ZnO Film Thickness Research Articles

Fe2O3 Modified ZnO Thick Film Resistors as H2S Sensor

Fe2O3 Modified ZnO Thick Film Resistors as H2S Sensor

Integrated Approach to the Optimization, Synthesis, Fabrication, and Application of ZnO-Based Sensors for Portable LPG Leakage Detection Systems

Liquefied petroleum gas (LPG) is used for cooking as well as in vehicles in the form of compressed natural gas (CNG) and in industries. As gas is volatile, there is the possibility of leakage which will be turned into take explosion or fire. It is a keen need to use the detection system for gas leakage for security purposes. ZnO thick film sensor was synthesized and fabricated by using the standard screen-printing method. The XRD pattern revealed that the ZnO thick film was polycrystalline, with an average crystallite size of around 27.1174 nm. The SEM scan revealed a ZnO particle size of around 1.88�m. Additionally, electrical and thermal properties were examined. This paper discussed the synthesized ZnO thick film LPG gas leakage detector prototype using Arduino ATMEGA8.

Preparation of ZnO Thick Films Activated with UV-LED for Efficient H2S Gas Sensing

In this work, ZnO thick films were synthesized via two simple and easy methods, mechanochemical synthesis and screen-printing deposition. The ZnO powders were obtained through milling at low temperature with milling times of 20, 40, and 60 min. The ZnO thick films were fabricated by depositing 10 cycles of ZnO inks onto glass substrates. The characterization of ZnO thick films revealed a thickness ranging from 4.9 to 5.4 µm with a surface roughness between 85 and 88 nm. The structural analysis confirmed a hexagonal wurtzite crystalline structure of ZnO, both in powders and in thick films, with a preferred orientation on the (002) and (101) planes. Nanostructures with sizes ranging from 36 to 46 nm were observed, exhibiting irregular agglomerated shapes, with an energy band found between 2.77 and 3.02 eV. A static experimental set up was fabricated for gas sensing tests with continuous UV-LED illumination. The ZnO thick films, well adhered to the glass substrate, demonstrated high sensitivity and selectivity to H2S gas under continuous UV-LED illumination at low operating temperatures ranging from 35 to 80 °C. The sensitivity was directly proportional, ranging from 3.93% to 22.40%, when detecting H2S gas concentrations from 25 to 600 ppm.

High gain NiO/ZnO heterojunction photodiodes operated in Deep-ultraviolet region

Epitaxially matched (0001) Al2O3 single substrates are utilized to design p-n heterojunctions (p-NiO/n-ZnO) as they offer low defect density for device fabrication due to small lattice mismatches. Using the radio frequency sputtering technique, the NiO/ZnO thin film-based heterojunction has been fabricated by varying the n-type film's (ZnO) thickness for ultra-violet (UV) photodiode application. It has been investigated how different ZnO film thicknesses affect junction parameters and photoresponse properties. The high photosensitivity (∼ 104), enhanced current gain (∼ 105) and fast response obtained at very low UV intensity (0.62μW/cm2) at 300 nm wavelength are attributed to the internal gain mechanism (recombination tunnelling and space-charge limited current conduction with the remarkable effect of the presence of excess free oxygen) in these devices. The prepared heterojunction photodiode with high speed and deep-UV sensitivity can be a potential solution for visible blind UV detection.

Enhancing Hydrogen Sulfide Gas Detection: Tailoring ZnO Films Through a Novel Sol–Gel Approach with Ultra-Sonication

In this study, nano-sized Zinc Oxide (ZnO) particles were synthesized using a novel sol–gel process with Zn(NO3)2 solutions, specifically tailored for the development of a highly efficient Hydrogen Sulphide (H2S) gas sensing element. The impact of ultra-sonication on the properties crucial for H2S detection was systematically investigated. The resulting ZnO materials exhibited a well-defined crystalline structure along (100), (002), (101), and (102) planes, confirming the formation of the hexagonal wurtzite phase of ZnO. Significantly, an increase in sonication treatment time led to a reduction in particle size. The gas sensing properties for H2S were meticulously analyzed in relation to the varying sizes of ZnO films. Remarkably, the ZnO film fabricated with a 30-minute ultra-sonication treatment demonstrated the highest response to H2S gas at 423 K. The ZnO-thick films exhibited notable sensitivity, coupled with rapid reactivity and recovery times upon exposure to H2S gas. Importantly, our findings establish a direct correlation between the sensitivity of the ZnO sensor and the particle size.

