Tag: Saturday Night Science

How to Build a Computer 14: Alignment

 

Last time we saw how you physically expose a panel. That is, how you shoot it with ultraviolet light to get a pattern into the stuff so that you can do things to that pattern later on. Today the plan is to talk about all the ways this can go wrong. We’ll start with the big one: alignment. If you’ll recall the profile of the jumping trace we looked at a couple weeks ago:

Hooray for a well-stocked media library!

See that trace on the top? Suppose you were to shift it over to the right. Eventually, you’d lose contact with your left via and you’ve got a hole in your wire. Busted circuit, sorry, can’t sell that one. Now imagine you’re shifting it forwards or backward; sooner or later you lose contact with your via and again you start making scrap. Or twist it side to side. Or shift it and twist it. Suddenly you’re wondering how they get these things on there at all. Don’t worry, it gets worse. Suppose both the vias and the top trace are aligning to the bottom traces. The vias get printed in an okay spot, but a little south of where they ought to be. Still in tolerance. The trace gets placed in its own okay spot, but a little north of where it ought to be. See where I’m going with this? The compounding of the two errors is enough to, again, cost you money. The problems compound when you have a second phototool on the bottom to align as well.

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How to Build a Computer 12: Exposing

 

We know how photoresist works and how to get it on your material. Or my material rather; most of you aren’t going to be running laminators but no matter. How about transferring a pattern to the photoresist? That’s what we’re going over today. To change the photoresist you’ve got to hit it with an ultraviolet photon. Here, let me demonstrate:

A chunk of photoresist with a bunch of common engineering tools on it. Especially the fez.

I set that out on my cubicle desk several hours before snapping this photo. The small amount of ambient ultraviolet light in the white office light has been bombarding it for hours. Now let’s take all those funny-shaped tools off and see what’s underneath

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How to Build a Computer 11: The Binary Search Algorithm

 

We’re taking a break from the manufacturing process to cover some ideas in programming. Algorithms, what that means and why. Sounds fancy, doesn’t it? It ain’t as bad as it sounds. Let’s jump right in:

What’s An Algorithm?

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Member Post

 

We’ve seen how photoresist works, now we’re going to see how that actually works in the real world. Before you can print things with the patterns you draw in your photoresist you’ve got to draw those patterns. Before you can draw those patterns you’ve got to stick your photoresist on there. Today we’re going to […]

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How to Build a Computer 8: Organic Chemistry

 

I started with a discussion of the magic of photoresist, however (say it with me!) it got long-winded and I cut it down to the organic chemistry review. Next week photoresist. This week we’re going over some basic organic chemistry. Sounds fun, right? It’s going to be even more fun than that! You wait and see. We’re going to start small though, with methane.

You smell something? No? It’s probably just me.

This is a carbon atom, often found in the presence of ranch dressing. It’s surrounded by four olives, or hydrogen atoms. The pimento is only there for flavor. Carbon though is much like Silicon in that it comes with four electrons in its outer shell. In terms of orbitals that works out to 1s2 2s2 2p2. Carbon is in something of a unique position; you can make long and interesting chains of molecules with it. You can try making chains of other molecules, say, oxygen, but the results get… explosive. Anyway, a single carbon atom makes the simplest possible carbon chain. Let’s make it a more complicated.

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How to Build a Computer 9: Photoresist

 

We’ve just got off a quick overview on organic chemistry. Now we’re getting back to photoresist. The point of photoresist, if you’ll recall, is to take a pattern so you can print stuff on your wafer. To do that it has to be a chemical that responds to ultraviolet light. And I mean more “responds to” than get a mild sunburn; it’s got to chemically change so you can transfer the pattern of light into a pattern of stuff.

It’s a polymer made of benzene rings. Someone’s showing off.

The word “Photoresist” covers a great deal of variation, but the nature of the job it has to do requires certain commonalities. For starters, rather than all one substance, it’s a mix of three different things. You’ve got a photoactive compound, naturally. You’ve also got a resin, for stability. And then you’ve also got a solvent, for instability. The solvent keeps your resist liquid so you can apply it evenly. The resin keeps it solid once it’s on, so that it doesn’t move around as you’re working with it. That picture up there is of a resin. A thing called meta-cresol novolac. Can’t tell you why.

