SiO2 Buffer Research Articles

Transparent conductive ITO/Cu/ITO films prepared on flexible substrates at room temperature

Transparent conductive ITO/Cu/ITO films were deposited on PET substrates by magnetron sputtering using three cathodes at room temperature. Effects of the SiO2 buffer layer and thickness of Cu interlayer on the structural, electrical and optical properties of ITO/Cu/ITO films were investigated. The optical transmittance was affected slightly by SiO2 buffer layer, but the electrical properties of ITO/Cu/ITO films were improved. The transmittance and resistivity of the SiO2/ITO/Cu/ITO films decrease as the Cu layer thickness increases. The ITO/Cu/ITO film with 5nm Cu interlayer deposited on the 40nm thick SiO2 buffer layer exhibits the sheet resistance of 143Ω/sq and transmittance of 65% at 550nm wavelength. The optical and electrical properties of the ITO/Cu/ITO films were mainly dependent on the Cu layer.

Low-Voltage Electric-Double-Layer TFTs on $ \hbox{SiO}_{2}$-Covered Paper Substrates

Low-voltage electric-double-layer (EDL) thin-fllm transistors (TFTs) have been fabricated on paper substrates at room temperature. The devices operated in depletion mode, and the resistivity of the Indium-Tin-Oxide (ITO) channel layer is measured to be 24 Ω · cm. An SiO2 film deposited by plasma enhanced chemical-vapor deposition method is used as the buffer layer to improve the smoothness of the paper substrate. TFTs on the SiO2-covered paper substrates show a saturation filed-effect mobility of 14.6 cm2V-1s-1, a subthreshold swing of 100 mV/dec, and a drain-current on/off ratio of 1.5 × 106, which are much better than that of the devices on bare paper substrates. Such EDL TFTs on paper substrates with an SiO2 buffer layer have potential application in portable sensors.

Diffractive gratings for crystalline silicon solar cells—optimum parameters and loss mechanisms

ABSTRACTIn this paper, we present guidelines for the design of backside gratings for crystalline silicon solar cells. We use a specially developed method based on a combination of rigorous 3D wave optical simulations and detailed semiconductor device modeling. We also present experimental results of fabricated structures. Simulation‐based optimizations of grating period Λ and depth d of a binary grating and calculations of the optical and electrical characteristics of solar cells with optimized gratings are shown. The investigated solar cell setup features a thickness of dbulk = 40 µm and a flat front surface. For this setup, we show a maximum increase in short‐circuit current density of ΔjSC = 1.8 mA/cm² corresponding to an efficiency enhancement of 1% absolute. Furthermore, we investigate different loss mechanisms: (i) an increased rear surface recombination velocity S0,b because of an altered surface caused by the introduction of the grating and (ii) absorption in the aluminum backside reflector. We analyze the trade‐off point between gain due to improved optical properties and loss due to corrupted electrical properties. We find that, increasing the efficiency by 1% absolute due to improved light trapping, the maximum tolerable recombination velocity is S0,b(max) = 5.2 × 103 cm/s. From simulations and measurements, we conclude that structuring of the aluminum backside reflector should be avoided because of parasitic absorption. Adding a dielectric buffer layer between silicon and the structured aluminum, absorption losses can be tuned. We find that for a planar reflector, the thickness of a SiO2 buffer layer should exceed = 120 nm. Copyright © 2011 John Wiley & Sons, Ltd.

Effect of Oxide Buffer Layers on the Optical and Electrical Properties of Ga-Doped Zinc Oxide Thin Film

The effects of oxide buffer layers on the optical and electrical properties of sputtered Gallium-doped zinc oxide (GZO) films were intensively investigated for developing the electrodes of photonic devices, which demand high optical transmittance and low resistivity. The use of Al2O3 and SiO2 buffer layers could increase transmittance of GZO films to 90.69% around the wavelength of 550 nm by controlling the optical spectrum. The resistivity of the deposited GZO films was much dependent on the deposition condition of O2 ratio during buffer layer deposition. It is considered that the carrier mobility of GZO films on SiO2 buffer is highly related to the lattice crystallinity of SiO2 and GZO films. In contrast, on the Al2O3 buffer layer, rough surface morphology could increase the resistivity of GZO films due to the doping effect of diffused Al atoms.

