A novel ferroelectric capacitor cell was developed using a (Ba,Sr)TiO3 (BST) heteroepitaxial technique on Si substrate. Strong ferroelectricity results from the c-axis being elongated due to lattice mismatch between the dielectric and electrode. The epitaxial BST capacitor showed strong ferroelectricity even at 30 nm thickness, which is the thinnest ferroelectric film so far. Its superior ferroelectric properties, reliability, and sub-micron silicon process compatibility were confirmed.