Ramamoorthy Ramesh
Ramamoorthy Ramesh (born 1960) is an American materials scientist of Indian descent who has greatly advanced the synthesis, assembly and understanding of complex functional oxides, such as ferroelectric materials, laying the foundation for development and application of multiferroic materials. In particular, his work pioneered the development of ferroelectric perovskites, manganites with colossal magnetoresistance, and multiferroic oxides with great impact on the materials physics and with the potential for significant benefits for modern information technologies.
He is a Professor at the University of California Berkeley in the Departments of Materials Science and Engineering, and Physics. He also leads more than 500 scientists as the Associate Laboratory Director for Energy Technologies at the Lawrence Berkeley National Laboratory. He has published over 540 papers in internationally recognized journals which have been cited more than 54,000 times. He has been issued 27 patents, and his approach for fabricating ferroelectric materials for random access memory has been employed by the world’s largest memory manufacturers.
Training and Career
In 1980 Ramesh received his Bachelor in Science degree in Chemistry at Madras University in India. In 1983 he received his Bachelors degree in Metallurgy from the Indian Institute of Science in Bangalore. He received his Doctorate in Materials Science from the University of California, Berkeley in 1987. He then served as a Postdoctoral Associate at the National Center of Electron Microscopy in Lawrence Berkeley National Laboratory (LBNL). He went to Bell Communications Research (Bellcore) in 1989 and initiated research in several key electrical device technologies, including ferroelectric nonvolatile memories. Ramesh joined the University of Maryland in 1995 and was promoted to Professor in 1999 and Distinguished Professor in 2003. The following year he joined the University of California faculty in the Materials Science and Engineering and Physics departments, and now serves as Purnendu Chatterjee Chair in Energy Technologies.
He joined Lawrence Berkeley National Laboratory in 2004 as a Faculty Scientist and became Associate Laboratory Director (ALD) for Energy Technologies in 2014. In his capacity as ALD, he serves as a strategic leader for three Laboratory Divisions focused on Energy Technologies. The Energy Technologies Area conducts research for the U.S. Department of Energy other federal entities, as well as state governments, with a focus on California and the private sector.
Ramesh served under Energy Secretary Chu as the founding Director of the SunShot Initiative, which aimed to bring the cost of solar electricity down to grid parity by the end of the decade. One significant impact of his role as the director has been to strengthen the scientific foundations for solar energy research to elucidate the complex science underpinning this technology. Later he also served in a leadership position at Oak Ridge National Laboratory.
Ferroelectric Thin Film Nonvolatile Memory
Ramesh pioneered the development of thin film ferroelectric materials for random access memory (FRAMS), first at Bellcore’s Red Bank, New Jersey facility, and then at the University of Maryland. These efforts paved the way for a reliable, high-density memory technology. He was the first to demonstrate that conducting oxide electrodes eliminate the 30-year old problem of polarization fatigue, achieved through careful control of the physics of the electrode-ferroelectric interface (Appl. Phys. Lett., 1992; Appl. Phys. Lett., 1993). This was a critical step in the development of reliable FRAM devices and became used pervasively by many semiconductor companies such as Fujitsu, which has operated the world’s largest FRAM production line, as well as Texas Instruments and others, directly benefiting technology worldwide.
Ramesh’s subsequent work explored the fundamental limits of switching dynamics and demonstrated the fastest switching speed in ferroelectric thin films, another key element that enabled high speed, nonvolatile random access memories. His work has also demonstrated a novel approach to create high density ferroelectric capacitors directly on the structure of silicon complementary metal–oxide–semiconductor (Si-CMOS) through the introduction of novel conducting barrier layers (see “Ferroelectric capacitor heterostructure and method of making same,” U.S. 5479317 A, 1994). Ramesh holds over 20 patents in the field of ferroelectric thin films and devices.
Colossal Magnetoresistance
Beginning in 1993, Ramesh collaborated with SungHo Jin (Bell Labs) to initiate joint research into manganite thin films. They epitaxially grew lanthanum calcium manganite films, with detailed measurements of resistivity responses to magnetic fields, observing huge changes in resistance (Science, 1994). They coined the term Colossal Magnetoresistance (Science 1994) and this seminal paper has been cited more than 4,000 times, launching an international research effort on these CMR materials.
