Patent ID: 7791124

Claim:
A semiconductor structure comprising: a semiconductor-on-insulator (SOI) substrate including a vertical stack, from bottom to top, of a bottom semiconductor layer, a buried insulator layer, and a top semiconductor layer, wherein a bottommost surface of said top semiconductor layer contacts a topmost surface of said buried insulator layer; an access transistor including a source region that is located in said top semiconductor layer; a bottle shaped trench located in said semiconductor-on-insulator (SOI) substrate, wherein a lower portion of said bottle shaped trench underneath said buried insulator layer is wider than an upper portion of said bottle shaped trench; an inner electrode comprising a conductive material having a top surface located between said topmost surface of said buried insulator layer and a bottom surface of said buried insulator layer; a conductive buried strap laterally contacting said source region and vertically contacting said inner electrode; and a graded thickness dielectric collar having a thickness that monotonically decreases with distance from a top surface of said top semiconductor layer, wherein topmost surfaces of said inner electrode and said graded thickness dielectric collar are in direct contact with a bottom surface of said conductive buried strap at a same vertical depth from said top surface of said top semiconductor layer.