ZnO Multilayer Films Research Articles

Magnetic and optical properties of ZnO/Ni/ZnO multilayer film on Si(100) and sapphire substrates

The optical absorption, band gap, and magnetic properties of ZnO/Ni(t)/ZnO multilayer film structures were investigated in various Ni layer thicknesses and substrates. We deposited 1, 4, and 5 nm of Ni film by thermal evaporation technique that sandwiched between ZnO films (~15 nm) via radio frequency magnetron sputtering method on both Si(100) and sapphire substrates. Although x-ray diffraction (XRD) analysis confirmed the (002) crystalline plane of ZnO without any Ni crystal phases on Si(100) surface, the better crystalline directions of ZnO, hexagonal wurtzite structure, was observed on the sapphire substrate. In the XRD analysis, we observed the cubic structure of NiO film formation due to thermally oxidation of Ni ions with interactions ZnO layer. Atomic force microscopy images confirmed the effect of the Ni layer on the average island size of 23.9 ± 2.9 nm and 25.6 ± 6.2 of ZnO films on 4 and 5 nm Ni films, respectively. Energy dispersive x-ray spectroscopy data confirmed that there is no other atom or impurity in the sample structure. The optical transparency of the multilayer films was reduced with increasing Ni layer thickness and maximum transparency was obtained as 97% at 800 nm of wavelength for the film with 1 nm Ni. The direct optical band gap of ZnO/Ni(t)/ZnO films was found to be 3.25, 3.20, and 3.12 eV with the contribution of 1, 4, and 5 nm Ni film in the multilayer film stack. The maximum Hc is found to be 1000 Oe for Si substrates and this value is reduced to around 400 Oe due to the crystal formation of the NiO layer for sapphire substrate samples.

Synthesis of ZnO sol-gel thin-films CMOS-Compatible.

Zinc oxide (ZnO) is a II–VI group semiconductor with a wide direct bandgap and is an important material for various fields of industry and high-technological applications. The effects of thickness, annealing process in N2 and air, optical properties, and morphology of ZnO thin-films are studied. A low-cost sol–gel spin-coating technique is used in this study for the simple synthesis of eco-friendly ZnO multilayer films deposited on (100)-oriented silicon substrates ranging from 150 to 600 nm by adjusting the spin coating rate. The ZnO sol–gel thin-films using precursor solutions of molarity 0.75 M exhibit an average optical transparency above 98%, with an optical band gap energy of 3.42 eV. The c-axis (002) orientation of the ZnO thin-films annealed at 400 °C were mainly influenced by the thickness of the multilayer, which is of interest for piezoelectric applications. These results demonstrate that a low-temperature method can be used to produce an eco-friendly, cost-effective ZnO sol–gel that is compatible with a complementary metal-oxide-semiconductor (CMOS) and integrated-circuits (IC).

Effects of BN layer on photoelectric properties and stability of flexible Al/Cu/ZnO multilayer thin film

This study focused on utilizing a boron nitride (BN) layer to improve the photoelectric property stability of the flexible Al/Cu/ZnO multilayer thin film, which was prepared on a polyethylene terephthalate (PET) substrate by radio frequency (RF) magnetron sputtering. By analyzing surface morphology, chemical composition and photoelectric properties of flexible BN/Al/Cu/ZnO multilayer films with different BN layer thicknesses, the BN/Al/Cu/ZnO film with a 100-nm-thick BN layer (BN100/Al/Cu/ZnO), which had the best comprehensive photoelectric property with a figure of merit of 0.82 × 10−3 Ω−1, was chosen to further study the performance stability with storage temperature and time. It was found that as compared to the Al/Cu/ZnO film, the BN100/Al/Cu/ZnO film had more stable photoelectric properties at different storage temperatures and times, which was inferred to be attributed to the excellent heat and oxidation resistances of the BN layer that were conducive to avoiding surface damage and oxidation of the film. The results in this work demonstrate the key role of the BN layer in enhancing photoelectric property stability of the flexible Al/Cu/ZnO film, and may provide a feasible strategy for improving thermal and long-time stability of single-layer or multilayer flexible transparent conductive films.

