Coating technology

A further step towards Printed Electronics

With the growing market for high-resolution panels, display makers are looking for high-mobility materials that can replace traditional semiconductors like amorphous silicon (a-Si) and low temperature polysilicon (LTPS). In recent years, metal oxide semiconductors like indium-gallium-zinc-oxide (IGZO) have become well known and fully investigated for their high mobility, reliability and other outstanding values (see section Metal oxides). To apply conventional metal oxides on the substrate, mainly sputtering (= physical vapor deposition) and chemical vapor deposition (CVD) are being used nowadays, yet processing seems to be very challenging.

With the possibility to coat its unique iXsenic metal oxide semiconductor, Evonik has developed a superior alternative to these traditional techniques which offers the following advantages:

  • Solution-processed metal oxides can be deposited in ambient conditions, i.e. no vacuum is necessary. As a consequence, the throughput is higher while process costs and CAPEX are lower.

  • The coating process is well established and used for numerous other materials in the industry (e. g. photo resist). It is therefore easy to implement into existing production lines. Another advantage that comes along with the mature coating technology is large area uniformity as well as scalability.

  • The film composition is controlled directly by the formulation. It guarantees stable results (stoichiometric homogeneity) and also allows adjusting to different compositions upon the customer’s request at any time.

  • For its process sensitivity, an etch-stop layer is necessary in current sputtered metal oxide TFT design. With our solution-processed metal-oxide materials, a modified film is generated by changing the composition and stoichiometry that resists the etchant of metal electrodes. Such superior material can realize a back channel etching (BCE) TFT with one mask less, resulting in savings compared with the sputtering technology.

  • Evonik is working on transforming the coating into a printing technology, e.g. inkjet printing. Additionally, this will increase production throughput and lower process costs.

Evonik is confident that, with the dramatically growing market of high-end display applications, solution-processed metal oxides are already now a serious alternative to the established technologies.