Nucleation of the ruthenium ͑Ru͒ precursor on low-k film surfaces during atomic layer deposition ͑ALD͒ of Ru was investigated. The adsorption tendency of the precursor decreased with increasing concentration of methyl groups on the low-k film surface, resulting in poor nucleation of Ru. The electron-deficient hydroxyl groups act as preferential adsorption sites for the electron-rich ligands of the aromatic Ru precursor through the formation of-bonds. This leads to the enhanced nucleation of Ru. The roles of the functional groups were corroborated by silylation experiments.
Effects of Ti top electrode on unipolar resistive switching characteristics are investigated for NiO based resistive switching memory with Ni-inserting layer, compared with those for Pt-electrode. Current-voltage curves for forming process are almost identical for Ti-Ni-NiO-Pt and Pt-Ni-NiO-Pt structure, which may suggest that Ti does not chemically react with NiO. However, I-V curves for reset and set operation with Ti top electrode show improved resistive switching behaviors, such as reduction of reset current and less variation of both high and low resistance states. In order to understand the mechanism for improved resistive switching properties, electro-thermal simulation is performed, which shows that improvement in resistive switching characteristics is ascribed to reduced heat flow through top electrode resulting from lower thermal conductivity of Ti as compared to Pt.
This study examined the various physical, structural and electrical properties of SiO(2) doped Ge(2)Sb(2)Te(5) (SGST) films for phase change random access memory applications. Interestingly, SGST had a layered structure (LS) resulting from the inhomogeneous distribution of SiO(2) after annealing. The physical parameters able to affect the reset current of phase change memory (I(res)) were predicted from the Joule heating and heat conservation equations. When SiO(2) was doped into GST, thermal conductivity largely decreased by ∼ 55%. The influence of SiO(2)-doping on I(res) was examined using the test phase change memory cell. I(res) was reduced by ∼ 45%. An electro-thermal simulation showed that the reduced thermal conductivity contributes to the improvement of cell efficiency as well as the reduction of I(res), while the increased dynamic resistance contributes only to the latter. The formation and presence of the LS thermal conductivity in the set state test cell after repeated switching was confirmed.
Threshold-switching (TS) and selector performances of Si-As-Te thin films for crossbar resistive memory were studied. Composition of the film was the major factor determining the emergence of TS. On-state conduction was found to occur at localized regions. The change of threshold voltage and off-state current by varying composition was observed, which were explained by the change in the concentration of defects and generation efficiency of carriers. The serially connected TiO2 unipolar switching memory and Si-As-Te threshold switch showed the resistance switching of the memory layer with the leakage current lowered by ∼120 times at 0.5 V.
This study examined the threshold switching voltage (VT) of 150 nm thick SiO2 doped Ge2Sb2Te5 (SGST) films for phase change random access memory applications. The VT of the SGST films increased from ∼0.9 V (for GST) to ∼1.5 V with increasing SiO2 content. The optical band gap and Urbach edge of the SGST films were similar regardless of the SiO2 concentration. The dielectric constant decreased by ∼37% and the electrical resistivity increased by ∼19%. The increase in VT of SGST films is associated with an effective increase in electric field and the decreased generation rate caused by impact ionization.
Abstract-Thermal stability of Ge 2 Sb 2 Te 5 (GST) and SiO 2 doped GST (SGST) films for phase change random access memory applications was investigated by observing the change of surface roughness, layer density and composition of both films after isothermal annealing. After both GST and SGST films were annealed at 325 o C for 20 min, root mean square (RMS) surface roughness of GST was increased from 1.9 to 35.9 nm but that of SGST was almost unchanged.
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