Effect of substrate curvature on thickness distribution of polydimethylsiloxane thin film in spin coating process

The polymer spin coating is critical in flexible electronic manufaction and micro-electro-mechanical system（MEMS）devices due to its simple operation, and uniformly coated layers. Some researchers focus on the effects of spin coating parameters such as wafer rotating speed, the viscosity of the coating liquid and solvent evaporation on final film thickness.In this work, the influence of substrate curvature on film thickness distribution is considered. A new parameter which represents the edge bead effect ratio（re） is proposed to investigate the influence factor of edge bead effect. Several operation parameters including the curvature of the substrate and the wafer-spin speed are taken into account to study the effects on the film thickness uniformity and edge-bead ratio. The morphologies and film thickness values of the spin-coated PDMS films under various substrate curvatures and coating speeds are measured with laser confocal microscopy. According to the results, both the convex and concave substrate will help to reduce the edge-bead effect significantly and thin film with better surface morphology can be obtained at high spin speed. Additionally, the relationship between the edge-bead ratio and the thin film thickness is like parabolic curve instead of linear dependence. This work may contribute to the mass production of flexible electronic devices.

Effect of Spin Coating Speed on Some Optical Properties of ZnO Thin Films

This paper reports the synthesis and characterization of ZnO thin films prepared by sol-gel spin coating technique. The sol-gel was prepared from zinc acetate dehydrate as a precursor, 2-me- thoxyethanol as a solvent and di-ethanolamine as a stabilizer, and then deposited on glass substrate using spin coater at the coating speed of 1000 rpm, 2000 rpm, 3000 rpm, 4000 rpm, 5000 rpm and 6000 rpm. After pre-heated at 150℃, the samples were post-heated at 250oC and also annealed at 400℃. X-ray diffraction (XRD) of the films showed polycrystalline hexagonal structure, with (002) orientation as most intense peak having a grain size of 28.1 nm. The absorbance of the film decreases with increasing wavelength and the transmittance was generally high between visible regions from 280 nm - 1200 nm. The ZnO films deposited at a spinning speed of 2000 rpm had highest transmittance of 88% in the visible region from 280 nm - 1200 nm. The energy band gap was found to be in the range of 3.23 - 3.40 eV. The thicknesses of the films decreased with increase in coating speed. Based on these results, ZnO thin films obtained could have useful application in transparent conducting oxide electrode in solar cells.

MgO and ZnO Composite Thin Films Using the Spin Coating Method on Microscope Glasses

In this study, a new route to produce pure and composite ZnO-MgO thin films has been presented. In the process the pure ZnO thin films were the starting point, ending up with MgO by doping various percentages (from 0% to 100%) of Mg with the help of sol-gel spin coating technique. The crystal phases in all doping levels have been obtained when the samples annealed at 600℃ for a duration of 6 hours. The X-ray diffraction (XRD) spectra, the scanning electron microscopy (SEM) micrographs and UV-Vis absorption spectra have been performed to elucidate the composed film structures.

Fabrication of LSGM thin films on porous anode supports by slurry spin coating for IT-SOFC

La0.9Sr0.1Ga0.8Mg0.2O3-δ（LSGM） and La0.7Sr0.3Cr0.5Mn0.5O3-δ（LSCM） powders were synthesized by glycine-nitrate process, and LSGM electrolyte thin film was successfully fabricated on porous anode substrate of LSCM by slurry spin coating technology. Some technical parameters for the preparation of LSGM thin films were systematically investigated, including ink composition,sintering temperature, and spin coating times. The electrolyte films with the best compactness and somewhat rough are obtained when the operating parameters are fixed as follows: the content of ethyl cellulose as binder is 5 wt%, the content of terpineol as modifier is 5 wt%, the optimum coating cycle number is 9 times, and the best post-deposition sintering temperature is 1,400 °C for 4 h.

