Zinc Oxide Film Thickness Research Articles

Investigating the electrical and thermal properties of Cu and Al-doped ZnO thick films using the screen-printing technique for thermal resistance applications

The important properties of prepared Zinc Oxide (ZnO) thick films were investigated. The electrical and thermal properties of ZnO thick films were measured and analyzed using the MATLAB simulation tool. On a glass substrate, thick films of pure ZnO as well as ZnO doped with Cu and Al materials were fabricated using the screen-printing technique. The electrical parameters were calculated using the half-bridge approach to determine the unknown resistance, change in current, and voltage. The half-bridge circuit having a 50 M Ω reference resistance with 30 V excitation voltage. The thermocouple transducer (K type) was used to measure the heating and cooling temperature between 40 °C to 370 °C. The measured maximum TCR values are 0.0095 ppm/°C for pure ZnO film, 0.0068 ppm/°C for Cu-doped ZnO film, and 0.0123 ppm/°C for Al-doped ZnO film. The maximum measured resistance values are 5.9 × 107 Ω for pure ZnO film, 5.9 × 107 Ω for Cu-doped ZnO film, and 5.9 × 107 Ω for Al-doped ZnO film. Using MATLAB simulation, it was possible to observe key factors including the activation energy, unknown resistance, IV characteristics, thermal properties, temperature coefficient resistance (TCR) and resistive linear behavior of the ZnO films.

Heat-Annealed Zinc Oxide on Flexible Carbon Nanotube Paper and Exposed to Gradient Light to Enhance Its Photoelectric Response.

Buckypaper (BP), a flexible and porous material, exhibits photovoltaic properties when exposed to light. In this study, we employed radio frequency (RF) sputtering of zinc oxide (ZnO) followed by rapid thermal annealing to enhance the photovoltaic response of BP. We investigated the impact of various sputtering parameters, such as the gas flow ratio of argon to oxygen and deposition time, on the morphology, composition, resistivity, and photovoltaic characteristics of ZnO-modified BP. Additionally, the photovoltaic performance of the samples under different illumination modes and wavelengths was compared. It was found that optimal sputtering conditions-argon to oxygen flow ratio of 1:2, deposition time of 20 min, and power of 100 watts-resulted in a ZnO film thickness of approximately 45 nanometers. After annealing at 400 °C for 10 min, the ZnO-modified BP demonstrated a significant increase in photocurrent and photovoltage, along with a reduction in resistivity, compared to unmodified BP. Moreover, under gradient illumination, the ZnO-modified BP exhibited a photovoltage enhancement of 14.70-fold and a photocurrent increase of 13.86-fold, compared to uniform illumination. Under blue light, it showed a higher photovoltaic response than under other colors. The enhancement in photovoltaic response is attributed to the formation of a Schottky junction between ZnO and BP, an increased carrier concentration gradient, and an expanded light absorption spectrum. Our results validate that ZnO sputtering followed by annealing is an effective method for modifying BP for photovoltaic applications such as solar cells and photodetectors.

First Results on Zinc Oxide Thick Film Deposition by Inverted Magnetron Sputtering for Cyclotron Solid Targets Production.

The magnetron sputtering technique has been investigated in recent years with ever-growing interest as a verifiable solid target manufacturing technology aimed at the production of medical radionuclides by using low-energy cyclotron accelerators. However, the possible loss of high-cost materials prevents access to work with isotopically enriched metals. The need for expensive materials for the supply of the growing demand for theranostic radionuclides makes the material-saving approach and recovery essential for the radiopharmaceutical field. To overcome the main magnetron sputtering drawback, an alternative configuration is proposed. In this work, an inverted magnetron prototype for the deposition of tens of μm film onto different substrates is developed. Such configuration for solid target manufacturing has been proposed for the first time. Two ZnO depositions (20-30 μm) onto Nb backing were carried out and analysed by SEM (Scanning Electron Microscopy) and XRD (X-ray Diffractogram). Their thermomechanical stability under the proton beam of a medical cyclotron was tested as well. A possible improvement of the prototype and the perspective of its utilisation were discussed.

