bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Ligand Density Gradient on the Adhesion Kinetics of Biological Membranes
Authors: Sarvestani Alireza , Jabbari Esmaiel
Published: April 2011

An analytical model is developed for the effect of surface gradient in ligand density on the adhesion kinetics of a curved elastic membrane with mobile receptors. The displacement and speed of spreading at the edge of the adhesion zone as well as the density profile of receptors along the membrane are predicted as a function of time. According to results, in the diffusion-controlled regime, the front edge displacement of adhesion zone and the rate of membrane spreading decreased with increasing ligand density in a certain direction. Furthermore, the displacement of the edge of the adhesion zone did not scale with the square root of time, as observed on substrates with uniform ligand density.
Aromatic Thermosetting Copolyester (ATSP)/UHMWPE Blends with Improved Wear Properties and Biocompatibility
Authors: Huang Yongqing , Economy James
Published: April 2011

Despite the recognized success and worldwide acceptance of ultrahigh molecular weight polyethylene (UHMWPE) for total joint arthroplasty, the generation of UHMWPE wear debris from the articulating surface is of major concern and limits the longevity of the artificial joint device. Blends of UHMWPE with an aromatic thermosetting copolyester (ATSP) at 50:50 volume ratio using poly(ethylene-co-acrylic acid) (PEA) as a compatibilizer were developed to address this problem. The amount of PEA was 0, 5, 10, 15 and 20 weight percent of the weight of ATSP, respectively. The wear properties of these blends were evaluated by a pin-on-disk wear test in which an ASTM F-75 cobalt-chromium alloy disk was chosen as a counterface and sterile filtered bovine serum diluted in deionized water to 75% (volume) was used as a lubricant. The wear tests from 0.2 to 3 million cycles showed that UHMWPE/ATSP blend with 10 wt% PEA had average weight loss smaller than UHMWPE and comparable to crosslinked UHMWPE. The wear debris study indicated that UHMWPE/ATSP blend with 10 wt% PEA created a smaller size percentage of the wear debris particles in the biologically active range than UHMWPE and crosslinked UHMWPE. The direct-contact cytotoxicity tests showed that ATSP and UHMWPE/ATSP blend with 10 wt% PEA were not toxic.
Dendrimer Nanocomposites as Multifunctional X-ray Contrast Agents
Authors: Ely Teyeb Ould , Sharma Manju , Lesniak Wojciech , Klippenstein Donald L. , Foster Barbara A. , Balogh Lajos P.
Published: April 2011

We synthesized dendrimer composite nanoparticles and investigated their potential for traditional X-ray imaging and Computed Tomography (CT). These new X-ray contrast agents show better contrast compared to traditional iodine-based contrast agents, and are expected to clear from the blood much slower than commercial agents, permitting longer imaging times. We have also investigated their safety profile in terms of viscosity and osmotic pressure.
Novel Hydrogel and Conducting Polymer-based Skin Surface Electrode Design
Authors: Alba Nicolas Alexander , Justin Gusphyl , Wadhwa Reecha , Sun Mingui , Sclabassi Robert J , Cui Xinyan Tracy
Published: April 2011

Various formulations of polymeric hydrogels were synthesized and evaluated with the goal of developing a novel skin-surface biopotential electrode. Materials explored within the study included poly(2-hydroxyethyl methacrylate) (polyHEMA) in pure form or impregnated with the conducting polymers polypyrrole or poly(3,4-ethylenedioxythiophene) (PEDOT), as well as polyacrylate. The drying dynamics, ionic conductivity, and impedance of the prototype materials were characterized when applied to porcine and human skin, in order to determine their utility for a minimum preparation and low specific impedance surface electrode. The addition of a fraction of PEDOT or polypyrrole within a polyHEMA gel was found to decrease hydrogel impedance when tested within PBS, as well as on non-abraded porcine skin. A polyacrylate component added to polyHEMA had no significant effect on hydrogel impedance in PBS, but significantly reduced impedance on the porcine skin surface. Although having much lower specific impedance (impedance normalized by the contact area) than the commercial skin surface electrode (3M Red Dot), polyHEMA based electrodes require skin abrasion. Pure cross-linked polyacrylate gel was found to provide the most attractive option, and yielded competitive low-impedance performance on non-abraded human skin.
Characterization of amorphous/crystalline silicon interfaces from electrical measurements
Authors: Kleider Jean-Paul , Gudovskikh A. S.
Published: April 2011

Electrical techniques based on capacitance and conductance measurements are powerful tools for interface characterization in semiconductor heterostructures. We here detail their application to the study of the heterointerface formed between hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si). The main parameters governing the device applications are the conduction and valence band mismatch, and the density of interface states. The presence of a high interface states density can be revealed by capacitance versus temperature and frequency measurements. For very high quality interfaces that are required for instance to reach high conversion efficiencies in solar cells, the usual measurements performed in the dark and at zero or reverse bias are not sensitive enough. We show that the sensivity to interface states can be enhanced by using capacitance measurements under illumination and at a forward bias close or equal to the open-circuit voltage. In this case, the measured capacitance is determined by the diffusion of free carriers in c-Si and limited by recombination at the interface. Regarding the determination of band offsets, the method using a plot of the inverse square capacitance as a function of bias to determine the intercept of the extrapolated linear region is shown to lead to errors even in the absence of any interface charge. This is due to the presence of a strong inversion layer in c-Si at the interface, the effect of which has been ignored so far in the literature. The presence of this strong inversion layer is evidenced from planar conductance measurements on (n) a-Si:H/(p) c-Si structures. We emphasize that these measurements are very sensitive to details of the band structure profile. In particular, it is shown that the temperature dependence of the sheet electron density allows the determination of the conduction band offset between a-Si:H and c-Si with a good precision. We find 0.15 ± 0.04 eV.
Boron Incorporation and Its Effect on Electronic Properties of Ge:H Films Deposited by LF Plasma
Authors: Kosarev Andrey , Torres Alfonso J , Checa Nery D , Kudriavtsev Yurii , Asomoza Rene , Hernandez Salvador G
Published: April 2011

