In this paper, recent progress of phase change memory (PCM) is reviewed. The electrical and thermal properties of phase change materials are surveyed with a focus on the scalability of the materials and their impact on device design. Innovations in the device structure, memory cell selector, and strategies for achieving multibit operation and 3-D, multilayer high-density memory arrays are described. The scaling properties of PCM are illustrated with recent experimental results using special device test structures and novel material synthesis. Factors affecting the reliability of PCM are discussed.

Phase Change Memory

Brain-inspired computing is an emerging field, which aims to extend the capabilities of information technology beyond digital logic. A compact nanoscale device, emulating biological synapses, is needed as the building block for brain-like computational systems. Here, we report a new nanoscale electronic synapse based on technologically mature phase change materials employed in optical data storage and nonvolatile memory applications. We utilize continuous resistance transitions in phase change materials to mimic the analog nature of biological synapses, enabling the implementation of a synaptic learning rule. We demonstrate different forms of spike-timing-dependent plasticity using the same nanoscale synapse with picojoule level energy consumption.

Nanoelectronic programmable synapses based on phase change materials for brain-inspired computing.

A phase-change memory element with side-wall contacts is disclosed, which has a bottom electrode. A non-metallic layer is formed on the electrode, exposing the periphery of the top surface of the electrode. A first electrical contact is on the non-metallic layer to connect the electrode. A dielectric layer is on and covering the first electrical contact. A second electrical contact is on the dielectric layer. An opening is to pass through the second electrical contact, the dielectric layer, and the first electrical contact and preferably separated from the electrode by the non-metallic layer. A phase-change material is to occupy one portion of the opening, wherein the first and second electrical contacts interface the phase-change material at the side-walls of the phase-change material. A second non-metallic layer may be formed on the second electrical contact. A top electrode contacts the top surface of the outstanding terminal of the second electrical contact.

Phase-change memory

The last decades a variety of portable or wearable navigation systems have been developed to assist visually impaired people during navigation in known or unknown, indoor or outdoor environments. There are three main categories of these systems: electronic travel aids (ETAs), electronic orientation aids (EOAs), and position locator devices (PLDs). This paper presents a comparative survey among portable/wearable obstacle detection/avoidance systems (a subcategory of ETAs) in an effort to inform the research community and users about the capabilities of these systems and about the progress in assistive technology for visually impaired people. The survey is based on various features and performance parameters of the systems that classify them in categories, giving qualitative-quantitative measures. Finally, it offers a ranking, which will serve only as a reference point and not as a critique on these systems.

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Wearable Obstacle Avoidance Electronic Travel Aids for Blind: A Survey

This article reviews the psychophysiological method in game research. Psychophysiological measurements provide an objective, continuous, real-time, noninvasive, precise and sensitive way to assess the game experience. However, the best results require controlled experiments with careful monitoring of variables, large enough sample sizes and expertise in electrical signal processing. We briefly explain the theory behind the method and present the most useful measures: electromyography (EMG), electrodermal activity (EDA), electroencephalography (EEG) and cardiac measures. We review previous studies that have used psychophysiological measures in game research and illustrate some future directions. Our article covers several research lines using the psychophysiological method in game studies, and offers a comprehensive list of references for those interested in the field.

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A review of the use of psychophysiological methods in game research

With the concept of 'human-machine interface', designed especially for visually impaired persons, we have developed an electric aid device for use in guiding orientation and locomotion. The device, which we call CyARM, measures the distance between a person and an object with an ultrasonic sensor and transmits the distance information to the user's haptic sense. In this report, we will: (1) outline the concept of CyARM, (2) describe its mechanism, and (3) demonstrate three preliminary experiments that verify the usability of CyARM. We conducted the experiments in terms of detection of objects, detection of space, and tracking object movement. As a result of these experiments, we have concluded that CyARM is potentially effective for visually impaired persons. Our study will encourage the related studies of user interfaces, particularly focusing on electric aid devices that guide visually impaired persons in detecting their environment.

CyARM: an alternative aid device for blind persons

The picture element (pixel) in conventional image sensors, such as CCD or CMOS imager, are placed in the form of a lattice for ease of implementation. Lattice placement of pixels intrinsically has directional dependency on the clarity of image representation; in other words, the image clarity is significantly dependent on the directions of the objects in the image, such as lines. For example, horizontal lines are perfectly represented by lattice pixels, while slanted lines have jagged edges. In this paper, we propose a pseudorandom pixel placement architecture for clear imaging with solving the directional dependency problems. We also discuss our evaluation of its characteristics based on the designed layout of CMOS image sensor with pseudorandom pixel placement, as well as its implementation.

A CMOS image sensor with pseudorandom pixel placement for clear imaging

We propose a novel architecture (phase change nonvolatile SRAM: PNSRAM) combining SRAM with PRAM. This architecture is possible solution to reduce the program cycle at the nonvolatile material to be divided a program sequence into volatile and nonvolatile. In this paper, we describe the PNSRAM architecture and a circuit simulation results of the volatile and nonvolatile operation

Nonvolatile SRAM based on Phase Change

Phase change nonvolatile memory devices composed of SeSbTe chalcogenide semiconductor thin film were fabricated. The resistivity of the SeSbTe system was investigated to apply to multi-level data storage. The chalcogenide semiconductor acts as a programmable resistor that has a large dynamic range. The resistance of the chalcogenide semiconductor can be set to intermediate resistances between the amorphous and crystalline states using electric pulses of a specified power, and it can be controlled by repetition of the electric pulses. The size of the memory cell used in this work is 200 nm thick with a contact area of 1 µm diameter. The resistance of the chalcogenide semiconductor gradually varies from 41 kΩ to 840 Ω within octal steps. The resistance of the chalcogenide semiconductor decreases with increasing number of applied pulses. The step-down characteristic of the resistance can be explained as the crystalline region of the active phase change region increases with increasing number of applied pulses. The extent of crystallization was also estimated by the overall resistivity of the active region of the memory cell.

/pdf/pulse-number-control-of-electrical-resistance-for-multi-5duw3joa00.pdf

Junichi Akita

Papers

CyARM: an alternative aid device for blind persons

A CMOS image sensor with pseudorandom pixel placement for clear imaging

Nonvolatile SRAM based on Phase Change

Pulse number control of electrical resistance for multi-level storage based on phase change

Wearable electromyography measurement system using cable-free network system on conductive fabric