Thickness dependent ultraviolet photoconductivity studies on sol-gel derived zinc oxide (ZnO) films

ZnO films of varying thicknesses (77–231 nm) were deposited using the sol-gel method for ultraviolet (UV) photodetection applications. The dependence of the photoconductivity parameters of the photodetector on the thickness of the ZnO films has been investigated for UV radiation having 365 nm wavelength and intensity of 24 µW/cm2. The deposited ZnO films exhibited poly-crystallinity with significant surface roughness (30–92 nm) and oxygen-related defects (Oi, Ozn, Vo), which were found beneficial for obtaining enhanced UV photosensitivity. The photoconducting mechanism has been studied in detail using the statistical interpretation of defects observed from the deconvolution of photoluminescence spectra. The 221 nm thick ZnO film showed improved photoconducting parameters (photoconductive gain, current responsivity, rise time and fall time) which are attributed to the increased density of all the defects under deep-level emission.

Effect of Carrier Gas Flow Rates on the Structural and Optical Properties of ZnO Films Deposited Using an Aerosol Deposition Technique

Aerosol deposition (AD) is a simple, dry raw-powder deposition process in which the targeted film is formed by direct bombardment of accelerated starting powder onto the substrate surface at room temperature. Despite the increased interest in AD film formation, no work has been completed to systematically investigate the formation of dense zinc oxide (ZnO) films using the AD method and their optical properties. Therefore, this study was carried out to investigate the effect of AD gas flow rate on the formation of AD films and the optical properties of aerosol-deposited ZnO films. ZnO films with nanosized (<40 nm) crystallites were successfully deposited on FTO substrates at room temperature. A dense and uniform layer of aerosol-deposited ZnO films with a roughened surface was obtained without subsequent heat treatment. With the increase in the AD gas flow rate, the crystal size and the AD film’s thickness were reduced. The Raman spectroscopy verified that the thin film was of a ZnO wurtzite structure. The room temperature photoluminescence of the ZnO thin film produced strong visible emissions. The findings of this work demonstrated that AD can be an alternative technique for the rapid deposition of dense and thick ZnO films for optoelectronic applications.

Fabrication, characterization and exploration of cobalt (II) ion doped, modified zinc oxide thick film sensor for gas sensing characteristics of some pernicious gases

The present research deals with the synthesis of zinc oxide (ZnO) nanoparticles by the co-precipitation (CPT) method. The CPT method was successfully utilized for the synthesis of ZnO nanoparticles. The structural properties of undoped ZnO and cobalt doped ZnO were confirmed by employing an X-ray diffraction (XRD) study, from which the average particle size for each prepared material was calculated from the Debye Scherer formula. The average particle size confirms the nano range fabrication of undoped and cobalt doped ZnO material. The surface characteristics, morphology, texture, and porosity properties of undoped ZnO and cobalt doped ZnO were investigated from scanning electron microscopy (SEM). The elemental composition was investigated from energy dispersive spectroscopy (EDS). The High-resolution transmission electron microscopy (HRTEM) results revealed the hexagonal phase of prepared material. Furthermore, the undoped ZnO and 5% cobalt doped ZnO gas sensors prepared by screen printing technology were utilized for gas sensing purposes for testing the gases like H2S, NO2, SO2, and methanol. For the gases examined, the cobalt modified ZnO sensor proved to be quite effective, especially for H2S and NO2 gas vapors. The Co2+ doped ZnO sensor showed 70.12% sensitivity for H2S gas at 150 0C and 68.75% gas response for NO2 gas vapors at 120 0C. In addition, the cobalt modified sensor was also investigated for reusability test to get concrete gas response results with the time interval of 15 days. In conclusion, it can be mentioned that the cobalt doped ZnO thick film sensor is a promising sensor for H2S and NO2 gas vapors.

