Atomic layer deposition of high-k oxides on graphene

Atomic layer deposition of high-k oxides on graphene.Comment: Graphene - Synthesis, Characterization, Properties and Applications, Jian Ru Gong (Ed.), ISBN: 978-953-307-292-0, InTech, Available from: http://www.intechopen.com/articles/show/title/atomic-layer-deposition-of-high-k-oxides-on-graphen

Atomic layer deposited nanolaminates of zirconium oxide and manganese oxide from manganese(III)acetylacetonate and ozone

Producción CientíficaAtomic layer deposition method was used to grow thin films consisting of ZrO2 and MnOx layers. All depositions were carried out at 300 ºC. Some deposition characteristics of the manganese(III)acetylacetonate and ozone process were investigated, such as crystallinity and the dependence of growth rate on the deposition temperature. All films were partly crystalline in their as-deposited state. Zirconium oxide contained cubic and tetragonal phases of ZrO2, while the manganese oxide was shown to consist of cubic Mn2O3 and tetragonal Mn3O4 phases. All the films exhibited nonlinear saturative magnetization with hysteresis, as well as resistive switching characteristics.Fondo Europeo de Desarrollo Regional (projects TK134 and TK141)Ministerio de Economía, Industria y Competitividad (project TEC2017-84321-C4-2-R)Estonian Research Agency (projects PRG4 and PRG753

Hafniumdioksiidi aatomkihtsadestamine – nukleatsioon, kasv, ja struktuuri muutused kiledes

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Õhukesed tahkismaterjalide kihid ehk kiled, mille paksus ulatub paarist nanomeetrist (10-9 m) kuni mõnesaja nanomeetrini, leiavad laialdast kasutust elektroonikas, optikas ja mikromehaanika seadistes, aga samuti näiteks pindaktiivsetes ja pindu kaitsvates katetes. Selliseid kilematerjale või nendel põhinevaid mitmekihilisi struktuure saab valmistada erinevate meetoditega, kuid üheks perspektiivikamaks on peetud aatomkihtsadestamist. See meetod võimaldab saada ühtlase paksusega kilesid väga erineva pinnaprofiiliga alusmaterjalidel, mistõttu selle meetodi võimalike rakenduste valdkond on lai. Sõltuvalt sadetusprotsessi parameetritest on aatomkihtsadestamise abil võimalik valmistada erinevate omadustega (nt. parema või halvema elektrijuhtivusega, suurema või väiksema murdumisnäitajaga) kilematerjale. Konkreetseid rakendusi silmas pidades on materjali sobivate omaduste tagamine aga äärmiselt oluline. Käesolevas töös uuriti hafniumdioksiidi (HfO2) aatomkihtsadestamist ning selles protsessis saadud kilede omadusi sõltuvuses sadestusprotsessi parameetritest. Kasutati mitmeid lähteainete kombinatsioone (HfCl4-H2O, HfI4-H2O ja HfI4-O2) ning laia sadestustemperatuuride (180–750 oC) ja kilepaksuste (0–320 nm) vahemikku, et uurida HfO2 kasvukiiruse sõltuvust kile alusmaterjalist, paksusest, kristallstruktuurist ja pinnakaredusest. Näidati, et lisaks aluse temperatuurile mõjutas kilede kasvu ja kristallstruktuuri kandegaasi voog ja rõhk kasvukambris. Tehti kindlaks kilede optiliste omaduste sõltuvus kilede kristallilisusest, tihedusest ja topograafiast. Selgus, et mida tugevam on kristalliitide eelisorientatsioon kiledes, seda suurem on murdumisnäitaja. Kilede pinnakaredus sõltub nende struktuurist ja avaldab tugevat mõju optilistele kadudele. Kõrgematel sadestustemperatuuridel on kilede kasv ränialustele HfCl4-põhise protsessi algfaasis äärmiselt ebaühtlane. Õhukeste kilede karedus on sellest tingituna suur, mistõttu tuleks nendel temperatuuridel eelistada HfI4 põhinevat aatomkihtsadestamist või kasutada kaheastmelisi protsesse, milles madalal temperatuuril sadestatud siirdekiht tagab ühtlase kasvu ka kõrgetel temperatuuridel. Madalamatel sadestustemperatuuridel on mõlema metallilähteaine puhul võimalik saada siledama pinnaga kilesid, kuid kilede amorfsust suurendavate ja optilisi omadusi kahjustavate jääklisandite eemaldamiseks tuleb nendel temperatuuridel kasutada suhteliselt suuri hapniku lähteaine doose.Various thin layers of solid state materials, often referred as thin films, are widely used in electronics, optics, micro-mechanics as well as catalytic and protective coatings. Depending on certain applications the thicknesses of the films may vary from few nanometers (10-9 m) to couple of hundreds nanometers. Single- or multilayer thin film structures can be prepared by various techniques. However, using atomic layer deposition (ALD), uniform films can be deposited with a precision at sub-nanometer level also on complex three-dimensionally profiled surfaces. Therefore this method has emerged as a potential solution for fabrication of device with nanometer-level sizes. When employing this technique one can control film properties (electrical conductivity, refractive index etc.) by choosing proper deposition parameters. As certain applications require defined material properties that are determined already in the fabrication process, exact understanding of the deposition process parameters on the material quality is crucial. In this thesis, ALD of technologically highly important hafnium dioxide (HfO2) and influence of ALD process parameters on the properties of HfO2 thin film is thoroughly investigated. Several precursor combinations (HfCl4-H2O, HfI4-H2O ja HfI4-O2) and wide ranges of growth temperatures (180–750 oC) and film thicknesses (0–320 nm) were used to study the dependence of HfO2 growth rate on the substrate material as well as crystal structure and surface roughness of growing film. It was shown that besides other process parameters, the carrier gas flow rate and the pressure in the growth zone influenced the growth rate. Optical properties depended on crystallinity, density and topography of the films, whereas higher refractive index was obtained for films showing preferential orientation of crystallites in a certain direction. Optical transmission of the films was influenced by the surface roughness and material inhomogeneity that were, in turn, related to the crystal structure of the films. At elevated growth temperatures, HfCl4-based processes yielded highly non-uniform HfO2 films with rough surfaces. Therefore, HfI4-based processes are more advantageous at these temperatures. Another solution is to use two-temperature growth process, where uniform seed layer deposited at lower temperature enhances uniformity of deposition at higher temperature. Generally, at lower growth temperatures smoother and more uniform films can be obtained but the purity and density of these films are low. In two-temperature processes, by contrast, relatively high uniformity together with high overall purity, density and refractive index of the films can be obtained