Boron (B) doping of plasma deposited silicon films have been widely studied and applied in many devices, while B-doping of germanium has been poorly reported in literature. We have reported previously about Ge:H films with low density of localized states deposited by LF plasma with optimal hydrogen dilution.

This work is devoted to a study of boron incorporation and its effect on electronic properties in Ge:H films. The films were obtained by low frequency (LF) plasma deposition from GeH4+SiH4 +B2H6 mixture diluted with hydrogen. The deposition parameters were as follow: substrate temperature Ts = 300 oC, discharge frequency f= 110 kHz, pressure P= 0.6 Torr, power W= 300 W, germane flow QGeH4= 50 sccm, silane flow, hydrogen flow QH2=3500 sccm, diborane flow was varied in the range of QB2H6=0 to 20 sccm providing boron concentration in gas phase in the range of Y=0 to 4%. Composition of the films was characterized by SIMS profiling. Hydrogen bonding was studied by FTIR. Temperature dependence of conductivity measured in DC regime in vacuum thermostat was employed to study carrier transport. Optical measurements provided optical gap, sub-gap absorption and refraction index. Boron incorporation in solid film demonstrated fast increase in the range of Y = 0 to 1.4% and then increase became slower. Hydrogen concentration in the films was determined by absorption of Ge-H stretching mode at k ≈ 1870 cm−1 and it showed weak increase with change of Y from 0 to 4%. Activation energy of conductivity increased in the range of Y = 0 to 1.5% suggesting a compensation of electron conductivity, reaching maximum value Ea =0.5 eV (corresponding approximately to Eg/2) at Y= 1.5%. Then Ea reduced to minimum value Ea = 0.27 eV at Y= 3.5% showing a trend to saturation with further Y increase. This behavior is related to change of charge transport from electron to intrinsic at Y= 1.5% and further to hole transport.
Low Temperature Deposition of Si-based Thin Films on Plastic Films Using Pulsed-Discharge PECVD under Near Atmospheric Pressure
Authors: Matsumoto Mitsutaka , Inayoshi Yohei , Suemitsu Maki , Nakajima Setsuo , Uehara Tsuyoshi , Toyoshima Yasutake
Published: April 2011

Low temperature (150 °C) deposition of doped and undoped polycrystalline Si (poly-Si) as well as SiNX films on polyethylene terephthalate (PET) films has been achieved with practical deposition rates by using pulsed-plasma CVD under near-atmospheric pressure. The precursor is SiH4 diluted in H2 for poly-Si while N2 has been additionally used for SiNx. No inert gases such as He was used. A short-pulse based power system has been employed to maintain a stable discharge in the near-atmospheric pressures. With this technique, deposition of poly-Si thin film with virtually no incubation layer is possible, which in the case of P-doped poly-Si shows a Hall mobility (μH) of 1.5 cm2/V·s.
Pulsed Laser Heating-induced Surface Rapid Cooling and Amorphization
Authors: Tian Longzhang , Wang Xinwei
Published: April 2011

In this work, hybrid atomistic-macroscale simulation is conducted to explore the crystallization process of Si surface in the situation of fast melting and solidification induced by ultrafast laser heating and heat conduction. Using the environment-dependent interatomic potential, samples containing 2,880 and 11,520 Si atoms are modeled to provide accurate details for the relationship between the finial crystal structure and the parameters of laser pulses. For different pulsed lasers, amorphous layers are found to form when the laser fluence exceeds a certain critical value. An empirical correlation Ec = 448.76 × (tg)0.56 is obtained to relate this critical fluence to the laser pulse width. It is found that the final thickness of amorphous layer is related to the fluence of the laser pulse with the same full width at half maximum (FWHM). Employing laser pulses with FWHM = 6.67 ns, the formation and recrystallization processes of a 12 nm thick amorphous layer is further investigated, which may have great potential in laser manufacture techniques for Si-associated structures.
Polycrystalline Silicon Thin-film Solar Cells on ZnO:Al Coated Glass
Authors: Becker Christiane , Dogan Pinar , Gorka Benjamin , Ruske Florian , Hänel Tobias , Behrends Jan , Fenske Frank , Lips Klaus , Gall Stefan , Rech Bernd
Published: April 2011

Thin film solar cells based on polycrystalline silicon are an appealing option combining the advantages of thin film technologies, namely low cost, and the superior electrical properties of crystalline silicon. The specific structure aimed at in this work uses the relatively simple contacting scheme used in amorphous silicon thin film solar cells which relies on a front contact consisting of a transparent conducting oxide (TCO). Electron beam evaporation is applied as preparation method for the silicon films with high deposition rate. Solid phase crystallization (SPC) is used to crystallize the silicon films after deposition.