Hydrothermal growth method for the deposition of ZnO films: Structural, chemical and optical studies

Hydrothermal growth method was used to grow the zinc oxide (ZnO) thick films on ZnO seed layer previously deposited by RF magnetron sputtering technique. The effect of introducing of zinc acetate and chloride salts on the structure, chemical and physical properties of the obtained films was investigated. Scanning electron microscope (SEM) and atomic force microcopy (AFM) were utilized to both justify the nanostructure growth of the ZnO thick films deposited by hydrothermal growth method, and to identify their morphology. Energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) confirmed the elemental stoichiometry of the prepared ZnO thick films with low contamination. X-ray diffraction (XRD), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR) characterizations approved the texturation of the ZnO thick films prepared by hydrothermal growth method and verified the nonstructural growth with (002) preferred orientation as well as hexagonal phase. XRD technique indicated that the ZnO films had a good quality (big grain size and preferential orientation) and the Raman and FTIR studies confirmed the XRD results. Moreover, photoluminescence (PL) spectroscopy verified the optoelectronic behavior and demonstrated a potential optical application in this field.

Optical Properties of Thick Zinc Oxide Films Doped with Gallium and Gold

Samples of thick (30–32 µm) films of pure and gallium- and gold-doped zinc oxide obtained by magnetron sputtering using an uncooled target have been investigated. It is shown that the main changes in the optical properties of undoped thick ZnO films during recrystallization annealing under atmospheric conditions occur for the first 2–3 h. It is found that doping of thick ZnO films with gallium (4 at %) without additional heat treatment doubles the transmittance (to a value of about 97%). At the same time, this introduced gallium concentration leads to concentration quenching of X-ray luminescence. The results of measuring temporal characteristics show that the shapes of X-ray luminescence kinetics of samples with a gold buffer layer after heat treatment and undoped ZnO samples are identical and characterized by a long shoulder of slow luminescence with a characteristic time of about a microsecond and low integrated intensity with a short decay time.

Deposition of Multilayer Films of ZnO by Sol-gel Process on Stainless Steel Substrates for Energy Harvesting Devices

The mechanical vibrations surrounding the environment can be converted in electrical energy by piezoelectric energy harvesters (PEH). The increase on the availability of Wireless Sensor Networks (WSN) increases the need for power supply that replaces ordinary batteries. In this paper, an electromechanical modelling and a deposition of multilayer zinc oxide (ZnO) films for an PEH are presented. The aim of the study is to obtain the thickness of the multilayer ZnO films in different conditions, in order to improve the energy harvesting capacity for a PEH device. The ZnO synthesis was performed by the sol-gel method with dehydrated zinc acetate as a precursor, making deposits of 5, 10 and 15 layers. The depositions were made at room temperature by spin coating at 1440 revolutions per minute for 16 s. An UV-Vis test showed that ZnO were present, with a percentage of peak reflectance at 370 nm and a XRD test showed a preferential crystalline orientation at (002). Also, a Finite Element Modelling (FEM) simulation of the substrate behaviour was performed, functioning as a cantilever beam. When adding a seismic mass and oscillating in the resonance frequency of 103.31 Hz and with 15 layers of ZnO deposited, 2.67 volts were obtained.

ZnO thick films for NO2 detection: effect of different nanostructures on the sensors’ performances

In this paper, the great sensitivity and selectivity to NO2 detection at low temperature down to ppb level of zinc oxide (ZnO) thick-film sensors are reported. Sensor performances of ZnO films prepared by screen-printing technique were evaluated comparing two different ZnO nano-powders in wurtzite crystal structure. Powders were synthesized by hydrothermal route (HT-ZnO) and by auto-combustion sol–gel synthesis (AC-ZnO). After proper characterization of the nano-powders, the thick-film sensors were fabricated by screen-printing technique onto α-alumina substrates equipped with Pt interdigitated electrodes, followed by a thermal treatment. The sensor response was studied in the range 50–250 °C. Best results were reached at 150 °C, with sensor response R (Zg/Z0)—defined as the ratio between impedance under NO2 (Zg) and impedance under dry air (Z0)—equal to 42.92 for HT-ZnO and to 23.18 for AC-ZnO under 0.5 ppm of NO2 in dry conditions. Finally, response and recovery time were measured, and selectivity of the sensors was determined by exposing the film toward O3, CO2, CH4, N2O and humidity at the best working temperature. Both sensors showed great sensitivity for NO2 detection, supporting the exploitation of these sensors as NO2 detectors at ppb level.

