Stress and resistivity analysis of electrodeposited gold films for MEMS application

Electroplated gold films have attracted much attention in recent years because of its desirable properties for microsystems applications such as resistance to oxidation, low electrical resistance, overall chemical inertness and low processing temperature. In order to use gold in microelectromechanical systems designs, systematic tests has to be conducted to characterize the material in terms of its electrical as well as mechanical properties. In this paper, the stress and resistivity behavior of a nanometer-scale gold film with respect to the deposition parameters and annealing condition is reported.     

Optical and ac conductivity investigations on Sn doped Ag2S thin films under the structural transition framework

This work deals with further optical and electrical investigations on Sn content in Ag₂S sprayed thin films and the beneficial effect of using this type of doping in addition to the results recently reported by R. Boughalmi, A. Boukhachem, I. Gaeid, K. Boubaker, M. Bouhafs, M. Amlouk, Mater. Sci. Semicond. Process. 16 (2013) 1584. The refractive index and extinction coefficient values in terms of Sn content were deduced from transmittance and reflectance data. Moreover, study of dielectric constants has been conducted; the dispersion parameters and high- frequency dielectric constant are determined. Finally, the electrical conductivity and conduction mechanism of these films are studied using an impedance spectroscopy technique in the frequency range 5 Hz–13 MHz at various temperatures (100–230 °C). Besides, the temperature dependence of ac conductivity measurements has been analyzed under the structural transition framework from β- to α-Ag₂S phases.     

Observation on Surface and Cross Section of Thin Film Solar Cells Using Atomic Force Microscope

Atomic force microscope (AFM) is able to produce thrce-dimensional digital data in both force-mode and heightmode and its applications are not limited to map the surfaces of conducting materials. It can use the force-mode to image the repulsive and attractive force patterns. The cross sections of polycrystalline CdS/CdTe and amorphous silicon heterojunction solar cells are observed with AFM. In case of short circuit, the microstructures of different layers in the samples are clearly displayed. When the cells are open circuit, the topographical images are altered, the potential outline due to the space charge in junction region is observed. Obviously, AFM can be employed to investigate experimentally built-in potential in junction of semiconductor devices, such as solar cells.     

Double modulated differential THz-TDS for thin film dielectric characterization

Terahertz differential time-domain spectroscopy (DTDS) is a new technique that uses pulsed terahertz radiation to characterize the optical properties of thin dielectric films. Characterizing thin films in the GHz to THz range is critical for the development of new technologies in integrated circuitry, photonic systems and micro-electro-mechanical systems. There are potential applications for gene and protein chips. This paper shows how DTDS can be combined with double modulation in the pump-probe system to improve sensitivity by an order of magnitude. An iterative algorithm is presented to estimate the optical properties of a given thin film. The technique is experimentally verified using 1-μm-thick samples of silicon dioxide on silicon.     

Zirconium oxide post treated tin doped TiO2 for dye sensitized solar cells

Sn doped TiO₂ nanorods with 0.1, 0.25%, 0.5% and 1% dopant compositions were grown by sol-gel and hydrothermal method. Synthesized Sn doped TiO₂ nanorods were post treated with Zr and HNO₃ and used as photo anode in DSSC with Ru dye and dye extracted from leaves of Camellia sinensis. The PCE of 1% Sn doped TiO₂ photo anode sensitized with Ru dye comparatively showed a better conversion efficiency of 4.96%. 1% Sn doped TiO₂ nanorods post treated and acid treated with Zr and HNO₃ sensitized with leaves of Camellia sinensis showed better PCE than untreated Sn doped TiO₂ photo anode. Increasing the oxygen vacancy by raising the dopant composition with low difference between successive levels improves the photocatalytic performance of the cell. The post treatment of zirconia and HNO₃ treatment enhances the photovoltaic parameters toward better performance of the cell. The synergistic effect of introduction of surface defects due to doping, surface modification by post treatment, retarding electron–hole recombination and protonation of the surface with acid treatment enhanced the efficiency of 1% Sn doped TiO₂ nanorods and it can be considered as a potential photo anode for DSSC.     

Threshold Reduction in Polymer Lasers Based on Poly(9,9‐dioctylfluorene) with Statistical Binaphthyl Units

We introduce novel statistical copolymers of poly(9,9‐dioctylfluorene), PFO, which contain various concentrations of 6,6′‐(2,2′‐octyloxy‐1,1′‐binaphthyl) spacer groups. We demonstrate that, owing to the large dihedral angle (> 60°) between neighboring naphthalene units, we could hinder the formation of the highly ordered β‐phase in thin films of the copolymers. In low‐temperature photoluminescence measurements, the typical signature of the PFO β‐phase at 442 nm is no longer observed for copolymers with a binaphthyl concentration of about 12 %. Moreover, the optical properties of the copolymers resembled those of the glassy α‐phase PFO. Second‐order distributed feedback (DFB) lasers based on thin films of the homopolymer PFO showed a minimum lasing threshold of 11.7 μJ cm^–2 (λ_max = 452 nm, excitation at λ = 337 nm with 500 ps pulses). With increasing binaphthyl concentration in the copolymer backbone, the lasing threshold steadily decreased to 3 μJ cm^–2 for a binaphthyl concentration of about 12 %. Therefore, our novel copolymers provide a vast improvement for PFO‐based optoelectronics.     

Micro-Raman characterization of Germanium thin films evaporated on various substrates

We perform an extensive micro-Raman analysis of Germanium thin films physically evaporated on several substrates including silicon, silicon oxide and glass. We investigate the dependence of crystal quality on thin film deposition parameters such as substrate temperature and growth rate. We also study the continuous transitional change of the material structure from amorphous to crystalline phases. Ge films obtained by this simple and low cost technique are a viable solution towards the realization of virtual substrates and devices.     

