Oxygen Out-diffusion Research Articles

Performance degradation due to thermal cycling in soldered Faraday and SuperPower HTS tape stacks

Soldering stacks of high temperature superconducting (HTS) tapes results in a current carrying matrix with high electrical, thermal, and mechanical stability. In some applications, these tape stacks may be exposed to elevated temperatures during thermal heat cycles. Previous research on thermal degradation of high temperature superconductors has been performed with isolated crystals or individual HTS tapes, showing that oxygen-out diffusion from the rare-earth barium copper oxide (REBCO) results in a reduction of the superconducting performance. In this work, the performance of Pb37Sn63 soldered HTS tape stacks with thermal cycling to 170∘ C is quantified through determination of the critical current Ic , the n-value, the linear resistance R in the pre-transition region of the tape stack current–voltage (I–V) traces, and the diffusion coefficient D associated with oxygen-out diffusion. The effect of tape manufacturer and nickel electroplating were considered; three soldered stacks each of unplated Faraday, nickel electroplated Faraday, unplated SuperPower, and nickel electroplated SuperPower tapes were fabricated. Across 20–30 one hour thermal cycles, there are no significant differences in degradation profiles observed between the unplated and nickel electroplated tape stacks for a given manufacturer. There is however a marked difference in degradation profiles observed between the SuperPower and Faraday tape stacks. For the unplated and plated SuperPower tape stacks, the degradation in Ic generally follows the model to describe oxygen-out diffusion from the superconducting REBCO layer. Significantly less degradation is observed in the unplated and plated Faraday tape stacks, and in some sections Ic even increases slightly across cycles. Further, cases of increasing Ic accompanied with decreasing n are observed, a decoupling between the two parameters. Across all samples, the linear resistance was highest in current-redistribution regions near the leads. Consistent with the model of oxygen-out diffusion and the formation of an increasingly wide oxygen deficient layer in the REBCO, the linear resistance increased with cycle number.

The Investigation of Vortex Motion in the YBCO Devices Manufactured Utilizing a Gaussian-shaped Optical Spot from a Continuous-wave Laser

The current report focuses on the analysis of the investigation results of the Abrikosov vortex motion in the YBa2Cu3O7-d (YBCO) device, which is a c-axis textured 0.3 ´ 50 ´ 100 µm3 (thickness ´ width ´ length) stripe of YBCO superconductor deposited on a LaAlO3 substrate. A laser beam focused in a Gaussian-shape optical spot of 5 mm in diameter modifies the stripe, initiating the oxygen out-diffusion and its uneven distribution in illuminated areas and in this way causing the appearance of a higher level of deoxygenation in the spot center and a lower level at its edges (slopes of weak superconductivity region). At temperatures below the temperature of the superconducting transition Tc, the current-self-produced magnetic field penetrates the optically modified area of the stripe in a form of Abrikosov magnetic vortices, and due to the current-self-produced Lorentz force, the vortices move toward their annihilation line resulting in energy dissipation. The vortices pinned on the slopes experience strong pinning and exert a magnetic drag force on moving vortices, which is confirmed by the stepped current-voltage dependences of the YBCO devices measured at temperatures 0.933·Tc £ T £ 0.958·Tc. Our results demonstrate the advantages of partially deoxygenated YBCO material for the development of superconducting electronic devices with electronic properties controlled by the motion of Abrikosov vortices at temperatures below Tc of the superconductor.

