bluuebunny/crossref_metadata_2025 huggingface dataset:
New Metal Organic Gas Supply System by Using an Advanced Flow Control System
Authors: Yamaji Michio , Yamashita Satoru , Hidaka Atsushi , Nagase Masaaki , Ikeda Nobukazu , Sugawa Shigetoshi , Ohmi Tadahiro
Published: April 2012

Gas flow control is important factor that influences the concentration of process gas and the pressure of the process chamber. In manufacturing processes that use metal organic (MO) gases, a system that controls the flow rate of MO gas must be developed to improve film performance and the reliability of film formation. We have developed a high temperature flow control system based on pressure measurements (HT-FCS) to control the flow rate of MO gas. Moreover, a liquid source control system that combines a HT-FCS and vaporizer was developed. Using this system, it was possible to control the flow rate of MO gas with high accuracy for extended periods. A flow control system that can supply MO gas with a stable flow rate by vaporizing MO material with the quantity needed at each time has been realized.
Hybrid Orientation Substrate Fabrication Using Electron Beam Induced Orientation Selective Epitaxial Growth of CeO2(100) and (110) Areas on Si(100) Substrates
Authors: Inoue Tomoyasu , Shida Shigenari
Published: April 2012

Hybrid orientation structure of CeO2(100) and CeO2(110) regions on Si(100) substrates is attained using electron beam induced orientation selective epitaxial (OSE) growth by reactive magnetron sputtering. CeO2(100) layers grow in an area simultaneously irradiated by electron beams during the growth process, whereas CeO2(110) layers grow in the area without electron irradiation, which result from surface potential differences. The spatially controlled OSE grown samples are made on Si(100) substrates with various resistvities. XRD measurements are carried out to obtain the lateral orientation mapping within the epitaxial layer surfaces and reveal existence of the transition regions in between the above mentioned two orientation areas. The width of the transition regions is clarified to reduce proportionally with the logarithm of underlying Si substrate resistivity. A surface potential distribution model is proposed to explain the results.
Investigation of Antimony Oxide Films Deposited by Atomic Layer Deposition
Authors: Kalkofen Bodo , Mothukuru Venu Madhav , Klingsporn Max , Burte Edmund P.
Published: April 2012

Atomic layer deposition of antimony oxide thin films was investigated in a temperature range between 50 and 250 °C using triethylantimony and ozone. Layer thickness was measured by spectroscopic ellipsometry using adapted layer models. It was proved that homogenous deposition could be achieved on flat silicon wafers and in trench structures. Little growth was found below 100 °C deposition temperature and linear temperature dependence on the growth rate between 100 and 250 °C. High-resolution transmission electron microscope measurements of as-deposited films showed the existence of SiO2 interface layer and crystalline grains within the antimony oxide. The thermal stability of antimony oxide layers was investigated by rapid thermal annealing experiments in the temperature range of 500 to 850 °C. The layers were not stable above 700 °C, which was assumed to be the reason for failing to apply this material as dopant source for ultra-shallow antimony doping of silicon so far.
(Invited) Micropatternable Multifunctional Nanocomposite Polymers for Flexible Soft NEMS and MEMS Applications
Authors: Khosla Ajit , Gray Bonnie L.
Published: April 2012

This paper describes the fabrication, micro-machining, and characterization of novel polydimethylsiloxane (PDMS) based multifunctional nanocomposite polymers for flexible M-(micro-) and N-(nano) EMS(electromechanical systems). We discuss and define a general fabrication and micropatterning process for polymeric nanocomposites which can be electrically conductive, magnetic, or both in nature, and combined with non-doped polymer substrates. These developed nanocomposite polymers allows manufacture of flexible PDMS based active microfluidics and MEMS devices. Two different processes were developed to fabricate nanocomposite polymers using PDMS as a matrix material. These processes mainly differ in the method used to uniformly disperse the nanoparticles: process 1 employed shear mixing, while process 2 used ultrasonic processing. Two different nanocomposites have been demonstrated: 1) carbon-nanotube doped PDMS, 2) NdFeB doped PDMS. We also present a novel low cost, large scale, hybrid micro-molding technique on 12" x 24" or larger PMMA micromolds, allowing us to batch fabricate very large numbers of microfabricated devices.
(Invited) Nano-Derived, Micro-Chemical Sensors for High-Temperature Applications
Authors: Sabolsky Edward M. , Wildfire Christina , Ciftyurek Engin , Sabolsky Katarzyna
Published: April 2012

The objective of our work is to develop high-temperature, micro-scale, chemical sensors and sensor arrays composed of nano-derived, metal-oxide semiconducting (MOS) materials to detect gases such as H2, SOx, and H2S within high-temperature environments (>500C). In order to incorporate the MOS sensing nanomaterials within the micro-sensor platform, new methods for micro-patterning these materials into 3-D architectures were developed for single and array chemical sensors. Current work focuses on the deposition of the refractory nanomaterials through a micro-casting method where lost-molds are fabricated by conventional photolithography. The combined effects of colloidal stabilization, suspension characteristics, photoresist-suspension interactions, substrate-suspension interactions (wetting), and thermal processing on the resultant sensor processing and performance were investigated.
(Invited) Engineering of Nanocomposite Materials for Sensing Applications
Authors: Amini Alborz , Bahreyni Behraad
Published: April 2012

Nanocomposite materials are an interesting family of composite materials that are created by mixing nanoparticles with desired properties with a host material. This paper discusses the issue of optimal choice of processing parameters for target design criteria for sensing applications. We will also demonstrate how our recently developed numerical model may be employed to study the effects of nanoparticle and processing parameters on the performance of materials and devices.
A Compact CMOS 3-D Magnetic Field Sensor
Authors: Wang Gang , Misra D.
Published: April 2012

