Periodic Reporting for period 4 - FOXON (Functionality of Oxide based devices under Electric-field: Towards Atomic-resolution Operando Nanoscopy)
Okres sprawozdawczy: 2023-05-01 do 2023-10-31
Within our project “Functionality of Oxide based devices under Electric-field: Towards Atomic-resolution Operando Nanoscopy” (FOXON) we want to correlate microscopic to macroscopic behavior and bridge the gap between theoretical models and experimental reality. It is a so far unrealized dream of many scientists in the field of oxide electronics to directly link the atomic structure to the physical properties during the operation of oxide-based devices inside a transmission electron microscope (TEM): the lab inside the microscope. The atomic resolution operando electron microscopy technique for the study of electronic devices is currently so relevant that its implementation and therefrom generated scientific knowledge could span beyond oxide electronics to related materials science and engineering fields of research. Our objectives are to establish state-of-the-art operando TEM of Metal-Insulator-Metal structured devices and tackle open questions in the field of oxide electronics. As an example, we are investigating the switching processes in metal-oxide functional devices to provide a comprehensive understanding of the atomic-level mechanisms that lead to tuneable physical properties in Resistive Random Access Memory (RRAM) devices. The fundamental understanding of microscopic processes provide a basis towards the development of new energy efficient computing devices which could allow the reduction of energy consumption of data centres and, thus reduce their ecological footprint. Another example, which we are investigating, are varactor heterostructures for tunable microwave technologies. The proposed development of atomic resolution electrical biasing operando TEM provides a technique to measure local ionic displacements with picometer precision. This allows to understand, for example, the formation of polar nanoregions or local atomic scale ordering under biasing conditions. This fundamental understanding supports developing suitable device designs for energy-efficient low-voltage applications in mobile communication applications.
To investigate the electrical behaviour and atomic structure during device operation we first focused on reliably measuring leakage currents of electron transparent thin film memristive and varactor devices for dedicated experiments inside a transmission electron microscope (TEM). We have successfully prepared fully operational TEM lamellas of several oxide electronic devices by Focused Ion Beam (FIB) using a novel preparation routine. Therefore, we have established a highly reproducible electrical contacting method. This is a major goal of FOXON and represents the overcoming of an experimental bottleneck which will benefit the community in the future. The electrical characterizations performed inside (in situ) and outside (ex situ) the microscope are comparable to the performance of the macroscopic devices. Based on this, we have probed the behaviour of local crystal defects under electric field and measured the atomic positions and lattice displacements under electrical field. Beside the state-of-the art operando TEM experiments we could acquire a fundamental understanding of a metal-insulator-metal (MIM)-RRAM device by using atomically resolved images as basis for theoretical calculations to provide a clear correlation between the microstructure of the insulator and its electrical properties. The gained theoretical models were also used as basis to calculate reasonable spectroscopic data. Additionally, we have thoroughly investigated the electrode and interface properties of epitaxial MBE-grown MIM stacks by looking at the density of point defects with the distance of interfaces.
The FOXON project represents a groundbreaking effort to push the boundaries of oxide electronics by correlating electrical behavior with atomic structure during device operation. By successfully preparing fully operational TEM lamellas of oxide electronic devices using a novel Focused Ion Beam (FIB) preparation routine, the project overcomes a significant experimental bottleneck. This achievement enables in-situ electrical characterizations within a transmission electron microscope (TEM), providing valuable insights into local crystal defects under electric field and atomic positions under electrical bias. Furthermore, FOXON's innovative approach of using atomically resolved images as a basis for theoretical calculations to correlate the microstructure of insulators with their electrical properties in metal-insulator-metal (MIM)-RRAM devices represents a leap beyond the state of the art. This strategy enhances our fundamental understanding of device behavior and facilitates the development of predictive models for future device design and optimization. The project's impact extends beyond scientific advancements, with potential socio-economic implications. By gaining insights into the atomic-scale mechanisms governing device behavior, FOXON contributes to the development of more efficient and sustainable electronic devices. This could lead to reduced energy consumption in data centers, thereby minimizing their ecological footprint. Moreover, the project's focus on varactor heterostructures for tunable microwave technologies holds promise for enhancing mobile communication applications, potentially improving connectivity and efficiency in a digitally interconnected society. Overall, FOXON's efforts have the potential to revolutionize oxide electronics and drive innovation in related fields, with far-reaching implications for technological progress and societal well-being.