Thin Films in Everyday Life
Thin film has become an essential aspect of human life, so that hardly can we find any field of activity where they are not present. The first use of thin films for optical purposes can be dated to exactly 1912. Pohl and Pringsheim published the famous work about the production of mirrors using a vaporization process of metals like Ag and Al out of a MgO crucible in high vacuum.
After that, thin film coatings use has extended to many other applications in the optics industry like e.g. anti-reflective coatings, scratch-resistant coatings, uv- and IR-reflective coatings, etc. In parallel, many other technological fields began to benefit from this technology: decorative coatings, tribologic coatings, biomedical coatings, self-cleaning coatings, etc.
One of the fields where thin films are not only useful, but also they constitute the key manufacturing technology, is the industry of semiconductors, which includes: telecommunications devices, integrated circuits (I.C), transistors, solar cells, LEDs, photoconductors, LCDs, magneto-optic memories, compact discs, electro-optic coatings, memories, flat-panel displays, smart windows, computer chips, magneto-optic drives, microelectromechanical systems (MEMS), and multifunctional coatings.
Follows a brief description about how thin film has found application in everyday life.
Thin film in optical coating
Optical coating involves depositing one or more layers of a metallic and/or ceramic material over an optical material such as a glass- or plastic-made lens, aiming to alter its transmission and reflection properties. The use of anti-reflective coating is an example of optical coating which reduces reflection of optical surfaces, e.g. photographic lenses. This effect can be obtained without significatively altering the cost of the component, since the substrate material, and the relative manufacturing technologies, remains the same, while the cost of the coating itself is remarkably low.
Another application of thin film in the optical coating fields is in thin film polarizers. Thin film polarizers are optical polarizers that are based on the interference effect in a thin film dielectric layer; they are used, for example, to reduce glare and flare in optical systems, or as a fundamental component of LCD displays.
Thin film in preventing corrosion and wearing
Thin films help in preventing the corrosion of metallic parts of many devices as well as protect against wear. Materials such as jewelry, wrist watches, and knives are often coated to avoid corrosion. Thin film coatings are used also as anti-tarnish protection for some sensitive materials, like Silver, in jewelry applications.
Metals such as chromium and zinc are commonly used for the coating to prevent corrosion, while some extremely hard ceramic materials like titanium nitride, chromium nitride and alumina are used for preventing wearing of devices and tools.
Thin film in a semiconductor
Integrated circuits and also discrete semiconductor devices are made from a stack of thin films of conductive, semiconductor, as well as insulating materials. Thin films are deposited on a very flat substrate when making an integrated circuit, often made of silicon or silicon carbide. Then, a carefully designed stack of thin films is deposited over this substrate -which is also known as the “wafer”, while each layer is carefully patterned using lithographic technologies, thus allowing for the manufacturing of a very large number of active and passive devices at the same time.
Each tiny device is in turn made from the interconnection of differently-doped thin film layers, and the interconnection between different devices is managed by the use of thin-film metallic layers, usually made with aluminum or copper. This technology led to the possibility of miniaturization of many fundamental semiconductor devices, like BJTs, FETs, MOSFETs and diodes, which -in turn- allowed for the manufacturing of the modern computers, memories and high-performance integrated circuits.
Thin film in Optoelectronics
Another field where thin film technology has become fundamental is optoelectronics. With technologies similar to that employed for the manufacturing of integrated circuits (deposition/lithography), the manufacturing of some very important devices in today’s life is possible: LED and OLED devices for lighting and for display applications, LCDs, CMOS sensors for video cameras, etc.
Remarkably, thin film technology allows also for the deposition of electrically conductive, transparent films: for example, indium tin oxide (ITO) coatings are often used in the form of plain and see-through electric conductive electrodes.
Thin film technology has also been used to produce thin-film batteries which have been then be inserted into chips.
Thin film in protective and decorative coatings
Thin films are used for protecting the surface of many material, especially optical elements, from wear, scratches, fingerprints, and even from corrosion. A protective thin film coating, can also possess secondary functions, like e.g. a decorative effect, modifying the surface glossiness, its apparent color, and its texture.
Sometime, thin films are used purely for decorative purposes, like in the case of metallic coatings made over a plastic substrate, which can be made also using an evaporation processes, under high-vacuum conditions, avoiding the harmful traditional processes base on galvanic deposition.
Thin film in solar cells
The depletion of fossil fuels and climatic change has made the use of renewable energy sources more prominent. For what concerns the use of solar energy as a viable mean for the production of energy with sustainable processes, there are two established technologies available: thermal solar, and photovoltaic.
Thermal solar systems convert energy from the sun (radiant energy) into thermal energy with the help of a energy exchanger called the solar collector. The solar collector is of two types; concentrating and non-concentrating. Thin films play a role in the coating of the solar collector which enhances the photo-thermal conversion efficiency.
The second technology i.e. photovoltaic is dominated by the use of silicon-based cells, which -in their manufacturing process- need the deposition of some thin-film functional layers to enhance their efficiency. Moreover, the niche technology of thin-film solar cells contributes to the manufacturing of very-high efficiency photovoltaic cells, which are used in room-critical applications (e.g. telecom satellites, military, etc.), where high reliability and efficiency are the key figures of merit.
Thin film in the Nanotechnologies
The application film in nanotechnology is one of the most recent advances in the study of thin films. This involves coating with nanocomposite materials thereby giving the materials improved mechanical properties due to a so-called “size effect”. The final functional effects which can be obtained are: oxidation resistance, high adherence, low thermal conductivity, wear-resistance, higher toughness, and hardness. In this field, primarily the magnetron sputtering method is used for deposition, due to the high purity and low level of defects which are allowed by this process.
In conclusion, the role thin films play in our day to day lives is endless as many more inventions are being made in the study of thin films. Thin film technology has been used so far from the textile or fabrics industry, to the gadgets, utensils, vehicles, tools, constructions (roads), medical examination, decoration, etc., all of which are products very useful in our everyday’s life.
Thin film technologies have played a vital role in making life easier for everybody.