Interlayer Deposition Research Articles

Circuits and AMOLED display with self-aligned a-IGZO TFTs on polyimide foil

A process to make self-aligned top-gate amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) on polyimide foil is presented. The source/drain (S/D) region's parasitic resistance reduced during the SiN interlayer deposition step. The sheet resistivity of S/D region after exposure to SiN interlayer deposition decreased to 1.5 kΩ/□. TFTs show field-effect mobility of 12.0 cm2/(V.s), sub-threshold slope of 0.5 V/decade, and current ratio (I ON/OFF) of >107. The threshold voltage shifts of the TFTs were 0.5 V in positive (+1.0 MV/cm) bias direction and 1.5 V in negative (-1.0 MV/cm) bias direction after extended stressing time of 104 s. We achieve a stage-delay of ~19.6 ns at V-DD = 20 V measured in a 41-stage ring oscillator. A top-emitting quarter-quarter-video-graphics-array active-matrix organic light-emitting diode display with 85 ppi (pixels per inch) resolution has been realized using only five lithographic mask steps. For operation at 6 V supply voltage (V-DD), the brightness of the display exceeds 150 cd/m2. A process to make self-aligned top-gate amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) is presented. TFTs show field-effect mobility of 12.0 cm2/(V.s), sub-threshold slope of 0.5 V/decade, and current ratio (I ON/OFF) of over 107. In applications, a 41-stage ring oscillator with a stage-delay of ~19.6 ns (at V-DD = 20 V) and a top-emitting quarter-quarter-video-graphics-array (QQVGA) active-matrix organic light-emitting diode (AMOLED) display with 85 ppi (pixels per inch) resolution using five lithographic mask steps have been realized on a polyimide foil. Copyright 2015 Society for Information Display.

On the hydrogenated silicon carbide (SiCx:H) interlayer properties prompting adhesion of hydrogenated amorphous carbon (a-C:H) deposited on steel

This work reports a systematic study of physical–chemical properties of SiCx:H interlayers deposited by using tetramethlysilane on AISI 4140 at different temperatures (100 °C–550 °C) and its effects on the adhesion of a-C:H thin films. The bi-layers were obtained by pulsed-DC PECVD assisted by electrostatic confinement. The results show that the thickness of the SiCx:H interlayer exponentially decreases as the deposition temperature increases, i.e., a thermally activated kinetic process controls the global chemical reaction in the interlayer. There is a transition temperature (∼300 °C) for interlayer deposition where adhesion of a-C:H is reached. Above ∼300 °C, the a-C:H thin films show critical loads to wedge spallation from 298 (300 °C) to 478 mN (550 °C). At higher temperatures, H and Si contents decrease whereas C content increases in the interlayer. The improved adhesion is associated with the nature of chemical bonds formed in the interlayer.

Nucleation and growth of CVD diamond on fused silica optical fibres with titanium dioxide interlayer

Nucleation and growth processes of thin diamond films on fused silica optical fibres have been investigated. Fibres were coated with diamond film using microwave plasma enhanced chemical vapour deposition (µPE CVD) system. Since the growth of diamond on the fused silica glass requires high seeding density, two types of glass pre‐treatment were applied: titanium dioxide (TiO2) interlayer deposition and sonication in nanodiamond suspension. In the experiment, high density, thin (∼20 nm) TiO2 films were deposited using high‐power impulse magnetron sputtering. Subsequently, a set of thin diamond films deposited in up to 60 min‐long process was investigated. Results obtained for the two pre‐treatment methods were compared. The nucleation processes were studied and compared using numerical analysis of scanning electron microscopy (SEM) images. The molecular structure of nucleated diamond was examined with micro‐Raman spectroscopy. The sp3/sp2 ratio was calculated using Raman spectra deconvolution method. Thickness, roughness and optical properties of the nanodiamond films in VIS–NIR wavelength range were investigated by means of spectroscopic ellipsometry. It was found that the high density TiO2 interlayer enhances CVD diamond film nucleation processes on fused silica and increases sp3/sp2 ratio of the film. The proposed growth method can be effectively applied in manufacturing of various types of optical fibre sensors. Due to high chemical and mechanical resistance of the diamond films such optical sensors are highly desired.

