A voltage applied across a magnetic tunnel junction increases the
device’s energy efficiency, thus enabling smaller devices — potentially as
small as 5 nanometers — for higher density data storage.
Operating tiny magnetic memories under electrical fields reduces power
demand and could enable storage and retrieval of data at much higher speeds
than conventional devices
Random-access memory (RAM) is a
fast electronic device used in computers to temporarily store data. Traditional
RAM is based on the flow of electrical current for data processing. To make RAM
faster, more energy efficient and capable of storing more information in a
smaller volume, hardware developers are investigating RAM based on magnetic
fields. Miniaturization of these devices, however, is hampered by thermal
instabilities. Hao Meng and his co-workers at the A*STAR Data Storage Institute
have now shown how electric fields can help to circumvent this instability in
tiny magnetic memories, as well as reduce operating power1. “This means more information
can be stored in a single chip at a cheaper price,” says Meng.
Meng and his team investigated a
type of memory that incorporates so-called ‘magnetic tunnel junctions’ (MTJs).
Other researchers have previously observed electric-field induced improvements
in MTJs, but only in fairly large devices — about 7 micrometers across. Large
structures limit the writing speed and suffer from poor compatibility with
other electronic components. Meng and his team demonstrated that the concept is
also applicable to smaller and faster MTJs that can be integrated more easily.
MTJs are an ideal building block
for magnetic memories because of their simplicity and large output signal. In
general, they consist of just two magnetic layers separated by a thin
insulating barrier (see image). A current passing through the device writes the
binary information by controlling the direction of the magnetization in one of
the magnetic layers. This process stores information as either a ‘one’ or a
‘zero’, depending on whether the induced magnetization is parallel or
antiparallel to the magnetization of the second magnetic layer. A measurement
of the resistance across the intermediate barrier can then read out the
information as it is needed.
The researchers are working to
make MTJs smaller so that they can squeeze in more information. However, smaller
devices require larger current densities to switch the magnetization: this
leads to heating and makes them less efficient. As a workaround, Meng and his
co-workers applied just 0.2 volts across electrodes attached to each side of a
150-nanometer MTJ made of CoFeB-MgO. This reduced the magnetic field required
to switch the magnetization by as much as 30% which, in turn, decreased the
writing current density.
“Such devices could improve the
data transfer rate; that is, how fast you can copy your files from one device
to another,” says Meng.
The A*STAR-affiliated researchers
contributing to this research are from the Data Storage Institute
References
- Meng, H., Sbiaa, R., Akhtar, M. A. K., Liu, R.
S., Naik, V. B. & Wang, C. C. Electric field effects in low resistance
CoFeB-MgO magnetic tunnel junctions with perpendicular anisotropy. Applied
Physics Letters 100,122405 (2012). | article
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