Multiferroics and Topological Materials Could Enable More Energy-Efficient Computers

Envisioning beyond the existing transistor technology, scientists from Intel Corp. and UC Berkeley are working to develop an innovative type of memory and logic circuit that could sooner or later be used in every computer on the planet.

In a paper published online on December 3^rd, 2018, in advance of publication in the Nature journal, the research team has put forward a method for transforming relatively new kinds of materials—topological materials and multiferroics—into logic and memory devices that will be 10–100 times more energy-efficient compared to predictable advancements to existing microprocessors, which are based on complementary metal-oxide-semiconductor (CMOS).

Compared to CMOS, the magneto-electric spin-orbit or MESO devices will also be able to pack five times more logic operations into the same space, persisting the trend toward more computations per unit area, a central concept of Moore’s Law.

The innovative devices will promote technologies that mandate intense computing power with low energy use, particularly highly automated, self-driving cars and drones, both of which need ever-increasing numbers of computer operations per second.

As CMOS develops into its maturity, we will basically have very powerful technology options that see us through. In some ways, this could continue computing improvements for another whole generation of people.

Sasikanth Manipatruni, Study Lead Author, Intel Corp.

Manipatruni is the head of the hardware development for the MESO project at Intel’s Components Research group in Hillsboro, Oregon. MESO was Invented by Intel scientists, and the first MESO device was designed by Manipatruni.

Invented seven decades ago, transistor technology is currently used in everything from appliances and cell phones to supercomputers and cars. Transistors work to shuffle electrons around within a semiconductor and store them as binary bits 0 and 1.

The binary bits in the new MESO devices are the up-and-down magnetic spin states in a multiferroic, a material first developed in 2001 by Ramamoorthy Ramesh, a UC Berkeley professor of materials science and engineering and of physics and a senior author of the paper, who is also a faculty scientist at Lawrence Berkeley National Laboratory.

The discovery was that there are materials where you can apply a voltage and change the magnetic order of the multiferroic. But to me, ‘What would we do with these multiferroics?’ was always a big question. MESO bridges that gap and provides one pathway for computing to evolve.

Ramamoorthy Ramesh, Professor of Materials Science and Engineering, Physics, UC Berkeley.

In the paper published in Nature, the team has reported that the voltage required for multiferroic magneto-electric switching from 3 V to 500 mV has been successfully, and predictions are that it should be feasible to further reduce this to 100 mV: one-fifth to one-tenth of that needed for CMOS transistors that are currently in use. Lower voltage relates to lower energy use: the total energy required to switch a bit from 1 to 0 would be one-tenth to one-thirtieth of the energy required by CMOS.

“A number of critical techniques need to be developed to allow these new types of computing devices and architectures,” said Manipatruni, who combined the functions of magneto-electrics and spin-orbit materials to propose MESO. “We are trying to trigger a wave of innovation in industry and academia on what the next transistor-like option should look like.”

Internet of things and AI

There is an emergent need for computers that are more energy efficient. The Department of Energy has predicted that with the computer chip industry anticipated to expand to several trillion dollars in the next few decades, energy use of computers could shoot up from the existing level of 3% of all U.S. energy consumption to 20%, almost equal to that of the current transportation sector. The incorporation of computers into everything—the purported Internet of Things—would be hampered without more energy-efficient transistors. Moreover, Ramesh stated that a lack of innovative science and technology would result in overshadowing of America’s lead in manufacturing computer chips by semiconductor manufacturers from other countries.

“Because of machine learning, artificial intelligence and IOT, the future home, the future car, the future manufacturing capability is going to look very different,” said Ramesh, who until recently was the associate director for Energy Technologies at Berkeley Lab. “If we use existing technologies and make no more discoveries, the energy consumption is going to be large. We need new science-based breakthroughs.”

Eight years ago, Ian Young, co-author of the paper and a UC Berkeley PhD, started a group at Intel, together with Manipatruni and Dmitri Nikonov, to explore for alternatives to transistors, and half a decade ago, they started focusing on multiferroics and spin-orbit materials, the purported “topological” materials with distinctive quantum characteristics.

Our analysis brought us to this type of material, magneto-electrics, and all roads led to Ramesh.

Sasikanth Manipatruni, Study Lead Author.

Multiferroics and spin-orbit materials

The atoms of multiferroics exhibit more than one “collective state.” For instance, in the case of ferromagnets, the magnetic moments of all the iron atoms in the material are aligned to produce a permanent magnet. By contrast, in the case of ferroelectric materials, the positive and negative charges of atoms are offset, thereby generating electric dipoles that align throughout the material and produce a permanent electric moment.

MESO is based on a multiferroic material that consists of bismuth, iron, and oxygen (BiFeO₃), which is not only magnetic but also ferroelectric. According to Ramesh, one of its major advantages is that both the states—magnetic and ferroelectric—are coupled or linked, such that a change to one influences the other. The magnetic state, critical to MESO, can be changed by controlling the electric field.

The main advancement was achieved with the rapid development of topological materials with spin-orbit effect, which enable the multiferroic’s state to be read out efficiently. In MESO devices, the dipole electric field throughout the material is flipped or altered by an electric field, thereby flipping or altering the electron spins that produce the magnetic field. This potential arises from spin-orbit coupling, a quantum effect in materials, which generates a current determined by electron spin direction.

In another paper that was published earlier this month in the Science Advances journal, Intel and UC Berkeley experimentally demonstrated voltage-controlled magnetic switching using the magneto-electric material bismuth-iron-oxide (BiFeO₃), a main requirement for MESO.

We are looking for revolutionary and not evolutionary approaches for computing in the beyond-CMOS era. MESO is built around low-voltage interconnects and low-voltage magneto-electrics, and brings innovation in quantum materials to computing.

Ian Young, PhD, UC Berkeley.

Chia-Ching Lin, Tanay Gosavi, and Huichu Liu of Intel and Bhagwati Prasad, Yen-Lin Huang, and Everton Bonturim of UC Berkeley are the other co-authors of the Nature paper. The study was supported by Intel.