Transformation of Poly(dimethylsiloxane) into thin surface films of SiO x by UV/Ozone treatment. Part I: Factors affecting modification

UV/ozone treatment of poly(dimethylsiloxane) (PDMS) was used to produce thin surface films of SiO _x . Films of PDMS were applied by spin-coating onto gold-coated silicon wafers having (100) orientation. Characterization of the UV/ozone system was performed to map the spatial distribution of intensities of UV radiation. This mapping was used to ensure reproducible modification of films and to aid in the understanding of modification as measured by advancing contact angle using deionized water and x-ray photoelectron spectroscopy (XPS). Rutherford backscattering spectroscopy (RBS) was used to measure thickness of the PDMS films. Treatment reduced the wetting angle, in some cases from a value greater than 100° to a value less than 5°. High resolution XPS spectra were used to study the nature of the modified PDMS film and its relationship to the characteristics of the unmodified PDMS. High resolution XPS spectra in the Si 2p region show that O–Si–C bonds in the siloxane, observed prior to treatment, are converted to SiO _x , where x is between 1.6 and 2. Modified films also contain some oxidized carbon components. The time required to reduce the contact angle to a minimum value was greater for the thicker PDMS film samples. The effects of ozone alone (without UV) and UV radiation at 184.9 and 253.7 nm (without ozone) were also investigated. The results of UV/ozone treatment are compared to results achieved by means of plasma surface oxidation.     

Bottom electrodes dependence of microstructures and dielectric properties of compositionally graded (Ba1−xSrx)TiO3 thin films

Compositionally graded (Ba_1−xSr_x)TiO₃ (BST) thin films, with x decreasing from 0.3 to 0, were deposited on Pt/Ti/SiO₂/Si and Ru/SiO₂/Si substrates by radio frequency magnetron sputtering technology. The microstructure and dielectric properties of the graded BST thin films were investigated. It was found that the films on Ru electrode have better crystallization, and that RuO₂ is present between the Ru bottom electrode and the graded BST thin films by X-ray diffraction and SEM analysis. Dielectric measurement reveals that the graded BST thin films deposited on Ru bottom electrode have higher dielectric constant and tunability. The enhanced dielectric behavior is attributed to better crystallization as well as smaller space charge capacitance width and the formation of RuO₂ that is more compatible with the BST films. The graded BST films on Ru electrode show higher leakage current due to lower barrier height and rougher surface of bottom electrode.     

Effects of niobium content on electrical and mechanical properties of (Na0.85K0.15)0.5Bi0.5Ti(1-x)Nb x O3 thin films

(Na_0.85K_0.15)_0.5Bi_0.5Ti_(1-x)Nb _x O₃ (NKBT-N100x) thin films were deposited on Pt/Ti/SiO₂/Si(100) substrates by metal–organic decomposition method and annealed in oxygen atmosphere at 750 °C. The effects of niobium concentration on the microstructures, ferroelectric, piezoelectric, leakage current and mechanical properties of the NKBT-N100x (x = 0, 0.01, 0.03, 0.05) thin films have been investigated in detail. The NKBT-3N thin film has the largest remnant polarization (7 μC/cm²) and statistically averaged d _33eff (140 pm/V), the smallest leakage current, elasticity modulus (102.0 Gpa), hardness (5.1 Gpa) and residual stress (297.0 Mpa). The evaluation of residual stresses of these thin films will offer useful guidelines of safe working condition for their potential application in microelectromechanical system.     

Structure of post-annealed ferroelectric PbZrxTi1-xO3 and SrBi2Ta2O9 thin films

In order to fabricate good quality ferroelectric thin films, PbZr_xTi_(1-x)O₃ (PZT) and SrBi₂Ta₂O₉ (SBT) films were fabricated on SiO₂/Si(100) substrates and on Pt/Ti/ SiO₂/Si(100) substrates by pulsed laser excimer deposition (PLD). X-ray diffraction, Rutherford backscattering analysis, and atomic force microscopy were used to characterize the structural properties of the samples, which were post-annealed at different temperatures. The results showed that the PZT and SBT films fabricated on Pt/Ti/SiO₂/Si(100) substrates and annealed at 700 °C exhibited optimum properties.     

Nanoindentation stress-strain curves of plasma-enhanced chemical vapor deposited silicon oxide thin films

Plasma-enhanced chemical vapor deposited (PECVD) silicon oxide (SiO_x) thin films have been widely used in Micro/Nano Electro Mechanical Systems to form electrical and mechanical components. In this paper, we explore the use of nanoindentation techniques as a method of measuring equivalent stress-strain curves of the PECVD SiO_x thin films. Four indenter tips with different geometries were adopted in our experiments, enabling us to probe the elastic, elasto-plastic, and fully plastic deformation regimes of the PECVD SiO_x thin films. The initial yielding point (σ_I) and stationary yielding point (σ_II) are separately identified for the as-deposited and annealed PECVD SiO_x thin films, as well as a standard fused quartz sample. Based on the experimental results, a shear transformation zone based amorphous plasticity theory is applied to depict the plastic deformation mechanism in the PECVD SiO_x.     

