We have elucidated the electronic states for Ru/SiON/Si(100) and Pt/HfO2/Pt structures under device operation by means of bias-application in hard x-ray photoelectron spectroscopy (BA-HXPES). For the Ru/SiON/Si(100) structure, interface electronic states are increased and new states near the conduction band minimum and valence band maximum are formed compared to the case of the Ru/SiO2/Si(100) structure. This is because nitrogen atoms at the SiO2/Si interface cause bond breaking and weakened the Si-O and Si-Si bonds at the interface. For the Pt/HfO2/Pt structure, oxygen atoms migrate to the top electrode under forward bias, forming Pt-O bond at the Pt/HfO2 interface. Under reverse bias, on the other hand, oxygen and Hf atoms are migrated to the top electrode, resulting in the formation of Pt-O and Pt-Hf bonds at the interface. The migration and bond formation at the interface should form vacancy in the HfO2 film, which might induce resistance switching behavior in this system. Here, it is emphasized that we present our approach using BA-HXPES, which successfully detects the electronic states under device operation. Therefore BA-HXPES could be applicable to various kinds of advanced materials and will be indispensable for evaluating their physical properties in detail.
