Arithmetic and Biologically‐Inspired Computing Using Phase‐Change Materials

Abstract

Phase‐change materials offer a promising route for the practical realisation of new forms of general‐purpose and ‘brain‐like’ computers. An experimental proof‐of‐principle of such remakable capabilities is presented that includes (i) the reliable execution by a phase‐change ‘processor’ of the four basic arithmetic functions of addition, subtraction, multiplication and division, (ii) the demonstration of an ‘integrate and fire’ hardware neuron using a single phase‐change cell and (iii) the expostion of synaptic‐like functionality via the ‘memflector’, an optical analogue of the memristor.

Optically reconfigurable metasurfaces and photonic devices based on phase change materials

“…The restored, re-crystallized pixels look slightly brighter than those crystallized in the first writing. Here we also note that, instead of point-to-point erasing, if necessary, the pattern can be erased in one step by using a single high energy pulse with large hot-spot 29 , dramatically simplifying and speeding up the process. We expect that rates at which pixels can be erased and rewritten should, in principle, be similar to the rates of information storage in DVD technology where the 20 ns recrystallization time in GST allows for bitrates of up to 35 megapixels per second.…”

“…When annealed to a temperature between the glass-transition and the melting point, the GST transforms from an amorphous state into a metastable cubic crystalline state, while a short high-density laser pulse melts and quickly quenches the material back to its amorphous phase with a pronounced contrast of dielectric properties observed between the two phases. Although nanosecond and microsecond laser pulses, which provide robust switching between amorphous and crystalline phases, are conventionally used in optical data storage technology, it was recently shown that femtosecond laser pulses can induce multi-level switching 29,30 . In the multi-level regime, metastable semi-crystallized states are created by carefully controlling the energy and the number of stimulating optical pulses.…”

Mixed‐Mode Electro‐Optical Operation of Ge2Sb2Te5 Nanoscale Crossbar Devices

“…For instance, by comparing the crystallization times of Ge 15 Sb 85 in planar films excited optically and in bridge nanodevices excited electrically, it was shown that optical and electrical properties are interrelated. [10] Furthermore, simultaneous measurements of reflectivity and electrical resistivity of GST thin films during isothermal crystallization showed a decrease in resistivity preceding an increase in reflectivity, explained by the appearance of small crystalline nuclei that enable electrical conduction by percolation prior to the formation of a crystalline region large enough to be optically detectable.…”

“…This property has been referred to as accumulation and occurs by means of optical as well as electrical pulses. [14][15][16] In this work therefore we investigate the phase transition of GST by simultaneously examining the optical and electrical responses of crossbar-type nanoscale devices exposed to cumulative optical and electrical excitations.…”

Threshold switching via electric field induced crystallization in phase-change memory devices

“…Electrical phase change memories (PCMs) are of much topical interest as a potential next-generation non-volatile memory technology 1,2 and for possible advanced applications in such areas as arithmetic and neuromorphic processing. 3,4 PCMs utilize a reversible switching transition from a high-resistance (amorphous) state to low-resistance (crystalline) state in order to store data. A characteristic feature of the electrically driven amorphous to crystalline (SET) transition is the existence of a threshold electric field that must be exceeded for switching to occur.…”