A ring-shape vertical hall device for X- and Y-direction, and a split-drain horizontal hall device for Z-direction are combined to implement the 3-D sensor. This merged design has the advantage of less area and lower power consumption. The sensitivities of vertical hall device (ring-shape magneto-resistor) and horizontal hall device (split-drain MAGFET) are estimated to be 0.11V/T and 2.88V/T respectively. Z-direction demonstrates a higher sensitivity. A high gain cascade differential amplifier is integrated with the sensor to further amplify the signal.
(Invited) Heterogeneous Integration of Ultra-Thin Sheets of Alternative Materials onto Silicon Substrates
Authors: Levin Scott M. , Kuang Jia , Cox Jacob , Mayer Jeffrey S. , Mayer Theresa S.
Published: April 2012

Electric-field-assisted assembly is used to position ultra-thin, micron-sized sheets of alternative materials in high density arrays on silicon substrates. Dielectrophoretic forces induced on the solution-suspended polarizable sheets by a spatially varying, non-uniform electric field attract and align the sheets to lithographically defined assembly electrodes on the substrate. Studying the assembly of 10 µm long, 100 nm thick chromium sheets fabricated in three different widths of 1.2, 2.4, and 3.0 µm showed that the maximum array density decreases with increasing width. This result provides insight into the assembly of sheets composed of doped semiconductor device layers and junctions.
(Invited) Low Frequency Noise Performance of State-of-the-Art and Emerging CMOS Devices
Authors: Claeys Cor , Aoulaiche Marc , Andrade M.G. C. , Rodrigues Michele , Martino Joao Antonio , Simoen Eddy
Published: April 2012

The development of future CMOS technologies in line with the ITRS roadmap necessitates not only a scaling of the critical device dimensions but also implies the introduction of new materials and even switching over to alternative horizontal, vertical or 3D device architectures. This paper aims to give an overview of the impact of some of these approaches on the low frequency noise performance and to give an outlook for the future.
(Invited) Heterogeneously Integrated III-V on Silicon for Future Nanoelectronics
Authors: Hudait Mantu K.
Published: April 2012

Shrinking feature sizes of CMOS transistor has enabled increase in transistor densities and this rising number of transistors increases the power consumption in ICs. Thus, the computing power is primarily constrained by power consumption and high-speed operation. Beyond sub 22 nm, high mobility III-V materials and new device architectures have the potential to provide higher switching speeds and to operate at <0.5V than Si FETs. Heterogeneous integration of such high mobility materials with QWFET architecture have recently emerged a promising transistor option for ultra-high speed and low voltage operation. This paper reviews the heterogeneous integration of InGaAs QWFETs on Si and provide a technological solution for making nanoscale transistors and various integration scheme. As a result, InGaAs quantum well FETs are poised to achieve higher Ion, low-off-state leakage, higher ION/IOFF ratio, higher fT, controlled short channel effect and thus have a potential for future high-speed and ultra-low-power electronics.
(Keynote) In Quest of a Fast, Low-Voltage Digital Switch
Authors: Theis Thomas N.
Published: April 2012

In a recent survey of the exploratory device literature (1), Theis and Solomon studied proposed low-voltage digital devices, and identified the underlying operating principles which enable those devices to overcome the voltage-scaling limit of the conventional field effect transistor. Here, I briefly summarize the status of the ongoing device research, and argue that the operating principles exemplified by these devices are quite general, and can be applied in ways that have not yet been explored. It is therefore likely that we are still in the early stages of the quest for a fast, low-voltage digital switch.
Pattern Dependency of Pure-Boron-Layer Chemical-Vapor Depositions
Authors: Mohammadi Vahid , De Boer Wiebe , Scholtes Tom L. , Nanver Lis K.
Published: April 2012

The pattern dependency of pure-boron (PureB) layer chemical-vapor depositions (CVD) is studied with respect to the correlation between the deposition rate and features like loading effects, deposition parameters and deposition window sizes. It is shown experimentally that the oxide coverage ratio and the size of windows to the Si on patterned wafers are the main parameters affecting the deposition rate. This is correlated to the gas depletion of the reactant species in the stationary/low-velocity boundary layer over the wafer. An estimation of the radius of gas depletion for Si openings and/or diffusion length of diborane in this study yields lengths in the order of centimeters, which is related to the boundary layer thickness. The deposition parameters; pressure and flow rates are optimized to minimize the pattern dependency of the PureB deposition rates.
P-type Doping of Silicon Suitable for Structures with High Aspect Ratios by Using a Dopant Source of Boron Oxide Grown by Atomic Layer Deposition
Authors: Kalkofen Bodo , Mothukuru Venu Madhav , Lisker Marco , Burte Edmund P.
Published: April 2012

For the first time successful application of thin boron oxide films grown by atomic layer deposition (ALD) as dopant source for shallow silicon doping is presented. ALD of B2O3 was carried out using tris(dimethylamido)borane and ozone as precursors. A growth per cycle of 0.3 Aå was obtained for 50 °C deposition temperature. Pure B2O3 films were highly instable after exposure to air but could be protected by thin Sb2O5 films that were in-situ grown by ALD as well. Rapid thermal annealing resulted in high concentration of active boron close to the silicon surface. The dependence of the doping results on the thickness of the initial B2O3 films could be shown and the favourable capping properties of the Sb2O5 material, which is chemically very stable in the as-deposited state but volatile and hence self-destructive at the annealing temperatures, were demonstrated.
Gas Source Depletion Study of High-Order Silanes of Silicon-Based Epitaxial Layers Grown with RPCVD and Low Temperatures
Authors: Chung Keith H. , Brabant Paul , Shinriki Manabu , Hasaka Satoshi , Francis Terry , He Hong , Sadana Devendra K.
Published: April 2012

