Low-Temperature Preparation of Sr2(Ta1-x, Nbx)2O7 Thin Films by Pulsed Laser Deposition and its Electrical Properties

Sr2(Ta1-x , Nbx)2O7(STN) ferroelectric thin films were prepared on Pt/Ti/SiO2/Si and SiO2/Si(100) substrates by the pulsed laser deposition (PLD) method. (151)-oriented STN thin films were deposited at a low temperature of 600°C in N2O ambient gas at 0.08 Torr for composition ratios of x=0.2, 0.3 and 0.4. A symmetrical polarization hysteresis loop of the STN film was observed for the composition ratio of x=0.3, where the remanent polarization was 0.4 µC/cm2 and the coercive force was 30 kV/cm. The dielectric constant at room temperature was as low as 55. The remanent polarization of postannealed films was not changed after 1010 cycles of polarization reversal. A counterclockwise capacitance–voltage (C–V) hysteresis was observed in the metal-ferroelectric-insulator-semiconductor (MFIS) structure using Sr2(Ta0.7,Nb0.3)2O7 on SiO2/Si at a deposition temperature of 600°C. The C–V curve spreads symmetrically in both positive and negative directions when applied voltage is increased and the window did not change in sweep rates ranging from 0.1 to 5.0 V/s.