bluuebunny/crossref_metadata_2025 huggingface dataset:
Alternative Routes to Porous Silicon Carbide
Authors: Friedel Bettina , Greulich-Weber Siegmund
Published: April 2011

A low-cost alternative route for large-scale fabrication of high purity porous silicon car-bide is reported. This allows a three-dimensional arrangement of pores with adjustable pore di-ameters from several 10 nanometers to several microns. The growth of SiC is here based on a combined sol-gel and carbothermal reduction process. Therein tetraethoxysilane is used as the primary silicon and sucrose as the carbon source. We provide two different sol-gel based ways for preparation of porous SiC, obtaining either a regular porous or a random porous type. Regu-lar porous SiC with monodisperse ordered spherical pores of predefined size is obtained via liq-uid infiltration of a removable opal matrix. Whereas random porous material with polydisperse pores of an adjustable size distribution range, but without order, can be achieved via free gas phase growth. This is performed by degradation of granulated sol-gel prepared material inside a sealed reaction chamber, resulting in a SiO/CO/SiC rich gas atmosphere, which causes SiC growth inside the granulate itself. For both types doping of the initially semi-insulating porous SiC is possible either during the sol-gel preparation or via the gas phase during the following annealing procedure. As probing dopants we have used P, N, B and Al, which are well known from 'conventional' SiC. Composition and structure of the obtained material was investigated using scanning electron microscopy, X-ray diffraction, nuclear magnetic resonance and Fourier transform infrared spectroscopy.
Influence of Crystal Growth Conditions on Nitrogen Incorporation During PVT Growth of SiC
Authors: Hansen Darren , Loboda Mark
Published: April 2011

The control and understanding of the incorporation of nitrogen during SiC PVT continues to play an important role in SiC crystal growth. Nitrogen acts both as a dopant and an impurity depending on the growth conditions and desired resistivity. Epitaxial growth by CVD provides some insight into N incorporation in terms of the face effects, temperature, and impact of the chemical species in terms of the C/Si ratio. This paper will present experimental results showing trends regarding nitrogen incorporation during SiC PVT. Various crystal growth processes operated under constant nitrogen partial pressures were found to produce wide ranges of SiC resistivity. These effects will be analyzed in light of the process impact on gas phase elemental composition (1), crystal stress (2), dopant activation (3) and crystal defectivity (4). The goal of this paper is to provide additional insights regarding nitrogen incorporation during SiC PVT, and in turn drive towards a more holistic approach to control the resistivity of 4H n+ SiC material, based on the understanding established from SiC epitaxy technology.
Residual Stress in CVD-grown 3C-SiC Films on Si Substrates
Authors: Volinsky Alex A. , Kravchenko Grygoriy , Waters Patrick , Reddy Jayadeep Deva , Locke Chris , Frewin Christopher , Saddow Stephen E.
Published: April 2011

Having superior mechanical properties, 3C-SiC is one of the target materials for power MEMS applications. Growing 3C-SiC films on Si is challenging, as there is a large mismatch in lattice parameter and thermal expansion between the SiC film and the Si substrate that needs to be accommodated, and results in high residual stress. Residual stress control is critical in MEMS devices as upon feature release it results in substantial deformation.

3C-SiC single crystalline films were deposited on 50 mm (100) and (111) Si substrates in a hot-wall CVD reactor. The film tensile residual stress was so high that it fractured on the (111) Si wafer. The resulting film thickness on the (100) Si wafer was non-uniform, having a linear profile along the growth direction. This presented a challenge of using the substrate curvature method for calculating residual stress. Finite Element Method correction was applied to the Stoney's formula for calculating the residual stress along the wafer radius. Suggestions for reducing the amount of residual stress are made.
Silicon Carbide Hot-Wall Epitaxy for Large-Area, High-Voltage Devices
Authors: O'Loughlin Michael , Irvine K. G. , Sumakeris J. J. , Armentrout M. H. , Hull B. A. , Hallin C. , Burk A. A.
Published: April 2011

The growth of thick silicon carbide (SiC) epitaxial layers for large-area, high-power devices is described. Horizontal hot-wall epitaxial reactors with a capacity of three, 3-inch wafers have been employed to grow over 350 epitaxial layers greater than 100 μm thick. Using this style reactor, very good doping and thickness uniformity and run-to-run reproducibility have been demonstrated. Through a combination of reactor design and process optimization we have been able to achieve the routine production of thick epitaxial layers with morphological defect densities of around 1 cm−2. The low defect density epitaxial layers in synergy with improved substrates and SiC device processing have resulted in the production of 10 A, 10 kV junction barrier Schottky (JBS) diodes with good yield (61.3%).
Effective Channel Mobility in Epitaxial and Implanted 4H-SiC Lateral MOSFETs
Authors: Haney Sarah Kay , Ryu Sei-Hyung , Dhar Sarit , Agarwal Anant , Johnson Mark
Published: April 2011

In this paper, we investigate the effective inversion layer mobility of lateral 4H-SiC MOSFETs. Initially, lateral n-channel MOSFETs were fabricated to determine the effect of p-type epi-regrowth on a highly doped p-well surface. The negative effects of the high p-well doping are still seen with 1500 Å p-type regrowth, while growing 0.5 um or more appears to be sufficient to grow out of the damaged area. A second experiment was performed to examine the effects of doping during epitaxial regrowth versus using ion implantation after regrowth. Comparable mobilities and threshold voltages were observed for equivalent epitaxial and implanted doping concentrations.
Effect of Annealing Temperature on SiC Wafer Bow and Warp
Authors: Xu Xueping , Martin Chris
Published: April 2011

