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    Better Than SST: Energy-Efficient Computer Memory Uses Voltage Rather Than Current
    By News Staff | December 16th 2012 10:48 AM | Print | E-mail | Track Comments

    By using voltage instead of current, researchers say they have made major improvements to magnetoresistive random access memory - MRAM -  a faster, higher-capacity class of computer memory.

    Current, magnetic memory is based on spin-transfer torque (STT), which uses the magnetic property of electrons - spin - in addition to their charge. STT utilizes an electric current to move electrons to write data into the memory.  

    STT is superior in many ways to other memory technologies but its electric current–based write mechanism still requires a lot of power and that generates heat when data is written into it. 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.

    The group at UCLA deem their improved version of  magnetoresistive random access memory MeRAM - magnetoelectric random access memory - and say it has potential for almost all electronic applications as well as data storage.  They say MeRAM's key advantage is that it combines extraordinarily low energy with very high density, high-speed reading and writing time, and non-volatility — like hard drives and flash memory, any widepsread solution will need to retain data when no power is applied, .

    MeRAM replaces 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 .  

    "The ability to switch nanoscale magnets using voltages is an exciting and fast-growing area of research in magnetism," said Pedram Khalili, UCLA research associate in electrical engineering and project manager for the UCLA–DARPA research programs in non-volatile logic. "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, 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."   

    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.

    Presented at the 2012 IEEE International Electron Devices Meeting in San Francisco,