What are semi-conductor chips?

Semi-conductors are materials in which nearly all the electrons are paired off and inert, but a very few electrons are sailing for the New World or taking jobs as pirates on the open sea. The exact impurities ("dopants") added to the original material (which is often but not always a crystal) affect the band gap that inhibits an electron from bolting. When semi-conductor materials are combined into the form we call a transistor, its band gap controls the precise amount of light or electric current needed to goose the transistor into its "on" position. ("Transistor" is a special form of semi-conductor that's sandwiched and wired up a particular way, but the terms are linguistically related: a transistor neither transfers nor resists indiscriminately, just as a semi-conductor neither conducts nor insulates completely. Instead, like an efficient doorman, they both let through just the electrons we want to pass.)

Tiny electrical-current devices that can be efficiently switched on and off with tiny amounts of electricity lend themselves to compact logic circuits. Transistors can be hooked up so that their output connections feed back into their inputs, an arrangement called a "logic gate." A transistor in one of these arrangements stays on even when the base current is removed, but when a new base current flows, the transistor flips back off, then on again with a new current, and so on. This is called a flip-flop, which amounts to a simple memory device that stores a zero (when it's off) or a one (when it's on). It is the basic technology behind computer memory chips. They are simple or complex depending on our ingenuity in constructing the interactive logic gates.

Modern, miniaturized logic circuits are laid down on a chip by a kind of etching process. For instance, a tiny little light pattern can be shone on the chip, and then a circuit material is painted on in an incredibly thin coat that sticks differently depending on where the light hit the surface. Chip-makers have gotten so good at this miniaturization that they're approaching the nano-scale--still bigger than an individual atom, but getting near that neighborhood. The smaller the wavelength of the light, the finer the pattern we can achieve. Visible light is in the 400-700 nanometer range, but of course wavelengths get smaller and smaller as you move up into the ultraviolet and gamma-ray ranges. If we can get the etching pattern down to the atomic scale (1/10 of a nanometer), we'll obviously be able to pack a lot more circuits into a small space.

I think I always had the notion that silicon chips were made of the same material as beach sand. Sand is really silicone dioxide, though, whereas the silicon in chips is elemental, crystallized silicon, which looks a bit like a silvery metal.


David Foster said...

May be of interest: my post about missed European opportunities in the semiconductor industry: Leaving a Trillion on the Table


(although in retrospect, "trillion" greatly understated the amount of wealth involved)

Texan99 said...

Thanks, David, I've just gone over and read your link, especially enjoying the thoughts about top-down and bottom-up economies and how they exploit technological advances. It was exciting to listen to my nanotech lecturers describe their research groups, where there is incredible ferment that would quickly be squelched if wise central bureaucrats were put in charge of deciding which ideas were worth expending society's resources on. Not that they aren't focused on how to write grant proposals that will yield federal money, but they're obviously also pitching to alert and eager venture capitalists. Both of them had a sharp eye on commercial applications, while keeping in mind that many of their best ideas are coming from undirected fooling around with first principles--"I wonder if we can do this? How about this?"--and then someone comes along and says, "Hey, you know what we might use that for?"

There's always some Goering in the wings saying, "My people don't need this or that," as if he had any idea what people need, or what will become useful and world-changing once it's out there. Guys like that can't tolerate the idea that someone else--lots of someone elses--will decide for themselves what's useful.

Ymar Sakar said...

Semiconductors really did feel like magic.

We obviously need more Wise Latinas and authentic Native Americans telling us, "you didn't build that".

RonF said...

An LED is a semi-conductor device. "Light Emitting Diode" is the full name. A diode is an electronic one-way valve that only allows electrons to pass though it in one direction. Like a mechanical one-way valve, however, sufficient back-pressure can exceed the valve's capacity to resist. In a mechanical one-way valve this would result in a broken valve or a burst pipe. In the case of an LED it results in the emittance of light - and compared to an incandescent or even a fluorescent bulb, a very efficient emittance.

Texan99 said...

No matter how hard I try to get used to the idea that electricity and light are part of the same phenomenon, I never quite get over the surprise and delight of seeing one turn into the other. You back up electricity and it gets spit out as light. You take light into a solar cell and it comes back out as electricity (or chemical bonds). I know that light is just a jiggling electromagnetic field, but I'm still bemused every time! Light, electricity, chemistry: all the same thing.