Single-side polished silicon carbide wafers could exhibit large bow and warp due to the presence of mechanical damage on the unpolished surface. In this study, we investigated the effect of thermal annealing on the wafer bow. Two commercial-grade, double-side polished 3¡¨ 6H SiC wafers with the bow less than 5 μm were lapped using 12 μm diamond grit. One wafer was lapped on the C-face and another on the Si-face. The lapped wafers were subjected to annealing in vacuum at temperatures between 500¢XC and 2040¢XC. The wafer bow and x-ray rocking curves were measured prior to annealing and after each annealing step in order to evaluate the extent of the surface damage and degree of healing. Thermal annealing led to a decrease in the wafer bow and sharpening of the x-ray rocking curves. However, the wafer bow generated by lapping was not completely removed until annealing temperature reached ∼2000°C.
Performance of SiC Microwave Transistors in Power Amplifiers
Authors: Azam Sher , Jonsson R. , Janzen E. , Wahab Q.
Published: April 2011

The performance of SiC microwave power transistors is studied in fabricated class-AB power amplifiers and class-C switching power amplifier using physical structure of an enhanced version of previously fabricated and tested SiC MESFET. The results for pulse input in class-C at 1 GHz are; efficiency of 71.4 %, power density of 1.0 W/mm. The switching loss was 0.424 W/mm. The results for two class-AB power amplifiers are; the 30-100 MHz amplifier showed 45.6 dBm (∼ 36 W) output powers at P1dB, at 50 MHz. The power added efficiency (PAE) is 48 % together with 21 dB of power gain. The maximum output power at P1dB at 60 V drain bias and Vg= -8.5 V was 46.7 dBm (∼47 W). The typical results obtained in 200-500 MHz amplifier are; at 60 V drain bias the P1dB is 43.85 dBm (24 W) except at 300 MHz where only 41.8 dBm was obtained. The maximum out put power was 44.15 dBm (26 W) at 500 MHz corresponding to a power density of 5.2 W/mm. The PAE @ P1dB [%] at 500 MHz is 66 %.
SiC-Based Power Converters
Authors: Tolbert Leon , Zhang Hui , Ozpineci Burak , Chinthavali Madhu S.
Published: April 2011

The advantages that silicon carbide (SiC) based power electronic devices offer are being realized by using prototype or experimental devices in many different power applications ranging from medium voltage to high voltage or for high temperature or high switching frequency applications. The main advantages of using SiC-based devices are reduced thermal management requirements and smaller passive components which result in higher power density. An overview of the SiC research effort at Oak Ridge National Laboratory (ORNL) and The University of Tennessee (UT) is presented in this paper.
Study on the Effect of RTA Ambient to Shallow N+/P Junction Formation using PH3 Plasma Doping
Authors: Do Seung-woo , Song Byung-Ho , Jung Ho , Kong Seong-Ho , Oh Jae-Geun , Lee Jin-Ku , Ju Min-Ae , Jeon Seung-Joon , Ku Ja-Chun , Lee Yong-Hyun
Published: April 2011

Plasma doping (PLAD) process utilizing PH3 plasma to fabricate n-type junction with supplied bias of −1 kV and doping time of 60 sec under the room temperature is presented. The RTA process is performed at 900 °C for 10 sec. A defect-free surface is corroborated by TEM and DXRD analyses, and examined SIMS profiles reveal that shallow n+ junctions are formed with surface doping concentration of 1021atoms/cm3. The junction depth increases in proportion to the O2 gas flow when the N2 flow is fixed during the RTA process, resulting in a decreased sheet resistance. Measured doping profiles and the sheet resistance confirm that the n+ junction depth less than 52 nm and minimum sheet resistance of 313 Ω/□ are feasible.
Source-drain Engineering for Channel-limited PMOS Device Performance: Advances in Understanding of Amorphization-Based Implant Techniques
Authors: Cowern Nick E.
Published: April 2011

This paper discusses the role of amorphisation and residual end-of-range defects in p-channel source/drain engineering. A comparison between preamorphisation and molecular implant approaches shows up some important common features of electrical activation, diffusion, and junction leakage, related to the formation and location of boron-interstitial and self-interstitial clusters. The success of these techniques depends on confining ‘end-of-range’ defects – whether TEM-visible defects or sub-microscopic clusters – within the narrow region between the boron implant peak and the source-drain/halo depletion region. This observation points to significant improvements that can still be made in implantation processing for ultrashallow junctions.
Optimization of Si:C Source and Drain Formed by Post-Epi Implant and Activation Anneal: Experimental and Theoretical Analysis of Dopant Diffusion and C Evolution in High-C Si:C Epi Layers
Authors: Cho Yonah , Moroz Victor , Zographos Nikolas , Thirupapuliyur Sunderraj , Date Lucien , Schreutelkamp Robert
Published: April 2011

Experimental and simulated P and As dopant diffusion profiles in Si:C epi films containing high C (>1 atomic %) are presented. A new set of physical effects were incorporated to accurately model P or As diffusion in the presence of high level of C. Evolution of substitutional C (Csub) profile in the Si:C epi film through dopant implant and activation anneal was characterized by high-resolution x-ray diffraction (HRXRD) technique. Three-layer analysis was utilized to obtain non-uniform Csub profile. Dependency of Csub retention on anneal thermal budget is studied. It is shown the initial Csub in the epi layer is lost during dopant implantation and conventional spike anneal sequence. Use of advanced millisecond (ms) laser anneal resulted in near 100% Csub retention in P-implanted Si:C epi film without compromising junction depth. Measured Csub (by HRXRD) and total C (by SIMS) profiles are compared with the ones predicted by the newly developed compact modeling in this study.
Atomistic Simulation Techniques in Front-End Processing
Authors: Marqués Luis A. , Pelaz Lourdes , Santos Iván , López Pedro , Aboy María
Published: April 2011

