bluuebunny/crossref_metadata_2025_split huggingface dataset:
Current Gain of an AlGaN/GaN Heterojunction Bipolar Transistor
Authors: Zhang Yumin , Ruden P. Paul 
Published: April 2011

ABSTRACTA novel hybrid model and simulation results for an advanced, graded base AlGaN/GaN heterojunction bipolar transistor structure are presented. The base of the n-p-n HBT examined has two parts, a linearly graded AlGaN layer on the emitter side and a heavily p-doped GaN layer on the collector side. In the hybrid model developed here the potential profile is first calculated self-consistently in the biased state taking into account ionized impurity charges, polarization charges, and majority carrier charges. The minority carrier transport is examined subsequently. Injection of electrons from the emitter is modeled as a thermionic emission process. The minority electron transport process in the graded region is drift-dominated due to the large built-in effective field strength. In the low-field GaN layer of the base, electron transport is assumed to be diffusion-dominated. High-level injection effects are modeled in the framework of the Gummel-Poon model. Example structure design parameters are presented and it is found that the calculated current gain can be greater than 25, with a collector current density of 104A/cm2.
Ab-Initio Calculation of the β-SiC/Ni Interface
Authors: Blasetti A. , Profeta G. , Picozzi S. , Continenza A. , Freeman A. J. 
Published: April 2011

ABSTRACTWe investigate the adsorption of a Ni monolayer on the β-SiC(001) surface by means of highly precise first-principles all-electron FLAPW calculations. Total energy calculations for the Si- and C-terminated surfaces reveal high Ni adsorption energies, with respect to other metals, confirming the strong reactivity and the stability of the transition metal/SiC interface. These high binding energies, about 7.3-7.4 eV, are shown to be related to strong p-d hybridization, common to both surface terminations and different adsorption sites, which, despite the large mismatch, may stabilize overlayer growth. A detailed analysis of the bonding mechanism, in terms of density of states and hybridization of the surface states, reveals the strong covalent character of the bonding. We also calculate and discuss the Schottky barrier heights at the Ni/SiC junction for both terminations.
Effect of Composition and Bead Settling on Debonding of Underfill Layers
Authors: Wang Lorraine C. , Dauskardt Reinhold H. 
Published: April 2011

ABSTRACTWith the increased complexity of microelectronic devices continuing to drive chip packages to smaller sizes, the need for reliable high-density flip chip packaging is increasingly important. In these packages, epoxy underfills are used to surround a solder ball grid array in order to support thermomechanical stresses in the system. This research focuses on determining the mechanisms that cause debonding at interfaces in these packages, particularly between the underfill and chip passivation. A fracture mechanics approach is used to study the adhesion of Si3N4to two model underfills, one based on aliphatic epoxy and the other based on bisphenol F epoxy. Interestingly, these two underfills, which are similar mechanically, appear to show very different critical and subcritical behavior. The aliphatic underfill exhibits subcritical debond growth under constant displacements, behavior typically seen in interface systems, while the bisphenol F underfill surprisingly shows little susceptibility to stress corrosion. Although both underfills show evidence of silica bead settling, the addition of filler has opposing effects on their critical adhesion values. The effects of varying filler content in these underfills as well as environmental effects on the critical and subcritical behavior of these systems will be examined.
Characterization and Soldering of Organic Modified Aluminum Thin Films and Bond Pads
Authors: Fang Rui , Dahlgren Eric , O'Keefe Matthew J. , O'Keefe Thomas J. , Shih Wu-Sheng , Gamota Daniel R. , Zhang Jie 
Published: April 2011

ABSTRACTAn immersion plating process using organic solutions was used to deposit a seed layer of copper and to activate the surface of thin film aluminum surfaces and bond pads. The seeded surfaces were subsequently electroless copper plated and tested for compatibility with soldering assembly. It was demonstrated that the copper particles deposited from the organic solution onto sputter deposited aluminum thin films were able to act as nucleation sites for the subsequent build up of adherent, continuous copper films from conventional electroless plating baths. In addition, the metal deposition from organic solution process was found to be very selective on patterned test vehicles and integrated circuits as metal deposition occurred only on the exposed aluminum bond pads and not on any passivated surfaces. Tests were conducted to determine the solderability of the samples after only seeding in the organic solution as well as the combination of seeding plus electroless copper deposition. In these tests, all attempts to directly solder without any pre-treatment were unsuccessful. Results on solder adherence varied with different substrates. Nevertheless, the concept of depositing metal seed layers in these applications is feasible. Additional work is needed, however, to optimize the deposition process for each particular surface to be soldered.
Using the Surface Potential Decay Method to probe electrical conduction in epoxy resins used for packaging
Authors: Sylvestre Alain , Gonon Patrice , Teysseyre Jérôme , Prior Christophe 
Published: April 2011