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How to Build a Computer 7: Patterning

 

We left off last time discussing circuits and logic and how to make your transistors do something useful. Fun stuff, but I wanted to swing back through a bit more of the manufacturing details. Let’s say I’m trying to make this circuit:

Don’t be fooled by the clever marketing; this is an OR gate with a NOT gate stuck on its nose. Wake up sheeple!

Yup, that’s a bunch of lines on a piece of paper. I want to manufacture these; to sell them and make money. So I can’t just make one, I need to make a lot. Okay, build the circuit. Let’s say I lay that out on a wafer, this is about what it’d look like.

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How to Build a Computer 6: Simple Transistor Circuits

 

The problem with simple transistor circuits is that any circuit with a transistor in it isn’t all that simple. And frankly, I don’t know how much you know about circuits; I’m guessing it ranges from “nothing at all” to “teach your grandmother to suck eggs why don’t you.” At the risk of boring the latter crowd we’re going to give this a slow and superficial treatment. Let’s start with a circuit that’s just about as simple as I can make it. So simple it doesn’t even have a transistor in it!

I’d make this circuit more interesting but I don’t know the symbol for ‘electric chair’.

 

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How to Build a Computer 5: Fundamental Chemistry

 

I know I promised simple transistor uses last time. Thinking about it though, I’d rather go into a bit more detail about the electron golfing I described earlier. It’s a neat analogy, but it doesn’t cover some things you can do with diodes. Interesting things. Therefore we’re gonna dive in for a deeper understanding of chemistry, atoms, and cartoons. Let’s look at a model of an atom using common household objects:

You all have your Ricochet mugs, right?

An atom consists of protons and neutrons in the middle and electrons outside. The common picture of an atom has those electrons whizzing in neat, well-defined orbits. That’s wrong. It’s closer to electrons having spaces they hang out in. We’re on the level of quantum mechanics here, so odd stuff happens. It’s not actually possible to tell where an electron is; it’s small enough that you can only give probabilities. Hmm… let me try it again.

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How to Build a Computer 4: Diodes and Transistors

 

We all love blasting things with ions, and most of us could spend all day shooting at wafers, but eventually someone is going to ask you to build something useful. What am I doing with all this mess of silicon anyhow? Here’s where we see the use of all that stuff. What do you suppose happens when you put a p-doped chunk of silicon next to an n-doped chunk of silicon?

One last cookie photo, then I’m going on a diet. Swearsies.

Diodes to Kill For

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How to Build a Computer 3: The Hows of Doping

 

First you gotta find a dealer. Right, not that kind of doping. Today we’re going to discuss how to how you mix your dopant atoms into your silicon wafer so you can make transistors.

How Do I Dope My Wafer?

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How to Build a Computer Part 2 of N: Crystallography

 

Last week we saw how to turn sand into silicon. This week I was planning on showing you how to turn silicon into a semiconductor. I mean more of one than it already is. Unfortunately my brief notes on crystallography went long. This week we’ll discuss crystals, next week we’ll do doping, and the week after that we’ll finally get to transistors. Unless I wax even more loquacious, which is the way the smart money is betting.

In a crystal every atom is slotted neatly into an ordered lattice, and every spot in the lattice has an atom in it. With some exceptions. Actually those exceptions are most of what we’re going to talk about today. Let’s assume this is a perfect silicon crystal:

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How to Build a Computer, Part 1 of N: Silicon

 

As the illustrious @JohnWalker no longer treads these halls, I figured there was an opportunity to thrust my metaphorical booties into his clodhoppers. I’ve been kicking the idea of this series around for a long time. Broadly speaking it covers everything you need to know to build a computer. Everything. Today, we’re going to learn how to make silicon wafers.

He’s Gone Silicon

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How to Crack Excel Files

 

This all starts with Mike Mahoney. Mahoney was the Excel guy, two Excel guys ago. To his credit, he wrote pretty good stuff. His macros don’t break often. Everything would have been cool except he was writing these things when Excel 2003 was the hot new thing. Mahoney was also excellent about locking things down from accidental damage. Trouble is, nobody remembers his passwords. Breaking through his protections makes an excellent case study on how to secure and how to bypass the security on an excel workbook.

