Electrical properties of Bi3.25La0.75Ti3O12 thin films on Si for a metal–ferroelectric–insulator–semiconductor structure

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Abstract
La-modified bismuth titanate [Bi3.25La0.75Ti3O12 (BLT)] thin films have been grown at a low processing temperature of 620 °C by pulsed-laser deposition on a p-Si substrate with a nitrogen-doped thermal oxide SiO2 layer. This metal–ferroelectric–insulator–semiconductor structure exhibited a capacitance–voltage (C–V) hysteresis (memory window) due to ferroelectric polarization. The memory window reached a maximum of 0.8 V at a sweep voltage of 6 V. In addition, BLT films grown on Si exhibited the asymmetric behavior of C–V and current–voltage (I–V) characteristics, i.e., asymmetric shift of the threshold voltage with the sweep voltage. It is found that appreciable charge injection (indirect tunneling) occurs from Si, before the memory window does not even reach the maximum (i.e., 6 V in this structure). The trapped electrons injected from Si cause Vfb1 to shift toward the positive direction rather than the negative direction. This leads to the asymmetric behavior of the C–V curve and the decrease in the memory window.