Ramesh and his collaborators also demonstrated several new device concepts, including a markedly improved, nonvolatile ferroelectric field effect device constructed of perovskite heterostructures with a highly magnetoresistive manganite as the channel semiconductor. In this case, he used lanthanum calcium manganite as the semiconductor and lead zirconate titanate as the ferroelectric gate (Science 1997). The carrier concentration of the semiconductor channel can be “tuned” by varying the manganite stochiometry. The enhanced interface characteristics enabled the fabrication of novel field effect devices.
Multiferroic Materials
In 2000, Ramesh began new explorations of coupled phenomena in complex oxides to develop the possibility of controlling ferromagnetism with an electric field. He was the first to discover large ferroelectric polarization in epitaxially grown thin films of bismuth ferrite (Science, 2003). He grew phase-pure BFO films in the thickness tens of nanometers by pulsed laser deposition. This work has stimulated a global research effort and has been cited more than 3,800 times, providing direct evidence of a very large spontaneous polarization in this ferroelectromagnet system, ideal for the development of sensors and actuators as well as electric field controlled magnetism.
Subsequently Ramesh and his colleagues prepared three-dimensional epitaxial nanocomposite of cobalt ferrite/barium titanate (Science, 2004). The self-assembled arrays of Cobalt ferrite nanopillars were embedded in the Barium titanate matrix. This approach to nanocomposite structures became quite generalized, with many others creating similar structures. This class of material facilitates the inter-conversion of energies stored in electric and magnetic fields and can play an important role in many devices.
His group also discovered a completely unexplored aspect of these materials, namely that ferroelectric domain walls in such multiferroics are electrically conducting [Nature Materials 8,(2009); Nature Materials 12, (2012); Reviews of Modern Physics, 84(2012)]. This discovery once again opened up a new avenue for worldwide research activity; many groups around the world are now actively engaged in exploring the intricacies and potential technological impact of such exotic phenomena. Following up on this work, his group demonstrated that such domain walls also exhibit anomalously large photovoltages [Nature Nanotechnology 5 (2010)] as well as the discovery of a new “super-tetragonal” phase of BiFeO3 [Science 326(2009)]. His research is now focused on exploring magnetotransport phenomena at such domain walls; for example, his group has shown that certain types of domain walls can be magnetic and thus also exhibit large magnetoresistance phenomena.
He is also focused on making Multiferroics and Magnetoelectrics a technological reality. In a development that holds promise for future magnetic memory and logic devices, Ramesh and his colleagues used an electric field to reverse the magnetization direction in a multiferroic material, pointing to a avenue towards spintronics and smaller, faster and cheaper ways of storing and processing data. They used heterostructures of bismuth ferrite and cobalt iron to fabricate a spin-valve this new spin valve (Nature, 2014). Ramesh’s research is now focused on exploring magnetotransport phenomena in multiferroic domain walls. For example, his group has shown that certain types of domain walls can be magnetic, and thus also exhibit large magnetoresistance phenomena. His most recent work (Nature, 2016) demonstrated the existence of polar vortices in ferroic superlattices, which could find potential applications for ultracompact data storage and processing.
New Photovoltaic Materials
Ramesh also developed bismuth ferrite materials as a type of photovoltaic material that produces voltages significantly higher than a typical semiconductor. He and his colleagues discovered a fundamentally new mechanism for photovoltaic charge separation, which operates over a distance of one to two nanometers and produces voltages that are significantly higher than conventional devices (Nat. Nanotechnology, 2010). This new degree of control, and the high voltages produced, may find application in photovoltaic cells and other optoelectronic devices.
U.S. Patents
Ramesh holds 27 patents, primarily in the field of ferroelectric thin films and devices. Examples include:
“Growth of a,b-axis oriented perovskite thin films,” U.S. Patent No. 5358927, Issued 25 October 1994, A.Inam, R.Ramesh and C.T.Rogers
“Epitaxial Ferromagnetic Manganese Aluminum Magnetic memory element and method for the preparation thereof,” U.S.Patent No.5169485, Dec. 8, 1992, S.J.Allen, J.Harbison, M.Leadbeater, R.Ramesh and T.D.Sands
“Crystalline ferroelectrics grown on silicon dioxide,” U.S.Patent No. 5248564, 28 September 1993, R.Ramesh
“Barrier layer for ferroelectric capacitor integrated on silicon,” R. Ramesh, patent No. 5838035, 17 November 1998.
