Plasma-enhanced atomic layer deposition of highly homogenous and pure TiO2 thin films for gas barrier applications
Maximilian Gebhard, Chemistry of Inorganic Materials, Ruhr-Universität Bochum, Bochum, GermanyFelix Mitschker, Electrical Engineering and Plasma Technology, Ruhr-Universität Bochum, Bochum, GermanyMartin Wiesing, Macromolecular and Technical Chemistry, Paderborn University, Paderborn, GermanyIgnacio Giner, Macromolecular and Technical Chemistry, Paderborn University, Paderborn, GermanyBoray Torun, Macromolecular and Technical Chemistry, Paderborn University, Paderborn, GermanyTeresa de los Arcos, Macromolecular and Technical Chemistry, Paderborn University, Paderborn, GermanyPeter Awakowicz, Electrical Engineering and Plasma Technology, Ruhr-Universität Bochum, Bochum, GermanyAnjana Devi, Chemistry of Inorganic Materials, Ruhr-Universität Bochum, Bochum, Germany
Titanium dioxide (TiO2) is used in a vast number of applications, ranging from self-cleaning coatings and photocatalysis to semiconductor devices. More recently, amorphous TiO2 attracted a lot of attention as gas barrier layers (GBLs) and the improvement of packaging materials like polyethylene terephthalate (PET) and polypropylene (PP). The dense amorphous structure of this material contributes to higher barrier performances while high stress durability can be preserved. In this context, the protection of sensitive goods like food, pharmaceuticals and advanced electrical devices (OLEDs) is of high importance. It was shown that materials such as SiOx, Al2O3 or TiO2 show promising barrier performance in terms of oxygen transmission rate (OTR) and water vapor transmission rate (WVTR). In addition, when compared to established GBLs fabricated from organic compounds, like ethylene vinyl alcohol (EVOH), only a few nanometer thin film of the above mentioned materials is necessary to reduce both OTR and WVTR by several orders of magnitude. Furthermore, these materials are easier to handle, microwaveable, can be recycled and show high transparency.
The fabrication of promising GBLs depends on the deposition technique. Respective thin films must exhibit high homogeneity even over large areas, free of pinholes and should adhere to the underlying substrate. Plasma enhanced atomic layer deposition (PE-ALD) processes offer the possibility to deposit highly uniform thin films that are dense and free of pinholes, achieved by the self-saturating steps of ALD. In addition, plasma species can cause a higher degree of cross-linking during film formation as well as substrate temperatures below the glass point of several polymers are sufficient for successful depositions without damaging the underlying substrate.
We present the comparison of two PE-ALD processes using TDMAT or TDMADT, the growth on Si(100) and the respective analysis using different techniques like XRD, AFM and RBS/NRA. In addition, thin films were deposited on PET to investigate GBL performance.
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 M. Gebhard. F. Mitschker, M. Wiesing, I. Giner, B. Torun, T. de los Arcos, P. Awakowicz, G. Grundmeier and A. Devi, J. Mater. Chem. C, 2016, 4, 1057.