Atomistic process models are beginning to play an important role as direct simulation approaches for front-end processes and materials, and also as a pathway to improve continuum modeling. Detailed insight into the underlying physics usingab-initiomethods and classical molecular dynamics simulations will be needed for understanding the kinetics of reduced thermal budget processes and the role of impurities. However, the limited sizes and time scales accessible for detailed atomistic techniques usually lead to the difficult task of relating the information obtained from simulations to experimental data. The solution consists of the use of a hierarchical simulation scheme: more fundamental techniques are employed to extract parameters and models that are then feed into less detailed simulators which allow direct comparison with experiments. This scheme will be illustrated with the atomistic modeling of the ion-beam induced amorphization and recrystallization of silicon. The model is based on the bond defect or IV pair, which is used as the building block of the amorphous phase. It is shown that the recombination of this defect depends on the surrounding bond defects, which accounts for the cooperative nature of the amorphization and recrystallization processes. The implementation of this model in a kinetic Monte Carlo code allows extracting data directly comparable with experiments.
Tight-Binding Theory of Phase-Change Materials
Authors: Harrison Walter A.
Published: April 2011

A simple theory of Ge, Sb, and Te crystals and glasses, based upon atomic valence orbitals with coupling given by universal parameters, is outlined. It is seen how dangling hybrids from Ge atoms can behave as negative U centers. In contrast, in Sb the nonbonding s orbitals play essentially no role, except to produce three-fold coordination and 90° bond angles. Te also has nonbonding s states, but also nonbonding p states causing two-fold coordination. These nonbonding p states form the top of the valence band, rather than the bond orbitals which formed the valence-band in Ge. We argue against lumping these totally different behaviors together as “lone pairs”. In the glass, bonds can form between all atom types, but bonds between different elements are energetically favored. Further, when Sb or Te atoms are involved, bonds can switch between neighbors with small energy change, in a manner suggested by Kastner, Adler and Fritsche. It is seen how to estimate the energy for these various different geometric configurations.
Effects of Oxygen-doping on Crystallization and Physical Properties of Ge2Sb2Te5 Films
Authors: Perng Yu-Hsung , Hsu Ying-Tai , Chou Lih-Hsin
Published: April 2011

Oxygen-doped Ge2Sb2Te5 films (denoted as Ge2Sb2Te5-O) with oxygen concentration in between 0 and 10.3 at. % were prepared by direct current magnetron reactive sputtering with Ge2Sb2Te5 target. Both the crystallization temperature and activation energy of Ge2Sb2Te5-O films increased, while the crystalline grain size refined with oxygen concentration. For both amorphous and crystalline phases, optical band gap Egopt increases with oxygen concentration – a similar trend as observed in resistivity measurements. X-ray diffraction results showed that the face center cubic (fcc) structure maintained even after 400°C anneal with oxygen addition in between 7.5 − 8.3 at.% - a different phenomenon from undoped Ge2Sb2Te5 film, but with crystallinity diminished gradually with oxygen concentration. Only Sb2Te3 diffraction peak was observed in the 10.3 at.% O film after 400°C anneal. In conjunction with the bonding information obtained from X-ray photoelectron spectroscopy (XPS), effects of oxygen on the microstructures, thermal properties, resistivity and stability of fcc structure are examined and the embedded mechanisms are discussed in this study.
Investigations of High Endurance Asymmetric Phase Change Random Access Memory
Authors: Lee Hock Koon , Shi Luping , Zhao Rong , Yang Hongxin , Lim Kian Guan , LI Jianming , Chong Tow Chong
Published: April 2011

Asymmetric PCRAM structure with the upper contact opening at an offset to the bottom contact opening allowed us to improve the thermal distribution within the phase change layer and lower the reset current to 50% that of a conventional symmetrical structure. In terms of endurance, asymmetric cell lasted for 1.1 × 108 cycles which is at least 10X higher than the conventional symmetrical cell. These results were based on Ge2Sb2Te5 as the phase change material.

In this paper, we used nitrogen doped Ge2Sb2Te5 [1] instead and the thickness of this phase change layer was 100 nm. During the sputtering of Ge2Sb2Te5, the Argon gas flow rate was fixed at 15 sccm while nitrogen flow rates of 0, 3, 4.5 and 6 sccm were introduced each time. Thus N2/Ar gas ratio of 0, 0.2, 0.3 and 0.4 were obtained respectively. After fabrication, the cell endurance of Asymmetric PCRAM cells incorporating Ge2Sb2Te5 doped with varying concentrations of nitrogen was tested. During testing, the PCRAM was repeatedly Reset/Set and the resistances of the two states were recorded at every 100k cycles. The cell was considered to be functioning well when its Reset/Set resistance ratio was greater than 10. From experiments, N-doped asymmetric cell with N2/Ar gas ratio of 0.2 lasted 2.4 × 1010 cycles which is 1000 times that of a conventional symmetrical PCRAM cells. The N2 doping concentration was also shown to be optimized when the N2/Ar gas ratio was fixed at 0.2. Higher doping concentrations with N2/Ar gas ratio of 0.3 and 0.4 decreased the cell endurance to 8.8 × 108 and 7.6 × 108 cycles respectively. Excessive doped nitrogen atoms might have degraded the phase change material, causing breakdown to occur sooner.

