MSE Colloquium Series

Paul Besser, Ph.D., Fellow
GLOBALFOUNDARIES, Inc.

Materials innovations and mechanical stress in integrated circuits

Abstract: The highest performing microprocessors, memory devices and other computer chips require the most advanced technologies. Improving performance is much more than just shrinking the dimensions: it requires novel materials innovations. In this presentation, the novel materials being researched to enhance performance, improve reliability and enable technology scaling for the Integrated Circuit (IC) Industry will be highlighted. The challenges with implementing materials innovations are tremendous, and advanced planning and coordination are required between the research, development, manufacturing and design community to guarantee that these innovations can be inserted into the process technology, product designs and manufacturing process seamlessly, reliably, with high yield and low cost.

The effect of novel materials innovations on mechanical stress in Copper interconnects is critical to the IC industry. Copper interconnects in a dual inlaid architecture and with low-K dielectrics are commonly employed in high performance technologies. Inlaid Cu lines offer higher conductivity, improved electromigration performance and a reduced cost of manufacturing over their Al predecessors; however, the damascene fabrication method and the introduction of low-K dielectrics and capping layers to improve performance present integration and reliability challenges to Cu interconnects and fundamentally change the mechanical stress state of the Cu lines used as interconnects. Thermal expansion mismatch between Cu and surrounding materials can induce significant tensile stresses in the metallization, affecting the reliability of Cu interconnect. Novel materials innovations and thermal excursions will be shown to affect the mechanical stress state of Cu lines, as quantified using synchrotron-based Grazing Incidence X-Ray Scattering.

Bio: Dr. Paul Besser graduated with honors from North Carolina State University (1988) and earned his M.S. (1990) and Ph. D. (1993) from Stanford University in Materials Science and Engineering.  He is currently a Fellow in the Technology Development Group at GLOBALFOUNDRIES, Inc. He was previously a Fellow in the Technology Research Group at Advanced Micro Devices before being Senior Director of Technology Development at Unity Semiconductor and Invisage Technologies. He has co-authored 93 research publications and hold >200 U.S. patents. He co-organized four Materials Research Society (MRS) symposiums and has given tutorials at the MRS and IEEE IRPS conferences. He was a meeting chair for the 2009 Spring Materials Research Society (MRS) meeting and 2011 Advanced Metallization Conference (AMC). He currently serves on the Advisory Boards for Materials Science and Engineering Departments at Stanford University and NCSU.

Prof. Mark Thompson
Department of Chemistry and Materials Science & Engineering
University of Southern California

Exciton Management in Organic Solar Cells

Abstract: The exciton is a critical part of each of the processes leading to photocurrents in Organic PhotoVoltaics (OPVs), and being able to control the location, lifetime and energy of the exciton is essential to achieving high efficiency. We have investigated methods for tuning exciton energies and controlling their migration paths, both intramolecularly and within a thin film.  I will discuss our most recent work with both organic dyes, such as squaraines and dipyrrins as well as porphyrinic materials for OPVs. This involves a careful materials design study that leads to both low energy absorption (into the nearIR) and the efficient use of multiple absorbers to efficiently harvest photons through the entire visible spectrum. To that end we have used transient absorption spectroscopy and measured the rates of singlet and triplet energy transfers between organic dyes (BODIPY and tetracenes). Both intra- and inter-molecular energy transfers take place on the picoseconds time scale. Thus, the systems are fully equilibrated into the lowest energy triplet state(s) before nonradiative decay. Using this approach we can efficiently harvest energy across the visible and into the NIR. In particular, we have used careful control of exciton and carrier energies to design and implement sensitizers that give fullerene films efficient light collection throughout most of the visible spectrum. Time permitting, I will also discuss our latest results with new singlet fission materials for efficient light harvesting in OPVs. Our control of singlet and triplet excitons has been important in exploring the use of singlet fission to enhance the efficiencies of OPVs.