In this work the properties of as-deposited and crystallized silicon films produced by e beam evaporation are investigated as a function of deposition temperature. It is shown that the largest crystallites are obtained for deposition around 300 °C and subsequent treatment at 600 °C, while deposition at higher temperatures leads to small crystal grains which are not changed significantly during SPC.

Solar cells have been prepared on TCO-coated glass and were studied by measurements of the external quantum efficiency.
Floating-Gate a-Si:H TFT Nonvolatile Memories
Authors: Kuo Yue , Nominanda Helinda
Published: April 2011

Charge and discharge phenomena of the floating-gate amorphous silicon thin film transistor have been studied under dynamic operation conditions. The charge storage capacity decreases with the increase of the drain voltage because it is easier for electrons to be transported to the drain electrode than to be injected into the gate dielectric layer. The discharge efficiency with respect to the drain voltage has been investigated using three different discharge methods: negative gate bias voltage, light exposure, and thermal annealing, separately. The channel length affected both the charge capacity and the discharge efficiency due to the charge storage mechanism and the channel resistance. Majority of the stored charges were removed with the above method through various mechanisms. The low temperature favors the charge storage but the high temperature favors the discharge. This study revealed key parameters for the optimum operation of the low temperature fabricated nonvolatile memory device.
The Positive Gate Bias Annealing Method for the Suppression of a Leakage Current in the SPC-Si TFT on a Glass Substrate
Authors: Park Sang-Geun , Park Joong-Hyun , Kuk Seung-Hee , Kang Dong-Won , Han Min-Koo
Published: April 2011

We fabricated PMOS SPC-Si TFTs which show better current uniformity than ELA poly-Si TFTs and superior stability compare to a-Si:H TFT on a glass substrate employing alternating magnetic field crystallization. However the leakage current of SPC-Si TFT was rather high for circuit element of AMOLED display due to many grain boundaries which could be electron hole generation centers. We applied off-state bias annealing of VGS=5V, VDS=−20V in order to suppress the leakage current of SPC-Si TFT. When the off-state bias annealing was applied on the SPC-Si TFT, the electron carriers were trapped in the gate insulator by high gate-drain voltage (25V). The trapped electron carriers could reduce the gate-drain field, so that the leakage current of SPC-Si TFT was reduced after off-state bias annealing. We applied AC-bias stress on the gate node of SPC-Si TFT for 20,000 seconds in order to verify that the leakage current of SPC-Si TFT could be remained low at actual AMOLED display circuit after off-state bias annealing. The suppressed leakage current was not altered after AC-bias stress. The off-state bias annealed SPC-Si TFT could be used as pixel element of high quality AMOLED display.
Improved Photon Absorption in a-Si:H Solar Cells using Photonic Crystal Architectures
Authors: Biswas Rana , Zhou Dayu
Published: April 2011

Improved light-trapping is a major route to improving solar cell efficiencies. We design a combination of a 2-dimensional photonic crystal and a one-dimensional distributed Bragg reflector as the back reflector for a-Si:H solar cells. This configuration avoids inherent losses associated with textured back-reflectors. The photonic crystals are composed of ITO and can easily serve as a conducting back contact. We have optimized the geometry of the photonic crystal to maximize absorption using rigorous scattering matrix simulations. The photonic crystal provides strong diffraction of red and near-IR wavelengths within the absorber layer and can enhance the absorption by more than a factor of 10 relative to the case without the photonic crystal. The optical path length with the photonic crystal can improve over the limit for a random roughened scattering surface.
Impurities and Grain Size Modeling in Recrystallized Silicon
Authors: Kalinin Valeri V. , Myasnikov Alexandre M. , Zyryanov Vladislav E.
Published: April 2011

In our previous publications [1, 2 and 3], spreading resistance probe (SRP) measurements for quality control of metal induced lateral crystallization (MILC) of amorphous silicon (a-Si) were studied, and the mechanism of nickel diffusion was simulated using technology computer-aided design (TCAD) modeling.

Now, we continue to present the explanation of experimental results by modeling with the Synopsys TCAD package, whereby models for resistivity vs. grain size in implanted recrystallized silicon layers are implemented and compared with experiments.

Findings show that the SRP method can be used for the characterization of the MILC process of amorphous silicon and that a comparison of experimental and calculated data allows both a turn from qualitative to quantitative analysis of recrystallized silicon film and an estimate of grain size. It has been found that grain size depends on location in the MILC region and on the time and temperature of recrystallization.
Improvement in pinpin Device Architectures for Imaging Applications
Authors: Louro P. , Fantoni A. , Fernandes M. , Lavareda G. , Carvalho N. , Vieira M.
Published: April 2011

In this paper we present results on the optimization of device architectures for colour and imaging applications, using a device with a TCO/pinpi'n'/TCO configuration. A set of different devices with different intrinsic back layers are analysed.