In this paper, silicon gas-source depletion of silane, disilane, and a high-order silane, TF, is studied on oxide wafers. Two different growth mechanisms were discovered for TF. The faster mechanism depletes readily at temperatures as low as 525 oC. The "slower" mechanism does not deplete even at temperatures as high as 600 oC. This second growth mechanism has a growth rate as high as 13 nm/min at 550 oC and 43 nm/min at 600 oC under a chamber pressure 100 Torr. Two techniques, of reducing growth temperature and reducing growth pressure, are shown to suppress gas-source depletion. After the suppression of gas-source depletion, the faster mechanism exhibited a growth rate of 35 nm/min at 550 oC and a chamber pressure of 10 torr. Due to the two different growth mechanisms of TF, uniform growth deposition can be achieved for both low and high pressures for temperatures up to 600oC.
Electrical and Reliability Characterization of Ti/TiN Thin Film Resistor
Authors: Cheng Yi-Lung , Chang W. Y , Wei B. J , Lu F. H , Wang Y. L.
Published: April 2012

The resistance, resistance versus temperature, thermal stability, electrical stress, and constant voltage reliability stress The Ti/TiN thin film resistors were studied. The results indicate that Ti/TiN thin film resistor has excellent thermal stability up to 350oC. According to the electrical measurements, Ti layer has a weaker electrical resistance than the TiN layer. Additionally, the main failure mechanism of Ti/TiN thin film resistors is thermally activated by Joule-heating effect. The thermal activation energy is determined to be 1.3 for failure of the Ti layer and 1.8 eV for failure of the TiN layer. Based on these results, Ti/TiN thin film resistors are projected to be electrically stable for ten years of operation if their temperature is kept below 311oC.
(Invited) From MEMS-CMOS towards Heterogeneous Integration over Scale
Authors: Fujita Hiroyuki , Toshiyoshi Hiroshi , Ishida Tadashi
Published: April 2012

Micromachining technology has created a great variety of micro/nanoelectromechanical systems (MEMS/NEMS) through the integration of moving mechanisms, sensors, and electronics in a chip-size system. Integration of CMOS circuitry and MEMS technology improves the performance of micro sensors and actuators, programmability, miniaturization and simplicity of total device packaging. It is expected that MEMS-CMOS technology enables a more-than-Moore solution for the next-generation electronics. Such heterogeneous integration will be expanded over scale and material. Organic and inorganic chemistry as well as bio technology can provide functional materials for sensing, energy conversion and actuation. Printing can be an inexpensive way to have micro patterns on a meter-size substrate or film. The concept and examples of heterogeneous integration are discussed.
Scaled Micro-Relay Structure with Low Strain Gradient for Reduced Operating Voltage
Authors: Chen I-Ru , Hutin Louis , Park Chanro , Lee Rinus , Nathanael Rhesa , Yaung Jack , Jeon Jaeseok , King Liu Tsu-Jae
Published: April 2012

A relatively thin structural film with low strain gradient is developed for micro-relay technology. Relays fabricated using this film as the structural material operate with relatively low pull-in voltage and hysteresis, which is desirable for achieving low-power and high-endurance relay integrated circuits. With the improved structural film, relays with scaled layout dimensions are demonstrated for the first time.
(Invited) Applications of Nanowire Enabled Micro Opto-Thermal Actuation
Authors: Lu Yuerui , Lal Amit
Published: April 2012

Optical actuation for MEMS takes advantage of directly coupling of energy into selected device areas without any electrical interconnects as required in integrated electrostatic and piezoelectric actuation. In opto-thermo-mechanical actuation, light incident onto the structures is absorbed and converted to heat via photon absorption. Here, we realized linear, high efficiency and broad-band optical actuation for circular Si/SiO2 membrane resonator with integrated vertical silicon nano-pillar photonic crystal arrays. The first-ever nanopillar membrane acoustic speaker, using nanoscale photonic crystal optical absorbers for thermo-mechanical excitation of speaker membrane, is demonstrated. Moreover, our device has a very high surface area-to-volume ratio, enabling DNA sensing of femtomolar concentration. Femtomolar concentration DNA detection is important as this is the concentration needed for early-stage cancer and bacterial infection diagnosis application. Our method represents a mass-based platform technology that can sense molecules at low concentrations.
(Invited) Advances in Materials and Processes for 3D-TSV Integration
Authors: Lu James J.
Published: April 2012

There are a number of materials considered for various processes in 3D integration. These materials are critical to the development of key processes, such as through-strata-via (TSV), wafer and chip bonding, and wafer handling. This paper reviews the recent advances of some variable materials and processes, compares their advantages and technical challenges, and discusses the options towards full 3D-TSV integration.
Ge/Si p-n Diode Fabricated by Direct Wafer Bonding and Layer Exfoliation
Authors: Gity Farzan , Byun Ki Yeol , Lee KoHsin , Cherkaoui Karim , Hayes John M. , Morrison Alan P. , Colinge Cindy , Corbett Brian
Published: April 2012