ABSTRACTIn this work we discuss the usefulness of the Surface Potential Decay (SPD) method to investigate electrostatic charges deposited on epoxy resins which are used for electronic packaging. Corona discharges were applied on epoxy resins with different degrees of Post Mold Curing (PMC). SPD studies were conducted at room temperature under a relative humidity of about 45%. In the first part of this study we analyze the flow of electrostatic charges as a function of time. Using the SPD method we evidence that 10% of the electrical charge is still present at the surface three hours after the corona discharge has been applied. We find that the surface potential decay is more important for samples with longer PMC duration. In the second part of this work we provide a physical interpretation of the surface charge decay. We suggest that it is related to polarization mechanisms within the bulk of the material.
Fatigue Processes in Silicon MEMS Devices
Authors: Renuart Emily D. , Fitzgerald Alissa M. , Kenny Thomas W. , Dauskardt Reinhold H. 
Published: April 2011

ABSTRACTMEMS devices may experience significant alternating loads during service, associated with both applied and vibrational loading. Long-term reliability and lifetime predictions require understanding of possible fatigue mechanisms in these structures. Although silicon is not generally considered susceptible to fatigue crack growth, recent studies suggest that there may be fatigue processes in silicon MEMS structures. The phenomenon, however, has still not been extensively studied. In this work, we used a compressive double cantilever beam geometry to examine stable crack growth. Crack length and loads were carefully monitored throughout the test in order to distinguish between the apparent role of environmentally assisted crack growth (stress corrosion) and mechanically induced fatigue. Results revealed similar step-like crack extension versus time for the cyclic and monotonic tests. The fatigue crack-growth curve extracted from the crack extension data exhibited a nearly vertical slope with no evidence of fatigue crack-growth. Fracture surfaces for the monotonic and cyclic tests were similar, further suggesting that a true mechanical fatigue crack-growth mechanism did not occur.
Dislocation Walls in Finite Media: The Case of an Infinite Slab
Authors: Surh M. , Wolfer W. G. 
Published: April 2011

ABSTRACTThe dislocation microstructure observed in solids exhibits cellular patterns. The interiors of these cells are depleted of dislocations while the walls contain dense bundles including the geometrically necessary dislocations leading to misorientations of the crystal lattice on either side. This clustering is the result of short-range interactions which favor the formation of dislocation dipoles or multipoles and tilt and twist boundaries. While this short-range ordering of dislocations is readily understood, the long-range pattern formation is still being studied. We examine finite tilt boundaries in an infinite medium, a model grain, and a free slab to investigate the conditions for long-range stress interactions. We find that finite tilt walls in a larger medium generally possess a long-range stress field because the local bending at the tilt wall is constrained by the surrounding material.
A Generalized Model of the Yield Drop for Impure Semiconductors
Authors: Petukhov Boris V. 
Published: April 2011

ABSTRACTThe Alexander-Haasen theory describing the deformation behavior of low-dislocated semiconductor crystals is generalized taking into account the dynamic ageing of dislocations due to the impurities dragging. The constitutive equations describing kinetics of the plastic deformation are modified for the case of a spectrum of age-dependent internal stresses. Besides the solution hardening, the theory developed explains a number of qualitative distinctions of the elastic-plastic transition in silicon crystals grown by the Czochralski and the float zone methods. Particularly, this concerns a dependence of the yield drop on the initial dislocation density, and a weakening of the strain rate sensitivity of the yield stress.
Radiation Hardening and Plastic Instability in Neutron Irradiated CuCrZr
Authors: Edwards Dan. J. , Singh Bachu. N. 
Published: April 2011