Rapid nanopatterning technique based on monolayer silica nanosphere close-packing by spin coating

Nanoparticles monolayer formation by spin coating is considered to be a simple, fast and inexpensive nanopatteming technique However, the parameters that govern the overall growth process in this technique are not completely quantified and techniques for the controlled and continuous growth of close packed monolayer particle arrays without defects need to be developed. In this paper, an ordered particle array formation process is analyzed theoretically, employing material flux balance and parti- cle-subjected forces balance, based on the film thickness model of spin coating and evaporation rate law. A series of experi- ments were conducted using silica particle suspensions with various particle volume fractions and different spin speeds. The results show that the spin speed should match the particle volume fraction to meet the requirements of material flux and particles movement in order to obtain a close packed monolayer film. The formation mechanism of fabrication defects involving particle agglomeration and uncontrollable voids were analyzed qualitatively based on crystal growth theory, and validation experiments were performed. The formation of highly uniform close-packed monolayer films was demonstrated and the condi- tion requirements for achieving monolayer nanoparticles array with good quality presented.

Low capacitance and highly reliable blind through-silicon-vias(TSVs) with vacuum-assisted spin coating of polyimide dielectric liners

Low-k and high aspect ratio blind through-silicon-vias （TSVs） to be applied in ＂via-last/backside via＂ 3-D integration paradigm were fabricated with polyimide dielectric liners formed by vacuum-assisted spin coating technique. MIS trench capacitors with diameter of-6 μm and depth of-54 μm were successfully fabricated with polyimide insulator step coverage better than 30%. C-V characteristics and leakage current properties of the MIS trench capacitor were evaluated under thermal treat- ment. Experimental results show that, the minimum capacitance density is around 4.82 nF/cm2, and the leakage current density after 30 cycles of thermal chock tests becomes stable and it is around 30 nA/cm2 under bias voltage of 20 V. It also shows that, the polyimide dielectric liner is with an excellent capability in constraining copper ion diffusion and mobile charges even un- der test temperature as high as 125℃. Finite element analysis results show that TSVs with polyimide dielectric liner are with lower risks in SiO2 interlayer dielectric （ILD） fracture and interfacial delamination along dielectric-silicon interface, thus, higher thermo-mechanical reliability can be expected.

Synthesis and Characterization of Indium Niobium Oxide Thin Films via Sol—Gel Spin Coating Method

In the present study, niobium-doped indium oxide thin films were prepared by sol-gel spin coating technique. The effects of different Nb-doping contents on structural, morphological, optical, and electrical properties of the films were characterized by means of X-ray diffraction （XRD）, field emission scanning electron microscopy （FESEM）, atomic force microscopy （AFM）, UV-Vis spectroscopy, and four point probe methods. XRD analysis confirmed the formation of cubic bixbyite structure of In203 with a small shift in major peak position toward lower angles with addition of Nb. FESEM micrographs show that grain size decreased with increasing the Nb-doping content. Optical and electrical studies revealed that optimum opto-electronic properties, including minimum electrical resistivity of 119.4 × 10^-3 Ω cm and an average optical transmittance of 85% in the visible region with a band gap of 3.37 eV were achieved for the films doped with Nb-doping content of 3 at.%. AFM studies show that addition of Nb at optimum content leads to the formation of compact films with smooth surface and less average roughness compared with the prepared ln2O3 films.

Effect of Catch Cup Geometry on 3D Boundary Layer Flow over the Wafer Surface in a Spin Coating

Recently, development of high technology has been required for the formation of thin uniform film in manufacturing processes of semiconductor as the semiconductor instruments become more sophisticated. Spin coating is usually used for spreading photoresist on a wafer surface. However, since rotating speed of the disk is very high in spin coating, the dropped photoresist scarers outward and reattaches on the film surface. A catch cup is set up outside the wafer in spin coating, and scattered photoresist mist is removed from the wafer edge by the exhaust flow generated at the gap between the wafer edge and the catch cup. In the dry process of a spin coating, it is a serious concern that the film thickness increases near the wafer edge in the case of low rotating speed. The purpose of this study is to make clear the effect of the catch cup geometry on the 3D boundary layer flow over the wafer surface and the drying rate of liquid film.

