The strain-induced ferroelectric properties of c-axis oriented (Ba,Sr)TiO3thin films

Metal-ferroelectric-insulator-semiconductor (MFIS) structures were formed b y a pulsed laser deposition (PLD) method for application to the metal-ferro electric-insulator-semiconductor field-effect transistor (MFIS-FET). In the se 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 induc e 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 bu ffer layer were c-axis oriented, normal to the substrate surface. X-Ray dif fraction revealed that the c-axis of the BST films in the MFIS structure wa s distorted due to the strain-induced into the BST films, compared to polyc rystalline BST. It was suggested that the mechanical strain developed in th e 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 no n-volatility and exhibit a memory window of 1.1 V maximum. (C) 2000 Elsevie r Science B.V. All rights reserved.