Low temperature preparation of PbTiO3 ultrathin films deposited by PbO gas phase reaction sputtering

Abstract

In silicon integrated circuit technology, ferroelectric thin films have been importantly studied since they are the most promising materials for future non-volatile memory devices due to their fast switching speed and long-term retention time. PbTiO3 (PTO) is the one of the most suitable material for non-volatile memory devices, because it has the highest spontaneous polarization (PS) value. The subject of size effect on ferroelecticity has been of highest interest for many years to overcome the limit of memory density. As the ferroelectric film thickness decrease, it is possible to make small domain size of penetrating the film thickness direction. Another issue of ferroelectric thin film is reducing the preparation temperature, because the high temperature during the fabrication might degrade the bottom electrode, and leads to interface reaction between the ferroelectric film and Si substrate. To make thin and smooth PTO films, TiO2 was deposited on the Pt bottom electrode, and PbO gas phase reaction was carried out by static and rotation mode at a temperature as low as 450�??. TiO2 seed layer increase the number of active sites for PTO nucleation and, hence, allows crystallization of perovskite phase. To prepare PTO films below TC (493�??), PbO deposition power and target to substrate distance were controlled. As the temperature decreases, PbO layer was remained on the PTO surface, and it degraded the ferroelectric property of PTO films. However, it is possible to eliminate PbO layer on PTO films by reducing the PbO deposition power and increasing the target to sample distance until 100 mm. Zr buffer layer was inserted between PTO film and Pt bottom electrode to enhance the leakage property, and layer-by-layer preparation method was adopted to exclude the un-reacted TiO2. These methods enhance the switching property of PTO films. In summary, thin and smooth PTO ultra-thin films successfully deposited using the gas phase reaction sputtering below TC, and this method suggest us the possibility for high-density memory device.