A Theoretical Approach to Investigating Gate Dielectrics

Researchers at Motorola have used first-principles computational methods based on density functional theory (DFT) to study potential gate dielectric materials.

A limiting factor to the on-going miniaturzation of semiconductors is the leakage current through silicon dioxide gates with a thickness of less than 20 Å. In other words, the insulating property of SiO₂ breaks down for layers of this thickness or less. A 1999 report from the Semiconductor Association, 'International Technology Roadmap for Semiconductors' predicts that silicon dioxide gates will no longer be viable after the 2012. The search is thus very much on for alternative gate dielectrics.

Alex Demkov at the Physical Sciences Research Laboratories, Motorola Inc., has taken up such a challenge. Reporting in the journal Physica Status Solidi (b), Demkov used computational physics techniques to examine possible alternative gate dielectric materials.

Using Accelrys' CASTEP, Demkov used a DFT approach to screen potential gate dielectrics. The perovskite SrTiO₃ was chosen as a potential gate dielectric candidate as it exhibits extremely large dielectric constants due to their high lattice polarisability. The thermodynamic stability of the SrTiO₃-Si interface was investigated and the reasons behind the formation of the silicates interfacial layer examined.

The surface of the cubic SrTiO₃ was also examined theoretically. It was found that SrO termination is thermodynamically more stable than TiO₂ termination under experimental conditions. The first ab initio study of the structure and electronic properties of the crystalline polymorphs of HfO₂ are also reported.

Demkov adds "This work emphasises the importance of computational tools in materials research in the semiconductor industry".

Reference

1. A. A. Demkov, Investigating Alternative Gate Dielectrics: A Theoretical Approach, Phys. Stat. Sol. (b), 2001, 226, 57-67.