Dimensionality of mobile electrons at x-ray-irradiated LaAlO3/SrTiO3 interfaces

Electronic structure of LaAlO3/SrTiO3 (LAO/STO) samples, grown at low oxygen pressure and post-annealed ex situ, was investigated by soft-x-ray ARPES focussing on the Fermi momentum (k F) of the mobile electron system (MES). X-ray irradiation of these samples at temperatures below 100 K creates oxygen vacancies (VOs) injecting Ti t 2g-electrons into the MES. At this temperature the oxygen out-diffusion is suppressed, and the VOs should appear mostly in the top STO layer. The x-ray generated MES demonstrates, however, a pronounced three-dimensional (3D) behavior as evidenced by variations of its experimental k F over different Brillouin zones. Identical to bare STO, this behavior indicates an unexpectedly large extension of the x-ray generated MES into the STO depth. The intrinsic MES in the standard LAO/STO samples annealed in situ, in contrast, demonstrates purely two-dimensional (2D) behaviour. The relevance of our ARPES data analysis is supported by model calculations to compare the intensity vs gradient methods of the k F determination as a function of the energy resolution ratio to the bandwidth. Based on self-interaction-corrected DFT calculations of the MES induced by VOs at the interface and in STO bulk, we discuss possible scenarios of the puzzling 3D-ity. It may involve either a dense ladder of quantum-well states formed in a long-range interfacial potential or, more likely, x-ray-induced bulk metallicity in STO accessed in the ARPES experiment through a short-range interfacial barrier. The mechanism of this metallicity may involve remnant VOs and photoconductivity-induced metallic states in the STO bulk, and even more exotic mechanisms such as x-ray induced formation of Frenkel pairs.

Formation pathways of oriented magnetite micro-inclusions in plagioclase from oceanic gabbro

Plagioclase hosted needle- and lath-shaped magnetite micro-inclusions from oceanic gabbro dredged at the mid-Atlantic ridge at 13° 01–02′ N, 44° 52′ W were investigated to constrain their formation pathway. Their genesis is discussed in the light of petrography, mineral chemistry, and new data from transmission electron microscopy (TEM). The magnetite micro-inclusions show systematic crystallographic and shape orientation relationships with the plagioclase host. Direct TEM observation and selected area electron diffraction (SAED) confirm that the systematic orientation relations are due to the alignment of important oxygen layers between the magnetite micro-inclusions and the plagioclase host, a hypothesis made earlier based on electron backscatter diffraction data. Precipitation from Fe-bearing plagioclase, which became supersaturated with respect to magnetite due to interaction with a reducing fluid, is inferred to be the most likely formation pathway. This process probably occurred without the supply of Fe from an external source but required the out-diffusion of oxygen from the plagioclase to facilitate partial reduction of the ferric iron originally contained in the plagioclase. The magnetite micro-inclusions contain oriented lamellae of ilmenite, the abundance, shape and size of which indicate high-temperature exsolution from Ti-rich magnetite constraining the precipitation of the magnetite micro-inclusions to temperatures in excess of ~ 600 °C. This is above the Curie temperature of magnetite, and the magnetic signature of the magnetite-bearing plagioclase grains must, therefore, be considered as the thermoremanent magnetization.

Grown and Characterization of ZnO Aligned Nanorod Arrays for Sensor Applications

ZnO nanorods are promising materials for many applications, in particular for UV detectors. In the present paper, the properties of high crystal quality individual ZnO nanorods and nanorod arrays grown by the self-catalytic CVD method have been investigated to assess their possible applicationsfor UV photodetectors. X-ray diffraction, Raman spectroscopy and cathodoluminescence investigations demonstrate the high quality of nanorods. The nanorod resistivity and carrier concentration in dark is estimated. The transient photocurrent response of both as grown and annealed at 550 °C nanorod array under UV illumination pulses is studied. It is shown that annealing increases the sensitivity and decreases the responsivity that is explained by oxygen out-diffusion and the formation of near surface layer enriched with oxygen vacancies. Oxygen vacancy formation due to annealing is confirmed by an increase of green emission band intensity.