“Annealing of a crystalline ferroelectric memory cell,” S. Aggarwal, A.M.Dhote and R.Ramesh, 6274,388, 14 August 2001.
“Bismuth ferrite films and devices grown on silicon,” R. Ramesh, 7696549, 13 April 2010.
A complete list of Ramesh’s patents is available at http://www2.lbl.gov/msd/people/investigators/ramesh_investigator.html
Awards and Honors
2014 TMS Bardeen Prize
Distinguished alumnus, Indian Institute of Science, 2012
Elected member, U.S. National Academy of Engineering, 2011
American Physical Society James McGroddy New Materials Prize, 2010
Materials Research Society Fellow, 2009
Materials Research Society David Turnbull Award, 2007
C.K. Majumdar Lectureship Award, Bose Institute, Calcutta, India
Brahm Prakash Chair, Indian Institute of Science, Bangalore, India, 2006
Fellow, American Association for the Advancement of Science, 2005
American Physical Society Adler Lectureship, 2005
Distinguished University Professor, University of Maryland, College Park, 2003
Fellow, American Physical Society, 2001
Alexander von Humboldt Senior Scientist Prize, 2001
Notable publications
1. J. Wang, J.B. Neaton, H. Zheng, V. Nagarajan, S.B. Ogale, B. Liu, D. Viehland, V. Vaithyanathan, D.G. Schlom, U.V. Waghmare, N.A. Spaldin, K.M. Rabe, M. Wuttig, and R. Ramesh, “Epitaxial BiFeO3 Multiferroic Thin Film Heterostructures,” Science 299, 1719 (2003).
2. H. Zheng, J. Wang, S.E. Lofland, Z. Ma, L. Mohaddes-Ardabili, T. Zhao, L. Salamanca-Riba, S.R. Shinde, S.B. Ogale, F. Bai, D. Viehland, Y. Jia, D.G. Schlom, M. Wuttig, A. Roytburd, and R. Ramesh, “Multiferroic BaTiO3-CoFe2O4 Nanostructures,” Science 303, 661 (2004).
3. T. Zhao, A. Scholl, F. Zavaliche, K. Lee, M. Barry, A. Doran, M.P. Cruz, Y.H. Chu, C. Ederer, N.A. Spaldin, R.R. Das, D.M. Kim, S.H. Baek, C.B. Eom, and R. Ramesh. Electrical control of antiferromagnetic domains in multiferroic BiFeO3 films at room temperature. Nature Materials 5, 823 (2006).
4. F. Zavaliche, et al., “Electric field-induced magnetization switching in epitaxial columnar nanostructures”, Nanoletters 5, 1793-1796 (2005).
5. R. Ramesh and N.A. Spaldin, “ Multiferroics: progress and prospects in thin films”, Nature Materials, 6, 21(2007).
6. Y.H.Chu, et al., Electric field control of ferromagnetism using a magnetoelectric multiferroic, Nature Materials, 7, 478(2008).
7. J. Seidel, et al., “Conduction at domain walls in oxide multiferroics”, Nature Materials 8 (3): 229-234.
8. R.J. Zeches, et al., “A Strain-Driven Morphotropic Phase Boundary in BiFeO3.” Science 326 (5955): 977-980.
9. Yang, CH, et al., “Electric modulation of conduction in multiferroic Ca-doped BiFeO3 films”, Nature Materials 8 (6): 485-493(2009).
10. S.M. Wu, et al., “Reversible electric field control of exchange bias in a multiferroic field effect t device.” Nature Materials 9 (5955): 756-760(2010).
11. S.Y. Yang, et al., “Above-bandgap voltages from ferroelectric photovoltaic devices.” Nature Nanotechnology 5, 143-147(2010).
