Experimental observations on the crystalline structures of YAlO3 single crystal at high temperatures

Abstract

To understand the effects of thermal annealing on a high-permittivity gate insulating material YAlO3, its single crystal was annealed at various high temperatures ranging from 900 to 1300 °C and was examined by various instrumental analyses such as X-ray diffraction, infrared absorption spectroscopy, laser confocal microscopy, and atomic force microscopy. As a result, it was clarified that the crystalline YAlO3 takes at least three structures in a temperature range up to 1300 °C. Namely, it is perovskite below 1160 °C, at which the garnet structure starts to appear, while an unknown structure appears at 1250 °C. On the other hand, the sample surface also shows drastic changes if the temperature exceeds 1160 °C. Furthermore, many elliptical spots are induced after the annealing at 1200 or 1250 °C. Moreover, hydroxyl groups are generated at 1300 °C. It is desirable to take these structural changes into account in determining the annealing temperature of YAlO3 for various industrial purposes such as the manufacture of semiconductor devices.