Characterization of a-SiC(x):H thin films as an encapsulation material for integrated silicon based neural interface devices

A fully integrated, wireless neural interface device is being developed to free patients from the restriction and risk of infection associated with a transcutaneous wired connection. This device requires a hermetic, biocompatible encapsulation layer at the interface between the device and the neural tissue to maintain long-term recording/stimulating performance of the device. Hydrogenated amorphous silicon carbide (a-SiC_x:H) films deposited by a plasma enhanced chemical vapor deposition using SiH₄, CH₄, and H₂ precursors were investigated as the encapsulation layer for such device. Si-C bond density, measured by Fourier transform infrared absorption spectrometer, suggests that deposition conditions with increased hydrogen dilution, increased temperature, and low silane flow typically result in increase of Si-C bond density. From the variable angle spectroscopic ellipsometry measurement, no dissolution of a-SiC_x:H was observed during soaking tests in 90 °C phosphate buffered saline. Conformal coating of the a-SiC_x:H in Utah electrode array was observed by scanning electron microscope. Electrical properties were studied by impedance spectroscopy to investigate the performance of a-SiC_x:H as an encapsulation layer, and the results showed long term stability of the material.     

Micromechanical properties of amorphous carbon coatings deposited by different deposition techniques

Amorphous carbon coatings about 20 nm thick are commonly used as an overcoat on magnetic thin-film rigid disks and tape and disk head surfaces to improve their wear performance. In this study, we deposited amorphous carbon coatings with thicknesses ranging from 20 to 400 nm on single-crystal silicon substrates by four deposition processes: cathodic arc, ion beam deposition, r.f.-plasma-enhanced chemical vapor deposition, and r.f. sputtering. R.f.-sputtered SiC coatings were also deposited for comparison. The hardness, elastic modulus, and scratch resistance of these coatings were measured by nanoindentation and microscratching using a nanoindenter. The cathodic arc carbon coatings followed by sputtered SiC coatings exhibited the highest hardness, elastic modulus, scratch resistance/adhesion, and residual compressive stresses. The critical load, a measure of the scratch resistance/adhesion of the coating, increases with thickness. The cathodic arc coatings of lower thicknesses (˜ 30 nm) exhibited instant damage when the normal load exceeded the critical load, whereas thick coatings (greater than or equal to 100 nm) exhibited gradual damage through the formation of tensile cracks. The sputtered carbon coatings exhibited damage to the coating at very low loads and ploughing of the tip into the coating occurred right from the beginning of the scratch.     

Enhanced dielectric properties of low density polyethylene with bismuth sulfide used as inorganic filler

A series of Bi₂S₃/LDPE composites, with low density polyethylene (LDPE) as matrix and bismuth sulfide as filler, are fabricated by a simple process. The microstructure, dielectric properties and tensile strength of the composites have been studied. The variation of dielectric properties of the Bi₂S₃/LDPE composites with the volume fraction of Bi₂S₃, frequency and temperature is discussed. The composites have significantly high dielectric constants and good thermal stability, with a quite low percolation threshold. The addition of low content of Bi₂S₃ significantly improves the dielectric constant of polymer matrix from 3 to above 60 at 100 Hz.     

Fractal properties of percolating film structures

We simulate nucleation and growth processes of thin films on the basis of the so-called rate equation approach allowing “atoms” to diffuse and rearrange whereby enhancing their co-ordination number. The resulting percolating structures are different from those obtained by the “pure” percolation model where “atomic diffusion” is not taken into account. However, the fractal properties for p = p_c are the same as for the percolation model with the fractal dimension of d_f = 1.896 and for random walks of d_w = 2.87. Moreover, d_f and d_w are independent on the diffusion time we choose for our simulations.     

Indium tin oxide coatings properties as a function of the deposition atmosphere

Indium tin oxide coatings were deposited by magnetron sputtering physical vapour deposition under different atmospheres. Microstructural, electrical, and optical properties were measured, finding a correlation among properties and process parameters. Texture analyses carried out by X-ray diffraction showed that films microstructure depended by the oxygen content in the deposition vessel: high values of the oxygen content (e.g., 5%) caused the film to grow along the <111> orientation; under pure Ar, the grains grew along the <100> orientation. Intermediate values of the oxygen content caused the growth of two families of grains, respectively oriented along the <111> and the <100> directions.     