Enhanced Performance of Solution-Processed Organic Thin-Film Transistors with a Low-Temperature-Annealed Alumina Interlayer between the Polyimide Gate Insulator and the Semiconductor

We studied a low-temperature-annealed sol-gel-derived alumina interlayer between the organic semiconductor and the organic gate insulator for high-performance organic thin-film transistors. The alumina interlayer was deposited on the polyimide gate insulator by a simple spin-coating and 200 °C-annealing process. The leakage current density decreased by the interlayer deposition: at 1 MV/cm, the leakage current densities of the polyimide and the alumina/polyimide gate insulators were 7.64 × 10(-7) and 3.01 × 10(-9) A/cm(2), respectively. For the first time, enhancement of the organic thin-film transistor performance by introduction of an inorganic interlayer between the organic semiconductor and the organic gate insulator was demonstrated: by introducing the interlayer, the field-effect mobility of the solution-processed organic thin-film transistor increased from 0.35 ± 0.15 to 1.35 ± 0.28 cm(2)/V·s. Our results suggest that inorganic interlayer deposition could be a simple and efficient surface treatment of organic gate insulators for enhancing the performance of solution-processed organic thin-film transistors.

Enhanced microwave dielectric tunability of Ba0.5Sr0.5TiO3 thin films grown with reduced strain on DyScO3 substrates by three-step technique

Tunable dielectric properties of epitaxial ferroelectric Ba0.5Sr0.5TiO3 (BST) thin films deposited on nearly lattice-matched DyScO3 substrates by radio frequency magnetron sputtering have been investigated at microwave frequencies and correlated with residual compressive strain. To reduce the residual strain of the BST films caused by substrate clamping and improve their microwave properties, a three-step deposition method was devised and employed. A high-temperature deposition at 1068 K of the nucleation layer was followed by a relatively low-temperature deposition (varied in the range of 673–873 K) of the BST interlayer and a high-temperature deposition at 1068 K of the top layer. Upon post-growth thermal treatment at 1298 K the films grown by the three-step method with the optimized interlayer deposition temperature of 873 K exhibited lower compressive strain compared to the control layer (−0.002 vs. −0.006). At 10 GHz, a high dielectric tunability of 47.9% at an applied electric field of 60 kV/cm was achieved for the optimized films. A large differential phase shift of 145°/cm and a figure of merit of 23°/dB were obtained using a simple coplanar waveguide phase shifter at 10 GHz. The low residual strain and improved dielectric properties of the films fabricated using the three-step deposition technique were attributed to reduced clamping of the BST films by the nearly lattice-matched substrate.

Emission stability enhancement of a tip-type carbon-nanotube-based field emitter via hafnium interlayer deposition and thermal treatment

Carbon nanotubes (CNTs) were deposited on a tip-type tungsten substrate via electrophoretic deposition, in which a hafnium thin film was used as an interlayer. The long-term (up to 24 h) emission stability of the CNT-based field emitter was remarkably enhanced when the hafnium interlayer was coated and thermally treated. This is attributed to the enhanced adhesion between the substrate and the CNTs. An x-ray photoelectron spectroscopy study and nano-scratch measurement provided a convincing evidence of the increase in the adhesive force.