Effects of annealing atmosphere and substrate on the photoluminescence and Raman scattering from Si nanocrystals in a SiO2 matrix

Thin films of SiO _x have been prepared on quartz or c-Si substrates by thermal evaporation of SiO in vacuum and post-annealed at 1373 K in an argon or hydrogen atmosphere. High-resolution electron microscopy has shown the existence of silicon nanocrystals in the annealed films, and this result has been confirmed by Raman scattering. Photoluminescence has been observed from annealed films and attributed to radiative recombination in Si nanocrystals. Its intensity is appreciably higher upon annealing in Ar than in H₂. It is shown that substrates strongly affect the Raman scattering from Si nanocrystals in nc-Si–SiO₂ thin films with low filling factors.     

Effect of the interface on the electrical properties of an indium zinc oxide/SiOx multilayer

In this work, indium zinc oxide (IZO) films have been deposited on a polyethylene terephthalate substrate coated with an SiO_x film. Based on a comparative investigation of an IZO monolayer and an IZO/SiO_x multilayer, it is shown that oxygen has a great effect on the electrical properties of the thin films. A mechanism is described to explain the influence of the introduced SiO_x buffer layer. It is considered that an interfacial layer has come into being at the interface between the SiO_x layer and IZO layer, and the properties of this layer have been evaluated. Moreover, the electrical properties of the IZO/SiO_x multilayer have been successfully improved by controlling the oxygen content of the interfacial layer.     

Ion beam synthesis of the diamond like carbon films for nanoimprint lithography applications

Ion beam deposited hydrogenated undoped as well as SiO_x (SiO_x + N₂, SiO_x + Ar) doped DLC thin films were deposited and evaluated as possible anti-adhesive layers for nanoimprint lithography. Film surface contact angle with water was investigated as a measure of the surface free energy and anti-sticking properties. Contact angle of the DLC films was independent of SiO_x doping and ion beam energy. Air-annealing resistance in terms of the contact angle with water of the synthesized diamond like carbon films was investigated. Optical transmittance spectra of the DLC films in UV-VIS range were measured to investigate it as possible anti-sticking layers for UV imprint lithography applications. DLC films with the most promising combination of the UV absorption and anti-sticking properties were revealed. Preliminary imprint tests with uncoated and thin DLC film coated hot imprint stamps were performed.     

Optical and electrical properties of 2 wt.% Al2O3-doped ZnO films and characteristics of Al-doped ZnO thin-film transistors with ultra-thin gate insulators

Al-doped ZnO (AZO) thin films have been prepared on the c-Si oriented direction of (100) and glass substrates, by radio frequency magnetron sputtering from ZnO-2 wt.% Al₂O₃ ceramic targets. The effects of the working pressure on the optical and electrical properties of the films have been studied. The optical properties, measured by the ultraviolet-visible system, show that the transmittance and optical bandgap energy are influenced by the working pressure. The Hall resistivity, mobility, and carrier concentration were obtained by a Hall measurement system and these parameters were also influenced by the working pressure. The AZO thin-film transistors (TFTs) were fabricated on highly doped c-Si substrates. The TFT structures were made up AZO as the active layer and SiO_xN_y/SiN_x/SiO_x as the gate layer with 20 nm and 35 nm thickness, respectively. The ultra-thin TFTs had an on/off current ratio of 10⁴ and a field-effect mobility of 0.17 cm²/V·s. These results show that it is possible to fabricate an AZO TFT that can be operated with an ultra-thin gate dielectric.     

Reactive pulse magnetron sputtered SiOxNy coatings on polymers

Amorphous SiO₂, Si₃N₄ and SiO_xN_y single layers have been deposited on silicon, glass and glycol modified polyethylene terephthalate substrates by reactive pulse magnetron sputtering. Apart from the expected correlation between refractive index, coating density and nitrogen content in the reactive gas mixture further results have been found regarding mechanical stress and the humidity barrier property of these thin films. The lowest compressive stress was observed in the coatings deposited with nitrogen contents of around 30% to 50% in the reactive gas mixture. The humidity barrier effect of the thin films already begins to increase significantly at low nitrogen contents of below 20% in the reactive gas. Additional investigations regarding chemical composition, coating adhesion and environmental stability complement this work with the main focus on optimizing these materials for optical multilayer systems on polymer substrates.     

