R.Q. Han

Bipolar switching behavior in TiN/ZnO/Pt resistive nonvolatile memory with fast switching and long retention

Highly stable bipolar resistive switching behaviors of TiN/ZnO/Pt devices were demonstrated for the first time. The excellent memory characteristics including fast switching speed (<20 ns for set and <60 ns for reset), long retention (in the order of 105 s) and non-electroforming process were demonstrated. The bipolar switching behaviors can be explained by formation and rupture of the filamentary conductive path consisting of oxygen vacancies. The excellent bipolar switching behavior can be attributed to the significant amount of oxygen vacancies in ZnO film and the effect of TiN layer serving as an oxygen reservoir.

Highly uniform resistive switching characteristics of TiN/ZrO2/Pt memory devices

We fabricated the TiN/ZrO2/Pt sandwiched resistive switching memory devices. Excellent bipolar resistive switching characteristics, including a large number of switching cycles and highly uniform switching parameters, as well as long retention time were achieved. The improved switching behavior of TiN/ZrO2/Pt could be attributed to the oxygen reservoir effect of TiN electrodes on the formation and rupture of the filamentary conducting paths by modifying the concentration distributions of the oxygen ions and vacancies in ZrO2 thin films. The results demonstrate the feasibility of high performance resistive switching memory devices based on transition metal oxides by using TiN as the top electrode.

Oxide-based RRAM: Physical based retention projection

Based on the retention failure mechanism of high resistance state due to reconstruction of oxygen vacancy filament in the rupture region, a physical model is proposed to quantify the retention failure behavior of oxide-based RRAM devices, supported by experiments. A new data retention evaluation methodology is proposed to predict the failure probability and lifetime of the memory devices.

Anticrosstalk characteristics correlated with the set process for α-Fe2O3/Nb–SrTiO3 stack-based resistive switching device

A resistive switching device based on the stacked α-Fe2O3/Nb–SrTiO3 is proposed and fabricated that demonstrates excellent bipolar resistive switching behaviors including the uniformity, endurance, and retention performance. The Schottky-like current-voltage characteristics correlated with set process were observed in both high resistive states (HRSs) and low resistive states (LRSs) of the device. Importantly, the anticrosstalk characteristic, possessing higher reversed-biased LRS resistance than the forwarded-biased HRS resistance, indicates the potential applications of the stacked α-Fe2O3/Nb–SrTiO3 for multilevel storage in the cross-bar memory arrays. The carrier injection and trapping mechanism is suggested to explain the observed phenomena.

Oxygen-Vacancies-Related Room-Temperature Ferromagnetism in Polycrystalline Bulk Co-Doped TiO2

Room-temperature ferromagnetism (RTFM) is observed in the bulk Co x Ti 1 - x O 2 - δ (0.06 ≤ x ≤ 0.1) samples synthesized by the solid-state reaction method for the mixed powder of Ti and Co oxides, followed by a 500°C furnace annealing process in a 10% hydrogen-argon mixture of ambient gases. The X-ray diffraction, X-ray photoelectron spectroscopy, and measurements of magnetic susceptibility, Χ, vs temperature, T, indicate polycrystalline Co-doped TiO 2 anatase without Co clusters was fabricated. A phase transformation from CoTiO 3 to Co x Ti 1 - x O 2 - δ occurs after the hydrogenation process. These results are strong indications for formation of oxygen vacancies near the high spin Co 2 + sites, and the formed oxygen vacancies are essential for the generation of RTFM in Co x Ti 1 - x O 2 - δ . Based on these observations, ferromagnetism in bulk Co x Ti 1 - x O 2 - δ anatase could be attributed to the exchange interaction between Co 2 + mediated by oxygen vacancies near Co 2 + sites, not being caused by Co clusters.

Epitaxial growth of CeO/sub 2/[100] films on Si[100] substrates by dual ion beam reactive sputtering

The epitaxial growth of CeO/sub 2/[100] films on [100] silicon substrates by dual ion beam sputtering has been studied. The measurements of X-ray /spl theta/-2/spl theta/ pattern, /spl phi/-scan, and rocking curve indicated that the CeO/sub 2/ films had good epitaxial characteristics with [100] orientation. The influences of the substrate temperature, the oxygen pressure, and amorphous SiO/sub 2/ layer of the Si substrate surface on the epitaxial growth of the CeO/sub 2/ layer were investigated.

Identification and application of current compliance failure phenomenon in RRAM device

A new current sweep measurement method is introduced to investigate the details of the set process. The electrode-dependent current compliance failure phenomenon is investigated in oxide-based resistive switching memory. The results indicate that the amount of conductive filaments formed in the oxide layer is the critical factor that influences the set behavior (sudden or slowly) and causes the compliance failure. The different switching behaviors measured by the current sweep mode could be used as a criterion for distinguishing the RRAM devices from the applications of 1D1R or multilevel storage.

A compact model of resistive switching devices

In this paper a compact model both for bipolar and unipolar resistive switching device is proposed. Basic I–V characteristics of RRAM are easily and correctly represented by this model. The model is verified by the bipolar RRAM experiment results. The model can be used as simple and fast tool to design and optimize RRAM.

Bipolar resistive switching behaviors of Ag/Si 3 N 4 /Pt memory device

The resistive switching behavior of Ag/Si₃N₄/Pt device was observed and studied for the first time. Resistance ratio larger than 4*10² and 10⁴s retention time were achieved which indicating its potential for resistive switching memory application. A physical model is proposed to explain the resistive switching behaviors of Ag/Si₃N₄/Pt devices.

Gd doping improved resistive switching characteristics of TiO2-based resistive memory devices

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