Measurement of Thermal Conductivity of TiO2 Thin Films Using 3ω Method

TiO₂ film has been used in many industrial components such as laser filters, protection mirrors, chemical sensors, and optical catalysts. Therefore, the thermal properties of TiO₂ thin films are important in, e.g., reducing the thermal conductivity of ceramic coatings in gas turbines and increasing the laser damage threshold of antireflection coatings. The thermal conductivity of four kinds of TiO₂ thin films, prepared by dc magnetron sputtering, was measured using the 3 method in the temperature range from 80 K to room temperature. The results showed that the thermal conductivity of TiO₂ thin films strongly depends on the thickness and the microstructure of the films. The films with smaller grain size and thinner thickness have smaller thermal conductivities.     

Thermal Characterization of SiC Amorphous Thin Films

The cross-plane thermal conductivity of SiC amorphous films was measured employing the transient thermoreflectance technique. The SiC films were deposited on silicon substrates by RF magnetron sputtering at room temperature. The thickness of the films was varied in the range from 100?nm to 2500?nm to analyze the size effect. The results found that the thermal conductivity of the SiC thin films is significantly smaller than that of the SiC material in bulk form. The small thermal conductivity stems from the structural disorder of the films, which was confirmed by high-resolution transmission electron microscopy and X-ray diffraction. In addition, the contribution of the thermal boundary resistance to the thermal conductivity of the films is discussed.     

Growth of highly c-axis oriented aluminum nitride thin films on β-tantalum bottom electrodes

We have investigated the influence of tantalum (Ta) bottom electrodes on the crystallinity and crystal orientation of aluminum nitride (AlN) thin films. AlN thin films and Ta electrodes were prepared by using rf magnetron sputtering method. The crystal structure of the Ta electrodes was tetragonal (β-Ta, a metastable phase) at room temperature. The crystallinity and orientation of the AlN thin films and Ta electrodes strongly depended on sputtering conditions. Especially, the crystallinity and crystal orientation of the Ta electrodes were influenced by their film thickness and the substrate temperature. When the thickness of the Ta bottom electrodes was 200 nm and the substrate temperature was 100 °C, the AlN thin films indicated high c-axis orientation (the full width at half maximum of rocking curve of 3.9°). The crystal orientation of the AlN film was comparable to that of AlN thin films deposited on face centered cubic (fcc) lattice structure metal, such as Au, Pt and Al, bottom electrodes.     

The influence of thickness and deposition temperature on the conduction activation energy of CdSe0.2Te0.8 thin films

The electrical conductivity and stability in resistance of CdSe_0.2Te_0.8 thin films in different ambients and deposited at different substrate temperatures were investigated. A reduction in conduction activation energy with increase in film thickness and deposition temperature is accounted for by the fact that in CdSe _x Te_1–x inhomogeneous semiconductor thin films, the potential relief inhomogeneity may be reduced with increase in film thickness and substrate temperature, which results in the decrease of conduction activation energy of the films.     

Film-thickness effects on the optical and electrical properties of Cu-GeO2 thin cermet films

The effect of film thickness on the optical and electrical properties of Cu-30 wt % GeO₂-70 wt % thin cermet films prepared by electron-beam deposition at about 10^–3 Pa and at a substrate temperature of 300 K is reported. The ultraviolet, visible and direct current (d.c.) conductivity results are analysed with the aim of determining the optical band gap,E _opt, the width of the band tails,E _e, and the d.c. thermal activation energy,E _a. It was found that the optical energy gap increases with increasing thickness and that the absorption was due to indirect transitions ink-space. The general feature of the absorption edge remains similar for both unannealed and annealed films, but annealing has the effect of decreasingE _opt. The d.c. conductivity results show thatE _a decreases with increasing thickness. From a knowledge ofE _opt andE _a, a probable model of the electronic band structure in Cu-GeO₂ thin films has been suggested.     