We report on the formation and electrical characterization of current transport across a p-Ge to n-Si diode structure obtained by direct wafer bonding and layer exfoliation. A low temperature anneal at 400 °C for 30 minutes improved the forward characteristics of the diode. The Ion/Ioff ratio > 5×104 and > 8×103 is obtained at -0.5 V and -1 V, respectively The carrier transport mechanism was analyzed based on the I-V and C-V measurements and direct tunneling is suggested as the transport mechanism. This fabrication technique using a low thermal budget (T ≤ 400 °C) is an attractive option for heterogeneous integration.
Wet-Chemical Silicon Wafer Thinning Process for High Chip Strength
Authors: Yoshikawa Kazuhiro , Miyazaki Takumi , Watanabe Naoya , Aoyagi Masahiro
Published: April 2012

We proposed the wet-chemical Si wafer-thinning process and evaluated the damage caused by this process. For the damage evaluation, we measured the die fracture stress and fracture energy, and compared various wafer-thinning processes (backgrinding, wet-chemical Si wafer-thinning, backgrinding + chemical mechanical polishing, backgrinding + wet etching). The result of comparative study shows that wet-chemical wafer-thinning process has very high fracture stress/energy and demonstrates that the damage of wet-chemical Si wafer-thinning process is very small.
(Invited) Scaling Requires Continuous Innovation in Thermal Processing: Low-Temperature Plasma Oxidation
Authors: Lerch W. , Kegel W. , Niess J. , Gschwandtner A. , Gelpey J. , Cristiano Fuccio
Published: April 2012

The required temperature in semiconductor process technology is going in two extreme directions. Either very high temperatures (up to 1300°C) with very short durations on the order of milliseconds are required for highest dopant activation, or extremely low temperatures are needed for forming high-quality dielectrics with minimum dopant deactivation and redistribution. This contribution describes a new microwave plasma oxidation apparatus with unique features addressing the before-mentioned low-temperature process requirements. With this new technique the oxide growth rate was studied as a function of time, gas ambient, pressure, applied microwave power and silicon substrate parameters to determine crystallographic oxidation rate anisotropy and dopant concentration independent oxidation at temperatures well below 500°C. The "More-Moore" approach of geometrical scaling in 2D will soon come to a physical end and therefore new requirements related to the thermal budget occur. Additionally, the transition from 2D- to 3D-devices requires extremely conformal oxide growth. Both the low temperature and the conformal oxide growth will be demonstrated on test structures.
Characterization of Grobal and Local Wafer Shape Change along Through Silicon Via Process Steps
Authors: Lee Chang Hwan , Jie Seok Ho , Park Sang Soo , Yoo Hyung Won , Han Il Keoun , Yoo Woo Sik
Published: April 2012

As demands for high performance and highly functional devices increase, device scaling by continuing miniaturization and alternative three dimensional (3D) packaging techniques are required. As an alternative approach to traditional device scaling, 3D packaging using through silicon vias (TSVs) filled with copper (Cu) is being actively investigated. The development of stress, during various TSV fabrication steps, poses a risk of compromised device performance, reliability and yield loss. We have characterized global and local wafer shape change, along various TSV process integration steps, using a newly developed laser-based wafer surface profiling system. The importance of global (wafer level) and local (chip or die level) profile (flatness, bow and/or distortion) characterization and its contribution to proper understanding of the mechanisms involved in wafer bowing, stress build up and/or pattern overlay problems are discussed.
Enhancement in Electron Mobility at the Interface between Gd2O3(100) and n-type Si(100)
Authors: Sitaputra Wattaka , Tsu Raphael
Published: April 2012

An epitaxial growth of a single crystalline gadolinium oxide (Gd2O3) layer with (100) orientation on a p-type Si(100) substrate is obtained when the growth temperature is 200°C and the oxygen partial pressure is in the range of 10-7-10-6 Torr using molecular beam epitaxy technique. The growth on n-type Si(100), on the other hand, results in a polycrystalline structure with a dominant Gd2O3(400) peak observed in the XRD spectrum. Despite a poorer crystal structure, an enhancement in carrier mobility can be found only from the interface between the Gd2O3(100) and n-type Si(100). The mobility of 1730 cm2/V·s was observed at room temperature. This accumulation of the electrons at the interface and the mobility enhancement arise from the two-dimensional confinement due to charges transfer across the interface almost like a transfer doping.
Ultra-Thin SOI/BOX Layers and Next Generations Planar Fully Depleted Substrates
Authors: Schwarzenbach Walter , Barec Vincent , Cauchy Xavier , Daval Nicolas , Kerdiles Sebastien , Boedt François , Bonnin Olivier , Nguyen Bich-Yen , Maleville Christophe
Published: April 2012

UTBOX25 substrates are now ready for high volume manufacturing, as first substrate of choice for planar Fully- Depleted technology. Smart CutTM technology demonstrates its capability to provide ultra thin SOI & BOX layers with extremely tight thickness control as low as ± 5 Aå. Substrates to support scaling down to 11 nm node, including strained SOI, are under development and first results are presented
(Invited) On-Current Variability Sources of FinFETs: Analysis and Perspective for 14nm-Lg Technology
Authors: Matsukawa Takashi , Liu Yongxun , Endo Kazuhiko , O'uchi Shinichi , Masahara Meishoku
Published: April 2012

On-current (Ion) variability in FinFETs is comprehensively investigated with regard to contributions of three independent sources, namely, threshold voltage (Vt), parasitic resistance (Rpara) and trans-conductance (Gm) variations. Origins of the Vt and Rpara variations are further analyzed. The Gm variation exhibits a linear relationship in Pelgrom plot as well as the Vt variation, and is not reduced with scaling the gate dielectric thickness unlike the Vt variation. Using the scalability data for the variation components, perspective of the Ion variability for 14-nm FinFETs reveals that the Gm variation will be the dominant Ion variation source. A solution to reduce the Gm variation for FinFETs is also proposed.
The Effect of Plasma Treatment on Reducing Electroforming Voltage of Silicon Oxide RRAM
Authors: Xue Fei , Chen Yen-Ting , Wang Yanzhen , Zhou Fei , Chang Yao-Feng , Fowler Burt , Lee Jack
Published: April 2012

