Growth and ferroelectric properties of yttrium-doped hafnium oxide/indium-tin oxide polycrystalline heterostructures with sharp and uniform interfaces

We report on the growth of polycrystalline yttrium-5%-doped HfO2 (YHO) films with sharp and uniform interfaces over a large area on indium-tin oxide (ITO) layers and their ferroelectric properties. On substrates of thermally oxidized silicon, YHO/ITO bilayers were deposited in amorphous form by mean...

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Veröffentlicht in:Journal of applied physics 2018-09, Vol.124 (10)
Hauptverfasser: Yamada, Hiroyuki, Toyosaki, Yoshikiyo, Sawa, Akihito
Format: Artikel
Sprache:eng
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Zusammenfassung:We report on the growth of polycrystalline yttrium-5%-doped HfO2 (YHO) films with sharp and uniform interfaces over a large area on indium-tin oxide (ITO) layers and their ferroelectric properties. On substrates of thermally oxidized silicon, YHO/ITO bilayers were deposited in amorphous form by means of pulsed-laser deposition and were subsequently crystalized by two-step post-deposition annealing (PDA) at low and high temperatures. The crystallized YHO/ITO heterostructures had ultraflat surfaces: atomic-force-microscopy images exhibited a root-mean-square roughness of 0.15 nm over an area of 100 μm2. The roughness was much smaller than that of single-component polycrystalline films of ITO. X-ray diffraction and transmission electron microscopy (TEM) suggested the formation of YHO in higher symmetry phases including ferroelectric orthorhombic (o) YHO. TEM also confirmed crystallization of YHO layers in a pseudo-coherent manner from the YHO/ITO interfaces and resultant sharp and uniform YHO/ITO interfaces. These results are attributable to good lattice matching between the o-YHO layer and the ITO layer. It is suggested that this lattice matching was realized by the reduction of ITO during the crystallization in the two-step PDA process. The reduction might occur in the vicinity of the YHO/ITO interface via H2O incorporated in the amorphous bilayers. Pt/YHO/ITO junctions fabricated by using the two-step PDA method showed a polarization–electric field (P–E) hysteresis loop with remanent polarizations (Pr) of no less than 13 μC/cm2 at YHO thicknesses of 12 and 6 nm. These results indicate that the two-step PDA method can be used to fabricate high-quality YHO/ITO heterostructures in terms of surface and interface morphology, as well as ferroelectric properties.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.5046866