RuO2 Electrodes Research Articles

The importance of combining disorder with order for Li-ion insertion into cryogenically prepared nanoscopic ruthenia

Cryogenically prepared RuO2 (cryo-RuO2), a material known for its ability to “self-wire” into continuous, nanoscopic electronic pathways, is proposed as an electrode for Li-ion microbatteries with three-dimensionally interpenetrated components. We determined processing guidelines that optimize Li-ion uptake in cryo-RuO2 powders by varying the solid-state structure of cryo-RuO2 with thermal processing at 50–250 °C in flowing O2(g) or Ar(g). The highly disordered structure of as-prepared cryo-RuO2 is transformed to rutile RuO2 at 200 °C in O2(g), resulting in a 60% loss of Li-ion capacity (as-prepared: 214 mA h g−1; rutile: 84 mA h g−1). In contrast, thermal processing in Ar(g) preserves structural disorder in the cryo-RuO2, even up to 250 °C. The highest Li-ion capacity occurs for the treatment that mixes order (crystallinity) with disorder: >250 mA h g−1 for cryo-RuO2 heated in oxygen to 50 °C. This study provides processing guidelines to achieve fabrication of 3-D microbattery architectures containing a nanoscopic RuO2 electrode component.

Characteristics of thin film supercapacitor with ruthenium oxide electrode and Ta2O5+x solid oxide thin film electrolyte

We report findings related to a solid-state thin film supercapacitors (TFSCs) fabricated with ruthenium oxide electrodes and hydrogen doped tantalum oxide electrolyte in order to investigate a feasibility for solid oxide thin film electrolyte in all solid state micropower sources with hydrogen conducting electrolyte. The TFSCs in this study has a cell structure of RuO2/Ta2O5/RuO2/Pt. Radio frequency, off-axis r.f. sputtering deposition of a Ta2O5 thin film was performed on the bottom amorphous RuO2 electrode which was deposited by an on-axis direct current reactive sputtering, within hydrogen atmosphere to enhance the concentration of mobile proton (H+) ions. Scanning electron microscopy (SEM) measurements reveal that the RuO2/Ta2O5/RuO2 hetero-interfaces have no inter-diffusion problems. Room temperature charge–discharge measurements with constant current clearly reveal typical supercapacitor behavior. Also, owing to the fast diffusion of H+ ions within the Ta2O5 lattice without any structural deterioration, the capacitance per volume of RuO2/Ta2O5/RuO2/Pt TFSCs was maintained to be constant during above 800 cycles. This result indicated that the solid oxide thin film has possibility as the solid proton conducting electrolyte for all solid state micropower sources.

RuO2 electrode surface effects in electrocatalytic oxidation of glucose

We have studied the electrocatalytic activity of RuO2-PVC film electrodes, fabricated using RuO2 powders prepared at five different temperatures, viz., 300, 400, 500, 600 and 700°C, for the oxidation of glucose in high alkaline media, 1 to 3 M NaOH. The RuO2-PVC film electrodes have been first characterized in 1 to 3 M NaOH solution by cyclic voltammetry (CV) and rotating disc electrode (RDE) techniques in a wide potential range −1,100 to 450 mV (SCE), and three redox pairs representing Ru(IV)/Ru(III), Ru(VI)/Ru(IV) and Ru(VII)/Ru(VI) transitions have been identified. The voltammetric peaks at low sweep rates have been analyzed using surface activity theory formulated for interacting electroactive adsorption sites, and interaction terms have been evaluated. The total voltammetric surface charges have been analyzed as per Trassatti’s formalism with respect to their dependence on potential sweep rate, and charges associated with less accessible and more accessible surface sites have been calculated. For glucose oxidation, the results have indicated that RuO2 (700°C)-PVC electrode shows two oxidation peaks in contrast to RuO2 (300°C)-PVC electrode. Also, RuO2 (700°C)-PVC electrode exhibits higher intrinsic electrocatalytic activity than the 300°C electrode, although the former possesses lower electrochemically active surface area. Additionally, kinetic analyses made from RDE results with reference to Michealis–Menten (MM) enzyme catalysis has shown that RuO2 (700°C) electrode possesses extended glucose-sensing range in terms of MM kinetic constant, K M , compared to other electrodes. Possible reasons for such differences in the behavior of the electrodes of different temperatures towards glucose oxidation are identified from studies on oxidation of glucose in solutions of different pH, oxidation of different glucose derivatives, and also from physicochemical results from BET, XRD, SEM, DTGA, XPS analysis of RuO2 powder samples.