In this paper, we fabricated and investigated the electroforming process and switching behavior of Al/SiOx/Si MOS resistive random access memory (RRAM) devices. The switching mechanism and device performance including forming voltage, set/reset voltage, on/off ratio and retention have been analyzed. Memory structure was formed, or electroformed by applying voltage across the MOS device. This SiOx RRAMs show a unique switching behavior with set voltage lower than reset voltage. Thus, unlike other RRAMs, our RRAM devices do not need current compliance in the switching process. Furthermore, our device utilizes SiOx, which has been extensively used and is completely compatible with CMOS technology. The results show that introducing a plasma treatment process and optimizing the plasma conditions significantly reduced electroforming voltage.
Development of High Selectivity Phosphoric Acid and its Application to Flash STI Pattern
Authors: Cho Sunghyuk , Lee Young Bang , Han Ji Hye , Park Hyung Soon , Kim Hyung Hwan , Kwak Sanghyon , Yang Kihong , Hong Kwon , Park Sung Ki , Kang Hyo Sang
Published: April 2012

In a manufacturing semiconductor device, silicon nitride (Si3N4) and silicon oxide (SiO2) materials are typically and widely used as dielectric materials. In general, phosphoric acid is used for etch of silicon nitride film. The etch rate of phosphoric acid decreases as etch time increases and phosphoric acid has low selectivity against oxide layer. Therefore, phosphoric acid of high selectivity between silicon nitride and silicon oxide without particle generation is needed to remove silicon nitride film. Especially, high selectivity between nitride and oxide is important for flash device application since both nitride and oxide materials exist during nitride remove process in flash Shallow Trench Isolation (STI) pattern. Therefore, control of EFH through high selectivity nitride etching is important for improvement of device performance and we developed Phosphoric Acid with high selectivity between nitride and oxide without particle generation for further devices.
Energy, Environment and IMCC
Authors: Mogensen Mogens
Published: April 2012

This paper gives a brief description of the important role that the ionic and mixed conducting ceramics (IMCC) type of materials will play in the R&D of energy and environment technologies of the - presumably - near future. IMCC materials based technologies for energy harvesting, conversion and storage as well as for monitoring and protection of our environment are exemplified. The strong impact of the international IMCC research on development of devices based on such materials is illustrated, and some recent trends in the scientific exploration of IMCC are highlighted. Important groups of genuine IMCC are the fluorite and perovskite structured metal oxides that have proven practically applicable, but also fine structured composite materials consisting of separate, but well mixed, electronic and ionic conducting phases may do the job of a mixed ionic and electronic conductor (MIEC). Recent years' research has pointed to ever more complicated multiphase structures that have superior performance.
Huge Electrical Conductivity Changes in SrTiO3 upon Reduction of the Grain Size to the Nanoscale
Authors: Gregori Giuliano , Lupetin Piero , Maier Joachim
Published: April 2012

In this contribution, we present the electron conduction properties of nanocrystalline as well as microcrystalline undoped SrTiO3 ceramics obtained over a broad range of oxygen partial pressures (pO2) via impedance spectroscopy. Remarkably, compared to the bulk properties, an increase of the n-type conductivity by almost three orders of magnitude and a decrease of the p-type conductivity by more than three orders of magnitude are observed in the nanocrystalline samples. This generates a shift of the p-n transition (conductivity minimum) by twelve orders of magnitude in terms of oxygen partial pressure. The results can be explained in the light of space charge effects occurring as a consequence of a positive excess charge in the grain boundary core.
(Invited) Electronic and Ionic Transport in Ce0.8PrxTb0.2-xO2-δ and Evaluation of Performance as Oxygen Permeation Membranes
Authors: Chatzichristodoulou Christodoulos , Hendriksen Peter V.
Published: April 2012

The electronic conductivity of Ce0.8PrxTb0.2-xO2-δ (x = 0, 0.05, 0.10, 0.15, 0.20) was determined in the oxygen activity range aO2 ≈ 103 to aO2 ≈ 10-17 at 700-900 °C by means of Hebb-Wagner polarisation. The electronic conductivity of all the Ce0.8PrxTb0.2-xO2-δ compositions was significantly enhanced as compared to that of Ce0.9Gd0.1O1.95-δ, and its value was found to increase with increasing Pr/Tb ratio. The ionic mobility of Ce0.8PrxTb0.2-xO2-δ is similar to that of Ce1-2δGd2δO2-δ at the same oxygen vacancy concentration. The calculated oxygen flux of a Ce0.8PrxTb0.2-xO2-δ membrane is significantly enhanced relative to that of a Ce0.9Gd0.1O1.95-δ membrane at high oxygen activities of the permeate gas (aO2an > 10-15) due to the enhanced electronic conductivity of the Ce0.8PrxTb0.2-xO2-δ compounds. Interference between the ionic and electronic flows has a significant positive effect on the deliverable oxygen flux, as evaluated for Ce0.8Pr0.2O2-δ (1).
Investigation of MIEC Materials Using an Amperometric Oxygen Titration Method
Authors: Niedrig Christian , Braun Philipp , Menesklou Wolfgang , Wagner Stefan F. , Ivers-Tiffée Ellen
Published: April 2012

