Anomalous temperature dependence of Al2O3/SiO2 and Y2O3/SiO2 interface dipole layer strengths

The temperature dependences of the dipole layer strength at Al2O3/SiO2 and Y2O3/SiO2 interfaces were investigated. The dipole layer strength at each temperature was quantified from the flatband voltage (V-fb) shift of metal-oxide-semiconductor capacitors with Al2O3/SiO2 and Y2O3/SiO2 bilayer gate dielectrics on Si substrates. In order to accurately extract the dipole layer strength, the effects of the difference between the gate metal work function and the Si Fermi level, the fixed charges at the SiO2/Si interface, and the fixed charges at the high-k/SiO2 interface on the V-fb shift were excluded. It was found that both interface dipole layer strengths increased but in the opposite direction at the approximated rates of +2.2 mV K-1 and -0.7 mV K-1 for Al2O3/SiO2 and Y2O3/SiO2 interfaces, respectively, when the temperature was raised from 100 K to 300 K. The temperature dependences are larger than expected if only the thermal expansion of the oxides was considered as the factor which changes the effective dipole length of the dipole layers.