Dongsoo Lee

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.

Reversible resistive switching of SrTiOx thin films for nonvolatile memory applications

Nonvolatile and reversible bistable and multistable resistance states of polycrystalline SrTiOx thin film were studied. The pulse-laser-deposition method was employed to grow the film, and the clear resistance switching was observed under dc bias sweep and voltage pulses. More than two controllable resistance states were observed by applying voltage pulses. These reversible states have a resistance difference by nearly two orders of magnitude, and we verified that this sharp resistance switching takes place at the metal-oxide interface. Excellent reliability characteristics, such as endurance cycles of up to 105 times and data retention time of up to 106s at 125°C demonstrate the promise of SrTiOx film for future nonvolatile random access memory applications.

Resistance switching of the nonstoichiometric zirconium oxide for nonvolatile memory applications

The resistance switching behavior and switching mechanism of nonstoichiometric zirconium oxide thin films were investigated for nonvolatile memory application. The Pt/ZrO/sub x//p/sup +/-Si sandwich structure fabricated by reactive sputtering shows two stable resistance states. By applying proper bias, resistance switching from one to another state can be obtained. The composition in ZrO/sub x/ thin films were confirmed from X-ray photoelectron spectroscope (XPS) analysis, which showed three layers such as top stoichiometric ZrO/sub 2/ layer with high resistance, transition region with medium resistance, and conducting ZrO/sub x/ bulk layer. The resistance switching can be explained by electron trapping and detrapping of excess Zr/sup +/ ions in transition layer which control the distribution of electric field inside the oxide, and, hence the current flow.

Resistance-switching Characteristics of polycrystalline Nb/sub 2/O/sub 5/ for nonvolatile memory application

The resistance switching characteristics of polycrystalline Nb/sub 2/O/sub 5/ film prepared by pulsed-laser deposition (PLD) were investigated for nonvolatile memory application. Reversible resistance-switching behavior from a high resistance state to a lower state was observed by voltage stress with current compliance. The reproducible resistance-switching cycles were observed and the resistance ratio was as high as 50-100 times. The resistance switching was observed under voltage pulse as short as 10 ns. The estimated retention lifetime at 85/spl deg/C was sufficiently longer than ten years. Considering its excellent electrical and reliability characteristics, Nb/sub 2/O/sub 5/ shows strong promise for future nonvolatile memory applications.

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

We have investigated single crystal Nb-doped SrTiO₃ in terms of its potential utility in nonvolatile memory applications. Compared with polycrystalline oxide (Nb₂O₅, ZrO _x and Cr-SrTiO₃), the Pt/single crystal Nb:SrTiO ₃ Schottky junction exhibits excellent memory characteristics including uniformity of set/reset bias, die-to-die reproducibility, data retention at high temperature, reliability under cycle stress, and multi-bit operation characteristics. The switching mechanism might be explained by modulation of the Schottky barrier height by charge trapping at the interface

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

We have investigated copper-doped carbon (CuC) as a new solid-state electrolyte material for resistive switching devices. Compared with CuS electrolytes, CuC devices demonstrate good memory characteristics such as a high resistance ratio of over two orders, higher operation voltage, and high temperature retention characteristics. Using 1000 cell array devices, we have also confirmed uniform distributions of resistance and switching voltages. Both high and low resistance states showed negligible degradation of resistance for over 104 s at 85 °C, confirming good retention characteristics.

Excellent resistance switching characteristics of Pt/SrTiO/sub 3/ schottky junction for multi-bit nonvolatile memory application

Introduction Since the first observation of the bi-stable resistance states in 1960s, a great amount of work has been done in an effort to understand the switching mechanism and to improve electrical properties for Resistance Random Access Memory (RRAM) applications. Consequently, numerous oxides materials such as Nb2O5 , TiO2 , NiO[1] , Al2O3 and ferroelectrics oxide have been reported for RRAM applications. However, high operating voltage and current, poor endurance, and low electrical uniformity made the resistance memory unfavorable. Recently, perovskite structure materials such as Pr1-xCaxMnO3 (PCMO)[2] and epitaxial Cr-doped SrTi(Zr)O3 [3-4] films have also shown welldeveloped resistance switching either by DC or AC modes. Considering perovskite oxides with more than three components system, it is difficult to apply these materials for conventional semiconductor manufacturing processes. In this point of view, binary oxides with good resistive switching behavior have advantages. In this paper, we have investigated the resistance switching characteristics of nonstoichiometric oxides such as ZrOx , STOx and Al doped ZnO (Al:ZnO) on the silicon for nonvolatile memory applications.