Characterization of diamond films deposited on titanium and its alloys

Titanium and its alloys have important applications for example in aerospace or as bioimplants. Some of these applications would be improved by diamond coatings. However the large thermal expansion mismatch between diamond and titanium or its alloys creates high residual stresses, up to about 7 GPa at 800 °C, which represent an important drawback. In this study, polycrystalline diamond films were deposited on pure titanium and Ti-6Al-4V in a classical tubular microwave plasma reactor from C-H(-O)-containing gas mixtures, at a temperature in the range 600–900 °C. Raman spectroscopy provided information about the diamond grain stress, which is obviously related to the deposition temperature. X-ray diffraction indicates the presence of titanium carbide or oxycarbide. Some other characterizations by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) are reported. It is shown that XPS coupled to argon ionic etching allows us to study the first steps of the deposition process. The structure and the chemical composition at the interface of a thicker deposit are obtained by TEM and EELS.     

Growth of a single-wall carbon nanotube film and its patterning as an n-type field effect transistor device using an integrated circuit compatible process

This study presents the synthesis of a dense single-wall carbon nanotube (SWNT) network on a silicon substrate using alcohol as the source gas. The nanosize catalysts required are made by the reduction of metal compounds in ethanol. The key point in spreading the nanoparticles on the substrate, so that the SWNT network can be grown over the entire wafer, is making the substrate surface hydrophilic. This SWNT network is so dense that it can be treated like a thin film. Methods of patterning this SWNT film with integrated circuit compatible processes are presented and discussed for the first time in the literature. Finally, fabrication and characteristic measurements of a field effect transistor (FET) using this SWNT film are also demonstrated. This FET is shown to have better electronic properties than any other kind of thin film transistor. This thin film with good electronic properties can be readily applied in the processing of many other SWNT electronic devices.     

Influence of processing variables on the structure and properties of ZnO films

Zinc oxide films of high optical quality have been deposited onto both silica and silicon substrates using reactive sputtering, pulsed laser deposition, and an aqueous solution based technique. Films have been characterized with respect to crystalline phase and phase stability, surface morphology, and optical response by means of X-ray diffraction, Raman spectroscopy, atomic force microscopy, optical transmission and ellipsometry measurements. All films studied were of the wurtzite phase, fine-grained, and exhibited varying degrees of c-axis orientation with respect to the substrate normal depending upon deposition conditions. Films showed some degree of residual tensile stress which was inferred from the E₂ Raman line shift relative to the single-crystal frequency. The wurtzite phase was found to be stable to temperatures near 800 °C, but at higher temperatures, reaction with silica led to evolution of Zn₂SiO₄ at the interface. Variations in Raman line intensities upon post-deposition annealing have been correlated with oxidation of excess zinc in the lattice.     

制冷技术在集成电路制造工艺设备中的应用

集成电路制造的刻蚀设备要求宽温区温度控制(-20℃～80℃)、光刻设备要求超精密温度控制(±0.01℃)、薄膜气相沉积设备要求的大功率温度控制。本文分析上述温控特点后,分别选择蒸汽式压缩制冷、热电制冷、水水热交换制冷技术,并介绍基于半导体制冷片的制冷系统设计,提出旁通式压缩机制冷系统、基于流量调节的温度控制系统及相关控制技术。     

Structure and photoconductive properties of dip-deposited SnS and SnS2 thin films and their conversion to tin dioxide by annealing in air

SnS and SnS₂ thin films have been prepared by the dip technique. In this technique, a substrate was dipped into an alcoholic solution of the corresponding chloride and thiourea and then withdrawn vertically at a controlled speed, and finally baked in a high temperature furnace at atmospheric condition. XRD and SEM data suggest that good quality SnS and SnS₂ films are obtained at a baking temperature of 300 and 360°C, respectively. Values of band gap for SnS and SnS₂ obtained from spectral response of photoconductivity are 1.4 and 2.4 eV, respectively. The indirect allowed band gap values for SnS₂ film obtained from optical absorption measurements are 1.95 and 2.05 eV. Open-air annealing of both SnS and SnS₂ films at 400°C converts them to transparent conducting SnO₂.     

Structural and magnetic properties of Ge0.7Mn0.3 thin films

Ge_0.7Mn_0.3 thin films were fabricated on Al₂O₃ (0001) and glass substrates at growth temperatures ranging from room temperature to 500 °C by a radio frequency magnetron sputtering. We found that the Ge_0.7Mn_0.3 thin films showed a polycrystalline-to-amorphous transition at about 360 °C, and the ferromagnetic transition temperature of each thin film depends on its structure — crystalline or amorphous states. Particularly, the Ge_0.7Mn_0.3 thin films showed room temperature ferromagnetism when they were fabricated at temperatures above the crystallization temperature.     

