Conductive Bridge Resistive Memory Research Articles

Ion beam-assisted solid phase epitaxy of SiGe and its application for analog memristors

Low dimensional defects such as dislocation in single crystal Si are known to serve as a fast diffusion path of metal ions. Recently, many efforts have been made to employ dislocations in single crystal based oxide and silicon as reliable Ag filaments in CBRAM (Conductive Bridge Resistive Memory). In this study, we report the synthesis of the SiGe epitaxy thin films by an ion beam-assisted solid phase epitaxy process and its application for analog CBRAM memristors. The epitaxial SiGe thin films were produced by implanting Ge ions into a LPCVD a-Si film, followed by post annealing. We found that the interface oxide between a-Si and c-Si hinders facile epitaxy growth of a-Si. Thus, the ion implantation parameters were carefully adjusted to effectively remove the interface oxide and produce the epitaxy thin films of high quality. The low dimensional defects, identified to be a stacking fault by TEM observations, were observed to be densely located near the surface region of the SiGe epitaxy thin film. We fabricated the CBRAM devices by sandwiching the epitaxial Si thin films between an active metal electrode of Ag and a heavily doped Si wafer. We investigated the performances of the CBRAM devices and discuss the effect of the low dimensional defects on the switching behaviors of the devices. We found that the Ge implantation enables forming-free CBRAM operation and also provides reduced variations in set and reset voltages. Furthermore, we performed the feasibility study on the use of the epitaxial Si based CBRAM for artificial synapse for neuromorphic computing.

Numerical analysis of a polysilicon-based resistive memory device

This study investigates a conductive bridge resistive memory device based on a Cu top electrode, 10-nm polysilicon resistive switching layer and a TiN bottom electrode, by numerical analysis for $$10^{3}$$ programming and erase simulation cycles. The low and high resistive state values in each cycle are calculated, and the analysis shows that the structure has excellent retention reliability properties. The presented Cu species density plot indicates that Cu insertion occurs almost exclusively along grain boundaries resulting in a confined isomorphic conductive filament that maintains its overall shape and electric properties during cycling. The superior reliability of this structure may thus be attributed to the relatively low amount of Cu migrating into the RSL during initial formation. In addition, the results show a good match and help to confirm experimental measurements done over a previously demonstrated device.

A numerical analysis and experimental demonstration of a low degradation conductive bridge resistive memory device

This study investigates a low degradation metal-ion conductive bridge RAM (CBRAM) structure. The structure is based on placing a diffusion blocking layer (DBL) between the device's top electrode (TE) and the resistive switching layer (RSL), unlike conventional CBRAMs, where the TE serves as a supply reservoir for metallic species diffusing into the RSL to form a conductive filament (CF) and is kept in direct contact with the RSL. The properties of a conventional CBRAM structure (Cu/HfO2/TiN), having a Cu TE, 10 nm HfO2 RSL, and a TiN bottom electrode, are compared with a 2 nm TaN DBL incorporating structure (Cu/TaN/HfO2/TiN) for 103 programming and erase simulation cycles. The low and high resistive state values for each cycle are calculated and the analysis reveals that adding the DBL yields lower degradation. In addition, the 2D distribution plots of oxygen vacancies, O ions, and Cu species within the RSL indicate that oxidation occurring in the DBL-RSL interface results in the formation of a sub-stoichiometric tantalum oxynitride with higher blocking capabilities that suppresses further Cu insertion beyond an initial CF formation phase, as well as CF lateral widening during cycling. The higher endurance of the structure with DBL may thus be attributed to the relatively low amount of Cu migrating into the RSL during the initial CF formation. Furthermore, this isomorphic CF displays similar cycling behavior to neural ionic channels. The results of numerical analysis show a good match to experimental measurements of similar device structures as well.

In Situ Biasing of Conductive Bridge Resistive Memory Devices Observed in a Transmission Electron Microscope

In Situ Biasing of Conductive Bridge Resistive Memory Devices Observed in a Transmission Electron Microscope

A numerical analysis of progressive and abrupt reset in conductive bridging RRAM

The authors investigate the conduction filament (CF) properties of a Cu---$$\textit{HfO}_{2}$$HfO2 based conductive bridging resistive memory device by implementing a numerical simulation of the low and high resistive states, starting from a random initial distribution of oxygen vacancies (OV) defects states in the resistive switching layer (RSL) to a formed CF and ending in a ruptured state. A calculation approach which accounts for both the statistical nature of the system and the synergetic effect of OV and Cu species on the overall conductance is presented. By defining a disorder parameter, the correlation between the OV initial distribution and the CF reset behavior is analyzed. A dependence of the reset transition, being either abrupt or progressive, on the physical shape of the CF which in turn is affected by this disorder is shown to exist based on the simulation results.

Physics of the Voltage Constant in Multilevel Switching of Conductive Bridge Resistive Memory

The multilevel switching of conductive bridge resistive memory is characterized by the ON-state resistance (RON) being inversely proportional to the compliance current (ICC). The constant of this relation is shown to be universally correlated to the minimum SET voltage (VSET(min)) for all conductive bridge devices. VSET(min), required to switch the memory from high resistance state to low resistance state, can be extracted using small voltage sweep rates. The correlation has been verified by experiments on Cu/TaOx/Pt devices and confirmed for data on resistive devices reported in the literature. The physical domain of validity for the RON–ICC relation has been established.