N-doped conventional symmetrical PCRAM was also fabricated and its overwrite cycles were measured only up to 1.2 × 109. With better thermal confinement, asymmetric PCRAM has proved to be better in endurance too. The above results were based on asymmetric PCRAM cells with 1 µm offset.

[1] H. Horii et al, “A Novel Cell Technology Using N-doped GeSbTe Films For Phase Change RAM”, p. 177-178, VLSI Tech. 2003
Oxygen Vacancies in Amorphous HfO2 and SiO2
Authors: Kaneta Chioko , Yamasaki Takahiro
Published: April 2011

Formation energies and electronic properties of oxygen vacancies in amorphous HfO2 gate dielectrics are investigated by employing the first-principles method based on the density functional theory. We have found that the formation energy of neutral oxygen vacancy in amorphous HfO2 distributes from 4.7 to 6.1 eV, most of which is lower than the value for cubic HfO2, 6.0 eV. We also investigated the stabilities of the Vo pairs in various charged state and compared with those in amorphous SiO2. We found that Vo++ is stabilized in the vicinity of Vo in SiO2. In HfO2, however, this does not happen. This suggests the difference of defect propagation mechanism in HfO2 and SiO2.
Work Function Tuning of MoxSiyNz metal gate electrode for Advanced CMOS Technology
Authors: Patel Pommy , Buchanan Douglas A , Wallace Robert M
Published: April 2011

Due to continued transistor scaling, the work function tuning of metal gates has become important for advanced CMOS applications. The primary objective of this research is to understand the tuning of the MoxSiyNz (also referred to as MoSiN) gate work function through the incorporation of nitrogen. A molybdenum silicide (MoSi2) target was reactively sputtered in nitrogen (N2) and argon (Ar) plasma. The amount of nitrogen in the MoSiN films was varied by controlling the gas flow ratio, RN = N2/(N2+Ar). Capacitance-voltage (CV) and internal photoemission (IPE) measurements are used to extract the work function (ϕm) of the MoSiN gate. A decrease in the MoSiN work function was observed from ∼4.7eV to ∼4.4eV for an increase in the gas flow ratios from 10% to 40%. The SIMS depth profiles suggested a uniform distribution of nitrogen throughout the films. The XPS surface analysis confirmed a steady increase in the total nitrogen concentration in the MoSiN films as gas flow ratio was increased. The increase in N2 concentration corresponded directly with the lowering of the MoSiN work function. These results clearly demonstrated that the MoSiN work function maybe altered over ∼0.3 eV tuning window by adjusting the N2 concentration in these films.
Combinatorial Pulsed Laser Deposition of ITO-ZnO:Al Thin Films for Solar Cells Applications
Authors: Craciun Doina , Socol Gabriel , Mihailescu Ion N. , Craciun Valentin
Published: April 2011

Transparent and conductive mixtures of ITO-ZnO and ITO-ZnO:Al have been deposited by a combinatorial pulsed laser deposition on Si and quartz substrates. Measurements of the In to Zn ratios along the transversal axis of the substrates were performed using energy dispersive x-ray spectroscopy. From simulations of the x-ray reflectivity spectra, collected with a 2 mm mask on different locations along the transversal axis of the samples, the density and thickness of the deposited films were calculated and then the In to Zn ratios. The crystalline structure and electrical properties of the deposited films were also investigated along the same axis. Changes in the ratio of In/Zn along this axis resulted in changes of the lattice constant, texture, optical and electrical properties of the films. By changing the In to Zn ration we could tailor the properties of the transparent electrode and found ways to partially replace the more expensive ITO material with ZnO.
Carrier Compensation Mechanism of Highly Conductive Anatase Ti0.94Nb0.06O2 Epitaxial Thin Films
Authors: Nogawa Hiroyuki , Hitosugi Taro , Kamisaka Hideyuki , Yamashita Kouichi , Chikamatsu Akira , Yoshimatsu Kouhei , Kumigashira Hiroshi , Oshima Masaharu , Nadao Syoichiro , Furubayashi Yutaka , Hirose Yasushi , Shimada Toshihiro , Hasegawa Tetsuya
Published: April 2011

We investigated electrical conduction of anatase Ti0.94Nb0.06O2 (TNO) epitaxial thin films in relation to oxygen defects generated by post-annealing. Annealing of TNO in oxygen was found to cause dramatic decreases in ne. Resonant photoemission spectroscopy measurements revealed that a deep acceptor state just above the top of valence band evolves, synchronized with the decrease of ne. We proposed that the acceptor state originates from interstitial oxygen atoms combined with Nb dopants and compensates electron carriers.
Integrated (Ba,Sr)TiO3 Thin-Film Technology for RF and Microwave Applications
Authors: Suzuki Toshimasa , Ishii Daiki , Iwazaki Yoshiki , Morito Kentaro , Mizuno Youichi
Published: April 2011

