Switching Transients in Memristors

Transient performance of nanowire memristors realized using different material systems is discussed. The approach is validated by comparing simulated results with experimental data obtained for a ZnO nanowire memristor. The ZnO nanowire memristors demonstrate bipolar resistive switching with an R_OFF/R_ON ratio of 684 that is 3 times higher than the previous best report. The transient switching model, derived from the physical mechanisms for memristor switching, show a material dependent switching delay greatly influenced by the mobility of the oxygen vacancies. Measured switching delay of 372 µs for ZnO memristor show excellent agreement with the simulated data. The switching delays for other material systems, namely – TiO_x, TaO_x, HfO_x, and ZrO_x are calculated to be 2.5 s, 5.5 ns, 11.8 ps, and 7.15 ps, respectively, for identical device geometry (length 2 µm and diameter 300 nm). Upon scaling devices down to 50 nm, the delay is observed to decrease by 3-4 orders of magnitude. ZrO_x based memristors showed the shortest switching delay owing to a mobility as high as 370 cm²/V-s. Experimental data for ZnO memristors suggest rise and fall times shorter than 7 µs and 10 ns, respectively. Ultralow switching power of 261 µW and 155 µW are achieved for SET and RESET switching, respectively. Measured switching energy less than 83 nJ and slew rates greater than 0.02 V/µs are attained.