The influence of annealing environment of ZnO thin film on its optical, structural and photovoltaics performance

For inverted organic solar cells (IOSC), the interface contacts between the ZnO electron transport layer and the organic active layer play an important role in device performance and stability. The light absorption effect is one of the major disadvantages of IOSC when metal oxides are used as the electron transport layer (ETL). Oxide ETL primarily causes the above effect due to the energy barrier, deep level defects and excess carrier tunneling. In this work, we studied the effects of annealing ZnO films under various environmental conditions. ZnO films were synthesized by the sol-gel method, and the films were annealed at a temperature of 450 °C in air, an inert nitrogen gas (N2), oxygen (О2) and vacuum. SEM images and EDX spectra of the surface of thin ZnO films showed a change in thickness and the quantitative content of Zn/O elements. It was found that the annealing environment has a great influence on the morphology and thickness of ZnO films. Numerical calculations of the extinction, absorption, and scattering spectra of ZnO nanoparticles of different sizes are in good agreement with the results of measurements. Volt-ampere and electrical impedance measurements showed that ZnO films not only change the overall electrical resistance of devices to the contribution of the ZnO film resistance, but also change the electrical properties of the P3HT-PC61BM heterojunction.

Room temperature AC electrical, surface micro texture analysis, microwave permittivity and dielectric loss tangent in ZnO films doped by Cu, Al, and CuAl

The purpose of this work is the study of the correlation between the thickness of ZnO films doped by transition metals and their three-dimensional (3D) micromorphology. The as deposited ZnO films became more irregular surface hence the maximum value of Sq belong to as deposited ZnO films was in a bout of 0.1038 mm. The core roughness height Sk calculated as a difference between two extreme levels (maximal and minimal) of surface core, for ZnO films annealed at 500 °C have maximum value in a bout of 0.7325 mm. Since the surface kurtosis (Sku) of all sample's films were above 7, therefore there were high peaks or valleys on the films surface and for as deposited CAZO films with value of with 8.883. The height distribution histograms shown that as deposited films respect to annealed films have more uniform distributions. The AZO films annealed at 500 °C have maximum value of DC conductivity in about 104.167 S cm−1. The value of log (dielectric loss tan(δ)) in AZO films have maximum value in range 0.05–0.15. As the frequency of incident photons were increased the polarization orientation were increased. Log AC conductivity values of films were shown almost linear behavior with increasing incident photons frequency that indicates conduction hopping is followed by a small polaron mechanism. AC conductivity values of as deposited AZO films in all frequencies have maximum value.

Effects of thermal annealing on analog resistive switching behavior in bilayer HfO2/ZnO synaptic devices: the role of ZnO grain boundaries.

The effects of thermal annealing on analog resistive switching behavior in bilayer HfO2/ZnO synaptic devices were investigated. The annealed active ZnO layer between the top Pd electrode and the HfO2 layer exhibited electroforming-free resistive switching. In particular, the switching uniformity, stability, and reliability of the synaptic devices were dramatically improved via thermal annealing at 600 °C atomic force microscopy and X-ray diffraction analyses revealed that active ZnO films demonstrated increased grain size upon annealing from 400 °C to 700 °C, whereas the ZnO film thickness and the annealing of the HfO2 layer in bilayer HfO2/ZnO synaptic devices did not profoundly affect the analog switching behavior. The optimized thermal annealing at 600 °C in bilayer HfO2/ZnO synaptic devices dramatically improved the nonlinearity of long-term potentiation/depression properties, the relative coefficient of variation of the asymmetry distribution σ/μ, and the asymmetry ratio, which approached 1. The results offer valuable insights into the implementation of highly robust synaptic devices in neural networks.

Vapor-phase zeolitic imidazolate framework-8 growth on fibrous polymer substrates

The use of metal-organic frameworks (MOFs) in practical applications is often hindered by synthesis related challenges. Conventional solution-based approaches rely on hazardous solvents and often form powders that are difficult to integrate into practical devices. On the other hand, vapor-phase approaches generally result in MOF films on silicon substrates that make it difficult to characterize the MOF surface area, which is an important quality indicator. We address these challenges by introducing a solvent-free synthesis method to form MOF–fiber composites, which can be more easily integrated into devices. Additionally, these vapor-phase-formed MOF–fiber composites are compatible with Brunauer–Emmett–Teller surface area analysis to characterize MOF quality. Atomic layer deposition is used to form a ZnO film on polypropylene, polyester, and nylon fibrous substrates, which is subsequently converted to zeolitic imidazolate framework-8 (ZIF-8) using 2-methylimidazole vapor. We describe the effects of the ZnO film thickness and MOF conversion conditions on MOF crystallinity and surface area. We report a ZIF-8 surface area of ∼1300 m2/gMOF, which is comparable to reported surface areas of ∼1250–1600 m2/gMOF from conventional synthesis techniques, demonstrating good quality of the solvent-free MOF–fiber composites. We expect these results to extend vapor-phase MOF formation to new, practical substrates for advanced sensing and catalytic applications.

