Jun-Ku Ahn

Nanoscale Silver-Based Al-Doped ZnO Multilayer Transparent-Conductive Oxide Films

Requirements of transparent-conductive oxide (TCO) films for solar cells and other optoelectronic applications are mainly focused on the electrical resistivity as low as 10- 5 Ω cm, optical transmittance above ∼85% in the visible region, a long-term stability in damp heat-treatment for 1000 h, a mechanical stability on flexible polymer substrates, and the large-area deposition technique for commercialization. In this study, the typical properties of the 45 nm thick Al-doped ZnO (AZO)/Ag/45 nm thick AZO multilayer films embedded by silver layers with various thicknesses were addressed to satisfy the requirements of TCO films for flexible electronic device applications. The AZO/9 nm thick Ag/AZO multilayer films as deposited on poly(ether sulfone) (PES) polymer substrates at 30°C by radio-frequency magnetron sputtering, which the deposition on large-area substrates is possible, exhibited the electrical resistivity of approximately 5 X 10- 5 Ω cm, optical transmittance of 88% at 550 nm wavelength, no appreciable change in electrical resistance and optical transmittance after damp heat-treatment for 1000 h, and a strong mechanical stability between multilayer films and PES substrates after a severe bending test. The results presented in the multilayer films can provide a platform for TCO films deposited on polymer substrates to enable the flexible electronic device applications.

Phase-change InSbTe nanowires grown in situ at low temperature by metal-organic chemical vapor deposition.

Phase-change InSbTe (IST) single crystalline nanowires were successfully synthesized at a low temperature of 250 degrees C by metalorganic chemical vapor deposition (MOCVD). The growth of IST nanowires by MOCVD, at very high working pressure, was governed by supersaturation. The growth mechanism of the IST nanowires by MOCVD is addressed in this paper. Under high working pressure, the InTe phase was preferentially formed on the TiAlN electrode, and the InTe protrusions were nucleated on the InTe films under high supersaturation. The Sb was continuously incorporated into the InTe protrusions, which was grown as an IST nanowire. Phase-change-induced memory switching was realized in IST nanowires with a threshold voltage of about 1.6 V. The ability to grow IST nanowires at low temperature by MOCVD should open opportunities for investigation of the nanoscale phase-transition phenomena.

Characteristics of Amorphous Lithium Lanthanum Titanate Electrolyte Thin Films Grown by PLD for Use in Rechargeable Lithium Microbatteries

(Li 0 . 5 La 0 . 5 )TiO 3 (LLTO) film electrolytes for use in a lithium rechargeable microbattery were prepared on a Pt collector using pulsed laser deposition (PLD) at various deposition temperatures. As-grown 360 nm thickLLTO films prepared at 400-600°C showed an amorphous phase and an ionic conductivity of ∼2.0 x 10 - 5 Scm - 1 at room temperature. A lithium metal anode in contact with the amorphous LLTO films had no influence on the electronic conductivity of the LLTO solid-electrolyte, contrary to crystalline films. The retention capacity of the LLTO/100 nm thick LiCoO 2 /Pt cells during 100 cycles in a 1 M LiClO 4 liquid electrolyte in propylene carbonate (PC) was ∼82.2% and the cells exhibited an increase of ∼30% compared with that for LiCoO 2 /Pt cells. The LLTO/LiCoO 2 /Pt cells had excellent rechargeability characteristies of ∼63% up to 300 cycles. 2004 The Electrochemical Society. [DOI: 10.1149/1.1843571] All rights reserved.

Structural and electrical properties of Bi1.5Mg1.0Nb1.5O7 thin films deposited on Pt/TiO2/SiO2/Si substrates by rf-magnetron sputtering

Bi1.5Mg1.0Nb1.5O7 thin films were deposited at various temperatures by rf-magnetron sputtering on Pt/TiO2/SiO2/Si substrates. The structural and electrical properties were investigated as a function of deposition temperature. The films deposited below 400 °C show an amorphous state and a dielectric constant of approximately 31–51. On the other hand, films deposited at 500 °C exhibit well-developed crystallinity and a high dielectric constant of approximately 104. However, for crystallized films deposited at 500 °C, the leakage current density is higher than that of the films deposited below 300 °C.