For any mixed ionic-electronic conducting (MIEC) oxide an assess¬ment of its basic material properties should include chemical stability as a function of oxygen partial pressure pO2. However, the stability range is not always easily experimentally accessible. Using a closed tubular zirconia "oxygen pump" setup with platinum electrodes facilitates precise control of the oxygen partial pressure in the enclosed volume within the whole pO2 range between 10-20 ... 1 bar at temperatures above 700 °C. By measuring the electric current necessary for pumping oxygen into or out of the sample chamber, the amount of oxygen transported can be determined with a high precision. In this way, the oxygen uptake or release of an oxide powder sample is determined as a function of pO2, temperature and time, yielding information on stoichiometry changes and the stability limits of an MIEC oxide.
Proton Incorporation in Rare-Earth Phosphates
Authors: Ray Hannah L. , Zhang Guojing , De Jonghe Lutgard C.
Published: April 2012

The microstructures and proton conductivities of Sr-doped LaPO4 synthesized by two different methods are compared. Though the microstructures and crystal structures obtained from the two methods are similar, the co-precipitation doping method proves to incorporate both more dopants and higher conductivity by about a factor of 5 than the mechanical mixing method. A possible origin of the increased Sr solubility is proposed.
Charge-Compensating Pyrophosphate Defect Structures in Sr-doped LaPO4
Authors: Solomon Jonathan , Adelstein Nicole , Asta Mark , De Jonghe Lutgard C.
Published: April 2012

Understanding the thermodynamics of proton incorporation into rare-earth phosphates via hydrolysis of pyrophosphate bonds is essential for its consideration as a viable proton-conducting fuel cell membrane. Specifically, such knowledge enables one to calculate expected proton concentrations as a function of various experimental conditions such as dopant level, temperature, and atmospheric environment. In order to develop a thermodynamic model, low energy defect structures must first be determined. In this work, the lowest energy oxygen vacancy (pyrophosphate defect) structure is calculated for LaPO4 using density functional theory.
Li-Ion Conductive Phosphate Glass Synthesized by Using Ion Exchange
Authors: Tsujimura Tomoyuki , Koike Akio , Kuroki Yuichi
Published: April 2012

To obtain Li-ion conductive glass materials, we synthesized SiO2-ZrO2-P2O5-Li2O glasses by Li+/Na+ ion exchange on Na-ion conducting SiO2-ZrO2-P2O5-Na2O glasses. The maximum ionic conductivity for Na-type phosphate glasses is 6.2 × 10-7, while that for Li-ion-exchanged phosphate glass is 5.5 × 10-5 S/cm at room temperature. The Li-ion phase obtained by ion exchange exhibited conductivities 1-4 orders of magnitude higher than that of the corresponding Na-ion phase. This may be attributed to the smaller size of Li+. Ion exchange is a useful technique for producing highly ionic glass electrolytes.
Incorporation of Hydroxyl Ions and Protons in Oxide Ion Vacancies in Nanoscale Yttria Stabilized Zirconia during Atomic Layer Deposition
Authors: Son Kyung Sik , Bae Min Young , Bae Kiho , Ha Jeong Sook , Shim Joon Hyung
Published: April 2012

This work provides direct evidence that protons are incorporated in yttria stabilized zirconia (YSZ) deposited by atomic layer deposition (ALD) during the fabrication of films and not from ambient water after deposition. An oxidant made of proton isotopes or deutrium was used as a tracer of the incorporated protons during the synthesis, and time-of-flight secondary mass ion mass spectrometry (TOF-SIMS) was conducted for depth profiling. We identified that protons or deutrium ions introduced during deposition truly favored to reside in the ALD YSZ layers and that the concentration of protons incorporated during ALD was related to the concentration of yttrium.
Defect Chemistry and Electrochemical Properties of BaZrO3 Heavily Doped with Fe
Authors: Kim Dong Young , Miyoshi Shogo , Tsuchiya Takashi , Yamaguchi Shu
Published: April 2012

To explore a novel concept of bi-percolating mixed conductor of proton and hole for a cathode material of solid oxide fuel cell (SOFC), we have studied a BaZrO3 heavily doped with Fe. The oxygen non-stoichiometry and electrical conductivity of BaZr1- xFexO3-δ with various x values have been prepared and examined by a thermogravimetry and ac two-probe impedance method as a function of temperature and Po2. At high oxygen partial pressures,the dominant charge carrier is estimated as holes, and the hole conductivity that exhibits a nonlinearity against the Fe concentration and marked increase at the percolation threshold is governed by a bond-percolation of Fe-O network. The effect of hydration on the electrical conductivity suggests that BaZr1-xFexO3-δ exhibits a mixed protonic-electronic conducting behavior in humidified conditions at lower temperature range.
Electronic Conductivity in Nanocrystalline Ce0.9Gd0.1O1.95 Thin Films at High Oxygen Partial Pressures
Authors: Gregori Giuliano , Göbel Marcus C. , Maier Joachim
Published: April 2012

Gadolinium doped cerium oxide (Ce0.9Gd0.1O1.95) thin films with different microstructure (epitaxial vs. nanocrystalline) were investigated by impedance spectroscopy in oxidizing conditions. As expected, with increasing grain boundary density the ionic conductivity decreased significantly. In addition to this, the sample with the smallest average grain size (10 nm) exhibited a remarkable electronic conductivity (25% of the total conductivity) at an oxygen partial pressure of 10-5 bar and temperature of 280°C despite the large dopant content. This at first surprising result can be fully explained in the framework of the space charge model.
Electronic Conductivity of Scandia-Stabilized Zirconia Doped with 1 mol% CeO2
Authors: Shimonosono Taro , Kishimoto Haruo , Yamaji Katsuhiko , Nishi Mina , Brito Manuel E. , Horita Teruhisa , Yokokawa Harumi
Published: April 2012