The microwave tunable capability and its related material optimization of (Ba,Sr)TiO3 thin films in the parallel-plate capacitor form is discussed in terms of the dependence of barium concentration, acceptor doping, and in-plane film stress, based on the present broadband microwave characterization technique under various bias fields. The barium-content dependence indicates the tradeoff between tunability and dielectric loss, and the notable field-induced loss in SrTiO3 is confirmed as an intrinsic quasi-Debye contribution. The Mg dopant incorporated into a perovskite lattice shows almost no effectiveness on tunable device performance, except for enhanced insulation as an electron acceptor, while the low bias-field dependence of the dielectric loss suggests the possibility of the partial occupation of the alkaline-earth-ion site by Mg. The reduction of in-plane thermal stress controlled by the pressure during sputtering deposition leads to higher permittivity and tunability while degrading the film crystallinity by ion bombardment. The low-frequency loss tends to increase with crystal damage; however, the microwave loss remains unchanged, revealing the applicability of sputtering stress control to real microwave devices. In addition, we demonstrate the operation of an analog phase shifter using parallel-plate ferroelectric tunable capacitors and its application to a phased array antenna monolithically integrated on a silicon substrate.
Characterisation of PZT in Thin Film Bulk Acoustic Wave Resonators
Authors: Conde Janine , Muralt Paul
Published: April 2011

Pb(Zr0.53, Ti0.47)O3 (PZT) thin films are potentially interesting as piezoelectric layer in bulk acoustic wave (BAW) resonators. We investigated properties and performance of {111} and {100} textured, dense films deposited by sol-gel techniques in the frequency range of 1 to 2 GHz. The resonators were fabricated on Si wafers using deep silicon etching to create a membrane structure and using platinum as top and bottom electrodes. The best response of the resonators was observed at a bias voltage of −15kV/cm with values of around 10% for the coupling constant and around 50 for the quality factor. This voltage corresponds to the maximal value of the piezoelectric constant d33 and minimal value of the dielectric permittivity measured as a function of the electric field. Resonance and antiresonance frequencies were strongly influenced by a bias voltage, showing a hysteretic behaviour as expected for ferroelectrics. Both of these frequencies shifted in the same direction. As a consequence, the dc voltage can be potentially used to shift the whole band of a filter. In unipolar operation, the coupling constant could be varied from 6 to 10 %. Materials parameters were extracted from the admittance as a function of frequency. Dielectric, piezoelectric and elastic properties of textured PZT films are reported and compared to direct (low frequency) measurements and to literature values. It was found that PZT thin films have lower stiffness than the one of PZT bulk ceramics and it was observed that {111}-textured films are stiffer than {100}-textured films.
Mechanical Integrity of Hybrid Components used in Flexible Optoelectronic Devices
Authors: Sierros Konstantinos A , Morris Nicholas J , Abell J Stuart , Cairns Darran R , Kukureka Stephen N.
Published: April 2011

Fabrication of truly flexible optoelectronic devices, such as flexible displays and flexible photovoltaics, is highly dependent on the mechanical integrity of individual thin inorganic/organic hybrid device components. A common feature of almost all thin composite film components for flexible optoelectronic applications is indium tin oxide (ITO) coated on polyester.

The mechanical mismatch of the ITO ceramic coating, a few tens of nm thick, with the polyester, either polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), 125 ìm thick, causes the flexible functional structure to fail at moderately low strains under various, externally applied, stress states. It is therefore important to assess the mechanical integrity of such hybrid systems experimentally. We report on the electromechanical behavior of such hybrid systems.
High-Speed, High-Sensitivity Polyimide Humidity Sensors Based on MEMS Microhotplates
Authors: Kim Jea Sung , Kim Tea Jin , Kang Moon Sik , Yoo Kum Pyo , Min Nam Ki
Published: April 2011

Polyimides thin films, which are the most commonly used group of sensing materials for capacitive humidity sensors, were cured locally using MEMS microhotplates. The polyimide locally cured at temperature over 350 °C for 1 hour was fully cured. There were no significant differences in the polyimide thin films between cured in convection ovens and locally cured on microhotplate. The locally cured polyimide humidity sensor showed a linearity of 0.9995, a sensitivity of 0.766pF/%RH, a hysteresis of 0.6%RH, and a time response of 3 s. These results show the possibility of locally-cured polyimide films as high speed, high-sensitivity humidity sensors.
UV Laser Ablation of PLZT and PSZT Films
Authors: Leech Patrick W , Holland Anthony S , Sriram Sharath , Bhaskaran Madhu
Published: April 2011

The ablation of strontium-doped lead zirconate titanate (PSZT) and lanthanum-doped lead zirconate titanate (PLZT) films has been examined using a 5 ns pulsed excimer laser. Individual squares were patterned with sides in the range of 10-30 µm using single and multiple pulses. The depth of ablation in PLZT films was higher at all fluences than in PSZT films. The morphology of the etched surfaces has comprised the formation of globules which had diameters of 200-250 nm in PLZT and 1400-1600 nm in PSZT films. The diameter of the globules has been shown to increase with fluence until reaching an approximately constant size at >20 J/cm2 in both types of film. The composition of the films following ablation has been analyzed using x-ray photoelectron spectroscopy (XPS) and energy dispersive x-ray (EDX) spectroscopy.
Quantum Well and Quantum Dot Based Detector Arrays for Infrared Imaging
Authors: Gunapala Sarath , Bandara Sumith , Hill Cory , Ting David , Liu John , Mumolo Jason , Keo Sam , Blazejewski Edward
Published: April 2011

A mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) 320x256 pixel quantum well infrared photodetector (QWIP) dualband focal plane arrays (FPAs) have been demonstrated with excellent imagery. Currently, we are developing a 1024x1024 pixel simultaneous pixel co-registered dualband QWIP FPA. In addition, epitaxially grown self-assembled InAs/InGaAs/GaAs quantum dots (QDs) are exploited for the development of large-format FPAs. The Dot-in-a-Well (DWELL) structures were experimentally shown to absorb both 45° and normal incident light, therefore a reflection grating structure was used to enhance the quantum efficiency. The devices exhibit peak responsivity out to 8.1 microns, with peak detectivity reaching ∼ 1 × 1010 Jones at 77 K. The devices were fabricated into the first LWIR 640x512 pixel QDIP FPA, which has produced excellent infrared imagery with NETD of 40 mK at 60K operating temperature.
Development Effort of the Lunar Orbiter Laser Altimeter Laser Transmitter
Authors: Shaw George B , Yu Anthony W , Novo-Gradac Anne-Marie D
Published: April 2011

The Lunar Orbiter Laser Altimeter (LOLA) is one of six instruments on the Lunar Reconnaissance Orbiter (LRO) with the objectives to determine the global topography of the lunar surface at high resolution, measure landing site slopes and search for polar ices in shadowed regions. The LOLA laser transmitter is a passively q-switched cross-Porro resonator. The flight laser beryllium bench houses two oscillators (a primary oscillator and a cold spare). The two oscillators are designed to operate sequentially during the mission. The secondary laser will be turned on if the primary laser can no longer provide adequate scientific data products. All components used in the laser have space flight heritage. In this paper we will summarize the development effort of the LOLA laser including the material choice, design criteria and contamination control as applied to the flight laser build.
Dielectric Recovery of Plasma Damaged Organosilicate Low-k Films
Authors: Huang Huai , Bao Junjing , Huang Huai , Liu Junjun , Smith Ryan Scott , Sun Yangming , Ho Paul S. , McSwiney Michael L. , Moinpour Mansour , Kloster Grant M
Published: April 2011

Methyl depletion and subsequent moisture uptake have been found to be the primary plasma damages leading to dielectric loss in porous organosilicate (OSG) low-k dielectrics. A vacuum vapor silylation process was developed for dielectric recovery of plasma damaged OSG low-k dielectrics. The methyl or phenyl containing silylation agents were used to convert the hydrophilic -OH groups to hydrophobic groups. Compared with Trimethylchlorosilane (TMCS) and Phenyltrimethoxysilane (PTMOS), Dimethyldichlorosilane (DMDCS) was found to be more effective in recovering surface carbon concentration and surface hydrophobicity. But the carbon recovery effect was limited to the surface region.

Alternatively, UV radiation with thermal activation was applied for dielectric recovery of plasma damaged OSG low-k dielectrics. The combined UV/thermal process was found to be efficient in reducing −OH, physisorbed water, and C=O bonds. The dielectric constant was recovered within 5% of the pristine sample and the leakage current was also much reduced. Aging test in air showed that no moisture retake was observed, indicating the repaired film was stable.
Patterned wafers backside thinning for 3-D Integration and multilayer stack achievement by direct wafer bonding
Authors: Charlet Barbara , Chiteboun Antoine , Zussy Marc , Bally Laurent , Leduc Patrick , Assous Myriam
Published: April 2011

Scaling down the devices to keep increasing the integrated circuits (ICs) performance at the rate defined by Moore's [1] law becomes more and more difficult and so costly that new circuits architectures and new integration technologies are investigated. One of the most promising ways in integration technology is the vertical stacking of circuits, also called “3D Integration”. One of the challenges in this technology is the patterned substrate backside thinning. Compatibility with the whole 3D Integration process has to be guaranteed, the existing circuit has to be kept intact and the bonding interface mustn't be damaged. In this study we discuss some experimental results of wafer thinning by grinding and polishing of molecular bonded silicon wafers applied to 3D Integration [2-4]. The wafer with patterned copper interconnections are stacked by direct SiO2 bonding and thinned down on one backside. These stacks are then bonded again to one or two circuits via a deposited oxide on the thinned surface. The top bulk Si surface was thinned down again on one backside, giving a multi layers stack. This wafer level vertical assembly demonstrates the possibility to adjust the remaining Silicon thickness to small values (<15μm) and then bond the thinned surface to achieve multiple layer 3D structure.
Changes of UV Optical Properties of Plasma Damaged Low-k Dielectrics for Sidewall Damage Scatterometry
Authors: Marsik Premysl , Urbanowicz Adam , Vinokur Klara , Cohen Yoel , Baklanov Mikhail R
Published: April 2011

Porous low-k dielectrics were studied to determine the changes of optical properties after various plasma treatments for development of scatterometry technique for evaluation of the trench/via sidewall plasma damage. The SiCOH porogen based low-k films were prepared by PE-CVD. The deposited and UV-cured low-k films have been damaged by striping O2Cl2, O2, NH3 and H2N2 based plasmas and CF4/CH2F2/Ar etching plasma. Blanket wafers were studied in this work for the simplicity of thin film optical model. The optical properties of the damaged low-k dielectrics are evaluated the using various angle spectroscopic ellipsometry in range from 2 to 9 eV. Multilayer optical model is applied to fit the measured quantities and the validity is supported by other techniques. The atomic concentration profiles of Si, C, O and H were stated by TOF-SIMS and changes in overall chemical composition were derived from FTIR. Toluene and water based ellipsometric porosimetry is involved to examine the porosity, pore interconnectivity and internal hydrophilicity.
Pd Segregation at (001) B2-NiSi/Si Epitaxial Interface Studied by Density Functional Theory
Authors: Kim Dae-Hee , Seo Hwa-Il , Kim Yeong-Cheol
Published: April 2011

