The End of the Roadmap for Silicon Dioxide: The Electronic Structure of Hyper-Thin Gate Oxides at the Atomic Scale

The smallest feature on a typical integrated circuit is the gate oxide. The semiconductor industry roadmap calls for gate oxides having a capacitance equivalent to that of 1.2 nm of silicon dioxide. As no suitable replacement materials for SiO sub 2 have yet been identified, we are forced to consider how thin can the thinnest SiO sub 2 gate oxide be? It is now technologically possible to produce nano-transistors with gate oxides only 5 silicon atoms thick. At least two of those 5 atoms are at the interfaces and their physical and electrical properties are very different to bulk SiO sub 2. Using atomic-scale energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM), we have mapped the chemistry and electronic structure profiles of gate oxides between 4 and 30 silicon atoms thick.