Influences of the Exhaust Flow on the Boundary Layer Flow on the Wafer Surface in Spin Coating System

Recently, development of high technology has been required for the formation of thin uniform film in manufacturing processes of semiconductor as the semiconductor become more sophisticated. Spin coating is usually used for spreading photoresist on a wafer surface. However, since rotating speed of the disk is very high in spin coating, the dropped resist scatters outward and reattaches to the film surface. So, the scattered resist is removed by the exhaust flow generated at the gap between the wafer edge and the catch cup. It is seriously concerned that the stripes called Ekman spiral vortices appears on the disk in the case of high rotating speed and the film thickness increases near the wafer edge in the case of low rotating speed, because it prevent the formation of uniform film. The purpose of this study is to make clear the generation mechanism of Ekman spiral vortices and the influence of exhaust flow on it Moreover the influence of the catch cup geometry on the wafer surface boundary layer flow is investigated.

Effect of iron doping on structural and optical properties of TiO_(2) thin film by sol-gel routed spin coating technique

Thin films of iron(Fe)-doped titanium dioxide(Fe:TiO_(2))T were prepared by sol–gel spin coating technique and further calcined at 450℃.The structural and optical properties of Fe-doped TiO_(2) thin films were investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),ultraviolet–visible spectroscopy(UV–vis)and atomic force microscopic(AFM)techniques.The XRD results confirm the nanostructured TiO_(2) thin films having crystalline nature with anatase phase.The characterization results show that the calcined thin films having high crystallinity and the effect of iron substitution lead to decreased crystallinity.The SEM investigations of Fe-doped TiO_(2) films also gave evidence that the films were continuous spherical shaped particles with a nanometric range of grain size and film was porous in nature.AFM analysis establishes that the uniformity of the TiO_(2) thin film with average roughness values.The optical measurements show that the films having high transparency in the visible region and the optical band gap energy of Fe-doped TiO_(2) film with iron(Fe)decrease with increase in iron content.These important requirements for the Fe:TiO_(2) films are to be used as window layers in solar cells.

Structural and optical properties of nano-spin coated sol-gel porous TiO_2 films

Three thicknesses of TiO2 films, 174, 195, and 229 nm, were deposited onto quartz substrates by sol–gel spin coating method. The as-deposited thin films were characterized by nano-crystallite with different sizes (19–46 nm) and relatively high porous structure. Optical constants were determined and showed the lowest refractive index of 1.66 for the as-prepared films that ever reported till now. Obtained results were discussed through current theoretical ideas.

Preparation of CulnS2 Thin Film Using Sulfides Nanoparticle Precursor Ink

A low cost spin coating route of fabricating CuInS2 polycrystalline thin films by reactive sintering method was put forward. The ink for spin coating was optimized by pre-reducing the precursor powders in hydrogen, which turned the nanoparticle precursor powders from mixed sulfides into a mixture of CuInS2 and Cu-In metal alloys. The results of scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and Raman spectra showed that this optimization could highly improve the performance of CuInS2 polycrystalline thin films, including higher packing density, less impurity phases, and better quality. The energy gap of optimized CuInS2 thin film was determined to be about 1.45 eV by absorption spectroscopy measurement.

Influence of Poly（methyl metacrylate） Addition on Resistive Switching Performance of P3HT/P（VDF-TrFE） Blend Films

Organic semiconducting/ferroelectric blend films attracted much attention due to their electrical bistability and rectification properties and thereof the potential in resistive memory devices. Blend films were usually deposited from solution, during which phase separation oc- curred, resulting in discrete semiconducting phase whose electrical property was modulated by surrounding ferroelectric phase. However, phase separation resulted in rough surface and thus large leakage current. To further improve electrical properties of such blend films, poly（methyl metacrylate） （PMMA） was introduced as additive into P3HT/P（VDF-TrFE） semiconducting/ferroelectric blend films in this work. It indicated that small amount of PMMA addition could effectively enhance the electrical stability to both large electrical stress and electrical fatigue and further improve retention performance. Overmuch PMMA addition tended to result in the loss of resistive switching property. A model on the configuration of three components was also put forward to well understand our experimental observations.