Properties of thin TiN films deposited onto stainless steel by an in-line dry coating process

A new coil-coating pilot plant, capable of utilizing ion plating, sputtering and plasma-assisted chemical vapor deposition (PACVD) processes, independently or in series, was developed and optimum conditions for TiN, TiC, Al_xO_y, SiO_x and Cr coating were established. This paper is mostly concerned with the results of characterization (conducted in parallel by the authors′ two institutions) of TiN films deposited by ion plating or sputtering onto type-304 stainless steel strips. In particular, the dependence of the basic properties such as chemical composition, structure, adhesion, and color on the coating process are discussed with respect to anti-corrosion, anti-wear, and decorative applications. TiN coatings with a very attractive gold coloration were obtained; they performed well in wear testing, but did not show satisfactory corrosion resistance. However, it was found that the latter can be improved significantly by depositing a SiO_x, top layer by PACVD above the TiN coating. Thus the in-line dry coating processes are capable of producing highly functional steel surfaces with decorative color and high corrosion resistance.     

Chemically deposited CdS films in an ammonia-free cadmium-sodium citrate system

In this work, we report the properties of chemically deposited CdS thin films in a cadmium-sodium citrate system. This chemical bath deposition process does not employ ammonia. We deposited four series of films at different cadmium content in the chemical bath process and determined their properties. The obtained information can be very useful for the optimization of the deposition process in order to reduce the amount of toxic chemical waste, mainly Cd-containing waste. The structural and optical properties of the CdS films were determined from X-ray diffraction, optical transmission and reflection spectroscopy and scanning electron microscopy measurements. We found that the properties of the films are very sensitive to the amount of cadmium in the deposition process. The process allows the deposition of good quality CdS thin films using 1.12, 0.84 and 0.76 mg of cadmium per milliliter of reaction solution.     

Formation of an epitaxial monolayer on graphite upon short-time surface contact with highly diluted aqueous solutions of 1-monostearoylglycerol

Short-time surface contact of highly diluted 1-monostearoylglycerol (1-MSG) aqueous solutions with highly oriented pyrolitic graphite results in the deposition of an epitaxial monolayer that can be detected by atomic force microscopy operating in tapping mode at the graphite-air interface. The monolayer obtained with the racemic mixture is then compared to that obtained with one of the pure enantiomers. The analogous behavior found for aqueous solutions of rac-1-MSG and 3-sn-MSG implies a two-dimensional self-assembly process with chiral discrimination. The results suggest that the monolayer originates from species located at the surface of the deposition drop. They also indicate that the simple experimental procedure reported, or more elaborate Langmuir-Schaefer methods, could be the method of choice to prepare other monolayers of similar surfactants.     

Effect of N2O/SiH4 ratio on the properties of low-temperature silicon oxide films from remote plasma chemical vapour deposition

Silicon oxide films have been deposited with remote plasma chemical vapour deposition (RPCVD) at low temperatures (<300 °C) from SiH₄---N₂O. The effect of a gas-phase reaction on the SiO₂ film properties and Si/SiO₂ interface was investigated. As the partial pressure ratio was increased above N₂O/SiH₄ = 4, a gas-phase reaction with powder formation was observed, which degraded film properties, increased surface roughness, and decreased deposition rate. When N₂O/SiH₄ <4, there was no detectable IR absorption in the film associated with hydrogen-related bonds (Si---OH and Si---H) but when N₂O/SiH₄ >4, the incorporation of Si---OH bond became significant and Si¹⁺, intermediate state silicon at the interface, was more abundant. The oxide fixed charge, interface trap density, surface roughness and leakage current were increased when there was powder formation in the gas phase. High plasma power also favoured the powder formation in the gas phase. C---V and I---V characteristics were measured and it was shown that these electrical properties were directly related to the process condition and material properties of the oxide and the Si/SiO₂ interface.     

