Dipole model explaining high-k/metal gate field effect transistor threshold voltage tuning

An interface dipole model explaining threshold voltage (V-t) tuning in HfSiON gated n-channel field effect transistors (nFETs) is proposed. V-t tuning depends on rare earth (RE) type and diffusion in Si/SiOx/HfSiON/REOx/metal gated nFETs 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 RE dopant allows distinction between a dipole model (dependent on EN and r) and an oxygen vacancy model (dependent on valence). (c) 2008 American Institute of Physics.