Dong-jun Seong

Reproducible hysteresis and resistive switching in metal-CuxO-metal heterostructures

Materials showing reversible resistance switching between high-resistance state and low-resistance state at room temperature are attractive for today’s semiconductor technology. In this letter, the reproducible hysteresis and resistive switching characteristics of metal-CuxO-metal (M-CuxO-M) heterostructures driven by low voltages are demonstrated. The fabrication of the M-CuxO-M heterostructures is fully compatible with the standard complementary metal-oxide semiconductor process. The hysteresis and resistive switching behavior are discussed. The good retention characteristics are exhibited in the M-CuxO-M heterostructures by the accurate controlling of the preparation parameters.

Resistance switching of copper doped MoOx films for nonvolatile memory applications

Nonvolatile and reversible resistance switching of copper doped MoOx film was studied. Hysteretic-type resistive switching was observed under dc. Reproducible resistance switching over 106cycles was observed under alternative voltage pulses. Two resistance states can be maintained for 25h at 85°C. The authors proved that resistance switching might be strongly related with the rupture and generation of multifilaments confirmed by spreading resistance images of a conducting atomic force microscope as well as filamentary conduction by double logarithmic plots. Based on the x-ray photoelectron spectroscopy analysis, local conducting filaments could be formed by thermally diffused copper into MoOx film from the bottom electrode.

An electrically modifiable synapse array of resistive switching memory

This paper describes the resistive switching of a cross-point cell array device, with a junction area of 100 nm x 100 nm, fabricated using ultraviolet nanoimprinting. A GdO(x) and Cu-doped MoO(x) stack with platinum top and bottom electrodes served as the resistive switching layer, which shows analog memory characteristics with a resistance ratio greater than 10. To demonstrate a neural network circuit, we operated the cell array device as an electrically modifiable synapse array circuit and carried out a weighted sum operation. This demonstration of cross-point arrays, based on resistive switching memory, opens the way for feasible ultra-high density synapse circuits for future large-scale neural network systems.

Uniform resistive switching with a thin reactive metal interface layer in metal-La0.7Ca0.3MnO3-metal heterostructures

A thin samarium (Sm) metal layer was introduced to improve the resistive hysteresis and switching uniformity. Sm reacts with the La0.7Ca0.3MnO3 and forms a thin interface oxide layer, which is responsible for the switching. The switching occurs without any forming process. Compared with conventional resistive memory device based on localized filament formation, Sm∕La0.7Ca0.3MnO3 devices show area-dependent resistance which indicates uniform resistive switching. Under a positive bias, electromigration of oxygen ions (O2−) forms thicker oxide (SmOx), which dissociates under a negative bias, causes high and low resistance states, respectively. Estimated data retention of more than 10yr was observed at 85°C.

Excellent Switching Uniformity of Cu-Doped

We have investigated a Cu-doped MoO_x/GdO_x bilayer film for nonvolatile memory applications. By adopting an ultrathin GdO_x layer, we obtained excellent device characteristics such as resistance ratio of three orders of magnitude, uniform distribution of set and reset voltages, switching endurance up to 10⁴ cycles, and ten years of data retention at 85degC. By adopting bilayer films of Cu-doped MoO_x/GdO_x, a local filament was formed by a two-step process. Improved memory characteristics can be explained by the formation of nanoscale local filament in the ultrathin GdO_x layer.

\hbox{MoO}_{x}/\hbox{GdO}_{x}

We investigated the effect of high-pressure hydrogen annealing (HPHA) on a Pt/Nb-doped SrTiO 3 Schottky junction for nonvolatile memory applications. Hysteretic current-voltage (I-V) characteristic curves reveal that the HPHA-treated Schottky junction interface has a higher resistance ratio than the control sample in dc bias sweep. The HPHA sample also exhibits switching behavior by pulsed voltage stress with excellent electrical characteristics including voltage pulse duration as short as 1 μs, endurance cycles of up to 10 6 times, and retention time as long as 10 5 s. These indicate that HPHA improved resistance switching characteristics of the Schottky junction.

Bilayer for Nonvolatile Memory Applications

We have investigated various doped metal oxides such as copper doped molybdenum oxide, copper doped Al₂O₃, copper doped ZrO₂, aluminium doped ZnO, and Cu_xO for novel resistance memory applications. Compared with non-stoichiometric oxides (Nb₂O_5-x, ZrO_x, SrTiO_x), doped metal oxides show higher device yield. Moreover, Cu:MoO_x have demonstrated excellent memory characteristics such as reliability under programming cycles, potential multi-bit operation, good data retention, highly scalable property, and fast switching speed. The switching mechanism of the copper doped molybdenum oxide can be explained by the generation and rupture of multi-filaments under the electrical stress

HPHA Effect on Reversible Resistive Switching of Pt ∕ Nb -Doped SrTiO3 Schottky Junction for Nonvolatile Memory Application

Materials showing reversible resistance switching between high-resistance state and low-resistance state at room temperature are attractive for today’s semiconductor technology. In this letter, the improvement of reproducible hysteresis and resistive switching characteristics of metal-La0.7Ca0.3MnO3-metal (M-LCMO-M) heterostructures is demonstrated. The fabrication of the M-LCMO-M heterostructures is compatible with the standard complementary metal-oxide semiconductor process. The effect of oxygen annealing on the improvement of the hysteresis and resistive switching is discussed. The good retention characteristics are exhibited in the M-LCMO-M heterostructures by the accurate controlling of the preparation parameters.

Excellent uniformity and reproducible resistance switching characteristics of doped binary metal oxides for non-volatile resistance memory applications

A systematic study on the switching mechanism of an Al/ Pr0.7Ca0.3MnO3 (PCMO) device was performed. A polycrystalline PCMO film was deposited using a conventional sputtering method. A thin Al layer was introduced to induce a reaction with the PCMO, forming aluminum oxide (AlOx). Transmission electron microscopy analysis of the interface between Al and PCMO showed that resistive switching was governed by the formation and dissolution of AlOx. Some basic memory characteristics, such as good cycle endurance and data retention of up to 104 s at 125°C, were also obtained. It also showed excellent switching uniformity and high device yield.

Improvement of reproducible hysteresis and resistive switching in metal-La0.7Ca0.3MnO3-metal heterostructures by oxygen annealing

We investigated the state stability of the low-resistance state (LRS) in a resistive switching memory having a Pt/Cu:MoOx/GdOx/Pt structure. Various resistance values of LRS were accurately controlled using an external load resistor connected in series with the resistive memory device. We found that the retention time decreased with an increase in the resistance of LRS. We performed accelerating tests for resistance transition from a low- to a high-resistance state under temperatures ranging from 200°C to 250°C. A predicted resistance of LRS for a ten-year retention period at 85°C was determined based on the Arrhenius law.