TCO and ITO Coatings

THE HEX SERIES

Transparent Conducting Oxides and Indium Tin Oxide

Many day-to-day items rely on transparent, conductive coatings to operate from windshields to touch screens. Glass in its pure form is not a great conductor of either heat or electricity and so for certain applications, a thin layer of material is needed to provide this functionality whilst maintaining the overall transparency. 

Transparent conducting oxides (TCOs) including indium tin oxide (ITO) can be coated to greatly alter the properties of glass, mylar or other transparent substrates when deposited as a thin film and unlock optoelectronic device applications. The main benefits of this TCO layer are the improvement of the conductivity and changing of the optical properties with the coated substrate. 

The thickness of the coating can vary depending on the application, with thicker TCO layers offering greater conductivity, but at the cost of reduced transparency. ITO is also very stable under heat loads of below 150 °C but can also be used in high-temperature applications such as strain gauges due to its high melting point and stability in air at high temperatures. 

Another key aspect of TCO coatings is their resistance to electromagnetic wave penetration. ITO-coated substrates can offer electromagnetic interference (EMI) and radiofrequency interference (RFI) protection for electronic displays, touchscreens and flexible membrane switches that must retain their transparency. 

TCO and ITO films can be deposited onto substrates via CVD, spin-coating and ink polymer-resin processes but is most commonly deposited through PVD. Korvus Technology has over 20 years of experience working within the PVD field and is the manufacturer of the HEX series of PVD instruments. These tools can be configured to allow for the optimised deposition of ITO coatings through magnetron sputtering, remote plasma sputtering and E-Beam evaporation processes. 

Due to the conductive nature of ITO targets, DC magnetron sputtering processes can be used to achieve high levels of uniformity across various wafer and substrate sizes. We recommend using the Korvus custom-tiltable FISSION 3’’ magnetrons to curate a balance between uniformity, target usage and deposition rate suitable to your process. Altering the source to sample distance is also crucial for ITO deposition to control the electron interactions between the generated plasma and the sample. 

Frequently Asked Questions

ITO coatings in PVD refer to thin films of Indium Tin Oxide (ITO) deposited using Physical Vapour Deposition (PVD) techniques. ITO is a transparent conducting oxide (TCO), meaning it is optically transparent and electrically conductive – a rare and extremely useful combination. It is widely used in applications where light needs to pass through a conductive surface. 

ITO coatings are commonly used in many applications such as: 

Touchscreens and smartphone displays

Flat panel displays (LCD, OLED, LED)

Solar cells (especially perovskite and organic photovoltaics)

Smart windows and electrochromic devices

Light-emitting diodes (LEDs)

Thin-film transistors and sensors

Typically 90% Indium Oxide (In₂O₃) + 10% Tin Oxide (SnO₂) (by weight)

This specific ratio balances:

  • High electrical conductivity
  • High optical transparency (especially in visible light)
  • Good adhesion and durability

There are several PVD methods to create ITO coatings:

1. RF or DC Magnetron Sputtering (most common)

Target: Pre-made ITO ceramic target

Process: Argon gas bombards the target, sputtering ITO atoms which deposit onto the substrate

Reactive mode (e.g., with O₂) can be used to tune stoichiometry

Can be done at room temp or elevated temp (~200–400 °C) for better crystallinity

2. Thermal or Electron Beam (E-Beam) Evaporation

Less common for ITO due to its high melting point and complex composition#

Needs special care to avoid phase separation of In and Sn during deposition Often followed by post-deposition annealing to improve conductivity and transparency

ITO properties can be optimised by adjusting:

 Oxygen partial pressure during sputtering (too little = poor transparency; too much = poor conductivity) 

Substrate temperature 

Post-deposition annealing 

Film thickness and deposition rate

This balance is critical depending on the application:

Solar cells: Maximise transparency and minimise resistive losses

Touchscreens: Prioritise conductivity and uniformity

Flexible electronics: Need good adhesion and possibly low-temp processing

In perovskite solar cell research, ITO is commonly used as the bottom electrode because it’s:

Transparent (lets light in)

Conductive (collects or injects charge)

Compatible with PVD and spin-coating processes