Thickness- and orientation- dependences of Curie temperature in ferroelectric epitaxial Y doped HfO2 films

The thickness- and orientation- dependences of Curie temperature were investigated for (111)-oriented, (100)-oriented and randomly-oriented 0.07YO1.5-0.93HfO2 films using high-temperature X-ray diffraction to study temperature stability of ferroelectric HfO2 based films. These (111)-, (100)- and randomly-oriented films with various film thickness were prepared at room temperature on (111)YSZ, (100)YSZ and Pt/TiOx/SiO2/Si substrates by pulsed laser deposition, respectively, and subsequent 1000 °C annealing to obtain ferroelectric orthorhombic phase. Although (111)-oriented films show that Curie temperature decreases with the decrease in thickness, the temperature was higher than 350 °C in 4.6–110 nm thickness range. (100)-oriented films show no thickness dependence of Curie temperature of 550 °C in 15–86 nm thickness range. Moreover, the Curie temperature of 10 nm thick randomly-oriented films was also 550 °C. These results revealed that the Curie temperature was above 350 °C, which is significantly high for the stable operation of memory application, regardless of the thickness and orientation.