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

Nanoscale metal/oxide/metal switches have the potential to transform the market for nonvolatile memory and could lead to novel forms of computing. However, progress has been delayed by difficulties in understanding and controlling the coupled electronic and ionic phenomena that dominate the behaviour of nanoscale oxide devices. An analytic theory of the ‘memristor’ (memory-resistor) was first developed from fundamental symmetry arguments in 1971, and we recently showed that memristor behaviour can naturally explain such coupled electron–ion dynamics. Here we provide experimental evidence to support this general model of memristive electrical switching in oxide systems. We have built micro- and nanoscale TiO2 junction devices with platinum electrodes that exhibit fast bipolar nonvolatile switching. We demonstrate that switching involves changes to the electronic barrier at the Pt/TiO2 interface due to the drift of positively charged oxygen vacancies under an applied electric field. Vacancy drift towards the interface creates conducting channels that shunt, or short-circuit, the electronic barrier to switch ON. The drift of vacancies away from the interface annilihilates such channels, recovering the electronic barrier to switch OFF. Using this model we have built TiO2 crosspoints with engineered oxygen vacancy profiles that predictively control the switching polarity and conductance. Nanoscale metal/oxide/metal devices that are capable of fast non-volatile switching have been built from platinum and titanium dioxide. The devices could have applications in ultrahigh density memory cells and novel forms of computing.

Memristive switching mechanism for metal/oxide/metal nanodevices.

Resistive switching in transition metal oxides

In this paper, recent progress of binary metal-oxide resistive switching random access memory (RRAM) is reviewed. The physical mechanism, material properties, and electrical characteristics of a variety of binary metal-oxide RRAM are discussed, with a focus on the use of RRAM for nonvolatile memory application. A review of recent development of large-scale RRAM arrays is given. Issues such as uniformity, endurance, retention, multibit operation, and scaling trends are discussed.

Metal–Oxide RRAM

Materials showing reversible resistive switching are attractive for today’s semiconductor technology with its wide interest in nonvolatile random-access memories. In doped SrTiO3 single crystals, we found a dc-current-induced reversible insulator–conductor transition with resistance changes of up to five orders of magnitude. This conducting state allows extremely reproducible switching between different impedance states by current pulses with a performance required for nonvolatile memories. The results indicate a type of charge-induced bulk electronic change as a prerequisite for the memory effect, scaling down to nanometer-range electrode sizes in thin films.

/pdf/current-driven-insulator-conductor-transition-and-38nvjzgy5s.pdf

Current-driven insulator–conductor transition and nonvolatile memory in chromium-doped SrTiO3 single crystals

The design of a 4-way SIMD streaming data processor emphasizes achievable performance in area and power. Software controls data movement and instruction flow, and improves data bandwidth and pipeline utilization. The micro-architecture minimizes instruction latency and provides fine-grain clock control to reduce power.

A streaming processing unit for a CELL processor

Low‐frequency square‐wave modulation of a rf discharge in silane diluted with a rare gas brought about an improvement in the deposition rate of amorphous hydrogenated silicon films and in the film quality as well as a drastic suppression of powder concentration in the discharge space. These results can be explained by a SiH3 density in the modulated discharge that is high compared to that without modulation, because of the electron density enhancement resulting from the modulation and also because the lifetime of SiH3 radicals is much longer than those of SiHn radicals (n=0–2).

Effects of low‐frequency modulation on rf discharge chemical vapor deposition

A process for producing a porous film or sheet, which comprises melt-molding a composition prepared by compounding 100 parts by weight of a polyolefin resin with 25 to 400 parts by weight of a filler and 1 to 100 parts by weight of a liquid or waxy hydrocarbon polymer into film or sheet, and stretching the resulting film or sheet.

Process for producing porous film or sheet

Current through ${(\mathrm{P}\mathrm{b},\mathrm{L}\mathrm{a})(\mathrm{Z}\mathrm{r},\mathrm{T}\mathrm{i})\mathrm{O}}_{3}$ ferroelectrics on perovskite semiconductors is found to exhibit diode characteristics of which polarity is universally determined by the carrier conduction-type semiconductors. A persisting highly reproducible resistance modulation by a dc voltage, which has a short retention, is observed and is ascribed to a band bending of the ferroelectric by the formation of charged traps. This interpretation is consistent with a large relaxation current observed at a low voltage. On the other hand, a reproducible resistance modulation by a pulse voltage, which has a long retention, is observed in metal/${(\mathrm{P}\mathrm{b},\mathrm{L}\mathrm{a})(\mathrm{Z}\mathrm{r},\mathrm{T}\mathrm{i})\mathrm{O}}_{3}/{\mathrm{SrTiO}}_{3}:\mathrm{Nb}$ but not in metal/${(\mathrm{P}\mathrm{b},\mathrm{L}\mathrm{a})(\mathrm{Z}\mathrm{r},\mathrm{T}\mathrm{i})\mathrm{O}}_{3}/{(\mathrm{L}\mathrm{a},\mathrm{S}\mathrm{r})}_{2}{\mathrm{CuO}}_{4}$ and is attributed to a possible band bending due to the spontaneous polarization $(P)$ switching. The observed current voltage $(\mathrm{IV})$ characteristics, the polarity dependence, the relaxation, and the modulation are explicable, if we assume a $p\ensuremath{-}n$ or a $p\ensuremath{-}p$ junction at the ferroelectric semiconductor interface (p: hole conduction type, n: electron conduction type). The analysis suggests that an intrinsically inhomogeneous P $(\ensuremath{\nabla}P)$ near the ferroelectric/metal interface is likely very weak or existing in a very thin layer, when a reaction of the metal with the ferroelectric is eliminated. Additionally, the various aspects of transport through ferroelectrics are explained as a transport in the carrier depleted region.

/pdf/electrical-transport-through-pb-z-r-t-i-o-3-p-n-and-p-p-2dvq3sf0md.pdf

Electrical transport through Pb ( Z r , T i ) O 3 p-n and p-p heterostructures modulated by bound charges at a ferroelectric surface: Ferroelectric p-n diode

Yukio Watanabe

Papers

Current-driven insulator–conductor transition and nonvolatile memory in chromium-doped SrTiO3 single crystals

A streaming processing unit for a CELL processor

Effects of low‐frequency modulation on rf discharge chemical vapor deposition

Process for producing porous film or sheet

Electrical transport through Pb ( Z r , T i ) O 3 p-n and p-p heterostructures modulated by bound charges at a ferroelectric surface: Ferroelectric p-n diode