Not even swordfish works.

The guy on the floor gives me a call. I don’t know the guy; IT gave him my name. They don’t support random excel macros, so I get these calls. His macro works fine on most computers, but it errors out right away on one. I’ve never seen this particular spreadsheet before, but I’ve got a pretty good idea why. His new computer is 64 bit, which messes with some function calls.

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Saturday Night Science: The Planet Remade

 

“The Planet Remade” by Oliver MortonWe live in a profoundly unnatural world. Since the start of the industrial revolution, and rapidly accelerating throughout the twentieth century, the actions of humans have begun to influence the flow of energy and materials in the Earth’s biosphere on a global scale. Earth’s current human population and standard of living are made possible entirely by industrial production of nitrogen-based fertilisers and crop plants bred to efficiently exploit them. Industrial production of fixed (chemically reactive) nitrogen from the atmosphere now substantially exceeds all of that produced by the natural soil bacteria on the planet which, prior to 1950, accounted for almost all of the nitrogen required to grow plants. Fixing nitrogen by the Haber-Bosch process is energy-intensive, and consumes around 1.5 percent of all the world’s energy usage and, as a feedstock, 3–5% of natural gas produced worldwide. When we eat these crops, or animals fed from them, we are, in a sense, eating fossil fuels. On the order of four out of five nitrogen molecules that make up your body were made in a factory by the Haber-Bosch process. We are the children, not of nature, but of industry.

The industrial production of fertiliser, along with crops tailored to use them, is entirely responsible for the rapid growth of the Earth’s population, which has increased from around 2.5 billion in 1950, when industrial fertiliser and “green revolution” crops came into wide use, to more than 7 billion today. This was accompanied not by the collapse into global penury predicted by Malthusian doom-sayers, but rather a broad-based rise in the standard of living, with extreme poverty and malnutrition falling to all-time historical lows. In the lifetimes of many people, including this scribbler, our species has taken over the flow of nitrogen through the Earth’s biosphere, replacing a process mediated by bacteria for billions of years with one performed in factories. The flow of nitrogen from atmosphere to soil, to plants and the creatures who eat them, back to soil, sea, and ultimately the atmosphere is now largely in the hands of humans, and their very lives have become dependent upon it.

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Saturday Night Science: Making Contact

 

“Making Contact” by Sarah ScolesThere are few questions in our scientific inquiry into the universe and our place within it more profound than “are we alone?” As we have learned more about our world and the larger universe in which it exists, this question has become ever more fascinating. We now know that our planet, once thought the centre of the universe, is but one of what may be hundreds of billions of planets in our own galaxy, which is one of hundreds of billions of galaxies in the observable universe. Not long ago, we knew only of the planets in our own solar system, and some astronomers believed planetary systems were rare, perhaps formed by freak encounters between two stars following their orbits around the galaxy. But now, thanks to exoplanet hunters and, especially, the Kepler spacecraft, we know that it’s “planets, planets, everywhere”—most stars have planets, and many stars have planets where conditions may be suitable for the origin of life.

If this be the case, then when we gaze upward at the myriad stars in the heavens, might there be other eyes (or whatever sense organs they use for the optical spectrum) looking back from planets of those stars toward our Sun, wondering if they are alone? Many are the children, and adults, who have asked themselves that question when standing under a pristine sky. For the ten year old Jill Tarter, it set her on a path toward a career which has been almost coterminous with humanity’s efforts to discover communications from extraterrestrial civilisations—an effort which continues today, benefitting from advances in technology unimagined when she undertook the quest.

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Saturday Night Science: The Pope of Physics

 

“The Pope of Physics” by Gino Segrè and Bettina HoerlinBy the start of the 20th century, the field of physics had bifurcated into theoretical and experimental specialties. While theorists and experimenters were acquainted with the same fundamentals and collaborated, with theorists suggesting phenomena to be explored in experiments and experimenters providing hard data upon which theorists could build their models, rarely did one individual do breakthrough work in both theory and experiment. One outstanding exception was Enrico Fermi, whose numerous achievements seemed to jump effortlessly between theory and experiment.

