An interface dipole model explaining threshold voltage ( V t ) tuning in HfSiON gated n -channel field effect transistors ( n FETs ) is proposed. V t tuning depends on rare earth (RE) type and diffusion in Si ∕ Si O x ∕ Hf Si O N ∕ REO x /metal gated n FETs as follows: Sr < Er < Sc + Er < La < Sc < none . This V t ordering is very similar to the trends in dopant electronegativity (EN) (dipole charge transfer) and ionic radius ( r ) (dipole separation) expected for a interfacial dipole mechanism. The resulting V t dependence on REdopant allows distinction between a dipole model (dependent on EN and r ) and an oxygen vacancy model (dependent on valence).
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