The effect of the applied voltage on the color selectivity is discussed. Results show that the spectral response curves demonstrate rather good separation between the red, green and blue basic colors. Combining the information obtained under positive and negative applied bias a colour image is acquired without colour filters or pixel architecture. A low level image processing algorithm is used for the colour image reconstruction.
Transient current in a-Si:H-based MIS photosensors
Authors: Fernandes Miguel , Vygranenko Yuriy , Vieira Manuela , Heiler Gregory , Tredwell Timothy , Nathan Arokia
Published: April 2011

Large-area amorphous silicon (a-Si:H) sensor arrays are widely used for medical x-ray imaging, nondestructive testing and security screening. Most of the commercially available detectors are of the indirect conversion type, in which an x-ray phosphor screen is optically coupled to an array of a-Si:H sensors. The a-Si:H PIN photodiode and the MIS photoelectric converter are two alternative sensing elements used in these detectors. The major advantage of the MIS structure over PIN is fact that this device has the same layer sequence as the a Si:H TFT switch and therefore, they can be fabricated simultaneously resulting in an effective reduction in the lithography mask count. The main disadvantage of the MIS structure is the higher noise level due to transient dark current. The transient dark current originates from traps at the semiconductor-insulator interface and i-layer bulk defects. In this work we analyze the transient current transport in segmented-gate/SiN/a Si:H/n+/ITO structures under different biasing conditions and temperatures. Using a home-made setup the dark current decay was measured within an interval of 1 second in the temperature range from 294 to 353K. It is found that the dark current component associated with charge trapping at the insulator-semiconductor interface can be largely eliminated by adjusting the bias voltage during the refresh period. Under optimized biasing conditions and elevated temperatures the bulk current component becomes dominant.
Optimized O/Si Composition Ratio for Enhancing Si Nanocrystal Based Luminescence in Si-rich SiOx Grown by PECVD with Argon Diluted SiH4
Authors: Chang Chung-Hsiang , Hsieh Chin-Hua , Chou Li-Jen , Lin Gong-Ru
Published: April 2011

Effect of O/Si composition ratio on near-infrared photoluminescence (PL) of PECVD grown Si-rich SiOx after 1100°C annealing are analyzed by Rutherford backscattering (RBS) and Fourier-transformed infrared spectroscopy (FTIR) to show nonlinear relationship with strongest PL at 760 nm at optimized O/Si = 1.24, total Si concentration of 44.6 atom.%, and N2O/SiH4 fluence ratio of 4.5. A nearly Gaussian function of the normalized PL intensity vs. O/Si composition ratio has been observed due to the significant variation on the Si nanocrystals size with the density of the excessive Si atoms.
Atomistic Understanding of a Single Gated Dopant Atom in a MOSFET
Authors: Lansbergen Gabriel , Rahman Rajib , Wellard Cameron , Caro Jaap , Collaert Nadine , Biesemans Serge , Klimeck Gerhard , Hollenberg Lloyd , Rogge Sven
Published: April 2011

Current semiconductor devices have been scaled to such dimensions that we need take an atomistic approach to understand their characteristics. The atomistic nature of these devices provides us with a tool to study the physics of very small ensembles of dopants right up to the limit of a single atom. Control and understanding of a dopants wavefunction and its coupling to the environment in a nanostructure could proof a key ingredient for device technology beyond-CMOS. Here, we will discuss the eigenlevels and transport characteristics a single gated As donor. The donor is incorporated in the channel of wrap-around gate transistors (FinFETs). The measured level spectrum is shown to consist of levels associated with the donors Coulomb potential, levels associated with a triangular well at the gate interface and hybridized combinations of the two. The level spectrum of this system can be well described by a NEMO-3D model, which is based on a numerical tight-binding approximation.
Suitability of 4H-SiC Homoepitaxy for the Production and Development of Power Devices
Authors: Hecht Christian , Thomas Bernd , Stein Rene , Friedrichs Peter
Published: April 2011

In this paper, we present results of epitaxial layer deposition for production needs using our hot-wall CVD multi-wafer system VP2000HW from Epigress with a capability of processing 6×100mm wafers per run. Intra-wafer and wafer-to-wafer homogeneities of doping and thickness for full-loaded 6×100mm runs will be shown and compared to results of the former 7×3″ setup. The characteristic of the run-to-run reproducibility for the 6×100mm setup will be discussed. To demonstrate the suitability of the reactor for device production results on Schottky Barrier Diodes (SBD) processed in the multi-wafer system will be given. Furthermore, we show results for n- and p-type SiC homoepitaxial growth on 3″, 4° off-oriented substrates using a single-wafer hot-wall reactor VP508GFR from Epigress for the development of PiN-diodes with blocking voltages above 6.5 kV. Characteristics of n- and p-type epilayers and doping memory effects are discussed. 6.5 kV PiN-diodes were fabricated and electrically characterized. Results on reverse blocking behaviour, forward characteristics and drift stability will be presented.
Lateral/vertical Homoepitaxial Growth on 4H-SiC Surfaces Controlled by Dislocations
Authors: Picard Yoosuf N. , Trunek Andrew J. , Neudeck Philip G. , Twigg Mark E.
Published: April 2011

This paper reports the influence of screw dislocations on the lateral/vertical growth behavior of chemical vapor deposited (CVD) on-axis homoepitaxial 4H-SiC films grown on patterned mesas. Electron channeling contrast imaging (ECCI) was utilized to image both atomic steps and dislocations while the film structure/orientation was determined using electron backscatter diffraction (EBSD). The presence and position of screw dislocations within the mesa impacted the resultant film thickness, lateral shape, and atomic step morphology. Mesa side walls that incline inwards due to faceting during screw-dislocation driven vertical film growth can intersect with the dislocation step sources near the side walls. If this occurs for all screw dislocations on a mesa, we observe a transition towards laterally dominated growth that produces webbed structures and films surfaces exhibiting significantly lower step densities. Transition from vertical to lateral dominated growth is consistent with ECCI imaged dislocation very near a mesa side wall.
Propagation and Density Reduction of Threading Dislocations in SiC Crystals during Sublimation Growth
Authors: Wu Ping , Xu Xueping , Rengarajan Varatharajan , Zwieback Ilya
Published: April 2011

SiC single crystal wafers grown by sublimation exhibit relatively high dislocation densities. While it is generally known that the overall dislocation density tends to decrease throughout crystal growth, there has been a limited quantitative analysis of such trend. In this study, we measured the density of threading dislocations in the wafers sliced from several SiC boules. Although the dislocation density in the wafers sliced from different boules could differ by orders of magnitude, a consistent empirical relationship was found between the dislocation density (ρ) and the axial wafer position within the crystal (w): ρ is proportional to w(−0.5).

