Effects Of O2 Plasma Treatment Research Articles

Suppressed current collapse and improved threshold voltage stability of AlGaN/GaN HEMT via O2 plasma treatment

A comprehensive study about the effects of O2 plasma treatment on the dynamic performance of AlGaN/GaN high electron mobility transistors (HEMTs) is presented. The drain current transient spectroscopy indicated a much decelerated and mitigated current degradation process for the HEMT with O2 plasma treatment. Upon negative gate bias stressing, current collapse of 10.7 % and minor threshold voltage shift of 0.16 V were achieved by O2 plasma treatment. In addition, current collapse ratio of the HEMTs as a function of stress/recovery time showed that the HEMT with O2 plasma treatment had a superior performance in various on-off conditions. Particularly in high-frequency switching events, current collapse ratio was reduced from about 50 % to 0.2 %. At last, the quality of AlGaN/metal interface with O2 plasma treatment is demonstrated by capacitance-frequency measurements, with the interface trap density Dit is estimated to be 1.39 × 1012 cm−2 eV−1. These results indicate that GaN HEMT with O2 plasma treatment is a promising technology in power switching applications.

Surface Modification of Screen-Printed Carbon Electrode through Oxygen Plasma to Enhance Biosensor Sensitivity.

The screen-printed carbon electrode (SPCE) is a useful technology that has been widely used in the practical application of biosensors oriented to point-of-care testing (POCT) due to its characteristics of cost-effectiveness, disposability, miniaturization, wide potential window, and simple electrode design. Compared with gold or platinum electrodes, surface modification is difficult because the carbon surface is chemically or physically stable. Oxygen plasma (O2) can easily produce carboxyl groups on the carbon surface, which act as scaffolds for covalent bonds. However, the effect of O2-plasma treatment on electrode performance remains to be investigated from an electrochemical perspective, and sensor performance can be improved by clarifying the surface conditions of plasma-treated biosensors. In this research, we compared antibody modification by plasma treatment and physical adsorption, using our novel immunosensor based on gold nanoparticles (AuNPs). Consequently, the O2-plasma treatment produced carboxyl groups on the electrode surface that changed the electrochemical properties owing to electrostatic interactions. In this study, we compared the following four cases of SPCE modification: O2-plasma-treated electrode/covalent-bonded antibody (a); O2-plasma-treated electrode/physical adsorbed antibody (b); bare electrode/covalent-bonded antibody (c); and bare electrode/physical absorbed antibody (d). The limits of detection (LOD) were 0.50 ng/mL (a), 9.7 ng/mL (b), 0.54 ng/mL (c), and 1.2 ng/mL (d). The slopes of the linear response range were 0.039, 0.029, 0.014, and 0.022. The LOD of (a) was 2.4 times higher than the conventional condition (d), The slope of (a) showed higher sensitivity than other cases (b~d). This is because the plasma treatment generated many carboxyl groups and increased the number of antibody adsorption sites. In summary, the O2-plasma treatment was found to modify the electrode surface conditions and improve the amount of antibody modifications. In the future, O2-plasma treatment could be used as a simple method for modifying various molecular recognition elements on printed carbon electrodes.

Methylene Blue Adsorption by Plasma Re-Activated Carbon

The effects of O2 plasma treatment on the adsorption capacity of activated carbon (AC) were investigated by varying the plasma treatment times. The surface properties of the AC were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Zeta potential. The carbon was then applied to remove methylene blue (MB). The adsorption kinetics and isotherm were also studied. Results showed that pseudo-second-order kinetics was the most suitable model for describing the adsorption of MB onto AC. Equilibrium data were well fitted to the Freundlich isotherm model. The highest adsorption capacity resulted from 4 minutes of O2 plasma treatment. The 4-minute plasma treated AC had the best adsorption capacity for MB at 0.467 mg/mg. This work shows that activation of AC by plasma can open the micropore and increase the effectiveness of chemical removal.