Effect of Plasma Treatment on the Luminescent and Scintillation Properties of Thick ZnO Films Fabricated by Sputtering of a Hot Ceramic Target

The paper presents the results of a comprehensive study of the structural-phase composition, morphology, optical, luminescent, and scintillation characteristics of thick ZnO films fabricated by magnetron sputtering. By using a hot ceramic target, extremely rapid growth (~50 µm/h) of ZnO microfilms more than 100 µm thick was performed, which is an advantage for the industrial production of scintillation detectors. The effects of post-growth treatment of the fabricated films in low-temperature plasma were studied and a significant improvement in their crystalline and optical quality was shown. As a result, the films exhibit intense near-band-edge luminescence in the near-UV region with a decay time of <1 ns. Plasma treatment also allowed to significantly weaken the visible defect luminescence excited in the near-surface regions of the films. A study of the luminescence mechanisms in the synthesized films revealed that their near-band-edge emission at room temperature is formed by phonon replicas of free exciton recombination emission. Particularly, the first phonon replica plays the main role in the case of optical excitation, while upon X-ray excitation, the second phonon replica dominates. It was also shown that the green band peaking at ~510 nm (2.43 eV) is due to surface emission centers, while longer wavelength (>550 nm) green-yellow emission originates mainly from bulk parts of the films.

Improving FTO/ZnO/In2S3/CuInS2/Mo solar cell efficiency by optimizing thickness and carrier concentrations of ZnO, In2S3 and CuInS2 thin films using Silvaco-Atlas Software

Optimization of optical and electrical properties of active semiconducting layers is required to enhance thin film solar cells' efficiency and consequently became the cornerstone for sustainable energy production. Computational studies are one of the ways forward to optimize solar cells’ characteristics. In this study, Silvaco-Atlas, a powerful software that excels in both 2D and 3D electrical simulations of semiconductors has been used for the simulation in order to investigate the solar cell properties. The architecture of the solar cell simulated was FTO/ZnO/In2S3/CuInS2/Mo. This study aims to optimize solar cell efficiency by optimizing film thicknesses and carrier concentrations via simulation. The designed solar cell was exposed to the presence of a sun spectrum of AM1.5 from a 1kW/m2 incident power density at 300K. The thickness values of the window (ZnO), absorber (CuInS2) and buffer (In2S3) layers were varied to record a solar cell's optimum thickness. The resulting FTO/ZnO/In2S3/CuInS2/Mo solar cell formed by simulation is presented. The best efficiency and fill factor of the solar cell simulated were found to be 41.67% and 89.19%, respectively. The recorded values of current density and the open circuit voltage of the cell were 40.33mA/cm2 and 1.15 V, respectively. Additionally, the maximum power of the simulated solar cell device was 41.68 mW. Optimization results revealed that the most efficient cell found was made up of a window layer with a thickness of 0.03μm, an absorber layer with a thickness of 6.0μm and a buffer layer with a thickness of 0.2μm. The optimized carrier concentration of ZnO, In2S3 and CuInS2 was respectively 1e21 cm-3, 1e20 cm-3, 3e18 cm-3 and the optimized Al-doped ZnO value was 1e25 cm-3. The Absorption spectra indicated that the solar cell's peak absorption occurs between 350 nm and 1250 nm and presented a good external quantum efficiency (EQE) of around 84.52% to 92.83% which indicates good efficiency in the visible domain. This performance is attributed to the transparency of FTO, ZnO and good absorption of In2S3 and CuInS2 thin films.

Investigation of the Effect of ZnO Film Thickness over the Gas Sensor Developed for Sensing Carbon Monoxide

Herein, a facile and inexpensive ZnO thin film‐based carbon monoxide gas sensor is fabricated using a solution‐process technique. To vary the thickness of ZnO thin films, the precursor solutions of two different molarities, 3 and 5 m, are spin coated over glass substrates. The 3 m ZnO thin‐film device demonstrates more than two times improvement in sensing response as compared to 5 m ZnO films, for 50 ppm carbon monoxide concentration. Additionally, the 3 m ZnO film is found to perform better for low carbon monoxide concentrations, whereas the 5 m ZnO film shows a linear response over a wider range of carbon monoxide concentrations. The gas sensing mechanism and the impact of film thickness on the performance of the device are thoroughly studied and discussed, which may open the doors for the design and development of facile and high‐sensitivity metal oxide‐based gas sensors.