Quantitative Assessment of Vapor Molecule Adsorption to Solid Surfaces by Flow Rate Monitoring in Microfluidic Channels.

Measuring parameters related to gas adsorption on the effective surfaces of solid samples is important in catalyst studies. Further attention on the subject has appeared due to the materials and methods required to concentrate the gaseous biomarkers for detection. The conventional methods are mainly based on the volumetric and gravimetric analyses, which are applicable to bulk samples. No standard method has yet been provided for such measurements on thin films, which are the most commonly used samples for material screening. Here, a novel method is presented for the adsorption coefficient measurement on thin-film samples. This method comprises coating of the inner walls of a microfluidic channel with the thin film under test. The recorded diffusion rates for a trace gas along this microchannel are compared with the solutions of the adsorption-diffusion equation of the channel for determining the adsorption coefficient of the gas molecule to the inner walls of the channel. The high ratio of surface-to-volume in such channels magnifies the gas sorption effects and improves accuracy. The method is fast, versatile, and cost-effective, allowing measurements at different temperatures and atmospheric pressures. The adsorption coefficients of different isomers of butanol on poly(methyl methacrylate) sheets, zinc oxide thick films, and gold thin films are determined as examples.

Generation and enhancement of surface acoustic waves on a highly doped p-type GaAs substrate.

Surface acoustic waves (SAWs) have been widely studied due to their unique advantage to couple the mechanical, electrical, and optical characteristics of semiconductor materials and have successfully been used in many industrial applications. In this work, we report a design that uses piezoelectric material Zinc Oxide (ZnO) to enhance the generation and propagation of SAWs on the surface of a highly doped p-type Gallium Arsenide (GaAs) substrate, which is more extensively used in optoelectronic devices than intrinsic GaAs structures. To maximize the piezoelectricity and successfully generate SAWs, high quality c-axis orientation of the ZnO film is needed; thus we experiment and develop optimized recipes of a radio frequency (RF) magnetron sputtering system to deposit ZnO on the GaAs substrate. To further optimize the SAW performance, an intermediate Silicon Oxide (SiO2) layer is added between the ZnO film and GaAs substrate. Additionally, we test samples with varied thickness of ZnO films and dimensions of interdigital transducer (IDT) fingers to figure out their individual effect on SAW properties. The results and techniques demonstrated in this paper will provide guidance for further studies on enhancing SAWs propagating along many other doped semiconductor materials. This combination of acoustics and optoelectronics in doped semiconductors is a promising start to building enhanced and hybrid devices in various fields.

CVD growth of zinc oxide thin films on graphene on insulator using a high-temperature platinum-catalyzed water beam

The characteristics of zinc oxide (ZnO) films with different thicknesses grown on graphene, i.e., single-layer graphene (SLG) and multilayer graphene (MLG), on insulators at 500 °C using a reaction between dimethylzinc and high-temperature water generated by a catalytic reaction on Pt nanoparticles were investigated. The growth rate of continuous ZnO layer on MLG was higher than that of SLG. XRD patterns for the ZnO films exhibited an intense diffraction peak associated with (0002) plane and small ones associated with (10–10) and (10–11) planes, suggesting the grown hexagonal wurtzite ZnO is not perfectly along c-axis direction due to the nature of the used graphene structures. The FWHM values of the 2θ for ZnO (0002) were < 0.20° and 0.16° for ZnO on SLG and MLG, respectively. The photoluminescence at room temperature exhibited strong emission peak at 3.28 eV with no significant level of green emission indicating negligible defect density in the grown ZnO films. The results suggest that accurate optical bandgap cannot be determined from the transmittance spectra for the ZnO films with thickness and roughness higher than 1 µm and 20 nm, respectively. The results also suggest that the thickness of ZnO films should be below 1 µm in order to obtain acceptable level of transmittance in visible up to near infrared region.

