For Dr. Tiffany Santos, the director of non-volatile memory materials research at Western Digital, forging a path for a new memory technology requires a blend of patience and optimism.
A holder of four patents, co-author on 41 academic publications, and presenter at more than 30 conferences, Santos and her team engineer novel materials, by computation and experiment, that can push the performance of emerging non-volatile memory technologies to the next level.
“It can take a long time to make progress, and you have a lot of failures along the way, so you need to be patient for that success to come along,” she said. “And you need to be optimistic that if you just keep trying and learn from every failure, eventually one approach is going to work.”
Or, as she sums up her flair for experimental research: “it’s an attitude.”
A magnetic attraction to the lab
Santos never expected to be a scientist, even when she began her college career at the Massachusetts Institute of Technology (MIT). She knew MIT was the best engineering school in the world and planned to study math. But once she put on a lab coat and began doing hands-on experiments her sophomore year, she never looked back.
“I had no idea if I would be any good at it or if I would be completely clumsy and drop things in the lab or set something on fire,” she said. “But it turned out I am very detail-oriented and very optimistic for the next experiment, and I think those qualities are good for somebody doing experimental research.”
During her scholastic career, Santos discovered her love of materials science. “It’s an interesting blend of physics and chemistry, and it’s very interdisciplinary,” she said. She continued her studies at MIT, eventually earning a Ph.D. in materials science and engineering, where her thesis work focused on thin-film magnetism and spin-polarized tunneling in magnetic tunnel junctions (MTJs).
The magnetic tunnel junction (MTJ) is a nanostructured device comprised of three sandwiched layers: two ferromagnetic electrodes with an ultrathin (about 1 nanometer) insulating tunnel barrier in between. Electrons tunnel across the insulating barrier when the magnetizations align and are suppressed when magnetizations are opposed, which is controlled by applying a magnetic field.
The concept was first proposed in 1975 and reached widespread commercialization nearly 30 years later when the technology was used in the read sensor of hard disk drives. With the widespread adoption of hard drives and the rise of digital data, MTJs became essential for data storage in consumer laptops, desktop computers, and today’s massive cloud data centers.
Innovation for MTJs has largely to do with tailoring the properties of its materials and thin films. Following her Ph.D., Santos then went to the U.S. Department of Energy’s Argonne National Lab for her post-doctorate work and conducted research in the Center for Nanoscale Materials. There, she won the prestigious L’Oreal USA Women in Science Fellowship for her work in materials science.
“If we can understand the origin of a material’s properties at the nanoscale, then we can design and create new materials for the next generation of electronic devices that meet these global challenges,” she said at the time, prophesizing where her career would take her.
From hard drives to memory
In 2011, Santos joined Hitachi Global Storage Technologies (HGST), later acquired by Western Digital, specifically to research materials for Heat Assisted Magnetic Recording (HAMR) media.
“I was hired to work on the media, the spinning disk of the hard drive, and do the deposition of the magnetic material on the media,” said Santos. “At the time, HAMR was a research project; now it’s a development one.” This is what Santos finds most rewarding, seeing a discovery made in the lab evolve into product development and, eventually, a product.
After several years working on HAMR media, Santos was tasked with how to apply magnetic thin film and hard drive expertise to emerging memory products.
“What’s exciting is you can also use Magnetic Tunnel Junctions (MTJ) as a memory element, and this is how we’re using it in MRAM,” she said. “MTJs have been around for decades, and we’re just trying to give it this new function.”
Today, Santos leads a team in the company’s state-of-the-art nanoscale lab, the only nanoscale lab in the magnetic storage industry, charged with exploring magnetic memory devices for future memory products at nanoscale.
“We’re really pushing the boundaries, creating an MRAM product that nobody’s created before,” said Santos. “What we’re trying to do is make really tiny bits, really close together, which would be what you need for a high density MRAM memory. And having really tightly spaced bits next to each other is a challenge in itself that throws on a major layer of complexity. But we think we’ve got some clever ideas to make it happen.”
Her team’s work has shown a capability of making magnetic tunnel junctions at the nanoscale, with minuscule bits around 20 to 25 nanometers in diameter. A nanometer is about 7,000 times smaller than a single red blood cell.
Santos herself holds patents for her work in both MTJs and spin-transfer torques (STTs). Spin-transfer torque (STT) is the means to pass the current to flip the magnetism in the MTJ from parallel to antiparallel and back without a magnetic field.
“These are ideas of how to optimize the performance of the magnetic tunnel junction, enabling switching with lower power and increasing the length of time for data retention,” said Santos. “We’re building off a technology that’s been around for [decades] [MTJ] and making it work with less power and the ability to stay stable longer.”
Speaking of magnetism
When she’s not in the nanoscale lab, Santos travels the globe as a seminar speaker, representing Western Digital and its groundbreaking research in the industry. She was one of only four 2022 IEEE Distinguished Lecturers for the IEEE Magnetics Society, delivering 41 lectures around the world.
Many of the lectures are held at universities, and meeting students is one of her favorite parts of the gig.
“It’s really rewarding to interact with students,” said Santos. “They’re very excited to meet me because I’m someone who does research at a high level for my day job.”
Western Digital is one of only a handful of companies in the world that conducts applied research at scale.
“Most research and development teams can take on risk only up to a certain point when they’re trying to innovate because you still need to stay on track for delivering your product to customers on time,” said Santos. “A great thing about working in Western Digital’s research is that we can take on a lot more risk with our innovation.”
Santos acknowledges that higher risk means a higher chance for failure, which happens a lot, and it’s part of the work. But she takes those setbacks as opportunities to learn, improve, optimize, and innovate.
“We take higher risks because from time to time we succeed in getting the higher reward, and that’s the exciting and fun part of the job; the thrill of discovery.”