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Bi3.15Nd0.85Ti3O12 (BNT) thin films were fabricated on Si (100) substrates with Al2O3 buffer layer by a sol-gel method to investigate the effect of a thermal annealing process for crystallization of BNT thin films on the C-V characteristics of the MFIS structures. From XRD results, a BNT thin film with a thickness of 150 nm was found to be sufficiently crystallized by annealing at 650 C by using a RTA process. However, a higher annealing temperature and a longer holding time were needed to sufficiently crystallize the thicker BNT film (250 nm). These results imply that reducing film thickness is one of the ways to reduce the thermal budget for crystallization of ferroelectric films. All the Pt/BNT/Al2O3/Si structures, except the one with the BNT films annealed at 750 C in a furnace, showed clockwise C-V hysteresis, meaning the existence of a memory window resulting from ferroelectric polarization of the BNT film. The maximum memory window was obtained from the BNT film annealed at 650 C by RTA, and its value is 1 V at a sweep voltage of 6 V. The memory window decreased with increasing annealing temperature and/or thermal budget. This is thought to be due to poor interface properties induced by a higher annealing temperature and/or larger thermal budget.l