Bright flexible organic light-emitting devices on copy paper substrates

We have developed flexible top emission organic light-emitting devices (OLEDs) using copy paper substrates. Poly-2-chloro-p-xylylene and SiO2 buffer layers were coated on the copy paper for protecting the water absorption and improving the barrier and morphological characteristics. Sputtered Ni and thermally evaporated Ca/Ag films were used as anode and semitransparent cathode, respectively. The electrical conduction, luminance, and efficiency characteristics of the copy paper-based flexible OLEDs were investigated. The SiO2 buffer layer was critically important in obtaining the high performance devices. The device exhibited a high luminance of 2200 cd/m2 at a driving voltage of 13 V.

Influence of SiO2 buffer layer on the crystalline quality and photoluminescence of ZnO thin films

In this work, a SiO2 buffer layer was first grown on Si substrate by thermal oxidation, and then ZnO thin films were deposited on SiO2 buffer layer and Si substrate by electron beam evaporation and sol-gel method. The influence of SiO2 buffer layer on the crystalline quality and photoluminescence of the films was investigated. The analyses of X-ray diffraction (XRD) showed that all the ZnO thin films had a hexagonal wurtzite structure and were preferentially oriented along the c-axis perpendicular to the substrate surface. The SiO2 buffer layer improved the crystalline quality and decreased the stress in ZnO thin films. The surface morphology analyses of the samples indicated that ZnO thin films deposited on SiO2 buffer layers had densely packed grains which obviously increased compared with those grown on bare Si substrate. The photoluminescence spectra of the samples showed that the ZnO thin films deposited on SiO2 buffer layers had stronger ultraviolet emission performance. The results suggest that SiO2 buffer layer can improve the crystalline quality and ultraviolet emission of ZnO thin films.

Microwave/Millimeter-Wave Garnet Films

A buffer liquid phase epitaxy method for lead free flux technology has been used to grow large size garnet single-crystal films. Lu2.1Bi0.9Fe5O12 (Bi:LuIG) films with excellent lattice match with the Gd3Ga5O15 (GGG) substrate and superior magnetic and magnetic-optical properties have been obtained by optimizing liquid phase epitaxy (LPE) technology. The saturation magnetization of the film is about 1562 Gs, the Faraday rotation is 1.6 ~ 2.0 deg/μm and the minimum ferromagnetic resonance (FMR) linewidth is 2ΔH = 5.1 Oe. Secondly, the growth of polycrystalline garnet films by radio-frequency (RF) magnetron sputtering has be introduced, and the effects of buffer layer, sputtering parameters and post annealing on the performance of Y3Fe5O12 (YIG) films have been investigated in details. It will be shown that garnet films with smooth surface and adjustable saturation magnetization can be obtained by using a SiO2 buffer layer.

The influence of using different substrates on the structural and optical characteristics of Bi2VO5.5 thin films

The BVO thin films have been successfully grown on Si (100) and SiO2/Si (100) substrates via sol-gel technique followed by rapid thermal annealing at 650°C. The crystalline nature of the films has been studied by X-ray diffraction and indicates all the films are well-crystallized. Atomic force microscopy was used to study the surface morphology of the BVO thin films which shows the films are compact and homogeneous. The BVO film with SiO2 buffer layer has a larger grain size and lower root mean square roughness than that directly grown on Si. The Raman spectra measurement in the range of 300–1500 cm−1 reveals that the buffer SiO2 layer definitely influences the structure of BVO thin films. The optical properties of the BVO thin films are investigated using spectroscopic ellipsometric in the wavelength range of 400–900 nm. In the visible range, the refractive index of the film is about 2.42 and the extinction coefficient is 0.036.

