Heedo Na

Anion-Migration-Induced Bipolar Resistance Switching in Electrochemically Deposited TiO x Films

TiO x films were electrochemically deposited on TiN and Pt electrodes with a subsequent annealing under N 2 or O 2 ambient. The resistive switching characteristics of such TiO x films were investigated. The electrodeposited TiO x films showed bipolar resistive switching and the operation voltages such as electroforming voltage, and reset/set voltages showed a dependence on the annealing ambient, displaying higher operation voltages for the annealing under O 2 than for the annealing under N 2 . The compositions of the different chemical states of species in TiO x films were observed to be modulated by the condition of electrochemical deposition and the subsequent annealing. The TiO x films annealed under the O 2 ambient showed a less concentration of nonlattice oxygen ions than under N 2 ambient. The reduction of nonlattice oxygen for annealing under O 2 was accompanied by the increase of Ti 3+ in TiO x films and the increased reset/set voltages. It was concluded that the bipolar resistive switching of the electrochemically deposited TiO x film was strongly related to the nonlattice oxygen anions in the films.

Effect of Al doping on resistive switching behavior of NiOx films for nonvolatile memory application

In this work, the authors investigated the effect of Al doping on the resistance switching characteristics of sputtered NiOx films. Pt/NiOx/Pt metal-insulator-metal (MIM) stacks were fabricated by reactive dc magnetron sputtering with various Al contents in NiOx films and the resistance switching behavior of the MIM stack was characterized in conjunction with physical property, such as chemical bonding of NiOx. Al doping into NiOx films improved the endurance of SET/RESET operations, the distribution of VSET, and the memory window compared to the undoped NiOx films. X-ray photoemission spectroscopy showed that the Al doping caused the density of metallic nickel (Ni0) to be increased with the reduction of Ni3+ concentration. It was considered that the increase of metallic nickel (Ni0) in Al-doped NiOx films enhanced the repeated formation and rupture of conductive filaments during resistive switching operation, resulting in the enhanced endurance and the narrowed VSET distribution.In this work, the authors investigated the effect of Al doping on the resistance switching characteristics of sputtered NiOx films. Pt/NiOx/Pt metal-insulator-metal (MIM) stacks were fabricated by reactive dc magnetron sputtering with various Al contents in NiOx films and the resistance switching behavior of the MIM stack was characterized in conjunction with physical property, such as chemical bonding of NiOx. Al doping into NiOx films improved the endurance of SET/RESET operations, the distribution of VSET, and the memory window compared to the undoped NiOx films. X-ray photoemission spectroscopy showed that the Al doping caused the density of metallic nickel (Ni0) to be increased with the reduction of Ni3+ concentration. It was considered that the increase of metallic nickel (Ni0) in Al-doped NiOx films enhanced the repeated formation and rupture of conductive filaments during resistive switching operation, resulting in the enhanced endurance and the narrowed VSET distribution.

Performance improvement of metal-Al2O3-HfO2-oxide-silicon memory devices with band-engineered Hf-aluminate/SiO2 tunnel barriers

Physical properties of Hf-aluminate (HA) films with various compositions, deposited by atomic layer deposition, were investigated in terms of microstructure, band-gap, and band-offset with respect to Si. Charge trap flash (CTF) memory devices based on HA/SiO2 stacks as tunnel barriers were also fabricated and characterized. Modulation of HA film composition produced controlled changes of the films band-gap and band-offset. Additionally, the tunneling efficiency of the HA/SiO2 tunnel barrier stacks was observed to be higher than that for a single SiO2 tunnel barrier, in particular at high voltage bias. The band-engineered CTF memory devices with HA/SiO2 tunnel barriers showed improved program/erase speed compared with those with single SiO2 tunnel barrier. The Al-rich HA/SiO2 tunnel barriers showed a longer charge retention time with superior endurance characteristics; in contrast, the Hf-rich HA/SiO2 tunnel barrier showed degraded charge retention because of current leakage through crystallized regions i...

High-mobility property of crystallized In-Te chalcogenide materials

In-Te films were deposited by ion beam sputtering deposition (IBSD) using In and Te targets. The crystallization characteristics of the resulting films were investigated by 4-point Rs measurement, x-ray diffraction (XRD), transmission electron microscopy (TEM), and the Hall-effect measurement system. As the amount of In was increased in In-Te, the crystallization temperature increased. X-ray data for the crystalline structure show that phase separation to In2Te3 and InTe occurred in InTe and In3Te2 samples after annealing at 350°C. The value of carrier mobility and concentration decreased in order of In2Te3, In3Te2, and InTe. The decreasing value is caused by phase separation and is the unique property of chemical composition.

Effect of oxygen diffusion into TiN on resistance switching characteristics of ZrO 2 films with annealing temperatures

In this study, the effects of annealing temperature on both physical and resistive switching properties of ZrO<inf>2</inf> films were investigated. XRD showed the increase of the monoclinic phase in the as-grown tetragonal ZrO<inf>2</inf> with annealing above 450°C. The ZrO<inf>2</inf> films exhibited the unipolar and the bipolar switching behaviors in Pt/ZrO<inf>2</inf>/TiN MIM structure. The HRS resistance in unipolar switching behavior was reduced with increasing annealing temperature. On the contrary, The HRS resistance in bipolar switching behavior was increased. XPS showed the increase of metallic Zr in annealed ZrO<inf>2</inf> films that could cause the reduction of HRS resistance in unipolar resistance switching of ZrO<inf>2</inf>. SIMS spectra confirmed the enlargement of interfacial TiO<inf>x</inf>N<inf>y</inf> layer in TiN bottom electrode with increasing the annealing temperature. The enlargement of interfacial TiO<inf>x</inf>N<inf>y</inf> layer was expected to cause an increase of HRS resistance because the larger amount of mobile oxygen ions in inter-facial TiO<inf>x</inf>N<inf>y</inf> layer was possible to migrate to ZrO<inf>2−x</inf> films.

Effect of aliovalent impurities on the resistance switching characteristics of sputtered hafnium oxide films

In this work, the effects of various aliovalent impurities on the resistance switching characteristics of hafnium oxide (HfO2) films were investigated in conjunction with analyses of chemical bonding states and film microstructure. HfO2 films were cosputtered with magnesium, aluminum, and niobium by reactive DC magnetron sputtering. Doping with aliovalent elements caused the nonlattice oxygen concentration of HfO2 to increase and grain size to decrease. Also, post-thermal annealing induced a further increase of the concentration of nonlattice oxygen in the doped HfO2. Impurity doping improved the uniformities of the resistances of the low and high resistance states for cycled SET/RESET operations of titanium nitride/doped HfO2/platinum stacks, particularly for the magnesium-doped HfO2 films.