Phase-change memory (PCM) is arguably the most advanced memristive technology. Similar to conventional metal-oxide based memristive devices, information is stored in terms of changes in atomic configurations in a nanometric volume of material and the resulting change in resistance of the device. 202 However, unlike the vast majority of memristive devices, PCM exhibits volumetric switching as opposed to filamentary switching. The volumetric switching is facilitated by certain material compositions along the GeTe–Sb2Te3 pseudo-binary tie line, such as Ge2Sb2Te5, that can be switched reversibly between amorphous and crystalline phases of different electrical resistivities. 203 Both transitions are Joule-heating assisted. The crystalline to amorphous phase transition relies on a melt-quench process, whereas the reverse transition relies mostly on crystal growth (Fig. 9).There are essentially two key properties that make PCM devices particularly well suited for neuromorphic computing 204 (see Fig. 10). Interestingly, this was pointed out by Stanford Ovshinsky, a pioneer of PCM technology, way back in 2003 when PCM was being considered just for memory applications. 205 The first property is that PCM devices can store a range of conductance values by modulating the size of the amorphous region typically achieved by partial RESET pulses that melt and quench a certain volume of the PCM material. This analog storage capability, combined with a crossbar topology, allows for matrix–vector multiplication (MVM) operations to be carried out in O (1) time complexity by leveraging Kirchhoff’s circuit laws. This makes it possible to realize an …