Growth and properties of silicon nitride films prepared by low pressure chemical vapor deposition using trichlorosilane and ammonia

Amorphous silicon nitride (a-SiN_x) films were prepared by low pressure chemical vapor deposition from SiHCl₃(Trichlorosilane, TCS)---NH₃---N₂ system to obtain stoichiometric film with low hydrogen content. The growth kinetics was investigated as a function of total pressure, NH₃/TCS flow ratio and deposition temperature. The film compositions and topography were characterized by X-ray photoelectron spectroscopy, Auger depth profile, Fourier transform infrared spectroscopy, elastic recoil detection and atomic force microscopy, respectively. The growth rate of the films follows an Arrhenius behavior with apparent activation energy of 171 kJ mol⁻¹ between 730 and 830 °C. At lower NH₃/TCS flow rate ratios, silicon-rich a-SiN_x films were obtained while all deposits were stoichiometric with a N/Si atomic ratio of approximately 1.30–1.33 as the ratios is higher. The hydrogen content of the prepared a-SiN_x films is 1.2 at.% that is approximately 15 times lower than those of traditional PECVD films and approximately three times lower than those of previous LPCVD films using silane or dichlorosilane and ammonia. The surface topography of the prepared film is smooth and uniform with a root mean square roughness value of 0.47 nm.     

Factors affecting the adoption and use of AVR technology in higher and tertiary education

The research study assesses the factors that determine the adoption of Augmented and Virtual Reality (AVR) technology in Higher and Tertiary Education. In spite of the well-established potential benefits of AVR technology in education, it appears that most Higher and Tertiary Institutions have not holistically adopted it as a method of teaching and learning. Thus, it is important to investigate the reasons why AVR has not been adopted. Inductive qualitative research was conducted virtually with the aid of a questionnaire instrument. The Technology Acceptance Model (TAM) was used to establish the determinants for the adoption of AVR Technology. The research study found out that the main reasons for the lack of adoption of AVR technology were due to the lack of coordinating policies; lack of enabling infrastructures; perceived complexity of the use of AVR technology and a lack of a framework that guides the holistic as well as homogenous adoption of AVR technology in Higher and Tertiary Education. The research concluded that an AVR technology was necessary and should factor in the barriers to adoption. The study recommends inter-professional working of key players such as the Ministry of Higher Education (in endorsing an AVR technology model), the lecturers (using and encouraging AVR technology), and the students (active participation and use of AVR technology to learn). Prior to this study, the aspect of inter-professional working as a solution to the adoption and use of AVR in Higher and Tertiary Education had not been explored. However, more still needs to be done within Virtual Training and the development of an AVR model for teaching and learning.     

Crystallographic properties of four-fold grain K3Li2Nb5O15 thin films

The structural properties of a potassium lithium niobate (KLN; K₃Li₂Nb₅O₁₅) thin film deposited by rf-magnetron sputtering on a Pt/Ti/SiO₂/Si(100) substrate were investigated. The crystalline structures of the Pt under layer and KLN thin films were examined using θ-2θ, θ-rocking, and mesh scan X-ray diffraction (XRD). The XRD results revealed that the Pt under layer was a strong (111) direction orientated poly crystal. Unlike the Pt under layer film, the KLN(001) peak was found to consist of two separate peaks, one with a broad full width half maximum (FWHM) and the other with a narrow FWHM, indicating that the KLN film had a single crystalline structure. The surface and cross-section morphology were investigated using a scanning electron microscope (SEM). Accordingly, from the results of the SEM and XRD experiments, it was concluded that the KLN film was composed of small single crystals, which had a four-fold symmetry morphology with a c-axis normal to the substrate.     

One step room temperature photodeposition of Cu/TiO2 composite films and its conversion to CuO/TiO2

Cu/TiO₂ composite films were prepared at low temperature on glass substrates by a photodeposition method. Films were deposited by irradiating the substrate while in contact with an aqueous TiO₂ suspension containing copper(II) nitrate and ethanol. Cu/TiO₂ composite films of 500 nm in thickness were deposited at room temperature after a short irradiation time (15 min) with a 125 W mercury vapour lamp. According to scanning electron microscopy observations, the obtained films were homogeneous and porous. Energy dispersive X-ray spectroscopy analysis revealed a 3:1 Cu:Ti atomic ratio. Grazing angle X-ray diffraction analysis showed that the films contained Cu and TiO₂ as major components and Cu₂O as a minor component. Heat treatment at 400 °C in air for a period of 3 h transformed the initial material into a CuO/TiO₂ composite, improved the adhesion to the substrate and favoured a more regular distribution of copper oxide according to backscattering micrographs.