Structural and electrical properties of AlN films deposited using reactive RF magnetron sputtering for solar concentrator application

AlN is an interesting material with some excellent properties like high hardness (>11GPa), high temperature stability (>2400°C), good electrical resistivity (>1010Ωcm), and good thermal conductivity (>100W/mK). These properties make it useful in the field of photo voltaic systems. Cooling of solar cells in solar concentrator application is of major concern because high temperature reduces their efficiency. In the present work we deposited AlN coating, with and without an Al interlayer, on various substrates like Si, quartz, and copper using RF magnetron sputtering. Deposition conditions such as Al interlayer (deposition time=5–20min), Ar:N2 ratio (N2%=0–75%) and substrate bias (0 and −50V) were changed in order to study their effect on coating properties. Coating surface roughness increased from 0.05 to 0.15μm with increase in Al interlayer thickness. The coating thickness decreased from 4.4 to 3.1μm with increase in N2 gas % and films grew in (002) orientation. Films deposited on copper using Al interlayer showed good electrical resistance of ∼1013Ω. Films deposited on copper without Al interlayer showed presence of voids or micro cracks and poor electrical properties. AlN films deposited at −50V bias show cracking and delamination.

Effect of chromium interlayer deposition on periodic silver nanoparticle array structure fabricated by nanosphere lithography

Effect of chromium interlayer deposition on 2-dimensional, periodic silver nanoparticle array structure was systematically investigated. The silver nanoparticle array was fabricated by nanosphere lithography with assembled polystyrene nanospheres being as a deposition mask. The chromium interlayer was deposited by thermal evaporation either on the nanosphere mask or directly on the silicon substrate. The structures of the achieved silver nanoparticle arrays were characterized by scanning electron microscope and were compared with that of silver nanoparticle array without the interlayer. With analysis of the anomalies among the structures the critical role of the interlayer in the periodic nanoparticle array fabrication was revealed.

Fibrous Composites With Anisotropic Distribution of Mechanical Properties After Layer‐by‐Layer Deposition of Aligned Electrospun Fibers

AbstractNanofibers and composite nanofibers have been used as mechanical reinforcement in a bulk matrix, but there is little research done on bulk nanocomposites made out of nanofibers. In the current study, in situ grown composite fibers of poly(DL‐lactide) (PDLLA) and hydroxyapatite (HA) were obtained with uniaxial distribution, which were deposited by layer‐by‐layer with different interlayer angles, and hot‐pressed into fibrous composites with anisotropic distribution of mechanical properties. Composite fibrous mats with the HA loading of 25.2 ± 2.1% and orientation degree of 75.4 ± 3.6% were obtained. Orthogonal experiments design was employed to qualitatively analyze effects of the hot‐pressing parameters on the mechanical properties. The holding temperature, pressure, and duration were optimized as 60 °C, 2 MPa, and 10 min, respectively, to maintain the fibrous structure, strengthen the interfiber bondings, and eliminate the dimensional shrinkage of the hot‐pressed fibrous composites. The ultimate tensile strength along the axial direction was 36.2 ± 2.2 MPa, which was significantly higher than that along the transverse direction. Furthermore, the aligned composite fibers were deposited by layer‐by‐layer with different interlayer angles, and the quantitative equations of the ultimate tensile strength along the axial and transverse directions were drafted as a function of the interlayer deposition angles. The results of cell culture indicated that the presence of HA nanoparticles in the fibrous composites improved the hydrophilicity and provided favorable conditions for cell proliferation and osteogenic differentiation. It is suggested that hot‐pressed fibrous composites with anisotropic distribution of mechanical properties be potential as bone substitutes and repairing devices.

The stress reduction effect by interlayer deposition or film thickness for diamond like carbon on rough surface

The effects of thermal stress resulting from thermal cooling for diamond like carbon (DLC) films on a rough surface are investigated by a finite element analysis. Two different schemes, interlayer deposition (metallic interlayer, multi-interlayer, grade interlayer) and film thickness increase are proposed to relieve the stress. The results show that the film thickness and coefficient of thermal expansion (CTE) are critical in stress reduction for a single interlayer. The metallic interlayer is effective in stress reduction only if the CTE of the interlayer is between that of the substrate and the film. Grade interlayer can further reduce the stress if the plasticity is graded in the interlayer. The increase of film thickness can also reduce the thermal stress, even though it is not as effective as the interlayer approach.