In vitro and in vivo biocompatibility study of surface modified TiN deposited on Ti6Al4V using high-power impulse magnetron sputtering technique

Although Ti6Al4V alloy is commonly used as a surgical implant, the toxicity of vanadium is always a serious concern. As a stable and protective coating for Ti6Al4V, TiN deposited using a high-power impulse magnetron sputtering (HiPIMS) technique exhibits great polarization resistance in simulated body fluid and shows excellent cell viability of osteoblast-like MG63 cell. Herein, we report further study on the in vitro and in vivo biocompatibility of the HiPIMS-deposited TiN coatings with various surface modifications. For the in vitro study, the effect of O2 plasma treatment, acrylamide (AAm) graft polymerization, and bone morphogenetic protein-2 (BMP2) immobilization on the viability of osteoblast-like MG63 cell were examined using the MTT assay. For the in vivo study, the pro-inflammatory cytokines and skin pathology in mice using subcutaneous sensitivity test were conducted. In vitro investigation shows that cell viability is significantly improved for TiN having BMP2 on the surface. When BMP2 was coated on bare TiN, the MG63 cell proliferation decreases with time. However, with surface pre-treatment of TiN using O2 plasma and AAm grafting, BMP2 coated TiN exhibits increasing MG63 cell proliferation with time. Likewise, in vivo investigation shows such sample has enhanced wound healing capability, significant increase of the body weights, obvious decrease of pro-inflammatory cytokines, and improved skin section structure, as compared to the bare Ti6Al4V. The pathological result shows that the TiN treated with O2 plasma and AAm graft polymerization, and with a surface BMP2 layer gives long-term stable immobilization of BMP2 and the best in vivo biocompatibility among all the samples.

Improvement of Ti/Al ohmic contacts on N-face n-type GaN by using O2 plasma treatment

The effect of O2 plasma treatment on the electrical properties of Ti/Al (20/200 nm) contact to N (Nitrogen)-face n-GaN of vertical light-emitting diodes (VLEDs) has been investigated by varying the O2 plasma treatment power and time. Both photolithography and chemical lift-off methods are used to prepare the circular transfer length method (CTLM) patterns on the N-face n-GaN for measuring the contact and sheet resistances. Both total and sheet resistances are decreased with the increase in plasma treatment power up to 250 W. It is found that the Ti/Al-based Schottky contact layer transforms to ohmic characteristics after plasma treatment. GaN chemical bonds on the n-GaN surface are broken due to O2 plasma treatment; thus, resulting in formed GaO bonds which are interactively understood by using X-ray photoelectron spectroscopy characteristics. After plasma treatment, the forward voltage of VLED is not only reduced owing to decrease in total resistance but also both the light intensity distribution and the light-output-power are improved because of increase in current spreading through the contact layer.

The effect of O2 plasma treatment and PA 6 coating on digital ink-jet printing of PET non-woven fabric

In the absence of pre-processing, polyethylene terephthalate (PET) non-woven have strong hydrophobicity. Therefore, patterns printed with pigment ink-jet printing have poor color yield and low resolution. In this study, the surface properties of PET non-woven fabric were modified by plasma treatment, and a coating solution made by waste polyamide 6 (PA 6) filament, methanol, and CaCl2 to prepare 3.5% and 6.8% PA 6 concentration. After that, plasma-treated sample, coated sample, and plasma treatment plus PA 6 coated sample results on pigment ink-jet printing were investigated to prepare good printing PET non-woven packaging fabric. Scanning electron microscopic image indicated that plasma makes etching on the fabric surface, hence increase the hydrophilic property of the fabric, which helps slight increase in the color yield and resolution. The contact angle shows PA 6 coating also achieved hydrophilic on the surface of PET non-woven fabric and facilitated the ink absorption in pigment ink-jet printing, which helped the printed fabric have higher color yield and clear resolution. However, for significant results it was very important to increase the absorption of coating solution. Plasma makes it easier for the fabric to absorb more coating solution containing dissolved waste PA 6 filament in both concentrations from 11.97% to 19.92% and 5.68% to 10.50%. This ultimately provides the capacities for the fabric to capture more ink and penetration of more colorant particles into the fabric. Therefore, plasma treatment first plus PA 6 coating can help prepare better-patterned PET non-woven fabric packing through pigment ink-jet printing, even though the plasma treatment and coating caused a little negative influence in whiteness and handle.