ABSTRACTThe effect of post-irradiation annealing at 300°C for 50 hours on the microstructure and mechanical properties of CuCrZr irradiated to 0.3 dpa at 100°C has been evaluated. The post- irradiation annealing restores some ductility and work hardening to the material as well as lowers the yield strength, however it does not completely remove the effects of irradiation. A comparison of the microstructural features and mechanical properties in the as-irradiated condition and in the post-irradiation annealed case highlights the fact that the observed microstructure does not necessarily correlate with the changes in tensile behavior, most notably in the removal of the yield point and lowering of the yield stress after annealing.
Modeling of Dislocation Mobility in Metals: Effect of Obstacles and Thermal Processes
Authors: Hiratani Masato , Zbib Hussein M. 
Published: April 2011

ABSTRACTThermally activated dislocation glide velocity through weak point obstacle arrays is studied analytically and computationally. Thermal activation rate is estimated using the modified Friedel relations under the weak obstacle approximation. The average flight velocity after an activation event as a function of stress and temperature is obtained by the discrete dislocation dynamics (DD). This numerical calculation includes the effect of self-stress, interaction with electrons and phonons, and the inertial effect. These results are implemented into a phenomenological model to study the dislocation velocity under various conditions. The model can reproduce both obstacle control and drag control motion in low and high velocity regions, and a flow stress anomaly at transient regions.
Marquette's Engineering Student Volunteer Outreach Program to Fifth Graders in the Public Schools, Choice Schools, and a Charter School in Milwaukee
Authors: Brower William E. 
Published: April 2011

ABSTRACTEducational efforts by the MSE profession can effect society in several ways: by producing more and better MSE graduates, by enhancing the Materials backgrounds of students from other engineering disciplines, by continuing education programs, and, in a nontraditional sense, by impacting the non-engineering community with outreach programs. I suggest that the effect on society of working with disadvantaged elementary school children, such as inner city fifth graders, is potentially far greater than efforts spent on non-engineering students already in college, high school students, or even middle school students. The Fifth Grade Volunteer Teaching Program (5GVP) at Marquette has attempted over the last ten years to inform Milwaukee's inner city fifth graders of the existence of an engineering career while showing them that science is something that they can actually do themselves and that the doing is fun. Maybe some of the roughly 5,000 students taught have stayed in the college prep track in math and science as a result of contact with our enthusiastic engineering student volunteers. Our lessons are self contained and heavy with things for the fifth graders to do themselves. One lesson, which portends Materials Science and Engineering, is called, “Phases of Matter”. This year I have expanded the 5GVP Program to include three of the Choice Schools operating in Milwaukee. These schools differ from the Milwaukee Public Schools (MPS) and from each other significantly. Class sizes in the Choice Schools vary from much smaller than MPS to about the same size as MPS. The school buildings range from ramshackle to very modern. The Charter School has science labs and the Choice Schools do not. The Charter School is for profit and these two Choice Schools are not for profit.
The Macroscope: A Macroscopic Tool for Validating Microscopic Force Relationships
Authors: Guerra-Vela Claudio , Zypman Redy R. 
Published: April 2011

ABSTRACTThe Force Macroscope (FM) was presented at the MRS-Spring-2000 as a laboratory teaching tool to introduce students to concepts of Scanning Force Microscopy (SFM). It is a macroscopic version of the SFM. The FM pedagogical advantage over the SFM is its size: students relate to the FM, only a few grasp at once the concepts for the 100 [.proportional]m-long SFM cantilever. In this work we will show how we take advantage of the FMs large size to teach concepts of force reconstruction.
Role of Fluorite Formation in Orientation Selection in Sol-Gel Derived Pb(Zr,Ti)O3 Films on Pt Electrode Layers
Authors: Norga G. J. , Fè L. , Vasiliu F. , Wouters D. J. , Biest O. Van der 
Published: April 2011

AbstractWe present evidence that the microstructure of the metastable fluorite phase Pb2(Zr,Ti)2O6, which forms during the pyrolysis treatment of sol-gel PZT layers by homogeneous nucleation throughout the film, has a larger impact on orientation selection than has previously been realized. Elaborate TEM studies demonstrate that by varying the pyrolysis time, temperature and duration, the crystallinity of the transient fluorite phase can be greatly influenced. Pyrolysis at 350°C leads to the formation of a well crystallized fluorite phase with a cubic structure (Fd3m space group) and a= 10.5-10.6 Å. Rapid crystallization of the transient fluorite phase is attributed to the low oxygen partial pressure conditions, prevailing during burnoff of acetate groups originating from the lead starting compound. A possible connection between the fluorite formation kinetics and orientation selection in the layers is discussed.
Precise Control of Nucleation and Growth in Lead Zirconate Titanate Thin Films by Scanning Rapid Thermal Annealing
Authors: Lee Jang-Sik , Joo Seung-Ki 
Published: April 2011

