bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic Detection of Nucleic Acid Molecules with a Field-Effect Transistor
Authors: Ingebrandt Sven , Han Yinhua , Sakkari Malla-Reddy , Stockmann Regina , Belinskyy Oleksandr , Offenhäusser Andreas
Published: April 2011

Currently, systems for the detection of nucleic acid sequences, known as DNA-chips, are getting lots of attention. Such systems usually involve either an enzymatic or chemical labelling reaction as part of the detection process. The next generation of DNA-chips aims at a labelfree, fully electronic readout system. Several new approaches to signal generation that avoid a labelling step have been developed in recent years. Besides other surface sensitive measurements the possibility of electrochemical impedance and field-effect measurements for the detection of biomolecules have been discussed. The fully electronic detection of charged biomolecules based on the field-effect principle offers a labelfree method, which combines the unique sensitivity and selectivity of biomolecular recognition reactions with an electronic chip-based readout. In this approach one type of molecules is fixed at a surface and the biomolecular reaction with complementary molecules is detected by change in the drain-source current of the transistor. This change can occur by a change of the interface capacitance of the transistor gate or by change of the surface potential during adsorption of the molecules. At the moment a complete theoretical description of the detection principle is still under discussion. However, the fully electronic readout of biomolecular reactions offers a unique principle for the construction of many different sensors for bioassays. We are working on an approach to detect the hybridization of DNA sequences using electrolyte-oxide-semiconductor field-effect transistor (EOSFET) arrays. This method allows direct and in situ detection of specific DNA sequences without any labelling.
Micro Sensor Operating at Room Temperature
Authors: Duk Song-Kap , Lee Duk-Dong
Published: April 2011

In the study, low power micro gas sensors operated at room temperature for the detection of NH3 and NOx gases are proposed. As candidate material of gas sensor for NH3 gas detection at room temperature, polyaniline(PANi) synthesized by chemical polymerization was selected. And Te(Tellurium) thin film was used for NOx gas detection at room temperature. By using these sensing materials, micro gas sensors for room temperature operation were prepared and measured the response characteristics for NH3 and NOx.

In case of PANi sensor, the structure was inverted staggered FET type having advantage of useful one for Lab-On-a-Chip. The operating principle of the sensor is based on the change in work function of PANi film caused by adsorption of gas molecules in air on the film surface. The change in work function was measured indirectly from that in gate voltage of the FET device. The responses to various gases (NH3, CH4, Methanol and CH3CN) were obtained in gate voltage step mode in R.H. 30%. And in case of Te sensor, the sensing material was thermally evaporated on glass substrate. The thickness and annealing temperature were 500 Å −2000 Å and 100 °C −300 °C, respectively. The Te-based micro gas sensor exhibited high sensitivity to NOx and good selectivity against CO and hydro-carbon gases. And by adding Ti to Te film, the sensor has a good selectivity to CO gas.
Interdiffusion and Reaction of Pd on Atomically Stepped 6H-SiC Surfaces: Progress Toward Thermally Stable High Temperature Gas Sensors
Authors: Stinespring C. D. , Peng C. Y. , Woodworth A. A. , Meehan K. , Murdoch-Kitt M. J. , Anderson C. L.
Published: April 2011

High temperature Pd-SiC Schottky diode gas sensors are known to thermally degrade due to interdiffusion and reaction at the metal-semiconductor interface. To understand and possibly eliminate this problem, detailed surface studies of thermally induced Pd-SiC surface interactions have been performed. These experiments compare standard 6H-SiC (0001) surfaces typical of those used in device fabrication with periodically stepped surfaces prepared by high temperature hydrogen etching. The Pd films range in thickness from the monolayer level (∼0.4 nm) to actual device dimensions (∼46.5 nm) and are deposited under ultrahigh vacuum conditions at ∼50 °C. These films are characterized in-situ using Auger electron spectroscopy both before and after annealing at 670 °C. The Auger lineshapes provide quantitative information on the chemistry of the reaction products. Ex-situ atomic force microscopy is used to characterize changes in surface morphology.
SiGe Thermoelectric Film for Gas Sensor Micro-Devices
Authors: Shin Woosuck , Tajima Kazuki , Choi Yeongsoo , Izu Noriya , Matsubara Ichiro , Murayama Norimitsu
Published: April 2011

A gas sensor micro-device using both thermoelectric film and catalyst film has been developed on the platform of micro-hotplate. Thermoelectric thin film of B-doped SiGe was deposited on the Si3N4/SiO2/Si substrate by helicon sputtering method and thermal annealing was carried out to crystallize the as-deposited amorphous-like film. With increasing the annealing temperature and time, the crystallization of the SiGe thin film progressed, resulting in high carrier mobility and large absolute value of Seebeck coefficient. The hydrogen sensitivity of the micro-thermoelectric gas sensors was investigated.
Lateral Distribution of Electrons Trapped in Nitride Layers
Authors: Lorenzini M. , Rosmeulen M. , Breuil L. , Haspeslagh L. , Van Houdt J. , De Meyer K.
Published: April 2011

The recent advent of nitride-based localized charge-trapping storage has raised much interest in the lateral characterization of the trapped charge distribution, which is fundamental in defining scalability and retention properties. A direct characterization technique based on amplitude-sweep charge-pumping measurements is exploited here to investigate the lateral distribution of trapped electrons along the channel length. Further, the technique is applied to monitor the charge redistribution in time at high temperature.
Long Time Data Retention and A Mechanism in Ferroelectric-Gate Field Effect Transistors with HfO2 Buffer Layer
Authors: Aizawa Koji , Kawashima Yoshihito , Ishiwara Hiroshi
Published: April 2011