High Conductivity Ionic Liquid- Nafion Mat Composites for High Speed Ionic Polymer Transducers

ABSTRACTIonomeric polymer transducers consist of an ion-exchange membrane plated with conductive metal layers on the outer surfaces. Such materials are known to generate large bending strain (> 9% is possible) at low applied voltages (typically less than 5 V). The main disadvantage of ionomer–ionic liquid transducers is the slow speed of response. The speed of response in such actuators has been correlated to the ionic liquid content and the conductivity of the membrane. To increase the conductivity of the transducers a Nafion™ mat is hydrated with 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf) ionic liquids and high surface area RuO2 electrodes are attached using the Direct Assembly Process (DAP). The Nafion™ mat is prepared from homogenous solution electrospinning. The solution is prepared by mixing 1 wt % of polyethylene oxide solution in methanol (PEO, Mol. wt 3×106) to 5 wt % Nafion 1100 solution.. The syringe needle is connected to a 15kV power supply and is placed 15cm away from the collecting drum. The measured conductivities of water hydrated Nafion electro-spun fibers are 16.8 mS/cm, which are lower than the nominal 110 mS/cm that of H+ Nafion membranes. The uptake is measured to be around 250 %wt compared to 58 %wt obtained in Nafion films. The ionic conductivity of 110 %wt swollen ionic liquids-Nafion mat composite is computed to be 0.9 mS/cm compared to 0.3 mS/cm in ionic liquid-Nafion membrane composite. The speed of response in actuators with an ionic liquid- Nafion™ mat is 1.34 %/s compared to 0.88 %/s for that in ionic liquid Nafion™ film transducers.

Effect of Surface Structure on Behavior of RuO2Electrodes in Sulfuric Acid Aqueous Solution

The electrochemical properties of RuO2 electrodes are studied by means of cyclic voltammetry, potential step, and impedance measurements in aqueous 0.5 mol/dm3 H2SO4 as a supporting electrolyte solution and applying the hanging electrolyte meniscus technique. Two types of the electrodes are used: bulk “as-grown” single-crystal having (101) exposed interface and 500 nm film produced by reactive RF magnetron sputtering at 450°C. The surface structure of the RuO2 electrodes prepared by different techniques is defined from X-ray LAUE backscattering. Experimental data show that, for both RuO2 electrodes, the charging components include a slow diffusion-controlled contribution, due to proton injection–ejection. The diffusion characteristics and the diffusion coefficients for the same electrodes are estimated and reported.

SrBi2Nb2O9 thin films epitaxially grown on Pt epitaxial bottom layers: structural characteristics and nanoscale characterization of the ferroelectric behaviour by AFM

We have prepared RuO2 and SrRuO3 thin films for application as gate electrodes in CMOS technology. RuO2 and SrRuO3 films exhibit satisfactory stability in oxygen atmosphere at elevated temperatures. RuO2 films decompose in reducing atmosphere. Extracted work function values for RuO2 electrode are around 5.1 eV, confirming that RuO2 is a suitable candidate for pMOS gate electrode application.

Metal oxide gate electrodes for advanced CMOS technology

AbstractWe have prepared RuO2 and SrRuO3 thin films for application as gate electrodes in CMOS technology. RuO2 and SrRuO3 films exhibit satisfactory stability in oxygen atmosphere at elevated temperatures. RuO2 films decompose in reducing atmosphere. Extracted work function values for RuO2 electrode are around 5.1 eV, confirming that RuO2 is a suitable candidate for pMOS gate electrode application.

Metal oxide gate electrodes for advanced CMOS technology

We have used in situ synchrotron x-ray scattering to investigate PbTiO3 films grown epitaxially on SrTiO3 (001) substrates. When the films are cooled below a thickness-dependent Curie temperature, the ferroelectric phase forms as 180° stripe domains with a well-defined period. With further cooling, the period changes fairly abruptly from a lower to a higher value, suggesting a transition between two stripe domain phases. The periods of both stripe phases are observed to depend on the square root of film thickness, in agreement with theory.

