Conduction mechanisms of ferroelectric La:HfO2ultrathin films

• Main Authors: Chen, F. (Author), Ding, C. (Author), Lu, C. (Author), Lu, L. (Author), Tang, M. (Author), Wang, S. (Author), Wen, Z. (Author), Xu, J. (Author), Xu, Z. (Author), Yu, Y. (Author), Zheng, W. (Author)
• Format: Article
• Language: English
• Published: American Institute of Physics Inc. 2022
• Subjects: Band alignments; CMOS integrated circuits; Complementary metal oxide semiconductor process; Conduction Mechanism; 'current; Current voltage curve; Ferroelectric films; Ferroelectricity; Hafnium oxides; Lanthanum compounds; Manganese oxide; Metals; MOS devices; Nano scale; Nonvolatile memory; Non-volatile memory; Oxide semiconductors; Strontium compounds; Temperature dependent; Thin-films; Ultrathin films; X ray photoelectron spectroscopy
• Online Access: View Fulltext in Publisher

 Recently, ion-doped HfO2 thin films are highly desirable for the next-generation nonvolatile memories due to excellent compatibility with current complementary metal-oxide-semiconductor processes and robust ferroelectricity persisted down to the nanoscale. In this work, we study conduction mechanisms of 4 and 8 nm-thick La:HfO2 ultrathin films sandwiched between Pt and (La0.67,Sr0.33)MnO3 (LSMO) electrodes based on band alignments of the Pt/La:HfO2/LSMO, measured by X-ray photoelectron spectroscopy, and temperature-dependent current-voltage curves from 50 to 300 K. In a 4 nm-thick La:HfO2 thin-film capacitor, the conduction mechanism is found to be governed by direct tunneling at 50-100 K and phonon-assisted indirect tunneling when the temperature is further increased to 300 K in which the (La Hf 4 + 3 +) ′ acceptors are served as localized states, facilitating hole hopping through the La:HfO2 barrier. When the thickness is increased to 8 nm, the tunneling through a La:HfO2 layer is suppressed, and the current-voltage character becomes rectifying, which is regulated by the dominated La:HfO2/LSMO interfacial barrier. The transport for a forward bias of the La:HfO2/LSMO barrier is found to be governed by thermionic-field emission, exhibiting a temperature-independent build-in potential of ∼2.77 V. For the reverse bias, the Fowler-Nordheim tunneling is observed. The revealing of conduction mechanisms in terms of band alignments sheds light on leakage problems and facilitates the design of HfO2-based ferroelectric devices with excellent insulating character for high-performance memory applications. © 2022 Author(s).