Ion Migration Barrier Research Articles

Theoretical studies on distribution of resistances in multilevel bipolar oxide resistive memory by Monte Carlo method

We simulate resistance distributions of multilevel oxide bipolar resistive random access memories (ReRAMs) through a physical model with Monte Carlo method. The model is used to explain frequently noticed proportionality relationship between distributions of resistances and multi-levels program voltages. By comparing with the experimental results obtained with TaOx/Ta2O5 bipolar ReRAM, the model is verified to have a good consistency with experiments not only qualitatively but also quantitatively. We demonstrate that the resistance distributions responses are basically determined by the ion migration barrier in the resistance varying thin oxide layer which means that it is a nearly intrinsic material property.

Gd-doping effect on performance of HfO2 based resistive switching memory devices using implantation approach

An implantation doping approach is implemented to fabricate Gd-doped HfO2 resistive random access memory (RRAM) devices. The significantly enhanced performances are achieved in the Gd-doped HfO2 RRAM devices including improved uniformity of switching parameters, enlarged ON/OFF ratio, and increased switching speed without obvious reliability degradation. This performance improvement in the Gd-doped HfO2 RRAM devices is clarified to the suppressed randomicity of oxygen vacancy filaments’ formation and the reduced oxygen ion migration barrier induced by trivalent Gd-doping effect. The achieved results also demonstrate the validity of implantation doping approach for the fabrication of RRAM devices.

The n-Cu0.9Ag0.1In3Se5 chalcopyrite, electronic as well as ionic conductor

A resistance increase with time of the n-Cu0.9Ag0.1In3Se5 chalcopyrite has been observed. This new effect is analysed in terms of a hypothesis of ion migration and Schottky barrier formation. These results might explain why different solar cell efficiencies are obtained for the chalcopyrites, CuInSe2 and CuIn x Ga1−x Se2, when an In-rich film is deposited on top of the chalcopyrite. In these solar cells, ion migration can exist and a new effect appears similar to the one observed in our compound.The ions, probably the cations, are moved by the electrical field towards the cathode. A gradient of mobile ions appears across the sample and the positive charge is accumulated near this electrode such that it varies the metal–semiconductor interface. This interface is a Schottky barrier where the contact potential is a function of time due to the arrival of ions.The electrical measurements have been carried out on a solid state device, graphite/n-Cu0.9Ag0.1In3Se5/graphite. The current intensity and the potential drop across the sample have been measured with time when a constant electrical potential is applied for 600 s at dark or under ultraviolet illumination and at room temperature. A comparative study in similar electrical conditions is done; the current intensity difference and the potential drop across the difference (under ultraviolet illumination minus at dark) are not constant and both measurements increase with time.

A molecular dynamics study of ion-conduction mechanisms in crystalline low-Mw LiPF6·PEO6

Molecular dynamics (MD) simulation has been used to probe ion-conduction mechanisms in crystalline LiPF6·PEO6 for smectic- and nematic-ordered models of methyl-terminated short-chain monodisperse poly(ethylene oxide) chains with the formula CH3–(OCH2CH2)23–OCH3; Mw = 1059. The effect of aliovalent substitution of the PF6− anion by ca. 1% SiF62− has also been studied. External electric fields in the range 3–6 × 106 V m−1 have been imposed along, and perpendicular to, the chain direction in an effort to promote ion transport during the short time-span of the simulation. Ion-migration barriers along the polymer channel are lower for the nematic models than for the smectic, with anions migrating along the channels more readily than Li-ions. Ion mobility within the smectic interface could also be confirmed, but at a higher field-strength threshold than along the chain direction. Li-ion migration within the smectic plane appears to be suppressed by ion pairing, while Li-ion transport across the smectic gap is facilitated by uncoordinated methoxy end-groups. Interstitial Li-ions introduced into the PEO channel through SiF62− doping are also shown to enhance Li-ion conduction.