Intermediate Oxide Layer Research Articles

Amorphous-to-crystalline transition of silicon-incorporated anodic ZrO2 and improved dielectric properties

Sputter-deposited zirconium and Zr–16 at.% Si alloy have been anodized to various voltages at several formation voltages in 0.1 mol dm−3 ammonium pentaborate electrolyte at 298 K for 900 s. The resultant anodic films have been characterized using X-ray diffraction, transmission electron microscopy, Rutherford backscattering spectroscopy, glow discharge optical emission spectroscopy, and electrochemical impedance spectroscopy. The anodic oxide films formed on Zr–16 at.% Si are amorphous up to 30 V, but the outer part of the anodic oxide films crystallizes at higher formation voltages. This is in contrast to the case of sputter-deposited zirconium, on which the crystalline anodic oxide films, composed mainly of monoclinic ZrO2, are developed even at low formation voltages. The outer crystalline layer on the Zr–16 at.% Si consists of a high-temperature stable tetragonal phase of ZrO2. Due to immobile nature of silicon species, silicon-free outermost layer is formed by simultaneous migrations of Zr4+ ions outwards and O2− ions inwards. An intermediate crystalline oxide layer, in which silicon content is lower in comparison with that in the innermost layer, is developed at the boundary of the crystalline layer and amorphous layer. Capacitances of the anodic zirconium oxide are highly enhanced by incorporation of silicon due to reduced film thickness, even though the permittivity of anodic oxide decreases with silicon incorporation.

Residual Stress Relaxation Induced by Mass Transport Through Interface of the Pd/SrTiO3

Metal interconnections having a small cross-section and short length can be subjected to very large mass transport due to the passing of high current densities. As a result, nonlinear diffusion and electromigration effects which may result in device failure and electrical instabilities may be manifested. Various thicknesses of Pd were deposited over SrTiO3 substrate. Residual stress of the deposited film was evaluated by measuring the variation of d-spacing versus sin2ψ through conventional X-ray diffraction method. It has been found that the lattice misfit within film and substrate might be relaxed because of mass transport. Besides, the relation between residual intrinsic stress and oxygen diffusion through deposited film has been expressed. Consequently, appearance of oxide intermediate layer may adjust interfacial characteristics and suppress electrical conductivity by increasing electron scattering through metallic films.

Oxide layer dissolution in Si/SiOx/Si wafer bonded structures

AbstractThe evolution of the interfaces of hydrophilic‐bonded Si wafers and the corresponding low‐angle twist boundary have been analysed in relation to thermal annealing and their relative crystallographic orientation. Two orientation relationships were investigated: Si<001>/Si<001> and Si<001>/Si<110>, where the interfaces are seperated by thin native SiO2 layers. The interfaces were analysed by TEM and STEM/EELS. It is found that the decomposition rate of the intermediate oxide layer and the formation of a Si(Si bonded interface depend very much on the lattice mismatch and on the twist angle. The velocity of the dissolution of the thin oxide layers and the formation of Si(Si bonds at the bonding interface depend on the orientation relations of the corresponding wafers. The processes of interface fusion and the dissolution of oxide layer are discussed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural and mechanical properties of titanium oxide thin films for biomedical application

Titanium oxide thin films were deposited by radiofrequency reactive sputtering in Ar–O 2 atmosphere on silicon (100) wafers and titanium alloy plates (Ti-6Al-4V). Thin films structural characterization was carried out by grazing incidence X-ray diffraction, atomic force microscopy, scanning and transmission electron microscopies. Chemical composition was checked by X-ray wavelength dispersive spectroscopy. Mechanical assessment was achieved by nano-indentation and nano-scratch measurements. The films deposited on silicon substrates are over-stoechiometric in oxygen, with an oxygen to titanium ratio of about 2.2. The growth of anatase and rutile phases was promoted by ranging the total and oxygen partial pressures between 0.17–1.47 Pa and 35–85%. The growth rate of films, determined by grazing incidence X-ray reflectivity, was ranging from 35 to 55 nm/h. The rutile single-phased films possess a hardness of about 2.5 times higher and a lower friction coefficient than the anatase films. The films which contain anatase possess a high surface root-mean-square roughness and a reduced elastic modulus of around 120 GPa close to reduced elastic moduli of hydroxyapatite bioceramic and titanium alloy. So the anatase film could be the best candidate as a titanium oxide intermediate layer between hydroxyapatite and titanium alloy in the field of biomedical implants.