Effect of indium concentration on the structural and electrical properties of Al-doped ZnO thin films grown by pulsed laser deposition

The Al-doped ZnO (AZO) films doped with different indium concentrations were grown on glass substrates (Corning 1737) at 200 °C by pulsed laser deposition. Indium doping in AZO films shows a critical effect on the crystallinity, resistivity and optical properties of the films. The AZO films doped with 0.3 atom% indium content exhibit the highest crystallinity, the lowest resistivity of 4.5 × 10−4 Ω cm and the maximum transmittance of 93%. The crystallinity of the indium doped-AZO films is strongly related to the resistivity of the films. The carrier concentration in the indium doped-AZO films linearly increases with increasing indium concentration. The mobility of the AZO films with increasing indium concentration was reduced with an increase in the carrier concentration and the decrease in mobility was attributed to the ionized impurity scattering mechanism. In optical transmittance, the shift of the optical absorption edge to a shorter wavelength strongly depends on the electronic carrier concentration in the films. The figure of merit FTC used for evaluating transparent electrodes reached 0.32 Ω−1 at 550 nm wavelength.

Low Resistivity ITO Thin Films Deposited by NCD Technique at Low Temperature: Variation of Tin Concentration

Due to the combined properties of high electrical conductivity and optical transparency in the visible region, transparent conducting oxides have become an essential component in liquid crystal displays and solar cells. There has been a growing interest in “transparent electronics.” Tin-doped indium oxide ITO, with a typical electrical conductivity of 3‐5 10 3 S/cm and transparency of 85‐90% in the visible region, has been employed on a large scale as a transparent electrode in many display technologies. 1-4 Additionally, the optimization of ITO thin films is a crucial part in the development of new technologies, i.e., transparent bottom contact electrodes for electrochromic displays, organic light emitting diodes, and organic photovoltaic cells. Donor generation in ITO films is governed by two mechanisms: the creation of double-charged oxygen vacancies Vo and the contribution of a single electron for each Sn 4+ cation substituted on the In 3+ site Sn In . The properties of ITO films are intimately associated with the microstructure and the lattice defects of the films as well as the deposition methods and conditions. Therefore, the investigation of the doping mechanism and chemical state of Sn atoms is the most important issue in low resistive ITO films. The easy and the most effective way of increasing electrical conductivity is tin doping in indium oxide matrix, but a limited doping and a precise control of the process parameters during growth is required to obtain high quality films at low substrate temperatures. Various deposition techniques, such as reactive evaporation, solution growth, spray pyrolysis, sputtering, pulsed laser deposition, and metallorganic chemical vapor deposition MOCVD have been employed to grow ITO thin films. For device fabrication, chemical vapor deposition CVD offers many attractive features such as low cost equipment and amenability to large area coverage with high throughput, conformal coverage, easy control of growth chemistry, and the possibility of creating metastable phases. Most of the high quality ITO films have been fabricated using MOCVD at a deposition temperature of more than 400°C. However, high temperature processing may cause a serious deterioration in the performance of ITO thin-film-based devices; thus, the investigation of ITO thin films crystallized at a low temperature 250°C is essential, but MOCVD is not suitable for the deposition of ITO thin films crystallized at low temperatures. In addition, low temperature deposition of thin films using the MOCVD technique causes heavy carbon contamination and/or amorphous films due to the incomplete decomposition of precursors, which leads to the degradation of film quality in terms of purity, crystallinity, and morphology and affects the surface chemical and optoelectronic properties. 5-8 Recently, we have reported the possibility of low temperature deposition of in situ crystallized ITO thin films using the NCD technique. 9 The NCD process is fundamentally different from that of conventional CVD and physical vapor deposition PVD processes. The principle of the NCD process is based on the maintenance of a showerhead at a temperature that is high enough to decompose the precursors, a sequential decomposition of the precursors in the showerhead, reaction with reactant gases, and the formation of ITO nanoclusters at the showerhead instead of a chemical reaction on a substrate surface, which is the case with the conventional CVD. By tuning the oxygen flow rate during deposition using the NCD technique, high quality ITO thin films with excellent optoelectronic and surface chemical properties were studied. In this study, the effect of Sn doping in In2O3 thin films deposited at a substrate temperature of 250°C is reported keeping other conditions same. All deposited films have the thickness of 140 10 nm. The tin concentration was varied from 0 to 15%, and this tin percentage is expressed by the tin weight percentage taken as the fraction of the total metal content, i.e., Sn/Sn + In in all the ITO films confirmed from the X-ray fluorescence XRF analysis, and henceforth, it is noted as CSn%.

