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Transparent Conducting Oxides (TCOs)


Transparent Conducting Oxides

Our Transparent Conducting Oxides (TCOs) can be used to support many different applications:

  • Photovoltaics

  • Flat panel displays

  • Flexible applications (Low temperature process)

Thin film TCOs play a major role in the fabrication of a wide range of devices from mobile phones and flat panel displays to solar cells and architectural glass applications. In any TCO coating, the requirement is for a thin film that is both electrically conducting and transparent to visible light. As one might expect, these two demands are not mutually compatible and hence there is active research into improving existing TCO materials as well as developing new ones that exhibit improved transparency and electrical conductivity. With the rapidly growing transparent and flexible electronics market there is also intense research into developing new transparent conducting materials that can be deposited onto plastic substrates.


One of the most widely used TCOs is Indium Tin Oxide (ITO). ITO is almost exclusively now used as a transparent electrode for a vast range of display and lighting devices. Using PQL’s HiTUS technology we can deposit ITO using no substrate heating with an average visible transmission of 90 % and a specific resistivity of less than 4.0 × 10-4 Ωcm. The absence of any substrate heating allows our ITO to be used for both rigid and flexible applications. However, indium is reportedly in short supply which is driving up the cost of the raw material and intensifying the search for alternative non-indium based TCOs. At Plasma Quest Limited we have many years of experience in depositing a range of TCO materials including ITO and Aluminium-doped Zinc Oxide (AZO), one of the most promising alternatives to ITO for transparent electrode applications.


Zinc Oxide (ZnO) and Indium doped Zinc Oxide (IZO) are other TCO materials that we have deposited for thin film transistor (TFT) applications. By varying the partial pressure of oxygen, the conductivity of HiTUS deposited ZnO can be controlled. Conducting ZnO has been used effectively to ensure a high quality Ohmic contact between the top contacts and the channel layer. By increasing the oxygen partial pressure, semiconducting ZnO can be deposited and has been successfully used for the channel layer in TFTs grown on glass. Using amorphous IZO as the channel layer, TFTs with improved field effect motilities and switching ratios of 20 cm2V-1s-1 and 106 respectively have been fabricated onto silicon wafers. These improvements in the transistors’ characteristics have been linked to the absence of grain boundaries in the IZO material. More detailed information on the use of HiTUS deposited ZnO and IZO for TFT applications can be found in the following publications written in collaboration with Cambridge University



The flexibility and control that the HiTUS system provides for thin film deposition enables us to vary parameters such as transmission, band gap, resistance, stress, surface roughness, structure, carrier concentration and mobility in order to tailor materials to specific needs. Using remotely generated plasma, PQL can deposit any of the above materials onto temperature sensitive plastic substrates making them suitable for a wide range of flexible electronics applications.

Download printable version of Transparent Conducting Oxides on Flexibles.pdf
Download printable version of ITO summary June09.pdf
Download our latest publication on ITO films.pdf

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