Optimization of ZnO:Al/Ag/ZnO:Al structures for ultra-thin high-performance transparent conductive electrodes

Al-doped ZnO (AZO)/Ag/AZO multilayer coatings (50-70 nm thick) were grown at room temperature on glass substrates with different silver layer thickness, from 3 to 19 nm, by using radio frequency magnetron sputtering. Thermal stability of the compositional, optical and electrical properties of the AZO/Ag/AZO structures were investigated up to 400 °C and as a function of Ag film thickness. An AZO film as thin as 20 nm is an excellent barrier to Ag diffusion. The inclusion of 9.5 nm thin silver layer within the transparent conductive oxide (TCO) material leads to a maximum enhancement of the electro-optical characteristics. The excellent measured properties of low resistance, high transmittance in the visible spectral range and thermal stability allow these ultra-thin AZO/Ag/AZO structures to compete with the 1 μm thick TCO layer currently used in thin film solar cells.     

Characterization of ZnO:Al/Au/ZnO:Al trilayers for high performance transparent conducting electrodes

Symmetric ZnO:Al/Au/ZnO:Al trilayers were sputter-deposited and characterized for transparent conducting electrodes, varying the thickness of the ZnO:Al (AZO) and Au layers. The optical transmission for normal light incidence is optimum for an AZO thickness of 50 nm, due to the suppression of reflection. In this case, the transmittance is more than 0.7 for wavelengths above 400 nm and for a Au thickness of 5 nm. At the same time, the sheet resistance is approx. 30 Ω, which can be decreased to 12 Ω with the increase of the Au thickness to 9 nm. This is achieved with a moderate loss in the optical transmission. The figure of merit for transparent conducting electrodes, as introduced by G. Haacke (J. Appl. Phys. 47 (1976) 4086) yields values from 29.4 × 10^− 3 to 6.9 × 10^− 3 Ω^− 1, depending on the Au thickness and the considered wavelength range.     

The stability of aluminium-doped ZnO transparent electrodes fabricated by sputtering

The stability of the electrical, optical and mechanical properties of sputtered aluminium-doped ZnO (AZO) films with a resistivity from 10^-3 to 10^-4 Ω cm was investigated. No significant change in these properties of AZO films was observed for use in air at room temperature for 1 year. It is shown that stable properties for use in vacuum and inert and nitrogen gases at temperatures as high as 400°C can be attained for AZO films sputtered with an Al₂O₃ content above 1.0 wt.%. After heat treatment in air at 400°C, the resistivity of AZO films increases by about five orders of magnitude. The resistivity can be returned to that of the as-deposited state by heat treatment in hydrogen gas at a temperature near 400°C.     

夹心结构FeNi/Cu/FeNi多层膜巨磁阻抗效应研究

采用MEMS技术在玻璃基片上制备了夹心结构FeNi/Cu/FeNi多层膜,并在1～40MHz范围内研究了它的巨磁阻抗效应.纵向巨磁阻抗效应先随着外加磁场的增大而迅速增加,在某一磁场下达到最大值后随磁场的增加而逐渐减小.在频率为5MHz时,Hext为0.8kA/m时巨磁阻抗效应最大值达到32.06%.另外,夹心结构多层膜表现出较大的负巨磁阻抗效应,在频率5MHz,Hext=9.6kA/m时,负最大巨磁阻抗效应可达-24.50%.     

Stress-impedance effects in sandwiched FeCuNbCrSiB/Cu/FeCuNbCrSiB films

Sandwiched FeCuNbCrSiB/Cu/FeCuNbCrSiB films with a meander structure have been realized on silicon cantilever by Microelectromechanical Systems (MEMS), and the stress-impedance (SI) effects have been studied in the frequency range of 1–40 MHz. Experimental results show that the values of SI ratio increase with the deflection, and a large SI ratio of − 24.5% at 5 MHz with the deflection of 2 mm is obtained in the sandwiched FeCuNbCrSiB/Cu/FeCuNbCrSiB films, and the strain gauge factor is 1255 at 5 MHz, and is larger than the conventional metal strain gauge and semiconductor strain gauge, which is attractive for the applications of strain sensors.     

Improved thermal stability of ZnO transparent conducting films with a ZnO overlayer

A study of the thermal stability of transparent conducting ZnO thin film in air is reported. By depositing a thin ZnO overlayer (~ 10 nm) on aluminum and gallium-codoped ZnO thin film (AGZO), the thermal stability of the AGZO thin film could be significantly improved. Electrical and structural characterizations of the AGZO thin films with and without the overlayer were performed and the mechanism of the enhanced thermal stability by the overlayer was proposed.     

