Study On The Transport Mechanism Of The Ultra-thin Orientated BaTiO₃Ferroelectric Films

Ferroelectric thin films with good ferroelectric, piezoelectric, pyroelectric, electro-optical and nonlinear optical properties can be widely used in the field of MEMS, optoelectronics and integrated optics etc. The ultra thin ferroelectric films with the new electronic characters are different from the body material and common film with the thickness under100nm. So it has good prospect of application in ferroelectric tunnel junction, resistance of the switch memory and other fields.In this paper, BaTiO3ferroelectric thin films with the thickness range from15to80nm were grown on the substrate of Pt/Ti/SiO2/Si and SrTiO3single crystal by magnetron sputtering and pulsed laser deposition method respectively. Analyze the microstructure and electrical properties of BaTiO3ferroelectric thin film, the main results and conclusions are as follows:(1)According to the optimized of magnetron sputtering process conditions,50nm and80nm thickness BaTiO3ferroelectric thin films were grown on the substrate of Pt/Ti/SiO2/Si. XRD analysis shows that the films are highly oriented. AFM show that the film surface is very smooth, no defects such as cracks and porous, and SEM test show the interface between the film and the substrate is clear. According to the optimized of pulsed laser deposition process conditions,15nm BaTiO3ferroelectric thin films were grown on the substrate of Nb:SrTiO3single crystal. XRD analysis shows that the films are highly oriented. Combined TEM HREM image confirmed the BaTiO3thin film is epitaxial and the epitaxial growth direction is BaTiO3(100)//Nb:SrTiO3(100).AFM tests show that the film surface is very smooth and the root mean square roughness (RMS) is only0.82nm.(2) The electrical properties of the film were characterized by the PV curve, the CV curves and IV curves. Thin PV tests show that the films have good ferroelectric properties. The Pr value of BaTiO3ferroelectric films decreases as the film thickness decreased. And the Pr value is3.5μC/cm,2.5μC/cm and0.15μC/cm with the film thickness80nm,50nm and15nm, respectively. The CV test confirmed the existence of a positive built-in electric field in the Pt/BaTiOs/Nb:SrTiO3structure.(3) Study the transport mechanism of BaTiO3ferroelectric thin films. Analyze the Ⅰ-Ⅴ characteristic curves of BaTiO ferroelectric thin films,the conduction mechanism of the films at low electric field performance of the Ohmic contact mechanism and space limit the current mechanism (SCLC) mechanism, and Schottky emission at medium electric field, in a high electric field is Pool-Frank emission mechanism (P-F). In the low electric field region is Ohm contact mechanism Regardless of positive and negative bias.(4)The Ⅰ-Ⅴ test also showed that the electroluminescent resistance effect of the BaTiO3ferroelectric thin film.Oxygen vacancy as a donor, N-type conductivity in the oxygen vacancy accumulation area. The trap can be moved, resulting in a conduction channel (in the low resistance state).When the voltage exceeds the threshold voltage, high current, high conductive filaments to generate heat, which led to the conductive channel, the electrons from a number of flaws, the storage unit into a high resistance state. When positive bias is applied, the oxygen vacancy of the top electrode interface is scheduled to open, result in the Schottky barrier become wider, so the memory cell is maintained at a high resistance state. When negative bias is applied on the top electrode, the number of oxygen vacancies are attracted to reach the top electrode greatly reduces the Schottky barrier height, result in the storage unit into a low resistance state.