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

Disclosed is a variable resistance element which can operate at a low voltage, while maintaining a low leak current. The variable resistance element includes a first electrode (101), a second electrode (103), and an ion conduction layer (102), which is provided between the first electrode and the second electrode. The ion conduction layer contains an organic oxide that contains at least oxygen and carbon, and the carbon concentration distribution in the ion conduction layer is configured such that the carbon concentration on the side (102a) close to the first electrode is higher than that on the side (102b) close to the second electrode.

Variable resistance element, semiconductor device including same, and method for manufacturing the element and the device

A fully 400°C-processed, standard Cu-BEOL compatible, robust Cu atom switch has been developed featuring an over-400°C high thermally tolerant polymer-solid electrolyte (TT-PSE). Hydrocarbons that have weak chemical bindings in the PSE are selectively eliminated in the TT-PSE, resulting in higher thermal stability. The TT-PSE also gives higher breakdown voltage (+1V) with keeping low set voltage (2V) due to the elimination of the fragile hydrocarbon bindings. Data retention characteristics after thermal cycle stress at temperature ranging from −65 to 150°C for 1000 cycles are confirmed for the first time. The developed atom switch is to be a technology enabler of reliable reprogrammable logics for future robotic/vehicle applications at high temperatures.

Robust Cu atom switch with over-400°C thermally tolerant polymer-solid electrolyte (TT-PSE) for nonvolatile programmable logic

A separator has a specimen separating area comprising a number of recesses defined in an inner wall of a flow passage through which a specimen passes For separating nucleic acid and protein, the recesses have openings whose maximum diameter is 300 nm or less, and adjacent ones of the recesses are spaced at an average interval of 300 nm or less

Separation apparatus and process for fabricating separation apparatus

A set/reset switching model of Cu atom switch based on electrolysis is newly proposed. A nanometer-thick solid electrolyte gives a high electric field of ~3.3 MV/cm in the solid electrolyte at 2 V, enabling an ionization of Cu and a formation of Cu bridge. It is revealed that the switching voltage depends on the resistance of electrolyte, where the modified Faraday’s law of electrolysis with exponential factors on current and time well falls on the experimental on-resistance. The proposed simple compact model is useful for estimating the resistance of the Cu atom switch programmed by any conditions.

Set/Reset Switching Model of Cu Atom Switch Based on Electrolysis

Programmable Logic (PL) with a high logic density is demonstrated by cross-bar (xbar) of atom switches, which are programmed through logic transistors. The PL has 4 4-input LUTs to minimize area-delay product owing to small area & capacitance of atom switch. Xbar with 50% and 100% populations mixed and programming lines shared architecture achieves a 2× higher logic density comparing to a commercial PL chip on same technology node of 40 nm. 3× higher operation frequency and 40% lower power consumption are also assessed.

Toshitsugu Sakamoto

Papers

Variable resistance element, semiconductor device including same, and method for manufacturing the element and the device

Robust Cu atom switch with over-400°C thermally tolerant polymer-solid electrolyte (TT-PSE) for nonvolatile programmable logic

Separation apparatus and process for fabricating separation apparatus

Set/Reset Switching Model of Cu Atom Switch Based on Electrolysis

A 2× logic density Programmable Logic array using atom switch fully implemented with logic transistors at 40nm-node and beyond