Satoru Takaki

Electrical and structural properties of low resistivity tin-doped indium oxide films

Tin‐doped indium oxide (ITO) films with the resistivity less than 1.35×10−4 Ω cm were formed by low voltage dc magnetron sputtering (LVMS) and highly dense plasma‐assisted electron beam (EB) evaporation using the arc plasma generator (HDPE). The structural properties of these films were investigated using x‐ray diffraction, scanning electron microscope, and electron spectroscopy for chemical analysis, in comparison with the films formed by conventional magnetron sputtering and EB evaporation, in order to clarify the key factors for low resistivity. With decreasing plasma impedance and sputtering voltages from 540 to 380 V, the resistivity of the films deposited at Ts=400 °C decreased from 1.92 to 1.34×10−4 Ω cm, due mostly to increase in the carrier density. This LVMS film showed higher crystallinity because of lower damages of high‐energy particles during the deposition, which might increase the number of electrically active species. For HDPE, the film with resistance of 1.23×10−4 Ω cm was deposited at T...

Origin of characteristic grain-subgrain structure of tin-doped indium oxide films

The microstructures of polycrystalline and heteroepitaxial tin-doped indium oxide (ITO) thin films prepared by sputtering and electron beam (EB) evaporation were investigated by electron microscopy, X-ray diffraction and reflection high-energy electron diffraction. The sputter-deposited ITO film on a glass substrate revealed a polycrystalline structure of grain size 400–800 nm. Within each grain, there were oriented subgrain regions 10–40 nm in size. This is a so-called “grain-subgrain structure” characteristic of sputter-deposited polycrystalline ITO films. These grains in sputter-deposited ITO films (“grain-subgrain structure”) were classified into three groups according to the morphology of the subgrains. The grains consisted of square, triangular and rectangular-shaped subgrains respectively. These three kinds of grain were oriented with the <400≫, <222≫ and <440≫ axes normal to the substrate surface respectively. It was also revealed that the film thickness of these three kinds of grain decreased in the order of the grains consisting of <400≫-, <222≫- and <440≫-oriented subgrains. However, heteroepitaxial ITO films sputtered on yttria-stabilized zirconia (YSZ) substrates, and EB-evaporated ITO films on both glass and YSZ substrates showed different structures. By comparing the microstructures of polycrystalline films with those of heteroepitaxial films, the origin of the above-mentioned “grain-subgrain structure” (variation of shapes and thickness of the subgrains) was described on the basis of the crystalline-plane-dependent resputtering rate of ITO films during sputter deposition. The resputtering rate during sputter deposition of ITO films is considered to be dependent on the crystalline planes of ITO and increases in the order of the (400), (222) and (440) planes.

Crystallinity and electrical properties of tin-doped indium oxide films deposited by DC magnetron sputtering

Abstract ITO films with thickness s between 1000 and 8000Awere deposited on glass substrates at 400°C by DC magnetron sputtering. The electrical and structural properties were compared to the same properties in evaporated ITO films and ITO powder using ESCA, SEM and X-ray diffraction. The resistivity decreased from 1.92 × 10−4 to 1.46 × 10−4 Ω cm as the thickness increased from 1140 to 7620A, due mostly to a monotonic increase in the carrier density. The (400) plane spacing in the films was higher than in pure In2O3 powder. However, the difference between the (400) plane spacings in the In2O3 and the films decreased as the film thickness increased, from 0.87% in an 1140Athick film to 0.54% in a 7620Athick film. For an EB evaporated ITO film having a thickness of 3860A, the spacing was 0.24% larger than in pure In2O3. X-ray diffraction analysis based on the integral breadth method demonstrated a clear positive correlation between random strain and uniform strain. The decrease of strain and of lattice constant with increasing thickness led to the conclusion that the increased carrier density in thicker films is due to an improvement in crystallinity, which leads to a higher density of electron donor centers.

Properties of highly conducting ITO films prepared by ion plating

Abstract Highly conducting In2O3:Sn films were prepared by electron enhanced ion plating onto glass substrates at 200–350°C. The films prepared under optimized conditions exhibited a resistivity of 1.0x10-4 Ω cm and an averaged visible transmission of 83% with a thickness of 82 nm. The high conductivity was explained to be due to effective and heavy doping of tin and good eletrical connections among grains on the basis of the structural examinations using SEM, SAM, AES and X-ray diffraction techniques.

Heteroepitaxial growth of tin‐doped indium oxide films on single crystalline yttria stabilized zirconia substrates

Heteroepitaxial growth of tin‐doped indium oxide (ITO) film was achieved for the first time by using single crystalline yttria stabilized zirconia (YSZ) as substrates. The epitaxial relationship between ITO film and YSZ substrate was ITO[100]∥YSZ[100]. By comparing the electrical properties of this epitaxial ITO film with that of a randomly oriented polycrystalline ITO film grown on a glass substrate, neither the large angle grain boundaries nor the crystalline orientation were revealed to be dominant in determining the carrier mobility in ITO films.

Microstructure of Low-Resistivity Tin-Doped Indium Oxide Films Deposited at 150∼200°C

Low-resistivity (~2×10-4 Ω cm) tin-doped indium oxide (ITO) films were deposited at a relatively low substrate temperature (T s) of 185° C by two representative low-temperature processes, i.e., dc magnetron sputtering using an oxide target and activated e-beam evaporation. Precise X-ray diffraction (XRD) measurements for both ITO films showed that all the XRD peaks split into two peaks with different intensity ratios depending on the deposition conditions and methods. The deconvolution analyses on the doublet XRD peaks and an investigation of the step-etched ITO films revealed that the films consisted of two differently strained layers. The weakly strained layer was consider to be formed as a result of crystallization of an as-deposited amorphous layer upon thermal annealing during deposition (solid-phase crystallization), whereas the strongly strained layer was an as-deposited crystalline layer (vapor-phase crystallization).

Development of Silver-Based Multilayer Coating Electrodes with Low Resistance for Use in Flat Panel Displays

Multilayer coatings consisting of thin silver layers sandwiched between layers of transparent conducting metal oxides were investigated from the view-point of low-resistance electrodes for use in flat panel displays. Optimization of the multilayer coatings resulted in a five-layer coating composed of indium and zinc oxide composite material (IZO) and silver containing 1 wt% of palladium (Ag–Pd). The coatings had satisfactory properties of low resistance, high transmittance, high moisture and alkali resistance, and good patterning.

Comparative study of heteroepitaxial and polycrystalline tin-doped indium oxide films

Abstract A comparative study of heteroepitaxial and polycrystalline tin-doped indium oxide (ITO) films grown by both dc magnetron sputtering (DCSP) and e-beam evaporation (EB) have been performed. Polycrystalline indium tin-oxide (ITO) films grown by DCSP had a crystalline orientation dependent surface morphology and film-thickness (up to 9% of the total thickness). This crystalline orientation dependent morphology and thickness of sputtered polycrystalline ITO films was attributed to the anisotropic resputtering by energetic particles during growth. Heteroepitaxial growth of ITO films resulted in a smaller resistivity in the case of EB. However, the resistivities of heteroepitaxial and polycrystalline ITO films grown by DCSP were identical within errors of measurement and the improvement of electrical properties by the epitaxial growth observed in EB was suppressed in the case of DCSP. This suppression was also attributed to the energetic particle bombardment during DCSP, which is absent in EB.

EFFECTS OF WATER PARTIAL PRESSURE ON THE ACTIVATED ELECTRON BEAM EVAPORATION PROCESS TO DEPOSIT TIN-DOPED INDIUM-OXIDE FILMS

The effects of water partial pressure (PH2O) during deposition on the structural and electrical properties of tin‐doped indium‐oxide (ITO) films have been investigated on an activated electron beam evaporation process using an arc plasma generator. The resistivity of the films deposited at 180 °C increased with an increase in PH2O in terms of a decrease both in Hall mobility and carrier density. X‐ray diffraction and scanning electron microscope analyses showed that the ITO films deposited at higher PH2O consisted of a major portion of larger crystalline grains with smaller internal strain and a small portion of amorphous regions which is supposed to be at the interface between the film and the substrate. Plasma diagnostics by optical emission spectroscopy revealed that atomic hydrogen was generated by electron‐impact dissociation of H2O and that the activation of Ar or O2 was suppressed in the higher PH2O process, which resulted in the deposition of less oxidized and lower‐damaged ITO films.

Growth Mechanism of Indium Tin Oxide Whiskers Prepared by Sputtering

Whisker structures of indium tin oxide were prepared on a glass substrate by conventional sputtering using an indium-tin alloy target. Whisker structures grew well at higher temperatures than the crystallization temperature of In2O3 and the melting temperature of the In–Sn alloy, and also under the sputtering conditions of comparatively scarce oxygen and a high sputtering rate. These sputtering conditions correspond to the transition mode of reactive sputtering. The whisker structures were categorized into a structure consisting of many needles and a structure consisting of many trunks with side branches. Each whisker was a bcc single crystal growing along the direction and had a spherical droplet-like structure on the tip. Consequently, it was revealed that In–Sn droplets acted as important cores of whisker growth. The indium tin oxide (ITO) whiskers were grown by a self-catalytic vapor–liquid–solid mechanism promoted by the supersaturation of indium vapor.