Chemically homogeneous complex oxide thin films via improved substrate metallization

A long-standing challenge to the widespread application of complex oxide thin films is the stable and robust integration of noble metal electrodes, such as platinum, which remains the optimal choice for numerous applications. By considering both work of adhesion and stability against chemical diffusion, it is demonstrated that the use of an improved adhesion layer (namely, ZnO) between the silicon substrate and platinum bottom electrode enables dramatic improvements in the properties of the overlying functional oxide films. Using BaTiO ₃ and Pb(Zr,Ti)O ₃ films as test cases, it is shown that the use of ZnO as the adhesion layer leads directly to increased process temperature capabilities and dramatic improvements in chemical homogeneity of the films. These result in significant property enhancements (e.g., 300% improvement to bulk-like permittivity for the BaTiO ₃ films) of oxide films prepared on Pt/ZnO as compared to the conventional Pt/Ti and Pt/TiO _x stacks. A comparison of electrical, structural, and chemical properties that demonstrate the impact of adhesion layer chemistry on the chemical homogeneity of the overlying complex oxide is presented. Collectively, this analysis shows that in addition to the simple need for adhesion, metal-oxide layers between noble metals and silicon can have tremendous chemical impact on the terminal complex oxide layers.