Monte Carlo simulations were performed based on two assumptions: (i) during growth the threading dislocations move randomly in the lateral directions, and (ii) two dislocations of opposite sign annihilate when they come within a critical distance between them. Good agreement was achieved between the model and experimental results. The critical distance determined from the simulations was in the range between a few hundred Ă and a micron.
Effect of Base Impurity Concentration on DC Characteristics of Double Ion Implanted 4H-SiC BJTs
Authors: Tajima Taku , Uchiumi Satoshi , Tsukamoto Kenta , Takenaka Kazumasa , Satoh Masataka , Nakamura Tohru
Published: April 2011

Double ion implanted 4H-SiC bipolar junction transistors (BJTs) are fabricated by Al and N ion implantation to the base and emitter. The current gain of 3 is obtained at the base Al concentration of 1 × ∼ 1017 /cm3. The collector current as a function of the base Gummel number suggests that double ion implanted 4H-SiC BJT operates in the intrinsic region below the emitter in the low injection level. The high base resistance restricts the base current at VBE as low as 3 V.
MOS Capacitor Characteristics of 3C-SiC Films Deposited on Si Substrates at 1270°C
Authors: Wang Li , Dimitrijev Sima , Hold Leonie , Kong Frederick , Tanner Philip , Han Jisheng , Wagner Gunter
Published: April 2011

SiC films were deposited on Si substrate by low pressure hot-wall CVD using C3H8 (5% in H2)-SiH4 (2.5% in H2)-H2 gas system at 1270°C and 1370°C. In this paper, we compare the electrical characteristics of MOS capacitors fabricated on the 3C-SiC films grown at high and low temperatures, 1370°C and 1270°C, respectively. Although the cross-sectional TEM images indicate similar micro-structural quality of the SiC/Si interface for both temperatures, a quicker elimination rate of stacking faults with increasing thickness was observed in the films grown at 1370°C. Rocking curves from XRD measurements also indicate better crystallinity of the films grown at 1370°C. On the other hand, atomic force microscopy shows that the average surface roughness reduces with the reduction in growth temperature. MOS capacitors were made on films grown at both temperatures and characterized by high-frequency capacitance-voltage (HFCV), conductance-voltage (G-V), and current-voltage (I-V) measurements at room temperature. The MOS capacitors fabricated on both films exhibit good and almost identical C-V characteristics. Measurements of current-voltage characteristics in accumulation region showed smaller leakage for the film deposited at 1270°C. It is concluded that the decrease of the deposition temperature from 1370°C to 1270°C does not bring any remarkable negative impact on the interface properties of fabricated MOS capacitors.
Modeling and Experiments of Dopant Diffusion and Defects for Laser annealed Junctions and advanced USJ
Authors: Noda Taiji , Vandervorst Wilfried , Felch Susan , Parihar Vijay , Vrancken Christa , Hoffmann Thomas Y.
Published: April 2011

Laser annealed junctions and advanced ultra shallow junctions are studied in both atomistic modeling and experiments. SIMS and sheet resistance measurement for spike-RTA + Laser annealing show that additional laser annealing after spike-RTA (“+Laser”) improve the dopant activation level without increasing in junction depth. “+Laser” effect become effective in the combination of low spike-RTA temperature and high laser temperature. This effect is significant for As doped layer. Spike-RTA based junction has a limitation in viewpoint of Rs-Xj trade-off. Laser-only annealing is promising candidate to overcome this limitation. Boron diffusion with laser-only annealing is investigated. As atomistic kinetic Monte Carlo modeling show that BnImcomplexes and End-of-Range (EOR) defects are formed during sub-millisecond annealing time range. Impact of F co-implant on Boron diffusion and EOR defect evolution during sub-millisecond annealing are also investigated.
Experimental Investigation of the Impact of Implanted Phosphorus Dose and Anneal on Dopant Diffusion and Activation in Germanium
Authors: Mazzocchi Vincent , Koffel Stéphane , Le Royer Cyrille , Scheiblin Pascal , Barnes Jean-Paul , Hopstaken Marco
Published: April 2011

