Wentai Lian

Highly Stable Radiation-Hardened Resistive-Switching Memory

In this letter, the resistive random access memory (RRAM) with metal-insulator-metal structure is investigated for the first time under radiation conditions. The fabricated Cu-doped HfO₂-based RRAM devices are found to have immunity from ⁶⁰Co γ ray of various dose ranges. The basic RRAM parameters such as high-resistance state, low-resistance state, SET/RESET voltages, operation speed, and endurance have nearly no degradation after ⁶⁰Co γ ray treatment with a total dose as high as 3.6 × 10⁵ rad (Si). Furthermore, a retention characteristic of 10⁵ s is also achieved during radiation. The highly stable characteristics of Cu-doped HfO₂ -based RRAM devices under radiation provide RRAM a great potential for aerospace and nuclear applications.

Improvement of resistive switching characteristics in ZrO2 film by embedding a thin TiOx layer.

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 ZrO(2)-based resistive memory devices has been investigated. Compared with the Cu/ZrO(2)/Pt structure device, by embedding a thin TiO(x) layer between the ZrO(2) and the Cu top electrode, the Cu/TiO(x)-ZrO(2)/Pt structure device exhibits much better resistive switching characteristics. The improvement of the resistive switching characteristics in the Cu/TiO(x)-ZrO(2)/Pt structure device might be attributed to the modulation of the barrier height at the electrode/oxide interfaces.

Improved Resistive Switching Uniformity in

In this letter, current sweeping programming mode is proposed as an efficient method to improve the uniformity of the switching properties of resistive memory devices. Based on the measurement results of the reset process of filament-based Cu/HfO2/Pt devices, current sweeping mode (CSM) can significantly reduce the distributions of Roff values, as compared with the standard voltage sweeping mode. The improvement is attributed to the elimination of the intermediate resistive states due to the positive feedback of joule heat generation by the use of current sweeping. Furthermore, the uniform distribution of the Vset values of the set process is also obtained by current sweeping, which stems from the localization of conductive filaments formation and rupture. CSM provides an effective way to achieve uniform resistance state of memory cell.

\hbox{Cu/HfO}_{2}/\hbox{Pt}

Memristor has been extensively investigated as the fourth fundamental circuit element. A common material in fabricating memristors is titanium oxide. The growth of titanium oxide has so far been focused on atomic layer deposition or sputtering, which is expensive. In this paper, a low-cost memristor device is demonstrated based on titanium oxide, grown by the thermal oxidation of deposited Ti film with a low-temperature process. Both the high and low resistance states of the device can be continually modulated by the successive voltage sweeps. Moreover, multilevel storage can be achieved in the device by using various maximum voltages during the set process.

Devices by Using Current Sweeping Mode

ZrO2-based resistive random access memory devices composed of a thin Cu doped ZrO2 film sandwiched between an oxidizable top electrode and an inert bottom electrode are fabricated by e-beam evaporation at room temperature. The devices show reproducible nonpolar resistive switching. The formation and annihilation of localized conductive filaments is suggested to be responsible for the resistive switching characteristics according to a series of convincing evidences. Temperature-dependent resistive switching behaviors show that a metallic conductive channel is responsible for the low resistance state. Further analysis reveals that the physical origin of this metallic channel is the nanoscale Cu conductive filament. The metal filaments are observed by TEM and the component is also confirmed. We propose that the set and reset process stem from the thermal effect assisted electrochemical reactions.

A low-cost memristor based on titanium oxide

1T1R-architecture devices were fabricated by integrating ZrO2 based crossbar structure ReRAM onto a foundry-built MOSFET platform. Multilevel operation was realized by using the current limit of a selected cell transistor in the set process. The current level was determined by the transistors gate voltage, resulting in the control of electrical resistance of the filamentary conductive paths in the low resistive state.

Resistive switching mechanism of Cu doped ZrO 2 -based RRAM

Voltage driving is a commonly used method to program the resistive switching memory. However, a question of whether voltage driving or current driving is preferred has never been answered. For periphery circuit design, one should first consider which kind of source should be adopted. In this work, we systematically evaluated the performance of Cu/HfO2/Pt memory device by using current sweeping or voltage sweeping to SET and RESET. The results show that, tight distribution of Roff and Vset can be achieved by using current driving to RESET, with effectively eliminating the intermediate resistance states. The possible reason for this improvement may arise from a positive-feedback of joule heat generation during RESET process. Besides, uniform Ron distribution can also be realized by current driving, due to more localized conductive filaments formation. The results demonstrate that the current driving method is an effective way to solve the uniformity issue of RRAM.

Multilevel storage characteristics in ZrO 2 -ReRAM brought about by ideal current limiter

The resistance switching characteristics of Cu doped HfO2 film are investigated for nonvolatile memory. Two stable states can be achieved under both pulse and DC electrical stress. Good performances including large storage window, fast operation speed, good endurance, and long time retention are shown in this device. The metallic filament is confirmed as the physical origin for resistance switching based on the temperature test.