Device performance and reliability characteristics of various types of Ru-Al-based metal gates on HfSiO gate dielectrics were investigated for p-type metal-oxide-semiconductor field effect transistor (pMOSFET) applications. Using the high work function of Ru and a dipole formed by Al atoms in a gate dielectric, the threshold voltage of the pMOSFET could be controlled successfully. However, the excessive diffusion of Al atoms generated more interface states and bulk trapping in the high-k dielectric layer and degraded the device performances and reliability characteristics. It was also found that the carefully tailored sequence of deposition and composition of Ru and Al metals can be used to prevent the excessive diffusion of Al atoms. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3514103]