12. Spaldin, N; Cheong, SW; Ramesh, R, Multiferroics: Past, Present, and Future Physics Today, 64, 9(2010).
13. Heron, J. T.; Trassin, M.; Ashraf, K.; Gajek, M.; He, Q.; Yang, S. Y.; Nikonov, D. E.; Chu, Y-H.; Salahuddin, S.; Ramesh, R., Electric-Field-Induced Magnetization Reversal in a Ferromagnet-Multiferroic Heterostructure, Physical Review Letters, 107, 217202(2011).
14. G. Catalan, et al., “Domain Wall Nanoelectronics.” Reviews of Modern Physics 84, 119-156(2012).
15. S. Jin, T.H. Tiefel, M. McCormack, R.A. Fastnacht, R. Ramesh, and L.H. Chen. Thousandfold change in resistivity in magnetoresistive La-Ca-Mn-O films. Science 264, 413-415 (1994).
16. S.Matthews, R.Ramesh, T.Venkatesan and J.Benedetto, "Ferroelectric field effect transistor based on epitaxial perovskite heterostructures", Science 276, 238(1997).
17. J.-H. Park, E. Vescovo, H.-J. Kim, C. Kwon, R. Ramesh, and T. Venkatesan. Direct evidence for a half-metallic ferromagnet. Nature 392, 794-796 (1998).
18. J.-H. Park, E. Vescovo, H.-J. Kim, C. Kwon, R. Ramesh, and T. Venkatesan. Magnetic properties of surface boundary of a half-metallic ferromagnet La0.7Sr0.3MnO3. Phys. Rev. Lett. 81, 1953-1956 (1998).
19. R. Ramesh, A. Inam, W.K. Chan, B. Wilkens, K. Myers, K. Remschnig, D.L. Hart, and J.M. Tarascon. Epitaxial cuprate superconductor/ferroelectric heterostructures. Science 252, 944-946 (1991).
20. R. Ramesh, W.K. Chan, B. Wilkens, H. Gilchrist, T. Sands, J.M. Tarascon, V.G. Keramidas, D.K. Fork, J. Lee, and A. Safari. Fatigue and retention in ferroelectric Y-Ba-Cu-O/Pb-Zr-Ti-O/Y-Ba-Cu-O heterostructures. Appl. Phys. Lett. 61, 1537-1539 (1992).
21. R. Ramesh, H. Gilchrist, T. Sands, V.G. Keramidas, R. Haakenaasen, and D.K. Fork. Ferroelectric La-Sr-Co-O/Pb-Zr-Ti-O/La-Sr-Co-O heterostructures on silicon via template growth. Appl. Phys. Lett. 63, 3592-3594 (1993).
22. O. Auciello, J.F. Scott and R. Ramesh, “The physics of ferroelectric memories”, Physics Today, 51, 22(1998).
23. R. Ramesh, S. Aggarwal and O. Auciello. Science and Technology of ferroelectric thin films for nonvolatile memories. Annu. Rev. Mater. Sci. 32, 191(2001).
24. Marti, X.; Fina, I.; Frontera, C.; Liu, Jian; Wadley, P.; He, Q.; Paull, R. J.; Clarkson, J. D.; Kudrnovsky, J.; Turek, I.; Kunes, J.; Yi, D.; Chu, J-H.; Nelson, C. T.; You, L.; Arenholz, E.; Salahuddin, S.; Fontcuberta, J.; Jungwirth, T.; Ramesh, R., Room-temperature antiferromagnetic memory resistor, Nature Materials, 13, 367-374(2014).
25. Heron, JT , Schlom, DG , Ramesh, R, Electric field control of magnetism using BiFeO3-based heterostructures, Applied Physics Reviews Volume: 1,021303(2014).
26. Heron, JT , Bosse, JL , He, Q , Gao, Y , Trassin, M, Ye, L , Clarkson, JD, Wang, C , Liu, J , Salahuddin, S ,Ralph, DC , Schlom, DG , Iniguez, J ,Huey, BD , Ramesh, R, Deterministic switching of ferromagnetism at room temperature using an electric field, Nature,516, 370-373(2014).
27. Khan, A.I., Chatterjee, K, Wang, B , Drapcho, S , You, L ,Serrao, C, Bakaul, SR, Ramesh, R , Salahuddin, S, Negative capacitance in a ferroelectric capacitor, Nature Materials 14, 182-186 (2015).
