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

Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

Bose-Einstein condensation in a gas of sodium atoms

Memristive devices are electrical resistance switches that can retain a state of internal resistance based on the history of applied voltage and current. These devices can store and process information, and offer several key performance characteristics that exceed conventional integrated circuit technology. An important class of memristive devices are two-terminal resistance switches based on ionic motion, which are built from a simple conductor/insulator/conductor thin-film stack. These devices were originally conceived in the late 1960s and recent progress has led to fast, low-energy, high-endurance devices that can be scaled down to less than 10 nm and stacked in three dimensions. However, the underlying device mechanisms remain unclear, which is a significant barrier to their widespread application. Here, we review recent progress in the development and understanding of memristive devices. We also examine the performance requirements for computing with memristive devices and detail how the outstanding challenges could be met.

Memristive devices for computing

Despite much progress in semiconductor integrated circuit technology, the extreme complexity of the human cerebral cortex, with its approximately 10(14) synapses, makes the hardware implementation of neuromorphic networks with a comparable number of devices exceptionally challenging. To provide comparable complexity while operating much faster and with manageable power dissipation, networks based on circuits combining complementary metal-oxide-semiconductors (CMOSs) and adjustable two-terminal resistive devices (memristors) have been developed. In such circuits, the usual CMOS stack is augmented with one or several crossbar layers, with memristors at each crosspoint. There have recently been notable improvements in the fabrication of such memristive crossbars and their integration with CMOS circuits, including first demonstrations of their vertical integration. Separately, discrete memristors have been used as artificial synapses in neuromorphic networks. Very recently, such experiments have been extended to crossbar arrays of phase-change memristive devices. The adjustment of such devices, however, requires an additional transistor at each crosspoint, and hence these devices are much harder to scale than metal-oxide memristors, whose nonlinear current-voltage curves enable transistor-free operation. Here we report the experimental implementation of transistor-free metal-oxide memristor crossbars, with device variability sufficiently low to allow operation of integrated neural networks, in a simple network: a single-layer perceptron (an algorithm for linear classification). The network can be taught in situ using a coarse-grain variety of the delta rule algorithm to perform the perfect classification of 3 × 3-pixel black/white images into three classes (representing letters). This demonstration is an important step towards much larger and more complex memristive neuromorphic networks.

Training and operation of an integrated neuromorphic network based on metal-oxide memristors

For the first time, an area-efficient nonvolatile carry chain combining look-up tables and a pass-transistor-logic-based adder is newly developed using complementary atom switches without additional CMOS circuits. A proposed tristate switch composed of three pairs of complementary atom switches selects one of "0", "1", and the "carry_in" signal as the input of a common multiplexer for both a look-up table and an adder. The developed nonvolatile carry chain achieves the reductions of 20% area, 17% delay, and 17% power consumption, respectively, in comparison with a conventional nonvolatile carry chain using dedicated CMOS gates.

http://iopscience.iop.org/article/10.7567/JJAP.55.04EF01/pdf

Area-efficient nonvolatile carry chain based on pass-transistor/atom-switch hybrid logic

The authors demonstrate an ultra-low-power microcontroller unit (MCU) with an embedded atom-switch ROM, which performs 0.39-V operation voltage and 18.26-pJ/cycle minimum active energy (or 18.26-µW/MHz minimum active power) at 14.3 MHz. The MCU is fabricated using an embedded atom-switch process with a hybrid silicon-on-thin-buried-oxide (SOTB) core and bulk I/O transistors. The atom switch is suitable for an ultra-low-voltage operation because of its high on/off conductance ratio. The SOTB CMOS with a body-bias voltage control realizes a high operation frequency of 40 MHz at 0.54 V and an ultra-low sleep power of 0.628 a#x00B5;W, simultaneously.

A Silicon-on-Thin-Buried-Oxide CMOS Microcontroller with Embedded Atom-Switch ROM

In switching elements each using a two-terminal-type variable resistance element, improper writing or any improper operation is often caused and the reliability of the switching elements cannot be improved easily. A switching element according to the present invention is equipped with a first variable resistance element equipped with a first input/output terminal and a first connection terminal, a second variable resistance element equipped with a second input/output terminal and a second connection terminal, and a rectifying element equipped with a control terminal and a third connection terminal, wherein the first connection terminal, the second connection terminal and the third connection terminal are connected to one another.

Switching element and method for fabricating semiconductor switching device

A variable resistance element includes a first electrode, a second electrode and an ion conduction layer interposed between the first and second electrodes. The ion conduction layer contains an organic oxide containing at least oxygen and carbon. The carbon concentration distribution in the ion conduction layer is such that the carbon concentration in an area closer to the first electrode is greater than that in an area closer to the second electrode.

Variable resistance element, semiconductor device including variable resistance element, and methods for manufacturing variable resistance element and semiconductor device

Toshitsugu Sakamoto

Papers

Area-efficient nonvolatile carry chain based on pass-transistor/atom-switch hybrid logic

A Silicon-on-Thin-Buried-Oxide CMOS Microcontroller with Embedded Atom-Switch ROM

Switching element and method for fabricating semiconductor switching device

Variable resistance element, semiconductor device including variable resistance element, and methods for manufacturing variable resistance element and semiconductor device

Electrical Transport in Nano-Scale Silicon Devices