Microchips can be used for many different tasks, from controlling a washing machine to being the nerve centre of a computer. Each microchip can hold up to 1,000,000 electronic components, which is amazing considering they are only visible to the human eye in any detail under a microscope.
These chips are made hundreds at a time. They are created on a slither of ultra-pure and artificially formed silicon crystal. It is so thin that it would take at least 250 slices to assemble a pile 1 inch (24 millimetres) high. The designs for the circuits are drawn on a computer and then each is reduced to the required chip size. They can then be arranged side by side on a glass plate known as a mask. Because many other components need to be built up in separate layers on a chip, a mask has to be made for each application. The masks are designed to block out any unwanted parts, and as they are created much larger than the chip, they have to be photographically reduced.
The chips are constructed by a build up of either p-type or n-type layers (or insulating silicon dioxide layers). The undesired sections are then etched out. This is achieved by firstly treating the layer with a coating which is susceptible to ultraviolet light, masking it, and then exposing it to the light. Any part that is exposed becomes resistant to acid, but the blocked areas do not. These are etched away when the layer is coated with acid.
What is not often realised is that the familiar black chip with silver legs is not the actual microchip. This is merely a casing which serves two purposes. It protects the microchip from the outside atmosphere, and it gives connection pins which are large enough to solder to a circuit board. The microchip itself is usually a 4-8mm square sliver of silicon buried deep within this casing.