The effect of SiO2 buffer layer on the electrical and structural properties of Al-doped ZnO films deposited on soda lime glasses

In this paper, the influence of SiO2 buffer layer on electrical and structural properties of AZO films on soda lime glasses has been investigated. The results showed that the Hall mobility and carrier concentration of AZO films deposited on soda lime glasses at high temperature could be enhanced by introducing SiO2 layers. The optical absorption edges of AZO films with SiO2 buffer layer are blue shifted compared with that of buffer layer free due to the increase of carrier concentration. SiO2 layers prepared at 400°C more effectively suppress the diffusion of Na atoms into AZO films compared with that prepared at room temperature. On the other hand, the in-plane stress dependence of optical band gap is linear for AZO films deposited on quartz glass substrates, but is deviated from linearity in the case of soda lime glass substrates.

Buffer layer investigations on MFIS capacitors consisting of ferroelectric poly[vinylidene fluoride trifluoroethylene

In this paper we present capacitance-voltage (CV) measurements on metal-ferroelectric-insulator-semiconductor (MFIS) capacitors with poly[vinylidene fluoride trifluoroethylene] (P[VDF/TrFE] as ferroelectric layer and SiO2, Al2O3 and HfO2 as buffering insulator layer. In order to discuss our data in a quantitative manner we perform fits to the data based on a model proposed by Miller and McWorther. The improvement of the polarization values and subsequently its effect on the hysteresis of the CV curve by the successive shrinking of the buffer layer thickness and the following choice of a high-k buffer material is demonstrated. Our data underline that a saturated polarization of P[VDF/TrFE] cannot be controlled with a SiO2 buffer layer and the insertion of a high-k buffer layer is essential for further improvements of the characteristics of MFIS stacks.

Effects of SiO2 and TiO2 on resistance stabilities of flexible indium-tin-oxide films prepared by ion assisted deposition

Inorganic buffer layers such as SiO2 or TiO2 and transparent conductive indium-tin-oxide (ITO) films were prepared on polyethylene terephthalate (PET) substrates by ion assisted deposition (IAD) at room temperature, and the effects of SiO2 and TiO2 on the bending resistance performance of flexible ITO films were investigated. The results show that ITO films with SiO2 or TiO2 buffer layer have better resistance stabilities compared to ones without the buffer layer when the ITO films are inwards bent at a bending radius more than 1.2 cm and when the ITO films are outwards bent at a bending radius from 0.8 cm to 1.2 cm. ITO films with SiO2 buffer layer have better resistance stabilities compared to ones with TiO2 buffer layer after the ITO films are bent several hundreds of cycles at the same bending radius, for the adhesion of SiO2 is stronger than that of TiO2. The compressive stress resulted from inward bending leads to the formation of more defects in the ITO films compared with the tensile stress arising from outward bending. SiO2 and TiO2 buffer layers can effectively improve the crystallinity of ITO films in (400), (440) directions.

Employing SiO2 buffer layer to improve adhesion of the frequency-doubled antireflection coating on LBO

Frequency-doubled antireflection coatings simultaneously effective at 1064 nm and 532 nm were deposited on the lithium triborate (LiB3O5 or LBO) crystals using the electron beam evaporation method. Comparing with the sample without buffer layer, it is found that the adhesion of the sample with buffer layer of SiO2 between coating and LBO substrate is improved significantly from 137.4 mN to greater than 200 mN. And the laser-induced damage threshold is increased by 20% from 15.1 J/cm2 to 18.6 J/cm2. The strengthening mechanism of adhesion of the buffer layer of SiO2 is discussed by considering full plastic indentation and shear theory.