High performance flexible transparent conductive electrode based on ZnO/AgOx/ZnO multilayer

The aim of this study is to investigate the optoelectrical properties of hybrid electrodes based on ZnO/Ag(or AgOx)/ZnO multilayer structures. ZnO/Ag/ZnO and ZnO/AgOx/ZnO multilayer films were prepared with the sputtering technique at room temperature. To evaluate the effect of thickness and oxidation of a middle Ag layer on the structural, electrical, and optical properties, the thickness and oxygen concentration of the mid-layer film were varied from 6 to 16 nm and from 0 to 2.1 at.%, respectively. Differences in the structural and opto-electrical characteristics of these hybrid electrodes were analyzed using several analytical techniques, including scanning electron microcopy, ultraviolet visible spectrophotometry, four-point probe, and Hall effect measurement. The characteristics of these ZnO/Ag(or AgOx)/ZnO multilayer films depended on the thickness and oxygen concentration of the mid-layer film. Haccke's figure of merit of a ZnO(30 nm)/AgOx(12 nm, oxygen 1.5 at.%)/ZnO(30 nm) electrode was calculated to be 24.53 × 10−3 Ω−1, with sheet resistance and average transmittance (λ = 400–800 nm) of 86.53 % and 9.59 Ω/sq, respectively.

Comparing the performance of transparent, conductive ZnO/Ag/ZnO thin films that have an interlayer coating formed by either DC magnetron sputtering or HiPIMS

Transparent electrodes (TEs) are essential components in many optoelectronic devices. Although indium tin oxide (ITO) has an excellent trade-off between optical transparency and electrical sheet resistance, it still suffers from several drawbacks, including the increasing cost of indium and poor long-term flexibility due to work hardening. This work presents the development of a new class of TEs based on ultrathin ZnO/Ag/ZnO samples in which Ag films with different film thickness are used as the metallic interlayer. XRD, XPS depth profiling, UV–vis-NIR spectrophotometer, Hall effect measurement, and a four-point probe system were used to characterize the properties of the fabricated films. Optimum thicknesses of Ag and ZnO top layer films were determined as those having high optical transmittance and good electrical conductivity. The main objective of this work has been to investigate how the density of the Ag interlayer in ZnO/Ag/ZnO film samples affects their optical and electrical properties. Silver layers prepared using DC magnetron sputtering (DCMS) have different densities to those prepared using high power impulse magnetron sputtering (HiPIMS). The optimum figure of merit at 3.53 × 10−3 Ω−1 was achieved for ZnO (0.6 nm)/Ag (9 nm)/ZnO (20 nm) multilayer films in which the Ag interlayer was fabricated using the HiPIMS method.

High photoelectric performance of Cu-based AZO multilayer films deposited via TiO2 barrier layer and oxygen-containing atmosphere

Cu-based Al: ZnO (AZO) multilayer films with different barrier layers (Al and TiO2) were deposited on glass substrates under different deposition atmospheres (oxygen and no oxygen) by magnetron sputtering. The effects of Al layer, TiO2 layer and oxygen gas on structural, morphological, optical and electrical properties of the multilayer films were investigated. The AZO/Cu/TiO2/AZO multilayer film deposited in oxygen-containing atmosphere possesses a resistivity as low as 5.12 × 10−5 Ω cm, a sheet resistance of 7.31 Ω/sq., and an average visible optical transmittance of about 81%. It has the optimum photoelectric performance among all the reported multilayer or single-layer transparent conductive thin films, being confirmed by the highest figure of merit (FOM) of 15.59 × 10−3 Ω−1. These results indicate that the insertion of the TiO2 barrier layer and the filling of oxygen during the deposition of the top AZO layer is an effective method for improving the optical and electrical properties of the Cu-based AZO multilayer film.

Effect of Ni-doped Ag on the thermal stability of ZnO/Ag/ZnO multilayer thin films

Abstract In this work, we investigated the thermal stability of ZnO/Ag(Ni)/ZnO multilayer thin films fabricated by using a magnetron reactive co-sputtering system at room temperature on Si (p-type, 100) and a glass substrate. We annealed the fabricated thin films in a furnace at between 0 and 600 °C. The properties of the ZnO/Ag(Ni)/ZnO multilayer films depended on the Ni doping of the mid-layer film. To evaluate effect of Ni doping on the electrical, optical, and structural properties, the concentration of Ni in the mid-layer film was fixed at 5 at.%. When the pure Ag thin film was annealed, the Ag atoms were agglomerated by the surface diffusion, so the grain size and the surface roughness were increased. As a result, the sheet resistance was increased and the transmittance was decreased. However, when Ni was doped, the Ni atoms inhibited the surface diffusion and aggregation of Ag atoms, thus improving the thermal stability of the Ag film. The XPS depth profile shows that the Ni atoms inhibited the diffusion of Ag atoms. For 500 °C, we evaluated the Haccke's figure of merit (FOM) of the ZnO (30 nm)/Ag(Ni) (10 nm)/ZnO (30 nm) multilayer film to be 45.8 × 10−3 Ω−1.