Fabrication and characterization of CdS doped ZnO nano thick films

In the present work, microstructural and optical properties of Cadmium Sulfide (CdS) doped Zinc Oxide (ZnO) thick film is investigated. Two samples undoped ZnO and 2 wt % CdS-doped ZnO thick film have been fabricated on the glass substrate. The fabricated film is characterized by X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM). X-ray diffraction patterns showed that crystallite size decreasing with CdS doping and it is 45 nm and 38 nm for ZnO and CdS-doped ZnO thick film. The variation on the surface morphology was observed using AFM measurement. The AFM results indicate that grain size and roughness parameter decreases, but microstrain increases with CdS content. The UV–Vis absorption spectra of the ZnO and ZnO-CdS showed that the optical band-gap decreased from 3.18eV to 2.10eV with 2 wt% CdS doping concentration. The present study demonstrates that fabricated films have polycrystalline structures and peaks matching the hexagonal ZnO structure.

Characterization of RF sputtered zinc oxide thin films on silicon using scanning acoustic microscopy

Zinc oxide (ZnO) thin films were grown on silicon (100) substrate using radio frequency (RF) sputtering under various processing parameters including deposition time and annealing temperature. A series of characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and scanning acoustic microscopy (SAM) have been used to analyze the crystallinity and crystal orientation, structural morphology, surface roughness, and acoustic properties of these films. In particular, quantitative analysis of elastic wave propagation in ZnO thin films by scanning acoustic microscopy has been performed for the first time in the present work. It has been shown that the propagation properties of acoustic waves on the surface of ZnO thin films strongly depend on film thickness, crystallinity, and surface roughness. The dispersion properties of surface acoustic waves (SAWs) are observed as a function of ZnO film thickness. The velocities of SAWs range from 5328.3 m/s to 4245.7 m/s with increasing film thickness from 32.5 nm to 2.04 μm, while smoother surface contributes to faster propagation of SAWs.

Effect of Thickness on Micro-Structural and Optical Properties of Al-Doped ZnO Films Prepared by Sol-Gel Spin Coating

Aluminium (Al) doped Zinc oxide (ZnO) thin films of different thicknesses were prepared on glass substrates by sol-gel spin coating method. The effect of thicknesses on micro-structural and optical properties was investigated for transparent conducting oxide (TCO) application in solar cells and other optoelectronic applications. Grazing incidence x-ray diffraction (GIXRD) showed maximum orientation along (002) plane of c-axis. The variation of different structural parameters like crystallite size, micro-strain, c-axis strain, dislocation density as a function of film thickness was investigated. The FTIR spectra confirmed the formation of Al-doped ZnO film. FESEM images showed spherical shaped nanosized grains and formation of micro pores. The optical absorption increased and absorption peak shifted towards longer wavelength (red shift) with increase in the thickness of the film respectively. The optical transmittance of all the films has a transparency of more than 75% in the visible region. The optical band gap (Eg) decreased with increase in the film thickness. The diffused reflectance (DRS) showed very low reflectance in the region of 400-800 nm, but increased in the 800-900 nm region. Photoluminescence (PL) spectra of the prepared films showed intense band edge UV and low intense visible emissions respectively. The effect of thickness of Al-doped ZnO film on micro-structure, surface morphology, optical absorption and transmittance, diffused reflectance and PL have been investigated and the results are reported.

Low-Concentration Indium Doping in Solution-Processed Zinc Oxide Films for Thin-Film Transistors.

We investigated the influence of low-concentration indium (In) doping on the chemical and structural properties of solution-processed zinc oxide (ZnO) films and the electrical characteristics of bottom-gate/top-contact In-doped ZnO thin-film transistors (TFTs). The thermogravimetry and differential scanning calorimetry analysis results showed that thermal annealing at 400 °C for 40 min produces In-doped ZnO films. As the In content of ZnO films was increased from 1% to 9%, the metal-oxygen bonding increased from 5.56% to 71.33%, while the metal-hydroxyl bonding decreased from 72.03% to 9.63%. The X-ray diffraction peaks and field-emission scanning microscope images of the ZnO films with different In concentrations revealed a better crystalline quality and reduced grain size of the solution-processed ZnO thin films. The thickness of the In-doped ZnO films also increased when the In content was increased up to 5%; however, the thickness decreased on further increasing the In content. The field-effect mobility and on/off current ratio of In-doped ZnO TFTs were notably affected by any change in the In concentration. Considering the overall TFT performance, the optimal In doping concentration in the solution-processed ZnO semiconductor was determined to be 5% in this study. These results suggest that low-concentration In incorporation is crucial for modulating the morphological characteristics of solution-processed ZnO thin films and the TFT performance.

