The goal of the Consortium’s two-year effort was to identify GMR-based technology trajectories that could make an impact, perhaps in both defense and civilian contexts, and in 1995, the Consortium’s verdict was in: GMR research could yield a host of new magnetic field sensors but, more importantly, a new kind of memory – magnetoresistance random access memory (MRAM). For one thing, the magnetic basis – rather than the charge-basis – of the storage technology opened the way to memory that would be retained even when power to a computer or storage device was shut off. For another, MRAM promised instant-on computer operation that would bypass the then standard need to boot-up by shuttling information from a hard drive to the powered-up computer chips. Crucially for national defense purposes, MRAM devices also could be “rad-hard” compared to semiconductor-based RAM chips, and therefore less vulnerable to radiation damage in places like space. On top of all of that, MRAM research looked like a good bet for winning a significant SWaP advance in memory technology.
Jon Slaughter was part of a semiconductor research group at Motorola that got in early on the DARPA push for new MRAM technology. At first, his team focused on a type of GMR structure in which electrons traveled between the two magnetic layers via a conductive pathway. But they soon realized that the way to go, one that IBM already had adopted, was with so-called tunnel magnetoresistance (TMR). In this process, electrons move between the two magnetic layers by “tunneling” through an intervening insulator layer in that mysterious quantum-mechanical sense. “This is mind-blowing,” Slaughter said, “because the electrons are never in the insulator.”
Mind-blowing yes, and a commercial coup to boot. Slaughter says his team, working on what was referred to within the company as the “Panther Project,” identified a variation on the TMR theme, called toggle switching, as the technology to bet the farm on. In 2004, Motorola spun off its vast Freescale semiconductor operation (including its MRAM research) as an independent entity and two years later Freescale became the first company in the world to sell an MRAM product – a 4 Mb MRAM chip based on toggle switching. Freescale did not have a memory business at the time and was not investing in new markets, Slaughter said in an interview. So he, with help from others in the community, attracted sufficient venture capital to spin out in 2008 what then was the MRAM startup Everspin Technologies. A decade later Slaughter is the director of research and development and, according to the company website, 70 million of its MRAM products are deployed “in data center, cloud storage, energy, industrial, automotive, and transportation markets.”
“People don’t realize it, but MRAM is out there,” Slaughter said. In a poetic twist, the process Everspin relies on for its rad-hard MRAM products depends on rad-hard silicon supplied by Honeywell, which was the other major company – besides IBM and Motorola – that the agency funded under the Magnetic Materials and Devices program.
A few years into that pioneering program, two fundamental physics discoveries expanded the already rich spintronics vista. A team of Japanese researchers found they could use an electric field – rather than a magnetic field – to induce magnetism in a semiconductor material (gallium manganese arsenide), though they needed to chill the material to 150 K (-123 Celsius). In the same 1997-1998 time frame, physicist and materials scientist David Awschalom and colleagues at the University of California Santa Barbara (UCSB) showed that they too could induce magnetism in a semiconductor material (gallium arsenide), but they did so with a laser.
“These two discoveries gave me the idea that there could be a new DARPA program to explore how to exploit these two effects,” Wolf said. That idea became, in 1998, the Spins in Semiconductors (SPINS) program, which also benefited from the availability of TRP money. One goal of this mostly fundamental-science program was to discover semiconductor materials like gallium manganese arsenide, but in which the magnetism could be induced with an electric field at the merely chilly temperature of 273 K rather than a frigid 150 K. About a third of the program’s funds underwrote what then was a still speculative goal of quantum computation based on “qubits,” which are physical entities such as isolated ions or well-engineered crystal semiconductor nanostructures that can embody a superimposition of the canonical one and zero states (and perhaps many more states) at the same time. This was driven by the surprising discovery by the Awschalom group at UCSB that light could create and control quantum coherent states of matter (akin to light waves or mechanical waves whose phases can be deliberately arranged) based on electron spins, and that engineers could use these quantum states for novel types of information processing. Moreover, the UCSB group found that it could turn to simple electrical gates to transport these quantum states across hundreds of microns in semiconductors, quite a long distance in these contexts.
Because this search for qubits was occurring within the specific context of spintronics (electronic spin states), however, several DARPA offices banded together and expanded the quest for physical incarnations of qubits by starting up an ambitious $100 million Quantum Information Science and Technology (QUIST) program. Running from 2001-2005, the program also supported research into new algorithms for computation with qubits.
Awschalom, now at the University of Chicago, embraced these particularly deep and speculative dives into the quantum physics of electron spins. “DARPA was largely responsible for launching the fields of semiconductor spintronics and quantum spintronics, the latter of which has also helped drive the emerging area of quantum computing,” he said. “This was high-risk science and, at the time, not obvious that the underlying physics and engineering would work out so well.”
“Development in MRAM took a long time,” Wolf noted. “It started in 1995, but it did not lead to a commercial technology until 2006.” That actually stands well against the several decades it commonly takes to develop scientific discoveries into hold-in-your-hand technology. The pathway to this end result in the MRAM adventure illustrates what, from DARPA’s institutional point of view, is an ideal sequence of events – fundamental research, to proof-of-concept technology, to good-to-go technology with national defense consequences. The end result was full-on DARPA, in this case a rad-hard MRAM chip, which was cheaper, more capable, more energy-efficient, and minuscule compared to the previous space-based storage technology.