Ferroelectric properties and current mechanisms of BaTiO3/Nb:SrTiO3 thin films

BaTiO3/Nb:SrTiO3 thin film oxides have been deposited on SrTiO3 substrates using a pulsed laser deposition system. Different annealing methods were thereafter used to assess the ferroelectricity of the grown films. The residual polarization value, 2Pr, of 4.205 mu C/cm(2) and saturated residual polarization value, 2Pmax, of 15.484 mu C/cm(2) were obtained using in-situ annealing. After performing rapid thermal annealing (RTA) annealing, the residual polarization value rose to 4.676 mu C/cm(2) and the saturated residual polarization value rose to 18.723 mu C/cm(2). Furthermore, a comparison of results showed that the saturation test frequency of the in-situ annealing was 10 times higher than the saturation test frequency of the RTA. This could be explained by the fact that the secondary high-temperature annealing led to a decrease in the conductivity of the doped oxide and, thereby, a decrease in the effective electric field that was applied to both ends of the BTO (BaTiO3) film. Thus, a lower frequency was required to ensure a flip of all ferroelectric domains within the BTO film. By testing the fatigue frequency at 100 kHz, 1012 stable cycles in both annealing methods and the results confirmed the good stability of the device performance. A linear fit analysis of the I - V curves showed under in-situ annealing the presence of both a bulk-limited current mechanism that was dominated by the space charge limited current (SCLC) and Pool-Frenkel (PF) mechanisms, and an interface-limited current that was dominated by the Fowler-Nordheim (FN) mechanism in the structure. After RTA annealing, the conducting mechanism is ohmic contact at low electric field and the SCLC mechanism at high field strength. The results show that after RTA annealing, the quality and ferroelectric properties of the films are significantly improved compared to those under in-situ annealing. These results showed that the BTO/NSTO/STO (BaTiO3/Nb:SrTiO3/SrTiO3) structure had a standard test frequency as well as reliable stability. The BTO/NSTO/STO structure showed, therefore, promising applications in future nonvolatile information memory devices.