Dislocation structure in interfaces between Si wafers with hybrid crystal orientation

AbstractDislocation structure in Si(110)/Si(001) wafer bonding (WB) structures have been studied by transmission electron microscopy (TEM). The behavior of intermediate native oxide layers during high temperature annealing, the nature of interfacial dislocations and dislocation generation mechanisms are the main issues of this work. Samples were fabricated by direct hydrophilic WB of 200 mm wafers with native oxide. The as‐bonded structures containing 140‐nm thick layers were thermally annealed in the temperature range 1150 to 1200 °C. The dislocation structure composed of a pattern of unidirectional parallel but broken dislocation arrays is formed in the structures with partial or entire dissolution of the oxide layer. The contrast of broken dark lines usually observed in TEM bright field micrographs is supposed to be caused by integral effect of steps compensating twist misorientation and arrays of 60‐degree dislocations. We suggest that nucleation of dislocation loops at the interface due to the agglomeration of intrinsic point defects is a plausible mechanism of dislocation generation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High-Temperature Stability of Palladium Membranes on Porous Metal Supports with Different Intermediate Layers

The effectiveness of intermediate layer to prevent intermetallic diffusion is a key factor for application of Pd membranes on porous stainless steel (PSS) support. In this work, electroless-plated Pd membranes were prepared on PSS disks with two different intermediate layers: in situ oxidized metal oxide and sol−gel derived mesoporous yttria stabilized zirconia (YSZ). A thinner, gastight Pd layer can be formed on PSS support with the YSZ intermediate layer, resulting in a higher hydrogen permeance than Pd membranes on PSS support with the in situ oxidized metal oxide intermediate layer. High temperature permeation and 100-h stability tests showed that both intermediate layers were effective as the diffusion barrier for Pd membranes on PSS supports in the temperature range of 773−873 K. At temperatures above 873 K, only the YSZ intermediate layer is effective in preventing intermetallic diffusion and gives a stable Pd membrane. At the elevated temperatures Pd membranes on PSS support with in situ oxidation layer suffer from a chemical and mechanical stability problem due to reduction of metal oxides in hydrogen atmosphere which results in intermetallic diffusion and possibly weakens the adhesion of the Pd layer on PSS support.

Cyclic oxidation of Cr2AlC between 1000 and 1300°C in air

Abstract Fully dense, monolithic ternary Cr2AlC compounds were synthesized via a powder metallurgical route, and their cyclic oxidation behavior was investigated between 1000 and 1300 °C in air for up to 100 h. At 1000 and 1100 °C, Cr2AlC displayed excellent cyclic oxidation resistance by forming a less than 5 μm-thick Al2O3 oxide layer and a narrow Cr7C3 underlayer. At 1200 and 1300 °C, an outer (Al2O3, Cr2O3)-mixed oxide layer, an intermediate Cr2O3 oxide layer, an inner Al2O3 oxide layer, and a Cr7C3 underlayer formed on the surface. From 1200 °C, scale cracking and spalling began to occur locally to a small extent. At 1300 °C, the cyclic oxidation resistance deteriorated owing to the formation of voids and the spallation of the scales.