Oxygen out-diffusion in REBCO coated conductor due to heating

Rare earth barium copper oxide (REBCO) coated conductor has emerged as one of the high T c superconductors suitable for future ultrahigh field superconducting magnet applications. In the design and fabrication of such ultrahigh field REBCO magnets, it is essential to understand the behavior of REBCO coated conductor. The effect of heating on the properties of commercial REBCO coated conductors is very important for many practical reasons. Nevertheless, a comprehensive study on this effect have not yet been presented in the published literature. This work studies a commercial REBCO coated conductor heat-treated at temperatures between 175 °C and 300 °C for various durations. Critical current and lap joint resistivity were measured at 77 K and 4.2 K for the heat-treated samples. We found that critical current degrades with heat treatment time and temperature. This degradation can be described by a one-dimensional oxygen out-diffusion model with a diffusion coefficient of D = 2.5 × 10−6 exp (−1.17eV kT−1) m2 s−1. The heat treatment also causes appreciable increase in joint resistivity. Comprehensive structural and chemical analyses were performed on Cu/Ag/RECBO interfaces by transmission electron microscopy. Our electron energy loss spectroscopy study provided direct evidence of oxygen deficiency in the heat treated REBCO samples. In addition, it is found that the oxygen diffused out of the REBCO layer forms mostly Cu2O at both Ag/REBCO and Cu/Ag interfaces. Cu2O is also observed at grain boundaries of the Ag layer. The oxygen out-diffusion model proposed in this work is used to predict REBCO thermal degradation in several engineering scenarios.

Variation in electrical and structural properties of Ga-doped ZnO films caused by oxygen out-diffusion

Variation in electrical and structural properties of Ga-doped ZnO films caused by oxygen out-diffusion

Floating zone silicon wafer bonded to Czochralski silicon substrate by surface-activated bonding at room temperature for infrared complementary metal-oxide-semiconductor image sensors

We propose to use a bonding wafer as an alternative epitaxial wafer with an extra thick epitaxial layer of more than 100 μm thickness to fabricate vertical time-of-flight (TOF) complementary metal-oxide-semiconductor (CMOS) imaging sensors that can detect infrared (IR) radiation of wavelength greater than 1120 nm. This bonding wafer comprises a floating zone (FZ)-grown silicon wafer bonded to a Czochralski (CZ)-grown silicon substrate by room-temperature surface-activated bonding. Because the device-fabricating region is formed by bonding the FZ-grown wafer to the CZ-grown silicon substrate at room temperature, the oxygen concentration in this region is decreased to less than that in an epitaxial wafer. In addition, our bonded wafer can have a strong gettering capability for oxygen and transition metals (nickel, copper, and iron) in the bonding interface. Furthermore, the bonded wafer can inhibit out-diffusion of oxygen or transition metal to the device-fabricating region from the CZ-grown silicon substrate, and the device-fabricating region can have fewer impurities after fabricating the devices in the bonded wafer. Therefore, we consider that this bonded wafer can be fabricated by the simple processes of bonding and grinding (polishing) at room temperature without thermal stress, and this method is effective for decreasing the dark currents and white-spot defects generated owing to the presence of oxygen or transition metal, which are undesirable in advanced TOF-CMOS imaging sensors of a vertical structure.

Proximity Gettering Design of Hydrocarbon⁻Molecular⁻Ion⁻Implanted Silicon Wafers Using Dark Current Spectroscopy for CMOS Image Sensors.

We developed silicon epitaxial wafers with high gettering capability by using hydrocarbon–molecular–ion implantation. These wafers also have the effect of hydrogen passivation on process-induced defects and a barrier to out-diffusion of oxygen of the Czochralski silicon (CZ) substrate bulk during Complementary metal-oxide-semiconductor (CMOS) device fabrication processes. We evaluated the electrical device performance of CMOS image sensor fabricated on this type of wafer by using dark current spectroscopy. We found fewer white spot defects compared with those of intrinsic gettering (IG) silicon wafers. We believe that these hydrocarbon–molecular–ion–implanted silicon epitaxial wafers will improve the device performance of CMOS image sensors.

Destructive role of oxygen in growth of molybdenum disulfide determined by secondary ion mass spectrometry.