Influence of Al/Cu thickness ratio and deposition sequence on photoelectric property of ZnO/Al/Cu/ZnO multilayer film on PET substrate prepared by RF magnetron sputtering

ZnO/Al/Cu/ZnO multilayer films were deposited on flexible polyethylene terephthalate (PET) substrates by radio frequency (RF) magnetron sputtering. The overall thickness of the intermediate Al and Cu metal layers maintained at 8 nm. The four different Al/Cu thickness ratios were 7:1, 6:2, 5:3 and 4:4. Other four reference samples were prepared by using the same process, i.e. ZnO single-layer film, ZnO/Al8 (8-nm-thick Al layer, the same below)/ZnO, ZnO/Cu8/ZnO and ZnO/Cu2/Al6/ZnO multilayer films. The effects of Al/Cu thickness ratio and deposition sequence of Al and Cu layers were investigated. The results revealed that with the increase of Cu layer thickness, sheet resistance of the multilayer film decreased, while transmittance increased first and then decreased. The ZnO/Al6/Cu2/ZnO multilayer film with a sheet resistance of 108 Ω/sq and an average visible transmittance of 84.73% had the optimum overall photoelectric property, being confirmed by the highest figure of merit of 1.77 × 10–3 Ω–1. Furthermore, ZnO/Cu2/Al6/ZnO and ZnO/Al6/Cu2/ZnO multilayer films exhibited almost the same average visible transmittance and sheet resistance, implying that the deposition sequence of Al and Cu layers has little influence on photoelectric properties. It is demonstrated that ZnO/Al/Cu/ZnO multilayer flexible films have great potential in various fields.

CO2 laser annealing effects for Al-doped ZnO multilayered films

In this research, comparative optical annealing effects on Al-doped ZnO multilayer thin films were analyzed. Both a CO2 laser and the rapid thermal annealing (RTA) process were carried out and compared to test their annealing effects. The uniformly distributed long wavelength of a CO2 laser can penetrate into deeper areas from the surface of a thin film compared to that of a short wavelength of lasers such as UV and IR lasers. 4 different types of Al-doped ZnO thin films showed different stress/strain behaviors. In this research, different compositions of Al-doped ZnO thin films were prepared and annealed through both an optical annealing method using a laser and the RTA process.

Characterization of Al2O3 and ZnO multilayer thin films deposited by low temperature thermal atomic layer deposition on transparent polyimide

Recently, flexible and stretchable displays with organic light emitting diodes are one of hottest technical issues in electronic industries. Therefore, the application of polymer substrates is required because current glass-based materials cannot meet the required properties of flexible and stretchable displays. But there are some limitations for using polymers in display substrate such as inferior surface characteristics such as low scratch resistance, low hardness, and so on. Polymers have many additional technical issues like low stiffness, low heat resistance, low barrier properties, and high sensitivity to degradation compared with glass material. The low temperature atomic layer deposition (ALD) can be a good solution as a functional coating on the polymer substrate to resolve such surface characteristic issues. In this study, two oxide thin films, i.e., Al2O3 and ZnO, are deposited on a transparent polyimide (TPI) film substrate using a low temperature thermal ALD technique. To fabricate a reliable and high quality thin film, the pretreatment using O2 plasma was conducted on the surface of TPI. Two oxide thin films are deposited as multilayer thin films by layer-by-layer process to investigate the effect of multilayer deposition of oxide thin films on mechanical properties. Surface morphologies of the deposited thin films are observed using optical microscopy and scanning electron microscope. Chemical characteristics of the deposited thin film are analyzed using x-ray photoelectron spectroscopy. The physical and mechanical characteristics of the Al2O3 and ZnO multilayer thin film are investigated using nanoindentation and microtensile tests.

