Abstract

Electronic devices based on Si-CMOS devices have exhibited an astonishing technological progress over the last 50 years or so, allowing the electronic revolution which now permeates every aspect of our current society. This can be quantitatively described by ‘Moore’s Law’: “the number of transistors in integrated circuits (ICs) doubles roughly every two years”. This extraordinary technological progress has been achieved by progressive improvements in lithographic patterning of ICs; in 1971, the minimum IC feature size achievable was 10 microns; now it is 14 nm. However, this seemingly inexorable progress will shortly come to a halt; such nanoscale dimensions mark the point at which dielectrics are no longer electrically insulating due to electron tunnelling, and semiconductors no longer behave like bulk materials but quantum-size effects start to appear. It is evident that a completely new electronic-memory technology needs to be developed. I will describe one very strong candidate, viz. non-volatile ‘phase-change random-access memory’ (PCRAM), in which applied voltage pulses can switch materials from a high-conductance crystalline state to a low-conductance amorphous state on the sub-ns time-scale. Here, binary data are stored in the atomic-structural state of the memory material, rather than as stored electronic charge in the case of Si-CMOS devices. I will describe how PCRAM devices are replacing flash memory and could be used as the basis of novel ‘neuromorphic’ (brain-like) computing devices – i.e. artificial synapses.