Model eyes with curved multilayer structure for the axial resolution evaluation of an ophthalmic optical coherence tomography device

Optical coherence tomography(OCT)has been widely applied to the diagnosis of eye diseasesduring the past two decades.However,valid evaluation methods are stil not available for theclinical OCT devices.In order to assess the axial resolution of the OCT system,standard modeleyes with micro-scale multilayer structure have been designed and manufactured in this study.Mimicking a natural human eye,proper Titanium dioxide(TiO_(2))materials of particles withdifferent concentrations were selected by testing the scattering coefficient of PDMS phantoms.The artificial retinas with multilayer films were fabricated with the thicknesses from 9.5 to 30 micrometers using spin coating technology,Subsequently,standard OCT model eyes were ac-complished by embedding the retina phantoms into the artificial frames of eyes.For ease ofmeasurement processing,a series of model eyes were prepared,and each contained flms withthree kinds of thicknesses.Considering the traceability and accuracy of the key parameters of the standard model eyes,the thicknesses of multilayer structures were verfed using ThicknessMonitoring System.Through the experiment with three different OCT devices,it demonstratedthe model eyes fabricated in this study can provide an effective evaluation method for the axialresolution of an ophthalmic OCT device.

The Effect of Fabrication Conditions for GDC Buffer Layer on Electrochemical Performance of Solid Oxide Fuel Cells

A Gd-doped ceria（GDC） buffer layer is required between a conventional yttria-stabilized zirconia（YSZ） electrolyte and a La-Sr-Co-Fe-O3（LSCF） cathode to prevent their chemical reaction. In this study,the effect of varying the conditions for fabricating the GDC buffer layer, such as sintering temperature and amount of sintering aid, on the solid oxide fuel cell（SOFC） performance was investigated. A finer GDC powder（i.e., ultra-high surface area）, a higher sintering temperature（1290℃）, and a larger amount of sintering aid（12%） resulted in improved densification of the buffer layer; however, the electrochemical performance of an anode-supported cell containing this GDC buffer layer was poor. These conflicting results are attributed to the formation of（Zr, Ce）O2 and/or excess cobalt grain boundaries（GBs） at higher sintering temperatures with a large amount of sintering aid（i.e., cobalt oxide）. A cell comprising of a cobalt-free GDC buffer layer, which was fabricated using a low-temperature process, had lower cell resistance and higher stability. The results indicate that electrochemical performance and stability of SOFCs strongly depend on fabrication conditions for the GDC buffer layer.

Tetranuclear yttrium and gadolinium 2-acetylcyclopentanoate clusters：Synthesis and their use as spin-coating precursors for metal oxide film formation for field-effect transistor fabrication

Lanthanide clusters [Ln4（μ3-OH）2（η2-accp）4（（μ-O）-η2-accp）6]（Ln = Y（4）,Gd（5）; accp = 2-acetylcyclopentanoate） are accessible by treatment of [M（NO33·6 H2 O]（M = Y（1）,Gd（2）） with 3 equiv. of Haccp（3） in presence of NaOH. The molecular structures of 4 and 5） in the solid-state are discussed. The thermal behavior of 4 and 5 was studied by TG under Ar and O2, showing multistep decomposition processes. Additionally, DSC studies were carried out under an atmosphere of O2. PXRD measurements of the TG residues confirm the formation of Ln2 O3.Spin-coating experiments were carried out with 4 and 5 for Ln2 O3 film deposition on silicon substrates. The layers are smooth, close and are of thicknesses of 18.87±1.13 nm and 25.59 ± 4.55 nm for Ln = Y and Gd, which was evidenced by SEM and EDX studies. Field-effect transistors were successfully fabricated by deposition of carbon nanotubes on top of the Y2 O3 films and formation of palladium contacts by a lift-off procedure. An on/off ratio of more than 4 orders of magnitude is achieved without considerable leakage currents. These results demonstrate the potential use of spin-coated Y2 O3 as a gate dielectric in electronic devices.

