Analysis on the Filament Structure Evolution in Reset Transition of Cu/HfO2/Pt RRAM Device

The resistive switching (RS) process of resistive random access memory (RRAM) is dynamically correlated with the evolution process of conductive path or conductive filament (CF) during its breakdown (rupture) and recovery (reformation). In this study, a statistical evaluation method is developed to analyze the filament structure evolution process in the reset operation of Cu/HfO₂/Pt RRAM device. This method is based on a specific functional relationship between the Weibull slopes of reset parameters' distributions and the CF resistance (R on). The CF of the Cu/HfO₂/Pt device is demonstrated to be ruptured abruptly, and the CF structure of the device has completely degraded in the reset point. Since no intermediate states are generated in the abrupt reset process, it is quite favorable for the reliable and stable one-bit operation in RRAM device. Finally, on the basis of the cell-based analytical thermal dissolution model, a Monte Carlo (MC) simulation is implemented to further verify the experimental results. This work provides inspiration for RRAM reliability and performance design to put RRAM into practical application

Quantum size effects in hafnium-oxide resistive switching

Discrete changes of conductance of the order of G0 = 2e2/h reported during the unipolar reset transitions of Pt/HfO2/Pt structures are interpreted as the signature of atomic-size variations of the conducting filament (CF) nanostructure. Our results suggest that the reset occurs in two phases: a progressive narrowing of the CF to the limit of a quantum wire (QW) followed by the opening of a spatial gap that exponentially reduces the CF transmission. First principles calculations show that oxygen vacancy paths in HfO2 with single- to few-atom diameters behave as QWs and are capable of carrying current with G0 conductance

Quantum size effects in hafnium-oxide resistive switching

Discrete changes of conductance of the order of G0 = 2e2/h reported during the unipolar reset transitions of Pt/HfO2/Pt structures are interpreted as the signature of atomic-size variations of the conducting filament (CF) nanostructure. Our results suggest that the reset occurs in two phases: a progressive narrowing of the CF to the limit of a quantum wire (QW) followed by the opening of a spatial gap that exponentially reduces the CF transmission. First principles calculations show that oxygen vacancy paths in HfO2 with single- to few-atom diameters behave as QWs and are capable of carrying current with G0 conductance

Conductance quantization in resistive random access memory

The intrinsic scaling-down ability, simple metal-insulator-metal (MIM) sandwich structure, excellent performances, and complementary metal-oxide-semiconductor (CMOS) technology-compatible fabrication processes make resistive random access memory (RRAM) one of the most promising candidates for the next-generation memory. The RRAM device also exhibits rich electrical, thermal, magnetic, and optical effects, in close correlation with the abundant resistive switching (RS) materials, metal-oxide interface, and multiple RS mechanisms including the formation/rupture of nanoscale to atomic-sized conductive filament (CF) incorporated in RS layer. Conductance quantization effect has been observed in the atomic-sized CF in RRAM, which provides a good opportunity to deeply investigate the RS mechanism in mesoscopic dimension. In this review paper, the operating principles of RRAM are introduced first, followed by the summarization of the basic conductance quantization phenomenon in RRAM and the related RS mechanisms, device structures, and material system. Then, we discuss the theory and modeling of quantum transport in RRAM. Finally, we present the opportunities and challenges in quantized RRAM devices and our views on the future prospects

Voltage and power-controlled regimes in the progressive unipolar RESET transition of HfO₂-based RRAM

Resistive switching (RS) based on the formation and rupture of conductive filament (CF) is promising in novel memory and logic device applications. Understanding the physics of RS and the nature of CF is of utmost importance to control the performance, variability and reliability of resistive switching memory (RRAM). Here, the RESET switching of HfO₂-based RRAM was statistically investigated in terms of the CF conductance evolution. The RESET usually combines an abrupt conductance drop with a progressive phase ending with the complete CF rupture. RESET1 and RESET2 events, corresponding to the initial and final phase of RESET, are found to be controlled by the voltage and power in the CF, respectively. A Monte Carlo simulator based on the thermal dissolution model of unipolar RESET reproduces all of the experimental observations. The results contribute to an improved physics-based understanding on the switching mechanisms and provide additional support to the thermal dissolution model