Growth of aligned ZnO nanorods on transparent electrodes by hybrid methods

The fabrication of ZnO (80 nm) thin film was achieved by hybrid atomic layer deposition (ALD) to prevent the reaction between the reactants and conductive layer of the substrates. ZnO nanorods (ZnO-NRs) growth over the substrates was performed by wet chemical procedure in which Zn(NO₃)₂ and hexamethylenetetramine were used as the precursors. HR-TEM, SAED, FE-SEM, X-ray diffraction (XRD), and UV–Vis spectroscopy were employed to characterize the ZnO-NRs samples on the substrates. XRD and HR-TEM analyses confirmed that the ZnO nanorod structure is hexagonal wurtzite type with growth in the [0001] direction. Length and thickness of the ZnO-NRs ranged between 45  and 90 nm and 480  and 600 nm, respectively. It was observed that the growth rate of NRs in [0001] direction is 10 times higher than in [1000] direction. The growth mechanism and resulted dimensions of nanorods are function of the synthesis parameters (in hybrid ALD process) such as reaction time, temperature, precursor molar ratio, and thickness of ZnO film.     

Development of Ga-doped ZnO transparent electrodes for liquid crystal display panels

Liquid crystal displays (LCDs) with Ga-doped ZnO (GZO) transparent electrodes on RGB color filters were fabricated to demonstrate the feasibility of using this new material as an alternative to indium tin oxide (ITO) electrodes. The process flow for fabricating LCDs with GZO electrodes was entirely compatible with that for commercially available LCDs using ITO electrodes. Concurrently, photolithography processing and wet-chemical etching techniques for the formation of GZO transparent electrodes on thin film transistor (TFT) arrays in LCD panels was developed. Fine-patterns of GZO with 2-μm line widths were successfully formed using lithography and wet -etching technology with a weakly acidic etchant of pH 5.5-6.8.     

三明治结构FeNi/Cu/FeNi多层膜巨磁阻抗效应研究

采用MEMS技术在玻璃基片上制备了三明治结构FeNi/Cu/FeNi多层膜,在1～40 MHz范围内研究了FeNi/Cu/FeNi多层膜中的巨磁阻抗效应特性.当磁场Ha施加在薄膜的长方向时,巨磁阻抗效应随磁场的增加而增加,在某一磁场下达到最大值,然后随磁场的增加而下降到负的巨磁阻抗效应.在频率为5MHz时,巨磁阻抗效应在磁场Ha=800 A/m时达到最大值26.6%.巨磁阻抗效应的最大值及负的巨磁阻抗效应与多层膜中磁各向异性轴的取向及发散有关.另外,当磁场施加在薄膜的短方向时,薄膜表现出负的巨磁阻抗效应,在频率5 MHz、磁场Ha=9600 A/m时,巨磁阻抗效应可达-15.6%.     

Annealing effect of ZnO/Au/ZnO transparent conductive films

Au intermediate ZnO (ZAZ) thin films were prepared by radio frequency and direct current magnetron sputtering on glass substrates and then vacuum annealed. The thickness of each layer of the ZAZ films was set at 50 nm, 3 nm, and 47 nm, respectively. The structural, electrical, and optical properties of ZAZ films were investigated with respect to the variation of annealing temperature.As-deposited AZO films showed X-ray diffraction peaks corresponding to ZnO (002) and Au (111) planes and those peak intensities increased with post-deposition vacuum annealing. The optical and electrical properties of the films were strongly influenced by post-deposition annealing. Although the optical transmittance of the films deteriorated with an Au interlayer, as-deposited ZAZ films showed a low resistivity of 2.0 × 10⁻⁴ Ω cm, and the films annealed at 300 °C had a lower resistivity of 9.8 × 10⁻⁵ Ω cm. The work function of the films increased with annealing temperature, and the films annealed at 300 °C had a higher work function of 4.1 eV than the films annealed at 150 °C. The experimental results indicate that vacuum-annealed ZAZ films are attractive candidates for use as transparent electrodes in large area electronic applications such as solar cells and large area displays.     

Design of ZnO/Ag/ZnO multilayer transparent conductive films

We have studied the properties of ZnO/Ag/ZnO multilayers prepared on glass substrates by simultaneous RF magnetron sputtering of ZnO and dc magnetron sputtering of Ag. The electrical and optical performance of Ag and ZnO single layer films was also investigated. Different optimization procedures were used for good transparent conductive film. Several analytical tools such as spectrophotometer, scanning electron microscope (SEM), four-point probes were used to explore the causes of the changes in electrical and optical properties. Low sheet resistance of 3 Ω/sq. and transmittance over 90% at 580 nm was achieved. The results of optimization condition of both oxide layers and metallic Ag layers were illustrated.     

