The strain-induced ferroelectric properties of c-axis oriented (Ba,Sr)TiO3 thin films

Metal–ferroelectric–insulator–semiconductor (MFIS) structures were formed by a pulsed laser deposition (PLD) method for application to the metal–ferroelectric–insulator–semiconductor field-effect transistor (MFIS-FET). In these structures, (Ba,Sr)TiO3 (BST), which is in a paraelectric state at room temperature, thin films were used as ferroelectric layer. Yttria stabilized zirconia (YSZ) thin films were used as an insulating buffer layer to induce the strain into BST films as well as to inhibit the charge injection from silicon substrate to BST thin films. Further BST films grown on the YSZ buffer layer were c-axis oriented, normal to the substrate surface. X-Ray diffraction revealed that the c-axis of the BST films in the MFIS structure was distorted due to the strain-induced into the BST films, compared to polycrystalline BST. It was suggested that the mechanical strain developed in the BST thin films induced a ferroelectricity in the BST films. These strain-induced BST thin films with the 9-nm thick YSZ layer are provided with a non-volatility and exhibit a memory window of 1.1 V maximum.