Atomic Layer Deposition Metal Oxide Resistance Research Variable Storage Device

As conventional flash memory facing a size limit in the near future, a surge of extensively investigation has been developed in resistive switching phenomena for potential applications in next generation memory devices called resistance random access memory (RRAM). Because of its simple cell structure, superior scalability, fast switching speed, low power operation, long retention time and CMOS compatibility, resistive switching behaviors in metal oxides have attracted considerable attentions for the possible application in next generation nonvolatile memory (NVM). Up to now, the details of the resistive switching mechanism are not yet been well understood, although various models have been proposed, including the filamentary model, the space charge limited model, the Mott transition model, and the Schottky-like barrier model. Recently, the formation and rupture of conductive filaments in oxide were frequently adopted to elucidate the resistive switching behavior. It appears that a certain portion of the filaments actively contributes to the switching under an external stimulus such as electrical field or temperature. However, the realization of RRAM is hampered by issues such as the set and reset voltage dispersion and unstable resistance states profile. Thus, how to effectively improve the stability of switching behavior is an essential issue for practical application of the RRAM. Although several research groups have reported the phenomena of improvements in characteristics, the fundamental physical mechanism is still not clear. Therefore, a profound understanding of the kinetics of the resistance state transition is urgent essentially for the realization of RRAM in industrial application. The conclusions obtained in this thesis are of high academically value for the applications of RRAM in next generation nonvolatile memory technology.Among various dielectric materials, La2O3, HfO2and Nb2O5are promising high-k dielectrics candidates in advanced CMOS technology, which have been extensively investigated for replacing conventional SiO2or SiON gate dielectrics in MOSFETs and MIM capacitors. Nb2O5, HfO2and La2O3based RRAM cells are systematically investigated for nonvolatile resistive random access memory applications. Nb2O5based RRAM show the low resistance ON state and high resistance OFF state can be reversibly altered under a low voltage about±1V. More than1000reproducible switching cycles by DC voltage sweep were observed with a resistance ratio above10, which was large enough to read out without obvious degradation. The effect of pulse time and deposition temperature on the growth rate was investigated. The low resistance ON state and high resistance OFF state can be reversibly altered under a low voltage about1.5Vand-0.6V. Moreover, the estimated working characteristics such as set and reset voltages distribution were sufficiently stable to fulfill requirement for memory application. Considering the excellent memory switching behavior, resistance switch device composed of a promising ALD high-k La2O3dielectric film is a possible candidate to be integrated into future memory processes. We have designed experimental method to demonstrate the presence of the conducting filaments and such conducting filaments rupture near the anode. And the existence of local conductive filaments induced set and reset behaviours were observed using conductive atomic force microscopy (CAFM).The critical RRAM parameters are investigated in HfLaO-based devices with TaN as top electrodes. The excellent resistive switching characteristics of atomic layer deposited HfLaO based devices were investigated for non-volatile memory applications. With the help of non-lattice oxygen ions which is designed to incorporate into the film by decomposition of H2O2during process, highly uniform and reproducible resistance switching cycles could be observed with the resistive ratio as high as106for more than10000cycles. And the fast operation speed (10ns) has been demonstrated. Moreover, the estimated readout characteristics under different read voltages from0.3V to1V were sufficiently stable to fulfill requirement for memory application. We found that Joule heat only cannot explain the resistive switching, and that the involved charge trapping effect needed to be addressed in detail, especially for resistive switching behaviors at low temperatures, we investigated the current voltage characteristics of HfAlO-based memory devices at low temperatures ranging from5to300K. It is very interesting that we found a critical temperature region for resistive switching. It is suggested that the resistive switching characteristics of the binary transitional metal oxides are governed by thermal assisted percolating conductive paths. The process of charge trap/de-trapping under the external electrical field plays a dominated role on the assumption that the same Joule heating is generated by internal conductive filaments at different temperatures.We proposed an electrical field modulating (EFM) resistive switching model to minimize the dispersion of the random resistive switching. Kinds of resistive switch stacks are used in the RRAM structure instead of a single resistive switching functional layer. Based on the facts that the different dielectric constant between the dielectric films can induce the electric field multiformity in the stack structure, the electric field distribution can be locally controlled. Al2O3/high-k oxides/Al2O3resistive switch stacks are utilized to expound the EFM resistive switching model in experimental. The electrical field in Al2O3is much larger than that in the film with high dielectric constant when a voltage is applied on anode. As a result, the formation and rupture of conducting filaments is designed to happen within the thin Al2O3region at anode. The minimized dispersions of memory switching parameters in robust oxide stack based RRAM with thin Al2O3buffer layers at metal-oxide interfaces has been observed. The EFM model provides an indication of how to optimize the switching parameters such as switching voltages dispersion, which is currently considered the most serious obstacle to practical RRAM applications.Typical controllable multilevel operations with different resistance states were successfully demonstrated through adjusting the current compliance during the set process precisely. Multilevel storage is believed to be feasible via applying different current compliance during the set process in RRAM cells. Resistive switching behaviors of Al2O3based memory devices with and without ruthenium nanocrystals (RuNCs) fabricated by atomic layer deposition are investigated for non-volatile memory applications. Large resistance ratios (>105) of high resistance state to low resistance state were observed with nanocrystals contribution. Moreover, improvements of stability device yield and retention performance were also achieved by embedding Ru nanocrystals.