Phase Stability, Phase Transformations, and Reactive Phase Formation in Electronic Materials XXI: Machine Learning and Phase Stability/Advanced Electronic Interconnections
Sponsored by: TMS Functional Materials Division, TMS: Alloy Phases Committee
Program Organizers: Hiroshi Nishikawa, Osaka University; Shih-kang Lin, National Cheng Kung University; Chao-hong Wang, National Chung Chung University; Chih Ming Chen, National Chung Hsing University; Jaeho Lee, Hongik University; Zhi-Quan Liu, Shenzhen Institutes of Advanced Technology; A.S.Md Abdul Haseeb, Bangladesh University of Engineering and Technology (BUET); Vesa Vuorinen, Aalto University; Ligang Zhang, Central South University; Sehoon Yoo, KITECH; Yu-chen Liu, National Cheng Kung University; Ting-Li Yang, National Yang Ming Chiao Tung University

Monday 2:00 PM
February 28, 2022
Room: 303A
Location: Anaheim Convention Center

Session Chair: Shih-kang Lin, National Cheng Kung University; Yu-chen Liu, National Cheng Kung University

2:00 PM  Invited
The Challenge of Machine Learning the Stability of Materials: Christopher Bartel1; 1University of California, Berkeley
    The realization of high-throughput materials discovery depends critically on the ability to predict whether a given material will be synthesizable. This problem is generally addressed in silico by calculating the thermodynamic stability of candidate materials using density functional theory (DFT). There have been many recent claims that this step can be greatly accelerated using machine learning instead of DFT to predict the formation energy of inorganic solids. However, thermodynamic stability is ultimately dictated by relative formation energies between chemically similar competing phases, and not by the absolute formation energy of any single compound. It is therefore essential to assess how well these machine learning predictions of intrinsic thermodynamic quantities generalize to the problem of relative materials stability. In this work, we systematically probe this question by testing a diverse set of materials representations and learning algorithms on a variety of problems that simulate real applications of materials discovery.

2:30 PM  
Role of Composition in the Phase Transition of Ge-Sb-Te Alloys: Robert Appleton1; Alejandro Strachan1; Zachary McClure1; 1Purdue University
    Ge-Sb-Te (GST) alloys are the predominate phase-change materials for use in data storage. GST has provided large success due to its fast phase transition and phase stability, however the mechanisms and physics that underly its interesting properties remains an open area of research. We investigated the relative stabilities of the crystalline and amorphous phases of GST using ab initio molecular dynamics simulations. From our simulations, we can analyze the free energy of the crystalline and amorphous structures at various temperatures along the phase transition. We compare results for the stable hexagonal and metastable rocksalt crystals of the Ge2Sb2Te5 alloy. To analyze the role of composition, we study the effects of Ge-poor stoichiometries (Ge2-xSb2Te5) of each crystal, as well as the effects of different concentrations (1, 5, and 10%) of carbon doping. We report structural analysis and predict Raman spectra directly from our simulations to compare our generated structures to experiment.

2:50 PM  
NOW ON-DEMAND ONLY - The Influence of Morphology in Ultrathin Ag Structure on ZnO/Ag/ZnO Transmittance Grown by Sputtering Compared with Simulation: Bao-Jhen Li1; 1National Central University
     The transmittance of the ZAZ structures is mainly affected by the Ag nanostructure. With the admittance method, the transmittance of the ZAZ structures with nanofilm Ag can be simulated accurately, and the main purpose of the simulation is to find the best thickness of each layer for the highest average transmittance in the visible light region without a trial and error experiment. Nevertheless, the lack of the influence of the actual situation on the simulation will make the admittance method inaccurate. The morphology variety of the nanoscale Ag effect intensively to the optical properties. The light scattering from Ag clusters would decrease the transmittance. Owing to the participation of the actual situation, the influence of the ultrathin Ag on the transmittance of the ZAZ structures will have further understood.

3:10 PM  
Ab Initio Interfacial Stability and Cu-segregation Effect upon η’ and η2 Precipitates in Al-Zn-Mg-Cu Alloys : Yu-ning Chiu1; Chung-yi Yu2; Shih-kang Lin1; 1National Cheng Kung University; 2China Steel Corp
    The benefit of Cu on the η-family strengthening precipitates in Al-Zn-Mg-Cu alloy has been well studied over the past decades. However, the role of Cu in the structure evolution during the transition from metastable η’ to stable η2 has yet to be understood clearly. As a result, the structures and energetics of η’ and η2 interface supercells in Al-Zn-Mg-Cu alloy were thoroughly investigated through ab initio calculations. The most feasible interface supercells with solute segregated in η’ and η2 were constructed, and with which, a comprehensive discussion on interfacial energy and strain energy as well as the atomic local strain hydrostatic invariant (ALSHI) were provided to plot the energy landscape for the transition with and without the consideration of Cu-segregation effect. Finally, an unreported mechanism of Cu-segregation was revealed, and based on which, a new strategy for the future optimal design of Al-Zn-Mg-Cu alloys was proposed.