Compact Microring Resonator With 2$\,\times\,$2 Tapered Multimode Interference Couplers

Compact microring resonator devices are realized by using a small SU-8 polymer strip waveguide that has an SU-8 polymer core (n ~ 1.573), an SiO2 buffer (n ~ 1.445), and an air cladding. Due to the high index contrast of the optical waveguide, a small bending radius ( ~ 150 mum) is used for the MRR. To enhance the coupling between the access optical waveguides and the microring, 2 times 2 multimode interference couplers are used. The measured spectral response of the through port shows a high extinction ratio of over 15 dB and a 3-dB bandwidth of about 0.38 nm (corresponding to a moderate Q-value of ~ 4500).

Fabrication and Characterization of Small Optical Ridge Waveguides Based on SU-8 Polymer

Small SU-8 ridge optical waveguides with an air cladding and a SiO2 buffer on Si substrate have been realized by using a direct ultraviolet (UV) photolithography technology. The propagation loss measured by the cut-back method is about 0.1 dB/mm (@1550 nm) when the core width is 2.8 ?m. The bending losses of the present SU-8 optical ridge waveguides are also characterized. The measured results show that the bending loss decreases exponentially as the bending radius increases and the total loss can be reduced effectively by introducing an appropriate offset between two connected sections with different curvatures. A small bending radius (as small as 75 ?m) is still allowed for the requirement of a small bending loss (< 0.1 dB) when an offset of 0.1 ?m is introduced. Finally, by using this kind of waveguide, a small 1 × 2 Y-branch power splitter is fabricated and characterized.

Comparative Study on Metal–Ferroelectric–Insulator–Semiconductor Diodes Composed of Poly(vinyliden fluoride-trifluoroethylene) and Poly(methyl metacrylate)-Blended Poly(vinyliden fluoride-trifluoroethylene)

Ferroelectric poly(vinyliden fluoride-trifluoroethylene) [P(VDF-TrFE)] and poly(methyl metacrylate) (PMMA)-blended P(VDF-TrFE) thin films were deposited by spin coating on Pt/TiO2/SiO2/Si and SiO2/Si structures, and their characteristics were investigated by forming metal–ferroelectric–metal (MFM) capacitors and metal–ferroelectric–insulator–semiconductor (MFIS) diodes. It was found that the data retention characteristics of MFIS diodes were significantly improved by blending PMMA and P(VDF-TrFE) and by optimizing the insulating buffer layer thickness. Under the present conditions, the longest data retention time of 6 h was obtained using a 1.5-nm-thick SiO2 buffer layer on Si.

CE immunoassay with enhanced chemiluminescence detection of erythropoietin using silica dioxide nanoparticles as pseudostationary phase

The measurement of serum erythropoietin (EPO) is important for the detection of recombinant human EPO misuse in sports. In this paper, we have developed a sensitive and rapid CE immunoassay with enhanced chemiluminescence detection of EPO, in which silica dioxide nanoparticles (SiO2 NPs) were used as the pseudostationary phase to improve the separation efficiency of analytes. By adopting SiO2 NPs in the CE immunoassay, the separation can be successfully performed in neutral running buffer solution. However, running buffer of extreme pH was still necessary for the conventional CZE mode. Neutral phosphate buffer (pH 7.4) containing SiO2 NPs and poly(ethylene oxide) (PEO) was chosen as running buffer. The influences of SiO2 NPs, PEO and buffer concentration on the separation efficiency and EPO detection were investigated. EPO-horse radish peroxidase (HRP) and immunocomplex were baseline separated in a 10 mM phosphate buffer (pH 7.4) consisting of 0.08% PEO and 0.08% SiO2 NPs. The linear range for EPO was 1.8-158.0 ng/mL and the detection limit was 0.9 ng/mL. The assay was successfully applied for the quantification of EPO in human sera and the results correlated well with those obtained using chemiluminescence immunoassay kits, thus demonstrating that the present method was a potential powerful tool for EPO misuse detection and clinical diagnosis.