Electrically conductive silver/polyimide fabric composites fabricated by spray-assisted electroless plating

High-performance fabrics with excellent electrical conductivity are increasingly attractive in modern industries. In this study, we report an electrically conductive silver/polyimide fabric (Ag/PIF) composite fabricated by combining an O2 plasma pretreatment and a spray-assisted electroless plating (SAELP) technique. O2 plasma treatment is firstly employed to roughen the surface of PIF and introduce functional aldehyde or ketone groups, which can act as a reducing agent and facilitate an even nucleation initiation of silver nanoparticles (Ag NPs) on the surface of the PIF. A silver ion solution and a reducing agent are then mixed evenly and sprayed to the PIF immediately to obtain Ag/PIF composites. The effects of O2 plasma treatment and SAELP duration on the Ag/PIF composites are investigated and discussed. The results demonstrate that the silver layer is coated on the PIF uniformly and densely with a surface resistance of 0.1 Ω/sq. The first decomposition temperature of the Ag/PIF composites is up to 600 °C, indicating excellent thermal stability. The enhanced adhesion between Ag NPs and PIF endows the composites excellent fastness and superior flexibility. This work gives a new strategy for fabricating flexible, electrically conductive functional metal coated fabrics with high-performance properties in an efficient, facile and scalable way.

Effects of O2 plasma treatment on moisture barrier properties of SiO2 grown by plasma-enhanced atomic layer deposition

Abstract We investigated the moisture barrier properties of SiO2 layers deposited via plasma-enhanced atomic layer deposition (PE-ALD) for encapsulation of an organic light-emitting diode (OLED). First, the growth characteristics and film properties of PE-ALD SiO2 using diisopropylamino silane (DIPAS) and O2 plasma were investigated. The film properties were significantly improved by applying proper O2 plasma treatment. The O2 plasma treatment increased the adsorption of the metal precursor by creating sufficient hydroxyl groups on the substrate. We not only increased the adhesion between the thin film and the polymeric substrate through O2 plasma treatment before the deposition process but also formed a high-density thin film, resulting in excellent moisture barrier properties. Consequently, the water vapor transmission rate (WVTR) was significantly reduced to 7.73 × 10−3 g/m2∙day, which was 10 times lower than that of a control sample. These newly developed methods can be applied to other metal oxides, such as Al2O3 and ZrO2, for OLED encapsulation with a low WVTR.

Effect of O2 plasma on properties of electrolyte-insulator-semiconductor structures

Prior to immobilization of biomolecules or cells onto biosensor surfaces, the surface must be physically or chemically activated for further functionalization. Organosilanes are a versatile option as they facilitate the immobilization through their terminal groups and also display self-assembly. Incorporating hydroxyl groups is one of the important methods for primary immobilization. This can be done, for example, with oxygen plasma treatment. However, this treatment can affect the performance of the biosensors and this effect is not quite well understood for surface functionalization. In this work, the effect of O2 plasma treatment on EIS sensors was investigated by means of electrochemical characterizations: capacitance–voltage (C–V) and constant capacitance (ConCap) measurements. After O2 plasma treatment, the potential of the EIS sensor dramatically shifts to a more negative value. This was successfully reset by using an annealing process. ConCap measurement of an EIS sensor. a) Reference measurement, b) after O2 plasma treatment, c) after annealing process.

Effect of O2 plasma treatment on density-of-states in a-IGZO thin film transistors

This work reports an efficient route for enhancing the performance of amorphous InGaZnO (a-IGZO) thin film transistors (TFT). The mobility was greatly improved by about 38% by means of O2 plasma treatment. Temperature-stress was carried out to investigate the stability and extract the parameters related to activation energy (E a) and density-of-states (DOS). The DOS was calculated on the basis of the experimentally obtained E a, which can explain the experimental observation. A lower activation energy (E a, ~0.72 eV) and a smaller DOS were obtained in the O2 plasma treatment TFT based on the temperature-dependent transfer curves. The results showed that temperature stability and electrical properties enhancements in a-IGZO thin film transistors were attributed to the smaller DOS.

Electrical Properties and Reliability Analysis of Solution-Processed Indium Tin Zinc Oxide Thin Film Transistors with O2-Plasma Treatment.

In this paper, we report the effects of O2-plasma treatment on the reliability and electrical properties of indium tin zinc oxide (ITZO) films. Excellent electrical properties, including a saturation mobility (μsat) of ~20.2 cm2/V · s, a threshold voltage (VTH) of ~-6.8 V, a sub-threshold swing (S.S) of ~0.956 V/decade, and an on/off current ratio (ION/OFF) of ~10(5) can be found with a molarity of 0.4 M and ratio of In:Zn:Sn = 2:1:2. Following O2-plasma treatment, it was confirmed that the electrical properties of the ITZO films are improved when compared to the untreated films. The devices showed a decreased S.S of ~0.51 V/decade, while the VTH and ION/OFF tended to increase. To determine the reliability of a-ITZO TFTs, we analyzed the electrical characteristics according to gate bias stress, VG,stress = 10 V for 4000 s. Improved reliability was confirmed when compared with the variation in threshold voltage prior to O2-plasma treatment, most likely stemming from a smooth surface on the active layer as a result of O2-plasma treatment. We were able to obtain a solution a-ITZO film transmittance of 92% in the visible light region (400~700 nm). These results show that a-ITZO TFTs fabricated via solution process with optimized molar ratio exhibit good electrical properties. a-ITZO films fabricated via spin-coating are a visible alternative to those fabricated via high-cost sputtering methods, and are applicable in flexible and transparent electronics.