Effect of the Microstructure and the Dopant Valence States on EL of ZnS Thin Film Devices

A systematic study of the effect of microstructure on the EL properties of ZnS:Er thin film devices fabricated by thermal evaporation was carried out using XRD, XPS and EL techniques. The experimental results indicate that the high brightness of the devices is attributed to the deposition growth of crystallites oriented in the (311), (400) directions. This can be explained by assuming a higher population of erbium being in the trivalent charge state in the (311), (400) planes of the films grown under certain deposition condition. It is concluded that only the part of rare earth dopant being in trivalent charge state in the film contributes to luminescence. The mechanism of the formation of luminescence center and the excitation of Er3+ ion by the electric field are discussed.     

Optically absorbing metallization

An electrode metallization is demonstrated that absorbs nearly all light incident upon it at specified wavelengths. This electrode may see application in reflective displays and spatial light modulators where stray light reflected off circuit metallization is deleterious. Reflection suppression of −35 dB is shown in a highly conductive metallization.     

Development and evolution of thin film microstructures: A Monte Carlo approach

A computer simulation procedure based on the Monte Carlo algorithm has been developed to study the thin film microstructure evolution in the Zone II regime. This is accomplished by letting the grain boundary movement on the film surface couple with the microstructure in the interior of the film. The grains when viewed in cross-section are found to reach a limiting size at which point all grain boundary motion ceases despite the presence of capillarity driving force. This results in a columnar morphology for the thin film. The cross-sectional size distribution function is found to be approximately log-normal in shape. The introduction of anisotropic solid-vapor interfacial energy is found to induce abnormal grain growth at the expense of the normal grain which has a relatively higher solid-vapor energy. An analytical model is proposed in which the formation of the columnar structure is explained in terms of the grain boundary drag at the growing interface due to sub-surface boundaries.     

薄膜介质材料特性参数的测试技术

在分析采用接触式电极测量薄膜介质材料特性参数所存在问题的基础上，介绍了一种非接触式电极的测量原理和方法，并提出水银探针电极的测试技术。     

基于MEMS的TiNi形状记忆合金薄膜研究进展

系统论述了近年来TiNi形状记忆合金(SMA)薄膜在MEMS技术中的应用研究。主要从该材料的特点在MEMS中的应用原理、制备技术方面进行了论述;探讨了MEMS技术中TiNi合金应用的关键技术、存在问题及发展前景。     

Plasma etching of ternary silicide top layers

Plasma etching of epitaxial CoSi₂ films with a ternary Co–Ti–Si top layer formed during solid phase reaction of Co/Ti bilayers on Si(100) was investigated. By using a pure argon-RF-plasma the ternary top layer was sputtered without formation of a disturbing overlayer. The main disadvantage of this process is the formation of a crater-like surface morphology connected with a strong increase of the surface roughness. Etching the ternary top layer by a reactive process (CF₄/Ar) leads to a smoother surface, but a Co–fluoride film was grown on top of the silicide surface. In a following argon etch process this disturbing overlayer can be removed completely, simultaneously the roughness of the etched silicide surface is reduced considerably.     

Microstructure,optical and magnetic properties of micro-crystalline γ-MnS film prepared by chemical bath deposition method

Micro-crystalline γ-MnS film was prepared by a cost effective low temperature chemical bath deposition method. The formation of wurtzite MnS was confirmed by X-ray diffraction and Raman measurements. The γ-MnS film exhibits a strong yellow emission band centered at 551 nm. First time, the magnetic property of γ-MnS film was investigated by superconducting quantum interference device magnetometer. The micro-crystalline γ-MnS film exhibits a paramagnetic behavior at low temperature. The data reported in this paper may be useful for rapid synthesis of γ-MnS film.     

Stress development during evaporation of Cu and Ag on silicon

This work presents results of stress measurements during deposition of thin silver and copper films on 100 μm Si substrate. The stress in thin films has been determined by means of an optical system for the measurement of sample’s curvature. This system was applied in situ in a high vacuum deposition system. For Ag films the stress occurring during deposition goes from a low compressive value to tensile for thickness less than 30 nm and to compressive above this. For Cu films we observe tensile stress for thickness less 20 nm and above 50 nm. The same general trend of stress evolution with thickness is present in all cases at initial stage. There is the same growth mode for Cu and Ag because of the similar shapes of stress curves for thickness lower than 30 nm The behavior of stress evolution was explained by island nucleation and growth, island coalescence and continuous film growth. The difference in the stress evolution above 30 nm is caused by the fact that silver may be less sensitive than copper to adsorption of impurities. Adsorbed contamination inhibits compressive stress increase generated by grain boundary and defects remaining in the film.     

Effect of Sb implantation on copper silicides formation and morphology after annealing of Cu/Si structures

In this work, the solid state reaction between a thin film of copper and silicon has been studied using Rutherford backscattering spectroscopy, X-ray diffraction, scanning electron microscopy and microprobe analysis. Cu films of 400 and 900 Å thicknesses are thermally evaporated on Si(1 1 1) substrates, part of them had previously been implanted with antimony ions of 5×10¹⁴ or 5×10¹⁵ at. cm⁻² doses. The samples are heat-treated in vacuum at temperatures in the range 200–700 °C for various times. The results show the growth and formation of Cu₃Si and Cu₄Si silicides under crystallites shape dispatched on the sample surface, independently of the implantation dose. On the other hand, it is established that the copper layer is less and less consumed as the antimony dose increases, resulting in the accumulation of Sb⁺ ions at silicide/Si interface and in the silicide layer close to surface. The exposure of samples to air at room temperature shows the stability of Cu₄Si phase whereas the Cu₃Si silicide disappears to the benefit of the silicon dioxide formation. The observed phenomena are discussed.