AbstractIn this paper, a novel annealing method, scanning-rapid thermal annealing (RTA), for the selectively nucleated lateral crystallization (SNLC) of Pb(Zr,Ti)O3 (PZT) thin films is discussed. The effects of lamp power and scan speed on the SNLC were investigated. It was found that scanning-RTA was very effective method for SNLC in reducing the process time and preventing undesirable nucleation at other than pre-determined positions.
Epitaxial Growth of LaVO3/(Ba,Sr)TiO3/(Pb,La)(Zr,Ti)O3/(La,Sr)CoO3 Semiconductor/Ferroelectric/Conductor Heterostructures
Authors: Choi Woong , Sands Tim 
Published: April 2011

AbstractThe feasibility of using LaVO3 as a semiconducting layer in all-oxide semiconductor/ferroelectric/conductor heterostructures was explored by growing epitaxial LaVO3/(Ba,Sr)TiO3/(Pb,La)(Zr,Ti)O3/(La,Sr)CoO3 heterostructures on (001) LaAlO3 single crystal substrates by pulsed laser deposition. A high degree of c-axis orientation and strong in-plane texture revealed by x-ray diffraction indicated the epitaxial crystallographic relationships between the layers. With a 30 nm layer of (Ba,Sr)TiO3, the heterostructure showed optimal ferroelectric hysteresis with remanent polarizations over 30 C/cm2. The capacitance measurement as a function of voltage might reveal the modulation of the depletion layer in the semiconducting LaVO3.
Al2O3/Si3N4 Buffer Layer for High Performance MFIS (Metal-Ferroelectric-Insulator-Semiconductor) Transistors
Authors: Fujisaki Yoshihisa , Ishiwara Hiroshi 
Published: April 2011

AbstractThe Al2O3 thin films were deposited on the Si3N4 (radical- Si3N4) prepared by the direct nitridation of a Si substrate using atomic nitrogen radicals. Because the radical- Si3N4 is highly resistive against the oxidation process, we can completely eliminate the metal phase in Al2O3 that degrades the insulating properties of Al2O3. The 1.3nm thick Al2O3 film was found to have a permittivity of 9.76 in this stacked Al2O3/Si3N4 structure. It was also found that no oxidation took place at the interface of Si3N4 and the Si substrate during the deposition and post-oxidation of the Al2O3 film on the radical-Si3N4/Si substrates. As a result, highly capacitive MIS (Metal-Insulator-Semiconductor) structures were realized using the Al2O3/Si3N4 stacked insulator. The MIS diode with Al2O3/Si3N4 is found to have 105 times less leakage current compared to the diode with Si3N4 insulator film with similar capacitance density. We have shown that the insulating properties of the Al2O3/radical-Si3N4 stack are suitable for the MFIS (Metal-Ferroelectric-Insulator-Semiconductor) transistors.
Raman Studies of the Soft Phonon Modes in BaxSr1−x.TiO3 thin Films
Authors: Tenne D. A. , Clark A. M. , James A. R. , Soukiassian A. , Chen K. , Xi X. X. 
Published: April 2011

AbstractThe vibrational properties of barium strontium titanate thin films were studied by Raman spectroscopy in the temperature range from 5 to 300 K. The films were grown by pulsed laser deposition on SrTiO3 and LaAlO3 substrates with SrRuO3 buffer layers. Soft phonons are observed in Raman spectra of BaxSr1−xTiO3 films with Ba contents x = 0.05, 0.1, 0.2 and 0.5. The temperature dependence of the soft phonon frequencies and the splitting of the triply degenerated soft mode into two components of A and E symmetries indicate the ferroelectric phase transition. The E soft mode line is overdamped over a broad range of temperatures near the ferroelectric phase transition, while it is clearly seen in the spectra at temperatures away from the phase transition. The relative Raman intensity of the A soft mode and hard modes decreases gradually over a broad range of temperatures. This indicates a broad ferroelectric phase transition in the thin films. Comparison of Raman spectra for films grown on SrTiO3 and LaAlO3 substrates shows the influence of strain on the temperature of the ferroelectric phase transition.
Fabrication and Characterization of a PZT thin Film Actuator for a Micro Electromechanical Switch Application
Authors: Hoffmann Marcus , Leuerer Timm , Krüger Clemens , Böttger Ulrich , Mokwa Wilfried , Waser Rainer 
Published: April 2011