Deposition of c-axis orientation aluminum nitride films on flexible polymer substrates by reactive direct-current magnetron sputtering

Aluminum nitride (AlN) piezoelectric thin films with c-axis crystal orientation on polymer substrates can potentially be used for development of flexible electronics and lab-on-chip systems. In this study, we investigated the effects of deposition parameters on the crystal structure of AlN thin films on polymer substrates deposited by reactive direct-current magnetron sputtering. The results show that low sputtering pressure as well as optimized N₂/Ar flow ratio and sputtering power is beneficial for AlN (002) orientation and can produce a highly (002) oriented columnar structure on polymer substrates. High sputtering power and low N₂/Ar flow ratio increase the deposition rate. In addition, the thickness of Al underlayer also has a strong influence on the film crystallography. The optimal deposition parameters in our experiments are: deposition pressure 0.38 Pa, N₂/Ar flow ratio 2:3, sputtering power 414 W, and thickness of Al underlayer less than 100 nm.     

Heating of polymer substrate by discharge plasma in radiofrequency magnetron sputtering deposition

The substrate used for the thin film deposition in a radiofrequency magnetron sputtering deposition system is heated by the deposition plasma. This may change drastically the surface properties of the polymer substrates. Deposition of titanium dioxide thin films on polymethyl methacrylate and polycarbonate substrates resulted in buckling of the substrate surfaces. This effect was evaluated by analysis of atomic force microscopy topography images of the deposited films. The amount of energy received by the substrate surface during the film deposition was determined by a thermal probe. Then, the results of the thermal probe measurements were used to compute the surface temperature of the polymer substrate. The computation revealed that the substrate surface temperature depends on the substrate thickness, discharge power and substrate holder temperature. For the case of the TiO₂ film depositions in the radiofrequency magnetron plasma, the computation indicated substrate surface temperature values under the polymer melting temperature. Therefore, the buckling of polymer substrate surface in the deposition plasma may not be regarded as a temperature driven surface instability, but more as an effect of argon ion bombardment.     

Synthesis and characterization of 4H-SiC on C-plane sapphire by C60 and Si molecular beam epitaxy

4H-SiC (silicon carbide) films were grown on (0001) sapphire substrate at rather low temperatures(1000-1100 °C) with relative high deposition rate by using fullerene (C₆₀) and silicon solid sources molecular beam epitaxy with substrate nitridation and aluminum nitride (AlN) buffer layer deposition prior to the SiC deposition. The effects of substrate nitridation and AlN buffer layer to the adhesion of the SiC thin films on sapphire have been studied. X-Ray diffraction, pole figure, atomic force microscope, Fourier transform infrared spectroscopy and photoluminescence were employed for the analysis of composition, orientation of the film and surface morphology. Relative high deposition rate at ∼ 165 nm/h was achieved.     

Thermal and Electrical Properties of a Suspended Nanoscale Thin Film

This paper reports on measurements of in-plane thermal conductivities, electrical conductivities, and Lorentz number of two microfabricated, suspended, nanosized thin films with a thickness of 28 nm. The effect of the film thickness on the in-plane thermal conductivity is examined by measuring other nanofilm samples with a thickness of 40 nm. The experimental results show that the electrical conductivity, resistance–temperature coefficient, and in-plane thermal conductivity of the nanofilms are much smaller than the corresponding bulk values from 77 to 330 K. However, the Lorentz number of the nanofilms is about two times that of the bulk value at room temperature, and even up to three times that of the bulk value at 77 K. These results indicate that the relation between the thermal conductivity and electrical conductivity of the nanofilms does not follow the Wiedemann–Franz law for bulk metallic materials.     

Enhancement of thermal conductivity of hydrogenated silicon film by microcrystalline structure growth

Hydrogenated silicon film is fabricated by plasma enhanced chemical vapor deposition method, and the enhancement of thermal conductivity of hydrogenated silicon film by microcrystalline structure growth is investigated. The thermal conductivity of films is measured based on Fourier thermal transmitting law by using platinum electrode. Raman spectroscopy characterization reveals the crystalline volume fraction (X _c) of microcrystalline silicon (μc-Si:H) and demonstrates it is embedded with nanocrystals. Spectroscopic ellipsometry with Forouhi–Bloomer model is used to obtain the thickness of films. The measurement results show that the thermal conductivity of μc-Si:H is much higher than amorphous silicon (a-Si:H).     

