MOS capacitors were fabricated from MOCVD HfO2 and HfxSiyO gate dielectrics with ALD TaN / PVD Ta metal electrodes. Dielectrics with 1.8 to 2.6 nm capacitance equivalent thickness (CET) were investigated with gate leakage (Jg) of 1×10−7 to 1×10−3 A/cm2 at Vg = Vfb−1V in accumulation. In addition to the C-V and I-V characterization of the MOSCAPs, XPS physical characterization was performed on monitor wafers to determine composition and physical thickness. From the combined results of the electrical and physical characterization, the relative dielectric constants of the Hf-Si-O films and the metal electrode work functions are determined, and simple models for the compositional dependence of the dielectric constant are formulated. Capacitors with the same dielectric composition and thickness exhibited 100 mV Vfb change when the thickness of the ALD TaN electrode layer was changed from 40-80Å. This change is attributed to a change in the work function of the aggregate TaN / Ta metal electrode. Workfunctions were found to be located near middle of the Si band gap, with workfunctions of 4.6 eV to 4.7 eV.