When Gordon Moore suggested in 1965 that the number of processors on a chip would double every two years, he predicted that the trend would continue for about a decade. Five decades – half a century – later, the trend is still holding true. CPU manufacturers use Moore’s law as a yardstick by which they measure their own successes. However, in order to achieve this, they’ve had to pull off some fairly incredible tricks in the field of photochemistry.
Computer chips – or rather, the circuits they contain – are made by photolithography and etching of metal oxide on semiconductors. In photolithography, a photoresist – usually a polymer – is exposed through a mask, which is a negative of the circuit design. This makes the polymer soluble in a solvent. The metal oxide in the areas where the polymer has been removed can then be dissolved, leaving behind tracks of metal oxide that form the basis of the circuit. However, because computer chips contain tiny components, engineers are always coming up against a barrier: the diffraction limit. This says that it’s impossible to focus light into a point smaller than half of its wavelength. To make ever smaller components using photolithography has required not only light with a shorter wavelength, necessitating the development of light sources and lasers that work in the ultraviolet, but new polymers that react to this wavelength. Both of these are barriers to the continuation of Moore’s law.
Scientists are always finding new ways to facilitate the continuation of Moore’s law, such as new radiation sources instead of light, including beams of electrons, and new photoresists, such as self-assembled monolayers. However, some scientists think that we are on the brink of a paradigm shift in computer technology similar to the barriers presented by vacuum technology immediately before the advent of the transistor, because the number of ways of continuing current technologies seems to be dwindling. Many advocate molecular electronics, which is an offshoot of solid-state physics, clever chemistry and nanotechnology. In contrast to what we’ve had for the past half-century, often termed ‘top down’ fabrication, the new methods are called ‘bottom up’. It means building circuits from atoms and molecules, instead of using physical processes (like photolithography) to try to make things that are nearly as small as molecules and atoms. Molecular electronics also opens up the possibility of quantum computers, which use quantum physics to perform many calculations simultaneously.
As a reminder that it can be very difficult to predict the future, here’s a statement from Popular Mechanics in 1949, before the transistor was invented: “Where a calculator on the ENIAC is equipped with 18,000 vacuum tubes and weighs 30 tons, computers of the future may have only 1,000 vacuum tubes and perhaps weigh 1½ tons.”