2022 IEEE Magnetics Society Distinguished Lecture

Sponsored by:  Stanford’s Electronic Systems Technology Seminars

The magnetic tunnel junction (MTJ), a device comprised of two ferromagnetic electrodes with a thin (about 1 nm) insulating tunnel barrier in between, was first proposed in a Ph.D. thesis by Michel Jullière in 1975 [1] and reached widespread commercialization nearly 30 years later as the read sensor in hard disk drives. MTJs became essential for data storage in consumer laptop and desktop computers, early-generation iPods, and now in data centers that store the information in “the Cloud.” The application of MTJs has expanded even further, becoming the storage element in non-volatile memory, first in toggle magnetic random access memory (MRAM) used in automotive applications and outer space, and now in the production of spin-transfer torque MRAM as a replacement for embedded flash memory.

This lecture will describe the seminal discoveries that enabled MTJs for pervasive use in hard disk drives, MRAM, and magnetic sensors, such as the discovery of tunnel magnetoresistance (TMR) at room temperature, the invention of spin-transfer torque as the means to flip magnetization without a magnetic field, and the prediction and realization of high TMR using MgO tunnel barriers.  It will describe the magnetic properties of MTJs that are essential for high-performance MRAM, including perpendicular magnetic anisotropy, damping parameter, exchange constant, thermal stability factor, and TMR, and how to engineer these properties to deliver high spin-transfer torque efficiency and high data retention in spin-transfer torque MRAM devices.

Speaker:

Tiffany S. Santos, a 2022 IEEE Magnetics Society Distinguished Lecturer. received the S.B. and Ph.D. degrees in materials science and engineering from the Massachusetts Institute of Technology (MIT), Cambridge, MA, USA, in 2002 and 2007, respectively.  She is the Director of Non-Volatile Memory Materials Research at the Research Division, Western Digital Corporation, San Jose, CA, USA, where she leads a team working on materials for magnetic random access memory technology and other exploratory projects. She first joined the company in 2011, when it was previously known as Hitachi Global Storage Technologies. Dr. Santos has played an active role in professional societies in the magnetism community, serving as a Secretary/Treasurer for the Topical Group on Magnetism and Its Applications (GMAG) of the American Physical Society, on the program committees of several magnetism and magnetic materials (MMMs) and international magnetics (INTERMAG) conferences, the Program Co-Chair of INTERMAG 2020, the Exhibits Chair of several MMMs and the International Conference on Magnetism, multiple terms on the MMM Conference Advisory Committee, and the Publicity Chair of the Magnetic Recording Conference. In 2009, she was awarded the L’Oréal USA Fellowship for Women in Science.