The application of secondary ion mass spectrometry (SIMS) in investigation and comparison of molybdenum disulfide (MoS2) films grown on SiO2, Al2O3 and BN substrates is presented. SIMS measurements of the MoS2/substrate interface reveals oxygen out-diffusion from the substrates containing oxygen and the formation of an amorphous MoOS layer in addition to MoS2. The total area of MoS2 domains covering the substrate is directly related to the type of substrate. For SiO2, small triangular domains of MoS2 separated by amorphous MoOS material are observed. For Al2O3, the sizes of the MoS2 domains are drastically improved due to the higher stability of sapphire. For a BN substrate, SIMS measurements reveal a uniform MoS2 coverage over the whole 2-inch wafer. These results show the destructive role of oxygen released from substrates such as SiO2 or Al2O3 during the growth process of MoS2. The fast and cheap growth process on a non-oxide substrate allows large wafer-scale uniform molybdenum disulfide material to be obtained, which is promising for device fabrication.

Oxygen out-diffusion and compositional changes in zinc oxide during ytterbium ions bombardment

Oxygen release and out-diffusion in zinc oxide crystals during heavy ions bombardment has been suggested by many experimental techniques. In this work we have employed secondary ion mass spectrometry to study ZnO implanted with ytterbium ions. Our measurements confirm formation of an oxygen-depleted layer and oxygen out-diffusion and agglomeration at the surface. Moreover, an average compositional change in a heavily damaged near-surface region can also be monitored. This reproducible measurement procedure with subnanometer depth resolution allows to localize precisely these altered layers at the depth of 14–28 nm (oxygen-depleted layer) and 9 nm (maximum of the amorphized region). Such precise measurements may prove to be valuable for further characterization of ion beam induced defects in wide bandgap compound semiconductors and optimization of optoelectronic devices based on these materials.

Interfacial Reaction between Metal and Oxide

Transparent oxide semiconductor thin film transistor (TFT) is being used in display such as OLED (organic light emitting diode) display and LCD (liquid crystal display). The active oxide layer in oxide TFT is transparent, comprising band gap higher than 3.0 eV. In TFT fabrication metal layer contacts to the active oxide layer and the reaction between active oxide layer and metal degrade TFT characteristics due to thin metal oxide formation. In this paper the reaction between the amorphous indium- gallium -oxide (a-IGZO) and metal was studied. Metal oxide formation was reported with interfacial micro-structures between a-IGZO and the metal electrode. TiOx is formed at the interfacial region between Ti and IGZO layers by oxygen out-diffusion from IGZO. The reaction depends on process parameters such as temperature, annealing time and the environment of annealing. For several metals such as Al, Ti, and Mo, the interfacial reaction by thermal anneal was compared for various annealing conditions. The a-IGZO was deposited on ITO electrode layer and the 0.8 mm diameter metal electrodes are formed on a-IGZO layer. After annealing at various conditions, formation of metal oxide was verified by electrical characteristics. The leakage current and breakdown voltages were measured. Figure 1 shows typical I-V characteristics between metal and ITO electrode. Figure 1

Mg and Al doped ZnO thin film: Photoinduced “oxygen breathing” under UV illumination