Electrochemical decomplexing and oxidation of organic (chelating) additives in effluents from surface treatment and metal finishing

AbstractThe electrochemical decomplexing and oxidation of two frequently used complexing agents in surface treatment and metal finishing—EDTA (ethylenediaminetetraacetic acid) and NTA (nitrilotriacetic acid)—and of organic non‐complexing additives used in nickel‐plating baths were the subject of this study. Using a Ti–RuO2 electrode, a partial indirect oxidation by in‐situ electrochemical generation of chlorine compounds could be achieved for EDTA and NTA. At a boron‐doped diamond (BDD) electrode however, complete decomplexing and high COD (Chemical Oxygen Demand) and TOC (Total Organic Carbon) (up to 95%) removal occurred at an average current density of 2 A dm−2. It is shown that direct electrochemical oxidation at a BDD electrode resulted in lower energy consumption and higher treatment rates than indirect oxidation at a Ti–RuO2 electrode. Decomplexing at the BDD electrode occurred at high current efficiencies ranging from 71% to 95% with decomplexing rates in the order of 3.13 mmol (Ah)−1 and 5.02 mmol (Ah)−1 for EDTA and NTA respectively. COD removal rates obtained were 0.090 g (Ah)−1 for EDTA, 0.100 g (Ah)−1 for NTA and 0.205 g (Ah)−1 for the nickel‐plating additives. Electrochemical decomplexing and oxidation of common chelating agents can render the subsequent metal precipitation and biological wastewater treatment of surface treatment and metal finishing effluents more efficient. Copyright © 2003 Society of Chemical Industry

Charge-discharge induced phase transformation of RuO2 electrode for thin film supercapacitor

We report on the preparation of an all solid-state thin film micro-supercapacitor using RuO2 electrode film and LiPON electrolyte film on a Pt/Ti/Si substrate with dual target dc and rf reactive sputtering. Room temperature charge-discharge measurements based on a symmetrical RuO2/LiPON/RuO2 structure clearly demonstrated the cyclibility dependence of the RuO2 electrode on the microstructure. Using both glancing angle X-ray diffraction (GXRD) and transmission electron microscopy (TEM) analysis, it was found that the characteristics of the thin film supercapacitor are dependent on the microstructure of the RuO2 film. In addition, high-resolution electron transmission microscopy (HREM) analysis after cycling demonstrates that the interface layer formed by interfacial reaction between the LiPON and RuO2 acts as the main factor in the degradation of the performance of the thin film micro-supercapacitor.

A Comparative Study on Chemical and Electrochemical Degradation of Reactive Blue 4 Dye

The degradation of a reactive blue 4 dye in acidic solution has been compared using electrochemical reduction and oxidation at reticulated vitreous carbon electrode (RVC) and Ti/SnO2/SbOx (3%mol)/RuO2 (30%mol) electrodes and photo–Fenton method under UV irradiation. The reduction of RB4 dye at –0.6 V on RVC electrode results in 50% of color removal and up to 64% of TOC removal. The direct oxidation of RB4 dye at +1 V on RVC promotes only the oxidation of amine group and there is no color removal. On SnO2 electrode, 58% TOC was removed and the decolorization is around 100 % after 1 hour of electrolysis at 2.4 V indicating good efficiency. Best performance was obtained by photo-Fenton method that indicates 80% elimination of TOC and 100% of color removal but the method requires oxidant addition and time of rest to remove the generated residues.

Material and Organic Destruction Characteristics of High Temperature-Sintered RuO2 and IrO2 Electrodes

For Ru and Ir oxide electrodes sintered at different temperatures, in this work, surface resistivity, X-ray photoelectron spectroscopy, electrode lifetime, voltammetric charge capacity, and total organic carbon of 4-chlorophenol (4CP) decomposition at the electrodes were measured, and then intermediates during the electrolysis were identified by gas chromatography-mass spectroscopy to predict the destruction path of 4CP at the electrodes. A sintering temperature of around 650°C, rather than 400-550°C suggested in the literature for the fabrication of Ru and Ir oxide electrode, showed the highest organic destruction yield. The sintering temperature strongly affected the electrode lifetime as well. During the high temperature sintering, increase of the sintering time caused the oxidation of the Ti substrate to result in the increase of oxide weight of the electrode and the solid diffusion of the generated to the electrode surface, which decreased the electrode activity so that the organic destruction yield went down slowly. The destruction path of 4CP at a high temperature-sintered electrode was suggested to be different from that at a low temperature-sintered one. The Ru oxide electrode sintered at 450°C generated several complicated aliphatic intermediates. © 2002 The Electrochemical Society. All rights reserved.