Characteristics of ZnO Multi-Layer Film Fabricated by Electrodeposition Method

Characteristics of ZnO Multi-Layer Film Fabricated by Electrodeposition Method

Electrical and optical characteristics of transparent conducting Si-doped ZnO/hole-patterned Ag/Si-doped ZnO multilayer films

Hole-patterned Ag layers were first used to form Si-doped ZnO (SZO)/hole-patterned Ag/SZO multilayers and their optical and electrical properties were characterized. Unlike conventional oxide/metal/oxide multilayers, all samples exhibited two characteristic features: (i) a sinusoidal wavelength dependence of the transmittance with double maxima, and (ii) undulation in the visible transmittance, but not in the infrared transmittance. With increasing SZO thickness, the transmittance maxima were red-shifted, and the visible transmittance window widened. The carrier concentration decreased from 7.42×1022 to 2.4×1022cm−3, and the sheet resistances varied from 7 to 10Ω/sq with increasing SZO thickness. Haacke's figure of merit (FOM) was calculated for the SZO-based multilayer films. The 40nm-thick SZO multilayers had the highest FOM of 15.9×10–3Ω–1. Finite-difference time-domain (FDTD) simulations were undertaken to interpret the measured transmittance. Based on the FDTD simulations, the undulating transmittance was attributed to surface plasmon-polaritons.

Comparative studies of the structural and magnetic properties in Cu, Co codoped ZnO multilayer films sputtered on different substrates

The Zn0.959Cu0.023Co0.018O multilayer films on silicon and polystyrene particles array were prepared using RF magnetron sputtering technique. The influences of the substrate on structural and magnetic properties of Cu, Co codoped ZnO multilayer films were investigated by X-ray diffraction, Scanning electron microscope, X-ray photoelectron spectroscopy, and vibrating sample magnetometer. The results indicated that all the samples were the wurtzite structure with hexagonal shapes of ZnO holding different degree of preferred orientation, the Cu2+, Cu+ and the Co3+, Co2+ ions would uniformly substitute into the Zn2+ sites of ZnO lattice in the samples sputtered on the different substrates. All the samples showed room temperature ferromagnetism, the saturation magnetization and the coercivity of the samples sputtered on the different substrates changed due to the chemical states of the Cu and anisotropy energy of the samples.

Effects of the sputtering gas conditions on the structural, optical and magnetic properties of Cu, Co codoped ZnO multilayer films

The Cu, Co codoped ZnO multilayer films were deposited by magnetron sputtering on silicon (100) in different sputtering gas and the substrates were held at 500 °C. The oxygen content in the films were correlated with the oxygen prevailed in the sputter chamber. The influences of the oxygen content in the sputtering gas on structural, optical and magnetic properties of Cu, Co codoped ZnO multilayer films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, UV absorption spectrophotometer and vibrating sample magnetometer. The results indicated that Cu2+ and Co2+ ions would uniformly substitute into the Zn2+ sites of ZnO lattice. The optical band gap of the films increased from 3.14 to 3.23 eV with increasing oxygen content of the sputtering gas. Oxygen concent have effected on the ferromagnetism of the samples.

New insights in the structural and morphological properties of sol-gel deposited ZnO multilayer films

This study shows how the structural and morphological properties of sol-gel deposited ZnO films can be precisely tuned and selectively controlled. For that purpose, ZnO films have been deposited through a multilayer sol-gel route using solutions of zinc acetate dihydrate (ZAD) diluted in 1-butanol. The opto-geometrical, morphological, and structural properties of these films have been thoroughly studied in relation to the ZAD concentration in butanol, number of deposited single-layers, and heat-treatment conditions. On this basis, different physical processes occurring over the multilayer deposition procedure have been discussed to explain how the experimental parameters influence the film properties and enable to tune the grain size, texture coefficient, and surface coverage rate in a wide range of values. This work is a first step toward the optimized growth of ZnO nanowires on sol-gel films and their subsequent integration in 2D or 3D nanowire-based biosensors.

Transparent Conductive AGZO/Ag/AGZO Multilayers on PET Substrate by Roll-to-Roll Sputtering.

Indium-free Al and Ga-codoped ZnO (AGZO) multilayer films with nanoscale Ag interlayer were deposited by dual target roll-to-roll RF for AGZO and DC sputtering systems for Ag at room temperature for a large scale. The thicknesses of AGZO/Ag/AGZO multilayer were optimized by changing the roll speed: 0.15/1.1/0.15 m/min for AGZO/Ag/AGZO multilayers, respectively. The optimum thicknesses of AGZO/Ag/AGZO multilayer are 9.21, 8.32 and 8.04 nm, respectively. Optimized AGZO/Ag/AGZO multilayer films showed an excellent transparency (84% at 550 nm) and a low sheet resistance (9.2 omega/sq.) on PET substrates for opto-electronic applications. The effects of nanoscale Ag interlayer on optical and electrical properties of AGZO/Ag/AGZO multilayer films were discussed.