Bio: Dr. Mark E. Thompson is Professor of Chemistry and Materials Science at the University of Southern California. He received his B.S. degree in Chemistry in 1980 (U.C. Berkeley) and his Ph.D. in chemistry in 1985 (California Institute of Technology). He spent 2 years as a postdoctoral fellow in the Inorganic Chemistry laboratory at Oxford University. Prof. Thompson took a position in the chemistry department at Princeton University in 1987, as an assistant professor. In 1995 he moved his research team to the University of Southern California, where he is currently a Professor of Chemistry. He has won a number of awards, including the MRS Medal in 2006, given by the Materials Research Society, and the Jan Rachman Prize for Outstanding Achievement in Flat Panel Displays, also in 2006, given by the Society for Information Display. In 2011 he was named the 12 of the top 100 most influential chemists in the world by Thomson-Rueters. In 2012 he was received the Alexander von Humboldt Research Award.  He currently has over 250 papers in print and over 125 US patents. His research interests involve the optical and optoelectronic properties of molecular materials and devices, particularly organic LEDs and solar cells, as well as nanoscale materials, catalysis and biosensors.

Prof. Samuel Graham
Department of Mechanical Engineering & Materials Science & Engineering
Georgia Institute of Technology

Packaging and Reliability Concerns in Organic Photovoltaic Devices

Abstract: The development of organic electronics provides exciting opportunities to enable a wide range of flexible electronics devices. However, it is well known that many of these devices are susceptible to exposure to water vapor and oxygen and must be protected from environmental degradation. This is especially true in the case of organic photovoltaic devices that will be subjected to photo-oxidative effects at elevated temperatures and are expected to possess long lifetimes. To improve the lifetime of such devices, researchers are currently developing more stable bulk heterojunction active layers, employing inverted OPV architectures, and utilizing semi-hermetic packaging through the use of barrier films. While much work has been done to develop these approaches for OPV devices, additional complications arise for flexible OPV devices that need to be addressed in the development of this technology.

In this talk, we will discuss the development and performance of ultrabarrier films using atomic layer deposition and PECVD. Methods for characterizing the water vapor transmission rates in the ultrabarriers and their integration with OPVs will be discussed. For flexible applications, the mechanical integrity of the barrier layers and electron selective contacts for inverted OPVs will be presented through measurements of their failure under monotonic and fatigue failure. In addition, adhesive and cohesive failure of different OPV architectures will be presented.  Finally, the prospects for improving both environmental and mechanical reliability of these devices will be discussed.

Bio:  Samuel Graham is an Associate Professor and the Joseph H. Anderer Faculty Fellow in the Woodruff School of Mechanical Engineering at the Georgia Institute of Technology. His group focuses on the processing, thermal analysis, and reliability of electronic devices including GaN HFETs, LEDs, graphene, and flexible electronics. He is an Associate Director of the NSF STC MDITR and is a member of the Center for Organic Photonics and Electronics at Georgia Tech. In this effort, he leads a technical thrust on the development of organic photovoltaics including processing and packaging of devices. He also holds a courtesy appointment in the School of Materials Science and Engineering at the Georgia Institute of Technology and a joint appointment with Oak Ridge National Laboratories.

Prof. Teri Odom
Department of Chemistry and Materials Science & Engineering
Northwestern University

Nanolasers with Unconventional Cavity Architectures

Abstract: Reducing the size of photonic and electronic elements is critical for ultra-fast data processing and ultra-dense information storage. The miniaturization of a key, workhorse optical instrument—the laser—is no exception. Coherent light sources at the nanoscale are important not only for exploring phenomena in small dimensions but also for realizing optical devices with sizes that can beat the diffraction limit of light. This talk will discuss how to manufacture nanolaser devices based on metal nanoparticles that can operate at room temperature. First, we will describe a new laser cavity structure made from dimers of particles with a 3D “bowtie” shape. These nanostructures support localized surface plasmons, collective excitations of electrons that have no fundamental size limitation when it comes to confining light. Directional emission could be obtained at surface plasmon grating orders associated with the lattice periodicity of the 3D bowties. Next, we will discuss how arrays of strongly coupled metal nanocavities can be used in a new type of surface-emitting laser. Lasing action could be realized by the optical amplification of band-edge lattice plasmons with a near-zero group velocity in plasmonic nanoparticle arrays surrounded by gain media. Finally, we will conclude with a self-consistent computational scheme that can investigate the microscopic properties of plasmon lasing action.

