General Trends in the History of Circuits

The material for the post is based primarily on a lecture by Thomas Szkopek in the class Nanoelectronic Devices that I am taking at McGill.

Electrons are very light and have a definite (constant) charge. Charge to mass ratio is a primary reason why electrons are better than nucleons or mechanical devices for the creation of semiconductor electronics.

What is a transistor? It is ‘transferred resistance’. We can control the resistance of a lump of material. By controlling the resistance we can control to flow of current through a semiconductor. This is the primary basis for decision making at the circuit level.

We have built more transistors than anything else? (is this true or is it computer bits (like those in a hard drive)? not sure what he said).

In semiconductors, germanium was eventually replaced by silicon. Why?

Not because of cost or availability (initially). It was primarily a question of easier fabrication. The key facet was the quality of the oxide you can grow on the silicon rather than on the germanium.

There has been a lot of talk for years about how this or that material was going to replace silicon. None of them have yet done so because silicon is really well established and quite good at what it does. “Gallium Arsenide is the material of the future and it always will be.” - Szkopek.

Why smaller and smaller integrated circuits? By making the parts smaller and closer together, we can eliminate a lot of the resistances, capacitances and inductances as well as reducing our overall material usage. This should mean cheaper integrated circuits that require less materials to create and less power to run.

Gordon Moore

Gordon Moore was a chemist by training but was also one of the most successful electronic engineers of all time. What was Moore’s major contribution? He figured out how to grow high quality oxide on silicon.

As a computer scientist, I am well aware of some of the many different ways Moore’s Law has been mis-represented. So what is it actually? We read “Cramming More Components onto Integrated Circuits” the famous paper that Moore wrote in 1965, from which ‘Moore’s Law’ was extrapolated.

Moore's Law: Relative manufacturing cost per component and number of components per integrated circuit (diagram in paper, or on the Wikipedia article).

Cost increase as we move to the right is primarily because fewer chips are successfully made when we try to jam more components onto the wafer. There is a minimum cost for each technology level.

Atomic Scale

What happens when transistor dimensions approach 10nm? We are looking at atomic scale.

He then showed us some pictures taken with scanning-tunneling microscopy of a tiny surface with iron atoms on it. The atoms were physically arranged into a circle. As this symmetry is created you can see the creation of a symmetric pattern of standing waves of electron position in the center. This is an incredible (and graphic) demonstration of quantum mechanics in action. The pictures are from this paper on “Confinement of electrons to quantum corrals on a metal surface.”

One of Szkopek’s main points with regards to these photos is that atomic scale disorder is going to be present when we are working at such ridiculously small scales. Some of this disorder can be dealt with through more careful manufacturing and usage techniques, but we are definitely getting into the realm where we are starting to touch upon the omnipresent low-level disorder of the universe.

Szkopek says that Intel is currently using a 1.2nm oxide layer. That is 4 layers of atomic oxide. We are at the atomic scale, and will have to be considering the facts that govern it.

In closing, Szkopek talked a bit about how the nice formulas we tend to see in the theoretical sections of courses devolve into complicated, ugly looking things when we try to do real problems. There is a tendency to term this “things getting crazy”. Szkopek makes his point clear when he closed the class with: “Things don't get crazy, they get physical!”

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