[en] Crossbar arrays are the most promising application of a resistive random access memory (RRAM) device for achieving high density memory. However, cross-talk interference in the crossbar array limits the increase in the integration density. In this paper, the combination of two anti-parallel connected diodes and a bipolar RRAM cell is proposed to suppress the sneak current in a crossbar array with anti-parallel connected diodes as the selector for the bipolar RRAM. By using the anti-parallel connected diodes as a selector, the sneak current can be effectively suppressed and the high density crossbar array of more than 1 Mb can be realized as estimated by the 1/2V _read voltage scheme. These results indicate that anti-parallel connected diodes can be used as a bipolar selector and have great potential for high density bipolar RRAM crossbar array applications. (papers)

[en] A crossbar array is usually used for the high-density application of a resistive random access memory (RRAM) device. However, the cross-talk interference limits the increase in the integration density. In this paper, anti-series connected Zener diodes as a selection device are proposed for bipolar RRAM arrays. Simulation results show that, by using the anti-series connected Zener diodes as a selection device, the readout margin is sufficiently improved compared to that obtained without a selection device or with anti-parallel connected diodes as the selection device. The maximum size of the crossbar arrays with anti-series connected Zener diodes as a selection device over 1 TB is estimated by theoretical simulation. In addition, the feasibility of using the anti-series connected Zener diodes as a selection device for bipolar RRAM is demonstrated experimentally. These results indicate that anti-series connected Zener diodes as a selection device opens up great opportunities to realize ultrahigh-density bipolar RRAM arrays. (paper)

[en] Cross-bar arrays are usually used for the high density application of resistive random access memory (RRAM) devices. However, cross-talk interference limits an increase in the integration density. In this paper, the Zener diode is proposed as a selection device to suppress the sneak current in bipolar RRAM arrays. Measurement results show that the Zener diode can act as a good selection device, and the sneak current can be effectively suppressed. The readout margin is sufficiently improved compared to that obtained without the selection device. Due to the improvement for the reading disturbance, the size of the cross-bar array can be enhanced to more than 10³ × 10³. Furthermore, the possibility of using a write-once-read-many-times (WORM) cross-bar array is also demonstrated by connecting the Zener diode and the bipolar RRAM in series. These results strongly suggest that using a Zener diode as a selection device opens up great opportunities to realize high density bipolar RRAM arrays. (paper)

[en] In this paper, the effect of a low constant current stress (CCS) treatment on the performance of a Cu/ZrO₂/Pt resistive switching device is investigated. The conductance of the device increases about two orders of magnitude after CCS treatment, indicating that some defects are introduced into the ZrO₂ matrix and the CCS treatment can be regarded as an electrical doping process. Benefiting from these introduced defects, better resistive switching performance is obtained after CCS treatment, including low forming voltage, low reset current, uniform resistive switching and good endurance characteristics. (paper)

[en] In this letter, we dynamically investigate the resistive switching characteristics and physical mechanism of the Ni/ZrO₂/Pt device. The device shows stable bipolar resistive switching behaviors after forming process, which is similar to the Ag/ZrO₂/Pt and Cu/ZrO₂/Pt devices. Using in situ transmission electron microscopy, we observe in real time that several conductive filaments are formed across the ZrO₂ layer between Ni and Pt electrodes after forming. Energy-dispersive X-ray spectroscopy results confirm that Ni is the main composition of the conductive filaments. The ON-state resistance increases with increasing temperature, exhibiting the feature of metallic conduction. In addition, the calculated resistance temperature coefficient is equal to that of the 10–30 nm diameter Ni nanowire, further indicating that the nanoscale Ni conductive bridge is the physical origin of the observed conductive filaments. The resistive switching characteristics and the conductive filament's component of Ni/ZrO₂/Pt device are consistent with the characteristics of the typical solid-electrolyte-based resistive random access memory. Therefore, aside from Cu and Ag, Ni can also be used as an oxidizable electrode material for resistive random access memory applications.

[en] The effect of nitrogen doping by the NH₃ plasma treatment approach on the resistive switching properties of a HfO₂-based resistive random access memory (RRAM) device is investigated. Test results demonstrate that significantly improved performances are achieved in the HfO₂-based RRAM device by nitrogen doping, including low operating voltages, improved uniformity of switching parameters, satisfactory endurance and long retention characteristics. Doping by nitrogen is proposed to suppress the stochastic formation of conducting filaments in the HfO₂ matrix and thus improve the performances of the Pt/Ti/HfO₂/Pt device. (paper)

[en] Diode-like volatile resistive switching as well as nonvolatile resistive switching behaviors in a Cu/ZrO_2/TiO_2/Ti stack are investigated. Depending on the current compliance during the electroforming process, either volatile resistive switching or nonvolatile resistive switching is observed. With a lower current compliance (<10 μA), the Cu/ZrO_2/TiO_2/Ti device exhibits diode-like volatile resistive switching with a rectifying ratio over 10"6. The permanent transition from volatile to nonvolatile resistive switching can be obtained by applying a higher current compliance of 100 μA. Furthermore, by using different reset voltages, the Cu/ZrO_2/TiO_2/Ti device exhibits multilevel memory characteristics with high uniformity. The coexistence of nonvolatile multilevel memory and diode-like volatile resistive switching behaviors in the same Cu/ZrO_2/TiO_2/Ti device opens areas of applications in high-density storage, logic circuits, neural networks, and passive crossbar memory selectors. (fast track communication)

[en] The stabilization of the resistive switching characteristics is important to resistive random access memory (RRAM) device development. In this paper, an alternative approach for improving resistive switching characteristics in ZrO₂-based resistive memory devices has been investigated. Compared with the Cu/ZrO₂/Pt structure device, by embedding a thin TiO_x layer between the ZrO₂ and the Cu top electrode, the Cu/TiO_x-ZrO₂/Pt structure device exhibits much better resistive switching characteristics. The improvement of the resistive switching characteristics in the Cu/TiO_x-ZrO₂/Pt structure device might be attributed to the modulation of the barrier height at the electrode/oxide interfaces.

[en] In this paper, the resistive switching characteristics in a Cu/HfO₂:Cu/Pt sandwiched structure is investigated for multilevel non-volatile memory applications. The device shows excellent resistive switching performance, including good endurance, long retention time, fast operation speed and a large storage window (R_OFF/R_ON>10⁷). Based on the temperature-dependent test results, the formation of Cu conducting filaments is believed to be the reason for the resistance switching from the OFF state to the ON state. By integrating the resistive switching mechanism study and the device fabrication, different resistance values are achieved using different compliance currents in the program process. These resistance values can be easily distinguished in a large temperature range, and can be maintained over 10 years by extrapolating retention data at room temperature. The integrated experiment and mechanism studies set up the foundation for the development of high-performance multilevel RRAM.