Effect of O2 plasma treatment on physical, electrical, and reliability characteristics of low dielectric constant materials

The degradation induced by oxygen (O2) plasma irradiation to the various low dielectric constant materials (low-k; k=3.0–2.5) has been investigated in this study. The dielectric constant was observed to increase upon O2 plasma treatment due to carbon atom depletion and SiOH bond formation, which is strongly influenced by the bonding structure or strength of the low-k materials, and less related to the porosity. Moreover, the O2 damage can be suppressed by densifying the low-k film's surface induced by He/H2 remote plasma treatment. Additionally, the role of ions, photons, and radicals in the plasma in inducing the low-k material degradation was clarified by using a special designed structure. The experimental results showed that all components in the plasma have contributions in degrading the electrical and reliability performance of low-k film. Moreover, the synergy between the radicals, the photons, and the ions enhanced the damage.

Immobilization of biorecognition molecules on O2 plasma-functionalized SWCNT electrodes for biosensors

Biointerfaces capable of biological recognition and specificity are very important for the development of carbon nanotube based biosensors. Here, we explore experimentally the effects of O2 plasma treatment on the biomolecule immobilization properties of single-walled carbon nanotube (SWCNT) electrodes for electrochemical biosensing. The SWCNT film was integrated into an electrochemical three-electrode system on a glass substrate and then treated with an O2 plasma to improve its electrochemical response. Glucose oxidases, antibodies, and deoxyribonucleic acids (DNAs) were covalently immobilized on the plasma-functionalized (pf) SWCNT working electrodes, and the electrochemical and bioelectrocatalytic properties of three biomolecular assemblies generated on the pf-SWCNT electrodes were investigated using cyclic voltammetry, square-wave voltammetry, and chronoamperometry. The pf-SWCNT films were found to provide electrochemical biosensing electrodes having high electroactivity and sensitivity for detecting glucoses, antigens, and DNA molecules.

Effect of O<SUB>2</SUB>-Plasma Treatment on Surface Characteristics and Osteoblast-Like MG-63 Cells Response of Ti-30Nb-1Fe-1Hf Alloy

In this study, the effect of O2-plasma treatment with various powers on the surface characteristics and also the cell response of the Ti-30Nb-1Fe-1Hf alloy were investigated. Surface characteristics of Ti-30Nb-1Fe-1Hf alloy were evaluated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray powder diffractometer (XRPD) and wettability test. The results show that the surface roughness of the alloy decreases after O2-plasma treatment, and also with increased plasma power. By XPS analyses, both Ti valence states of Ti2+, Ti3+ and Ti4+ as well as Nb valence states of Nb2+, Nb4+ and Nb5+ can be detected in the oxide films. Also, the concentrations of TiO2 and Nb2O5 increase with increasing O2-plasma power. The results also show that the contact angle decreases as the alloy is modified by O2-plasma treatment, and therefore, the treated alloys can be expected to be more hydrophilic. On the other hand, for the evaluation of cell response, cell (MG-63) culture was performed. The results show that the oxidation effect on the alloy surface brought about by O2-plasma treatment enhances the spreading of cells. In addition, in vitro tests suggest that cell spreading on Ti-30Nb-1Fe-1Hf alloy is similar to that on Ti-6Al-4V alloy, whereas, cell adhesion on Ti-30Nb-1Fe-1Hf alloy is better than that on Ti-6Al-4V alloy.

