Thin films measuring anywhere from less than a nanometer to a few micrometers thick are far too thin and delicate to handle without the aid of a substrate. The films must be created on the surface of a substrate and remain attached to this material after they are made. There are many different types of thin film substrates, and engineers chose a substrate based on the intended use of the thin film. The substrates can be made out of metal, ceramic, glass, plastic or combinations of these materials.
Ceramic thin film substrates are used for a variety of thin films, including those intended for use in electronics. Superconductors, semiconductors and microchips commonly use a thin film that is grown on a ceramic substrate. Some common ceramic substrates are alumina, beryllia and aluminum nitride.
Alumina is the most commonly used ceramic substrate largely because the materials used to create it are readily available and inexpensive. The material is durable, conducts heat well and is resistant to strong acids and bases. Beryllia is another common choice because it has a high melting point and is an excellent insulator.
A material that remains stable up to 2,498 degrees Fahrenheit (1,370 degrees Celsius), aluminum nitride is a another one of the most common ceramic thin film substrates. It also conducts heat rapidly and does not expand when heated. The chemicals used to make the substrate do not react with those used in typical semiconductors. This material is often used for heat sinks, microwave devices, power transistors and in materials used to handle objects at high temperatures.
Glass or clear plastic are commonly used thin film substrates found in optical devices, such as microscopes and telescopes. These substrates can be outfitted with various thin film lenses, which can be designed to perform a variety of functions. They can narrow the range of light frequencies that are allowed through a lenses or enhance certain frequencies of light. Different lenses are designed to different specifications, and a single substrate of glass can be outfitted with a number of different thin film filters that change the qualities of light in a number of different ways.
Some metals can also be used as thin film substrates. The properties of specific metals are used to determine which thin films they would best support. Metallic substrates are used in a variety of thin film devices, including some electronic devices.
