Effects of coercive voltage and charge injection on memory windows of metal-ferroelectric-semiconductor and metal-ferroelectric-insulator-semiconductor gate structures

We have prepared Pt/SrBi2Ta2O9 (SBT)/Si metal-ferroelectric-semiconductor (MFS) and Pt/SBT/Y2O3/Si metal-ferroelectric-insulator-semiconductor (MFIS) ferroelectric gate structures and investigated the changes in memory window with different thickness of SBT and Y2O3 in the MFS and MFIS. As a result, it is found that the memory window increases with increasing thickness of SBT and decreasing thickness of Y2O3. The experimental and theoretical analysis reveals that the memory window equals to the difference between the effective coercive voltage (2V(c)) applied to the ferroelectric film and the flat band voltage shift due to charge injection (V-ci). Increasing the thickness of SBT, the 2V(c) seems to be saturated at higher voltage, whereas the V-ci starts to increase exponentially at the higher gate voltage. In contrast, the V-ci decreases with decreasing thickness of Y2O3, resulting in the enhancement of the memory window due to the reduction of charge injection. (C) 2002 American Institute of Physics.