Germanium has regained attention in the semiconductor industry for MOSFET application because of the higher mobility of carriers – two times higher mobility for electrons and four times for holes – as compared to silicon. In the opposite of the Silicon, the major issue with Germanium is to limit the n-dopant diffusion. Usual n-dopants (Phosphorus and Arsenic for example) are not electrically activated at an acceptable level without a large diffusion of the doping profile and a substantial dose loss. In this work, we have studied the influence of low energy and dose implant (15KeV to 40KeV @ 8E13 to 1E15at.cm−2) and low temperature anneal (515°C to 600°C) on diffusion, exodiffusion and activation of the phosphorus dopant into Germanium. The annealing steps were made in RTP furnace, the chemical profile and electrically active profiles were extracted by using Secondary-Ion-Mass Spectroscopy (SIMS) and sheet resistance measurement (Rs). To investigate the implantation-induced defects in depth, cross-sectional micrographs were made by using Transmission Electron Microscopy (TEM). Experimental results show that we achieved an efficient activation level by tuning both dose implant and anneal temperature, limiting the exodiffusion with pratically no diffusion of the dopant. We also show that very abrupt profile can be achieved with appropriate implant and thermal annealing conditions. To limit the leakage current in devices, we suppose we have to limit the defects generated during the implantation. Specially for dopant activation temperature anneal below 550°C, we have shown and observed by cross-sectional micrograph that the defects are totally removed by addition of a pre step of annealing at 400°C.
Phosphorus diffusion and activation in silicon: Process simulation based on ab initio calculations
Authors: Sahli Beat , Vollenweider Kilian , Zographos Nikolas , Zechner Christoph , Suzuki Kunihiro
Published: April 2011

We present the results of extensive ab initio simulations for phosphorus clustering and diffusion in silicon and the application of these results in a state-of-the-art process simulator. The specific defects and the parameters that are investigated are selected according to the needs of diffusion and activation models, taking into account the availability of experimental data, the capabilities of current ab initio methods and the requirements for advanced technology development. The calculated formation energies, binding energies and migration barriers are used to determine a good starting point for the calibration of a new charged cluster model implemented in the process simulator. The defect species V, I, P, PV, PI, PI2, P2, P2V, P2I, P3, P3V, P3I and P4V are considered in all relevant charge states. The ab initio results are discussed as well as the transfer of this information into the process simulation model and the impact on model quality.
Indirect Diffusion Mechanism of Boron Atoms in Crystalline and Amorphous Silicon
Authors: Mirabella Salvo , De Salvador Davide , Napolitani Enrico , Bruno Elena , Impellizzeri Giuliana , Bisognin Gabriele , Pecora Emanuele Francesco , Carnera Alberto , Priolo Francesco
Published: April 2011

The diffusion of B atoms in crystalline and amorphous Si has been experimentally investigated and modeled, evidencing the indirect mechanism of these mass transport phenomena. The migration of B occurs after interaction with self-interstitials in crystalline Si (c-Si) or with dangling bonds in amorphous Si (a-Si). In the first case, an accurate experimental design and a proper modeling allowed to determine the microscopic diffusion parameters as the B-defect interaction rate, the reaction paths leading to the diffusing species and its migration length. Moreover, by changing the Fermi level position, B atoms are shown to interact preferentially with neutral or doubly positively charged self-interstitials. As far as the amorphous case is concerned, B diffusion is revealed to have a marked transient character and to depend on the B concentration itself. In particular, boron atoms can move after the interaction with dangling bonds whose density is transiently increased after ion implantation or permanently enhanced by the presence of boron atoms themselves. Unexpectedly, B diffusivity in a-Si is seen to be orders of magnitude above than in c-Si and to depend on the thermal history, i.e. the relaxation status of the amorphous phase. These data are presented and their implications discussed.
Effect of Elevated Implant Temperature on Amorphization and Activation in As-implanted Silicon-on-insulator Layers
Authors: Saenger Katherine L. , Bedell Stephen W. , Copel Matthew , Majumdar Amlan , Ott John A. , de Souza Joel P. , Koester Steven J. , Wall Donald R. , Sadana Devendra K.
Published: April 2011

The ion implantation steps used in fabricating field effect transistors in ultrathin (6 to 30 nm) silicon-on-insulator (UTSOI) substrates present many challenges. Deep source/drain (S/D) implants in UTSOI layers are a particular concern, since it can be difficult to implant the desired dose without amorphizing the entire SOI thickness. In a first study, we investigated the effect of implant temperature (20 to 300 °C) on the sheet resistance (Rs) of 28 nm thick SOI layers implanted with As+ at an energy of 50 keV and a dose of 3 × 1015 /cm2, and found Rs values after activation sharply lower for samples implanted at the highest temperature. In a second study, on 8 nm thick SOI layers implanted with As+ at an energy of 0.75 keV and doses in the range 0.5 to 2 × 1015/cm2, the benefits of the elevated implantation temperature were less clear. Explanations for these effects, supported by microscopy, medium energy ion scattering (MEIS), and optical reflectance data, will be discussed.
First Principles Study of Boron in Amorphous Silicon
Authors: Santos Iván , Windl Wolfgang , Pelaz Lourdes , Marqués Luis Alberto
Published: April 2011

We have carried out an ab initio simulation study of boron in amorphous silicon. In order to understand the possible structural environments of B atoms, we have studied substitutional-like (replacing one Si atom in the amorphous cell by a B atom) and interstitial-like (adding a B atom into an interstitial space) initial configurations. We have evaluated the Fermi-level dependent formation energy of the neutral and charged (±1) configurations and the chemical potential for the neutral ones. For the interstitial-like boron atom, we have find an averaged formation energy of 1.5 eV. For the substitutional case, we have found a dependence of the chemical potential on the distance to Si neighbors, which does not appear for the interstitial ones. From MD simulations, we could observe a diffusion event for an interstitial-like boron atom with a migration barrier of 0.6 eV.
Modeling Evolution of Temperature, Stress, Defects, and Dopant Diffusion in Silicon During Spike and Millisecond Annealing
Authors: Moroz Victor , Martin-Bragado Ignacio , Zographos Nikolas , Matveev Dmitri , Zechner Christoph , Choi Munkang
Published: April 2011