Saturating current characteristic of 120 μm thick ZnO film and its X-ray sensing features

We report a saturating current characteristic of a 120 μm thick ZnO film and explore its X-ray sensing features. The film was deposited using a sol-gel spin coating technique. The film has a polycrystalline nature. Measurement of current-voltage (I–V) characteristic under dark condition shows two sublinear regions from 0 to 6.0 V and 6.0–8.0 V followed by a saturation region between 8.0 and 12.0 V bias voltage. The electrical resistivity in each region is found to be ∼1.0 × 1011, 1.2 × 1011 and 1.6 × 1011 Ω cm. The I–V characteristic was further recorded under X-ray irradiation. The current under the X-ray irradiation shows a linear region from 0 to 6.0 V followed by two sublinear regions from 6.0 to 8.0 V and 8.0–12.0 V with higher magnitude than the dark current. The resistivity in each region was found to decrease by ∼101 order of magnitude under X-ray. Analysis of X-ray sensing features reveals that the signal-to-noise ratio of the device is consistent between 3.0 and 12.0 V. The rise-time and fall-time are nearly 1 s. The device shows sublinear dose rate response between 0.015 and 0.293 Gy/s with a minimum sensitivity of 28.46 μC.Gy−1.cm−3 at 0.292 Gy/s. The device is also found to be visible-blind between 375 and 750 nm. The physical mechanism responsible for sublinear and saturating current characteristics have been explained based on retrapping and recombination of conduction electrons.

ОКСИДНЫЕ ПЛЕНКИ С РАЗЛИЧНЫМИ ХАРАКТЕРИСТИКАМИ ПРОПУСКАНИЯ И ПОГЛОЩЕНИЯ В УФ-ОБЛАСТИ, ПОЛУЧЕННЫЕ ЭКСТРАКЦИОННО-ПИРОЛИТИЧЕСКИМ МЕТОДОМ

UV and visible transparency of ZrO2, CuO, TiO2, Y2O3, ZnO and NiO oxide films of various thickness obtained by the extraction-pyrolytic method on fused silica supports at pyrolysis temperature 500°C and crystallization temperature 700°C. The characterization of their optical performances demonstrated a possibility for obtaining coatings providing either reduction of increase of the transmission in different UV regions.

Highly selective ppm level LPG sensors based on SnO2-ZnO nanocomposites operable at low temperature

The nanoscaled SnO2, ZnO and SnO2-ZnO nanocomposite powders were prepared by microwave aided ultrasonication technique by employing centrifuge for the collection of dried powder of the materials. The fabrication of thick films of the pure ZnO and SnO2-ZnO nanocomposite powders were made by simple screen printing technique. The crystallographic phases of the pure ZnO and SnO2 doped ZnO are hexagonal in nature. The average crystallite size of 0 (pure), 1, 3, 5, 7 and 9 wt% of SnO2 doped ZnO films was found to be 30.2, 30.3, 109.7, 37.9, 36.8 and 45.6 nm, respectively. The SEM micrographs depict the porous nature of the thick films. The EDS analysis reveals that the pure ZnO and SnO2 doped ZnO films are oxygen deficient and show a semiconducting nature. The symmetric I-V characteristics depict the ohmic and non-ohmic natures of the thick films. The electrical resistivity measurements indicate a negative temperature coefficient of resistance. The gravimetric analysis shows that the average thickness of the pure ZnO thick film is 28 µm. The LPG response versus doping concentration plot suggests that the (1 wt%) SnO2 doped ZnO thick film exhibits crucial response to 100 ppm LPG at 50 °C and 100 °C. Therefore, the SnO2 doped ZnO thick film can be applicable in the field of LPG sensing with rapid response and recovery.

Magnetron sputtering of ZnO thick film for high frequency focused ultrasonic transducer

In this study, ZnO thick films suitable for high frequency focused ultrasonic transducers with high piezoelectric properties, and low tensile stress were prepared by DC magnetron sputtering. The ZnO films were analyzed in detail by X-ray diffraction and scanning electron microscope. The sputtering growth process of ZnO films was optimized by improving the structural zone models (SZM). Based on the optimized process, a focused ultrasonic transducer, with a fused quartz acoustic lens structure, was fabricated by sputtering the ZnO thick films. The finite element method was used to complete the design, simulation, and evaluation of the transducer. Test results show that there was no crack in the piezoelectric layer of the transducer. The transducer had a center frequency of 50 MHz, with a high − 6 dB bandwidth of 119%.

