  Phase-change memory devices have found applications in in-memory computing
where the physical attributes of these devices are exploited to compute in
place without the need to shuttle data between memory and processing units.
However, non-idealities such as temporal variations in the electrical
resistance have a detrimental impact on the achievable computational precision.
To address this, a promising approach is projecting the phase configuration of
phase change material onto some stable element within the device. Here we
investigate the projection mechanism in a prominent phase-change memory device
architecture, namely mushroom-type phase-change memory. Using nanoscale
projected Ge2Sb2Te5 devices we study the key attributes of state-dependent
resistance, drift coefficients, and phase configurations, and using them reveal
how these devices fundamentally work.