A mechanism of the long-time data retention in the p-channel MFIS FETs with Pt/SBT/HfO2/Si gate structures was proposed. The MFIS FETs used in this study exhibited the drain current on/off ratio of approximately 6×103 even after 30 days had elapsed at room temperature. From the leakage current characteristics of the MFIS diode, the bulk leakage current density lower than 10-12 A/cm2 was presumed for 30-days data retention. On the other hand, we showed that the decrease of on-state drain current in the retention characteristics was explained by the flat-band voltage shift of approximately -0.3V for 30 days toward negative voltage direction. Therefore, it was also found that the trapped charge density as low as 1011 cm-2 was needed for obtaining the data retention of 30 days.
Excimer (XeCl) Laser Annealing of PbZr0.4Ti0.6O3 Thin Film at Low Temperature for TFT FeRAM Application
Authors: Xianyu W. X. , Cho H. S. , Kwon J. Y. , Yin H.X. , Noguchi T.
Published: April 2011

In this study, we successfully produced PbZr0.4Ti0.6O3 (PZT (40/60)) thin films with high crystallinity and high remnant polarization (Pr) at low process temperatures using pulsed excimer (XeCl) laser irradiation. In our experiments, amorphous PZT films were prepared on Pt/Ti/SiO2/Si substrates by a sol-gel method. A two-step process was used to crystallize the amorphous thin films: the films were annealed at 550°C for 10 min to initiate the nucleation of the PZT perovskite phase, and then annealed with an excimer laser heating at 400°C in a 120 Torr nitrogen gas atmosphere. Laser energy density was varied from 150 to 750 mJ/cm2 per pulse. x-ray diffraction (XRD) patterns show that 150–200 mJ/cm2 range multi-shot excimer laser irradiation drastically improved the crystallinity of the PZT perovskite phase, and FESEM photographs show that the PZT thin film has uniform-sized crystal grains. The ferroelectric properties were found to depend on the laser energy density and shot number. Before the laser annealing, the films show hysteresis loops with low Pr and the loops do not saturate. After laser annealing, the films show highly saturated hysteresis loops, with the Pr increasing from 2.2 μC/cm2 to 23.0 μC/cm2. We also propose a new technology for fabrication of thin film transistor (TFT)-driven FeRAM devices on arbitrary insulator substrate such as on glass.
Development of Nonvolatile Memory using Well-Ordered Ferroelectric Linear Molecules
Authors: Ishida Kenji , Katsumoto Kazunari , Kuwajima Shuichiro , Horiuchi Toshihisa , Yamada Hirofumi , Matsushige Kazumi
Published: April 2011

Ferroelectric vinylidene fluoride (VDF) molecular films were fabricated by simple vacuum evaporation method, and the ferroelectric properties and its fatigue were investigated. Formation of ferroelectric phase in VDF oligomer with low molecular weight is favored at low substrate temperature around -150°C. The well-ordered VDF oligomer thin films exhibit a lager value of remanent polarization(130mC/m2) than that of Poly(VDF). Fatigues of polarization reversal can be performed over 10∧5 cycles. The VDF oligomer films can be one of candidates for disposable nonvolatile memory with unique features such as flexible, wide areas and low cost processing.
Manipulation of 2D arrays of Si nanocrystals by ultra-low-energy ion beam-synthesis for nonvolatile memories applications
Authors: Bonafos C. , Cherkashin N. , Carrada M. , Coffin H. , Ben Assayag G. , Schamm S. , Dimitrakis P. , Normand P. , Perego M. , Fanciulli M. , Muller T. , Heinig K. H. , Argawal A. , Claverie A.
Published: April 2011

In silicon nanocrystal (nc) based metal-oxide-semiconductor (MOS) memory structures a fine control of the Si nc location in the gate oxide is required for the pinpointing of optimal device architectures. In this work, we show how to manipulate and control the depth-position, size and surface density of two dimensional (2D) arrays of Si ncs embedded in thin (<10 nm) SiO2 layers, fabricated by ultra-low-energy (typically 1 keV) ion implantation and subsequent annealing. Particular emphasis is placed upon the influence of implantation, annealing conditions and oxide thickness on the nanocrystal characteristics (e.g. size, density) and the charge storage properties of associated MOS structures. Structural investigation is performed by using specific characterization methods including Fresnel imaging for the measurement of the injection distance between the substrate and the nc band, as well as spatially resolved Electron Energy Loss Spectroscopy using the spectrum-imaging mode of a Scanning Transmission Electron Microscope to evaluate the size distribution and density of the ncs.
Reliable, Fast and Long Retention Si Nanocrystal Non-Volatile Memories
Authors: Carreras Josep , Garrido B. , Arbiol J. , Morante J. R.
Published: April 2011

