.

To be precise, in 1897, Professor J.J.

Thomson at the Cambridge University in England.

In doing some, by today's standards,

a primitive experiment using something that looked like an old fashioned TV tube.

A cathode ray tube.

And he realized that the images that are being created

on the fluorescent screen were created by these subatomic particles.

He hypothesized the existence of an electron, that subatomic

particle that would be orbiting around a nucleus composed of protons and neutrons.

And that those electrons then, were

what he was accelerating in that high voltage cathode ray tube.

Well, that discovery in 1897 was followed in fairly short order, only 50 years

later, by the invention of the transistor at the Bell Laboratories in New Jersey.

And those three physicists that made that important discovery,

open up the era of modern solid state electronics.

They created a small transistor using a small, single crystal of germanium.

That has lead now, of course, to the the use of silicon,

that element just above germanium in the periodic table, as the more or

less ubiquitous platform for modern integrated circuits.

And so that integrated circuit was actually invented just

less than 25 years after the invention of the transistor itself.

1971, Intel Corporation introduced that first

microprocessor that contained a couple of thousand transistors and

a small printed circuit on a platform of silicon.

That technology has continued to be miniaturized over the decade since.

And in fact, Gordon Moore, one of the co-founders of Intel Corporation,

using his scientific intuition, said that we should be able to double the number of

transistors in these fine scale integrated circuit patterns every two years.

Well, that's turned out to be a remarkably precise projection of the technology.

And so now over more than four decades, the scientists and

engineers in the electronics industry have been able to follow that,

what is now known as Moore's Law.

Doubling the number of transistors on the integrated circuit chip every two years.

So, now we're going to go to a series of video clips of

lectures on the nature of semiconductors in modern electronic devices.

But before we do that, we should cover a few vocabulary terms.

You'll hear reference to Fermi function, to valence band and conduction band.

A Fermi function is nothing more than the probability that an electron

will be at a particular energy level.

We see that the Fermi function goes from one, or

100% probability at low energies, up to zero at high energies.

And follows something of an S-shaped curve as we go from low to high energies.

Now the result is that, that S-shaped curve

will overlap the valence band and conduction band.

So the Fermi function, named after the great Italian physicist Enrico Fermi.

Who discovered so

much of the nature of electronics and modern physics in the early 20th century.

His prediction of that energy population, as I say,

allows us to overlap the valance band and the conduction band.

Now, the valence band is simply the energy range

corresponding to the energy of the valence electrons that are providing that covalent

bonding between the silicon atoms in the silicon.

And so then, the conduction band simply acknowledges the fact that,

as we might remember from an introductory physics or chemistry course,

that we can accelerate electrons.

Stimulate them to higher energy levels as a result of some energy input.

Thermal energy is a common way to do that.

So we can promote a valence electron up to a higher conduction

electron band as a result of thermal energy input.

And so again, the Fermi function overlaps the valence band and

the conduction band, and that gives us a quantitative indication of how many

such electron promotions are likely to happen.

And so that's really how semiconductor Is conducted

by the thermal promotion of electrons from a lower

band level to a higher conduction band.

And then, we will see that that is another example of the Arrhenius relationship.

We've seen this a number of times, of course, previously,

mostly talking in the context of mechanical behavior.

Such as heat deformation, heat treatment of steels, and so on,

in which we're talking about the thermal activation of atomic transport.

Well, the same thing is true here as we see,

in electron transport in electroconductivity,

that that's a thermally activated process.

And again, the great contribution of the Swedish chemist Svante Arrhenius

comes into play in the changing conductivity of a semiconducting device,

let's say composed of silicon, in again, a modern electronic device.

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