Hayato Tanaka

Opposite bias polarity dependence of resistive switching in n-type Ga-doped-ZnO and p-type NiO thin films

A hypothesis based on the model that explains the resistance change effect of resistive random access memory by redox reaction is proposed. This hypothesis leads to the conclusion that the relationship between the polarity of the applied bias voltage and the resultant resistance change in p-type semiconductors is opposite to that for n-type semiconductors. The bias polarity dependence of the resultant resistance change in ZnO and Ga-doped ZnO (GZO), which are n-type semiconductors, and that in NiO, which is a p-type semiconductor, were investigated using conducting atomic force microscopy. Opposite bias polarity was confirmed to induce GZO and NiO into the same resistance state, which is consistent with the hypothesis.

Correlation between filament distribution and resistive switching properties in resistive random access memory consisting of binary transition-metal oxides

Large variation in basic memory properties is a serious issue that hinders the practical use of ReRAMs. This study revealed that one of the main factors causing variation is the presence of multiple filaments in each memory cell. An operating filament switches to another filament having the smallest set voltage at each instant of switching. We propose a resistive switching model that takes the presence of multiple filaments into consideration. A Monte Carlo simulation based on the resistive switching model reproduces the V set distribution. The dependence of on the number of switching cycles was predicted by the model and confirmed experimentally.

Insight into distribution and switching of resistive random-access memory filaments based on analysis of variations in memory characteristics

Two hypotheses were formulated to validate a multi-filament model (MFM) as a mechanism for the cycle-to-cycle dispersion of Vset in resistive random-access memory. The first is that the probability of Δ(1/Vset) > 0, P[Δ(1/Vset) > 0], increases with the number of filaments in one memory cell, Nfila, and decreases with increasing switching cycle, n. Here, Δ(1/Vset) is the difference between the inverse of the set voltages after the n-th and (n + 1)-th reset processes [1/Vset(n) − 1/Vset(n + 1)]. Thus, Vset decreases with increasing Nfila and increases with n. The second hypothesis is that the probability of Δ(1/R) > 0, P[Δ(1/R) > 0], agrees with P[Δ(1/Vset) > 0], assuming that vset depends on d in the MFM. Here, Δ(1/R) = 1/Rn − 1/Rn + 1, and Rn, vset, and d represent the resistance in the high-resistance state after the n-th reset process, the set voltage of each filament, and the thickness of a gap between the electrode and the end of the filament, respectively. The validity of these two hypotheses was con...

Flexible and transparent ReRAM with GZO-memory-layer and GZO-electrodes on large PEN sheet

Fabrication of flexible transparent ReRAM consisting of the GZO memory layer and GZO-electrodes on the PEN sheet with large area was attained by the introduction of the RF plasma assist DC magnetron sputtering method. Resistive switching mechanism of all-GZO-FT-ReRAM can be explained by the redox model as well as that of conventional binary transition metal oxides. Reset switching of all-GZO-FT-ReRAM which memory layer is GZO(RH2=5%) is smooth and continuous, which enables the verify operation and the multilevel application.

Fabrication of Bi2Sr2Can-1CunOy / Al2O3-Particles on MgO Films by rf Magnetron Sputtering Method

We deposited Bi2Sr2Ca1Cu2Oy (Bi-2212) superconducting thin films on MgO substrates with or without Al2O3 particles by the rf magnetron sputtering method. From the results, we found that optimum target-substrate distance, rf powers and substrate temperature for obtaining the Bi-2212 films on the MgO substrates were 5mm, 150W and 830°C, respectively. The Bi-2212 films were Bi-2212 single-phase and had the Tc of about 54K . The particle size and the distribution density of Al2O3 were controlled by annealing temperature. The Bi-2212/Al2O3/MgO film showed Bi-2212 single-phase, whereas did not show zero-resistance.