Self-Assembly Lowers PRAM Operating Currents

By harnessing self-assembling nanomaterials, scientists have made flexible phase-change random access memory devices more feasible.

AsianScientist (Jun. 23, 2015) – Using self-assembling silicon nanoinsulators, researchers have successfully lowered the operating current of a flexible phase-change random access memory (PRAM) device. Their results, published in two papers in ACS Nano, support PRAM as one of the strongest candidates for next-generation nonvolatile memory for flexible and wearable electronics.

Although PRAM has the advantage of large cycling endurance, high speed and excellent scalability, the high operating currents required to reset memory hinders practical applications.

One solution would be to decrease cell size to the sub-micron region as in commercialized conventional PRAM. However, the scaling to nano-dimension on flexible substrates is extremely difficult due to soft nature and photolithographic limits on plastics.

Recently, a team led by Professors Lee Keon Jae and Jung Yeon Sik of the Department of Materials Science and Engineering at Korea Advanced Institute of Science and Technology (KAIST) has developed the first flexible PRAM enabled by self-assembled block copolymer (BCP) silica nanostructures with an ultralow current operation on plastic substrates.

BCP is the mixture of two different polymer materials, which can easily create self-ordered arrays of sub-20 nm features through simple spin-coating and plasma treatments. The BCP silica nanostructures successfully lowered the contact area by localizing the volume change of phase-change materials and thus resulted in significant power reduction.

Furthermore, the ultrathin silicon-based diodes were integrated with phase-change memories (PCM) to suppress the inter-cell interference. The resulting device demonstrated random access capability for flexible and wearable electronics.

Another way to achieve ultralow-powered PRAM is to utilize self-structured conductive filaments (CF) instead of the conventional resistor-type heater. Using a self-structured CF nanoheater developed from a unipolar memristor, the researchers were able to strongly heat phase-change materials due to the high current density passing through the nanofilaments.

Their results show that the sub-10 nm filament heater—without using expensive and non-compatible nanolithography—could achieve nanoscale switching volume of phase change materials. The resulting device had a PCM writing current of below 20 uA, the lowest value among top-down PCM devices.

In addition, due to self-structured low-power technology compatible to plastics, the research team has recently succeeded in fabricating a flexible PRAM on wearable substrates.

“The demonstration of low power PRAM on plastics is one of the most important issues for next-generation wearable and flexible non-volatile memory. Our innovative and simple methodology represents the strong potential for commercializing flexible PRAM,” said Lee.

The articles can be found at:
Mun et al. (2015) Flexible One Diode-One Phase Change Memory Array Enabled By Block Copolymer Self-Assembly.
You et al. (2015) Self-Structured Conductive Filament Nanoheater for Chalcogenide Phase Transition.


Source: KAIST.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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