Odom has received numerous honors and awards, including a Radcliffe Institute for Advanced Study Fellowship at Harvard University; the ACS Akron Section Award; an NIH Director's Pioneer Award from the National Institutes of Health; the Materials Research Society Outstanding Young Investigator Award; the National Fresenius Award from Phi Lambda Upsilon and the ACS; the Rohm and Haas New Faculty Award; an Alfred P. Sloan Research Fellowship; a DuPont Young Investigator Grant; a National Science Foundation CAREER Award; a Dow Teacher-Scholar Award; the ExxonMobil Solid State Chemistry Faculty Fellowship; and a David and Lucile Packard Fellowship in Science and Engineering. Odom was also the first Chair of the Noble Metal Nanoparticles Gordon Research Conference, whose inaugural meeting was in 2010. In addition, Odom is an Associate Editor for Chemical Science (RSC) and is on the Editorial Advisory Boards of ACS Nano, Chemical Physics Letters, and Nano Letters.

Christian M. Schlepuetz, Ph.D., Physicist
Argonne National Laboratory

Strain And Symmetry-dependent Structural Phase Transitions in Ultra-thin BiFeO3 Films

Abstract: As one of very few room temperature multiferroic materials, bismuth ferrite (BiFeO3: BFO) has been studied extensively in recent years. The bulk form of BFO is known to have a rhombohedrally distorted quasi-cubic perovskite structure with an (a−,a−,a−) octahedral tilt pattern, exhibiting both anti-ferrodistortive displacements and a spontaneous polarization along the<111> axes. Investigating epitaxial thin films under compressive strain, several studies have reported that the polarization direction is tilted towards the [001] out-of-plane direction, while maintaining a significant in-plane component, depending on the amount of epitaxial strain from the substrate. This effect is accompanied by a significant enhancement of the spontaneous polarization and a series of phase transitions from rhombohedral (R) for small strains to R-like monoclinic (MA) to T-like monoclinic (MC) and to tetragonal (T) for larger strains, the latter two of which exhibit a giant c/a lattice constant ratio.

Through synchrotron-based reciprocal space mapping (RSM), facilitated by using X-ray area detectors (Pilatus 100K pixel detector), we have investigated the structure of ultra-thin BFO films with thicknesses of only several unit cells on various substrates. In this thickness regime, the influence of the substrate atomic structure on the properties of the ultra-thin films is very pronounced, and the films exhibit perfect heteroepitaxy up to a critical thickness when the build up of strain energy forces the films into a relaxed structure. This change in the atomic film structure and symmetry has profound effects on the physical properties of the films, such as the polarization strength and direction, transition temperatures, etc. A detailed understanding of these structural changes is therefore paramount to tailor the fabrication process necessary for the design of novel electronic devices.

In this talk, we will present the results obtained from ultra-thin BFO films grown by MBE on SrTiO3 (STO), LaAlO3 (LAO), and TbScO3 (TSO) substrates. Both on STO and LAO, the BFO assumes a tetragonal structure, but with very different c/a axis ratios. On TSO, on the other hand, a very pronounced and well-ordered stripe domain structure evolves where the domain sizes are strongly thickness dependent. Details of the technique will also be described to highlight its broad applicability to study various material systems.

Argonne National Laboratory's work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract DE-AC02-06CH11357.

Bio: Christian Schlepuetz is a beamline scientist in the Surface Scattering and Micro-diffraction Group at Sector 33 of the Advanced Photon Source (APS), Argonne National Laboratory. His current research interests include surface and interface structure determinations on complex metal oxide thin films using Surface X-ray diffraction and X-ray reflectivity. Furthermore, he is responsible for user support and instrumentation development at both the undulator and bending magnet beamlines of Sector 33.