Fermi was born in 1901 to a middle class family in Rome, the youngest of three children born in consecutive years. As was common at the time, Enrico and his brother Giulio were sent to be wet-nursed and raised by a farm family outside Rome and only returned to live with their parents when two and a half years old. His father was a division head in the state railway and his mother taught elementary school. Neither parent had attended university, but hoped all of their children would have the opportunity. All were enrolled in schools which concentrated on the traditional curriculum of Latin, Greek, and literature in those languages and Italian. Fermi was attracted to mathematics and science, but little instruction was available to him in those fields.

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Saturday Night Science: Cellular Automata

 

This will be a somewhat different Saturday Night Science. While most installments discuss a topic in science, technology, or mathematics, often in conjunction with a book, this month’s edition describes a project on which I’ve been working, off and on, since 1988 (mostly off, but with intense bursts of effort from time to time), which has just been re-released in a new, completely overhauled, updated, and extended edition concurrent with the publication of this article. CelLab, or Cellular Automata Laboratory, is a Web resource which allows you to explore a frontier of computing: cellular automata. But what are cellular automata, and why should you explore them?

What are Cellular Automata?

Cellular automata are massively parallel computer systems. For decades, most computers had a single processor or CPU (Central Processing Unit), which executed programs in a serial manner: one instruction at a time. Today, many desktop and notebook computers use chips that implement “multiple cores”, which are just multiple CPUs on a single chip. For example, the notebook machine on which I’m typing this has…hmm…I forget, let’s see…

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Saturday Night Science: Phenomena

 

“Phenomena” by Annie JacobsenAt the end of World War II, it was clear that science and technology would be central to competition among nations in the postwar era. The development of nuclear weapons, German deployment of the first operational ballistic missile, and the introduction of jet propelled aircraft pointed the way to a technology-driven arms race, and both the U.S. and the Soviet Union scrambled to lay hands on the secret super-weapon programs of the defeated Nazi regime. On the U.S. side, the Alsos Mission not only sought information on German nuclear and missile programs, but also came across even more bizarre projects, such as those undertaken by Berlin’s Ahnenerbe Institute, founded in 1935 by SS leader Heinrich Himmler. Investigating the institute’s headquarters in a Berlin suburb, Samuel Goudsmit, chief scientist of Alsos, found what he described as “Remnants of weird Teutonic symbols and rites … a corner with a pit of ashes in which I found the skull of an infant.” What was going on? Had the Nazis attempted to weaponise black magic? And, to the ever-practical military mind, did it work?

In the years after the war, the intelligence community and military services in both the U.S. and Soviet Union would become involved in the realm of the paranormal, funding research and operational programs based upon purported psychic powers for which mainstream science had no explanation. Both superpowers were not only seeking super powers for their spies and soldiers, but also looking over their shoulders afraid the other would steal a jump on them in exploiting these supposed powers of mind. “We can’t risk a ‘woo-woo gap’ with the adversary!”

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Saturday Night Science: The Analytical Engine

 
Charles Babbage
Charles Babbage in 1860. Engraving from the Illustrated London News, 1871-11-04, public domain.

Charles Babbage was one of the preeminent polymaths of the 19th century. He worked in mathematics (appointed Lucasian Professor of Mathematics at Cambridge—Newton’s chair, later Stephen Hawking’s—in 1828), astronomy, economics (his work on the division of labour in manufacturing was one of the first in the field now called operations research), mechanical engineering (he invented an algebraic notation for describing the design of mechanisms), and cryptography. He was a founder of the British Association for the Advancement of Science and the Statistical Society of London. He invented the cow-catcher for locomotives and the ophthalmoscope.

During his studies at Cambridge, Babbage became dismayed by the quality of the mathematical tables used by mathematicians, scientists, and engineers in their calculations. At the time, all computations requiring more precision than the two or three digits of a slide rule were done manually, using printed tables of logarithms, trigonometric functions, ephemerides for astronomy, and sight reduction tables for celestial navigation at sea. Examining these tables, Babbage discovered that they contained numerous errors, and that there were even discrepancies among different editions of the same tables. These errors were both due to calculation errors computing the tables, plus those introduced in typesetting printed editions. Errors in mathematical tables were not just a matter of pedantry or aesthetics; the Royal Navy used these tables for navigation, and flaws could lead to Her Majesty’s ships running aground or failing to be in the right place at the right time in a naval battle.

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