28. A.K. Yadav, et al, “Observation of Polar Vortices in Oxide Superlattices, Nature, accepted, November 2015.
Additional notable papers and a complete list of publications is available at http://www2.lbl.gov/msd/people/investigators/ramesh_investigator.html
Editorial Board Memberships
Ramesh has served on the Editorial Board of the Journal of Applied Physics, Applied Physics Letters, Integrated Ferroelectrics, Journal of Materials Research, Japanese Journal of Applied Physics and the Journal of Electroceramics.
Sources Cited
1. Ramesh, R., Chan, W. K., Wilkens, B., Gilchrist, H., Sands, T., Tarascon, J. M., ... & Safari, A. (1992). Fatigue and retention in ferroelectric Y‐Ba‐Cu‐O/Pb‐Zr‐Ti‐O/Y‐Ba‐Cu‐O heterostructures. Applied Physics Letters, 61(13), 1537-1539.
2, Ramesh, R., Gilchrist, H., Sands, T., Keramidas, V. G., Haakenaasen, R., & Fork, D. K. (1993). Ferroelectric La‐Sr‐Co‐O/Pb‐Zr‐Ti‐O/La‐Sr‐Co‐O heterostructures on silicon via template growth. Applied Physics Letters,63(26), 3592-3594.
3. Jin, S., Tiefel, T. H., McCormack, M., Fastnacht, R. A., Ramesh, R., & Chen, L. H. (1994). Thousandfold change in resistivity in magnetoresistive La-Ca-Mn-O films. Science, 264(5157), 413-415.
4. Mathews, S., Ramesh, R., Venkatesan, T., & Benedetto, J. (1997). Ferroelectric field effect transistor based on epitaxial perovskite heterostructures. Science, 276(5310), 238-240.
5. Wang, J. B. N. J., Neaton, J. B., Zheng, H., Nagarajan, V., Ogale, S. B., Liu, B., ... & Ramesh, R. (2003). Epitaxial BiFeO3 multiferroic thin film heterostructures. Science, 299(5613), 1719-1722.
6. Zheng, H., Wang, J., Lofland, S. E., Ma, Z., Mohaddes-Ardabili, L., Zhao, T., ... & Ramesh, R. (2004). Multiferroic BaTiO3-CoFe2O4 nanostructures. Science, 303(5658), 661-663
7. Zeches, R. J., Rossell, M. D., Zhang, J. X., Hatt, A. J., He, Q., Yang, C. H., ... & Ramesh, R. (2009). A strain-driven morphotropic phase boundary in BiFeO3. Science, 326(5955), 977-980.
8. Yang, S. Y., Seidel, J., Byrnes, S. J., Shafer, P., Yang, C. H., Rossell, M. D., ... & Ramesh, R. (2010). Above-bandgap voltages from ferroelectric photovoltaic devices. Nature nanotechnology, 5(2), 143-147.
9. Polking, M. J., Zheng, H., Ramesh, R., & Alivisatos, A. P. (2011). Controlled synthesis and size-dependent polarization domain structure of colloidal germanium telluride nanocrystals. Journal of the American Chemical Society,133(7), 2044-2047.
10. Heron, J. T., Bosse, J. L., He, Q., Gao, Y., Trassin, M., Ye, L., ... & Ramesh, R. (2014). Deterministic switching of ferromagnetism at room temperature using an electric field. Nature, 516(7531), 370-373.
11. Yadav, A. K., Nelson, C. T., Hsu, S. L., Hong, Z., Clarkson, J. D., Schlepüetz, C. M., ... & Ramesh, R.. (2016). Observation of polar vortices in oxide superlattices. Nature. (16416). doi:10.1038/
External Links
Lawrence Berkeley National Laboratory
Energy Technologies Area, LBNL (http://eetd.lbl.gov/
Building Technology & Urban Systems Division (http://eetd.lbl.gov/about-us/organization/building-technology-and-urban-systems)
Energy Analysis & Environmental Impacts Division (http://eetd.lbl.gov/about-us/organization/energy-analysis-and-environmental-impacts)
Energy Storage & Distributed Resources Division SunShot Initiative | Department of Energy (http://www.energy.gov/eere/sunshot/sustainable-and-holistic-integration-energy-storage-and-solar-pv-shines)
References
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