Hydrogen induced dipole at the Pt/oxide interface in MOS devices

Thanks to its good thermal stability, including resistance to oxidation, platinum (Pt) is widely used in prototyping a wide spectrum of electron devices ranging from metaloxide- semiconductor (MOS) transistors to resistive switching memory cells. In this work, the energy barriers for electrons between the Fermi level of Pt and the conduction band of several oxide insulators (SiO2, Al2 O3, HfO2, Hf0.8Al0.2Ox, Sr0.53Ti0.47O3) were determined by using internal photoemission of electrons. By combining this barrier value with the electron affinity of the particular oxide, the effective work function (EWF) of Pt was determined for different interfaces. As studied over the reference Pt/oxide/Si stacks de-gassed in high vacuum at 400 8C, the EWF of Pt is found to differ significantly from the accepted vacuum WF value of 5.6 eV. The EWF is equal to 5.2 eV at the Pt/Al2O3 interface, 5.1 eV at Pt/HfO2, 5.3 eV at Pt/Hf0.8Al0.2Ox, 4.8 eV at Pt/SiO2, and 5.8 eV at the Pt/Sr0.53Ti0.47O3 interface indicating the presence of a polarization layer of which the contribution to the EWF depends on the oxide composition. Furthermore, annealing in H2 at 400 8C reduces the Pt EWF by 0.5 eV at all interfaces except for the Pt/Sr0.53Ti0.47O3 one. This observation indicates the formation of an additional H-related dipole at the Pt/oxide interfaces and suggests that the vacuum WF of Pt cannot be used as the value relevant for the MOS properties.status: publishe