# From a handful of sand to a fistful of dollars

A transistor is just like a garden hose with your foot on it

Sitting at the heart of your computer, mobile phone or DVD player is the microprocessor that makes it all work. These electronic 'chips' have millions of tiny electronic circuits on them allowing the calculations needed to make your gizmos work. But it may be surprising to learn that these silicon chips, now a billion pound industry worldwide are in fact mostly made of the same stuff that you find on beaches, namely sand. Sand is mostly made of silicon dioxide, and silicone, the second most abundant substance in the earth's crust, has useful chemical properties as well as being very cheap. You can easily 'add' other chemicals to silicon and change its electrical properties, and it's by using these different forms of silicon that you can make mini switches, or transistors, in silicon chips.

## House Hose

A transistor on a chip can be thought of like a garden hose, water flows from the tap (the source) through the hose and out onto the garden (the drain), but if you were to stand on the hose with your foot and block the water flow the watering would stop. An electronic transistor on a chip in its most basic form works like this, but electrical charge rather than water runs through the transistor (in fact the two parts of a transistor are actually called the source and drain). The 'gate' plays the part of your foot; this is the third part of the transistor. Applying a voltage to the gate is like putting your foot on and off the hose, it controls whether charge flows through the transistor.

## Lots of letter T's

If you look at a transistor on a chip it looks like a tiny letter T, the top crossbar on the T is the source/drain part (hose) and the upright part of the T is the gate (the foot part). Using these devices you can start to build up logic functions. For example if you connect the source and drain of two transistors together one after another it can work out the logic AND function. How? Well think of this as a long hose with you and a friend's foot available. If you stand on the hose no water will flow. If your friend stands on the hose no water will flow. If you both stand on the hose defiantly no water will flow. It is only when you don't stand on the hose AND your friend also doesn't stand on the hose that the water flows. So you've build a simple logical function.

## Printing chips

A billion pound industry made of sand

From such simple logic functions you can build very complex computers, if you have enough of them, and that's again where silicon comes in. You can 'draw' with silicon down to very small sizes. In fact a silicon chip is printed with many different layers. For example one layer has the patterns for all the sources and drains, the next layer chemically printed on top are the gates, the next the metallic connections between the transistors and so on. These chips take millions of pounds to design and test, but once the patterns are correct it's easy to stamp out millions of chips. It's just a big chemical printing press. It's the fact that you can produce silicon chips efficiently and cheaply with more and more transistors on them each year that drives the technology leaps we see today.

## Beautiful silicon

Finally you might wonder how the chip companies protect their chip designs? They in fact protect them by registering the design of the masks they use in the layer printing process. Design registration is normally used to protect works of artistic merit, like company logos. Whether chip masks are quite as artistic doesn't seem to matter. What does matter is that the chemical printing of silicon and lots of computer scientists have made all today's computer technology possible. Now there is a beautiful thought to ponder when next on the beach.