Structural and photoluminescence investigation of ZnSe nanocrystals dispersed in organic and inorganic matrices

In this work, we report on the investigation of the effect of dispersion of zinc selenide (ZnSe) nanocrystallites into polystyrene (PS) and silica (SiO₂) thin films on their structural, morphological and photoluminescence properties. The ZnSe/PS nanocomposites thin films were synthesized by a direct dispersion of ZnSe crystallites into polymers solution, whereas the ZnSe–SiO₂ films were prepared on glass substrates by the sol–gel dip-coating technique. X-ray diffraction (XRD), Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-rays (EDX), UV–visible spectrophotometry and photoluminescence spectroscopy (PL) techniques have been used to study the structural, morphological and optical properties of the prepared nanocomposite thin films. XRD patterns have demonstrated the incorporation of cubic ZnSe in both organic and inorganic matrices. SEM micrographs have indicated that ZnSe dispersion in the films is homogeneous. UV–visible absorption spectra of the nanocomposite thin films have put into evidence that the dispersion of ZnSe nanocrystals in the thin film matrices improved their optical absorption. Room temperature PL spectra have shown that the addition of ZnSe enhanced the UV emission of PS and all the emission of SiO₂ thin films.     

Preparation and characterization of Ba1 − xSrxTiO3 thin films deposited on Pt/SiO2/Si by sol-gel method

BST thin films have been investigated as potential candidates for use in frequency agile microwave circuit devices. Stoichiometric (Ba_1 − xSr_x)TiO₃ (BST) thin films have been prepared on Pt/SiO₂/Si substrates using sol-gel method. The BST films were characterized by X-ray fluorescence (XRF) spectroscopy analysis, X-ray diffraction (XRD), scanning electron microscope (SEM) and electrical measurements. The relationships of processing parameters, microstructures, and dielectric properties are discussed. The results show that the films exhibit pure perovskite phase through rapid thermal anneal at 700 °C and their grain sizes are about 20-40 nm. The dielectric constants of BST5, BST10, BST15 and BST20 are 323, 355, 382 and 405, respectively, at 80 kHz.     

Characterisation of SiOxCyHz thin films deposited by low-temperature PECVD

SiO_xC_yH_z thin films were deposited from hexamethyldisiloxane (HMDSO)/O₂ mixtures in a parallel plate, capacitively coupled, RF plasma reactor. Polyethylene terephthalate (PET), Si(1 0 0) wafers and KBr tablets were chosen as substrates. Effect of HMDSO/O₂ ratio, total treatment pressure and power input on the properties of the deposited films were investigated. The structure and bondings were studied by means of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Wettability characteristics of the deposited thin films were investigated by means of water droplet contact angle measurements. Surface morphology was investigated with atomic force microscopy. Barrier properties of the SiO_xC_yH_z thin films were investigated by measuring the water vapour transmission rate of the coated PET substrates. Correlations between the characteristics of the deposited film and their barrier properties were discussed.     

Effect of the orientation on the ferroelectric-antiferroelectric behavior of sol-gel deposited (Pb,Nb)(Zr,Sn,Ti)O3 thin films

The (Pb,Nb)(Zr,Sn,Ti)O₃ (PNZST) antiferroelectric thin films were prepared on two different substrates by sol-gel methods. Films derived on the LNO/Pt/Ti/SiO₂/Si substrates showed a strong (100) preferred orientation. The dependence of electrical properties derived on the Pt/Ti/SiO₂/Si and LNO/Pt/Ti/SiO₂/Si substrates have been studied, with the emphasis placed on field-induced phase switching from the antiferroectric to the ferroelectric state. The PNZST thin films deposition on two kinds of substrates show different phase transition behavior and associated properties such as antiferroelectric (AFE) to ferrroelectric (FE) switching field E_AFE-FE, FE to AFE switching field E_FE-AFE and the hysteresis ΔE=E_AFE-FE−E_FE-AFE.     

SiOx-doped DLC films: Charge transport, dielectric properties and structure

In the present study, SiO_x-doped diamond-like carbon (DLC) films were synthesized by ion beam deposition on different substrates. Electrical properties, morphology and structure of the DLC films were investigated. Poole-Frenkel emission was the main carrier transport mechanism in all investigated metal-SiO_x-doped DLC-metal samples. Dielectric properties of the samples were dependent on both the bottom and top electrode metal. The trans-polyacetylene chain vibrations detected from the Raman spectra have been observed for all the SiO_x-doped DLC films. Different dielectric properties of the film deposited onto the different metal interlayers were explained both by different roughness of the metal films and by different structure of the ion beam-synthesized SiO_x-doped DLC films.     

