Phase change random access memory appears to be the strongest candidate for next-generation high density nonvolatile memory. The fabrication of ultrahigh density phase change memory (≫1 Gb) depends heavily on the thin film growth technique for the phase changing chalcogenide material, most typically containing Ge, Sb and Te (Ge–Sb–Te). Atomic layer deposition (ALD) at low temperatures is the most preferred growth method for depositing such complex materials over surfaces possessing extreme topology. In this study, [(CH3)3Si]2Te and stable alkoxy-Ge (Ge(OCH3)4) and alkoxy-Sb (Sb(OC2H5)3) metal–organic precursors were used to deposit various layers with compositions lying on the GeTe2–Sb2Te3 tie lines at a substrate temperature as low as 70 °C using a thermal ALD process. The adsorption of Ge precursor was proven to be a physisorption type while other precursors showed a chemisorption behavior. However, the adsorption of Ge precursor was still self-regulated, and the facile ALD of the pseudobinary solid solutions with composition (GeTe2)(1‑x)(Sb2Te3) x were achieved. This chemistry-specific ALD process was quite robust against process variations, allowing highly conformal, smooth, and reproducible film growth over a contact hole structure with an extreme geometry. The detailed ALD behavior of binary compounds and incorporation behaviors of the binary compounds in pseudobinary solid solutions were studied in detail. This new composition material showed reliable phase change and accompanying resistance switching behavior, which were slightly better than the standard Ge2Sb2Te5 material in the nanoscale. The local chemical environment was similar to that of conventional Ge2Sb2Te5 materials.

The role of Al dopant in rutile-phased TiO2 films in the evaluation of the mechanism of leakage current reduction in Al-doped TiO2 (ATO) was studied in detail. The leakage current of the ATO film was strongly affected by the Al concentration at the interface between the ATO film and the RuO2 electrode. The conduction band offset of the interface increased with the increase in the Al dopant concentration in the rutile TiO2, which reduced the leakage current in the voltage region pertinent to the next-generation dynamic random access memory application. However, the Al doping in the anatase TiO2 did not notably increase the conduction band offset even with a higher Al concentration. The detailed analyses of the leakage conduction mechanism based on the quantum mechanical transfer-matrix method showed that Schottky emission and Fowler-Nordheim tunneling was the dominant leakage conduction mechanism in the lower and higher voltage regions, respectively. The chemical analyses using X-ray photoelectron spectroscopy corroborated the electrical test results.

The influence of structural disorder on the electronic structure of amorphous ZnSnO3 was examined by ab-initio calculations. The calculation results are compared with the experimental results using as-deposited and annealed ZnSnO3 films grown by atomic layer deposition. The O K-edge X-ray absorption spectroscopy, X-ray diffraction, and thin-film transistors were employed in the experiment. The conduction band minima of amorphous and crystalline ZnSnO3 mainly consisted of Sn 5s state, while a higher non-uniform localization of these states was observed in the amorphous phase compared with the crystalline counterpart. The experimental results coincide well with the theoretical results.

This study experimentally examined the physical and electrical characteristics of Zn x Sn y O z (ZTO) thin films grown by a metal-organic chemical vapor deposition (MOCVD) method with various Zn/Sn atomic compositions. The corresponding defect structures of the deposited films were investigated in detail using negative bias illumination stability (NBIS) analysis in the thin film transistor (TFT) structure. The ZTO thin films were deposited at a substrate temperature of 400 C and post-deposition annealed at 600 C, which still resulted in the amorphous structure except for the Sn-rich film where a nanocrystalline SnO 2 phase is detected. Among the films with different Zn/Sn atomic compositions, the film with a Zn/Sn atomic composition of $50/50 showed the best electrical performance. After applying NBIS stress for 1000 s, the transfer curves of the Zn-rich ZTO TFT showed a hump, but the transfer curves of the Sn-rich ZTO TFT exhibited a parallel shift to the negative bias direction. These phenomena were attributed to the difference in the oxygen vacancy energy states generated in the ZTO band gap by light illumination. The Zn-and Sn-related oxygen vacancies generated deep donor like trap states at $0.3 eV and shallow states at $0.1 eV from the conduction band (or mobility) edge, respectively, which were identified by the quantitative simulations of the transfer curves of the TFTs.

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