We report in this work a Si-nanocrystal (Si-nc) MOS basic cell which shows, at the same time, fast writing times and long charge retention. This has been achieved by optimizing a structure reported previously that exhibited excellent retention characteristics. For the new structure, 15 keV Si ions have been implanted in a 40 nm thick oxide at high doses in order to obtain Si excess ranging from 10 to 20 atomic % at projected range (25nm). An annealing step at 1100 °C has been performed to precipitate the nanocrystals. We show that there is a Si excess compromise (density depth profile of Si-nc) in which write times are improved by at least 3 orders of magnitude (to the submillisecond range) while still maintaining a virtually infinite retention time. Such behavior has been correlated with structural characterization by EFTEM, which reveals a control oxide completely free of Si clusters and thick enough (11 nm) to prevent tunnelling from/to the gate electrode. The Si-ncs are located around the projected range and show a mean size of 2.7 ± 0.2 nm. The tunnel oxide is not completely free of Si-nc or clusters, as observed by EFTEM, but there is a significant reduction in mean size and density when approaching to the p-type substrate. We believe that these small Si-nc or clusters in the tunnel oxide play an important role in improving the performance of the devices. For charging (writing), when a gate bias is applied to the structure, these clusters assist like traps when tunneling to the central region. However, when the Si-nc are already charged, these nanoclusters do not similarly enhance the discharge process because they have larger band-gaps (due to quantum confinement) than the bigger Si-nc in the center of the layer, and therefore act as an insulating material. This simple model, based on the correlation of the most important electrical memory parameters and the structural information, has allowed us to engineer the implantation dose as a technological parameter when a trade-off between write and retention times is required. For our samples, this dose is about of 15% Si excess. Finally, endurance tests have been performed, showing a completely flat and stable programming window after 106 Write/Erase programming pulses.
Improved size dispersion of silicon nanocrystals grown in a batch LPCVD reactor
Authors: Wan Y. M. , van der Jeugd K. , Baron T. , De Salvo B. , Mur P.
Published: April 2011

Nanocrystal memories are widely invoked as potential solutions to overcome the scaling limitations of conventional FLASH memories beyond the 80nm technology node. In this study, the deposition of uniform silicon nanocrystals has been developed and optimized in a commercially available vertical furnace, an A400 from ASM.

It has been shown that low pressure chemical vapor deposition (LPCVD) of nanocrystals is feasible in a batch reactor but with a bad size dispersion of the silicon nanocrystals. To improve the size dispersion of the nanocrystals, a novel 2-step process with silane was introduced. In the conventional 1-step process, the oxide surface is exposed to silane at the same partial pressure and temperature during both nucleation and growth of the silicon nanocrystals. In this novel 2-step process, the surface is first exposed briefly to silane at a higher temperature (580–600°C) and following that, the temperature is lowered to allow selective growth on the existing silicon nuclei over the oxide surface. With such an approach, the nucleation step can be separated from the growth step and consequently the size dispersion can be improved by 50%.
Small “Magnetic” Clusters of Ga and In with As and V
Authors: Pozhar Liudmila A. , Yeates Alan T. , Szmulowicz Frank , Mitchel William C.
Published: April 2011

Several small clusters of Ga and In with As and V atoms are pre-designed to study effects of spatial constraints on electronic and magnetic properties of such clusters by means of the Hartree-Fock (HF) method. The obtained electronic energy level structures (ELSs), optical transition energies (OTEs) and spin densities of these clusters are compared to those specific to the corresponding clusters nucleated without spatial constraints. The pre-designed indium-based clusters demonstrate the enhanced spin densities as compared to those of the gallium-based clusters with equal numbers of V atoms, and thus can be of interest for applications in spintronic and magneto-optic memory materials development.
All-organic single-transistor permanent memory device
Authors: Schroeder Raoul , Majewski Leszek A. , Voigt Monika , Grell Martin
Published: April 2011

We present an all-organic permanent memory transistor using an amorphous spin-cast gate insulator. This gate insulator exhibits a remanent polarisation in its amorphous state, a unique property, which is best described as “ferroelectric-like”. The memory transistor thus built perform extremely well, even when compared to inorganic ferroelectric memory transistors; the memory “on” to memory “off” current ratio is close to 3×10-a4, while time-dependent studies show retention times of 14 hours and more.
Chemical Vapor Deposition of Germanium Nanocrystals on Hafnium Oxide for Non-Volatile Memory Applications
Authors: Wang Ying Qian , Chen Jing Hao , Yoo Won Jong , Yeo Yee-Chia
Published: April 2011

In this paper, we investigate the chemical vapor deposition (CVD) of Ge nanocrystals (NCs) directly on hafnium oxide HfO2 dielectric for non-volatile memory applications. Germane GeH4 was used as a precursor. Atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were used to characterize the Ge NCs. The dependence of the Ge NC size and density on the deposition temperature, deposition time, and flow rate was explored. A high Ge NC density of 1011 cm-2 was obtained at a deposition temperature of 600°C, with a mean diameter of about 16 nm. MOS capacitors with CVD Ge NCs embedded in the HfO2 gate dielectric were fabricated. Hysteresis of capacitance-voltage (C-V) characteristics of capacitors with Ge NCs was observed, demonstrating memory effect.
Effect of Ta2O5 on Dielectric Properties of Forsterite Ceramics
Authors: Kim Dong-Young , Lee Hong-Yeol , Jun Dong-Suk , Lee Sang-Seog
Published: April 2011

For the millimeter-wave dielectrics, forsterite-based ceramics were produced. Stoichiometric forsterite ceramics (Mg2SiO4) shows porous microstructure and very low Q*f values, which is not suitable for dielectrics in the microwave and millimeter-wave bands. The small addition (0.025 mol%) of Ta2O5 instead of SiO2 enhanced the sinterability of forsterite ceramics. The sintering temperature was reduced more than 150°C by the addition of Ta2O5. The density was greatly increased by Ta2O5 addition. The dielectric constant and Q*f of 0.025 mol% Ta2O5 modified forsterite sintered at 1500°C was 7.3 and 150, 000, respectively in microwave band (8–11GHz). The dielectric constant and Q*f of the same sample measured at 55GHz was 6.7 and 179, 000, respectively. Further addition of Ta2O5 decreases the sintering temperature.
Ferrite Properties and Technology Issues for Improved Microwave Systems
Authors: Dionne Gerald F. , Oates Daniel E.
Published: April 2011