SiC填料对光伏封装用EVA导热复合胶膜的影响

目的探讨乙烯-醋酸乙烯酯共聚物(EVA)胶膜中加入晶须碳化硅(SiC)无机填料后,对EVA胶膜交联度、力学性能及导热性能的影响。方法通过将晶须SiC无机填料导入EVA,使得在整个体系内呈连续相的有机大分子与呈分散相的无机填料共混成一体,再通过挤出流延成形得到厚度均一的胶膜。结果随着晶须SiC含量的增加,EVA复合胶膜的抗拉强度和断裂伸长率均有所下降。交联度随着SiC含量的增加而略微增大,最终达到平衡,剥离强度先增大后减小。使用不同的偶联剂对SiC表面进行处理,EVA导热复合胶膜导热性能存在差异。使用同一种偶联剂对SiC表面进行处理,SiC粒径尺寸的差异同样对EVA导热复合胶膜导热性能存在差异。结论添加晶须SiC的尺寸规格、添加量、表面处理情况对EVA导热复合胶膜的力学性能、交联度影响较大。     

Growth of 3C-SiC on 150-mm Si(100) substrates by alternating supply epitaxy at 1000 °C

To lower deposition temperature and reduce thermal mismatch induced stress, heteroepitaxial growth of single-crystalline 3C-SiC on 150 mm Si wafers was investigated at 1000 °C using alternating supply epitaxy. The growth was performed in a hot-wall low-pressure chemical vapor deposition reactor, with silane and acetylene being employed as precursors. To avoid contamination of Si substrate, the reactor was filled in with oxygen to grow silicon dioxide, and then this thin oxide layer was etched away by silane, followed by a carbonization step performed at 750 °C before the temperature was ramped up to 1000 °C to start the growth of SiC. Microstructure analyses demonstrated that single-crystalline 3C-SiC is epitaxially grown on Si substrate and the film quality is improved as thickness increases. The growth rate varied from 0.44 to 0.76 ± 0.02 nm/cycle by adjusting the supply volume of SiH₄ and C₂H₂. The thickness nonuniformity across wafer was controlled with ± 1%. For a prime grade 150 mm virgin Si(100) wafer, the bow increased from 2.1 to 3.1 μm after 960 nm SiC film was deposited. The SiC films are naturally n type conductivity as characterized by the hot-probe technique.     

Micro-structures of BF2- and As-implanted polycrystalline silicon thin films of various thicknesses and heat treatments

Characterization of annealed BF₂⁺- and As⁺-doped polycrystalline silicon (polysilicon) films is presented. Effects of heat treatment, doping concentration, and thickness of film on the grain size and mobility of polysilicon films are investigated and discussed. By using transmission electron microscopy (TEM), it is found that the grain size, effective carrier concentration, and carrier mobility of a polysilicon thin film increases with increasing film thickness. Our results show that a high concentration of As dopant could enhance the recrystallization of the polysilicon films. Heavily As⁺-doped samples were seen to have a relatively larger grain size compared to the lightly doped film. The maximum grain size of about 278 nm can be realized in a polysilicon film with 150 nm in thickness. In contrast, the B dopant has a negligible effect on the recrystallization of polysilicon films. With increasing film thickness and thermal annealing temperature, a high performance polysilicon film with high mobility and grain size can be obtained.     

Growth and properties of CuInS2 thin films

Single phase copper indium disulphide (CuInS₂) thin films of thickness between 60 nm and 650 nm with the chalcopyrite structure are obtained on NaCl and glass substrates by flash evaporation. The films were found to ben-type semiconducting. The influence of the substrate temperature on the crystallinity, conductivity, activation energy and optical band gap was studied. An improvement in the film properties could be achieved up to a substrate temperature of 523 K at a molybdenum source temperature of 1873 K.     

Thermal conductivity of copper films

The thermal conductivity of thin films of copper (400–8000 Å) has been measured in the temperature range 100–500 K. It decreases with decreasing film thickness. An electrical-thermal transport analogy has been used to calculate the size-dependent thermal conductivity of the thin copper films. The decrease of the thermal conductivity with thickness is attributed partly to the scattering of the conduction electrons from the film surfaces and partly to the scattering by lattice impurities and frozen-in structural defects in the films. The variation of the thermal conductivity with temperature agrees with the variation for bulk copper. The Lorentz ratio has been determined and is found to vary from 2.4 × 10^-8 to $\text{2.0 × 10}{}^{-8}\text{W}\text{Ω/}\text{deg}{}^2$ for film thicknesses ranging from 400 to 8000 Å.     