Deposition of Hard and Adherent Diamond-Like Carbon Films Inside Steel Tubes Using a Pulsed-DC Discharge

A new, low cost, pulsed-DC plasma-enhanced chemical vapor deposition system that uses a bipolar, pulsed power supply was designed and tested to evaluate its capacity to produce quality diamond-like carbon films on the inner surface of steel tubes. The main focus of the study was to attain films with low friction coefficients, low total stress, a high degree of hardness, and very good adherence to the inner surface of long metallic tubes at a reasonable growth rate. In order to enhance the diamond-like carbon coating adhesion to metallic surfaces, four steps were used: (1) argon ion sputtering; (2) plasma nitriding; (3) a thin amorphous silicon interlayer deposition, using silane as the precursor gas; and (4) diamond-like carbon film deposition using methane atmosphere. This paper presents various test results as functions of the methane gas pressure and of the coaxial metal anode diameter, where the pulsed-DC voltage constant is kept constant. The influence of the coaxial metal anode diameter and of the methane gas pressure is also demonstrated. The results obtained showed the possibilities of using these DLC coatings for reduced friction and to harden inner surface of the steel tubes.

Highly spin-polarized electron photocathode based on GaAs–GaAsP superlattice grown on mosaic-structured buffer layer

We successfully developed a transmission-type photocathode, and a high polarization (90%) with a super-high brightness (1.3×10 7 A cm −2 sr −1) of electron beam was achieved. In this research, we found that the polarization of electrons from the GaAs–GaAsP superlattice on the GaP substrate was lower than that from the same superlattice on the GaAs substrate, and that a GaAs inter-layer deposition on the GaP substrate recovered that from the GaAs–GaAsP superlattice. Mechanism of the polarization degradation was investigated from a viewpoint of strain-relaxation process in the GaAsP buffer layer that was adopted between the superlattice and the substrates. The buffer layer with in-plain tensile strain was relaxed by inducing cracks, but that with in-plain compressive strain was relaxed by inducing dislocations. The dislocations may disturb the spin-polarization of electrons more effectively than the cracks do.

Phase and structure transformations in the titanium interlayer during the nickel silicidation on Si(1 0 0) substrate

Recently, promising results for epitaxial cobalt and nickel silicide formation have been obtained using a thin titanium interlayer and as a mechanism for such an interlayer promoting effect the removal of a native oxide from a silicon substrate due to the gettering effect of titanium was suggested. However, detailed information about transformations in the Ti layer during its growth and annealing process still lacks. In this paper, phase and structure transformations in the Ti interlayer during growth and consequent silicidation annealing are studied on the system Ni/Ti/Si(1 0 0). The Ni (4 nm)/Ti (1.4 nm) bilayers were deposited onto unheated (1 0 0) Si substrate with a native oxide layer by rf sputtering inside the AES – microscope and analyzed by in situ Auger electron spectroscopy, X-ray photoelectron spectroscopy and ex situ transmission electron microscopy. During the Ti interlayer deposition process a following sequence of the growth mechanism and phases were revealed. Initially, small 3D TiO 2 islands are formed due to reduction of a native silicon oxide followed by the formation of the TiO and TiO x phase between TiO 2 islands as well as on their top. During the silicidation annealing at 300 °C the continuous Ti-related interlayer, composed mainly (∼85%) of Ti oxides (TiO and TiO 2) transforms into less compact island-like TiO 2 layer what promotes Ni diffusion into silicon resulting in the nickel silicide, NiSi 2 formation.

Comparative study of mechanical properties of a-C:H films produced on tungsten pre-implanted stainless steel substrate by plasma immersion ion implantation and deposition

Amorphous carbon (a-C) films have good mechanical properties but poor adhesion on substrates such as tool steels limits its applications. In this work, a-C films were deposited by plasma immersion ion implantation and deposition (PIII&D) on steel substrates using different pretreatment procedures. Our experiments show that a-C:H films with good adhesion strength can be produced on W pre-implanted steel substrates but this is not so on the untreated substrate or on the steel substrate with a W buffer layer. Moreover, altering the pre-implantation parameters gives rise to different distributions and amounts of W in the modified layer and they influence film growth at a later stage. The hardness, elastic properties, and adhesion strength of the deposited a-C films are also strongly affected by the pretreatment parameters. Our results suggest an alternative means to improve the mechanical properties of a-C films on steel substrate in lieu of traditional processes such as the use of an interlayer and multilayer deposition.

