How is silicon used in the electronics industry

Silicon: the basis for glass production

Jack of all trades silicon

Pure silicon was first produced in 1823 by the Swedish chemist Jöns Jakob Berzelius (1779-1848). He also found that silicon turns into silica when burned. That is why it was later named after the Latin word for pebble ("silex").

Stones, rocks, mountains and continents are made of silicon, which, however, always occurs in connection with other elements. Mostly with oxygen, then it's called silicon dioxide or, more simply, quartz.

In its purest form in nature we know silicon dioxide as rock crystal. In a loose, contaminated form, we call it sand. Compounds with other elements such as aluminum, calcium or magnesium are called silicates. Silicon has even been found in lunar rocks and meteorites.

Once silicon has bonded with oxygen, it is very difficult to break it off again. Silicon dioxide is therefore a very hard solid with a high melting and boiling point. Because of its hardness, ground quartz is ideal as an abrasive, powdered quartz is a basic component of porcelain.

Melted as glass

One of the oldest products that humans make from silicon is glass. It was produced as early as 2000 BC. In essence, glass is nothing more than fused silica. In most cases, however, other materials are also mixed in, for example sodium and calcium oxide in the case of window glass.

When the melt cools down, the molecules do not form ordered crystals, but lie around in the glass in a disordered manner. Glass is very brittle and has a high compressive strength, but only a very low tensile strength.

Sealant and breast implant

Silicone is also a silicon product. Both the silicone that craftsmen use as a sealant and the silicone that is used in cosmetic surgery.

Chemically, silicone consists of long chains that are made up of alternating silicon and oxygen atoms. Hydrocarbon residues are attached to the silicon atoms, which ensure that silicones repel water while water vapor can penetrate through.

Semiconductors and transistors

Silicon has a property that has revolutionized its use over the past 50 years: it is a semiconductor. Semiconductors are materials that can conduct electricity but are "reluctant" to do so because they have only a few free electrons.

Strictly speaking, pure silicon has no free electrons at all, they are all required for crystal bonds. Nevertheless, silicon conducts electricity when energy is supplied in the form of heat or light.

The conductivity can be influenced. Targeted impurities in the crystal lattice of silicon further improve the electrical properties. Then you can even determine in which direction the current should flow.

The conductive properties of silicon make it possible to build small electronic switches that can be used to switch currents on and off: transistors. These miniature switches do not need any springs or joints, they work without any mechanical components. They are therefore so tiny that microchips can be built from them.

As early as 1965, Gordon E. Moore of the computer company Intel predicted that the number of transistors per square centimeter of chip area would double every one to two years. The mere fact that this prophecy is now called "Moore's Law" shows that the man was right.

The increase in storage density on microchips followed the forecast of 1965 to this day and even exceeded it at times. In 2000, around 40 million transistors fit on a microprocessor, and development is far from over.

Basis for solar power

Another important application for silicon is solar cells, which can be used to generate electricity from sunlight. Solar cells consist of two silicon layers, both of which are somewhat contaminated ("doped"): the upper layer, for example, with phosphorus atoms, the lower with boron atoms.

An electric field forms at the transition between the two layers. If a beam of light hits an electron in the upper layer, it can move freely and migrate outwards. This creates an electrical voltage that can then be tapped via external contacts.

A cell with an area of ​​12.5 by 12.5 centimeters generates a voltage of around 0.5 volts with a current of around four amps, which in turn corresponds to an output of around two watts. That's just enough for a pocket calculator.

For more power you have to couple several cells together. The environmentally friendly solar energy is used more and more frequently; Solar cells have become indispensable in watches, pocket calculators and even satellites. The demand is increasing so strongly that silicon production can hardly keep up.

The main thing is pure

Silicon is literally a dime a dozen. However, a lot of energy is required to extract raw silicon from sand, because the oxygen has to be removed from the silicon dioxide. In order to use semiconductors, this raw silicon has to be cleaned with great effort.

About 99.999999999 percent purity is required for the manufacture of computer chips, which means that there can only be one "wrong" item out of 100 billion atoms. No other element in the world is produced in such purity.

Such a degree of purity is not necessary for solar cells, which is why solar cell manufacturers usually obtain silicon from waste from the electronics industry, which is still extremely pure.

Author: Martin Rosenberg