The Effect of the Annealing on the Properties of ZnO/Cu/ZnO Multilayer Structures

Study of ZnO / Cu / ZnO multilayer film stack using Cu film as a sandwich layer, in order to improve the overall performance of the transparent conductive film, structural, electrical and optical properties. ZnO / Cu / ZnO multilayer films prepared at room temperature by a DC and RF magnetron sputtering technique. The results showed that ZnO / Cu / ZnO multilayer film has good crystalline properties. With an increasing Cu layer thickness, a visible light transmittance of the multilayer film is reduced, while the electrical performance improved significantly. In the Cu layer thickness of 20nm, ZnO / Cu / ZnO multilayer film optoelectronic integrated for optimal performance

Highly flexible Al-doped ZnO/Ag/Al-doped ZnO multilayer films deposited on PET substrates at room temperature

We investigated the effects of the Ag layer thickness on the electrical and optical properties of AZO (36nm)/Ag/AZO (36nm) multilayer films that were deposited on polyethylene terephthalate (PET) substrates using a radio frequency magnetron sputtering method. The AZO/Ag/AZO films had transmittances over 74–89% at 550nm. The relationship between the transmittance and the Ag layer thickness was investigated with three-dimensional finite-difference time-domain (3D FDTD) simulations to understand high transmittance. As the Ag layer thickness increased from 15 to 23nm, the carrier concentration increased from 5.84×1021 to 9.66×1021cm−3, while the sheet resistance decreased from 10.15 to 3.47Ωsq−1. The Haacke figure of merit (FOM) was calculated for the samples with various Ag layer thicknesses; it was a maximum at 19nm (43.9×10−3Ω−1). The resistance change for the 100nm-thick ITO only films was unstable even after 5 cycles, while that of the AZO (36nm)/Ag (19nm)/AZO (36nm) film remained constant up to 1000 cycles.

Al-doped ZnO/Ag/Al-doped ZnO multilayer films with a high figure of merit

In this study, we investigated the effects of the Al-doped ZnO (AZO)-layer thickness on the optical and electrical properties of AZO/Ag/AZO multilayer films deposited on glass substrates at room temperature. The optimal AZO/Ag/AZO (36nm/19nm/36nm) multilayer sample exhibited a transmittance of approximately 93% at 550nm. As the AZO-layer thickness increased from 9 to 45nm, the carrier concentration gradually decreased from 1.87×1022 to 6.36×1021cm−3, while the sheet resistance slightly increased from 3.86 to 4.47Ωsq−1 and the charge mobility increased from 24.15 to 25.42cm2V−1s−1. The samples had smooth surfaces with a root mean square (RMS) roughness ranging from 0.40 to 1.23nm. The Haacke figure of merit (FOM) was calculated for the samples as a function of the AZO-layer thickness. The optimal AZO/Ag/AZO multilayer film had the highest FOM of 99.9×10−3Ω−1.

Highly flexible ZnO/Ag/ZnO conducting electrode for organic photonic devices

We investigated the electrical, optical and bending characteristics of ZnO (40nm)/Ag (18.8nm)/ZnO (40nm) multilayer film deposited on polyethylene terephthalate (PET) substrate and compared them with those of indium-tin-oxide (ITO) (100nm thick). The ITO single and ZnO/Ag/ZnO multilayer films gave maximum transmittance of 92.9% and ~95% at ~530nm, respectively. For the ITO single and ZnO/Ag/ZnO multilayer films, the carrier concentration was measured to be 1.19×1020 and 6.68×1021cm−3, respectively and the mobility was 32.06 and 21.06cm2/Vs, respectively. The sheet resistance was 175.99 and 4.98Ω/sq for the ITO single and ZnO/Ag/ZnO multilayer films, respectively. Haacke׳s figure of merit (FOM) of the ITO single and ZnO/Ag/ZnO multilayer films was calculated to be 2.36×10−3 and 104.5×10−3Ω−1. The ZnO/Ag/ZnO multilayer films showed dramatically improved mechanical stability when subjected to bending test.