CrN/NbN superlattice structured coatings with enhanced corrosion resistance achieved by high power impulse magnetron sputtering interface pre-treatment

In physical vapour deposition the ion etching pre-treatment prior to thin film deposition strongly influences the substrate/coating interface structure and chemistry and consequently properties such as adhesion and corrosion performance. This study compares CrN/NbN superlattice coatings grown by unbalanced magnetron sputtering on 304L stainless steel (SS) and M2 high speed steel (HSS) pre-treated with Nb ions at bias voltages of − 600 V with three different methods: (1) high power impulse magnetron sputtering (HIPIMS), (2) HIPIMS with subsequent Nb HIPIMS interlayer deposition and (3) steered cathodic arc (CA) metal ion etching with CA interlayer deposition. The discharge during the pre-treatment step was analysed by optical emission spectroscopy of the Nb plasma, revealing a HIPIMS plasma dominated by singly charged Nb 1+ ions. Two-fold charged Nb 2+ ions were also present. HIPIMS pre-treatment promoted the formation of a clean and droplet-free interface and growth-defect free and dense coatings. Localized epitaxial growth of the films, as examined by cross-sectional transmission electron microscopy, resulted in significantly improved coating adhesion ( L C = 56 N) compared to CA pre-treatment ( L C = 45 N). The introduction of a 30 nm thick Nb metal interlayer resulted in clearly defined and sharp interfaces with coherent base layer growth further improving the adhesion ( L C = 65 N). Furthermore, the corrosion performance was studied by potentiodynamic polarisation in 3% NaCl solution. Results show superior corrosion performance for the HIPIMS pre-treated coatings. The HIPIMS pre-treatment prior to coating deposition provided passivation up to + 1000 mV on 304 stainless steel (SS) substrates. An additional Nb interlayer significantly enhanced the corrosion performance with lower current densities of 4 × 10 − 5 A cm − 2 . CrN/NbN superlattice structured coatings were also sufficient to effectively protect non-noble M2 high speed steel (HSS) substrates. However, passivation is only retained up to potentials of + 660 mV. The substrate/coating system corroded unimpeded when exceeding these values. The CrN/NbN coating with CA etch did not show passivation on both SS and HSS. CrN/NbN nanoscale multilayer coatings both with HIPIMS and CA pre-treatment outperform 20 μm thick commercial electroplated hard chrome with the HIPIMS pre-treated coatings being superior to the CA pre-treated ones.

Mechanisms of bending of threading dislocations in MOVPE‐grown GaN on (0001) sapphire

AbstractIn this article, we describe possible mechanisms associated with the bending of threading dislocations (TDs) through 90° in GaN. In‐situ ELOG using SiNx masking on a sapphire substrate and in‐situ SiNx interlayer (IL) deposition on a GaN pseudo‐substrate have been used to reduce the TD density in GaN. The bending of TDs through 90° is essential in order to reduce their numbers in the upper growing layer. The bending of TDs is facilitated by a change in growth mode, i.e. predominantly 2D to 3D and then 3D to 2D. A new mechanism is tentatively proposed which can explain the bending of all types of TDs (edge, screw, and mixed). This new mechanism is based on first, step formation at 3D island side facets when TDs terminate there, following which, depending on the subsequent change in growth mode (3D to 2D) and the direction of the atomic ledge movement, the TDs will bend over. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Buffer design for nitrogen polarity GaN on sapphire [formula omitted] by RF-MBE and application to the nanostructure formation using KOH etching

