New Processes in Modern ReRAM Memory Cells Decoded
September 29, 2015 | Forschungszentrum JülichEstimated reading time: 3 minutes
Resistive memory cells or ReRAMs for short are deemed to be the new super information-storage solution of the future. At present, two basic concepts are being pursued, which, up to now, were associated with different types of active ions. But this is not quite correct, as Jülich researchers working together with their Korean, Japanese and American colleagues were surprised to discover. In valence change memory (VCM) cells, not only are negatively charged oxygen ions active, but – akin to electrochemical metallization memory (ECM) cells – so too are positively charged metal ions. The effect enables switching characteristics to be modified as required and makes it possible to move back and forth from one concept to the other, as reported by the researchers in the journals Nature Nanotechnology and Advanced Materials.
The memristive behaviour of ReRAMs relay on mobile ions. These ions move in a similar manner to in a battery, flowing back and forth between two electrodes in a metal oxide layer no more than a few nanometres thick. For a long time, researchers believed that VCMs and ECMs functioned very differently. In ECMs, the ON and OFF states are achieved when metal ions move and form whisker-like filaments. This happens when an electric voltage is applied, causing such filaments to grow between the two electrodes of the cell. The cell is practically short-circuited and the resistance decreases abruptly. When the process is carefully controlled, information can be stored. The switching behaviour of VCMs, in contrast, were primarily associated with the displacement of oxygen ions. Contrary to metal ions, they are negatively charged. When a voltage is applied, the ions move out of an oxygen-containing metal compound. The material abruptly becomes more conductive. In this case as well, the process needs to be more carefully controlled.
Formation of metallic Tantalum (Ta) filament within Ta/TaO(x)/Pt ReRAM memory cell. Positively charged Ta(5+)-ions and oxygen vacancies (V(O)) contribute to the process. Copyright: Forschungszentrum Jülich / RWTH Aachen / Pössinger
Jülich researchers working together with their partners from the Chonbuk National University, Jeonju, the National Institute for Materials Science in Tsukuba and the Massachusetts Institute of Technology (MIT) in Boston discovered an unexpected second switching process in VCMs: metal ions also help to form filaments in VCMs. The process was made visible because the scientists suppressed the movement of the oxygen ions. To do so, they modified the surface by applying a thin carbon layer directly at the interface of the electrode material with the solid electrolyte. In one case, they used the “miracle material” graphene, which comprises only one single layer of carbon. “Graphene was used to suppress the transport of oxygen ions through the phase boundary and to slow down the oxygen reactions. Suddenly, we observed a switching characteristic similar to that of an ECM cell and therefore assume that free metal ions are also active in VCMs. This was additionally verified using scanning tunnelling microscopy (STM) and diffusion experiments. It appears that the metal ions provide additional support for the switching process,” says Dr. Ilia Valov, electrochemist at Jülich’s Peter Grünberg Institute (PGI-7).
Incorporating such a carbon interlayer would make it possible to jump from one switching process to the other in VCMs. This would lead to new options for designing ReRAMs. “Depending on the application, our findings could be exploited and the effect purposely enhanced or intentionally suppressed,” says Valov. The scientists’ findings give rise to several questions. “Existing models and studies will have to be reworked and adapted on the basis of these findings,” says the Jülich scientist. Further tests will clarify how such novel components behave in practice.
Suggested Items
Argonne, Toyota Collaborate on Cutting-Edge Battery Recycling Process
05/01/2024 | BUSINESS WIREThe U.S. Department of Energy’s (DOE) Argonne National Laboratory has recently launched a collaboration with Toyota Motor North America that could reduce the nation’s reliance on foreign sources of battery materials.
Real Time with… IPC APEX EXPO 2024: Outlining Rehm's Innovations and Global Presence
05/01/2024 | Real Time with...IPC APEX EXPOMichael Hanke, the chief sales officer for Rehm Thermal Systems, shares insights on the North American market, new machinery, and software development. He also discusses Rehm's turnkey solutions, process flexibility, global presence, and the dedicated team of 700 employees working on global solutions.
The Knowledge Base: A CM’s Perspective on Box Build Practices
04/30/2024 | Mike Konrad -- Column: The Knowledge BaseIn the ever-evolving landscape of electronics manufacturing, the box-build process stands out as a critical phase that bridges the gap between individual component manufacturing and the delivery of a fully functional electronic system. This intricate procedure, encompassing the assembly of everything from PCBs to wire harnesses and mechanical enclosures, demands a high level of precision, efficiency, and innovation. As the electronics assembly industry expands and diversifies, understanding the best practices within box-build assembly has become paramount for manufacturers aiming to stay ahead in a competitive market.
TSMC Certifies Ansys Multiphysics Platforms, Enabling Next-Gen AI and HPC Chips
04/30/2024 | PRNewswireAnsys announced the certification of its power integrity platforms for TSMC's N2 technology full production release. Both Ansys RedHawk-SC and Ansys Totem are certified for power integrity signoff on the N2 process, delivering significant speed and power advantages for high performance computing, mobile chips, and 3D-IC designs.
Koh Young Showcases Award-winning Inspection Solutions at SMTconnect with SmartRep in Hall 4A.225
04/25/2024 | Koh Young TechnologyKoh Young Technology, the industry leader in True 3D measurement-based inspection solutions, will showcase an array of award-winning inspection and measurement solutions at SMTconnect alongside its sales partner, SmartRep, in booth 4A.225 at NürnbergMesse from June 11-13, 2023. The following offers a glimpse into what Koh Young will present at the tradeshow: