Deposition of aluminum oxide-doped zinc oxide transparent nano-films on glass substrates for electrostatic discharge applications

Aluminum oxide-doped zinc oxide (ZnO:Al₂O₃) transparent thin films were deposited by DC magnetron sputtering on glass substrates; film thickness can be correlated with deposition time. The effect of ZnO:Al₂O₃ film thickness on electrical properties, ultraviolet (UV) transmission, surface morphology and structure, solvent resistance, and scratch hardness was investigated. The surface roughness and crystallite size of deposited films increased from 0.75 to 2.22 nm and from 14 to 57 nm, respectively, as the film thickness was increased from 18 to 112 nm. In contrast, the percent UV transmission (% T) of ZnO:Al₂O₃ deposited glass plates at a wavelength of 365 nm increased when the film thickness was decreased. The electrical properties of nano-film deposited glass plates such as electrical resistance, tribo-charge voltage, and decay time were in the range of electrostatic discharge (ESD) specifications. The ZnO:Al₂O₃ nano-film deposited glass substrate possessed good acetone and iso-propanol resistance as well as high scratch hardness. This work opens up the possibility of using the ZnO:Al₂O₃ transparent ultra-thin film on glass substrate in ESD applications based on their excellent properties in terms of the relatively thin and adjustable ZnO:Al₂O₃ film thickness needed.     

Nanotribological properties of ALD-processed bilayer TiO2/ZnO films

TiO₂/ZnO films grown by atomic layer deposition (ALD) demonstrated nanotribological behaviors using scratch testing. TEM profiles obtained an amorphous structure TiO₂ and nanocrystalline structure ZnO, whereas the sample has significant interface between the TiO₂/ZnO films. The experimental results show the relative XRD peak intensities are mainly contributed by a wurtzite oxide ZnO structure and no signal from the amorphous TiO₂.With respect to tribology, increased friction causes plastic deformation between the TiO₂ and ZnO films, in addition to delamination and particle loosening. The plastic deformation caused by adhesion and/or cohesion failure is reflected in the nanoscratch traces. The pile-up events at a loading penetration of 30 nm were measured at 21.8 μN for RT, 22.4 μN for 300 °C, and 36 μN for 400 °C. In comparison to the other conditions, the TiO₂/ZnO films annealed at 400 °C exhibited higher scratch resistance and friction with large debris, indicating the wear volume is reduced with increased annealing temperature and loading.     

Fabrication of Ag nanoparticle/ZnO thin films using dual-plasma-enhanced metal-organic chemical vapor deposition (DPEMOCVD) system incorporated with photoreduction method and its application

We report a novel method to grow silver nanoparticle/zinc oxide (Ag NP/ZnO) thin films using a dual-plasma-enhanced metal-organic chemical vapor deposition (DPEMOCVD) system incorporated with a photoreduction method. The crystalline quality, optical properties, and electrical characteristics of Ag NP/ZnO thin films depend on the AgNO₃ concentration or Ag content and annealing temperature. Optimal Ag NP/ZnO thin films have been grown with a AgNO₃ concentration of 0.12 M or 2.54 at%- Ag content and 500 °C- rapid thermal annealing (RTA); these films show orientation peaks of hexagonal-wurtzite-structured ZnO (002) and face-center-cubic-crystalline Ag (111), respectively. The transmittance and resistivity for optimal Ag NP/ZnO thin films are 85% and 6.9×10⁻⁴ Ω cm. Some Ag NP/ZnO transparent conducting oxide (TCO) films were applied to InGaN/GaN LEDs as transparent conductive layers. The InGaN/GaN LEDs with optimal Ag NP/ZnO TCO films showed electric and optical performance levels similar to those of devices fabricated with indium tin oxide.     

Synthesis of ZnO: Ge nanocomposite thin films by plasma gas condensation

In this work, we introduce a new method for the synthesis of Ge nanoparticles embedded ZnO thin films that are considered to be a potential candidate for photovoltaic applications. As opposed to current techniques, for the independent preparation of Ge nanoparticles, we propose using Cluster Deposition Source (CDS), which utilizes gas condensation of sputtered Ge atoms. For the synthesis of ZnO thin film host material conventional sputtering technique is employed. In the proposed technique independently synthesized Ge nanoparticles and ZnO thin films are combined into a composite structure on (100) oriented Si substrates. X-ray diffraction (XRD) patterns of the samples have revealed that Ge nanoparticles preferentially settle on (113) planes on top of the (002) oriented ZnO layer. It is realized that Ge nanoparticles with sizes ranging from 16 nm to 20 nm could be embedded into a well-defined ZnO matrix. In fact, transmission electron microscopy (TEM) studies performed on Ge nanoparticles captured on a Cu grids placed just above the substrate during deposition for about 60 s have manifested that Ge nanoparticles reach to ZnO matrix as clusters composed of particles with sizes of about 7–8 nm and then eventually grow larger due to substrate heating implemented during capping layer deposition. Optical absorption measurements have revealed that Ge nanoparticle inclusion lead to an additional absorption edge at about 2.75 eV along with 3.17 eV edge resulting from ZnO host.     

Synthesis of Sn doped ZnO/TiO2 nanocomposite film and their application to H2 gas sensing properties

Tin doped Zinc oxide/Titanium oxide nanocomposite (TZO/TiO₂) was prepared by two methods: TiO₂ nanotube (Nt) arrays are grown by anodic oxidation of titanium foil and TZO films was deposited on the TiO₂ Nt obtained by hydrothermal process. The morphological characteristics and structures of ZnO/TiO₂ and TZO/TiO₂ were examined by (scanning elecron miscroscopy) SEM, (X rays diffraction) XRD and (energy dispersive spectroscopy) EDS analysis. The diameter of TiO₂ Nts was ranged from 40 nm to 90 nm with wall thicknesses of approximately 10 nm. The anatase structure of Titania, the hexagonal Zincite crystal of zinc oxide and tetragonal structure of tin oxide were identified by XRD. EDS analysis revealed the presence of O, Zn, Ti and Sn elements in the obtained deposits.These nanocomposites have been used as active layer in hydrogen gas sensing application. The hydrogen sensing characteristics of the sensor was analyzed by measuring the sensor responses in the temperature of 100 °C and 160 °C. The highest gas response is approximately 1.48 at 160 °C.The sensing mechanism of the nanocomposite sensor was explained in terms of H₂ chimisorption on the highly active nanotube surface.     

Effects of the substrate temperature and solution molarity on the structural opto-electric properties of ZnO thin films deposited by spray pyrolysis

Zinc oxide (ZnO) was largely studied in various applications such as photovoltaic conversion, optoelectronics and piezoelectric, because of its interesting physical properties (morphological, structural, optical and electrical). The present work deals with the preparation of zinc oxide thin films (ZnO) deposited by the spray pyrolysis method. The starting solution was zinc chloride (ZnCl₂). Effects of solution molarity and substrate temperature on films properties were investigated. All films deposited were characterized by various techniques such as X-ray diffraction for structural characterizations, profilometry for thickness measurements, UV–vis transmission spectrophotometry for optical properties and the four probes conductivity measurements for electrical characterization. The X-ray diffraction (XRD) patterns show that the films deposited are polycrystalline with (0 0 2) plan as preferential orientation. The UV–vis spectroscopy confirms the possibility of good transparent ZnO thin films deposition with an average transmission of about ∼85% in the visible region. However, the measured electrical resistivities of the deposited films were in the order of 10⁴ Ω cm     

Influence of Sn content on properties of ZnO:SnO2 thin films deposited by ultrasonic spray pyrolysis

The present work is devoted to the preparation of zinc oxide (ZnO): tin oxide (SnO₂) thin films by ultrasonic spray technique. A set of films are deposited using a solution formed with zinc acetate and tin chloride salts mixture with varied weight ratio R=[Sn/(Zn+Sn)]. The ratio R is varied from 0 to 100% in order to investigate the influence of Sn concentration on the physical properties of ZnO:SnO₂ films. The X rays diffraction (XRD) analysis indicated that films are composed of ZnO and SnO₂ distinct phases without any alloys or spinnel phase formations. The average grain size of crystallites varies with the ratio R from 17 to 20 nm for SnO₂ and from 24 to 40 nm for ZnO. The obtained films are highly transparent with a transmission coefficient equal to 80%. An increase in Sn concentration increases both the effective band gap energy from 3.2 to 4.01 eV and the photoluminescence intensity peak assigned defects to SnO₂. The films electrical characterization indicated that films are resistive. Their resistivities vary between 1.2×10² and 3.3×10⁴ (Ω cm). The higher resistivity is measured in film deposited with a ratio R equal to 50%.     

Effect of gate barrier and channel buffer layer on electric properties and transparence of the a-IGZO thin film transistor

Different structures of a-IGZO (amorphous indium gallium zinc oxide) transparent thin film transistor (TTFT) were developed on glass substrate for study of gate barrier and channel buffer layer effects. The used gate barrier and the channel buffer layer are high energy band gap dielectric Al₂O₃ and the rapid thermally annealed ZnO film, respectively. With both gate barrier and channel buffer layers, the TTFT promoted ∼3 orders in on/off current ratio and reduced leakages current ∼800 times. Furthermore, the average transparence was also enhanced from 84% to 86.4% in the range of 500–800 nm wavelengths. The improvement mechanisms are interpreted with comprehensive models in details.     

Charge injection in metal/organic/metal structures with ZnO:Al/organic interface modified by Zn1−xMgxO:Al layer

Aluminum-doped zinc oxide (ZnO:Al, AZO) electrodes were covered with very thin (∼6 nm) Zn_1−xMg_xO:Al (AMZO) layers grown by atomic layer deposition. They were tested as hole blocking/electron injecting contacts to organic semiconductors. Depending on the ALD growth conditions, the magnesium content at the film surface varied from x = 0 to x = 0.6. Magnesium was present only at the ZnO:Al surface and subsurface regions and did not diffuse into deeper parts of the layer. The work function of the AZO/AMZO (x = 0.3) film was 3.4 eV (based on the ultraviolet photoelectron spectroscopy). To investigate carrier injection properties of such contacts, single layer organic structures with either pentacene or 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine layers were prepared. Deposition of the AMZO layers with x = 0.3 resulted in a decrease of the reverse currents by 1–2 orders of magnitude and an improvement of the diode rectification. The AMZO layer improved hole blocking/electron injecting properties of the AZO electrodes. The analysis of the current-voltage characteristics by a differential approach revealed a richer injection and recombination mechanisms in the structures containing the additional AMZO layer. Among those mechanisms, monomolecular, bimolecular and superhigh injection were identified.     

Study on thermal solid-phase crystallization of amorphous ZnO thin films stacked on vanadium-doped ZnO films

Thermal solid-phase crystallization (SPC) of an amorphous ZnO film stacked on a vanadium-doped ZnO (VZO) film was investigated. ZnO films were deposited on 30-nm-thick amorphous VZO films on c-face sapphire substrates at room temperature by RF magnetron sputtering. Stacked film was subsequently calcined at 800 °C in a nitrogen atmosphere. ZnO film grew in an amorphous state up to about 150-nm thick on the amorphous VZO film, but self-orientation occurred in a thicker layer. Any secondary phase such as Zn₂VO₄ was not formed in the case of total film thickness (t_total) ≥100 nm. V concentration decreased by thermal diffusion of V through the ZnO layer from the VZO film, and thereby the formation of secondary phase was effectively avoided. The amorphous ZnO layer was crystallized from highly-aligned initial thin layer of VZO film when t_total ≤200 nm and crystal orientation of the stacked film was superior to single VZO film. However, the c-axis orientation was deteriorated drastically at t_total ≈400 nm due to SPC affected by the tilted regions existed in the as-deposited ZnO film. Therefore, it is suggested that careful selection of ZnO film thickness is necessary to obtain the high-quality ZnO films in this method.     

Polymer films with multilayer low-E coatings

The paper presents the experimental results on depositing a multilayer low-emissivity (low-E) coating with oxide–metal–oxide structure on polyethylene terephthalate (PET) and polyethylene (PE) films by magnetron sputtering. The TiO₂/ZnO:Ga/Ag/ZnO:Ga/TiO₂ coating on the PET film with high water-resistance and capability to be used outside of sealed double-glazed panes was proposed. The optimal thickness of coating layers was experimentally determined. The coating with the optimal structure has 82% transmittance over the visible spectrum and 91% reflection over the infrared spectrum. The window with a PET film and low-E coating was investigated in terms of heat engineering. It was revealed that heat transfer resistance increased up to 0.73 m² °C W⁻¹ for the windows with a PET film and low-E coating. Heat transfer resistance of the windows without a polymer film was 0.38 m² °C W⁻¹. The water-resistant ZnO:Ga/Ag/ZnO:Ga/SiO₂ coating on a PE film with 77% transmittance and 91–92% reflection in the IR range was proposed to be used as greenhouse covering material. The possibility of using the PE film with a low-E coating to reduce heat loss in greenhouses and enhance yielding capacity was demonstrated.     

