Realization and study of functional nano-circuits created by nanolithography on artificial multi-ferroic oxide heterostructures .
Wednesday, September 18th - 2:00 PM
Bloch Amphitheater, Building 772 (CEA-Saclay, Orme des Merisiers, Ground Floor)
Dear all,
I am pleased to invite you to my PhD defense entitled "Realization and study of functional nano-circuits created by nanolithography on artificial multi-ferroic oxide heterostructures".
The defense will be held in English at 2:00 PM on Wednesday, September 18th, at the Bloch Amphitheater, Building 772 (CEA-Saclay, Orme des Merisiers, Ground Floor).
For those unable to attend in person, the defense can also be followed remotely via Zoom using the link below.
https://cnrs.zoom.us/j/99822503564?pwd=u9CRZDKNw1bF0Hjm7au4LfnYCaznuE.1
A buffet will follow in the entrance hall of Building 772, and you are cordially invited to join.
Abstract:
Oxide electronics have attracted significant attention due to their rich variety of applicable mechanisms, such as resistive-switching and 2D electron gas. Conversely, artificial multiferroic oxide heterostructures, combing multiple functional ferroic properties, offer several degrees of freedom and functionalities for circuits. By integrating these two strategies, this study focuses on pioneering novel reconfigurable circuits based on epitaxial FeOx (ou NiFe2O4)/BaTiO3 heterostructures.
An initial thorough investigation into the ferroic properties of the NiFe2O4/BaTiO3 system not only established a solid foundation for later circuits designs, but also unveiled the diminished magnetic properties at the interface, for which issue a cure is proposed. Subsequent X-ray Photoemission Electron Microscopy (XPEEM) studies indicate that electric field poling can induce local chemical reduction, potentially increasing local conductance, which is a fundamental prerequisite for designing reconfigurable circuits. Through iterations of electrical testing, analysis, and improvement, we realized devices written by piezoresponse force microscopy (PFM) in epitaxial FeOx (ou NiFe2O4)/BaTiO3 heterostructures, where two electrodes defined by lithography are connected by a biased-PFM-tip-written conduction channel. The devices demonstrate a remarkable resistance change ratio of up to 9444% in the FeOx/BaTiO3 system. The scalability of resistance with device size indicates a homogeneous switching effect, pivotal for industrial applications.
In situ and operando measurements have been developed and performed at multiple synchrotron beamlines to investigate the local chemical and structural changes with current injection. Intriguingly, two distinct breakdown patterns, in-plane and out-of-plane, were identified. The in-plane breakdown is typically characterized by the melting of electrodes, aggregation of Ti and Fe (observed by XPEEM and μ-X-ray fluorescence mapping), and degradation of crystallinity of the multilayers both beneath the electrode and the conduction channel (revealed by μ-X-ray diffraction). Conversely, the out-of-plane breakdown pattern exhibited multiple significant resistance drops with increasing injected current, without apparent in-plane structural or chemical variations. Complementary ex situ HRTEM (High resolution transmission electron microscopy) investigations of the cross-section of post mortem device suggest that the origin of out-of-plane breakdown is the formation of amorphous-phase vias (conduction paths) through the original epitaxial BaTiO3 layer. These phenomena offer unique insights into current injection and breakdown effects in oxide electronics, paving the way for targeted optimization to enhance the robustness and reliability of oxide-based devices.
Best regrads,
Haowen LIN
Contact : Haowen LIN et Cristian MOCUTA