Pd segregation at (001) B2-NiSi/Si epitaxial interface was studied by using density functional theory (DFT). An epitaxial interface between 2×2×4 (001) B2-NiSi supercell and 1×1×2 (001) Si supercell was first constructed by adjusting the lattice parameters of B2-NiSi structure to be matched with those of Si structure. We chose Ni atoms as terminating layer of the B2-NiSi, and an equilibrium gap between the B2-NiSi and Si was calculated to be 1.1 Å. The Ni atoms in the structure moved away from the original positions along z-direction in a systematic way during the energy minimization. Two different Ni sites were identified at the interface and the bulk, respectively. The Ni sites at the interface farther away from the interface were more favorable for Pd substitution.
Dependence of thermal stability of NiSi and Ni(Pt)Si /Si on crystal orientation
Authors: Okubo Kazuya , Kawamura Kazuo , Akiyama Shinich , Kotaka Yasutoshi , Itani Tsukasa , Watatani Hirofumi , Yanai Kenichi , Nakaishi Masafumi , Kase Masataka
Published: April 2011

We report NiSi and Ni(Pt)Si films with excellent thermal stability showing a particular crystal orientation on Si(001). The Ni-silicide film with a deposition temperature of about 200 °C consists of a conformal domain structure. We examined detail crystallographic analysis of silicide and clarified the psudo-epitaxial growth of NiSi(202)//Si(220) [or NiSi(211)//Si(220)] was the key scheme of superior thermal stability. By using this optimized Ni-silicide formation process, we have fabricated Ni-silicide that is thermally stable up to 650 °C and shows low fluctuation in sheet resistance and low leakage current in electrical measurements. This process is a promising candidate for future silicidation technology.
Electromigration of Cu Interconnect Lines Prepared by a Plasma-based Etch Process
Authors: Liu Guojun , Kuo Yue
Published: April 2011

The electromigration performance of Cu lines patterned by a Cl2 plasma-based etch process has been studied with the accelerated isothermal lifetime test. An electromigration activation energy of 0.6 eV and a current density acceleration exponent of 2.7 were obtained. Both the copper-silicon nitride cap layer interface and the copper grain boundary were active diffusion paths. The applied mechanical bending stress changed the electromigration void distribution in the film, which leaded to the shorter lifetime and lower activation energy.
Fabrication and Electronic Characteristics of Silicon Nanowire MOSFETs
Authors: Yoshioka Hironori , Nanen Yuichiro , Suda Jun , Kimoto Tsunenobu
Published: April 2011

The n-type silicon nanowire MOSFETs with a nanowire shape being triangular or trapezoidal, have been fabricated on SOI substrates and characterized. The height and bottom-width of the triangular nanowire has been 10 nm and 19 nm, respectively. The devices have shown good gate control, such as a nearly ideal subthreshold slope of 63 mV/decade, high Ion/Ioff ratio of 107, and small drain-induced barrier lowering of 5 mV/V at room temperature. The low field mobility of triangular nanowire has been estimated to be 130 cm2/V·s and shown no difference with the change of the nanowire shape and direction within the investigated range.
Electrospinning of Ultrahigh-Molecular-Weight Polyethylene Nanofibers
Authors: Rein Dmitry M. , Cohen Yachin , Ronen Avner , Zussman Eyal , Shuster Kim
Published: April 2011

The electrospinning method was employed to fabricate extremely fine nanofibers of ultra-high molecular weight polyethylene (UHMWPE) for the first time, using a mixture of solvents with different dielectric constant and conductivity. A novel experimental device for elevated temperature electrospinning of highly volatile and quickly crystallizing polymer solutions and melts was developed. The possibility to produce the highly oriented nanofibers from ultra-high molecular weight polymers suggests new ways for fabrication of ultra-strong, porous, surface modified fibers and single-component nanocomposite yarn with improved properties.
Nanoscale Elastic and Tribological Properties of Poly(Acrylic Acid) Superabsorbent Gels
Authors: Talavera Beatriz , Martínez Juan J. , Santiago Francisca , Cuberes M. Teresa
Published: April 2011

Ultrasonic Force Microscopy and Friction Force Microscopy have been applied to the characterization of the elastic and tribological responses of poly(acrylic acid) hydrogels at ambient conditions. The gels were prepared by free radical polymerization of acrylic acid monomers partially neutralized by sodium hydroxide, using N, N'-methylen-bis-acrylamide as a crosslinker. Nanoscale domains with different stiffness and friction are observed. Increasing the amount of crosslinker leads to the formation of smaller, more densely packed domains. The domains with higher stiffness also exhibit higher friction and lower topographic high. The results can be understood by assuming that (i) neutralization by sodium hydroxide leads to the formation of both acrylic acid and sodium acrylate polymeric strands (ii) the observed domains differ in their acrylic acid / sodium acrylate content. In the acrylic acid rich domains, hydrogen bonding among the polymeric strands explains a higher stiffness and lower topography. In the sodium acrylate rich domains, lubrication by water molecules linked by solvation to the sodium counterions accounts for a lower friction.
Ultra-Thin Layer Activation as a Potential Tool for Nano-wear Characteriation
Authors: Popa-Simil Liviu
Published: April 2011

