Two Different Mechanisms for Determining Effective Work Function (fm,eff) on High-k - Physical Understanding and Wider Tunability of fm,eff

We have experimentally found two different mechanisms characterizing effective work function (Phi_m,eff) of a gate electrode on Hf-based high-k dielectrics. Interface dipoles induce both positive and negative Phi_m,eff shifts. The positive shift is almost independent of gate electrode materials, while the negative one is sensitive to Si composition of the gate electrode. Surface densities of the dipoles are estimated to be the order of 10¹⁴ cm^-2. By making the most of two types of interface dipoles, we can expand a tunability of Phi_m,eff of gate electrodes on high-k (Phi_m,high-k)