Strain Dependence of Dielectric Properties and Reliability of High-k Thin Films
The effect of strain on both electronic and structural characteristics of HfO2 used for sub-50-nm semiconductor devices was analyzed by a quantum chemical molecular dynamics analysis. The band structure of HfO2 is strongly affected by strain in the film. Based on the change rate of band gap obtained from our simulations, the strain sensitivity of the relative permittivity of HfO2 film is predicted to about 2.4%/1%-strain. The predicted strain sensitivity was validated quantitatively by measuring the change of the capacitance of MOS capacitors using a HfO2 gate dielectric film. It is very important, therefore, to minimize the mechanical strain in the dielectric film to assure the reliability of MOS transistor.
First-Principles Calculation of High Strain-Induced Leakage Current in Silicon Dioxide used for Gate Dielectrics
l.Introduction Increasing capacitance of a gate dielectric and decreasing resistivity of a gate electrode are indispensable for improving electronic performance of MOSFETs. However, simple thinning of a gate oxide film causes high leakage current because of an increase in the tunneling current through the oxide film. In addition, it has been found that tensile stress higher than I GPa often occrus in new materials, such as metal-silicides and tungsten, that are used for a gate elecffode [1]. Since it is well known that tensile strain in crystals reduces the bandgap of materials, such a high tensile stress may decrease the bandgap of the thin gate oxide and, thus, further increase leakage current [2]. In light of this background, we investigated the mechanical stress (strain)-induced leakage current through a SiO2 gate dielectric. The change in the bandgap of SiO2 caused by crystallographic strain was analyzed by a firstprinciples calculation. The leakage current was estimated by applyrng the Wentzel-Kramers-Brillouin (WKB) approximation [3]. A finite element method (FEM) was also used to analyze the strain fietd in a MOSFET structure. The increase in the leakage current caused by a tungsten gate electrode was evaluated quantitatively.
First Insights into the Draft Genome Sequence of the Endophyte Paenibacillus amylolyticus Strain GM1FR, Isolated from Festuca rubra L.
ABSTRACT Paenibacillus amylolyticus strain GM1FR is an endophyte isolated from aerial plant tissues of Festuca rubra L. Here, we report the draft genome sequence (7.3 Mb) of GM1FR containing 6,241 protein-coding genes, some of which are potentially involved in plant growth promotion and biocontrol.