Extremely thin layers of glass are an attractive proposition for many engineering applications. For example, coating steel components in glass could impart protection against corrosion, while layering microelectronic circuitry with glass could provide dielectric protection. However, producing extremely thin pieces of glass can be challenging, especially via conventional routes such as float glass manufacturing. Instead, for this type of application, glass can be deposited directly onto surfaces to form a film.
Thin Glass Films vs. Thick Glass Films
Glass films can be broadly divided into two categories: thick films and thin films. While thin glass films are, of course, generally thinner than thick glass films, there is some overlap — so in some cases, a “thick film” can actually be thinner than a “thin film.”
In fact, thin and thick glass films are generally differentiated on the basis of the manufacturing technique used. Thin glass films, which generally range from sub-nanometer to several microns in thickness, tend to be produced by vapor deposition techniques, in which vaporized silicon compounds are oxidized, and the resulting silicon oxide (glass) condenses on a substrate.
Thick glass films, on the other hand, range in thickness from several microns to several millimeters and are usually deposited in the form of suspensions such as slurries, pastes, or inks. Thick film techniques include the likes of screen printing and tape-casting.
Applications of Thick Glass Films
Glass is widely used as a sealing material thanks to its tunable coefficient of thermal expansion.1 This means that glass seals can be tailored so that their thermal expansion properties match those of the components they form a seal between, thus producing a reliable seal in applications that involve thermal cycling.
Glass seals are manufactured using thick film methods. Glass is first prepared in a powder form, with glass composition and particle sizes tuned to the specific application. The powdered glass is mixed with an agglomeration agent, then applied directly to a component with the help of robotic dispensers, tape casting, or screen printing. Finally, the entire assembly is heat treated, typically for several hours, in a furnace to melt and vitrify the glass powder into a bonded glass seal.2
Glass seals are widely used in energy storage where seal integrity across a wide temperature is critical — in particular for sealing solid oxide fuel cells and metal ion and thermal batteries. Glass is also used to provide high-performance seals in high-temperature sensors and sensitive perovskite photovoltaic cells.
Tape casting — in which a suspension of powdered ceramic or glass is cast in a thin, “tape” like layer across a flat surface before drying and sintering — is also used in the manufacture of electronics. Glass boasts excellent dielectric properties and creates a strong anti-corrosion barrier for sensitive electronics, making such tape-cast coatings valuable in the production of single-layer or laminated microelectronic circuits and components.3 In particular, thick glass films are very widely used for thick film resistors, which are the most common type of resistor available today.4
Glass coatings can be directly applied to stainless steel to provide protection against corrosion and high-temperature oxidation. Such coatings are widely used to make corrosion-resistant steel tanks and silos. Like glass seals, glass coatings can be tuned for thermal and mechanical compatibility with a substrate, making them suitable for a wide range of materials, including titanium and titanium superalloys.5
Applications of Thin Glass Films
Thin glass films can be produced through vapor deposition processes, including physical vapor deposition (PVD) and chemical vapor deposition (CVD), to vaporize solid material into individual molecules. The vaporized material can then either condense on a substrate (PVD) or chemically react with the substrate (CVD) to form a thin film coating. In the case of glass, vapor deposition processes often start with a silicon-containing precursor compound such as hexamethyldisilane. These precursors can be heated to produce vapor, which is then oxidized to form silicate (the primary ingredient of glass) and deposited on a substrate.
Vapor deposition processes typically produce extremely pure glass. In addition, the glass produced tends to be extremely stable compared to conventionally produced glass. Both of these qualities give vapor-deposited glass the edge for specialist applications.
Vapor-deposited glass is widely used for the production of specialist optical components, including optical fibers and telescope mirrors. Thin glass films produced using vapor deposition are particularly useful in electronics applications and are currently used in OLED displays and cellphone screens, with applications in organic electronics (such as photovoltaics) expected to increase.
Partnering with clients across multiple industries, Mo-Sci specializes in developing unique glass solutions for virtually any application. From prototyping through to commercialization, Mo-Sci offers unparalleled expertise in glass production and processing, including thin and thick glass film technologies. To find out more about our capabilities and solutions, get in touch with us today.
References and Further Reading
- Sealing Glass – Mo-Sci Corporation.
- Processing technologies for sealing glasses and glass‐ceramics – Pablos‐Martín – 2020 – International Journal of Applied Glass Science – Wiley Online Library. https://ceramics.onlinelibrary.wiley.com/doi/full/10.1111/ijag.15107.
- Yu, T., Ju, K., Liu, J. & Li, Y. Tape casting and dielectric properties of SiO 2 -filled glass composite ceramic with an ultra-low sintering temperature. Journal of Materials Science: Materials in Electronics 25, (2014).
- Thin and Thick Film | Resistor Materials | Resistor Guide. https://eepower.com/resistor-guide/resistor-materials/thin-and-thick-film/.
- Chen, M., Li, W., Shen, M., Zhu, S. & Wang, F. Glass coatings on stainless steels for high-temperature oxidation protection: Mechanisms. Corrosion Science 82, 316–327 (2014).