Strain induced (Ba,Sr)TiO₃ thin films for Metal-Ferroelectric-Insulator-Semiconductor memory devices

Strain induced Metal-Ferroelectric-Insulator-Semiconductor (MFIS) has been proposed for non-volatile ferroelectric random access memory (NV-FRAM). This MFIS structure employs (Ba,Sr)TiO₃ (BST) thin films as a ferroelectric layer. These BST thin films were at paraelectric composition and were transformed to have a tetragonality due to the strain induced into the BST films. X-ray diffraction study on the BST layer revealed that the in-plane and plane normal lattice parameters of BST films were different. This suggests that the strain induced into the BST thin films distorts the BST lattices. In order to obtain the epitaxial nature of the BST thin films as well as to prevent charge injection from silicon to the BST film, yttria stabilized zirconia (YSZ) thin films was used as a buffer layer. The MFIS structures with the strained BST thin films exhibited memory window, i.e., non-volatility of 0.6 V in C-V measurements at the maximum bias voltage of 5 V. We have reported the ferroelectric and structural properties in the strain-induced MFIS structure.