Cathodic electrophoretic deposition of barium titanate films from aqueous solution

Cathodic electrophoretic deposition (EPD) of barium titanate from aqueous suspensions was performed on nickel substrate. Cathodic deposition allows preparation of thin layers from aqueous solution on base metal electrodes, such as Ni or Cu, without creating an intermediate oxide layer during the deposition. This opens the opportunity to prepare complex shapes of dielectric layers onto base metals for co-firing, using relatively cheap and environmentally benign aqueous EPD. Stable barium titanate colloidal suspension with a concentration of 10 g/100 mL at pH of 9.2 has been prepared for the deposition. The characteristics of electrophoretic deposition of those positively charged particles onto cathode were investigated. A uniform and dense layer was obtained for films deposited at 3 V for 2 min. The calculated film thickness for the sintered layer at these conditions was ∼1 μm. The morphology can be controlled, and in particular the pore size and distribution can be controlled via the applied voltage. At low voltage a uniform layer can be obtained whereas at high voltage a large number of macropores appears in the deposit and their size increase with the increasing of the voltage due to gas bubble formation.

High efficiency protocrystalline silicon/microcrystalline silicon tandem cell with zinc oxide intermediate layer

The authors develop a hydrogenated protocrystalline silicon (pc-Si:H)/hydrogenated microcrystalline silicon (μc-Si:H) double-junction solar cell structure employing a boron-doped zinc oxide (ZnO:B) intermediate layer. Highly stable intrinsic pc-Si:H and μc-Si:H absorbers are prepared by a 60MHz very-high-frequency plasma-enhanced chemical vapor deposition technique. Degenerate ZnO:B intermediate and back reflectors are deposited via a metal organic chemical vapor deposition technique. Because the ZnO:B intermediate layer reduces the potential thickness for the pc-Si:H absorber in the top cell, this double-juncion structure is a promising candidate to fabricate highly stable Si-based thin-film solar cells. Consequently, the high conversion efficiency of 12.0% is achieved.

Cubic InN growth on sapphire (0001) using cubic indium oxide as buffer layer

Cubic InN layers were grown by molecular beam epitaxy on buffer layers of indium oxide prepared onto sapphire (0001) substrates. The structure was analyzed by means of electron diffraction and transmission electron microscopy. The intermediate indium oxide layer presents a body centered cubic (bcc) structure, with bcc-In2O3(001)‖Al2O3(0001) plane relationship. Thereupon, a zinc-blende phase of InN (001) was grown with a reticular misfit of 1.6% and a significant reduction of mismatch-related defects. This good coherence offers a promising expectation to obtain high quality cubic InN layers superior to other highly mismatched cubic substrates used previously.

Layered WO3/ZnO/36° LiTaO3 SAW gas sensor sensitive towards ethanol vapour and humidity

Ethanol sensing in dry and humid air by layered surface acoustic wave (SAW) devices is presented. The transducing platform is based on 36° YX LiTaO3 layered SAW device, utilising a 1.2μm zinc oxide (ZnO) intermediate layer and 150nm tungsten trioxide (WO3) sensing layer. Sheet conductivity calculations show that maximum sensitivity is achieved for ZnO layer thickness between 1 and 1.5μm. Sensor performance was analyzed in terms of response magnitude as a function of operational temperature and different relative humidity (RH). Frequency shifts of 119, 90 and 86kHz towards 500ppm of ethanol in synthetic air were observed for 0, 25 and 50% RH, respectively. All RH levels were measured at 20°C. At an operating temperature of 300°C, the largest response towards 500ppm of ethanol was observed. Response magnitude was found to decrease with increasing RH and decreasing operating temperature. Furthermore, the effect of elevated temperatures on the sensors surface morphology is characterised by AFM and SEM techniques. It is suggested that the morphological modifications, due to elevated temperatures play an important role in the sensing behaviour of the WO3 films.

