Utilizing Functional Films in Glass Substrates

Glass is an incredibly versatile material. For example, tempered glass can be produced by simply altering the heating and cooling process during manufacturing. The shape of glass lenses can be changed to modify their optical characteristics, while adding pores into bulk glass facilitates an array of high-tech applications such as catalyst supports and bio-scaffolds.

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Changing the chemical composition of glass, such as through the use of glass modifiers, can alter almost all of its properties, allowing the production of high-resistance electrical components and corrosion-resistant labware.

By depositing films on glass, the properties of glass can be augmented without changing the glass itself. From heating elements integrated directly onto glass surfaces to thin-film solar cells, these films allow the development of components and products to combine the properties of glass with those of other technologies and materials.

Film deposition can be separated into two categories: thick and thin film deposition. There is some overlay between the thicknesses of films in these categories. However, “thick films” and “thin films” remain distinct, mainly due to the differences in the technology used to construct them. 

Thin films range from less than one nanometer to several microns in thickness and are usually produced using sophisticated processes such as vapor deposition. In comparison, thick films generally range from several microns up to a millimeter in thickness. Thick films are typically deposited in pastes or inks via tape-casting or screen-printing processes.

Depositing Thick Films on Glass

Electronics

Thick films are used widely in electronics. Here, alternating layers of resistive and conductive materials can be deposited and patterned onto a substrate to build up electric circuits. While ceramic substrates are common, these films are often deposited onto glass instead.

When applied this way, thick films are usually deposited on glass via screen printing, forming layers from 5 to 20 μm thick.

Insulating thick film pastes often contain glass in the form of frit, which provides high resistivities.⁷ After deposition, these thick films are typically fused at high temperatures before the next layer is deposited. This provides a low-cost and reliable production route for microelectronic devices.

An alternative application of thick films is the production of printed heater elements on glass substrates.⁸ The direct deposition of a heating element onto glass allows the manufacture of self-defrosting windows or glass appliances (such as cookers or kettles) which provide uniform heating with the modern appearance of glass.

Low-cost fabrication and versatility are some of the advantages thick films offer, making them perfect for manufacturing electronic components across various industries. For precision applications, however, thin film technologies have much greater control over surface characteristics and film thickness.

Depositing Thin Films on Glass

Optics

One primary application area of thin films on glass is in optics. The most widely known application of thin films is probably the household mirror. Here, the mirrors are manufactured by depositing a thin metal layer on the back of a sheet of glass that increases its reflectivity.

Optical interference effects can be produced by depositing thin films on glass. This can result in particular regions of wavelengths being absorbed, reflected, or transmitted.² These films alter light because of their nanoscale structure rather than the color of the bulk material itself. This allows for the precise tuning of optical parameters such as the color of transmitted light and reflectivity by changing layer thickness.

The wings of some butterfly species use the same fundamental “optical thin film” principles to create their remarkable iridescent coloring.³

Low emissivity, or “Low-e”, glass is a significant application of thin film deposition on glass, manufactured by the successive deposition of thin metal oxide films on glass.

This makes the reflection of radiated heat possible (i.e., the infrared portion of the spectrum) while transmitting visible light.

Such optical films enable Low-e windows to reflect the sun’s light in hot environments or to prevent heat loss through windows in cold environments.

These films can support anti-reflective coatings, reducing glare in architectural applications and consumer electronics.

High-precision deposition of thin optical films facilitates the manufacture of specialist optical filters such as dichroic filters. These filters require exceptionally precise film deposition to transmit or reject specific wavelength bands for precision applications in industry and research.

Electronics

Glass substrates for thin films have several vital roles in electronics, particularly in producing transparent conducting films (TCFs). TCFs are a type of film made of electrically conductive and optically transparent materials.

They are manufactured by growing or depositing thin films of materials, such as metal oxides or graphene, on glass substrates. Here, the glass offers the additional benefit of blocking infrared wavelengths of light. TCFs are applied in various devices, including LCD and OLED displays, touchscreens, and photovoltaic panels.⁴

Directly depositing conductive traces onto glass substrates allows circuitry and functional electronic components to be integrated into glass, with widespread applications in consumer electronic devices (including smartphones), automobiles, and aviation.⁵ 

Additional applications of thin films on glass substrates in electronics include the manufacture of transparent electrodes and thin film resistors produced by sputtering metal films onto glass⁶.

Mo-Sci is an expert in creating custom glass solutions for demanding and unique applications, whether that is ultra-pure glass frit for the production of resistive thick film pastes or glass substrates for a specific thin film application.

References

1. Bach, H. & Krause, D. Thin Films on Glass. (Springer Science & Business Media, 2003).
2. Anderson, A.-L., Chen, S., Romero, L., Top, I. & Binions, R. Thin Films for Advanced Glazing Applications. Buildings 6, 37 (2016).
3. Butterflies Hack Light Waves to Produce Brilliant Color — Biological Strategy — AskNature. https://asknature.org/strategy/wing-scales-cause-light-to-diffract-and-interfere/.
4. Rosli, N. N., Ibrahim, M. A., Ahmad Ludin, N., Mat Teridi, M. A. & Sopian, K. A review of graphene based transparent conducting films for use in solar photovoltaic applications. Renewable and Sustainable Energy Reviews 99, 83–99 (2019).
5. Kim, H.-G. & Park, M.-S. Fast Fabrication of Conductive Copper Structure on Glass Material Using Laser-Induced Chemical Liquid Phase Deposition. Applied Sciences 11, 8695 (2021).
6. Thin Film Applications | Bourns. https://www.bourns.com/pdfs/thinfilm.pdf.
7. Zargar, R. A. & Arora, M. Screen Printed Thick Films on Glass Substrate for Optoelectronic Applications. in Photoenergy and Thin Film Materials (ed. Yang, X.) 253–282 (Wiley, 2019). doi:10.1002/9781119580546.ch6.
8. Radosavljevic, G. & Smetana, W. 15 – Printed heater elements. in Printed Films (eds. Prudenziati, M. & Hormadaly, J.) 429–468 (Woodhead Publishing, 2012). doi:10.1533/9780857096210.2.429.

This information has been sourced, reviewed and adapted from materials provided by Mo-Sci.

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