The bulk CMOS devices continue as the dominant player for at least another couple of technology nodes. This drives the increasingly contradicting requirements for the channel, source/drain extension, and heavily doped source/drain doping profiles. To analyze and optimize the transistors, it is becoming necessary to combine a number of effects that have been treated as decoupled so far. The temperature gradients, combined with stress engineering techniques such as embedded SiGe and Si:C source/drain and stress memorization technique, create non-uniform stress distributions determined by the layout patterns. The interaction of implant-induced damage with dopants, stress, and defect traps shapes up the dopant activation, retention of useful stress, and junction leakage. This work reviews recent trends in modeling these effects using continuum and kinetic Monte Carlo methods.
F+ implants in crystalline Si: the Si interstitial contribution
Authors: Lopez Pedro , Pelaz Lourdes , Duffy Ray , Meunier-Beillard P. , Roozeboom F. , van der Tak K. , Breimer P. , van Berkum J. G. M. , Verheijen M. A. , Kaiser M.
Published: April 2011

In this work the Si interstitial contribution of F+ implants in crystalline Si is quantified by the analysis of extended defects and B diffusion in samples implanted with 25 keV F+ and/or 40 keV Si+. We estimate that approximately 0.4-0.5 Si interstitials are generated per implanted F+ ion, which is in good agreement with the value resulting from the net separation of Frenkel pairs obtained from MARLOWE simulations. The damage created by F+ implants in crystalline Si may explain the presence of extended defects in F-enriched samples and the evolution of B profiles during annealing. For short anneals, B diffusion is reduced when F+ is co-implanted with Si+ compared to the sample only implanted with Si+, due to the formation of more stable defects that set a lower Si interstitial supersaturation. For longer anneals, when defects have dissolved and TED is complete, B diffusion is higher because the additional damage created by the F+ implant has contributed to enhance B diffusion.
Computer Simulation of the Phase-change Cycle of GST-225
Authors: Elliott Stephen , Hegedus Jozsef
Published: April 2011

We have simulated for the first time, by ab initio molecular dynamics, the complete phase-transformation cycle (liquid-crystal, liquid-amorphous-crystal) of the phase-change (PC) memory material Ge2Sb2Te5 (GST-225). We have observed that rapid cooling of the simulated melt leads to an amorphous product, whereas slow cooling results in the metastable rocksalt crystal. Furthermore, crystallization to the same structure is observed to occur on annealing the quenched amorphous model to temperatures below the melting temperature. The RDF of the energy-relaxed amorphous GST-225 structure agrees very well with experimental neutron-diffraction data, reproducing the shortening of the Ge-Te bond length relative to that in the rocksalt crystal structure observed experimentally.We have observed crystal-nucleation events in the simulated liquid that have been identified as the creation of connected near-regular square fourfold rings, the basic structural units of the rocksalt structure. These crystal nuclei are invariably found to be quenched into the amorphous state on rapid cooling of the simulated melt. This observation therefore explains why GST materials crystallize so readily and why homogeneous nucleation is so facile.
Crystal Growth Rates in Doped SbxTe Fast-Growth Phase-Change Films Studied with Transmission Electron Microscopy
Authors: Kooi Bart J. , Pandian Ramanathaswamy , De Hosson Jeff Th. M.
Published: April 2011

Isothermal crystallization of doped SbxTe fast-growth phase-change films was investigated using transmission electron microscopy with in situ heating. SbxTe films with four different values for the Sb/Te ratio, x=3.0, 3.3, 3.6 and 4.2, were analyzed and the films were sandwiched between two types of dielectric layers. One dielectric layer type is based on 80at.%ZnS-20at.%SiO2, the other on (Ge,Cr)N. The crystal growth rates reduce if the phase-change films are sandwiched between amorphous dielectric layers. The reduction is very pronounced at the lowest measured temperatures (150 °C), becomes smaller at higher temperatures and probably disappears at around 200 °C. The crystal growth rates increase with increasing Sb/Te ratio, but the activation energy for crystal growth is not significantly affected by the Sb/Te ratio. Finally a systematic study of the effect of the electron beam of the TEM on the crystal growth rates is performed showing accelerated growth rates. The present work shows that particularly at relative low temperatures, just above the glass-transition temperature, the growth rates as limited by the atomic mobilities are sensitive to various (boundary) conditions, e.g. capping layers and irradiation.
SET Characteristics of Phase Change Bridge Devices
Authors: Krebs Daniel , Raoux Simone , Rettner Charles T. , Shelby Robert M. , Burr Geoffrey W. , Wuttig Matthias
Published: April 2011

Scaling studies have demonstrated that Phase Change Random Access Memory (PCRAM) is one of the most promising candidates for future non-volatile memory applications. The search for suitable phase change materials with optimized properties is therefore actively pursuit. In this paper, SET (crystallization) characteristics of an ultra fast switching material Ge15Sb85 in phase change memory bridge cell devices are presented. It was found that reproducible switching between two stable states with one decade resistance contrast and current pulses as short as 10 ns for SET and RESET (re-amorphization) operation is possible. Particular emphasis was placed on the difference in crystallization kinetics between the as-deposited and melt-quenched amorphous phase. Evidence is given for the existence of an electrical field as the critical parameter for threshold switching rather than a threshold voltage. For Ge15Sb85 a threshold switching field of 9MV/m was measured and it was shown that switching from the melt-quenched amorphous phase to the crystalline phase is about 600 times faster than crystallization from the as-deposited amorphous phase.
Investigation of SET and RESET States Resistance in Ohmic Regime for Phase-Change Memory
Authors: Savransky Semyon D. , Karpov Ilya V
Published: April 2011

New technique to separate bulk and interface electrical properties of polycrystalline and glassy Ge2Sb2Te5 (GST) in phase-change memory (PCM) devices is proposed. PCM with different GST thicknesses are measured. The average activation energies for bulk conductivity are 0.37 eV and 0.09 eV as well as bulk resistivities are about μOhm*cm2 and 20 μOhm*cm. The contact barriers is 0.07eV and specific contact resistance is about 0.3 μOhm*cm2 in studied PCM devices.