Christian received his Ph.D. in 2009 from the University of Zurich, Switzerland, for his studies on the structural determination of thin YBa2Cu3O7 films performed in the Material Science group lead by Philip Willmott at the Swiss Light Source (SLS). He then moved to the United States for a postdoctoral appointment in the group of Prof. Roy Clarke at the University of Michigan, Ann Arbor. In 2011, he joined the X-ray Science Division at Argonne National Laboratory, starting his current position.

Prof. Yuri Suzuki
Department of Applied Physics
Stanford University

Emergent Magnetic Phenomena at Complex Oxide Interfaces

Abtract: Interfaces of complex oxides materials provide a rich playground for the exploration of novel properties not found in the bulk constituents but also for the development of functional interfaces to be incorporated into applications. With recent advances in thin film deposition techniques, emergent phenomena at perovskite oxide interfaces have been studied intensively in order to understand how mismatches in bands, valences, and interaction lengths give rise to novel interfacial ground states. Surprisingly, there have been only a handful of successful efforts demonstrating new magnetic ground states at interfaces. In this talk, I will describe one recent example of our work demonstrating the generation of long-range ferromagnetic order at CaMnO3 interfaces. We demonstrate ferromagnetism in superlattices composed of the antiferromagnetic insulator CaMnO3 and an itinerant metal. We have performed experiments on CaMnO3/CaRuO3 and CaMnO3/LaNiO3 superlattices and have found that the ferromagnetism is confined to one unit cell as theoretically predicted. Moreover LaNiO3 exhibits a thickness dependent metal-insulator transition and we find the emergence of ferromagnetism to be coincident with the conducting state of LaNiO3 in CaMnO3/LaNiO3 superlattices. That is, only superlattices in which the LaNiO3 layers are metallic exhibit ferromagnetism. Together these results suggest that ferromagnetism can be attributed to a double exchange interaction among Mn ions mediated by the adjacent itinerant metal.

Bio: Yuri is currently a professor in the Department of Applied Physics at Stanford University. She received an A.B. from Harvard University and a Ph.D. in Applied Physics from Stanford University. After a postdoc at AT&T Bell Labs, she was an assistant and associate professor in the Department of Materials Science and Engineering at Cornell University. She then moved to the Department of Materials Science and Engineering at UC Berkeley as an associate professor and was later promoted to professor. Most recently, she moved to Stanford University. Her research is focused on the study of novel ground states and functional properties in condensed matter systems synthesized via atomically precise thin film deposition techniques. Her recent emphasis has been on highly correlated electronic systems, especially new spintronic materials that address fundamental questions that still exist in magnetism. She has been recognized with an NSF Career Award, ONR Young Investigator Award, David and Lucile Packard Foundation Fellowship, Robert Lansing Hardy Award of TMS, Maria Goeppert-Mayer Award of APS, American Competitiveness and Innovation Fellowship of NSF and as an APS Fellow.

Prof. Junqiao Wu
Department of Materials Science & Engineering
University of California, Berkeley

0D imperfections in 2D and 3D electronic materials

Abstract: Most functionalities of electronic materials are enabled by introduction of selected imperfections such as dopants and native defects. The understanding and database of the behavior of imperfections are relatively established for electronic properties of bulk semiconductors, but much less for non-electronic properties and in semiconductors with low dimensionalities. We seek to develop a full picture of the physics of imperfections generally applicable to, for example, 2D semiconductors, as well as acoustic, optical and thermoelectric properties.

In this presentation I will highlight some of our most recent work in this area. In the first part I will discuss a general defects model that describes the electronic effects of native defects in semiconductors, followed by extension of the model to thermal and thermoelectric properties. In this context I will show the possibility of enhancing thermoelectric performance by intentionally introducing point defects. The second part will focus on effects of imperfections in the recently discovered 2D (monolayer) semiconductors, specifically, atomic vacancies and their interactions with gas molecules. It will be shown that again imperfections can be engineered to drastically improve certain materials performance.