Screen printed ZnO thick films for NH3 gas sensing

The paper reports the synthesis of ZnO powder by self-propagation solution combustion method and the development of screen-printed ZnO thick films for sensing ammonia gas. The surface and structural examination of the thick film was studied by using SEM and XRD techniques. The particle and grain size of the thick film were determined using SEM and XRD respectively. The temperature coefficient of resistance (TCR), electrical, and NH3 gas sensing characteristics of ZnO thick film were observed with varying temperatures. Thick films show the inverse relations of resistance with respective temperatures. The sensitivity, response, and recovery time toward NH3 gas sensing were discussed.

Photoresponse improvement of a MAPbI3 p-i-n heterojunction photodetector by modifying with a PCBM layer and optimizing ZnO layer thickness

In this manuscript, a series of Spiro-OMeTAD/CH3NH3(MA)PbI3/ZnO p-i-n heterojunction PDs are prepared and the photoresponses are well studied by modifying the MAPbI3/ZnO interface with a PCBM layer and modulating the ZnO film thickness ranging from 20 to 95 nm. The PD shows an excellent self-powered capability due to the suitable band alignment. After introducing the PCBM layer, both the photoresponse and stability are greatly improved, which can be attributed to its suitable band level and outstanding properties of contact passivation and interfacial modification. Besides, it is indicated that the photoresponse is strongly dependent on the thickness of the ZnO layer. The PD with a 65 nm-thick ZnO layer achieves the best performances in a broadband spectral range of ∼350 to ∼800 nm with the maximum responsivity (R) of 0.443 A/W and response times of 0.25/0.14 s. This work provides an essential insight for designing high-performance ZnO electron-transport layer-based perovskite heterojunction PDs.

A Sagnac Interferometer Ultraviolet Sensor Based on ZnO-Coated No-Core Fiber

A Sagnac interferometer based optical fiber ultraviolet (UV) sensor is theoretically proposed and experimentally demonstrated in this work. A layer of ZnO film was deposited upon the surface of a silica no core fiber (NCF) using the magnetron sputtering method. Since the ZnO film was sensitive to UV, the ZnO-coated NCF was introduced into the Sagnac interferometer to help convert changes of the UV irradiance to the wavelength shifts of the interference spectrum. In comparison with the preparation of ZnO nanostructures, the ZnO film had the advantage of simple operation, high deposition rate, good adhesion and stable structure. The influence of the ZnO film thickness on the UV response was investigated, which proved that with the increase of the film thickness, the UV sensitivity decreased gradually. When the ZnO film thickness was 30 nm and the UV irradiance varied from 0 mW/cm² to 19.95 mW/cm², the designed sensor had the highest sensitivity of −124.9 pm/(mW/cm²) (R² = 0.9854) and a detection accuracy of 0.4 mW/cm². The proposed sensor has competitive sensitivity, high linearity, satisfactory repeatability and stability, which can be expected to conduct high-precision UV sensing in industrial, biomedical and military regions.

An ultraviolet sensor based on surface plasmon resonance in no-core optical fiber deposited by Ag and ZnO film

A new ultraviolet (UV) optical fiber sensor based on surface plasmon resonance (SPR) is suggested in this research, which is fabricated by splicing a segment of no-core optical fiber (NCF) between two multimode optical fibers (MMFs). An Ag film and a ZnO film are successively deposited upon the surface of the NCF by magnetron sputtering, and the UV detection function is accomplished by utilizing SPR's sensitivity to ambient refractive index (RI) and ZnO RI's sensitivity to the UV irradiance. Due to the hydrophilic properties of ZnO, the sensor is encapsulated in absolute ethanol to produce stable SPR and isolate water molecules. The effects of film thickness (Ag and ZnO) and UV irradiance on sensor performance are discussed in detail. It is discovered that the UV sensitivity of the sensor increased with the ZnO thickness. At the deposition of a 10 nm thick ZnO film, the sensitivity can reach -1.462 nm / (mW/cm2), which is 6 times that of 2 nm thick film. The exploratory combination of SPR and UV sensitive materials tremendously simplifies UV detection technology, making the sensor highly reproducible and UV detection more efficient in the fields of environmental monitoring, food hygiene, and medical health.