Materials Horizons Emerging Investigator Series: Professor Yiyang Li, University of Michigan, USA

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Abstract

Our Emerging Investigator Series features exceptional work by early-career researchers working in the field of materials science.

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Yiyang Li is an assistant professor in the Department of Materials Science and Engineering at the University of Michigan (USA). He received his BS in Electrical Engineering from the Olin College of Engineering and PhD in Materials Science and Engineering from Stanford University (USA). After his PhD, he was a Harry Truman Fellow at Sandia National Laboratories. His research primarily studies ion transport in ceramic materials, with applications in microelectronics and energy storage. His awards include the Intel Rising Star Faculty Award and the International Solid State Ionics Young Scientist Award.

Read Professor Yiyang Li's Emerging Investigator Series article ‘Oxygen tracer diffusion in amorphous hafnia films for resistive memory’ ( https://doi.org/10.1039/d3mh02113k ) and read more about him in the interview below:

Materials Horizons (MH): Your recent Materials Horizons Communication investigates oxygen isotope tracer diffusion measurements in amorphous hafnia (a-HfO ₂ ) thin films. How has your research evolved from your first article to this most recent article and where do you see your research going in future?

Yiyang Li (YL): I did my PhD research (2011–2017) on the electrochemistry of Li-ion battery materials,^1,2 but I wanted to expand my knowledge to the field of electronic materials and microelectronic devices. During my postdoc (2017-20) and early stages of my faculty career, I worked on lithium-based electrochemical memory³ and then on oxygen-based electrochemical memory.^4,5 However, this paper on oxygen tracer diffusion in hafnium oxide is my first paper that does not discuss lithium, batteries, or electrochemistry. Although it is applied to microelectronics, it follows my broad interest in understanding ion transport in metal oxides. It could not have been done without my students, especially the lead author Dongjae Shin, and my collaborators at Oak Ridge and the University at Albany.

Going forward, I look forward to working at the intersection of energy storage and microelectronics. Last year, we published a paper in the RSC's Energy and Environmental Science, where we used microfabrication to charge and discharge individual battery particles.⁶ Our process is not too different from creating a device using a nanowire or an exfoliated flake of a 2D material, but has almost never been done in the field of energy storage. It is worth remembering that Profs John Goodenough,⁷ Stanley Whittingham,⁸ and Akira Yoshino⁹ all researched electronic materials before they worked on the Li-ion battery that won them the Nobel Prize in 2019. I believe there remain significant unexplored opportunities in the overlap of energy storage & electrochemistry with electronic materials & microelectronic devices.

MH: What aspect of your work are you most excited about at the moment?

YL: I am most excited about our research on ionic transport in amorphous transition-metal oxides. Previously, most research on ion transport has focused on crystalline materials, with applications spanning batteries, solid oxide fuel cells, and others. However, many microelectronics applications utilize amorphous metal-oxide thin films like hafnium oxide, tungsten oxide, and tantalum oxide due to the lower-temperature processing and lack of grain boundaries; examples of amorphous devices include resistive memory, high-k dielectrics, and thin-film transistors. I am most excited about understanding ion transport properties in these amorphous metal oxides. This would require translating knowledge from the glass community; however, we expect new knowledge because amorphous thin films for electronic applications are processed very differently from bulk glasses for structural applications.

MH: In your opinion, what are the most important questions to be asked/answered in this field of research?

YL: The most important question is to understand the physical descriptors that explain ion transport in amorphous thin-film metal oxides. In crystalline solids, ion conductivity is given as the product of the defect (e.g., vacancy) concentration and the defect mobility, which is governed by the defect migration enthalpy (i.e., activation energy). Unfortunately, this descriptor does not describe the ionic conductivity in amorphous materials. In this work and our other work,¹⁰ we found that oxygen-deficient metal suboxides have much lower ionic conductivity than near-stoichiometric metal oxides. Instead, amorphous hafnium oxide made through atomic layer deposition has much lower oxygen tracer diffusivity than ones made through reactive sputtering. Similarly, my colleagues Prof. Becky Peterson and Neil Dasgupta's groups observed that electron mobility is higher in denser zinc oxide films for thin-film transistors.¹¹

MH: What do you find most challenging about your research?