Influence of cathode roughness on the performance of F8BT based organic–inorganic light emitting diodes

Hybrid light emitting diodes (HyLED) with a structure of FTO/ZnO/F8BT/MoO₃/Au/Ag is fabricated and the influence of surface roughness of cathode (FTO/ZnO) is investigated. The roughness of FTO could be decreased from 9.2 nm to 2.2 nm using a mild polishing process. The ZnO film, deposited by spray pyrolysis, functions as an electron injection layer. The roughness of the FTO/ZnO surface is found also highly dependent on the ZnO thickness. For thin ZnO films (20 nm), polishing results in better efficacy and power efficiency of LED devices, with nearly a two times improvement. For thick ZnO films (210 nm), the overall FTO/ZnO roughness is almost independent of the FTO roughness, hence both polished and unpolished substrates exhibit identical performance. Increasing ZnO thickness generally improves the electron injection condition, leading to lower turn on voltage and higher current and power efficiencies. However, for too large ZnO thickness (210 nm) the ohmic loss across the film dominates and deteriorates the performance. While the polished substrates show less device sensitivity to ZnO thickness and better performance at thin ZnO layer, best performance is obtained for unpolished substrates with 110 nm ZnO thickness. Larger interface area of ZnO/F8BT and enhanced electric filed at sharp peaks/valleys could be the reason for better performance of devices with unpolished substrates.     

Uniform 3D hydrothermally deposited zinc oxide nanorods with high haze ratio

We present low cost hydrothermally deposited uniform zinc oxide (ZnO) nanorods with high haze ratios for the a-Si thin film solar cells. The problem of low transmittance and conductivity of hydrothermally deposited ZnO nanorods was overcome by using RF magnetron sputtered aluminum doped zinc oxide (ZnO:Al ~300 nm) films as a seed layer. The length and diameters of the ZnO nanorods were controlled by varying growth times from 1 to 4 h. The length of the ZnO nanorods was varied from 1 to 1.5 µm, while the diameter was kept larger than 300 nm to obtain various aspect ratios. The uniform ZnO nanorods showed higher transmittance (~89.07%) and haze ratio in the visible wavelength region. We also observed that the large diameters (>300 nm) and average aspect ratio (3–4) of ZnO nanorods favored the light scattering in the longer wavelength region. Therefore, we proposed uniformly deposited ZnO nanorods with high haze ratio for the future low cost and large area amorphous silicon thin film solar cells.     

Effects of deposition pressure on the properties of transparent conductive ZnO:Ga films prepared by DC reactive magnetron sputtering

Gallium (Ga)-doped zinc oxide (ZnO:Ga) transparent conductive films were deposited on glass substrates by DC reactive magnetron sputtering. Effects of deposition pressure on the structural, electrical and optical properties of ZnO:Ga films were investigated. X-ray diffraction (XRD) studies show that the films are highly oriented with their crystallographic c-axis perpendicular to the substrate almost independent of the deposition pressure. The morphology of the film is sensitive to the deposition pressure. The transmittance of the ZnO:Ga thin films is over 90% in the visible range and the lowest resistivity of ZnO:Ga films is 4.48×10⁻⁴ Ω cm.     

Effects of annealing technique and TiO2 seed layer on the phase composition of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 film

The lead magnesium niobate–lead titanate (PMN–PT) thin films with and without the TiO₂ seed layer were prepared by a pulsed laser deposition (PLD) deposited on Pt/Ti/SiO₂/Si substrates. The films were treated by two-step annealing and normal annealing with rapid thermal annealing (RTA). The effects of two-step annealing and the TiO₂ seed layer on the phase composition of PMN–PT films were studied. The results show that the PMN–PT film with TiO₂ seed layer can gain a pure perovskite phase with a high (1 0 0) preferential orientation after the two-step annealing technique.     

Synthesis of highly selective and sensitive Cu-doped ZnO thin film sensor for detection of H2S gas

Copper (Cu) doped zinc oxide (ZnO) thin films were successfully prepared by a simple sol-gel spin coating technique. The effect of Cu doping on the structural, morphology, compositional, microstructural, optical, electrical and H₂S gas sensing properties of the films were investigated by using XRD, FESEM, EDS, FTIR, XPS, Raman, HRTEM, and UV–vis techniques. XRD analysis shows that the films are nanocrystalline zinc oxide with the hexagonal wurtzite structure and FESEM result shows a porous structured morphology. The gas response of Cu-doped ZnO thin films was measured by the variation in the electrical resistance of the film, in the absence and presence of H₂S gas. The gas response in relation to operating temperature, Cu doping concentration, and the H₂S gas concentration has been systematically investigated. The maximum H₂S gas response was achieved for 3 at% Cu-doped ZnO thin film for 50 ppm gas concentration, at 250 °C operating temperature.     