Microwave device engineers continually seek materials advances to improve performance of magnetic components at reduced size and cost. Wherever possible, microstrip or stripline device configurations are adopted in preference to bulky waveguide structures. In radar and communications applications, the nonreciprocal propagation properties of ferrites are essential for realizing phase shifters, circulators, isolators, and power limiters. The introduction of superconductor circuits has led to the development of very low-loss phase shifters and circulators. Recent demonstrations of tuning reciprocal rf permeability by varying the state of magnetization at very low magnetic fields has led to the development of high-speed, high-Q tunable filters. In this paper, design issues of four classes of microwave device are reviewed from the standpoint of their ferrite material requirements: (1) low-loss microstrip phase shifters (2) microstrip tunable resonators, (3) self-biased microstrip circulators with normal or in-plane uniaxial anisotropy, and (4) high-power quasi-optical circulators.
A High K Nanocomposite for High Density Chip-to-Package Interconnections
Authors: Kim Taeyun , Nath Jayesh , Wilson John , Mick Stephen , Franzon Paul D. , Steer Michael B. , Kingon Angus I.
Published: April 2011

AC-coupled interconnects (ACCI) is a very exciting technology for achieving high-density chip-to-package interconnects while simultaneously providing a simple, mechanically robust interface. The technology combines the stress-relieving ‘underfill’ layer with the dielectric medium for capacitive coupling. For good AC coupling, it is desirable for the underfill material to have a permittivity around 20 at operating frequencies. However, there is a lack of microwave frequency data for high permittivity ceramic-polymer composite systems in the literature. This paper describes the development and microwave frequency characterization of high K nanocomposite underfill. For composite thick film preparation, 200 nm BaTiO3 nano-sized powder and photosensitive epoxy were used. The thermal behavior of composites was evaluated by DSC (differential scanning calorimetry). Dielectric properties were evaluated as a function of ceramic loading and curing temperature. The microwave dielectric properties were measured from 45 MHz up to 26.5 GHz to extract the capacitance and quality factor of the capacitor over the frequencies of interest using floating plate capacitors and T-resonator CPW structures. The permittivity was found to be ∼ 18 up to 14 GHz and the total Q factor of the capacitors was found to be 2 at 26.5 GHz for BaTiO3 (30 vol%)-epoxy composite. Dielectric loss was found to be 0.3 at 3 GHz, which would satisfactorily allow signaling well into the muti-gigabits range. The high K nanocomposite shows higher permittivity compared to materials currently used (air, K=1 or SiO2, K∼3.9) in capacitively coupled interconnects for chip-to-package communications.
Photodefinable Metal Oxide Dielectrics II: Direct Fabrication of Patterned High-k Dielectrics for Low Cost RF Capacitive MEMS Switches
Authors: Romeo Michael , Finger Isaac , Jeyakumar Augustin , Wang Guoan , Papapolymerou John , Henderson Clifford L.
Published: April 2011

In this paper, recent advancements related to a novel approach for fabricating low cost capacitive radio frequency microelectromechanical (RF MEMS) switches using directly photodefinable high dielectric constant metal oxides are discussed. In this approach, a radiation sensitive metal-organic precursor is deposited via spin coating and converted patternwise to a metal oxide using exposure to ultraviolet light. The feasibility of this approach has previously been demonstrated by fabricating bridge-type and cantilever-type RF MEMS switches. These early experiments showed that the photopatterned oxides displayed dielectric breakdown strengths that were insufficient for reliable operation of MEMS switches which required actuation voltages on the order of 20 V to 30 V. Recent work has focused on developing advanced processes based on the photodefinable metal-organic approach that can produce oxides with higher dielectric breakdown strengths and higher dielectric constants. A variety of post-patterning processes, including thermal baking and oxygen plasma annealing, were investigated and the impact of such processing on the resulting dielectric properties are discussed in this paper. It is shown that a combination of thermal annealing and oxygen plasma treatment can substantially improve the dielectric breakdown strength of the metal oxides produced using the photosensitive metal-organic process.
Novel High-Q Suspended Inductors on Alumina Ceramic Substrates
Authors: Woodward Lisa , Woo Paul , Capanu Mircea , Koutsaroff Ivo , Selvakumar C. R. , Cervin-Lawry Andrew
Published: April 2011

The growth of the wireless industry over the past ten years has created a need for good quality passive components, and in particular high Q factor inductors. There has been a large amount of work aimed at improving the quality factors of inductors on both silicon and ceramic/insulating substrates. KAIST and other research groups have explored a MEMS technique, releasing the inductor coil to create an air gap between the coil and underpass, on silicon [1]. Typically the inductor coil has been separated by a 50 to 100μm air gap and has required special processing such as a dual exposure photoresist mold [1]. In the present work, suspended inductor coils have been fabricated and characterized on an alumina ceramic substrate [2]. The gap used was only 1μm and this was enough to increase the self-resonance frequency by up to 4GHz after release. The inductor coils were created in 6–10μm thick electroplated gold and the underpass in an aluminum layer. A sacrificial LPCVD oxide layer was used as the released dielectric. In the present study a range of inductance from 1 to 30nH was explored before and after release. The Q factors achieved in this work range from 40 to 70 in the 2 to 10 GHz range, which are some of the best Q factors reported for planar inductors (see Table I). In addition, since the architecture allowed the use of three metal layers, released transformers were also fabricated. They showed promising high frequency performance, which also will be presented. Minimum insertion loss better then –2dB was achieved between 10–12 GHz. The above described process is simple, precise, and manufacturable with the ability to extend the useful range of inductors to higher frequencies (1–10 GHz).
A Silicon Nitride Based Shallow Trench Isolation with Side-Gate for CMOS Integration with MEMS Components for System-On-Chip Applications
Authors: Gokirmak Ali , Tiwari Sandip
Published: April 2011

