August 2014 - Msepostdoc-list

REVISED: Seminar Notice: S. Leach PhD Final Exam Sept. 4 2014
by Stacey, Lisa A 29 Aug '14

29 Aug '14

Please note corrected seminar time is 1:30 pm MATERIALS SCIENCE AND ENGINEERING SEMINAR MSE PhD Final Examination Size and Texture Effects on Ferroelectrics by: Sarah E. Leach Advisor: Prof. R. E. Garcia ABSTRACT Thin film ferroelectric materials have generated a great deal of interest for use as low-voltage non-volatile memory, sensors, and actuators. The commercial market for non-volatile memory alone is projected to exceed 20 billion dollars in 2014. Ferroelectric materials are characterized by a reorientable spontaneous electric dipole moment, or polarization domain. A detailed understanding of the underlying domain switching processes in a ferroelectric material is of critical importance for the engineering of memories, where the total switching time affects the write/read time of the device, and the polarization values affect the difference between memory states. An imposed temperature or stress field alters the material’s crystallographic symmetry, which controls the electrostrictive, ferroelectric, or piezoelectric behavior. This study presents analytical and numerical theories to describe the polarization hysteresis behavior for three different configurations: regions within grains of a polycrystalline thin film, a single crystal, and individual grains in a polycrystalline thin film. First, the polarization hysteresis behavior for regions within individual PZT (PbTiO3) grains as a function of epitaxial strain and crystallographic orientation is modeled. In agreement with published experimental results, enhanced or inhibited hysteresis behavior is described, depending on proximity to the grain boundaries, the orientation of the grain to adjacent grains, and the orientation of the grain with respect to the geometry of the thin film. Grain boundaries with different misorientation angles create different local strain fields that couple to the local electric field via the piezoelectric effect, and change the switching behavior of adjacent regions. For 100 nm diameter grains, the coercive field required for polarization switching can vary approximately ±10% between a region near a grain boundary and one near the grain center. Secondly, for single-crystal thin-film devices formed into discrete mesas, the film stresses and average remnant polarization are shown to be controlled by the aspect ratio of the mesa. Calculations demonstrate that the stresses at the edges are relaxed for film height, hf , to width, w, ratios hf /w ≤ 1 x 10-4. For hf /w ≥ 1 x 10-2, the effective in-plane stress is relaxed throughout the deposited film. Moreover, the effective stresses at the center of the mesa are 15% of the stresses of an infinitely wide film, hf /w → 0. Finally, the overall texture, or orientation distribution, of the grains in a polycrystalline film is shown to influence the polarization hysteresis behavior through coupling of the mechanical and electrical fields. For films with hf /w = 0.0011, the remnant polarization decreases from 0.69 C/m2 to 0.66 C/m2 as the orientation distribution becomes more random. Results show that as hf /w → 1, the average value of remnant polarization decreases to approximately 0.64 C/m2 which means that small devices will have a reduced value of remnant polarization compared with infinitely wide films, but the remnant polarization does not decrease to zero. These modeling results are useful for optimizing the performance of PZT devices, but can also be applied to other ferroelectric materials, including lead-free formulations such as Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3. Date: Thursday, September 4, 2014 Time: 1:30 PM Place: ARMS 3115 Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100

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Seminar Notice: S. Leach PhD Final Exam Sept. 4 2014
by Stacey, Lisa A 29 Aug '14

