Flexible Memory Device Composed of Metal-Oxide and Two-Dimensional Material (SnO2/WTe2) Exhibiting Stable Resistive Switching

Two-terminal, non-volatile memory devices are the fundamental building blocks of memory-storage devices to store the required information, but their lack of flexibility limits their potential for biological applications. After the discovery of two-dimensional (2D) materials, flexible memory devices are easy to build, because of their flexible nature. Here, we report on our flexible resistive-switching devices, composed of a bilayer tin-oxide/tungsten-ditelluride (SnO2/WTe2) heterostructure sandwiched between Ag (top) and Au (bottom) metal electrodes over a flexible PET substrate. The Ag/SnO2/WTe2/Au flexible devices exhibited highly stable resistive switching along with an excellent retention time. Triggering the device from a high-resistance state (HRS) to a low-resistance state (LRS) is attributed to Ag filament formation because of its diffusion. The conductive filament begins its development from the anode to the cathode, contrary to the formal electrochemical metallization theory. The bilayer structure of SnO2/WTe2 improved the endurance of the devices and reduced the switching voltage by up to 0.2 V compared to the single SnO2 stacked devices. These flexible and low-power-consumption features may lead to the construction of a wearable memory device for data-storage purposes.

Демонстрация эффекта резистивного переключения отдельных филаментов в мемристорных структурах Ag/Ge/Si методом атомно-силовой микроскопии

Resistive switching effect of separate dislocations in Ag/Ge/Si(001) memristor structures was demonstrated experimentally by Conductive Atomic Force Microscopy. Hysteresis loops typical for bipolar resistive switching were observed in the current-voltage curves of the dislocations due to formation and rapture of Ag filament in the Ge layer as a result of Ag+ ion drift along the dislocation core.

Effect on Resistive Switching by Inserting TiOx Thin Layer in SiOx: Ag-Based Memristor

An approach to design a memristor by inserting a TiOx thin layer in Pt-Ag/SiOx:Ag/TiOx/P++-Si memristor in order to exhibit analog resistive switching has been proposed. The device shows continuous resistance change under positive and negative DC sweeping bias, and the device conductance can also be modulated by consecutive potentiating and depressing pulse programming. These primitive results are beneficial to realize the learning and computing in such kind of memristor devices. High-resolution transmission electron microscopy observations demonstrate a clear interface between the thin layers of Ag nanoclusters embedded SiOx and the amorphous TiOx. The I-V analysis of Pt-Ag/SiOx:Ag/TiOx/P++-Si memristor confirms that the presence of TiOx thin layer controls the formation/rupture of Ag-filament across the Pt-Ag and P++-Si electrodes, realizing the gradual conductance modulation, which is essential to emulate the bio-synaptic characteristics.

Drilling holes in silver ionic conductor using the high current density STEM probe

High current density STEM probe can be used to drill holes and to draw wonderful pictures through samples such as metal β-aluminas, feuoride and titaniun oxide etc. Resently, we have also found that the high current density subnanometer probe in the HB-5 and HB-501 STEM rapidly drills small holes in samples of Ag ionic conductor (Agl+XZr2Si2P3−xO12,x between 0 and 3) from which silver filaments can be easily extruded under the irradiation of electron beam. By means of electron diffraction, EDX, MAP pattern,HREM and EELS,we discovered that the filaments are absolute pure, and there are not any element distribution of Zr,Si,P and O on the filaments, except for a little carbon contamenation. Most of the Ag filaments were single crystal, and others were polycrystal with the length of crystal grains over 100nm. It would interrupt the extrusion to remove the electron beam, but if the irradiation restore in several seconds the Ag filament will be continued to extruse slowly, otherwise never again for the root of the filament has crystallized quite well and solidly connected with the sample grain. We suggest that there exist lot of miniature tunnels in the sample for the Ag filaments do not contain any other elements, and the filament must be formed by the collection of some tunnels. Whether the hole-drilling is easily and the dimension of holes are related to the thickness, drill tine and beam current intensity, but they mainly depend on the content of silver in the drilling region. The less the content of Ag, the easier the hole- drilling. We can not drill any hole in the silver filaments and Ag particles on the surface of sample grains. The holes are easily contaminted for the EELS we obtained was almost belong to carbon as the tine passed. A silver filament on the right had been extruded from a sample grain as shown in Fig.1a, and the root of the silver filament was connected with a pear-shaped Ag-rich region. When the electron beam gradually approached near the edge of the pear-shaped region from the edge of the grain, we found that the dimension of holes increased from 10nm to 30 nm. But we could not obtain holes with more than 10 nm in diameter after entering the pearshaped region. As soon as the electron probe entered the centre of the Ag-rich region, the pear-shaped region was broken into two parts and a hole with 26 nm in diameter appeared. Meanwhile, a new Ag filament with 24 nm in diameter was extruded from the left broken part shown in Fig.1b. It was proved by EDX that there was not any content of silver in this hole-drilling region. The Ag filament on the right was still connected with the right broken part, and it was not continued to extrude. The nearer to the root of the Ag filament, the more difficult to drill holes in the right part,e.g., it spent 180 seconds to drill a hole with only 5 nm in diameter where 40 nm to the root of the filament. Holes could not be drilled in such sample grains in which x is not between 0 and 3 and any Ag filaments can not be extruded.