We have developed a hydrofluoric acid (HF) resistant, composite shallow trench isolation (STI) process for MOSFETs utilizing silicon nitride as isolation material for on-chip integration of micro-electro-mechanical (MEMS) resonators and CMOS devices. Peripheral leakage currents in silicon nitride isolated MOSFETs are suppressed by employing an independently controlled polysilicon side-gate, surrounding the active area of the devices. Electrostatic control of the threshold voltage at the device periphery alleviates the need for edge implants, resulting in increased thermal budget. Compatibility with HF release processes and high temperature anneal cycles allows integration of MEMS components in close proximity to CMOS devices for system-on-chip applications. nMOSFET devices fabricated using this composite STI process show excellent device characteristics.
Three-dimensional magnetophotonic crystals based on artificial opals: fabrication and properties
Authors: Baryshev A. V. , Kodama T. , Nishimura K. , Uchida H. , Inoue M.
Published: April 2011

We have fabricated three-dimensional magnetophotonic (3D MPCs) crystals based on artificial opals. Structural and magnetic properties of 3D MPCs were studied by field emission scanning electron microscopy, x-ray diffraction analysis, and vibrating sample magnetometer. It was shown that increase of volume fraction of magnetite in the opal lattice leads to a dramatic decrease of transmitted light intensity in the visible region. We also found considerable changes in the Faraday rotation inside the (111) photonic bandgap of an opal—magnetite magnetophotonic crystal.
Fabrication of Integrated Magneto-Optic Isolator
Authors: Sung Sang-Yeob , Qi Xiaoyuan , Reinke John , Mondal Samir K. , Lee Sun Sook , Stadler Bethanie J. H
Published: April 2011

In optical applications, especially in optical communications, protecting light sources from harmful reflected energy is very important. With magneto-optic isolators, these light sources can be protected to extend their lifetimes and performance by blocking back-reflected light. The active element in these optical isolators is a magneto-optical garnet. However, garnet is difficult to integrate with semiconductors due to the high thermal budget usually required to obtain the garnet crystal structure. For example, current isolator garnets cannot be integrated monolithically into a photonic integrated circuit due to the growth process, liquid phase epitaxy, which requires growth temperatures of >900 °C and also garnet substrates. In this work, magneto-optical garnets were grown monolithically by low-temperature reactive RF sputtering, followed by an ultra-short (<15 sec) anneal. The refractive indices of the resulting garnets were measured using Fourier transform infrared (FTIR) spectroscopy. Various rib waveguides were fabricated by both wet etching and reactive ion etching (RIE). The width of the waveguides varied from 2 to 12 μm and the heights were varied from 0.5 to 1.0 μm. Sm-Co thin films were used for integrated biasing magnets. They were deposited on top of claddings of both magnesium oxide and yttrium oxide, all using the same sputtering system that was used to deposit the garnet films. These magnetic films had high enough remanent fields to saturate the garnet waveguides, and they had coercivities of 700 Oe. The Faraday rotations and waveguide losses of the subsequent isolators were measured to be 10 degrees and 0.1 dB/μm at 632 nm, respectively. Although this prototype is promising, optimization of the device designs is ongoing. In summary, this work succeeded in providing the first comprehensive report on etching YIG by RIE, in developing all of the steps required for integrating isolators on non-garnet substrates, and in proving the feasibility of these isolators.
Waveguide Optical Isolators Fabricated by Wafer Bonding
Authors: Mizumoto Tetsuya , Yokoi Hideki
Published: April 2011

Wafer bonding of a magnetooptic garnet crystal to III-V compound semiconductor and LiNbO3 is discussed for the application to waveguide optical isolators. Two types of waveguide isolators, an interferometric isolator and a semileaky isolator, are discussed. The interferometric isolator uses nonreciprocal phase shift and is composed of the GaInAsP guiding layer. The isolator has the advantage of integratability with optical active devices. The semileaky isolator composed of a magnetooptic garnet guiding and LiNbO3 upper cladding layer has the advantages of large fabrication tolerance and wide operating wavelength range. The performance of isolators is also demonstrated.
Magneto-Optical Properties of Multilayered FePt for High Density Recording
Authors: Ryu Hojun , Suh Dongwoo , Park Yongwoo , Kim Eunkyung , Yoo Yonggoo , Jung Woosug , Paek Mun Cheol
Published: April 2011

The Si3N4/FePt/Si3N4/Al/Si structures have been fabricated. 57 nm silicon nitride films have been used as dielectric layer for heat dissipation and 500 nm Al film used for reflection layer. The Kerr rotation angle was changed with the FePt layer thickness. At the 65 % Pt composition in 10 nm FePt layer, the maximum Kerr rotation angle was 0.82°. As increase with FePt thickness the Kerr angle is slightly decreased. The change of Kerr rotation angle and the thermal behavior of multilayered structure according to FePt thickness variation were also calculated by computer simulation.
Magnetorefractive effect in magnetophotonic crystals
Authors: Erokhin Sergey G. , Boriskina Yulia V. , Granovsky Alexander B. , Vinogradov Alexey P. , Zhao X.S. , Inoue Mitsuteru
Published: April 2011

