Data retention characteristics of metal-ferroelectric-metal-insulator-semiconductor diodes with SrBi2Ta2O9 ferroelectrics and Al2O3 buffer layers

Data retention characteristics of metal-ferroelectric-metal-insulator-semiconductor (MFMIS) diodes were investigated, in which SrBi2Ta2O9 (SBT) was used as a ferroelectric film and Al2O3 was used as an insulating buffer layer. Al2O3 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 Al2O3 layer with an equivalent oxide thickness (EOT) of 4.6 nm that the maximum induced charge was about 3.2 muC/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 MFMlS 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 Al2O3. 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.