In 2011, scientists from Radboud University in Nijmegen (Netherlands) published a paper in Nature, announcing their successful use of ultra-short laser pulses to invert a material’s magnetization status. This breakthrough raised the prospect of optically-written magnetic memory. Replacing today’s spin-polarized electric currents with laser pulses would enable write times to be reduced from nanoseconds (10-9 s) to picoseconds (10-12 s), representing a thousandfold speed increase while also reducing power consumption by a factor of 100.
SPINTROWHAT ?
Spintronics marries electronics and magnetism. While the current electronics is entirely based on the manipulation of the electric charge carried by the electrons, spintronics uses their spin. Electrons have three physical characteristics: their mass, their charge and their spin. For this last intrinsic characteristic, everything happens as if the magnetic moment of the electron was related to the direction of internal rotation of this one around an imaginary fixed axis. For the electrons, the spin can take only two values:
- +1/2 spin said "up"
- or -1/2 spin said "down",
corresponding to the fact that it can only turn in one direction or in the 'other.
This property can be used to obtain new functionalities, for example to code, process or transmit information. A wide variety of innovative devices using electron spin can be realized. These devices combine magnetic materials that serve as a polarizer or spin analyzer and conductive, insulator or semiconductor materials.
Hybrid optomagnetic and spintronic technology
The goal of the Spice project, coordinated by Aarhus University in Denmark, is to apply the experience gained by Dutch physicists at integrated circuit scale and develop a low-consumption (0.6 picojoule per written bit), optically-written eight-bit magnetic memory device. This memory should be viewed as a “proof of concept” of an innovative technology that combines optomagnetism, spintronics and cutting edge electronics manufacturing processes. Within ten years, this technology may be able to meet the need for petabit/s processor memory and exaflop (1018 floating operations /s) datacenters with low carbon footprints.
An optical-spintronic sandwich
The new memory will resemble a sandwich comprising two matching “slices”, one optical, the other spintronic. One of these layers channels laser pulses generated by a separate laser, prepares the optical polarization state and switches them to the desired location on the second slice, thereby writing a data bit. Data is read from memory electrically, in the spintronics layer, as in current MRAM devices.
INAC/SPINTEC, a specialist in MRAM magnetic stacks, is responsible for developing new magnetic tunnel junction materials, in which the storage layers may be written optically. “
We have successfully adapted our stacks, including new ferromagnetic materials compatible with the optical write process”, explains Lucian Prejbeanu, the INAC research scientist responsible for the CEA’s contribution to Spice.
“We still have to develop a substitute for the tantalum hard mask, which is too opaque for the laser beam.” Generic technology
INAC brings SPICE its world class expertise in the design and integration of magnetic tunnel junction-based spintronic memory systems. “Heat-assisted magnetic recording (HAMR) is a high-density magnetic storage technology for hard disks that also uses nanosecond laser pulses to enhance data bit writing”, notes Lucian Prejbeanu. “This technology will soon be released commercially, but it does not use an integrated spintronic+optical approach. This means that SPICE will be a genuine world first!”
“When Spice technology has been validated for memory systems, we may be able to go further, developing integrated solutions with memory, magnetic sensors and radiofrequency oscillators all on the same chip”, predicts Ioan-Lucian Prejbeanu. S
uch is the goal of the GreatEuropean project based on conventional electrically-written spintronic technology, which INAC is coordinating with a view to developing solutions for the Internet of Things. Spice is truly a generic technology!” About SPICE
Gathering five partners from four countries and coordinated by the Aarhus University, the SPICE H2020 project targets to realize a novel integration platform that combines photonic, magnetic and electronic components. From October 2016 until September 2020, the EU is granting SPICE with 3.4 M€.