29 Aug '14

MATERIALS SCIENCE AND ENGINEERING SEMINAR MSE PhD Final Examination Size and Texture Effects on Ferroelectrics by: Sarah E. Leach Advisor: Prof. R. E. Garcia ABSTRACT Thin film ferroelectric materials have generated a great deal of interest for use as low-voltage non-volatile memory, sensors, and actuators. The commercial market for non-volatile memory alone is projected to exceed 20 billion dollars in 2014. Ferroelectric materials are characterized by a reorientable spontaneous electric dipole moment, or polarization domain. A detailed understanding of the underlying domain switching processes in a ferroelectric material is of critical importance for the engineering of memories, where the total switching time affects the write/read time of the device, and the polarization values affect the difference between memory states. An imposed temperature or stress field alters the material’s crystallographic symmetry, which controls the electrostrictive, ferroelectric, or piezoelectric behavior. This study presents analytical and numerical theories to describe the polarization hysteresis behavior for three different configurations: regions within grains of a polycrystalline thin film, a single crystal, and individual grains in a polycrystalline thin film. First, the polarization hysteresis behavior for regions within individual PZT (PbTiO3) grains as a function of epitaxial strain and crystallographic orientation is modeled. In agreement with published experimental results, enhanced or inhibited hysteresis behavior is described, depending on proximity to the grain boundaries, the orientation of the grain to adjacent grains, and the orientation of the grain with respect to the geometry of the thin film. Grain boundaries with different misorientation angles create different local strain fields that couple to the local electric field via the piezoelectric effect, and change the switching behavior of adjacent regions. For 100 nm diameter grains, the coercive field required for polarization switching can vary approximately ±10% between a region near a grain boundary and one near the grain center. Secondly, for single-crystal thin-film devices formed into discrete mesas, the film stresses and average remnant polarization are shown to be controlled by the aspect ratio of the mesa. Calculations demonstrate that the stresses at the edges are relaxed for film height, hf , to width, w, ratios hf /w ≤ 1 x 10-4. For hf /w ≥ 1 x 10-2, the effective in-plane stress is relaxed throughout the deposited film. Moreover, the effective stresses at the center of the mesa are 15% of the stresses of an infinitely wide film, hf /w → 0. Finally, the overall texture, or orientation distribution, of the grains in a polycrystalline film is shown to influence the polarization hysteresis behavior through coupling of the mechanical and electrical fields. For films with hf /w = 0.0011, the remnant polarization decreases from 0.69 C/m2 to 0.66 C/m2 as the orientation distribution becomes more random. Results show that as hf /w → 1, the average value of remnant polarization decreases to approximately 0.64 C/m2 which means that small devices will have a reduced value of remnant polarization compared with infinitely wide films, but the remnant polarization does not decrease to zero. These modeling results are useful for optimizing the performance of PZT devices, but can also be applied to other ferroelectric materials, including lead-free formulations such as Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3. Date: Thursday, September 4, 2014 Time: 2:30 PM Place: ARMS 3115 Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100

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Reminder: Seminar Notice: M. Kammer PhD Final Exam 9-2-14
by Stacey, Lisa A 29 Aug '14