The individual effect of coating thicknesses and deposition temperatures on Raman spectra of carbon films deposited on silica glass fibers by thermal chemical vapor deposition

Abstract

Carbon films are deposited on silica glass fibers by thermal chemical vapor deposition using pure methane as the precursor gas, and the individual effect of coating thicknesses and deposition temperatures on Raman spectra of carbon films is investigated. The results show that if the temperature is fixed at 950°C, the D peak position, the full‐width‐at‐half maximum of D band, and the integrated intensity ratio of the D band to the G band increase with increasing the coating thickness. This is because the size and number of particles grown on the carbon film surface increase with increasing the coating thickness and the carbon film becomes more disordered. Alternatively, if the coating thickness is fixed at 1200 nm, the D peak position, the full‐width‐at‐half maximum of D band, and the integrated intensity ratio of the D band to the G band decrease with increasing the deposition temperature. This indicates that the carbon film becomes more ordered and its nano‐grain size increases as the deposition temperature increases from 925 to 1025°C.     

Thermal Conductivity and Interfacial Thermal Resistance in Bilayered Nanofilms by Nonequilibrium Molecular Dynamics Simulations

A nonequilibrium molecular dynamics study of the cross-plane thermal conductivity and interfacial thermal resistance of nanoscale bilayered films is presented. The films under study are composed of argon and another material that is identical to argon except for its atomic mass. The results show that a large temperature jump occurs at the interface and that the interfacial thermal resistance plays an important role in heat conduction for the whole films. The cross-plane thermal conductivity is dependent on the average temperature. The interfacial thermal resistance is found to be dependent apparently on the atomic mass ratio of the two materials and the temperature, but to be independent of the film thickness. A linear relationship is observed between the reciprocal of the cross-plane thermal conductivity and that of the film thickness with the film thickness between 5.4 nm and 64.9 nm, which is in good agreement with results in the literature for a single film.     

沉积温度对化学气相沉积法制备铜薄膜性质的影响

以双(2,2,6,6-四甲基-3,5-庚二酮)化铜(Cu(DPM)₂)为前驱体,使用智能化学气相沉积设备在673 K至1173 K下于AlN多晶基板上制备Cu薄膜。研究了不同沉积温度对Cu薄膜的相组成、择优取向、宏观表面、微观结构、元素组成及电导的影响。在873 K至1173 K时制备了具有(111)择优取向的紫铜色铜薄膜,同时存在(200)和(220)取向,且铜晶粒呈岛状生长模式。随着沉积温度的升高,薄膜的导电性先增强后减弱。在1073 K时,制得了导电性最好且高度(111)择优取向的最纯紫铜色Cu薄膜,即1073 K为制备Cu薄膜的最佳沉积温度。     

碳化硅薄膜制备方法及光学性能的研究进展

碳化硅薄膜有密度小、热导率高、热膨胀系数低、硬度高等优异的性能。介绍了制备碳化硅薄膜的2种常用方法。即化学气相沉积和磁控溅射技术,比较了2种方法的各自优势。总结了碳化硅薄膜光学性能及短波发光特性的研究进展。     

Study of annealing effects in In-Sb bilayer thin films

The thin films of In-Sb having different thicknesses of antimony keeping constant thickness of indium was deposited by thermal evaporation method on ITO coated conducting glass substrates at room temperature and a pressure of 10⁻⁵ torr. The samples were annealed for 1 h at 433 K at a pressure of 10⁻⁵ torr. The optical transmission spectra of as deposited and annealed films have been carried out at room temperature. The variation in optical band gap with thickness was also observed. Rutherford back scattering and X-ray diffraction analysis confirms mixing of bilayer system. The transverse I-V characteristic shows mixing effect after annealing at 433 K for 1 h. This study confirms mixing of bilayer structure of semiconductor thin films.