Combined effect of thickness and stress on ferroelectric behavior of thin BaTiO3 films

Abstract

Thin BaTiO3 (BTO) layers were deposited by magnetron sputtering on a Si substrate between two thin LaNiO3 (LNO) electrodes (LNO/BTO/LNO/Si structure). The thickness of the BTO layer was varied between 35 nm and 1 μm. The stress, dielectric permittivity, and ferroelectric hysteresis loop were measured after deposition and during heating. It was found that the BTO layers are under tensile stress at the Curie temperature. The tensile stress increases with decreasing layer thickness leading to a shift of the Curie point to a lower temperature, a decrease of remanent polarization, and an increase of the coercive field. The effect of tensile stress on the Curie temperature is dominant within a restricted range of stresses between 300 and 450 mega Pascals (MPa), where the Curie temperature decreases linearly by about 0.16 °C/MPa. A good correlation was found between stress and dielectric measurements with respect to the temperature of the Curie point. The ferroelectric hysteresis loops showed that the ferroelectric-paraelectric phase transition starts at the Curie temperature of the BTO layer and continues within a range of temperatures until about the Curie temperature of the bulk BTO material. The ferroelectric behavior indicates dominance of domains within the interior part of the BTO layer and minor contribution of surface domains. The results are compared with a theoretical approach of size-driven phase transition in stress-induced ferroelectric thin films.