Charge transport in monolayer poly(3-hexylthiophene) thin-film transistors

It is found that ultrathin poly（3-hexylthiophene） （P3HT） film with a 2.5 nm-thick layer exhibits a higher mobility of 5.0× 10-2 cm2/V-s than its bulk counterpart. The crystalline structure of the as-fabricated ultrathin P3HT layer is verified by atomic force microscopy as well as grazing incidence X-ray diffraction. Transient measurements of the as-fabricated transistors reveal the influence of the interface traps on charge transport. These results are explained by the trap energy level distribution at the interface manipulated by layers of polymer film.

Modelling of Photovoltaic Modules Optical Losses Due to Saharan Dust Deposition in Dakar, Senegal, West Africa

This study aims to evaluate the optical losses of photovoltaic modules due to Saharan dust deposition in Dakar, Senegal, West Africa. For this purpose, an air-dust-glass system is modeled to simulate optical losses in transmittance and reflectance. To do this, we have collected dust samples from Photo-Voltaic (PV) surface in Dakar area (14°42'N latitude, 17°28'W longitude), Senegal. X-ray fluorescence reveals that silicon (Si), iron (Fe), calcium (Ca) and potassium (K) mainly composed these dust samples. Then, dust refractive indices obtained from an ellipsometer were used as an input to be used in the model. Simulations show that for radiation (at normal incidence) arriving on a dust layer of 30 μm-thick (corresponding to a dust deposit of 1.63 g/m2), 79% of the visible spectrum is transmitted; 19% is reflected and 2% is absorbed. Overall, the transmittance decreases by more than 50% as of dust layer of 70 μm-thick corresponding to a dust deposit of 3.3 g/m2.

Kinetics of Photocatalytic Degradation of Formic Acid over Silica Composite Films Based on Polyoxometalates

The composite films, XW11O39n-/SiO2, (X refers to Si, Ge or P, respectively) were prepared by tetraethoxysilane (TEOS) hydrolysis sol-gel method via spin-coating technique. Formation of the composite films is due to strong chemical reaction of organic silanol group with the surface oxygen atoms of XW11O39n-, resulted in the saturation of the surface of the lacunary polyoxometalates (POMs). Therefore, the coordination structural model of the films was proposed. As for the films, retention of the primary Keggin structure was confirmed by UV-vis, FT-IR spectra and MAS NMR. The surface morphology of the films was characterized by SEM, indicating that the film surface is relatively uniform, and the layer thickness is in the range of 250~350 nm. Aqueous formic acid (FA) (0-20 mmol/L) was degraded into CO2 and H2O by irradiating the films in the near-UV area. The results show that all the films have photocatalytic activities and the degradation reaction follows Langmuir-Hinshelwood first order kinetics.

Fluorine,chlorine,and gallium co-doped zinc oxide transparent conductive films fabricated using the sol-gel spin method

Transparent conductive films(TCFs)are crucial components of solar cells.In this study,F,Cl,and Ga codoped ZnO(FCGZO)TCFs were deposited onto a glass substrate using the sol-gel spin-coating method and rapid thermal annealing.The effects of F-doping content on the structural,morphological,electrical,and optical properties of FCGZO films were examined by XRD,TEM,FE-SEM,PL spectroscopy,XPS,Hall effects testing,and UVeviseNIR spectroscopy.All prepared ZnO films exhibited a hexagonal wurtzite structure and preferentially grew along the c axis perpendicular to the substrate.Changes in the doping concentration of F changed the interplanar crystal spacing and O vacancies in the film.At a doping ratio of 2%(in mole),the F,Cl,and Ga co-doped ZnO film exhibited the best photoelectric performance,with a carrier concentration of 2.62×10^(20)cm^(-3),mobility of 14.56 cm^(2)/(V·s),and resistivity of 1.64×10^(-3)Ucm.The average transmittance(AT)in the 380-1600 nm region nearly 90%with air as the reference,and the optical band gap was 3.52 eV.