Memory Effects in Nanolaminates of Hafnium and Iron Oxide Films Structured by Atomic Layer Deposition

HfO2 and Fe2O3 thin films and laminated stacks were grown by atomic layer deposition at 350 °C from hafnium tetrachloride, ferrocene, and ozone. Nonlinear, saturating, and hysteretic magnetization was recorded in the films. Magnetization was expectedly dominated by increasing the content of Fe2O3. However, coercive force could also be enhanced by the choice of appropriate ratios of HfO2 and Fe2O3 in nanolaminated structures. Saturation magnetization was observed in the measurement temperature range of 5–350 K, decreasing towards higher temperatures and increasing with the films’ thicknesses and crystal growth. Coercive force tended to increase with a decrease in the thickness of crystallized layers. The films containing insulating HfO2 layers grown alternately with magnetic Fe2O3 exhibited abilities to both switch resistively and magnetize at room temperature. Resistive switching was unipolar in all the oxides mounted between Ti and TiN electrodes

Nanoscale Characterization of TiO₂ Films Grown by Atomic Layer Deposition on RuO₂ Electrodes

Topography and leakage current maps of TiO₂ films grown by atomic layer deposition on RuO₂ electrodes using either a TiCl₄ or a Ti­(O-i-C₃H₇)₄ precursor were characterized at nanoscale by conductive atomic force microscopy (CAFM). For both films, the leakage current flows mainly through elevated grains and not along grain boundaries. The overall CAFM leakage current is larger and more localized for the TiCl₄-based films (0.63 nm capacitance equivalent oxide thickness, CET) compared to the Ti­(O-i-C₃H₇)₄-based films (0.68 nm CET). Both films have a physical thickness of ∼20 nm. The nanoscale leakage currents are consistent with macroscopic leakage currents from capacitor structures and are correlated with grain characteristics observed by topography maps and transmission electron microscopy as well as with X-ray diffraction