The magnetorefractive effect in one-dimensional magnetophotonic crystals was investigated at a wavelength of about 3 μm. It is shown that the magnitude of magnetorefractive effect can be increased to 10–15 times in comparison with one magnetic layer of the same thickness positioned on a metallic mirror.
The Effect of Mn Concentration on Curie Temperature and Magnetic Behavior of MOCVD Grown GaMnN Films
Authors: Berkman Erkan Acar , Reed Mason J. , Erdem Arkun F. , El-Masry Nadia A. , Zavada John M. , Oliver Luen M. , Reed Meredith L. , Bedair Salah M.
Published: April 2011

We report on the growth and characterization of dilute magnetic semiconductor GaMnN showing ferromagnetism behavior above room temperature. GaMnN films were grown by MOCVD using (EtCp2)Mn as the precursor for in-situ Mn doping. Structural characterization of the GaMnN films was achieved by XRD, SIMS and TEM measurements. XRD and TEM confirmed that the films were single crystal solid solutions without the presence of secondary phases. SIMS analysis verified that Mn was incorporated homogeneously throughout the GaMnN layer which was ∼0.7μm thick. Ferromagnetic behavior for these films was observed along the c-direction (out of plane orientation) in a Mn concentration range of 0.025–2%. The saturation magnetization ranged from 0.18–1.05 emu/cc for different growth conditions. Curie temperatures of the GaMnN films were determined to be from 270 to above 400K depending on the Mn concentration. This dependence of Curie temperature on concentration of Mn in GaMnN indicates that the grown films are random solid solutions. SQUID measurements ruled out the possibility of spin-glass and superparamagnetism in these MOCVD grown GaMnN films. The grown films were electrically semi-insulating; however PL measurements showed that the films were still optically active after Mn doping. This study showed that the growth of III-Nitride films doped with Mn requires a small window of growth conditions that depend on growth temperature and (EtCp)2Mn flux to achieve ferromagnetism above room temperature, and the magnetic response of the film depends on the Fermi level position. We suggest that ferromagnetism occurs when the Fermi level lies within the Mn energy level which is 1.4 eV above the GaN valence band.
Recent Advances in Three Dimensional Thin Film Microbatteries
Authors: Nathan M. , Golodnitsky D. , Yufit V. , Strauss E. , Ripenbein T. , Shechtman I. , Menkin S. , Peled E.
Published: April 2011

Autonomous MEMS require similarly miniaturized power sources. We present the first three-dimensional (3D) working thin-film microbattery (MB) technology that is compatible with MEMS requirements. Our 3D MBs are formed in perforated substrates (silicon chip or glass microchannel plate), in which a sandwich-like thin-film battery structure is deposited conformally and sequentially on all available surfaces, using wet chemistry. The area of high aspect ratio holes in the substrate enhances the capacity and energy density per given substrate footprint by more than an order of magnitude. Full 3D cells were manufactured on both glass and silicon substrates. A 3D cell on a micro-channel plate substrate exhibited a capacity of ca. 2mAh/cm2, in good agreement with the ca. 23 times area gain provided vs an identical footprint 2D cell.
Structural and Electrochemical Properties of LiMn0.4Ni0.4Co0.2O2
Authors: Ma Miaomiao , Chernova Natasha A. , Zavalij Peter Y. , Stanley Whittingham M.
Published: April 2011

The layered oxide LiMn0.4Ni0.4Co0.2O2 was synthesized by heating the mixed hydroxide precursor. This 442 composition was found to show high capacity. It has the optimum cobalt concentration to both substantially order the lattice, yet leave enough nickel on the lithium sites to minimize conversion to the 1T structure of CoO2 on deep charging. A combined x-ray and neutron diffraction study showed conclusively that only nickel, not manganese or cobalt is found on the lithium sites at room temperature. Magnetic measurements also confirmed the presence of nickel on the lithium sites, and showed the effectiveness of cobalt at minimizing nickel disorder. Heating above 800°C always leads to nickel disorder. The structural and thermal stability of reduced lithium content materials was studied; the structure remains rhombohedral except for x≤0.05, and cobalt substitution improves the thermal stability of the layered compound, but not the chemical stability.
Intermediate Temperature Electrochemical Ceramic Oxygen Generators
Authors: Sin Agusti , Aricò Antonino S. , Gullo Laura , Rosa Daniela La , Kopnin Evgeny , Dubitsky Yuri , Zaopo Antonio , Antonucci Vincenzo
Published: April 2011

In the present work, an electrochemically driven ceramic oxygen generator (ECOG) device is investigated. The present device is based on an electrode supported architecture. Structural and electrochemical characterizations of the electrochemical cell have been carried out. The O2 production rate has been measured showing a performance four times higher than the generally accepted targets for practical applications. The high performance obtained with this device, indicates that there are good perspectives to decrease the O2 production costs significantly decreased as well as small and light weight devices for portable uses are envisaged.
Electrochemical behaviour of Co-doped LSGM perovskites prepared by sol-gel synthesis
Authors: Polini Riccardo , Falsetti Alessia , Traversa Enrico , Schäf Oliver , Knauth Philippe
Published: April 2011

