Data Retention Characteristics of Metal–Ferroelectric-Metal–Insulator–Semiconductor Diodes with SrBi2Ta2O9Ferroelectrics and Al2O3Buffer Layers

Data retention characteristics of metal–ferroelectric-metal–insulator–semiconductor (MFMIS) diodes were investigated, in which SrBi 2 Ta 2 O 9 (SBT) was used as a ferroelectric film and Al 2 O 3 was used as an insulating buffer layer. Al 2 O 3 was deposited by an electron cyclotron resonance (ECR)-sputtering method using an Al target, while an SBT film was deposited by a sol–gel method. It was found in an Al 2 O 3 layer with an equivalent oxide thickness (EOT) of 4.6 nm that the maximum induced charge was about 3.2 µC/cm 2 and the layer thickness was hardly changed even after annealing at 800°C for 3 h in O 2 atmosphere. With the formation of the MFMIS structure, the area of the top electrode was made smaller than that of the floating gate electrode, so that the area of the MFM capacitor became smaller than that of the MIS capacitor. In the MFMIS capacitor composed of SBT and Al 2 O 3 , variation of the capacitance value after 30000 s was less than 15%, when the area ratio of the MFM capacitor to the MIS capacitor was larger than 8.