In this work we investigate the dependence of UV photocurrent of ZnO thin films on the presence of ambient oxygen. Comparative studies were carried out for undoped, Mg-doped and Al-doped ZnO thin films deposited by the sol-gel process. The photocurrent generated by UV excitation was observed to increase sharply under vacuum conditions compared to that measured in an air ambience. The undoped and Al-doped ZnO samples also showed extremely long persistent photocurrent under vacuum conditions, which reduced only when oxygen was re-introduced. This has been linked to surface adsorption of ambient oxygen which traps free electrons under atmospheric conditions, reducing the photocurrent levels. On UV excitation under vacuum the oxygen is irreversibly desorbed, leading to an increase in free electrons, and hence of photocurrent. Mg-doped ZnO thin films however did not show such effects, indicating that UV excitation induced oxygen de-trapping is retarded in these samples. These results were correlated with photoluminescence and optical absorption measurements. Presence of long band-tails was observed for undoped and Al-doped samples, which was absent for Mg-doped films. Additionally, room temperature photoluminescence spectra from undoped and Al-doped samples show multiple near band-edge peaks, which are eliminated by Mg doping. Since Mg doping leads to a larger grain size as determined by the width of the X-Ray Diffraction peaks, we postulate that both the optical properties are affected by the presence of defect states linked to grain boundaries in these materials. We believe that our photocurrent transients are related to UV-induced out-diffusion of oxygen from grain boundaries, and are influenced by the relative magnitude of the OMg and OZn bonds.

(Invited) Proximity Gettering Design of Hydrocarbon Molecular Ion Implanted Silicon Wafers Using Direct Bonding Technique for Advanced CMOS Image Sensors: A Review

We developed high gettering capability silicon wafers for advanced CMOS image sensors using hydrocarbon molecular ion implantation and surface activated direct wafer bonding (SAB). We found that this novel wafer has three unique characteristics for the improvement of CMOS image sensor device performance. The first is metallic impurity gettering capability in the hydrocarbon ion implantation projection range during CMOS device fabrication. The second is the oxygen out-diffusion barrier effect; this wafer can control out-diffusion to the device active region from the CZ grown silicon substrate during CMOS device heat treatment. The third is the hydrogen passivation effect; hydrogen passivates to the Si/SiO2 gate oxide interface state defects which out-diffuse to the device active region from the hydrocarbon ion implantation projection range during the CMOS device fabrication. Moreover, we demonstrated that this novel wafer can improve the pn-junction leakage current under the actual device fabrication.

Room-temperature bonding of epitaxial layer to carbon-cluster ion-implanted silicon wafers for CMOS image sensors

We propose a fabrication process for silicon wafers by combining carbon-cluster ion implantation and room-temperature bonding for advanced CMOS image sensors. These carbon-cluster ions are made of carbon and hydrogen, which can passivate process-induced defects. We demonstrated that this combination process can be used to form an epitaxial layer on a carbon-cluster ion-implanted Czochralski (CZ)-grown silicon substrate with a high dose of 1 × 1016 atoms/cm2. This implantation condition transforms the top-surface region of the CZ-grown silicon substrate into a thin amorphous layer. Thus, an epitaxial layer cannot be grown on this implanted CZ-grown silicon substrate. However, this combination process can be used to form an epitaxial layer on the amorphous layer of this implanted CZ-grown silicon substrate surface. This bonding wafer has strong gettering capability in both the wafer-bonding region and the carbon-cluster ion-implanted projection range. Furthermore, this wafer inhibits oxygen out-diffusion to the epitaxial layer from the CZ-grown silicon substrate after device fabrication. Therefore, we believe that this bonding wafer is effective in decreasing the dark current and white-spot defect density for advanced CMOS image sensors.

Large positive linear magnetoresistance in the two-dimensional t2g electron gas at the EuO/SrTiO3 interface

The development of novel nano-oxide spintronic devices would benefit greatly from interfacing with emergent phenomena at oxide interfaces. In this paper, we integrate highly spin-split ferromagnetic semiconductor EuO onto perovskite SrTiO3 (001). A careful deposition of Eu metal by molecular beam epitaxy results in EuO growth via oxygen out-diffusion from SrTiO3. This in turn leaves behind a highly conductive interfacial layer through generation of oxygen vacancies. Below the Curie temperature of 70 K of EuO, this spin-polarized two-dimensional t2g electron gas at the EuO/SrTiO3 interface displays very large positive linear magnetoresistance (MR). Soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) reveals the t2g nature of the carriers. First principles calculations strongly suggest that Zeeman splitting, caused by proximity magnetism and oxygen vacancies in SrTiO3, is responsible for the MR. This system offers an as-yet-unexplored route to pursue proximity-induced effects in the oxide two-dimensional t2g electron gas.