Oxygen-Plasma-Treated Indium–Tin-Oxide Films on Nonalkali Glass Deposited by Super Density Arc Plasma Ion Plating

The effects of O2 plasma treatment on both the chemical composition and work function of an indium–tin-oxide (ITO) film were investigated. ITO films were deposited on non-alkali glass substrate by super density arc plasma ion plating for application in active-matrix organic light-emitting diodes (OLEDs). The water contact angle decreased from 38 to 11° as the ITO films were treated with O2 plasma for 60 s at a plasma power of 150 W, indicating an increase in the hydrophilicity of the surface. It was found that there were no distinct changes in the microstructure or electrical properties of the ITO films with O2 plasma treatment. Synchrotron radiation photoemission spectroscopy data revealed that O2 plasma treatment decreased the amount of carbon contamination and increased the number of unscreened states of In3+ and (O2)2- peroxo species. This played the role of increasing the work function of the ITO films by 1.7 eV. As a result, the turn-on voltage of the OLED decreased markedly from 24 to 8 V and the maximum luminance value of the OLED increased to 2500 cd/m2.

Effect of O2 Plasma Treatment on Hole-Injection Enhancement for Organic Light-Emitting Devices with Transparent Au:Al Anodes

Effect of O2 Plasma Treatment on Hole-Injection Enhancement for Organic Light-Emitting Devices with Transparent Au:Al Anodes

Stability of the hydrophilic behavior of oxygen plasma activated SU-8

The effect of O2 plasma treatment on surface energy, topography and surface chemistry of the negative photoresist epoxy novolak SU-8 was investigated by contact angle goniometry, atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS). Directly after plasma treatment, the surfaces were completely wetted by water with a contact angle between water and the SU-8 surface below 5°. The surface free energy can be increased significantly depending on the plasma dose. The surfaces remained hydrophilic for several months showing a moderate hydrophobic recovery. The surface topography of the plasma treated SU-8 showed a formation of nanoscale aggregates. The rms-roughness of the topography was correlated with the plasma dose. An increased plasma dose induced aggregates of up to 200 nm in size. XPS measurements revealed changes in surface chemistry due to the oxygen plasma process and an increased antimony concentration on the surface.

Improvement of electrical properties of Cu/SiCOH low-kfilm integrated system by O2plasma treatment

This paper investigates the effect of O2 plasma treatment on the electric property of Cu/SiCOH low dielectric constant (low-k) film integrated structure. The results show that the leakage current of Cu/SiCOH low-k integrated structure can be reduced obviously at the expense of a slight increase in dielectric constant k of SiCOH films. By the Fourier transform infrared (FTIR) analysis on the bonding configurations of SiCOH films treated by O2 plasma, it is found that the decrease of leakage current is related to the increase of Si-O cages originating from the linkage of Si dangling bonds through O, which makes the open pores sealed and reduces the diffusion of Cu to pores.

Surface modification of SU8 photoresist for shrinkage improvement in a monolithic MEMS microstructure

The effect of O2 plasma treatment on the surface property of exposed and unexposed SU8 photoresist has been investigated for the fabrication of a monolithic MEMS microstructure. It can solve the non-uniformity problem of second resist coating on the SU8 with high intrinsic shrinkage after exposure and post-exposure baking (PEB) in the fabrication of the stacked polymer–metal or polymer–polymer structure, which was used in the application of microfluid, bio and chemistry. The thickness difference of untreated SU8 before PEB between the exposed and unexposed SU8 was about 0.3% while that after PEB increased to about 6%. It could result in large non-uniformity of about 18 µm thickness difference for the following second resist coating on the hydrophobic surface without plasma treatment. The surface property of SU8 in terms of the contact angle and surface energy can be adjusted by O2 plasma treatment for enhancing the coating uniformity of the following resist. The measured contact angles of the exposed and unexposed SU8 decrease with O2 plasma time, corresponding to the increased surface energy determined by the Lifshitz–van der Waals/Lewis acid–base approach. It displayed that the similar hydrophilic surface property can minimize the thickness difference of second resist coating on the first shrunken SU8. A monolithic nozzle plate with a physical resolution of 600 dpi in a single column was demonstrated for an inkjet application based on the improved uniformity.

Electric characteristics of poly(3-hexylthiophene) organic field-effect transistors fabricated on O2 plasma-treated substrates

Soluble conjugated polymers such as poly(3-hexylthiophene) (P3HT) are very promising candidates for a cheap electronic device on various substrates. In this study we report the effects of O2 plasma treatment of the substrates on the electrical properties of P3HT organic thin-film transistors and metal/insulator/organic semiconductor capacitors. Based on the results of a capacitance–voltage measurement, the effective charge density in the interface between P3HT and SiO2 layer treated by O2 plasma for 30 s was approximately −18.3 nC/cm2. When the period of O2 plasma treatment was longer than 30 s, the field-effect mobility decreased since the amount of charge and the relaxation time constant of interface traps increased.