Real-time switching dynamics of ferroelectric tunnel junctions under single-shot voltage pulses

In ferroelectric memory devices, information is stored within the polarization direction whose reversal usually occurs by the nucleation and propagation of domains. In ultrathin ferroelectrics, ultrafast dynamics may be achieved by nucleation-limited switching, avoiding the inherently speed-limited propagation of domain walls. Here, we investigate polarization reversal dynamics in ultrathin ferroelectric films by transient current measurements. Thanks to the tunnel electroresistance, the start of polarization reversal induces sharp variations of the transmitted current under voltage pulses. These single-shot measurements show extremely fast switching with durations down to 3 ns that is only limited by the current device geometry. While the OFF-to-ON switching shows finite nucleation times that scale with the pulse amplitude, the ON-to-OFF switching speed cannot be detected under such rectangular pulses. Resorting to triangular pulse excitations allows us to detect the dynamics of this switching direction. Both cases can be interpreted by nucleation switching models following Merz's law.