La0.8Sr0.2Ga0.8Mg0.2-xCoxO3-δ (LSGMC) powders containing different amounts of Co (x = 0.05 and 0.085) were prepared by a citrate sol-gel method. Crystalline powders were obtained by firing at 1000°C (10 h) and dense high-purity pellets were prepared by pressing (300 MPa) and sintering in air at 1475°C (5, 10 and 20 h). The sintered pellets of LSGMC were characterized by X-Ray Diffraction (XRD) Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The conductivity of sintered LSGMC pellets containing different amounts of Co ions in the B sites of the perovskite lattice was assessed by electrochemical impedance spectroscopy (EIS) in the 250–750 °C temperature range. Conductivity values and apparent activation energies were in good agreement with previously published data referring to materials with same composition, but prepared by solid-state reaction.
NMR and impedance study of H+-ion irradiated TlH2PO4
Authors: Kim Se Hun , Lee Kyu Won , Jang Jae Won , Lee Cheol Eui , Noh S. J.
Published: April 2011

The H+-ion treatment effect on TlH2PO4, a KH2PO4 (KDP)-type ferroelectrics, was studied by nuclear magnetic resonance (NMR) and AC dielectric measurements. A sample of TlH2PO4 was irradiated by 1-MeV H+ ion beams to a dose of 1015 ions/cm2. The irradiation changed the hydrogen-bond geometry, presumably affecting the order-disorder proton dynamics. The deformation of the PO4 tetrahedra was identified by the isotropic chemical shift and the full width at half maximum (FWHM) of the high-resolution 31P NMR spectra. A prominent decrease in the dielectric constant was also observed after the irradiation. The macroscopic and microscopic changes due to the irradiation are discussed in the light of the proton dynamics.
Synthesis, Characterization and Thermal Stability of Highly Crystallized Titania Nanotubes
Authors: Poudel B. , Wang W. Z. , Dames C. , Huang J. Y. , Kunwar S. , Wang D. Z. , Banerjee D. , Chen G. , Ren Z. F.
Published: April 2011

Gram quantities of titania (TiO2) nanotubes, with typical outside diameter about 9 nm, wall thickness about 2.5 nm, and length about 600 nm, were synthesized from anatase nano- and micro-powder using the hydrothermal method. The crystallization, structure, and phase stability of the nanotubes at high temperatures were systematically studied. A morphology change from nanotube to nanowire was observed at 650°C. The as-prepared nanotubes were usually contaminated with sodium impurities, other TiO2-derived phases and were poorly crystallized, but under optimized synthesis conditions the impurity phases was completely removed, resulting in highly crystallized pure nanotubes. The volume filling fraction of the autoclave as well as the concentration of the acid treatment were found to be particularly important for controlling the purity and crystallinity of the resulting nanotubes.
Dye Sensitized Solar Cells Using Nanostructured Thin Films of Titanium Dioxide
Authors: Gish Douglas A. , Kiema Gregory K. , Jensen Martin O. , Brett Michael J.
Published: April 2011

Dye sensitized solar cells (DSSCs) were fabricated using porous thin films of TiO2. These films were deposited by electron beam evaporation and an advanced substrate motion technique called PhiSweep. PhiSweep, an extension of glancing angle deposition (GLAD), allows for greater control over the surface area of nanostructured thin films than is possible with traditional GLAD. The as-deposited films were amorphous, so the films were annealed to improve their crystal structure. The films were sensitized with a photoactive dye and implemented into a DSSC configuration as the electron collecting electrode. It was expected that the higher surface area of the films produced using the PhiSweep method would improve the cell performance compared with cells made using traditional GLAD films of TiO2. However, the performance of the cells prepared using PhiSweep films was likely hindered by higher internal resistance of the films compared to the films prepared by traditional GLAD. The highest photoelectric conversion efficiency of the dye sensitized solar cells produced using the PhiSweep method was 1.5%.
Bulk Heterojunction Photovoltaic Cells from Polymer Mixtures with Soluble Oxadiazole and Quinoline Polymers as Electron Acceptors
Authors: Economopoulos Solon , Chochos Christos L. , Govaris Giannis K. , Yiannoulis Panagiotis , Kallitsis Joannis K. , Gregoriou Vasilis G.
Published: April 2011

The interplay between phase separation in polymer blends consisting of the electron donating poly(3-hexylthiophene-2, 5-diyl) (P3HT) or poly[2-methoxy-5-(2'-ethylhexyloxy)-, 4-phenylenevinylene] (MEH-PPV), with either polyquinoline or a fluorene-oxadiazole copolymer as the electron accepting polymers is presented herein. The bulk heterojunction photovoltaic performance has been examined for these blends along with a new copoly(aryl ether) containing substituted anthracene and fluorene segments coupled with aromatic 1, 3, 4-oxadiazole moieties. Photoluminescence quenching in the MEH-PPV blends as well as a 100-fold photocurrent enhancement of the bulk heterojunction device P3HT/SDPQ photovoltaic device were observed compared to the single layer P3HT device. Finally, the structure and morphology of these films was investigated using atomic force microscopy and scanning electron microscopy in an attempt to correlate the role of morphology to photovoltaic performance.
III-V Multi-Junction Materials and Solar Cells on Engineered SiGe/Si Substrates
Authors: Ringel Steven A. , Andre Carrie L. , Lueck Matthew , Isaacson David , Pitera Arthur J. , Fitzgerald Eugene A. , Wilt David M.
Published: April 2011

