UCLA engineers develop new energy-efficient computer memory using magnetic materials
MeRAM is up to 1,000 times more energy-efficient than current technologies
December 10, 2012
By using electric voltage instead of a flowing electric current, researchers from
UCLA's Henry Samueli School of Engineering and Applied Science
have made major improvements to an ultra-fast, high-capacity class of computer memory known as magnetoresistive
random access memory, or MRAM.
The UCLA team's improved memory, which they call MeRAM for magnetoelectric random access memory, has great potential to
be used in future memory chips for almost all electronic applications, including smart-phones, tablets, computers and
microprocessors, as well as for data storage, like the solid-state disks used in computers and large data centers.
MeRAM's key advantage over existing technologies is that it combines extraordinary low energy with very high density,
high-speed reading and writing times, and non-volatility — the ability to retain data when no power is applied, similar
to hard disk drives and flash memory sticks, but MeRAM is much faster.
Currently, magnetic memory is based on a technology called spin-transfer torque (STT), which uses the magnetic property of
electrons — referred to as spin — in addition to their charge. STT utilizes an electric current to move electrons to write data
into the memory.
Yet while STT is superior in many respects to competing memory technologies, its electric current–based write mechanism still
requires a certain amount of power, which means that it generates heat when data is written into it. In addition, its memory
capacity is limited by how close to each other bits of data can be physically placed, a process which itself is limited by the
currents required to write information. The low bit capacity, in turn, translates into a relatively large cost per bit, limiting
STT's range of applications.
With MeRAM, the UCLA team has replaced STT's electric current with voltage to write data into the memory.
This eliminates the need to move large numbers of electrons through wires and instead uses voltage — the difference in electrical
potential — to switch the magnetic bits and write information into the memory. This has resulted in computer memory that generates
much less heat, making it 10 to 1,000 times more energy-efficient. And the memory can be more than five-times as dense, with more
bits of information stored in the same physical area, which also brings down the cost per bit.
The research team was led by principal investigator Kang L. Wang, UCLA's Raytheon Professor of Electrical Engineering,
and included lead author Juan G. Alzate, an electrical engineering graduate student, and Pedram Khalili, a research associate
in electrical engineering and project manager for the UCLA–DARPA research programs in non-volatile logic.
"The ability to switch nanoscale magnets using voltages is an exciting and fast-growing area of research in magnetism,"
Khalili said. "This work presents new insights into questions such as how to control the switching direction using voltage pulses,
how to ensure that devices will work without needing external magnetic fields, and how to integrate them
into high-density memory arrays.
"Once developed into a product," he added, "MeRAM's advantage over competing technologies will not be limited to its lower power
dissipation, but equally importantly, it may allow for extremely dense MRAM. This can open up new application areas where low cost
and high capacity are the main constraints."
Said Alzate: "The recent announcement of the first commercial chips for STT-RAM also opens the door for MeRAM, since our devices
share a very similar set of materials and fabrication processes, maintaining compatibility with the current logic circuit
technology of STT-RAM while alleviating the constrains on power and density."
The research was presented Dec. 12 in a paper called "Voltage-Induced Switching of Nanoscale Magnetic Tunnel Junctions"
at the 2012 IEEE International Electron Devices Meeting in San Francisco, the semiconductor industry's "pre-eminent forum for
reporting technological breakthroughs in the areas of semiconductor and electronic device technology."
MeRAM uses nanoscale structures called voltage-controlled magnet-insulator junctions, which have several layers stacked on top of
each other, including two composed of magnetic materials. However, while one layer's magnetic direction is fixed, the other can be
manipulated via an electric field. The devices are specially designed to be sensitive to electric fields. When the electric field
is applied, it results in voltage — a difference in electric potential between the two magnetic layers. This voltage accumulates
or depletes the electrons at the surface of these layers, writing bits of information into the memory.
"Ultra-low–power spintronic devices such as this one have potential implications beyond the memory industry," Wang said.
They can enable new instant-on electronic systems, where memory is integrated with logic and computing, thereby completely
eliminating standby power and greatly enhancing their functionality."
The work was supported by the Defense Advanced Research Projects Agency (DARPA) NV Logic Program. Other authors included
researchers from the UCLA Department of Electrical Engineering; UC Irvine's Department of Physics and Astronomy; Hitachi Global
Storage Technologies (a Western Digital Company); and Singulus Technologies, of Germany.
Wang is also director of the Western Institute of Nanoelectronics (WIN), director of the Center on Functional Engineered Nano
Architectonics (FENA) and a member of the
California NanoSystems Institute.
The UCLA Henry Samueli School of Engineering and Applied Science, established in 1945, offers 28 academic and professional
degree programs and has an enrollment of more than 5,000 students. The school's distinguished faculty are leading research
to address many of the critical challenges of the 21st century, including renewable energy, clean water, health care, wireless
sensing and networking, and cybersecurity. Ranked among the top 10 engineering schools at public universities nationwide, the
school is home to nine multimillion-dollar interdisciplinary research centers in wireless sensor systems, wireless health,
nanoelectronics, nanomedicine, renewable energy, customized computing, the smart grid, and the Internet, all funded by federal
and private agencies and individual donors.