Browsing by Author "Karppinen, Maarit, Acad. Prof."

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High-k ternary rare earth oxides by atomic layer deposition
(2010) Myllymäki, Pia
Aalto-yliopiston teknillinen korkeakoulu | Doctoral dissertation (article-based)
The present thesis describes atomic layer deposition (ALD) of ternary rare earth (RE) oxides and characterization of compositional, structural and electrical properties of the films. The REScO3, LaLuO3 and ErxGa2-xO3 thin films investigated are potential high-κ materials for future metal-oxide-semiconductor field-effect transistors, i.e. MOSFETs. The dissertation consists of five peer reviewed publications. As a background for the work, issues related to the miniaturization of MOSFETs and the feasibility of rare earth oxides as new high-κ dielectrics are discussed. Also some challenges of manufacturing Ga-based MOSFETs with high quality gate oxide having satisfactory interface properties and the role of rare earth oxides in GaAs passivation are presented. In addition the basic principle of the ALD method is briefly introduced and recent literature concerning deposition of rare earth oxides is reviewed. A series of REScO3 thin films was deposited by ALD using rare earth β-diketonate precursors RE(thd)3 together with ozone. The films were characterized for growth rate, elemental composition, crystallization upon annealing and electrical properties. Amorphous films of high quality with low impurity contents and promising electrical characteristics were produced. Several gradually evolving properties of the films were examined and the effect of the RE3+ cation size was discussed. YScO3 films were also deposited using novel cyclopentadienyl metal precursors and water. Deposition of LaLuO3 films having similar properties but even higher dielectric constant (κ ≈ 30) than ternary scandates was examined at two different temperatures. The relationship between the crystallization behaviour and the dielectric constant of REScO3 and LaLuO3 thin films was discussed. Finally deposition of a possible gate oxide for GaAs MOSFETs, viz. ErxGa2-xO3 by two different precursor approaches was investigated. In addition to β-diketonate metal precursors novel cyclopentadienyl and amidinate metal precursors together with water as oxygen source were utilized. For both YScO3 and ErxGa2-xO3 films the choice of precursor system affected e.g. the electrical properties and the crystallization behavior.
Thin Al2O3 barrier coatings grown on bio-based packaging materials by atomic layer deposition
(2011) Hirvikorpi, Terhi
Kemian tekniikan korkeakoulu | Doctoral dissertation (article-based)
Growing environmental concerns related to the use of synthetic non-biodegradable polymers in the packaging industry have led to the need for new, especially bio-based, materials. Currently, petroleum-based synthetic polymers are widely used due to their relatively low cost and high performance. Biodegradable plastics and fibre-based materials have been proposed as a solution to the waste problems related to these synthetic polymers. Fibre-based packaging materials have many advantages over their non-biodegradable competitors, such as stiffness vs. weight ratio and recyclability. However, poor barrier properties and sensitivity to moisture are the main challenges restricting their use. Application of a thin coating layer is one way to overcome these problems and to improve the barrier properties of such materials. Atomic layer deposition (ALD) is a well suited technique for depositing thin inorganic coatings onto temperature-sensitive materials such as polymer-coated boards and papers and polymer films. In the present work, thin and highly uniform Al2O3 coatings were deposited at relatively low temperatures of 80, 100 and 130 °C onto various bio-based polymeric materials employing the ALD technique. The study demonstrates that a 25-nm-thick ALD-grown Al2O3 coating significantly enhances the oxygen and water vapour barrier performance of these materials. Promising barrier properties were obtained with polylactide-coated board, hemicellulose-coated board as well as various biopolymer (polylactide, pectin and nanofibrillated cellulose) films after coating with a 25-nm-thick Al2O3 layer. Thin Al2O3 coatings can improve the properties of biopolymers, enabling the use of these renewable polymers in the production of high-performance materials for demanding food and pharmaceutical packaging applications. The future roll-to-roll ALD technology for coating polymers with inorganic thin films will increase the industrial potential of these materials and could lead to further opportunities for their commercialization.