Bio: Professor Junqiao Wu received a B.S. from Fudan University and a M.S. from Peking University, China, both in physics. He obtained a Ph.D. degree from the University of California, Berkeley for work on nitride semiconductors and highly mismatched semiconductor alloys. He did postdoctoral research in the Department of Chemistry and Chemical Biology at Harvard University on phase transitions in transition metal oxide nanomaterials. He began his faculty appointment in the Department of Materials Science and Engineering at the University of California, Berkeley in July, 2006, and was promoted to Associate Professor in 2012. His honors include the Berkeley Fellowship, the 29th Ross N. Tucker Memorial Award, the U.C. Regents' Junior Faculty Fellowship, the Berkeley Presidential Chair Fellowship, the NSF Career Award, and the DOE Early Career Award. The Wu group explores novel properties and applications of strongly correlated electron materials with reduced dimensions, phase transitions at the nanoscale, and optoelectronic, thermal and thermoelectric properties of semiconductor alloys and interfaces. For more information visit http://www.mse.berkeley.edu/~jwu/

Prof. Deji Akinwande
Department of Electrical and Computer Engineering University of Texas, Austin

Adventures in the Flatland: From Materials to Ubiquitous Smart Systems

Abstract: Over the past decade, two-dimensional space aka the flatland has been an intriguing realm to explore nanomaterials (graphene, MX2, hBN, etc) and access unique and rich phenomena over a vast landscape from theoretical physics to demonstrated electronic systems. In this talk, we discuss progress in the flatland focusing on basic research on material synthesis and properties, and applied research employing 2D nanomaterials for energy-efficient and high-performance electronic systems. Basic science research including temperature-dependent pressure studies has indicated semiconducting-metallic transition in MoS2, while sonochemistry of hBN shows tunable inversion of the electrical and optical properties. Several material innovations including embedded precursors, catalyst crystallization and record grain growth have enabled wafer-scale graphene synthesis that has now been deployed in commercial 300mm wafer systems, and direct delamination are scaling up for environmentally-sustainable roll-to-roll processes. Likewise innovations in interface interactions and polarization, heat management, perforated metal-2D contacts have led to state-of-the-art flexible 2D nanoelectronics featuring extremely robust properties, anti-bacterial protection, and record 25GHz cut-off frequencies on plastics. We conclude this talk by presenting our vision of a new paradigm of the flatland beyond the beautiful offerings of nature.

Bio: Dr. Deji Akinwande received the Ph.D. degree in Electrical Engineering from Stanford University, Stanford, CA in 2009, where he conducted research on the synthesis, device physics, and circuit applications of carbon nanotubes and graphene. His Master’s research in Applied Physics at Case Western Reserve University pioneered the design and development of non-contact near-field microwave probe tips for nondestructive imaging and studies of materials.

He is currently an Assistant Professor with the University of Texas, Austin. The current focus of his research explores electronic systems from new 2D nanomaterials, flexible nanoelectronics and bio-electronics. He is a co-inventor of a high-frequency chip-to-chip interconnect and an electrically small antenna for bio-electronics. Prof. Akinwande has been honored with the IEEE Nano Geim and Novoselov Graphene Prize, the NSF CAREER award, the Army and DTRA Young Investigator awards, an ONR award, the 3M Nontenured Faculty Award, and was a past recipient of the “2005 Stanford Cheesy Award” for outstanding LNA design in addition to the Ford Foundation, Alfred P. Sloan Foundation, and Stanford DARE Fellowships. He is a thrust director of the NASCENT ERC center at UT-Austin. He recently co-authored a textbook on carbon nanotubes and graphene device physics by Cambridge University Press. His work on flexible graphene systems was selected as among the “best of 2012” by the nanotechweb online technology news site.