Thin metal oxide films for application in nanoscale devices

To scale MOS transistors beyond 100 nm, it is imperative to find a dielectric of high permittivity (high-k dielectric) to replace the current SiO₂ as a gate insulator. In principle, a high dielectric can deliver an equivalent SiO₂ thickness of 1 nm with a greater physical thickness (20 nm if k=80) and, hence lower leakage current. Realizing the promise of high-k dielectrics in the ULSI technology is an enormously challenging task. There are several classes of dielectric, such as oxides and fluorides. The simplest such oxides have one metallic element, e.g. HfO₂, ZrO₂, Y₂O₃ with rare earth metals. Their dielectric constant range is from 10-30. More complex such oxides have two different metallic elements such as BaTiO₃ and SrTiO₃. They can form solid-state solutions with each other at all ratios, because of their identical crystal structures. That is why thin films of barium titanate (BTO) and barium strontium titanate (BSTO) of a permittivity in the range of 100-400 and greater specific capacitance, have emerged as a leading contender as a gate dielectric for sub - 0.1 mm MOS transistors. In this study results are reported of the structural and dielectric properties of several thin films prepared by the sol-gel method. The electrical properties are investigated on MIS structures and the results are related to the effect of reaction with the silicon substrate upon thermal annealing.