Tommi Kääriäinen

Roll-to-roll atomic layer deposition process for flexible electronics encapsulation applications

At present flexible electronic devices are under extensive development and, among them, flexible organic light-emitting diode displays are the closest to a large market deployment. One of the remaining unsolved challenges is high throughput production of impermeable flexible transparent barrier layers that protect sensitive light-emitting materials against ambient moisture. The present studies deal with the adaptation of the atomic layer deposition (ALD) process to high-throughput roll-to-roll production using the spatial ALD concept. We report the development of such a process for the deposition of 20 nm thickness Al2O3 diffusion barrier layers on 500 mm wide polymer webs. The process uses trimethylaluminum and water as precursors at a substrate temperature of 105 °C. The observation of self-limiting film growth behavior and uniformity of thickness confirms the ALD growth mechanism. Water vapor transmission rates for 20 nm Al2O3 films deposited on polyethylene naphthalate (PEN) substrates were measured a...

Continuous atomic layer deposition: Explanation for anomalous growth rate effects

Spatial atomic layer deposition (ALD) on moving substrates has recently been the subject of increasing interest and development. Recent results of deposition on flexible substrates in a cylindrical rotating continuous ALD system showed that in certain regions of operation, deviations from ideal ALD behavior occurred showing excess deposition during the trimethylaluminium (TMA)/water process for aluminum oxide. It was speculated that this was due to boundary layer gas entrainment at the surface of the moving substrate and consequent drag-through of precursors between the different precursor vapor zones. In this paper a study has been made of these gas entrainment effects by using helium as a tracer gas to determine how the transport between zones takes place. A simple model of the process based on physical principles has been constructed which replicates the observed helium transport behavior in the boundary layer. Based on this, it has been shown that gas entrainment is not the reason for the anomalous ex...

Nanoscratch testing of atomic layer deposition and magnetron sputtered TiO2 and Al2O3 coatings on polymeric substrates

Titania and alumina thin films are commercially important materials, finding a wide variety of applications. These materials are commonly deposited onto glass substrates by reactive magnetron sputtering techniques, or more recently by atomic layer deposition (ALD). Such films have been well-characterized in terms of their structures and properties, including their nanomechnical and nanotribological properties. There is increasing demand, though, to deposit thin (<100 nm) functional films onto polymeric substrates, which can provide cost and weight savings and opens up the potential of deposition in large throughput roll-to-roll coating systems. However, polymeric substrates impose severe limitations due to both their thermal and mechanical properties. In the former case, production is restricted to low temperature processes and in the latter case, the substrate offers negligible load support for the thin ceramic coating. While nanoindentation and nanotribological testing of thin ceramic coatings on rigid ...

Surface modification of acetaminophen particles by atomic layer deposition

Active pharmaceutical ingredients (APIs) are predominantly organic solid powders. Due to their bulk properties many APIs require processing to improve pharmaceutical formulation and manufacturing in the preparation for various drug dosage forms. Improved powder flow and protection of the APIs are often anticipated characteristics in pharmaceutical manufacturing. In this work, we have modified acetaminophen particles with atomic layer deposition (ALD) by conformal nanometer scale coatings in a one-step coating process. According to the results, ALD, utilizing common chemistries for Al2O3, TiO2 and ZnO, is shown to be a promising coating method for solid pharmaceutical powders. Acetaminophen does not undergo degradation during the ALD coating process and maintains its stable polymorphic structure. Acetaminophen with nanometer scale ALD coatings shows slowed drug release. ALD TiO2 coated acetaminophen particles show cytocompatibility whereas those coated with thicker ZnO coatings exhibit the most cytotoxicity among the ALD materials under study when assessed in vitro by their effect on intestinal Caco-2 cells.

Atomic layer deposition of cerium oxide for potential use in diesel soot combustion

The particulate soot emission from diesel motors has a severe impact on the environment and peoples health. The use of catalytic convertors is one of the ways to minimize the emission and decrease the hazard level. In this paper, the activity of cerium oxide for catalytic combustion of diesel soot was studied. Thin films of cerium dioxide were synthesized by atomic layer deposition using tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)cerium [Ce(thd)4] and ozone as precursors. The characteristics of the films were studied as a function of deposition conditions within the reaction temperature range of 180–350 °C. Thickness, crystallinity, elemental composition, and morphology of the CeO2 films deposited on Si (100) were characterized by ellipsometry, x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy, and field emission scanning electron microscopy, respectively. The growth rate of CeO2 was observed to be 0.30 A/cycle at temperatures up to 250 °C with a slight increase to 0.37 A/...

Atomic layer deposition—A novel method for the ultrathin coating of minitablets

We introduce atomic layer deposition (ALD) as a novel method for the ultrathin coating (nanolayering) of minitablets. The effects of ALD coating on the tablet characteristics and taste masking were investigated and compared with the established coating method. Minitablets containing bitter tasting denatonium benzoate were coated by ALD using three different TiO2 nanolayer thicknesses (number of deposition cycles). The established coating of minitablets was performed in a laboratory-scale fluidized-bed apparatus using four concentration levels of aqueous Eudragit® E coating polymer. The coated minitablets were studied with respect to the surface morphology, taste masking capacity, in vitro disintegration and dissolution, mechanical properties, and uniformity of content. The ALD thin coating resulted in minimal increase in the dimensions and weight of minitablets in comparison to original tablet cores. Surprisingly, ALD coating with TiO2 nanolayers decreased the mechanical strength, and accelerated the in vitro disintegration of minitablets. Unlike previous studies, the studied levels of TiO2 nanolayers on tablets were also inadequate for effective taste masking. In summary, ALD permits a simple and rapid method for the ultrathin coating (nanolayering) of minitablets, and provides nanoscale-range TiO2 coatings on porous minitablets. More research, however, is needed to clarify its potential in tablet taste masking applications.