An extremely high dielectric constant in bismuth-based pyrochlore multilayer film capacitors combined with percolative structure

The percolative film capacitor structure of Pt/Bi2Mg2/3Nb4/3O7 [BMN(Ar) films deposited at pure argon atmosphere]/Pt was addressed for achievement of a high dielectric constant in the films deposited at room temperature by radio frequency magnetron sputtering. The deterioration of the leakage current characteristics in the percolative capacitor was mitigated using the multilayer films of BMN(O)/BMN(Ar)/BMN(O), where ultrathin BMN(O) films were deposited at a mixed atmosphere of argon and oxygen. An extremely high dielectric constant of 120 and a low leakage current density of 6×10−6 A/cm2 at 3 V were observed in percolative BMN multilayer films as-deposited at room temperature.

Metalorganic chemical vapor deposition of non-GST chalcogenide materials for phase change memory applications

The feasibility of InSbTe (IST) chalcogenide new materials by metalorganic chemical vapor deposition (MOCVD) was demonstrated for PRAM applications. IST-MOCVD at a low temperature of 250 °C resulted in a favorable conformal deposition in the trench structure with a high aspect ratio. The IST films grown at 250 °C showed the highest resistance of approximately 108 Ω/sq, suggesting the amorphous phase of IST and the films grown at 300 °C include various crystalline phases of IST, In–Sb, and In–Te. MOCVD-IST films exhibited a step-coverage of about 95% in the trench structure with a 5 : 1 aspect ratio (a height of 500 nm and a diameter of 100 nm) and also showed reliable filling of the trench under appropriate deposition conditions. Phase switching between amorphous and crystalline states in the IST films grown on a trench structure at a high-aspect ratio (3.5 : 1) was demonstrated showing functional characteristics for applications in memory devices. The IST-based chalcogenide films used included various crystallized phases of In–Sb–Te, In–Sb and In–Te, which proved to be favorable for multilevel data storage.

Experimental investigation of interfacial and electrical properties of post-deposition annealed Bi2Mg2/3Nb4/3O7 (BMN) dielectric films on silicon

The effects of post-deposition annealing process on the material and electrical properties of radio frequency (RF) reactive magnetron sputter-deposited Bi2Mg2/3Nb4/3O7 (BMN) dielectric films integrated with silicon were investigated. All post-deposition annealed samples show the presence of a silicate-type amorphous interfacial layer. The films show smooth, continuous, crack-free surfaces and preserve an amorphous phase up to an annealing temperature of 700 ◦ C. The samples subjected to rapid thermal annealing in O2 ambient and subsequently in N2 ambient exhibit enhanced electrical characteristics, such as low values of capacitance equivalent thickness, interface state density, trap oxide charge density, reduced hysteresis and frequency dispersion, low leakage current, together with high electric field breakdown. These values are comparable to those of some of the most widely investigated high-k gate dielectrics.

Structural and electrical properties of high-κ Bi2Mg2∕3Nb4∕3O7 pyrochlore films on silicon for possible gate dielectric applications

Bi2Mg2∕3Nb4∕3O7 pyrochlore films were deposited on p-type Si (100) substrates using radio frequency reactive magnetron sputtering technique. Rapid thermal annealing (RTA) in O2 ambient followed by RTA in N2 ambient was carried out. The structural, morphological, and chemical bonding features of these films were studied by x-ray diffraction, scanning electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. All the films exhibit smooth, homogeneous, continuous, crack free, and dense films surfaces with root-mean-square roughness values in the range of 1.91−4.16 A. The films show high crystallization temperature at about 900 °C. High temperature annealing gives rise to more oxygen incorporation in the films with probable formation of silicate type bonding at the interface. Effective oxide charge density, flatband voltage, hysteresis, oxide trap charge density, and interface state density values are comparable to those of some of the most widely investigated high-k gate dielectrics....