Equivalent oxide thickness (EOT) scaling still remains one of the main facilitators to increase transistor performance. The use of rare-earth (RE) elements has been shown to effectively increase permittivity of the gate-stack interfacial layer between substrate and high-k dielectric, reducing its EOT contribution. In this paper, we have studied the optimal RE-to-SiO2 ratio using Dy2O3 as a test case. Capacitance-voltage and leakage current-voltage measurements were performed on Pt-gated capacitors with a SiO2/Dy2O3/Sc-doped HfO2 gate stack and varying ratios of Dy2O3 to SiO2 after a 1000 degrees C anneal. Optimal EOT-leakage performance was found for a Dy2O3-to-SiO2 ratio of similar to 0.5 to 0.6.