29 Aug '14

(Please note location in HAMP) MATERIALS SCIENCE AND ENGINEERING SEMINAR MSE PhD Final Examination Technology, Science and Environmental Impact of a Novel Cu-Ag Core-Shell Solderless Interconnect System by: Milea J. Kammer Advisor: Prof. C. Handwerker ABSTRACT Tin-based solder is ubiquitous in microelectronics manufacturing and plays a critical role in electronic packaging and attachment. While manufacturers of consumer electronics have made the transition to the use of lead-free solder, there are still a variety of reliability issues associated with these lead-free alternatives, particularly for high performance, high reliability applications. Because of these performance short-comings, researchers are still searching for a material, an alloy, or a unique alternative that can meet the thermal, mechanical, and electrical requirements for conventional reflow solder applications. In an effort to produce a more reliable alternative, Kim et al. proposed the low-temperature (200°C) sintering of copper-silver core-shell particles as a viable solderless interconnect technology. This technology is based on the silver atoms from the shell diffusing by surface diffusion to form sintered necks between copper particles, and therefore dewetting most of the copper surfaces. This study presents a 3-fold, in-depth evaluation of this Cu-Ag core-shell lead-free solderless interconnect technology focusing on solder paste development and prototyping, silver thin film stress relaxation and dewetting kinetics, and the environmental impacts associated with this new technology. First, an evaluation of the starting particle consistency and sintered compact mechanical properties determined that a specific core-shell particle geometry (1µm average core diameter and 10nm shell thickness) outperformed other combinations, exhibiting the highest modulus and yield strengths in sintered compacts, of 620 MPa and 40-60 MPa respectively. In particular, yield strengths for sintered compacts are similar to those reported for Sn-3.5Ag-0.75Cu (a commonly used lead-free solder) for the same strain rate. Following particle evaluations, the development of a functioning flux formulation was a key factor in the creation of a viable drop-in replacement. The processing of the final flux/particle paste combination was optimized at a commercial test facility for printing on test boards containing a wide variety of pad shapes, sizes, and pitches and thus, validated the ability of the Cu-Ag core-shell paste to be a drop-in replacement for traditional solder paste using conventional manufacturing techniques. The second study addresses the fundamental mechanisms behind interconnect formation. An assessment of the kinetics and microstructure evolution during silver thin film dewetting and defect formation provides essential materials science knowledge to understand and control the functionality of the Cu-Ag core-shell system. From an interrupted annealing study used to quantify dewetting kinetics, a range of surface diffusion coefficients were calculated from the experimental results, assuming that surface diffusion controlled dewetting. The two order of magnitude range in calculated diffusion coefficient demonstrates that the diffusion-limited kinetic models traditionally used to quantify hillock and hole growth kinetics during thin film relaxation and dewetting do not apply to the dewetting of Ag films. The presence of interface-limited kinetics was then validated through the non-uniform growth of individual hillocks over time. Lastly, an environmental assessment compares the impacts associated with the manufacturing and materials for the Cu-Ag core-shell particle system and SAC 305, the most commonly used lead-free solder alloy that contains 96.5% tin, 3% silver, and 0.5% copper. By comparing the impacts on global warming, acidification, eutrophication, ozone depletion, ecotoxicity, smog, carcinogenics, non-carcinogenics, and respiratory effects associated with each technology, the environmental advantages and disadvantages of each system are clearly communicated. By utilizing this information and the versatility of the core-shell system, possible methods for reducing impacts of the Cu-Ag core-shell system are addressed in order to reduce its environmental footprint. This multidimensional assessment provides a comprehensive validation in terms of technology, science, and environmental impacts of the Cu-Ag core-shell interconnect technology as a viable drop-in replacement for lead-based and lead-free solders for microelectronic manufacturing. Date: Tuesday, September 2, 2014 Time: 8:30 AM Place: HAMP 1113

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Fwd: PPDA fall call out, Sept. 4th, 4:30PM, BRNG 2291
by Donna Bystrom 29 Aug '14

29 Aug '14

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FW: CORRECTION: Seminar Notice: M. Kammer PhD Final Exam 9-2-14
by Stacey, Lisa A 26 Aug '14

26 Aug '14

Correction: Seminar time is 8:30 AM not PM Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100 (Please note location in HAMP) MATERIALS SCIENCE AND ENGINEERING SEMINAR MSE PhD Final Examination Technology, Science and Environmental Impact of a Novel Cu-Ag Core-Shell Solderless Interconnect System by: Milea J. Kammer Advisor: Prof. C. Handwerker ABSTRACT Tin-based solder is ubiquitous in microelectronics manufacturing and plays a critical role in electronic packaging and attachment. While manufacturers of consumer electronics have made the transition to the use of lead-free solder, there are still a variety of reliability issues associated with these lead-free alternatives, particularly for high performance, high reliability applications. Because of these performance short-comings, researchers are still searching for a material, an alloy, or a unique alternative that can meet the thermal, mechanical, and electrical requirements for conventional reflow solder applications. In an effort to produce a more reliable alternative, Kim et al. proposed the low-temperature (200°C) sintering of copper-silver core-shell particles as a viable solderless interconnect technology. This technology is based on the silver atoms from the shell diffusing by surface diffusion to form sintered necks between copper particles, and therefore dewetting most of the copper surfaces. This study presents a 3-fold, in-depth evaluation of this Cu-Ag core-shell lead-free solderless interconnect technology focusing on solder paste development and prototyping, silver thin film stress relaxation and dewetting kinetics, and the environmental impacts associated with this new technology. First, an evaluation of the starting particle consistency and sintered compact mechanical properties determined that a specific core-shell particle geometry (1µm average core diameter and 10nm shell thickness) outperformed other combinations, exhibiting the highest modulus and yield strengths in sintered compacts, of 620 MPa and 40-60 MPa respectively. In particular, yield strengths for sintered compacts are similar to those reported for Sn-3.5Ag-0.75Cu (a commonly used lead-free solder) for the same strain rate. Following particle evaluations, the development of a functioning flux formulation was a key factor in the creation of a viable drop-in replacement. The processing of the final flux/particle paste combination was optimized at a commercial test facility for printing on test boards containing a wide variety of pad shapes, sizes, and pitches and thus, validated the ability of the Cu-Ag core-shell paste to be a drop-in replacement for traditional solder paste using conventional manufacturing techniques. The second study addresses the fundamental mechanisms behind interconnect formation. An assessment of the kinetics and microstructure evolution during silver thin film dewetting and defect formation provides essential materials science knowledge to understand and control the functionality of the Cu-Ag core-shell system. From an interrupted annealing study used to quantify dewetting kinetics, a range of surface diffusion coefficients were calculated from the experimental results, assuming that surface diffusion controlled dewetting. The two order of magnitude range in calculated diffusion coefficient demonstrates that the diffusion-limited kinetic models traditionally used to quantify hillock and hole growth kinetics during thin film relaxation and dewetting do not apply to the dewetting of Ag films. The presence of interface-limited kinetics was then validated through the non-uniform growth of individual hillocks over time. Lastly, an environmental assessment compares the impacts associated with the manufacturing and materials for the Cu-Ag core-shell particle system and SAC 305, the most commonly used lead-free solder alloy that contains 96.5% tin, 3% silver, and 0.5% copper. By comparing the impacts on global warming, acidification, eutrophication, ozone depletion, ecotoxicity, smog, carcinogenics, non-carcinogenics, and respiratory effects associated with each technology, the environmental advantages and disadvantages of each system are clearly communicated. By utilizing this information and the versatility of the core-shell system, possible methods for reducing impacts of the Cu-Ag core-shell system are addressed in order to reduce its environmental footprint. This multidimensional assessment provides a comprehensive validation in terms of technology, science, and environmental impacts of the Cu-Ag core-shell interconnect technology as a viable drop-in replacement for lead-based and lead-free solders for microelectronic manufacturing. Date: Tuesday, September 2, 2014 Time: 8:30 AM Place: HAMP 1113