Low temperature produced calcium-doped zinc oxide thick film via screen printing technique as thermal interface material in LED application

Pure and calcium-doped zinc oxide thick films were deposited on Aluminium substrate by screen printing technique using nanocrystalline powder synthesized from co-precipitation method. Shear thinning phenomenon with increment of shear rate was observed during the rheological analysis for all pastes. X-ray diffraction results confirmed the formation of ZnO with preferred orientation along (101) plane. Peak shifting to lower angle was observed upon increment of doping concentration of calcium. Crystallite size of doped ZnO powder decreased in the range (from 35.4 to 42.4 nm) from 116.1 nm of pure ZnO. Surface morphology analysed by FESEM had revealed the reduction of voids with increasing doping concentration up to 7 wt% of doping, followed by a slightly increase in the number of voids at 9 wt% doping. AFM analysis showed that the surface roughness of films exhibited a decreasing trend with the increase of calcium dopant until 7 wt% but became rougher at 9 wt%. Peaks shifting of ZnO to lower wavenumber revealed by FTIR study indicated that doping had affected the lattice structure of ZnO in the films. Thermal characterization showed the introduction of calcium dopant had increased the thermal resistance of the thick films. This led to a better junction temperature (Tj) of LED of 46.4 °C when compared with Tj of pure ZnO film at 47.3 °C.

Structure and morphology of magnetron sputter deposited ultrathin ZnO films on confined polymeric template

The structure and morphology of ultra-thin zinc oxide (ZnO) films with different film thicknesses on confined polymer template were studied through X-ray reflectivity (XRR) and grazing incidence small angle X-ray scattering (GISAXS). Using magnetron sputter deposition technique ZnO thin films with different film thicknesses (<10nm) were grown on confined polystyrene with ∼2Rg film thickness, where Rg∼20nm (Rg is the unperturbed radius of gyration of polystyrene, defined by Rg=0.272 √M0, and M0 is the molecular weight of polystyrene). The detailed internal structure, along the surface/interfaces and the growth direction of the system were explored in this study, which provides insight into the growth procedure of ZnO on confined polymer and reveals that a thin layer of ZnO, with very low surface and interface roughness, can be grown by DC magnetron sputtering technique, with approximately full coverage (with bulk like electron density) even in nm order of thickness, in 2–7nm range on confined polymer template, without disturbing the structure of the underneath template. The resulting ZnO-polystyrene hybrid systems show strong ZnO near band edge (NBE) and deep-level (DLE) emissions in their room temperature photoluminescence spectra, where the contribution of DLE gets relatively stronger with decreasing ZnO film thickness, indicating a significant enhancement of surface defects because of the greater surface to volume ratio in thinner films.

Chloride contamination of electrochemically grown zinc oxide thick films

Electrochemically grown zinc oxide thin films have applications in photovoltaics, optoelectronics, and piezoelectrics. Potentiostatic electrodeposition using zinc nitrate typically includes the use of an Ag/AgCl electrode to measure solution potential, which can leak silver chloride into the growth solution. The effects of chloride contamination in the growth solution on the properties of potentiostatically and galvanostatically grown zinc oxide films were investigated. The incorporation of the chloride was particularly notable for galvanostatically grown films deposited for longer than 2 h. The effects of the chloride on the electronic and crystallographic properties of the film were examined with scanning electron microscopy, X-ray diffraction, energy-dispersive spectroscopy, and resistance measurements. Using an Ag/AgCl electrode during the long-term growth of zinc oxide films contaminated the films with chloride, resulting in poor crystallinity, reduced chemical purity, inconsistent electrical conductivity, poor transparency, and a rough film surface.