An application of the nuclear kinematics selective reaction is the usage of the recoil nuclear reaction in generating radioactive ion beams which may de used for MEMS and fine machinery parts labeling used for ultra thin layer activation techniques. The classical Thin or Ultra Thin Layer method relies in creation of a very thin layer on the technologic surface that to exhibit radioactivity of short life radioisotopes. For classical material loss applications concentrations of the order of ppb of different material generated by nuclear reaction were offering plenty of gamma or X radiation to be easily detected over the natural background level directly by a radiation gauge placed above the entire functional mechanism, or by accumulating these in the third tribologic medium – a lubricant or a fluid. In the case of MEMS devices the material concentrations are required to be high enough in order to produce a good radioactive signal or other methods based on resonant energies on isotopic materials may be used such as particle activated prompt gamma, connected with the possibility of the MEMS device of removing from the spot of the dislocated material that becomes technologically useless but carrying out tracer material. There are various possibilities of applying tracer materials on the MEMS devices in order to clearly determine in-situ and in operation the material loss and to correlate with the operation regime.
Ab Initio DFT Study of Ideal Strength of Crystal and Surfaces in Covalent Systems
Authors: Umeno Yoshitaka
Published: April 2011

Ab initio density functional theory (DFT) calculations were performed to examine various factors which may influence the ideal strength, namely multiaxial loading condition and structure with low symmetry. First, the effect of normal stress on the ideal shear strength (ISS) in covalent crystals, Si, C, Ge and SiC, was evaluated. It was found that the response of ISS to normal stress differs depending on the material, while in metals the trend is unchanged. Obtained ISS as a function of normal stress is useful to understand criteria of dislocation nucleation in a pristine crystal because local lattices at the nucleation site undergo superimposed stress components in experiment. Secondly the ideal tensile strength of silicon surface was evaluated to examine how atomistic-level structure affects the mechanical property. The theoretical tensile strength of Si nanofilms with (100) surface, which is flat with dimer-row structures, shows only 20-30% reduction even though the thickness is down to 1 nm, meaning that the flat surface possesses high strength.
Simultaneous Improvement of Ductility and Strength by Minute Doping in Ultrafine Grained Au Wires-Experiment and First Principle Study
Authors: Chew Yeong Huey Effie , Wong Chee Cheong , Ferraris Cristiano , Kim Hui Hui
Published: April 2011

Achieving both high strength and ductility is a common goal in the design of fine-grained materials. Here we report that with only ppm level of calcium doping, ductility and strength in ultrafine-grained gold wires can be concurrently improved by 108% and 65% respectively. Preferential segregation of calcium to stacking faults and grain boundaries in gold has reduced stacking fault energy of the system effectively, as shown by TEM and first principle simulation study. Through the modification of stacking fault energy, one can simultaneously increases the strength and ductility of a system.
Experimental Evidence that the Onset of Mechanical Softening in Nanocrystalline Metals is Strain Rate Dependent
Authors: Wang Liwei , Prorok Bart
Published: April 2011

This paper reports on the influence of strain rate on the onset of mechanical softening of nanocrystalline gold at room temperature. Micro-tensile testing was performed with applied strain rates on the order of 10−4 s−1 to 10−6 s−1. Our results defined a threshold strain rate, whereby plastic deformation at larger rates was dominated by dislocation processes and at smaller rates by one or more other deformation mechanisms. Furthermore, the data suggested that the critical grain size for inverse Hall-Petch behavior was strain rate sensitive.
The Effect of Surface Roughness on the Extinction Spectra and Electromagnetic Fields around Gold Nanoparticles
Authors: Li Shuzhou , Schatz George C.
Published: April 2011

Electromagnetic enhancement arising from plasmon resonance excitation plays a major role in surface-enhanced Raman spectroscopy (SERS), and as a result nanoparticle morphology can significantly affect SERS intensities. In this paper we have calculated these enhancements as well as extinction spectra using the discrete dipole approximation for a system consisting of a dimer of gold disks that is made using on-wire lithography. Including surface roughness in the calculations leads to SERS enhancements for the disks whose dependence on disk spacing and thickness is in agreement with experimental measurements, with a maximum enhancement when the thickness of the disk and the disk-disk gap are 100 nm and 32 nm, respectively. These results are in better agreement with experiments than earlier estimates based on flat surfaces.
Atomistic Study of Creation of Bimetallic Clusters by Coalescence
Authors: Mizuno S. , Shintani K.
Published: April 2011

Metallic clusters show excellent performance as catalysts because of their high surface-to-volume ratio. An inert-gas aggregation source is an experimental method by which clusters are produced. In such a method, cluster coalescence is one of growth modes of clusters. Bimetallic clusters also attract much attention of researchers because of their novel physical and chemical properties. At coalescence of two metallic clusters of different species, alloying or core-shell structuring tends to occur spontaneously. Resulting alloyed clusters or core-shell clusters will behave as unique catalysts. In this paper, morphological evolution of two metallic clusters of different elements at coalescence is investigated using molecular-dynamics simulation. All pair combinations of the elements Au, Ag, Pt, and Pd are considered. The interactions between such metallic atoms are calculated by using generic embedded-atom method (GEAM) potential. Two clusters of icosahedral structure are equilibrated at specified temperature beforehand. The two clusters are put close to each other, where the nearest two atoms belonging to the two clusters, respectively, start to interact with each other. After coalescence the original surfaces of the two clusters decrease, and the surface energy is transformed into the kinetic energy. Consequently, the temperature of the united cluster rises. If this temperature is higher than the melting temperature, melting and local alloying at the interface occur. If alloying spreads into the united cluster, an alloyed bimetallic cluster is synthesized. If melting occurs only in one of the two clusters, and the atoms in liquid phase gradually cover the surface of the other cluster, a core-shell cluster appears. The morphological evolutions in the two modes of coalescence are followed, and under what conditions each mode of coalescence occurs is discussed.

The results show that the surface energy and atom size of two clusters determine which mode is selected at coalescence.