Characteristics of transparent ZnO based thin film transistors with amorphous HfO2 gate insulators and Ga doped ZnO electrodes

Coplanar type transparent thin film transistors (TFTs) have been fabricated on the glass substrates. The devices consist of intrinsic ZnO, Ga doped ZnO (GZO), and amorphous HfO₂ for the semiconductor active channel layer, electrode, and gate insulator, respectively. GZO and HfO₂ layers were prepared by using a pulsed laser deposition (PLD) and intrinsic ZnO layers were fabricated by using an rf-magnetron sputtering. The transparent TFT exhibits n-channel, enhancement mode behavior. The field effect mobility, threshold voltage, and a drain current on-to-off ratio were measured to be 14.7 cm²/Vs, 2 V, and 10⁵, respectively. High optical transmittance (> 85%) in visible region makes ZnO TFTs attractive for transparent electronics.     

Characteristics of sputtered Al-doped ZnO films for transparent electrodes of organic thin-film transistor

Aluminum-doped ZnO (AZO) thin-films were deposited with various RF powers at room temperature by radio frequency (RF) magnetron sputtering method. The electrical properties of the AZO film were improved with the increasing RF power. These results can be explained by the improvement of the crystallinity in the AZO film. We fabricated the organic thin-film transistor (OTFT) of the bottom gate structure using pentacene active and poly-4-vinyl phenol gate dielectric layers on the indium tin oxide gate electrode, and estimated the device properties of the OTFTs including drain current-drain voltage (I_D-V_D), drain current-gate voltage (I_D-V_G), threshold voltage (V_T), on/off ratio and field effect mobility. The AZO film that grown at 160 W RF power exhibited low resistivity (1.54 × 10^− 3 Ω·cm), high crystallinity and uniform surface morphology. The pentacene thin-film transistor using the AZO film that's fabricated at 160 W RF power exhibited good device performance such as the mobility of 0.94 cm²/V s and the on/off ratio of ~ 10⁵. Consequently, the performance of the OTFT such as larger field-effect carrier mobility was determined the conductivity of the AZO source/drain (S/D) electrode. AZO films prepared at room temperature by the sputtering method are suitable for the S/D electrodes in the OTFTs.     

Magnetoimpedance effect in FeCoB/Cu/FeCoB sandwiched films with Permalloy underlayer

We studied the magnetoimpedance (MI) effect of FeCoB(100 nm)/Cu(100 nm)/FeCoB(100 nm) sandwiched films with different thickness of Permalloy as underlayer for the FeCoB ferromagnetic layer. The maximum MI ratio of sandwiched film is 9.2% when the thickness of the Permalloy underlayer is 2-3 nm. The improvement of MI ratio of sandwiched films with Permalloy underlayer was explained by exchange induced ripple reduction mechanism.     

Deposition of the ZnO transparent electrodes at atmospheric pressure using a DC Arc Plasmatron

Structure and electrical properties of ZnO films deposited by a DC Arc Plasmatron were studied. Films were deposited at atmospheric pressure on a cold substrate. Effect of annealing and plasma treatment was investigated. It was shown that in the as-deposited state the films have an amorphous structure and resistance of about 2 MΩ/cm. Annealing in hydrogen atmosphere at 550 °C improves the crystalline structure and decreases the resistivity of the films down to 5 Ω/cm. Also treatment of surface by hydrogen-argon plasma can be used for decreasing of the resistance of the ZnO films.     

A Cu/ZnO Nanowire/Cu Resistive Switching Device

Nano-Micro Letters - A new device has been realized using flip-chip joining two printed circuit boards (PCBs) on which zinc oxide (ZnO) nanowires were synthesized. Energy dispersive X-ray...     

Increased thermal stability of Al-doped ZnO-based transparent conducting electrodes employing ultra-thin Au and Cu layers

The paper examines the influence of heating in air on the structural, electrical and optical properties of Al-doped ZnO (AZO)-based transparent conducting electrodes employing ultra-thin Au and Cu layers, sputter-deposited onto unheated glass substrates. The results are compared with the ones obtained for single AZO layers. For these, the quality factor in the visible wavelength range degrades continuously with the heating temperature, as the result of increasing sheet resistance. Contrary to this behavior, symmetric AZO/Au/AZO and AZO/Cu/AZO trilayers improve their quality factor for temperatures up to 250 °C. At the same time, these trilayers offer 4-times lower roughness than single AZO layers of comparable sheet resistance, which can be a significant advantage when active optoelectronic or solar-cell device layers are to be deposited on the transparent electrode.