The monolithic integration of high efficiency III-V compound solar cell materials and devices with lower-cost, robust and scaleable Si substrates has been a driving force in photovoltaics (PV) basic research for decades. Recent advances in controlling mismatch-induced defects that result from structural and chemical differences between III-V solar cell materials and Si using a combination of SiGe interlayers and monolayer-scale control of III-V/IV interfaces, have led to a series of fundamental advances at the material and device levels, which establish that the great potential of III-V/Si PV is within reach. These include demonstrations of GaAs epitaxial layers on Si that are anti-phase domain-free with verified dislocation densities at or below 1×106 cm−2 and negligible interface diffusion, minority carrier lifetimes for GaAs on Si in excess of 10 ns, single junction GaAs-based solar cells on Si with open circuit voltages (Voc) in excess of 980 mV, efficiencies beyond 18%, and area-independent PV characteristics up to at least 4 cm2. These advances are attributed in large part to the use of a novel “engineered Si substrate” based on compositionally-graded SiGe buffers such that a high-quality, low defect density, relaxed, “virtual” Ge substrate could be developed that can support lattice-matched III-V epitaxy and thus merge III-V technology based on the GaAs (or Ge) lattice constant with Si wafers. This paper focuses on recent results that extend this work to the first demonstration of high performance III-V dual junction solar cells on SiGe/Si. Open circuit voltages in excess of 2 V at one-sun have been obtained for the conventionally “lattice-matched” In0.49Ga0.51P/GaAs dual junction cells on inactive, engineered SiGe/Si; to our knowledge is the first demonstration of > 2V solar power generation on a Si wafer. Comparisons with identical cells on GaAs substrates reveal that the Voc on engineered Si retains more than 94% of its homoepitaxial value, and that at present both DJ/GaAs and DJ/SiGe/Si cells are similarly limited by current mismatch in these early cells, and not fundamental defect factors associated with the engineered Si substrates.
Preparation and characterization of monolithic HgCdTe/CdTe tandem cells
Authors: Wang S. L. , Drayton J. , Parikh V. , Vasko A. , Gupta A. , Compaan A. D.
Published: April 2011

A prototype monolithic HgCdTe/CdTe superstrate tandem cell has been fabricated by RF sputtering, comprising a CdTe/CdS top cell, a ZnTe:N/ZnO:Al interconnect junction and a HgCdTe/CdS bottom cell. The Hg1−xCdxTe film as the bottom absorption layer was deposited by RF sputtering with 70% or 85% Cd content in the Hg1−xCdxTe magnetron target. Hg1−xCdxTe films with band gap from 0.98 eV to 1.45 eV were obtained by controlling the deposition temperature. CdCl2 thermal treatments were used to improve the Hg1−xCdxTe film electrical properties. A nitrogen-doped ZnTe film combined with an aluminium (Al) doped ZnO film formed a good interconnect junction. Results of Voc = 0.99 V and Jsc = 2.1 mA/cm2 were obtained in the best such tandem cell at one sun (AM1.5).
Harvesting Betavoltaic and Photovoltaic Energy with Three Dimensional Porous Silicon Diodes
Authors: Sun Wei , Kherani Nazir P. , Hirschman Karl D. , Gadeken Larry L. , Fauchet Philippe M.
Published: April 2011

Conventional two-dimensional p-n diodes can be used for betavoltaic and photovoltaic energy conversion, but the device efficiency is limited by the planar geometry. We propose and demonstrate a novel three-dimensional diode geometry based on porous silicon. The 3D pore array provides two very important features: (1) the storage of the radioisotope energy source and (2) its extreme proximity to the p-n junction on each pore wall. The particle energy losses are thereby minimized prior to entering the conversion layer. In betavoltaics, our 3D betavoltaic device efficiency is 10 times that of a similar planar device. In photovoltaics, photons play the role of beta particles and photon trapping inside the pores enhances the conversion efficiency. Further fabrication and geometry optimization can result in practical, high performance devices.
Density of States in Tritiated Amorphous Silicon Measured Using CPM
Authors: Pisana Simone , Costea Stefan , Kosteski Tome , Kherani Nazir P. , Zukotynski Stefan , Shmayda Walter T.
Published: April 2011

The constant photocurrent method has been used to obtain the density of occupied electronic states of tritiated amorphous silicon thin films. The analyses showed a peak of defects located 1.24 eV below the conduction band edge, suggesting that the main type of defect present in the films was a doubly occupied dangling bond. The concentration of defect states increases as a result of tritium decay by about two orders of magnitude over a period of 500 hours. The defect density in the tritiated amorphous silicon samples could be reduced by thermal annealing, after which it increased once more.
Structure and stability of complex metal hydrides – theoretical approach
Authors: Łodziana Zbigniew , Vegge Tejs
Published: April 2011

In this paper systematic approach to study the structural stability of the complex hydride, LiBH4 is presented. The ground state energies of various symmetry structures are determined by means of Density Functional Theory. Simulated annealing method is used to confirm if ground state structures represent real energy minima. The vibrational spectrum and temperature dependence of the free energy of the structures with the lowest energies is determined. Calculated Raman active modes for three symmetries are presented. We show that at high temperatures LiBH4 possesses monoclinic symmetry and some of the low energy structures are unstable with respect to atomic vibrations. Our studies point to the necessity of calculation of the phonon spectra for complex metal hydrides that contain covalently bounded hydrogen.
In situX-ray and neutron powder diffraction study of LaNi5-xSnx–H systems
Authors: Nakamura Yumiko , Bowman Robert C. , Akiba Etsuo
Published: April 2011

We have studied structural change and lattice strain formation during absorption and desorption of hydrogen (deuterium) by high purity LaNi5-xSnxalloys (x= 0.22, 0.25) usingin situX-ray and neutron diffraction along with simultaneously measuring theP-Cisotherms. From profile analysis of the X-ray diffraction data, lattice parameter and lattice strain in each hydriding state are evaluated.In situneutron diffraction data provided hydrogen occupation changing with hydrogen content. Significant lattice contract and strain formation were observed in the hydride phase in desorption. This behavior was related with decrease in hydrogen occupation in the hydride phase revealed from the neutron diffraction data.