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Seminar Notice: M. Kammer PhD Final Exam 9-2-14
by Stacey, Lisa A 26 Aug '14

26 Aug '14

(Please note location in HAMP) MATERIALS SCIENCE AND ENGINEERING SEMINAR MSE PhD Final Examination Technology, Science and Environmental Impact of a Novel Cu-Ag Core-Shell Solderless Interconnect System by: Milea J. Kammer Advisor: Prof. C. Handwerker ABSTRACT Tin-based solder is ubiquitous in microelectronics manufacturing and plays a critical role in electronic packaging and attachment. While manufacturers of consumer electronics have made the transition to the use of lead-free solder, there are still a variety of reliability issues associated with these lead-free alternatives, particularly for high performance, high reliability applications. Because of these performance short-comings, researchers are still searching for a material, an alloy, or a unique alternative that can meet the thermal, mechanical, and electrical requirements for conventional reflow solder applications. In an effort to produce a more reliable alternative, Kim et al. proposed the low-temperature (200°C) sintering of copper-silver core-shell particles as a viable solderless interconnect technology. This technology is based on the silver atoms from the shell diffusing by surface diffusion to form sintered necks between copper particles, and therefore dewetting most of the copper surfaces. This study presents a 3-fold, in-depth evaluation of this Cu-Ag core-shell lead-free solderless interconnect technology focusing on solder paste development and prototyping, silver thin film stress relaxation and dewetting kinetics, and the environmental impacts associated with this new technology. First, an evaluation of the starting particle consistency and sintered compact mechanical properties determined that a specific core-shell particle geometry (1µm average core diameter and 10nm shell thickness) outperformed other combinations, exhibiting the highest modulus and yield strengths in sintered compacts, of 620 MPa and 40-60 MPa respectively. In particular, yield strengths for sintered compacts are similar to those reported for Sn-3.5Ag-0.75Cu (a commonly used lead-free solder) for the same strain rate. Following particle evaluations, the development of a functioning flux formulation was a key factor in the creation of a viable drop-in replacement. The processing of the final flux/particle paste combination was optimized at a commercial test facility for printing on test boards containing a wide variety of pad shapes, sizes, and pitches and thus, validated the ability of the Cu-Ag core-shell paste to be a drop-in replacement for traditional solder paste using conventional manufacturing techniques. The second study addresses the fundamental mechanisms behind interconnect formation. An assessment of the kinetics and microstructure evolution during silver thin film dewetting and defect formation provides essential materials science knowledge to understand and control the functionality of the Cu-Ag core-shell system. From an interrupted annealing study used to quantify dewetting kinetics, a range of surface diffusion coefficients were calculated from the experimental results, assuming that surface diffusion controlled dewetting. The two order of magnitude range in calculated diffusion coefficient demonstrates that the diffusion-limited kinetic models traditionally used to quantify hillock and hole growth kinetics during thin film relaxation and dewetting do not apply to the dewetting of Ag films. The presence of interface-limited kinetics was then validated through the non-uniform growth of individual hillocks over time. Lastly, an environmental assessment compares the impacts associated with the manufacturing and materials for the Cu-Ag core-shell particle system and SAC 305, the most commonly used lead-free solder alloy that contains 96.5% tin, 3% silver, and 0.5% copper. By comparing the impacts on global warming, acidification, eutrophication, ozone depletion, ecotoxicity, smog, carcinogenics, non-carcinogenics, and respiratory effects associated with each technology, the environmental advantages and disadvantages of each system are clearly communicated. By utilizing this information and the versatility of the core-shell system, possible methods for reducing impacts of the Cu-Ag core-shell system are addressed in order to reduce its environmental footprint. This multidimensional assessment provides a comprehensive validation in terms of technology, science, and environmental impacts of the Cu-Ag core-shell interconnect technology as a viable drop-in replacement for lead-based and lead-free solders for microelectronic manufacturing. Date: Tuesday, September 2, 2014 Time: 8:30 PM Place: HAMP 1113 PURDUE MSE [cid:image003.png@01CFC13E.440C8CC0] Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100