The electronic conductivity of scandia-stabilized zirconia doped with 1 mol% CeO2 was measured at 1173 - 1273 K in the oxygen partial pressure range (p(O2)) of 10-4 - 10-20 MPa. At 1273 K, the electronic conductivity of 1Ce10ScSZ was in proportion to the 1/4 and -1/4 power of p(O2) due to the hole and electron conductions in higher and lower p(O2) regions (> 10-6 and < 10-17 MPa), respectively. Upper deviation of electronic conductivity was observed at 1273 K in p(O2) range of 10-6 - 10-17 MPa. Such a deviation had the p(O2) dependency similar to the product of Ce3+ and Ce4+ concentrations obtained by thermodynamic calculations. The deviation of electronic conductivity disappeared at 1173 K. This indicates that the activation energy of electronic conduction contributed by 1 mol% Ce dopant was significantly higher than 2.01 eV reported for (CexZr1-xO2)0.8(YO1.5)0.2 with Ce content of x = 0.1.
(Invited) Ion Transfer and Ion Transport in Thin Oxide Films Investigated by Complementary Tracer Diffusion and Impedance Spectroscopy Measurements
Authors: Fleig Juergen , Kubicek Markus , Huber Stefanie , Ahrens Martin , Langer-Hansel Katharina , Gerstl Matthias , Hutter Herbert
Published: April 2012

Tracer diffusion experiments and impedance spectroscopic measurements are presented for three thin film systems: Sr-doped LaCoO3-x (LSC) on YSZ, SrTiO3 on sapphire and YSZ on SrTiO3. It is shown that different effects can be probed by the two techniques and thus both methods complement each other very well. Among others, it is shown that a SrTiO3/YSZ interface does not lead to a high ionic mobility and that tracer concentration steps in LSC help correctly understanding oxygen reduction kinetics. Moreover, indication of space charge zones near the surface of SrTiO3 thin films is given
Sheet Resistance in Thin Film Solid Oxide Fuel Cell Model Cathodes: A Case Study on Circular Bi1-xSrxFeO3-δ Microelectrodes
Authors: Wedig Anja , Lynch Matthew E. , Merkle Rotraut , Maier Joachim , Liu Meilin
Published: April 2012

The potential solid oxide fuel cell cathode material Bi1-xSrxFeO3-δ exhibits low electrical conductivities (1-12 S cm-1 at 750°C) and is therefore especially susceptible for significant sheet resistance effects when investigated in thin film form. Impedance spectra of circular thin film microelectrodes of Bi1-xSrxFeO3-δ (x = 0.2, 0.5 and 0.8) show remarkable features such as an increase in apparent ohmic resistance (high-frequency intercept) and the appearance of a semicircle at intermediate frequencies, due unlikely to an interfacial resistance contribution. To understand the origin of these features, a 2D empirical numerical model developed by Lynch et al. to account for sheet resistance in thin electrode films was applied to simulate the experimental spectra. All spectral features were reproduced qualitatively and, in most cases, nearly quantitatively indicating high sheet resistance to be the reason for the observed peculiarities. In the presence of a lateral electrical potential gradient, the apparent chemical capacitance strongly underestimates the real material properties, whereas the electrode surface resistance remains largely unaffected.
(Invited) Methodologies for Characterizing Mixed Conducting Oxides for Oxygen Membrane and SOFC Cathode Application
Authors: Hendriksen Peter V. , So̸gaard Martin , Plonczak Pawel
Published: April 2012

Two methods for detailed characterization of the process of oxygen exchange between the gas phase and a mixed conducting solid oxide are discussed. First, the use of solid electrolyte probes for measuring the change in oxygen activity over the surface of a mixed conductor is presented and advantages of the technique discussed. Secondly, the use of thin film model electrodes is treated. Studies of thin films applied by PLD on both sides of a YSZ single crystal are presented for three different film materials; La0.85Sr0.15MnO3, La0.6Sr0.4Fe0.8Co0.2O3 and La0.6Sr0.4CoO3. Varia-tions in electrode performance with film structure is elucidated and the rate of the exchange process on the films is compared to that observed on bulk samples.
Catalytic CO Oxidation over Au Nanoparticles Supported on Yttria-Stabilized Zirconia
Authors: Dole Holly A. , Kim Jong Min , Lizarraga Leonardo , Vernoux Philippe , Baranova Elena A.
Published: April 2012

Gold nanoparticles supported on yttria-stabilized zirconia (YSZ) were synthesized using a modified alcohol method which involves the stabilizing agent, polyvinylpyrrolidone (PVP). Two different average sizes (13.1 and 17.1 nm) of Au nanoparticles were synthesized. These catalysts were tested for gas phase CO oxidation. Since PVP is known to block the active Au sites, the catalysts were calcined at 300°C and 600°C in order to remove the PVP. Overall, higher catalytic activity was found for the smaller Au nanoparticles. It was also found that calcination is required in order to achieve activity, even though the particle size increases with this treatment. The effect of calcination temperature did not prove to be significant. It is demonstrated that O2- ionically conductive YSZ is a promising catalyst support that can finely disperse and stabilize Au nanoparticles for CO oxidation.
Understanding Surface Reactions in SOFC Cathodes Prepared by Infiltration
Authors: Küngas Rainer , Yu Anthony , Levine Julie , Vohs John M. , Gorte Raymond J.
Published: April 2012