Correlation between the microstructures and the cycling performance of RuO2 electrodes for thin-film microsupercapacitors

We have fabricated all solid-state thin-film microsupercapacitors (TFSCs) using RuO2 electrodes and LiPON electrolytes. The RuO2 electrodes were grown at oxygen gas flow ratios [O2/(O2+Ar)] of 10% and 30%. Room-temperature charge–discharge measurements show that specific capacitance is dependent on the oxygen gas flow ratio. Glancing angle x-ray diffraction (GXRD) and transmission electron microscopy (TEM) results show that the RuO2 electrodes grown at 10% contain nanocrystallites (0.7–10 nm across) embedded in the amorphous matrix, while the electrodes grown at 30% are polycrystalline (with grains of 0.7–15 nm in diameter). Based on the GXRD, TEM, Auger electron spectroscopy depth profile, and scanning electron microscopy results, the oxygen flow ratio dependence of the cycling performance of the RuO2-based TFSCs are discussed in terms of the combined effects of the microstructures of the electrodes, interfacial products, and the surface morphology of the electrodes.

Novel Pb(Ti, Zr)O3(PZT) Crystallization Technique Using Flash Lamp for Ferroelectric RAM (FeRAM) Embedded LSIs and One Transistor Type FeRAM Devices

A novel method of ferroelectric capacitor formation for Ferroelectrie random access memory (FeRAM) embedded LSIs and one-transistor-type FeRAMs has been developed. Amorphous Pb(Ti, Zr)O3(PZT) films were successfully transformed to the perovskite phase by a flash lamp technique with a crystallization time of 1.2 ms at a substrate temperature of 350°C. A flash lamp energy of 27 J/cm2 was sufficient to form a ferroelectric crystal structure due to rapid thermal effects with little heat diffusion in the depth direction. This technique enabled PZT film crystallization in Pt/PZT/Pt structures on multi-Al wiring layers. Granular PZT grains were observed on Pt, Ru and RuO2 electrodes, which indicates that crystal growth begins from the film surfaces. Ferroelectric property was verified by the process at 350°C maximum temperature. PZT films were also crystallized directly on SiO2. This is useful for the fabrication of embedded FeRAM devices and 1Tr-type FeRAMs. The flash lamp process was found to have great potential for application to dielectric film formation, annealing processes and so on.

Application of Taguchi method and orthogonal arrays for characterization of corrosion rate of IrO2-RuO2 film

Ti/TiO2/IrO2–RuO2 electrodes were evaluated with an aid of Taguchi method and orthogonal arrays to elucidate the effect of the experimental parameters, such as type of intermediate layer between Ti substrate and IrO2–RuO2 film, heat treatment temperature, heat treatment time, and flow rate of air, on the corrosion resistance of the electrodes. Although the chemical composition of the as-deposited IrO2–RuO2 films was almost identical regardless of the processing conditions, it was found that the presence and the type of the TiO2 intermediate layer was a critical factor to the anticorrosion properties of the Ti/TiO2/IrO2–RuO2 electrodes among four different experimental parameters investigated. The optimal condition was the dip-coated IrO2–RuO2 film having the TiO2 intermediate layer prepared by plasma spray and subsequently heat treated for 120 min at 450°C with air flow rate of 3 sccm.

Electrical properties of Ru and RuO2 gate electrodes for Si-PMOSFET with ZrO2 and Zr-silicate dielectrics

In this work, we have studied the electrical and thermal stability of Ru and RuO2 electrodes on ZrO2 and Zr-silicate dielectrics. Very low resistivity Ru and rutile stoichiometric RuO2 films, deposited by reactive sputtering, were evaluated as gate electrodes on ultrathin ZrO2 and Zr-silicate (∼2.7 nm) films for Si-PMOS devices. Thermal and chemical stability of the electrodes were studied at annealing temperatures up to 800°C in N2 followed by a forming gas anneal. X-ray diffraction (XRD), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS) methods were used to study grain structure and interface reactions. Electrical properties were evaluated using MOS capacitors. The role of oxygen in these dielectrics was studied by comparing equivalent oxide thickness (EOT) changes as a function of annealing temperature for capacitors with ZrO2 and Zr-silicate dielectrics. For capacitors with Ru and RuO2 gate electrodes on both ZrO2 and Zr-silicate, excellent stability of EOT was detected. Flatband voltage and gate current as a function of annealing temperature were also studied. These studies indicate that Ru and RuO2 are promising gate electrodes for P-MOSFETs.