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Fwd: Sept. 19th Mixer Survey Link
by Donna Bystrom 22 Aug '14

22 Aug '14

You are cordially invited to attend the * MSE Alumni, Faculty, Staff and* *Current Students Mixer* Friday, September 19, 2014 5:30 – 7:00 pm Outside Neil Armstrong Hall of Engineering (Corner of Stadium and University Streets) Please _RSVP by September 5th_ through the survey link below https://purdue.qualtrics.com/SE/?SID=SV_55r7JDPSdg2lU2x <https://purdue.qualtrics.com/SE/?SID=SV_55r7JDPSdg2lU2x>

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Fwd: Hydrofluoric acid in MSE
by Donna Bystrom 21 Aug '14

21 Aug '14

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REMINDER: MSE Seminar Notice: S. Xia PhD Prelim Pt I
by Stacey, Lisa A 21 Aug '14

21 Aug '14

MATERIALS SCIENCE AND ENGINEERING SEMINAR MSE PhD Examination Part I A Model to Evaluate the Creep Rate Caused by Dislocation Bias Absorption in Dilute FCC Solution Under Irradiation Condition by: Shengxu Xia Co-Advisors: Prof. A. El-Azab and Prof. R. Trice ABSTRACT SIPA is an important mechanism responsible for irradiation damage that occurs in nuclear materials. SIPA comes from the bias absorption of interstitials towards dislocation sink. In order to minimize its effect, dilute solute is added to the solvent, hoping that the preferred interstitials would be trapped during the travel to dislocation sinks. However, recent study reveals the existence of dilute solute might facilitate SIPA effect rather than suppress. So it is necessary to build a theoretical model to consider both sides of solute atoms. This paper proposes such a model based on reaction-diffusion equation and effective capture radius of pure edge dislocation. Date: Thursday, August 21, 2014 Time: 1:30 PM Place: ARMS 1028 Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100

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HVAC Maintenance 8/14–8/15
by Stacey, Lisa A 12 Aug '14

12 Aug '14

All, Physical Facilities will be performing routine maintenance on our HVAC system Thursday, August 14th and Friday, August 15th. Please be aware that you may notice fluctuations in air flow, pressure and temperature during this time. Thanks, Phil Qualio<https://engineering.purdue.edu/Engr/People/ptProfile?resource_id=59120> Building Deputy Neil Armstrong Hall of Engineering Potter Engineering Center 765.496.9757 — 765.494.7020

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