Nanograins dependent dielectric constant, tunability, phase transition, impedance spectroscopy and leakage current of (Pb1 − xSrx)TiO3 thin films

Nanostructured (Pb_1 − xSr_x)TiO₃ (PST) (x = 0.1, 0.2 and 0.3) thin films have been prepared by chemical solution deposition process using spin coating technique. The solution as such was deposited on Pt/Ti/SiO₂/Si substrates and annealed at 650 °C/3h. Nanograins dependent dielectric properties of PST films show dielectric constant up to the higher frequency region, low losses, large tunability and phase transition at small temperature. The impedance data has been fitted by Cole-Cole model to study the effect of grain boundaries on the dielectric properties. The current-voltage characteristics have been measured to study leakage current in PST films and described by Poole-Frenkel emission model. It is suggested that the key carrier transport process in PST films is emission of electrons from a trap state near the metal-film interface into a continuum of states associated with each conductive dislocation. The activation energy value for carrier transport in PST films is obtained from temperature-dependent current-voltage characteristics.     

The structure and ferromagnetic properties of (Fe0.12CuxZn0.88−x)O thin films deposited on Si substrates by R.F. sputtering

Fe–Cu co-doped ZnO thin films deposited on silicon substrates were prepared by R.F. magnetron sputtering. The effects of various amounts of copper on the microstructure, surface morphology, composition, and magnetic properties of ZnO thin films were examined. The results of the experiments show that the structures of the ZnO thin films grown on the silicon substrate have a preferred orientation of (002). By increasing the copper concentration, the Fe ions exist as Fe²⁺ in the Fe_0.12Cu_xZn_0.88−xO system, but Cu²⁺ and Cu¹⁺ ions coexist when the Cu replaces the Zn. In addition, the ZnO thin films show ferromagnetic behaviour at room temperature and the largest saturation magnetization (Ms) is 5.64 × 10⁴ A/m for the as-grown Fe_0.12Cu_0.02Zn_0.86O thin film.     

Compositionally graded Pb(Zr,Ti)O3 thin films with different crystallographic orientations

Compositionally graded ferroelectric PbZr_xTi_1−xO₃ (PZT) films were deposited using a sputtering method and crystallized in situ at 500 °C. The films showed purely (100) or (111) crystallographic orientation when grown on Si/SiO₂/TiO₂/Pt substrates, while they exhibited c-axis epitaxial microstructure when prepared on MgO/Pt substrates. Their crystallographic orientation was controlled owing to a thin TiO_x layer sputtered on substrates prior to PZT deposition. Analysis performed by Auger depth profile clearly confirmed the variation of composition in the films. Coercive fields from 80 kV/cm to 200 kV/cm and remnant polarization as large as 45 μC/cm² were obtained. However, no typical offset was observed on hysteresis loops, unlike previous works related to graded PZT films.     

Characterization of the Polarity Dependent Memory and Switching effect in sandwiches of metal/a-Si/ITO

The Polarity Dependent Memory and Switching effect (PDMS) has been observed in sandwiches of metal/a-Si/ITO layers and metal/a-Si/In. The film composition has been analysed by Auger Electron Spectroscopy and peak heights of the metals, Si and SiO_x have been measured as a function of film depth. No penetration of electrode material into the a-Si film was observed and the interfaces were abrupt even after many cycles of switching. A mechanism based on dendrite formation does not therefore operate in this type of PDMS. Traces of SiO_x have been found at the ITO/a-Si interface which are attributed to the presence of ITO or the deposition of In after exposure of a-Si to air. The SiO_x layer appears only in the OFF state and not in the ON state of the device. Hence a model based on voltage formation and destruction of an approximately 500 Å thick SiO_x layer at the a-Si/ITO interface is given.     

Preparation and electric characteristics of gadolinium-substituted bismuth titanate ferroelectric thin films

Gadolinium-substituted bismuth titanate (Bi_4 − xGd_xTi₃O₁₂, BGT) thin films were deposited on the (111)Pt/Ti/SiO₂/(100)Si substrates by a modified Sol–Gel process. With the aid of X-ray diffraction (XRD), the structure and appropriate Gd-substituted content x of BGT thin films were detected. The surface quality of the films was measured by means of an atomic force microscope (AFM) in tapping mode. The surface of BGT thin films was smooth and the phase was homogeneous. The ferroelectric properties of the films were investigated. When the Gd-substituted content x was equal to 0.75, the remanent polarization was the largest. The remanent polarization 2Pr value was equal to 15.4 μC/cm² and the coercive field Ec value was 54.17 kV/cm.