The processes limiting the performance of solid oxide fuel cell (SOFC) were examined for composite cathodes made by infiltrating La0.8Sr0.2FeO3-δ (LSF) into porous yttria-stabilized zirconia (YSZ). Impedance spectra measured on symmetric cells calcined to 1123 K consisted of a single arc with a polarization resistance of 0.3 Ω cm2 at 973 K in air. The higher impedance of cells deactivated by calcination to 1373 K could be attributed to an additional low-frequency surface process. The addition of a conformal oxide coating of less than 1 nm in thickness further deactivated the LSF-YSZ cathode. At 873 K, the polarization resistance of Al2O3-coated cells increased by almost an order of magnitude. This deactivation was reversible; performance could be restored by a heat treatment that caused the conformal oxide coating to disintegrate.
Transient 3D FEM Impedance-Model for Mixed Conducting Cathodes
Authors: Häffelin Andreas , Joos Jochen , Ender Moses , Weber André , Ivers-Tiffée Ellen
Published: April 2012

The performance of solid oxide fuel cells (SOFCs) is often determined by the polarization resistance of the electrodes. Electrochemical impedance spectroscopy (EIS) enables a deconvolution of individual electrochemical processes. In case of mixed ionic-electronic conducting (MIEC-) cathodes the impedance spectra result from the coupling of gas diffusion, surface exchange and bulk diffusion of oxygen ions. In this paper we present a three-dimensional (3D) finite element method (FEM) model which allows the transient simulation of the underlying processes in a porous cathode structure. The developed model is validated with a well established homogenized 1D model by comparing the area specific resistance and the corresponding impedance spectra. In case of a homogeneous 3D microstructure the FEM simulation results show an excellent agreement with the homogenized 1D model. Furthermore, the 3D FEM model is applied for impedance simulations of a technical MIEC cathode which microstructure was reconstructed from FIB tomography.
Electrochemical Properties of Silver Based Composite Electrodes for SOFC Cathodes and Current Collectors
Authors: Sarikaya Ayhan , Petrovsky Vladimir , Dogan Fatih
Published: April 2012

Performance of the cathode and cathode current collecting layers is of vital importance for development of stable solid oxide fuel cells (SOFCs) during long-term operational conditions. Although pure silver electrodes densify and become impermeable for gas transport at operating temperatures (e.g. 800oC) of SOFCs, incorporation of oxide particles introduces open porosity to silver composites. Previously, it was demonstrated that stable porosity and electrical properties of porous silver composites were achieved at 800oC in air for >5000 hours. Stable open porosity of obtained silver current collectors was utilized to fabricate LSM (lanthanum-strontium manganite), LSF (lanthanum-strontium ferrite), and LSCF (lanthanum-strontium-cobalt ferrite) composites of silver for SOFC cathode applications. Impedance spectroscopy techniques were applied to reveal polarization mechanisms of fabricated cathode/current collector layers. While infiltration of LSM gave rise to the performance of porous silver as cathode, infiltration of LSF and LSCF lowered the cathode polarizations further due to their enhanced ionic conductivities.
(Invited) Defect Chemistry of Mixed Conducting Oxides for SOFC Cathode
Authors: Zhou Xiao-Dong
Published: April 2012

Two universal defect chemistry models are presented to relate the properties of a variety of p type perovskite conductors, including chromites, manganites, and ferrites, which can be tailored as mixed ionic and electronic conductors (MIECs). It is found that oxygen nonstoichiometry in these p type MIECs can be correlated using a term we call the ability for oxygen vacancy generation (AOG). The values of AOG can be obtained by simulating the electronic conductivity as a function of oxygen activity and temperature with two existing universal models that are based on the concept of delocalized electron holes and localized electron holes, respectively. Both the global defect chemistry models yield a significant difference of ability for oxygen vacancy generation for all the oxides in this study, which allows us to better understand and predict the electrochemical properties of perovskite type p-type conductors.
Electrical Properties of Electrosprayed YSZ Thin Films for Intermediate Temperature - Solid Oxide Fuel Cells (IT-SOFC)
Authors: Bailly Nicolas , Georges Samuel , Djurado Elisabeth
Published: April 2012

8 mol. % yttria stabilized zirconia (8YSZ) thin films, 0.5 - 9 µm thick, were deposited by Electrostatic Spray Deposition (ESD) on porous supported NiO-8YSZ anode substrates. The process and physico-chemical parameters related to this technique were adjusted in order to obtain dense coatings from both solutions and suspensions. The resulting microstructures were observed by scanning electron microscopy (FEG-SEM). The electrical properties, determined by AC impedance spectroscopy using an original calibration method of a bulk platinum micro-electrode, were compared to that of a YSZ dense bulk sample.
Parametric Electrochemical Impedance Spectroscopy Analysis on High Pressure In-Plane SOFC
Authors: Lee Shung Ik , Ohrn Theodore , Liu Zhien , Xing Zhengliang , Goettler Richard
Published: April 2012

Electrochemical Impedance Spectroscopy (EIS) analysis was conducted using various cell geometries at different operating conditions including fuel composition, pO2, temperature, and pressure in order to study the characteristics of Rolls-Royce in-plane SOFC. Parametric tests and RC circuit modeling facilitated EIS peak deconvolution to understand each parameter's effect on performance. By comparing EIS peak responses from symmetric button cell and unit cell geometry, four primary processes were identified which are related to 1) anodic activation, 2) fuel diffusion in porous layer, 3) cathodic activation, and 4) cathodic gas diffusion in porous layer. Polarization resistance (Rp) of cathodic activation (process2, p2) with a characteristic frequency range of about 100 to 600 Hz demonstrates (pO2)^-0.6 dependence throughout 1 to 6.4 bar range of operating pressure