Effect of acceptor doping on phase transitions of HfO2 thin films for energy-related applications. (June 2017)

• Record Type: Journal Article
• Authors: Park, Min Hyuk; Schenk, Tony; Hoffmann, Michael; Knebel, Steve; Gärtner, Jan; Mikolajick, Thomas; Schroeder, Uwe
• Is Part Of: Nano energy. Volume 36(2017:Jun.)
• Page Start: 381
• Page End: 389
• Publication Date: 2017-06
• Subjects: ΔT adiabatic temperature change -- ΔS isothermal entropy change -- ESD energy storage density -- ALD atomic layer deposition -- HED harvestable energy density -- TMA trimethyl aluminium; Hafnium oxide -- Ferroelectricity -- Phase transition -- Pyroelectricity -- Electrocaloric effect -- Energy harvesting; Nanoscience -- Periodicals; Nanotechnology -- Periodicals; Nanostructured materials -- Periodicals; Power resources -- Technological innovations -- Periodicals; Nanoscience; Nanostructured materials; Nanotechnology; Power resources -- Technological innovations; Periodicals; 621.042
• DOI: 10.1016/j.nanoen.2017.04.052
• Languages: English
• ISSNs: 2211-2855

Abstract

Abstract: Fluorite structured HfO2 or ZrO2 thin films have been intensively studied for memory- and energy-related applications since their ferroelectricity was first reported in 2011. The phase transition between the nonpolar tetragonal and the polar orthorhombic phase in these new ferroelectric materials is believed to be promising for energy harvesting, energy storage and solid state cooling. The temperature dependent phase transition and resulting strong pyroelectric and electrocaloric effect have been reported for Si-doped HfO2 and (Hf, Zr)O2 thin films. In this study, the effect of acceptor (Al and Gd) doping into HfO2 thin films on their temperature dependent phase transition was systematically examined. The phase transitions in Al- and Gd-doped HfO2 thin films were much broader compared to Si-doped HfO2 and (Hf, Zr)O2 films. The maximum adiabatic temperature change (ΔT) values of Al- and Gd-doped HfO2 film were 5.7 and 3.1 K, respectively. A giant negative electrocaloric effect with ΔT of −7.4 K could be observed for Al-doped HfO2 . The various factors which can potentially affect the phase transitions of HfO2 films, such as dopant size, grain size distribution, spatial dopant distribution, and oxygen vacancy distribution were carefully examined to understand the different phase transition behavior. From the various factors, the distribution of oxygen vacancies is suggested as the origin of the different phase transitions of HfO2 films doped with trivalent and tetravalent dopants. Graphic abstract: Highlights: Phase transition of Al- and Gd-doped HfO2 films are reported for the first time. The effect of acceptor doping on the phase transition of fluorite ferroelectrics is investigated in depth. The energy harvesting and storage as well as electrocaloric effect of Al- and Gd-doped HfO2 thin films is examined and compared to other materials.