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\TaO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> \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.
Highlights
Today’s memory technologies inevitably approach the end of Moore’s law, which raises the need for new memory technologies [1]
The information in Redox-based random-access memory (ReRAM) devices is stored in its resistance, which can be programmed between a high resistive state (HRS) and a low resistance (LRS) by applying electrical stimuli
One class of ReRAM devices is the valence change memory (VCM), which is usually realized by a vertical stack of two metallic electrodes and a transition metal oxide (e.g., TaOx) sandwiched between the two electrodes [2]
Summary
Today’s memory technologies inevitably approach the end of Moore’s law, which raises the need for new memory technologies [1]. Applying a positive voltage to the active electrode repels the positively charged oxygen vacancies This results in a rupture of the conductive filament at the active electrode, bringing the device to the HRS. The strong non-linearity origins from the thermally accelerated drift of oxygen vacancies within the conducting filament occurring due to Joule heating during the SET and the RESET operation [6]–[9] This increase in temperature was observed experimentally [10]–[13]. By means of the estimated effectively applied voltage, we show that the SET kinetics of all three devices depend on their feature sizes and are mainly limited by the electrical charging time. We provide suggestions for the optimal integration of ReRAM devices into CPW structures
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