GaN films were grown by radiofrequency plasma-assisted molecular beam epitaxy on a variety of sapphire ( 0 0 0 1 ) substrates with different buffer layer and/or preparation processes, to show the controllability of lattice-polarity selection as well as their applicability to the nanostructure fabrication. Film polarities, which have been checked by reflection high-energy electron diffraction reconstructions and etched morphologies in KOH aqueous solution, were very sensitive to these preparation processes. Ga-polarity GaN could be obtained by an introduction of a high-temperature nitridation and an AlN interlayer deposition, and the N-polarity film with a flat surface and large grains could be grown on a low-temperature-nitrided sapphire in combination with a use of nitrogen-flux modulation sequence, while other pretreatment resulted in the mixed polarities. The resultant morphology of N-polarity GaN after KOH etching clearly reflects crystallographic orientation and the highly anisotropic-etching behavior show the usefulness of the low-temperature-nitrided sapphire for obtaining large-domain N-polarity GaN and the feasibility of nanostructure fabrication without the use of an expensive dry-etching process.

TEM characterization of a Cr/Ti/TiC graded interlayer for magnetron-sputtered TiC/a-C:H nanocomposite coatings

A TiC/a-C:H nanocomposite coating is deposited on top of a Cr/Ti/TiC graded interlayer. Cross-section transmission electron microscopy is employed to investigate the detailed structure of the interlayer and the coating. Five different phases are formed as a consequence of the compositional gradient within the interlayer: pure Cr, a solid solution of Ti in Cr, a Ti/Cr amorphous/nanocrystalline phase, α-Ti and TiC. Solid state amorphization occurs during the interlayer deposition to give a dispersion of TiCr β-phase nanocrystals in an amorphous matrix. The TiC phase is textured and contains numerous stacking faults as a result of the growth in under-stoichiometric carbon concentration. C-enriched columnar boundaries are present within the coating, originating from the TiC column boundaries of the interlayer. The work indicates that an interlayer of amorphous/nanocrystalline Ti/Cr phase would reduce the presence of growth defects such as columnar boundaries within nanocomposite TiC/a-C:H coatings.

Strain effects of AlN interlayers for MOVPE growth of crack-free AlGaN and AlN/GaN multilayers on GaN

The effect of growth conditions and thickness of AlN interlayers on the strain state of MOVPE-grown Al x Ga 1− x N epilayers on GaN/sapphire templates has been investigated. It was found that in almost all cases, the AlN interlayers apply a compressive strain to the AlGaN layer and prevent the formation of cracks. From use of both atomic force microscopy and cross-sectional electron microscopy, it appears that micro-cracking of the AlN interlayer itself occurs, thereby causing compression of the subsequent AlGaN layer. These cracks appear not to propagate beyond the AlN and are covered during AlGaN deposition. The growth conditions of the interlayer affect the crack network and surface morphology, which in turn determine the strain state of the AlGaN: the compressive strain was found to increase with interlayer thickness, decreasing V/III ratio and decreasing interlayer deposition temperature. The growth of crack-free AlN/GaN multilayers with individual layer thicknesses exceeding 60 nm has also been achieved.

Effect of Capping Silicon Nitride Layer and Nitrided Gate Oxide on Hump of Transistors

In this letter, we investigate the effect of capping silicon nitride and nitrided gate oxide on the hump in the sub-threshold slope of various transistors. Silicon wafers having both high- and low-voltage transistors are fabricated. The thin gate oxide is grown by nitric oxidation, while two step process of dry oxidation and low-pressure chemical vapor deposition (LPCVD) is used for the thick gate oxide. Note that the thickness of thin gate oxide is 4.5 nm, and 29 nm for thick gate oxide. It appears that both low-voltage nMOS and pMOS do not show any hump, nor does high-voltage pMOS. The subthreshold hump of high-voltage nMOS depends on process conditions. It shows severe hump without capping silicon nitride layer due to moisture diffusion during thermal anneal after interlayer oxide deposition by LPCVD. It also appears that nitrided oxide is effective to prevent hump by stopping moisture diffusion.