Memristive behaviour of Si-Al oxynitride thin films: the role of oxygen and nitrogen vacancies in the electroforming process

The resistive switching properties of silicon-aluminium oxynitride (SiAlON) based devices have been studied. Electrical transport mechanisms in both resistance states were determined, exhibiting an ohmic behaviour at low resistance and a defect-related Poole−Frenkel mechanism at high resistance. Nevertheless, some features of the Al top-electrode are generated during the initial electroforming, suggesting some material modifications. An in-depth microscopic study at the nanoscale has been performed after the electroforming process, by acquiring scanning electron microscopy and transmission electron microscopy images. The direct observation of the devices confirmed features on the top electrode with bubble-like appearance, as well as some precipitates within the SiAlON. Chemical analysis by electron energy loss spectroscopy has demonstrated that there is an out-diffusion of oxygen and nitrogen ions from the SiAlON layer towards the electrode, thus forming silicon-rich paths within the dielectric layer and indicating vacancy change to be the main mechanism in the resistive switching.

Improved interfacial properties of GaAs MOS capacitor with NH3-plasma-treated ZnON as interfacial passivation layer**Project supported by the National Natural Science Foundation of China (Nos. 61176100, 61274112, 61404055).

The GaAs MOS capacitor was fabricated with HfTiON as high-k gate dielectric and NH3-plasma-treated ZnON as interfacial passivation layer (IPL), and its interfacial and electrical properties are investigated compared to its counterparts with ZnON IPL but no NH3-plasma treatment and without ZnON IPL and no plasma treatment. Experimental results show that low interface-state density near midgap (1.17 × 1012 cm−2 eV−1) and small gate leakage current density have been achieved for the GaAs MOS device with the stacked gate dielectric of HfTiON/ZnON plus NH3-plasma treatment. These improvements could be ascribed to the fact that the ZnON IPL can effectively block in-diffusion of oxygen atoms and out-diffusion of Ga and As atoms, and the NH3-plasma treatment can provide not only N atoms but also H atoms and NH radicals, which is greatly beneficial to removal of defective Ga/As oxides and As-As band, giving a high-quality ZnON/GaAs interface.

Growth of isolated domains induced by focused ion beam irradiation in congruent lithium niobate

ABSTRACTFormation of isolated domains induced by i-beam irradiation in single crystals of congruent lithium niobate with polar surface covered by uniform resist layer was studied. The change of domain shape with dose increase was attributed to gradual penetration of charge through the resist layer caused by i-beam milling. The appearance of the dendrite structures was attributed to formation of the surface dielectric gap due to out-diffusion of oxygen to electrode. We applied the obtained knowledge for creation of the 1-µm-period 2D square arrays of isolated domains with minimal radius about 300 nm and the 1-µm-period 1D pattern of stripe domains.

Device instability of amorphous InGaZnO thin film transistors with transparent source and drain

The investigations on the device instabilities of a-InGaZnO thin film transistors with transparent source and drain have been performed according to the different thermal annealing treatment after positive gate bias stress (PBS) and hot carrier stress. The controlled devices with a rapid thermal processing (RTP) treatment in addition to conventional thermal annealing showed less degradation after PBS and hot carrier stress at the same stress biases. The reason for lower device degradation could be explained by the higher effective barrier energy which may be resulting from oxygen out-diffusion. However, the controlled device showed more serious degradation at the same actual stress voltages to the intrinsic part of device. This result may be attributed to the increased channel electron concentrations which were resulted from the increased oxygen vacancies. The degradation of the controlled devices was more serious after hot carrier stress than after PBS. From C-V measurement and transfer characteristics in forward and reverse mode measurements, hot carrier induced degradation could be attributed to the interface state generation and the electron trappings at interface between the active channel layer and the gate dielectric layer.