Determining the Electrical Charging Speed Limit of ReRAM Devices

Abstract

Redox-based random-access memory (ReRAM) has the potential to successfully address the technological barriers that today's memory technologies face. One of its promising features is its fast switching speed down to 50 ps. Identifying the limiting process of the switching speed is, however, difficult. At sub-nanosecond timescales three candidates are being discussed: An intrinsic limitation, being the migration of mobile donor ions, e.g. oxygen vacancies, the heating time, and its electrical charging time. Usually, coplanar waveguides (CPW) are used to bring the electrical stimuli to the device. Based on the data of previous publications, we show, that the rise time of the effective electrical stimulus is mainly responsible for limiting the switching speed at the sub-nanosecond timescale. For this purpose, frequency domain measurements up to 40 GHz were conducted on three Pt\TaOx\Ta devices with different sizes. By multiplying the obtained scattering parameters of these devices with the Fourier transform of the incoming signal, and building the inverse Fourier transform of this product, the voltage at the ReRAM device can be determined. Finally, the rise time of the voltage at the ReRAM device is calculated, which is a measure to the electrical charging time. It was shown that this rise time amounts to 2.5 ns for the largest device, which is significantly slower than the pulse generator's rise time. Reducing the device's rise time down to 66 ps is possible, but requires smaller features sizes and other optimizations, which we summarize in this paper.

Intrinsic RESET Speed Limit of Valence Change Memories

“…Recently, we have shown that 50 ps fast SET times can be achieved for TaO x - and ZrO x -based VCM devices, which corresponds to the limitation of the experimental setup. We also demonstrated that the SET kinetics are mainly delayed by the electrical charging time in the subnanosecond regime and not by intrinsic processes, such as the migration of ions or the heating of the filamentary region . The fast heating results from the narrow filament, which has only a diameter in the range from 1 nm to 3 nm .…”

Intrinsic RESET speed limit of valence change memories

“…Recently, we have shown that 50 ps fast SET times can be achieved for TaO x -and ZrO x -based VCM devices [39], which corresponds to the limitation of the experimental setup. We also demonstrated that the SET kinetics are mainly delayed by the electrical charging time in the sub-nanosecond regime and not by intrinsic processes, such as the migration of ions or the heating of the filamentary region [40]. The fast heating results from the narrow filament, which has only a diameter in the range from 1 nm to 3 nm [41].…”

“…At the center the inner conductor is tapered to 2 µm, matching the dimensions of the 2 × 2 µm 2 devices. More information and illustrations of this structures are given in [40].…”

“…These CPW structures have gained more attention in recent years, as they can be used to realize radio frequency (RF) switches with memristive devices [55,56]. Recently, we have shown for the TaO x -based device that the electrical charging occurs within less than 80 ps, if the device is integrated in a proper CPW structure [40]. The scattering parameters of both devices are shown in the supplementary Fig.…”

“…As the 50 Ω transmission line is terminated with a high ohmic VCM device (even the resistance of the LRS is much larger than 50 Ω), the voltage at the device effectively doubles. This is due to the overlap of incoming pulse and the reflected pulse at the VCM device (see also supplementary section S.1 or [40]) 2 The measurement cycles of the ZrOx-based device at a voltage of 1.6 V were repeated 20 times to achieve a smooth line of R Post /R PRE . FWHM of the applied pulse.…”