Study of the SET switching event of VCM-based memories on a picosecond timescale

In this paper, we present an approach of measuring the SET kinetics of redox-based resistive memories at timescales below 100 ps. Automatic measurements with an RF pulse generator and a source measure unit allow the consecutive application of short electrical pulses and the precise detection of the device resistance. In addition, a statistical evaluation of the SET kinetics has been performed. By increasing the pulse duration in small steps, varying the pulse amplitude and collecting a comprehensive dataset, the transient resistance of a device can be determined at a picosecond timescale. With this setup, we measured the SET kinetics of two different valence change memory-based resistive switching oxides, namely, TaO_x and ZrO_x, between 50 ps and 250 ps. Two characteristic times were measured: the SET time, being the delay after which the transition to the low resistance state sets in, and the transition time, which is the timespan during which the resistance shifts from the high to the low resistive state. We measured SET times down to 50 ps and transition times below 15 ps for both materials. The intrinsic maximum switching speed is not reached yet, which is limited by the ion migration in the oxides, possibly corresponding to the phonon THz frequency. Although charging times and heating times potentially slow down the measured SET times, they still allow 50 ps writing times at voltages of less than 5.0 V.