Thin films are layers of ferromagnetic, semiconductor or ceramic materials not more than 1μm thick which are used in a number of applications like electronics and optics. Semiconductor device technology greatly benefits from thin film construction. Solar cells, also called photovoltaic cells, can be manufactured cheaply.
Applications of thin film technology
Silicon, both crystalline and amorphous, is widely used in thin film technology. Many electronic devices are manufactured using thin films. This has particularly benefited photovoltaic systems.
Ferromagnetic thin films are beginning to be used in the manufacture of computer memory.
Electroplating is a technique that uses thin film deposition on metals.
Thin films are used to make reflective or non-reflective surfaces in optical devices.
Ceramic thin films are commonly used in making coatings for the protection of tools and other metallic equipment from corrosion and oxidation because of their excellent hardness and chemical inertness. Also, as a result of their sacrificial wear, ceramic thin films prevent machinery and equipment from early damage.
How thin films are deposited
Thin films are deposited onto substrate material or onto layers of materials that have been previously deposited by a number of modern techniques. Thin film technology is also applied in the new field of nanotechnology, which may require the deposition of layers of materials atom by atom.
The process of deposition depends on whether chemical means are deployed, or mechanical. Chemical means involve a so-called ‘fluid precursor’ that leaves behind a thin coating on the solid surface after initiating a chemical reaction. The fluid precursor may be a liquid reagent, often with a dissolved salt of the metal to be deposited on the required surface. This method is commonly used in electroplating of metals.
The fluid could also be a gas, as in the metal-organic chemical vapour deposition (MOVCD) which is used to facilitate the epitaxial growth of layers of semiconducting materials on a substrate. Usually, a gas which is the hydride or halide of the element to be deposited is used for the reaction. Precursor gases are used at very low pressures.
Mechanical processes involve the deposition of certain materials onto substrates by physical means like thermal evaporation and electron beam evaporation. The first method is suitable for the deposition of metals with high vapour pressures while the second is suitable for the deposition of metals with low vapour pressures. To eliminate the problem of uneven evaporation of the metal to be deposited, a new method called sputtering is used. This involves the use of a noble gas like argon in order to dislodge atoms one by one.
Other important methods are reactive sputtering, in which oxygen or nitrogen may be used in order to deposit an oxide or nitride of the target material and molecular beam epitaxy (MBE), in which a stream of the metal to be deposited is directed to the substrate.