Systematic Investigation of Ferroelectric Properties in x%YO_1.5–(100–x%)Hf_1–yZr_yO₂ Films

Abstract

The effect of composition on the ferroelectric properties was investigated using epitaxial x%YO 1.5 −(100−x%)Hf 1−y Zr y O 2 films. The tetragonal phase, with a composition near the phase boundaries with the orthorhombic or monoclinic phase, exhibits ferroelectricity through the field-induced phase transition from the tetragonal to the orthorhombic phase. Remarkably, the orthorhombic phase generated via the fieldinduced phase transition has a lower coercive field (E c ). The E c could be controlled from 1400 (5%YO 1.5 −95%(Hf 0.50 Zr 0.50 )O 2 ) to 2400 kV/cm (5%YO 1.5 − 95%(Hf 0.75 Zr 0.25 )O 2 ) with the same remnant polarization (P r ) value of ∼17 μC/cm 2 . These results are important for ferroelectric device applications with low-voltage drives.

No‐Heating Deposition of Ferroelectric x%YO1.5–(100−x%)(Hf1−yZry)O2 Films

“…[ 14 ] At x = 0, pure HfO 2 ( y = 0) and (Hf 0.50 Zr 0.50 )O 2 ( y = 0.50) consist of a monoclinic phase similar to the previously annealed samples, whereas pure ZrO 2 ( y = 1.0) has a tetragonal phase. [ 23 ] Using sputtering methods, the oxygen partial pressure and RF power significantly affect the crystal structure. The investigation of the sputtering conditions for no‐heating deposited (Hf 1 −y Zr y )O 2 films is a topic for future work.…”

“…These results suggest that an increase in x and y sequentially changes the crystal structure from monoclinic to orthorhombic and tetragonal, similar to the annealed samples in our previous study. [ 23 ] Therefore, the ferroelectric phase region expanded from a limited 7%YO 1.5 –93%HfO 2 in no‐heating‐deposited HfO 2 ‐based films. A ferroelectric orthorhombic phase was obtained for four samples: 5%YO 1.5 –95%HfO 2, 6%YO 1.5 –94%HfO 2 , 7%YO 1.5 –93%HfO 2 , and 5%YO 1.5 –95%(Hf 0.25 Zr 0.75 )O 2 .…”

“…Recently, we reported ferroelectricity over a wider range in epitaxial x %YO 1.5 –(100− x %)(Hf 1 −y Zr y )O 2 films prepared by pulsed laser deposition (PLD) and subsequent high‐temperature annealing at >1000 °C. [ 23 ] Similar to 7%YO 1.5 –93%HfO 2 , a ferroelectric film could be produced in an x %YO 1.5 –(100− x %)(Hf 1 –y Zr y )O 2 system by no‐heating deposition using the RF magnetron sputtering method.…”

“…The compositional regions where each crystal phase was formed were almost the same as those of the previously annealed epitaxial films. [ 23 ] Moreover, no‐heating‐deposited films exhibit similar ferroelectric behaviors, including field‐induced phase transitions. [ 23 ] The P r and coercive field ( E c ) were 12–19 μC cm −2 and 2000–2500 kV cm −1 , respectively.…”

“…[ 23 ] Moreover, no‐heating‐deposited films exhibit similar ferroelectric behaviors, including field‐induced phase transitions. [ 23 ] The P r and coercive field ( E c ) were 12–19 μC cm −2 and 2000–2500 kV cm −1 , respectively. The piezoelectric response of 1 μm thick films was investigated using 6%YO 1.5 –94%HfO 2 , 7%YO 1.5 –93%HfO 2 , and 5%YO 1.5 –95%(Hf 0.50 Zr 0.50 )O 2 films, which exhibited ferroelectric responses in epitaxial films.…”