Enhancement of Memory Retention Time of Metal/Ferroelectric/Insulator/Semiconductor Structure by Using Fast Annealing and Nitrogen Radical Irradiation

Fast annealing was used to improve the electronic properties of ferroelectric and buffer layers in Pt/SrBi2Ta2O9(SBT)/SiO2/n-Si metal-ferroelectric-insulator-semiconductor (MFIS) structures. Damage of the SiO2 layer due to SBT constituent diffusion was reduced significantly as annealing time at high temperature of the ferroelectric SBT can be reduced from 1 − 2 hours to few minutes. Leakage currents through both the SiO2 buffer and the SBT ferroelectric layers were decreased in the sample prepared by using fast annealing. The C-V and the I-V characteristics also show electronic improvement at the interface and reduced of thermal diffusion of constituent elements. It is shown by SEM and atomic force microscopy(AFM) images revealed that the SBT thin film with fast annealing had a gets better surface morphology. The retention time of a capacitor with a MFIS structure in the ON and the OFF states was improved, and the maximum is retention time was longer than 23 days.

Flexible High-Performance Amorphous InGaZnO4 Thin-Film Transistors Utilizing Excimer Laser Annealing

We have investigated an excimer laser annealing (ELA) process for use in fabricating high-performance amorphous InGaZnO4 (IGZO) thin-film transistors (TFTs) on flexible plastic substrates. We numerically estimate the temperature increase of the IGZO film and substrate as a function of laser energy density. This is one of the most important measures for optimizing ELA conditions in order to apply plastic-based TFT fabrication. Because the optical absorption coefficient of IGZO film is three orders of magnitude higher than that of plastic substrates with respect to 308-nm laser light, it is possible to selectively increase the temperature of the IGZO film. The temperature of the IGZO film is estimated to increase to approximately 1500 °C at typical laser energy levels. Furthermore, incorporating a SiO2 buffer layer (some hundreds of nm) between the IGZO film and the plastic substrate is found to effectively suppress thermal damage to the substrate. We have experimentally investigated the properties of IGZO films irradiated with various excimer-laser energy densities. X-ray diffraction patterns and carrier densities of the IGZO films are found to significantly vary with laser energy density. We have used calculations and experimental results to optimize the ELA process; this has enabled us to produce high-performance IGZO-TFTs having a field-effect mobility of 15.6 cm2 V-1 s-1.

Ultra Thin Oxide by Chemical Vapour Oxidation of Si

Continued MOSFET scaling necessitates the use of high-k materials which in turn need an ultra thin (<0.6nm) SiO2 buffer layer between the high-k material and the silicon substrate, to obtain a better interface. In this paper a novel technique to grow extremely thin (as low as 0.6 nm) oxide by nitric acid vapour at low temperature and effect of ac anodization on these oxides are discussed. The effective oxide thickness obtained for these chemical oxides has been found to be ranging from 0.6 nm to 1.5 nm. C-V, I-V and reliability characteristics have been studied. The oxide thickness increases with increase in molarity of the HNO3. At an electric field of 10 MV/cm, the leakage current density for the thinnest oxide is 0.6 A/cm2. These values are better than those for oxides grown in HNO3 solution. Anodization improved the quality of the chemical vapour oxides further.

Band alignments and improved leakage properties of (La2O3)0.5(SiO2)0.5/SiO2/GaN stacks for high-temperature metal-oxide-semiconductor field-effect transistor applications

The band alignments of (La2O3)0.5(SiO2)0.5(LSO)/GaN and LSO/SiO2/GaN gate dielectric stacks were investigated comparatively by using x-ray photoelectron spectroscopy. The valence band offsets for LSO/GaN stack and LSO/SiO2/GaN stack are 0.88 and 1.69 eV, respectively, while the corresponding conduction band offsets are found to be 1.40 and 1.83 eV, respectively. Measurements of the leakage current density as function of temperature revealed that the LSO/SiO2/GaN stack has much lower leakage current density than that of the LSO/GaN stack, especially at high temperature. It is concluded that the presence of a SiO2 buffer layer increases band offsets and reduces the leakage current density effectively.