Thickness-dependent crystal structure and electric properties of epitaxial ferroelectric Y2O3-HfO2 films

Abstract

The thickness dependences of the crystal structure and electric properties of (111)-oriented epitaxial 0.07YO1.5-0.93HfO2 (YHO7) ferroelectric films were investigated for the film thickness range of 10–115 nm. The YHO7 films were grown by pulsed laser deposition or sputtering at room temperature and subsequent heat treatment. As a substrate for the epitaxial growth of the YHO7 film, (111)-oriented 10 wt. % Sn-doped In2O3(ITO)//(111) yttria-stabilized zirconia was used. X-ray diffraction measurements confirmed that the main crystal phase of these YHO7 films was ferroelectric orthorhombic for up to 115-nm-thick films. Small film-thickness dependences of remanent polarization (Pr) and saturation polarization (Ps) were observed. Thickness dependence of the coercive field (Ec) is also small, and this behavior does not resemble that of conventional ferroelectric films such as Pb(Zr,Ti)O3. Additionally, non-oriented polycrystalline YHO7 films are reported to have similar thickness dependence of Ec and almost the same Ec value to epitaxial YHO7 films. We suggest that the ferroelectric domain is significantly small for both epitaxial and polycrystalline films. Such small domains remain even in thicker films, giving rise to thickness-independent Ec.

Electric‐Field‐Induced Ferroelectricity in 5%Y‐doped Hf0.5Zr0.5O2: Transformation from the Paraelectric Tetragonal Phase to the Ferroelectric Orthorhombic Phase

“…[28,29] The details of the phase assignments can also be found in previous studies. [30,31] No spots are shown in Figure 1b, indicating that the 1100 C-treated film consists of the tetragonal phase because the existence of the other phase should lead to the appearance of the peak. On the other hand, two spots are shown in Figure 1a, which suggests the existence of monoclinic films.…”

“…The targets for the deposition used the handmade sintered body. Obtained films were heat-treated using an image furnace under N 2 flow at 1000 or 1100 C for 10 s. [30][31][32] The crystalline phases of the films were examined using XRD (D8 Discover, Bruker) with a 2D detector. P-E hysteresis loops were measured at room temperature and 10 kHz by a ferroelectric tester (FCE-1, Toyo corp.).…”

Ferroelectric Properties and Polarization Fatigue of La:HfO2 Thin‐Film Capacitors

“…[ 12 ] In lanthanide ion (such as La 3+ , Gd 3+ , and Y 3+ ) doped HfO 2 thin films robust polarizations in the range 8–25 μC cm −2 have been achieved. [ 13–17 ] In addition, the phase transition and polarization can also be optimized by annealing HfO 2 under asymmetrical stress, [ 3 ] introducing epitaxial strains from substrates, [ 18,19 ] and controlling the grain size in polycrystalline thin films. [ 20 ]…”

Growth Window of Ferroelectric Epitaxial Hf0.5Zr0.5O2 Thin Films

“…3,[6][7][8][9][10][11][12][13] The ferroelectric orthorhombic phase can be also stabilized in epitaxial films. [14][15][16][17][18][19][20][21] In epitaxial films, the orthorhombic phase is generally formed during deposition at high temperature, without need of annealing. [14][15][16][17][18][19][20] Epitaxial films are of high interest for better understanding of the properties of ferroelectric hafnia, as well as for prototyping devices with ultrathin films or having small lateral size, for which the higher homogeneity of epitaxial films respect to polycrystalline films is an advantage.…”

“…[14][15][16][17][18][19][20] Epitaxial films are of high interest for better understanding of the properties of ferroelectric hafnia, as well as for prototyping devices with ultrathin films or having small lateral size, for which the higher homogeneity of epitaxial films respect to polycrystalline films is an advantage. In spite of the evident interest, epitaxial ferroelectric hafnia is still in a nascent state, and few groups have reported epitaxial films on YSZ, [14][15][16]21,22 oxide perovskite, 17,19,23 and Si 18,20 substrates. Up to now, the epitaxial films have been grown by pulsed laser deposition (PLD), and only the influence of thickness has been discussed.…”