Effect of seed layer on the growth of rutile TiO2 nanorod arrays and their performance in dye-sensitized solar cells

In order to improve the performance of TiO₂ photoanode-based dye sensitized solar cells (DSSCs), rutile TiO₂ nanorod arrays (NRAs) were grown on SnO₂:F (FTO) conductive glass coated with TiO₂ seed layer by a hydrothermal method. The TiO₂ seed layer was obtained by spin-coating titanium tetraisopropoxide (TTIP) isopropanol solution with concentration in the range of 0~0.075 M. Then the effect of the thin TiO₂ seed layer on the crystal structure and surface morphology of TiO₂ NRAs and the photoelectric conversion properties of the corresponding DSSCs were investigated. It is found that TiO₂ NRAs are vertically oriented, about 1.7 μm long and the average diameter is about 35 nm for the samples derived from TTIP in the range of 0.005~0.05 M, which are more uniform and better separated from each other than those without TiO₂ seed layer (average diameter 35~85 nm). The photoelectric conversion efficiency of DSSCs based on TiO₂ NRAs with TiO₂ seed layer is larger than that without TiO₂ seed layer. Typically, the energy efficiency of DSSCs obtained from the seed solution of 0.025 M TTIP is 1.47%, about 1.8 times greater than that without TiO₂ seed layer. The performance improvement is attributed to the thinner, denser and better oriented NRAs grown on seeded-FTO substrate absorbing more dye and suppressing charge recombination at the FTO substrate/electrolyte interface.     

Improvement in crystal quality of ZnO film on Si substrate by using a homo-buffer layer

ZnO thin films without and with a homo-buffer layer have been prepared on Si(1 1 1) substrates by pulsed laser deposition (PLD) under various conditions. Photoluminescence (PL) measurement indicates that the optical quality of ZnO thin film is dramatically improved by introducing oxygen into the growth chamber. The sample deposited at 60 Pa possesses the best optical properties among the oxygen pressure range studied. X-ray diffraction (XRD) results show that the films directly deposited on Si are of polycrystalline ZnO structures. A low-temperature (500 °C) deposited ZnO buffer layer was used to enhance the crystal quality of the ZnO film. Compared to the film without the buffer layer, the film with the buffer layer exhibits aligned spotty reflection high-energy electron diffraction (RHEED) pattern and stronger near-band-edge emission (NBE) with a smaller full-width at half-maximum (FWHM) of 98 meV. The structural properties of ZnO buffer layers grown at different temperatures were investigated by RHEED patterns. It is suggested that the present characteristics of the ZnO epilayer may be raised further by elevating the growth temperature of buffer layer to 600 °C.     

Effect of 100 MeV O7+ ion beam irradiation on radio frequency reactive magnetron sputtered ZnO thin films

Zinc oxide (ZnO) thin films were deposited on sapphire substrates at room temperature by radio frequency (RF) magnetron sputtering. These films were irradiated with 100 MeV O⁷⁺ ions of the fluencies 5×10¹³ ions/cm² at room temperature (RT) and at liquid nitrogen temperature (LNT). Profilometer studies showed that the roughness of pristine and LNT irradiated ZnO thin films were higher than that of the RT irradiated ZnO thin film. The glancing angle X-ray diffraction analysis reveals a reduced intensity and increased full width at half maximum (FWHM) of the (002) diffraction peak in the case of LNT irradiated film indicating disorder. However, the intensity and FWHM of the (002) diffraction peak in the case of RT irradiated ZnO thin films are comparable to those of the pristine film. UV–visible transmission spectra show that the percentage of transmission and band gap energy are different for RT and LNT irradiated films. While the pristine ZnO thin film exhibits two emissions—a broad emission at 403 nm and a sharp emission at 472 nm in its photoluminescence spectrum; the emission at 472 nm was absent for the irradiated films. The atomic concentrations of zinc and oxygen during the irradiation process were obtained using auger electron spectroscopy.     

Sputtered oxides used for passivation layers of amorphous InGaZnO thin film transistors

Four sputtered oxide films (SiO₂, Al₂O₃, Y₂O₃ and TiO₂) along with their passivating amorphous InGaZnO thin film transistors (a-IGZO TFTs) were comparatively studied in this paper. The device passivated by an Al₂O₃ thin film showed both satisfactory performance (μ_FE=5.3 cm²/V s, I_on/I_off>10⁷) and stability, as was probably related to smooth surface of Al₂O₃ thin films. Although the performance of the a-IGZO TFTs with a TiO₂ passivation layer was also good enough (μ_FE=3.5 cm²/V s, I_on/I_off>10⁷), apparent V_th shift occurred in positive bias-stress tests due to the abnormal interface state between IGZO and TiO₂ thin films. Sputtered Y₂O₃ was proved no potential for passivation layers of a-IGZO TFTs in this study. Despite unsatisfactory performance of the corresponding a-IGZO TFT devices, sputtered SiO₂ passivation layer might still be preferred for its high deposition rate and excellent transparency which benefit the mass production of flat panel displays, especially active-matrix liquid crystal displays.