It is discovered that bulk resistivities for both SET and RESET states in PCM obey Meyer-Neldel rule with almost identical isokinetic temperatures 335K − 340K. This information is discussed in terms of GST structure.
Atomic Layer Deposition of HfO2 Thin Films on Si and GaAs Substrates
Authors: Hackley Justin C , Demaree J. Derek , Gougousi Theodosia
Published: April 2011

The atomic layer deposition of HfO2 thin films is studied on Si(100) and GaAs(100) surfaces. The films are grown using tetrakis(dimethylamido)hafnium (TDMAH) and H2O precursors at a deposition temperature of 275°C. The Si surfaces used include a H-terminated surface and an OH-rich chemical oxide. GaAs substrates are subjected to two different pre-deposition treatments involving an HF and a NH4OH wet chemical etch that has been shown to remove most of the Ga and As native oxides. Spectroscopic ellipsometry (SE) confirms linear growth rates of 1.05±0.05 Å/cycle for all surfaces. Rutherford backscattering spectrometry (RBS) shows that steady-state growth of 2.6×1014 Hf/cm2/cycle is reached after 10 ALD cycles for the HF-etched GaAs surface. X-ray photoelectron spectroscopy (XPS) indicates the presence of native oxides on both GaAs starting surfaces after 10 cycles due to postdeposition surface oxidation. However, the presence of the native oxide is not detected for thicker 15 and 20 cycle samples indicating passivation of the surface and suppression of the interfacial layer formation.
Physical origin of colossal dielectric constant in CaCu3Ti4O12 thin film by Pulsed Laser Deposition
Authors: Deng Guochu , Yamada Tomoaki , Muralt Paul
Published: April 2011

The (001) preferentially oriented CCTO thin film was grown on Pt/Ti/TiO2/Si (100) substrate by pulsed laser. I-V and C-V relationships of the CCTO thin film showed characteristics typical of a tunnel metal-insulator-semiconductor (MIS) structure and its capacitance response is the origin of the high apparent dielectric constant observed in CCTO thin films. The very thin insulating layer on top of the film can be reduced in thickness by treatment in HCl acid, as shown by smaller threshold voltages in the I-V curves. The overall behavior is compatible with a conduction activation energy of ∼80 to 100 meV in the bulk of the film, and a diffusion potential at the interface of 500 to 800 meV. The acceptor concentration is of the order of 1019cm−3.
Optical Detection of SiN Stress Layer Induced Carrier Mobility Enhancement in Silicon
Authors: Wirbeleit Frank , Pedrero Victoria , Thron Dominik , Stephan Rolf , Schwalke Udo
Published: April 2011

Strain engineering is key element for improving MOSFET device performance in today's advanced high performance microelectronics. Strained SiN layers are well established in this regard to generate near surface strain effects for carrier mobility enhancement. Non destructive detection of effects from strain layers has not been resolved yet, especially during the processing of patterned wafers. Since optical reflective measurements are well established for non destructive thickness measurements in semiconductor manufacturing, the signals out of those spectra can be used to investigate stress induced carrier mobility enhancement effects, as shown in this work. This provides direct access to the effectiveness of the applied near surface strain to the carrier mobility. By this novel method, SiN films at different stress levels and under different process conditions are investigated on silicon bulk wafers. On these wafers, the optically detected spectra shift, known as plasmon shift, can be correlated with standard wafer bow stress measurement results. These results are correlated to the electrical performance of microelectronic test structures. Based on this, the relative variation of the stress levels of SiN films after different process treatments, and the impact on carrier mobility in microelectronic devices is shown.
MeV Si Ions Bombardment Effects on the Properties of Nano-Layers of SiO2/SiO2+Ag
Authors: Guner Sadik , Budak Satilmis , Muntele Claudiu I , Smith Cydale C , Ila Daryush
Published: April 2011

We have grown 100 periodic SiO2/SiO2+Ag multi-nano-layered systems where the SiO2+Ag layers were 7.26 nm and SiO2 buffer layer were 4 nm, total thickness is 563 nm. Using interferometer as well as in-situ thickness monitoring, we measured the thickness of the layers; using Rutherford Backscattering Spectrometry (RBS) measured the concentration and distribution of Ag in SiO2. The electrical conductivity, thermal conductivity and the Seebeck coefficient of the layered structure were measured at room temperature before and after bombardment by 5 MeV Si ions. The energy of the Si ions were chosen such that the ions are stopped in the silicon substrate and only electronic energy due to ionization is deposited in the layered structure. The electrical conductivity measured using Van der Pauw method. Thermal conductivity of the thin films was measured using an in-house built 3ω thermal conductivity measurement system. Using the measured Seebeck coefficient, thermal conductivity and electrical conductivity we calculated the figure of merit (ZT). We will report our findings of change in the figure of merit as a function of the bombardment fluence.