Strained-Silicon on Silicon and Strained-Silicon on Silicon-Germanium on Silicon by Relaxed Buffer Bonding

We report the creation of two novel complementary metal oxide semiconductor (CMOS)-compatible platforms: strained-silicon on silicon (SSOS) and strained-silicon on silicon-germanium on silicon (SGOS). SSOS substrate has an epitaxially defined, strained-silicon layer directly on silicon wafer without an intermediate SiGe or oxide layer. SSOS is a homochemical heterojunction, i.e., a heterojunction defined by strain state only and not by an accompanying compositional change. SGOS has an epitaxially defined SiGe layer between the strained-silicon channel and the Si substrate, which may prove necessary to prevent excessive off-state leakage in metal oxide semiconductor (MOS) devices due to overlap of source-drain contacts and the interfacial misfit array

Wafer bonding for high-brightness light-emitting diodes via indium tin oxide intermediate layers

A direct wafer-bonding technique has been used to fabricate high-brightness light emitting diodes (LEDs). However, bonding processes were usually performed at elevated temperatures, possibly causing degradation in the quality of the LED structure. In addition to this, misorientation between the two bonded wafers may have caused defects between the wafers. In this study, these two problems were solved by bonding the InGaP/GaAs and GaAs wafers with an indium tin oxide (ITO) polycrystalline film at temperatures below 650 °C. It was found that the bonding occurred mainly through the In transport from the InGaP to ITO, and that the electrical resistance decreased with the bonding temperature.

Towards intersubband quantum box lasers: Electron-beam lithography update

We report on the progress in the patterning and fabrication of the intersubband quantum-box (QB) laser structure. From a patterning point of view our goal is to make 30-nm-diameter SiO2 and/or hydrogen silsesquioxane (HSQ) disks on 60–80nm centers on a GaAs surface to serve as masks for in situ etch and regrowth of QBs. Electron-beam lithography with high-resolution negative resist HSQ was used, and two processes have been investigated. The first process is to pattern HSQ directly on the GaAs surface, while the second one involves putting down an intermediate oxide layer first, followed by the e-beam lithography and the transfer of the pattern into the oxide. Problems were encountered with the e-beam patterning of HSQ directly on the GaAs surface because of the broad scattering from the substrate and not very good adhesion. Excellent patterning was demonstrated when the intermediate oxide layer was present between the GaAs substrate and the HSQ resist.

Metal organic chemical vapor deposition of Al 2O 3 and Cr 2O 3 on nickel as oxidation barriers

Aluminum oxide and chromium oxide were deposited onto untreated and pre-oxidized Ni coupons by metal–organic chemical vapor deposition. Oxidizing the surface prior to the deposition of the ceramic coating has been studied to determine the effect of the intermediate oxide layer. The metal oxide coatings were obtained from their respective metal acetylacetonate precursors. The pyrolysis reactions were carried out under atmospheric conditions. Amorphous Al 2O 3 was obtained at a deposition temperature of 500 °C and crystalline Cr 2O 3 with the corundum structure was obtained at 450 °C. The effectiveness of the metal oxide coatings as barriers were evaluated by oxidation experiments at 800 °C for 120 h. Samples coated with Al 2O 3 exhibited a significant decrease in oxidation rate. However, Cr 2O 3 coated on both untreated and pre-oxidized samples were not effective barrier coatings. Samples involving Cr 2O 3 deposited on untreated Ni showed an increase in oxidation rate whereas samples with Cr 2O 3 on heat-treated Ni showed a similar oxidation rate as uncoated Ni. The microstructures were investigated with scanning electron microscopy. Composition and crystalline structures were determined with X-ray diffraction and elemental analysis.