AbstractMicromachined silicon cantilever beams actuated by the converse piezoelectric effect are of great interest for actuator applications, e.g. micro relays or micro mirrors. For the miniaturization and cost saving aspects the combination of silicon bulk micromachining and chemical solution deposition (CSD) technique for the ceramic thin films is very promising.This paper presents the results of such a fabrication process for a PbZr0.45Ti0.55O3 (PZT) thin film micro actuator for a switch application. The actuator was designed with lengths of 190-990 μm, widths of 60-120 μm, and a complete thickness of 1.5 μm. Wherein the piezoelectric PZT function layer has a thickness of 350 nm. For a distance of 10 μm between the switch contacts and an applied voltage of 10 V a finite element analysis simulation (FEA) was carried out to obtain the principal stress contribution, the optimum cantilever length, the sensitivity, the resonance frequency and the switch contact force. The bending beams were characterized by laser interferometry, resonance frequency, and force measurements. These characterization results are compared to the FEM analyses and to an analytical approach.
Infrared Spectroscopy of Epitaxial Antimony Sulpho Iodide Thin Films
Authors: Kotru S. , Surthi S. , Pandey R. K. , Donnelly D. 
Published: April 2011

AbstractThin films of antimony sulpho iodide (SbSI) were grown on platinized silicon substrates by the pulsed laser deposition method. As grown films were amorphous and annealing at 250 °C for 5 minutes introduced crystallinity in the films. Infrared reflectance measurements were done in the frequency range ∼ 500 – 5000 cm−1 (wavelength ∼ 2–20 μm). The reflectance measurements were taken at temperatures above and below the ferroelectric transition of SbSI ∼ 20° C. The index of refraction for a (121) oriented film was determined to be 2.83 ± 0.35 at a temperature of 25.6 °C, and 2.80 ± 0.35 at a temperature of 9.6 °C. For a (002) oriented film, the index was 3.82 ± 0.48 at a temperature of 26.5 °C, and 3.76 ± 0.48 at a temperature of 8.0 °C. Pyro-optic coefficients of 1.5 × 10−3 °C−1 for the (121) oriented film, and 3.2 × 10−3 °C−1 for the (002) oriented film were obtained. These results are consistent with measurements done in the visible region, and demonstrate the potential of SbSI as an infrared detector material.
PZT and PMN-PT Thin Film Cantilevers: Comparison between Monomorph and Bimorph Structures
Authors: Hoffmann Marcus , Kügeler Carsten , Böttger Ulrich , Waser Rainer 
Published: April 2011

AbstractPiezoelectric and electrostrictive materials are potential candidates for integrated micro systems. They can be used in cantilever laminated structures for different applications, e.g. active vibration control or agile transducers [1-3]. Due to the necessity of miniaturization of MEMS devices and the reduction of process costs and time, the use of chemical solution deposition (CSD) technique with microlithography and reactive ion etching (RIE) are essential.Within this work we used these techniques in combination with silicon bulk micro machining technique to fabricate piezoelectric Pb(Zr,Ti)O3 (PZT) and electrostrictive Pb(Mg1/3,Nb2/3)O3-PbTiO3 (PMN-PT) coated micro cantilevers with different lengths which can be used in micro switch or micro mirror applications. In general PMN shows no elastic hysteresis and a better aging behavior than PZT ceramics. Since the electrostrictive effect is smaller than the piezoelectric effect the tip deflection of PMN-PT coated beams is much lower. Cantilevers with two ceramic thin film layers and an internal electrode (bimorph) were designed and compared to such with single ceramic thin film layers (monomorph). For fabrication control and electrical characterization SEM, polarization hysteresis-, and CV-measurements were performed. Laser interferometry measurements were used to characterize the electromechanic performance of the ceramic thin films and cantilevers.