3:30 PM Break

3:50 PM  
Study of Ferroelectricity and Phase Transitions in Hafnia: Sesha Behara1; Anton Van der Ven1; 1University of California Santa Barbara
    Ferroelectric materials are of considerable interest for memory and logic device applications such as ferroelectric random-access memory (FRAM), ferroelectric field-effect transistors (FeFET) and negative-capacitance field-effect transistors (NC-FET). While much effort has been devoted to ferroelectric perovskites, it is increasingly recognized that a ferroelectric orthorhombic form of HfO2 is in many ways superior. HfO2 can adopt a multitude of polymorphs depending on temperature, dopant/alloy composition, strain state, electric field and film thickness. In this work, we study the structural phase transformations between orthorhombic HfO2 and its other polymorphs from first principles. By combining density functional theory with the group theory of symmetry, we develop a generalized free energy description that is a function of shuffle order parameters, strain and dopant composition and connects all known polymorphs of HfO2. The free energy surface provides crucial insights about the coercive field, nucleation barriers for switching, coherent phase equilibrium and twin boundary migration.

4:10 PM  
Interfacial Reactions between Sn-0.7 Cu Alloys C194, Alloy25, and C1990 Substrates: Yong-Chi Chang1; Tzu-Yang Tsai1; Tai-Hsuan Chung1; Yee-Wen Yen1; 1NTUST
    The liquid/solid interfacial reactions in the Sn-0.7 wt.% Cu (SC)/C194 (Cu-2.2 wt.%Fe), SC/Alloy 25 (Cu-2 wt.%Be), and SC/C1990 (Cu-3.3wt.%Ti) couples at 240, 255 and 270°C for 0.5 to 10 h were investigated in this study. The (Cu, Fe)6Sn5 with micro-island shape and a thin layer of (Cu, Fe)3Sn phase were formed in the SC/C194 couple. In SC/Alloy 25 couples, the (Cu, Be)6Sn5 and (Cu, Be)3Sn phases were formed at the interface. As the reaction time was increased, the (Cu, Be)6Sn5 phase was repined to form the large grain and mass spalling of the (Cu, Be)6Sn5 phase was observed. Only the (Cu, Ti)6Sn5 phase was observed at the SC/C1990 interface. Total spread distance of the intermetallic compounds in three couples were increased as the increase of the reaction temperature and times.

4:30 PM  
Mechanical Performance of Advanced Multicomponent Solder Alloy under Thermal Aging: Ding Zhou1; A.S.M.A. Haseeb1; Andri Andriyana1; 1University of Malaya
    Reliability of lead free solders, used in harsh conditions such as in automotive, is still a serious concern. Simultaneous additions of multiple alloying elements like Bi, Sb, Ni etc. to conventional Sn-Ag-Cu (SAC) based solders have recently been investigated as a way to improve their reliability. The additional elements can bring about the improvements through solid solution and precipitation strengthening. In this study, the effects of simultaneous additions of Bi, Sb and Ni to SAC 305 solder on the evolution of microstructure and mechanical properties during thermal aging at 125 C for up to 1008 hours are investigated. Superior microstructural stability and improved mechanical strength of the multicomponent alloy at long aging time and its fracture behaviour are discussed.

4:50 PM  
Investigation of Thermal Properties and Thermal Reliability of Ga-based Low Melting Temperature Alloys as Thermal Interface Materials (TIMs): Yifan Wu1; Rajath Kantharaj1; Albraa Alsaati1; Amy Marconnet1; Carol Handwerker1; 1Purdue University
    Gallium-based low melting temperature alloys have been proposed as candidates for next generation thermal interface materials (TIMs) due to their high thermal conductivity (~30 W/m*K) and liquidity. However, poor wettability as well as embrittling and corroding effect of Ga on metals have limited their use by the electronics industry. Studies on the relationship between the evolution of thermal properties and interfacial reactions between Ga-based TIMs and metal substrates are thus vital for creating a path forward. We measured thermal conductivity and thermal interface resistance of eutectic Ga-In alloy (EGaIn) sandwiched between two Ni-plated Cu substrates following simulated assembly and accelerated aging. The rapid interfacial reaction between EGaIn and both Ni and Cu at elevated temperatures led to an increase in the thermal conductivity. Further study showed the change in thermal properties was due to the depletion of Ga in the system through intermetallic formation, creating a higher conductivity In-rich alloy.