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Computer Science

Memories of the Future

Scientists at CNRS have worked with the binary coding found in electronic devices to allow for a smoother encryption and viewing of stored data. This promises significant memory optimization in miniature computers.

memories of the future

© V. Garcia, S. Fusil, K. Bouzehouane/Unité Mixte de Physique CNRS/Thales

Tunnel electroresistance cartography of a BaTiO3 thin film (conductive-tip atomic force microscope technique). The different colors correspond to square shaped ferroelectric domains of different polarities rotated at 45° angles.

Two CNRS teams have focused their research on refining the manipulation and readout of polarization and magnetization states used to encode information respectively in ferroelectric and ferromagnetic memory systems. This type of so-called non-volatile memory uses electric and magnetic signals to access data that can be stored long term, even when the device is not powered. Volatile memory, on the other hand, disappears as soon as the computer is off.
Manuel Bibes and co-workers, from CNRS/Thales,1 have made major advances in the use of ferroelectric memory (FeRAM).2 Up to now FeRAM, which is actually faster than the flash memory used in most electronic devices, was hindered by a limited storage density and by a “destructive” data readout process (the voltage sweeps that read the tiny current peaks also destroy the data). To fix this problem, the team showed that the direction of the polarization (0 or 1) may be more simply read in terms of the magnitude of the tunnel current passing across an ultrathin ferroelectric film: It turns out that the amount of tunnel current varies depending on the direction of the polarization within the device. With tunnelling, one can detect these amounts, and decipher the data's binary code. “We have found the right conditions so that the layers can maintain their ferroelectric quality in spite of their very thin dimensions. The main advantage is that one can view the information without destroying it,” explains Bibes.
In a related study, Jean-Yves Bigot's group3 managed to increase the magnetic memory access rate by speeding up the process of magnetization reversal required to view the data. The researchers obtained this by shining very short laser pulses on a thin metallic ferromagnetic film.4 The action takes place within a millionth of a billionth of a second, which is 100,000 times faster than the swiftest devices on today's market. According to Bigot, “the brief laser pulse triggers a magnetization reversal much more effectively than the slower pulses produced by an electric current or a simple magnetic field.”
The goal is to reduce the focusing of the laser beam so that the memory's code may be accessed within an increasingly tiny volume–paving the way for an even further miniaturization of electronic devices, as in the FeRAM/ tunnelling discovery. The market is likely to quickly capitalize on these high-speed technologies, which promise to reduce costs and energy consumption, as well as increase storage density and longevity.

Melisande Middleton

Notes :

1. CNRS / Thales / Université Paris-XI, in collaboration with the University of Cambridge.
2. V. Garcia et al. “Giant tunnel electroresistance for non-destructive readout of ferroelectric states,” Nature, 2009. 460: 81-4.
3. Institut de physique et de chimie des matériaux de Strasbourg (CNRS / Université de Strasbourg).
4. J.-Y. Bigot et al., “Coherent ultrafast magnetism induced by femtosecond laser pulses,” Nature Physics, 2009. 5: 515-20.

Contacts :

Manuel Bibes,
Thales, Palaiseau.
Jean-Yves Bigot,
IPCMS, Strasbourg.


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