Preparation and Characterization of Pb(Zr,Ti)O3 Films Deposited on Pt/RuO2 Hybrid Electrode for Ferroelectric Random Access Memory Devices

Polycrystalline Pb(Zr,Ti)O3 (PZT) films were fabricated at a low temperature of 450°C by the electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD) method. Stoichiometric PZT films with the pure perovskite phase could be obtained over a wider range of deposition conditions on Pt/RuO2 hybrid electrodes than on RuO2 electrodes. PZT capacitors fabricated on Pt/RuO2 hybrid electrodes showed low leakage current and superior polarization characteristics compared with those on RuO2 electrodes. PZT capacitors fabricated on Pt/RuO2 were not as fatigue-free as those on RuO2 but had higher resistance to fatigue than those on Pt. The introduction of a PbTiO3 buffer layer prior to PZT film deposition on Pt/RuO2 improved the fatigue characteristics by suppressing the formation of nonstoichiometric interfacial layers. Good leakage current property (J: 5.8 ×10-7 A/cm2 at 200 kV/cm) and fatigue characteristic (P* - P∧: 9% drop after 4 ×109 fatigue cycles) could be obtained for the 110-nm-thick PZT film using Pt/RuO2 hybrid top and bottom electrodes. This electrode structure is thought to be promising for use as a capacitor of high-density ferroelectric random access memory (FRAM) devices. The fatigue model that can explain the fatigue characteristics of PECVD-PZT capacitors with various hybrid electrode configurations is also suggested.

Oxygen transport during annealing of Pb(Zr,Ti)O3 thin films in O2 gas and its effect on their conductivity

Lead zirconate titanate (PZT) thin films were deposited in a reactive argon/oxygen gas mixture by radio-frequency-magnetron sputtering. The use of a metallic target allows us to control the oxygen incorporation in the PZT thin film and also, using oxygen 18 as a tracer, to study the oxygen diffusion in the thin films. Electrical properties and crystallization were optimized with a 90-nm PZT thin film grown on RuO2 electrodes. These PZT films, annealed with a very modest thermal budget (550 °C) show very low leakage current densities (J = 2 × 10−8 A/cm2 at 1 V). In this article we show that a strong correlation exists between the oxygen composition in the PZT film and the leakage current density.

Characterization of RuO2 electrodes on Zr silicate and ZrO2 dielectrics

The rutile stoichiometric phase of RuO2, deposited via reactive sputtering, was evaluated as a gate electrode on chemical vapor deposited ZrO2 and Zr silicate for Si–p-type metal–oxide–semiconductor (PMOS) devices. Thermal and chemical stability of the electrodes was studied at annealing temperatures of 400, 600, and 800 °C in N2. X-ray diffraction was measured to study grain structure and interface reactions. The resistivity of RuO2 films was 65.0 μΩ cm after 800 °C annealing. Electrical properties were evaluated on MOS capacitors, which indicated that the work function of RuO2 was ∼5.1 eV, compatible with PMOS devices. Post-RuO2 gate annealing up to 800 °C, resulted in only a 1.4 Å equivalent oxide thickness (Tox-eq) change and 0.2 V flatband voltage change for Zr silicate and a 4 Å Tox-eq change for ZrO2 dielectrics. Tantalum electrodes were also studied on ZrO2 as a comparison of the stability of RuO2 electrodes.

Promising Gate Stacks with Ru & RuO2 Gate Electrodes and Y-silicate Dielectrics

ABSTRACTIn this work, we studied the electrical and thermal stability of Ru and RuO2 electrode on Y-silicate dielectrics in contrast to ZrO2 and Al2O3 dielectrics. Very low resistivity Ru and rutile stoichiometric RuO2 films, deposited via reactive sputtering, were evaluated as gate electrodes on ultrathin Y-silicate, ZrO2 and Al2O3 films for Si-MOS devices. Thermal and chemical stability of the electrodes was studied at annealing temperatures up to 800°C in N2 and subsequently forming gas anneal. XRD and XPS were measured to study grain structure and interface reactions. The morphology of the films was tested by atomic force microscopy (AFM). Electrical properties were evaluated via MOS capacitors. The role of oxygen inside dielectrics was studied by comparing equivalent oxide thickness change as a function of annealing temperature for capacitors with Y-silicate, ZrO2and Al2O3 dielectrics. Good stability of Ru and RuO2 gate electrodes on all dielectrics studied was found. Flatband voltage and gate current as a function of annealing temperature was also studied. It was found that capacitors with Y-silicate after high-temperature anneal had less positive flatband voltage shift than ZrO2 and Al2O3. For capacitors with Ru gate electrode, the significant flatband voltage shift after high temperature anneal could be partially removed by a forming gas anneal.