YL: It is challenging to have to read and synthesize literature from different communities. I was trained in the defect chemistry of crystalline materials. However, these metal oxides are amorphous, so I have to review the literature on glasses and non-crystalline solids. Additionally, I have always worked on functional materials like microelectronics and batteries, which are usually nanosized in at least one dimension; however, most studies on glasses research bulk materials for structural applications. These communities often have different ways of describing the same concepts, which makes it difficult to learn and synthesize. Luckily, I am fortunate that the University of Michigan is a large research institution with expertise in many different fields, but it still requires me to go substantially outside my previous knowledge base.

MH: In which upcoming conferences or events may our readers meet you?

YL: In 2024, I have confirmed plans to be at the Electrochemical Society Meeting in San Francisco, the Solid State Ionics Conference in London, and the American Vacuum Society Conference in November. I often attend Materials Research Society and Electrochemical Society conferences.

MH: How do you spend your spare time?

YL: Outside of academics and raising a young child, I like to go bicycling in Ann Arbor. I do not bike competitively, but I enjoy the exercise and the mind-cleansing effect of feeling the wind pass my ears.

MH: Can you share one piece of career-related advice or wisdom with other early career scientists?

YL: For those considering a tenure-track position: try to be an expert in more than one field. Ideally, try to be one of only a handful of people who is an expert in both (or more) fields that you have chosen.

References

1. Y. Li, F. El Gabaly, T. R. Ferguson, R. B. Smith, N. C. Bartelt, J. D. Sugar, K. R. Fenton, D. A. Cogswell, A. L. D. Kilcoyne, T. Tyliszczak, M. Z. Bazant and W. C. Chueh, Nat. Mater., 2014, 13, 1149–1156.
2. Y. Li, H. Chen, K. Lim, H. D. Deng, J. Lim, D. Fraggedakis, P. M. Attia, S. C. Lee, N. Jin, J. Moškon, Z. Guan, W. E. Gent, J. Hong, Y.-S. Yu, M. Gaberšček, M. S. Islam, M. Z. Bazant and W. C. Chueh, Nat. Mater., 2018, 17, 915–922.
3. Y. Li, E. J. Fuller, S. Asapu, S. Agarwal, T. Kurita, J. J. Yang and A. A. Talin, ACS Appl. Mater. Interfaces, 2019, 11, 38982–38992.
4. Y. Li, E. J. Fuller, J. D. Sugar, S. Yoo, D. S. Ashby, C. H. Bennett, R. D. Horton, M. S. Bartsch, M. J. Marinella, W. D. Lu and A. A. Talin, Adv. Mater., 2020, 32, 2003984.
5. D. S. Kim, V. J. Watkins, L. A. Cline, J. Li, K. Sun, J. D. Sugar, E. J. Fuller, A. A. Talin and Y. Li, Adv. Electron. Mater., 2023, 9, 2200958.
6. J. Min, L. Gubow, R. Hargrave, J. Siegel and Y. Li, Energy Environ. Sci., 2023, 16, 3847–3859.
7. J. B. Goodenough, Phys. Rev., 1955, 100, 564–573.
8. M. S. Whittingham, Mater. Res. Bull., 1974, 9, 1681–1689.
9. A. Yoshino, Angew. Chem., Int. Ed., 2012, 51, 5798–5800.
10. J. Li, A. Appachar, S. Peczonczyk, E. Harrison, B. Roest, A. Ievlev, R. Hood, S. Yoo, K. Sun, A. Talin, W. Lu, S. Kumar, W. Sun and Y. Li, Thermodynamic origin of nonvolatility in resistive switching, Research Square, 2022, preprint DOI:10.21203/rs.3.rs-2365752/v1.
11. C. R. Allemang, T. H. Cho, O. Trejo, S. Ravan, R. E. Rodríguez, N. P. Dasgupta and R. L. Peterson, Adv. Electron. Mater., 2020, 6, 2000195.

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