Improvement of interfacial adhesion of Al/Cr films deposited on indium tin oxide coated glasses by interfacial oxidation

Metallization of aluminum (Al)/chromium (Cr) composite thin metal film on indium-tin-oxide (ITO) coated glass has been carried out to improve the bondability of optoelectronic devices. In this study, we have introduced various amounts of oxygen at the Cr/ITO interface during the early stage of Cr deposition to form the intermediate oxide layer, which enhances interfacial adhesion strength between Cr/ITO. The results show that the adhesion strength is increased as the flow rate of oxygen increases. Maximum improvement occurs as the flow rate of oxygen reached 6 standard cubic centimeter/minute (sccm), which is dependent on the chemical composition and interphase boundary structure of Cr/ITO interface. The interfacial layer thickness and chemical composition of metal/oxide interface have been analyzed by the Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The results indicate maximum improvement of adhesion strength is probably due to the presence of higher thickness of interfacial Cr 2O 3 oxide contained strong oxide-to-oxide bonding on the interface of Cr/ITO surface.

Scaling limits of hafnium–silicate films for gate-dielectric applications

The scaling limits of hafnium–silicate (Hf–silicate) films for use as the gate dielectric material in complementary metal–oxide–semiconductor field-effect transistors are investigated. Scalability is gauged by a figure of merit taken from the analytical model for direct tunneling leakage current. Based on the compositional dependence of this figure of merit, pure HfO2 is more scalable than Hf–silicates. However, the formation of intermediate oxide layers at the Si interface can limit the scalability of HfO2 to ∼1.0 nm equivalent SiO2 thickness (EOT). The use of Si3N4 as a diffusion barrier can prevent the formation of these interfacial layers and thereby yield lower EOT. Alternatively, 20% Hf–silicate may be more scalable than pure HfO2 with interfacial oxide layers.

Enhanced adhesion and thermal stability of Al/Cr film on indium-tin-oxide (ITO)-coated glass

Metallization of indium-tin-oxide (ITO)-coated glass using an Al/Cr composite thin film is a common practice for chip-on-glass packaging. However, the reliability of the Cr/ITO interface is always a problem because of poor adhesion due to the chemical inertness of ITO. In this study, the adhesion strength between a Cr film and ITO coated glass was enhanced by forming an intermediate oxide layer at the interface. To find out the optimal interface condition, various amounts of oxygen were doped at the interface. The results show that the adhesion strength and thermal stability are both enhanced by the interfacial doping of oxygen. This enhancement is found to be related to the flow rate of oxygen and, therefore, to the oxide thickness. Maximum improvement occurs when the flow rate of oxygen is set at 6 sccm during doping, and at this rate the interface oxide thickness also reaches its maximum value. Under this condition, the Cr/ITO interface also shows the best thermal stability. Wire bond testing shows that the wire pull strength is affected by the thickness of Al film. The results of this study show that the Al film should not be thicker than 1 μm.

Fabry-perot-type antireflective coating for deep-ultraviolet binary photomask applications.

We demonstrate an antireflective coating structure, which is based on the three-layer metal interference called the Fabry-Perot structure, for a deep-ultraviolet binary mask. The antireflective coating structure is composed of a metal-oxide-metal stack. By addition of different optimized structures, reflectances of less than 1.5% at both 248 and 193 nm have been achieved. At the three-layer Fabry-Perot structure, the bottom chrome layer provides suitable absorption. By controlling the thickness of the intermediate silicon oxide layer, we can tune the minimum-reflection regime to the desired exposure wavelength. The top metal layer can prevent charge accumulation during e-beam writing.

Preparation and Characterization of Antiferroelectric PZT Thin Films on Steel Substrates Using Intermediate Oxide Layers

Antiferroelectric lead zirconate titanate PZT (95/5) has been prepared by chemical solution deposition using alkoxide precursor compounds and was spin-coated on metallic substrates of Hastelloy. In order to better adapt the substrate to the PZT and thus to improve the crystallization behavior of the PZT films, different interface layers have been studied. The annealing parameters have been optimized in the case of an intermediate RuO 2 layer. Other interface layers like indium tin oxide (ITO) or lanthanum strontium manganate (LSMO) can be compared to deposition of the PZT on Hastelloy and on platinum coated Hastelloy. Using conventional multi-coating technique, homogeneous antiferroelectric films of up to 2.5 w m thickness have been obtained.