Many metal–insulator–metal systems show electrically induced resistive switching effects and have therefore been proposed as the basis for future non-volatile memories. They combine the advantages of Flash and DRAM (dynamic random access memories) while avoiding their drawbacks, and they might be highly scalable. Here we propose a coarse-grained classification into primarily thermal, electrical or ion-migration-induced switching mechanisms. The ion-migration effects are coupled to redox processes which cause the change in resistance. They are subdivided into cation-migration cells, based on the electrochemical growth and dissolution of metallic filaments, and anion-migration cells, typically realized with transition metal oxides as the insulator, in which electronically conducting paths of sub-oxides are formed and removed by local redox processes. From this insight, we take a brief look into molecular switching systems. Finally, we discuss chip architecture and scaling issues.

http://chialvo.org/Curso/UBACurso/DIA7/Papers/Aono_NatMat_07_Ionic%20Switching%20Memory.pdf

Nanoionics-based resistive switching memories

Redox‐Based Resistive Switching Memories – Nanoionic Mechanisms, Prospects, and Challenges

The resistance switching behaviour of several materials has recently attracted considerable attention for its application in non-volatile memory (NVM) devices, popularly described as resistive random access memories (RRAMs). RRAM is a type of NVM that uses a material(s) that changes the resistance when a voltage is applied. Resistive switching phenomena have been observed in many oxides: (i) binary transition metal oxides (TMOs), e.g. TiO(2), Cr(2)O(3), FeO(x) and NiO; (ii) perovskite-type complex TMOs that are variously functional, paraelectric, ferroelectric, multiferroic and magnetic, e.g. (Ba,Sr)TiO(3), Pb(Zr(x) Ti(1-x))O(3), BiFeO(3) and Pr(x)Ca(1-x)MnO(3); (iii) large band gap high-k dielectrics, e.g. Al(2)O(3) and Gd(2)O(3); (iv) graphene oxides. In the non-oxide category, higher chalcogenides are front runners, e.g. In(2)Se(3) and In(2)Te(3). Hence, the number of materials showing this technologically interesting behaviour for information storage is enormous. Resistive switching in these materials can form the basis for the next generation of NVM, i.e. RRAM, when current semiconductor memory technology reaches its limit in terms of density. RRAMs may be the high-density and low-cost NVMs of the future. A review on this topic is of importance to focus concentration on the most promising materials to accelerate application into the semiconductor industry. This review is a small effort to realize the ambitious goal of RRAMs. Its basic focus is on resistive switching in various materials with particular emphasis on binary TMOs. It also addresses the current understanding of resistive switching behaviour. Moreover, a brief comparison between RRAMs and memristors is included. The review ends with the current status of RRAMs in terms of stability, scalability and switching speed, which are three important aspects of integration onto semiconductors.

https://iopscience.iop.org/article/10.1088/0034-4885/75/7/076502/pdf

Emerging memories: resistive switching mechanisms and current status.

Creating functional electrical circuits using individual or ensemble molecules, often termed as “molecular-scale electronics”, not only meets the increasing technical demands of the miniaturization of traditional Si-based electronic devices, but also provides an ideal window of exploring the intrinsic properties of materials at the molecular level. This Review covers the major advances with the most general applicability and emphasizes new insights into the development of efficient platform methodologies for building reliable molecular electronic devices with desired functionalities through the combination of programmed bottom-up self-assembly and sophisticated top-down device fabrication. First, we summarize a number of different approaches of forming molecular-scale junctions and discuss various experimental techniques for examining these nanoscale circuits in details. We then give a full introduction of characterization techniques and theoretical simulations for molecular electronics. Third, we highlig...

Molecular-Scale Electronics: From Concept to Function

Through a simple industrialized technique which was completely fulfilled at room temperature, we have developed a kind of promising nonvolatile resistive switching memory consisting of Ag/ZnO:Mn/Pt with ultrafast programming speed of 5 ns, an ultrahigh R(OFF)/R(ON) ratio of 10(7), long retention time of more than 10(7) s, good endurance, and high reliability at elevated temperatures. Furthermore, we have successfully captured clear visualization of nanoscale Ag bridges penetrating through the storage medium, which could account for the high conductivity in the ON-state device. A model concerning redox reaction mediated formation and rupture of Ag bridges is therefore suggested to explain the memory effect. The Ag/ZnO:Mn/Pt device represents an ultrafast and highly scalable (down to sub-100-nm range) memory element for developing next generation nonvolatile memories.

Fully room-temperature-fabricated nonvolatile resistive memory for ultrafast and high-density memory application.

In this review, possibilities to modify intentionally the electronic transport properties of metal/molecule/metal devices (MMM devices) are discussed. Here especially the influence of the metal work function, the metal–molecule interface, the molecule dipole and different tunneling mechanisms are considered. A route to evaluate the effective surface work function of metal–molecule systems is given and, based on experimental results, an exemplary estimation is performed. The electron transport across different metal–molecule interfaces is characterized by relating transmission coefficients extracted from experimentally derived molecular conductances, decay constants or tunneling barrier heights. Based on the reported results the tunneling decay constant can be assumed to be suitable to characterize intrinsic molecular electron transport properties, while the nature of the metal–molecule contacts is properly described by the transmission coefficient. A clear gradation of transmission efficiencies of metal–anchoring group combinations can be given.

https://iopscience.iop.org/article/10.1088/0953-8984/23/1/013001/pdf

Control of molecule-based transport for future molecular devices

Thin films of 1,3-diethylbenzimidazol-2-ylidene (BIEt) were fabricated from THF solution on solid gold substrates and characterised by high-resolution X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy. The surface-analytical data are in accord with the formation of self-assembled monolayers of BIEt molecules exhibiting an approximately vertical orientation on the substrate. The crystal structure of (BIEt)2 was also determined.

NHC-Based Self-Assembled Monolayers on Solid Gold Substrates

A self-assembled monolayer of dodecanethiol is grown onto (111) oriented gold by vacuum phase deposition and studied by ultrahigh vacuum scanning tunneling microscopy (STM). The films consist of do...

A new phase of the c(4 x 2) superstructure of alkanethiols grown by vapor phase deposition on gold.

The origin of faceting of ultraflat gold films epitaxially grown on mica

The resistive switching behavior of devices consisting of aluminum top electrode, molecular layer (rose bengal), and bottom electrode (zinc oxide and indium tin oxide) is examined. By measuring the current versus voltage dependence of these devices for various frequencies and by systematically varying the composition of the device, we show that the switching is an extrinsic effect that is not primarily dependent on the molecular layer. It is shown that the molecular layer is short circuited by filaments of either zinc oxide or aluminum and that the switching effect is due to a thin layer of aluminum oxide at the zinc oxide/aluminum interface.

/pdf/resistive-switching-of-rose-bengal-devices-a-molecular-3vhveh892v.pdf

Silvia Karthäuser

Papers

Control of molecule-based transport for future molecular devices

NHC-Based Self-Assembled Monolayers on Solid Gold Substrates

A new phase of the c(4 x 2) superstructure of alkanethiols grown by vapor phase deposition on gold.

The origin of faceting of ultraflat gold films epitaxially grown on mica

Resistive switching of rose bengal devices: A molecular effect?