Understanding the Origin of Dipole Layer Formation at Interfaces between Two Dielectric Materials

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The purpose of this study is to understand the origin of dipole layer formation at gate dielectric interfaces which shifts the threshold voltage of advanced MOSFETs. Therefore two dielectric interfaces, Al2O3/AlFxOy and MgO/Al2O3, were studied.Dipole layer formation at AlFxOy/Al2O3 and MgO/Al2O3 interfaces was studied by both experiments and classic Molecular Dynamics simulation. Positive dipole layer formation was observed for AlFxOy/Al2O3 while negative for MgO/Al2O3. The simulation has suggested oxygen migration playing an important role on charge separation at AlFxOy/Al2O3 and Mg cations migration playing an important role at MgO/Al2O3. Different roles of ionic motion at these two interfaces are considered to be the result of the properties of the interfaces. The ionic motions are mainly determined by stress relaxation at AlFxOy/Al2O3 while formation of chemically stable compound determines the ionic motions at MgO/Al2O3. The results indicate a combined effects of cation and anion motion during the dielectric interface formation to caused charge separation at dielectric interfaces.The study on dipole layer formation at various dielectric interfaces provides us with an insight in understanding the relationship between the dipole layer formation at dielectric interfaces and interface ionic motions