  Chalcogenide phase change materials enable non-volatile, low-latency
storage-class memory. They are also being explored for new forms of computing
such as neuromorphic and in-memory computing. A key challenge, however, is the
temporal drift in the electrical resistance of the amorphous states that encode
data. Drift, caused by the spontaneous structural relaxation of the newly
recreated melt-quenched amorphous phase, has consistently been observed to have
a logarithmic dependence in time. Here, we show that this observation is valid
only in a certain observable timescale. Using threshold-switching voltage as
the measured variable, based on temperature-dependent and short timescale
electrical characterization, we experimentally measure the onset of drift. This
additional feature of the structural relaxation dynamics serves as a new
benchmark to appraise the different classical models to explain drift.
