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Posted: Oct 25, 2013

Rewritable, transferable, and flexible sticker-type organic memory

(Nanowerk Spotlight) Future electronics will look nothing like today's rigid metal and plastic boxes, be they the latest smartphones, tablets, digital cameras or any other computer device. Instead, they will be extremely light, soft, flexible, transparent, and integrated into everyday objects like paper, clothes, leather gloves, diapers, or packaging material (read more: "Nanotechnology electronics at the tip of your gloved finger"). If you want to go really futuristic, think electronic skin, health monitor tattoos on teeth ("Graphene nanosensor tattoo on teeth monitors bacteria in your mouth"), or sensor films placed directly onto internal organs (see: "Electronic sensing with your fingertips").
These advanced electronic systems will be fabricated on soft substrates by integrating multiple crucial components such as logic and memory devices as well as their power supply. Organic memory with a simple sandwich structure has been considered a promising information storage element in future soft electronics for its exceptional merits such as low production cost, mechanical elasticity, flexibility, low-temperature processing and roll-to-roll printability. However, so far, rewritable organic memories have been fabricated mostly on rigid, flat, and smooth substrates, such as metal, glass, plastic and silicon, which greatly limits their superior soft and flexible merits.
Due to the fact that organic films are often fabricated by solution processes – i.e., spin-coating or ink-jet printing – there exists a great hurdle in constructing flexible organic memory in stack or 3D architecture. The reason for this is that the use of solution processes can result in severe damage to the bottom soft organic device or substrate arising from the solvent used for the vertical integration of the subsequent devices.
Therefore, for future applications, it is essential to establish a proper fabrication strategy for rewritable organic memory onto diverse substrates or devices.
In new work, a team of researchers in Taiwan has reported a methodology to overcome the above-mentioned challenges. Reporting their work in the October 18, 2013 online edition of Advanced Functional Materials ("Rewritable, Moldable, and Flexible Sticker-Type Organic Memory on Arbitrary Substrates"), the team has, for the first time, successfully demonstrated a rewritable, transferable, and flexible sticker-type organic memory on arbitrary nonconventional substrates through a simple, low-temperature and cost-effective one-step methodology.
re-writable sticker-type organic memory
a) Schematic of the fabrication processes for the sticker-type organic memory. b) Arrangement for electrical measurement of re-writable sticker-type organic memory along with the chemical structures of PMMA and P3HT. c) Photo of as-prepared re-writable sticker-type organic memory under bending. (Reprinted with permission from Wiley-VCH Verlag)
The researchers demonstrate that this re-writable organic memory can be simply stuck on various desired substrates, including rigid, flexible, non-planar, and rough substrates, and so forth, promising that the information storage devices can be greatly broadened in diversified future applications.
"Compared to traditional bottom-up solution processes for organic bistable memory, the advantages of our transferable and flexible memory device include several unique aspects," Yang-Fang Chen, a professor in the Department of Physics at National Taiwan University, tells Nanowerk. "Most importantly, the transferable and self-adhered features of the organic memory pave an easy route to vertically integrate digital organic memories with other flexible organic devices with minimal solvent issue; hence harsh synthesis and unaccustomed fabrication steps on non-conventional substrates can be avoided."
Secondly, as Chen notes, the combination of organic memory and protective layer for transferring graphene electrode eliminated the need for chemical treatment processes for the graphene’s protective layer. With the flexible and adhesive graphene-electrode underlay, the presented memory can be simply molded and functioned on desired non-conventional substrates, including non-planar and soft ones. This versatile substrate selection advantage might greatly broaden memory applications.
Thirdly, considering the cost-effective production and because both the organic materials and the bottom CVD-graphene possess the capability for roll-to-roll processes, the resulting memory is suitable for industrial large-area printing manufacture.
CVD-grown graphene with a unique ultrathin feature is a crucial conductive material in this novel label-like memory. Due to its good conductivity, mechanical flexibility together with low-cost and capability for roll-to-roll fabricating features, the researchers chose it as their flexible conductive layer for the organic memory.
"In particular" says Chen, "utilization of its astonishing mechanical properties and strong attractive interfacial adhesion force make CVD-grown graphene an ideal interfacial electrode for adhering to non-conventional surfaces and flexible electronic applications. Moreover, its unique ultrathin characteristic can significantly reduce our device thickness, which is beneficial for adhesion and bending operation."
Thanks to its combination of low fabrication cost, facile processes, and mechanical flexibility combined with high-speed electrical access capability, application areas for this flexible memory could potentially be found in low-cost digital information storage area such as smart labels, e-tags, and portable disks. By introducing an antenna circuit it could be accessed wirelessly. Also, it is nonvolatile, which means it can keep the data without a battery.
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