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Flexible Organic Flash Memory for Foldable and Disposable Electronics Developed

07 November 2017

This is foldable flash memory. Source: KAISTThis is foldable flash memory. Source: KAIST

A KAIST team reported ultra-flexible organic flash memory that is bendable down to a radius of 300 μm. The memory exhibits a significantly-long projected retention rate with a programming voltage on par with the present industrial standards.

A joint research team led by Professor Seunghyup Yoo of the School of Electrical Engineering and Professor Sung Gap Im of Department of Chemical and Biomolecular Engineering said that their memory technology can be applied to non-conventional substrates, like plastics and papers, to demonstrate its feasibility over a wide range of applications.

Dr. Seugwon Lee and Dr. Hanul Moon were the lead authors of the paper on this research.

Flash memory is a non-volatile, transistor-based data-storage device that has become essential in most electronic systems in daily life. With straightforward operation mechanisms and easy integration into NAND or NOR array architecture, flash memory has been established as the most successful and dominant non-volatile memory technology by far.

Despite promising demonstrations in the early stages of organic electronics, the overall progress in this field has been far slower than that of thin-film transistors (TFTs) or other devices based on flexible materials. It has been challenging to develop the flash memory that simultaneously exhibits a significant level of flexibility and performance. This is mostly due to the scarcity of flexible dielectric layers, which are responsible for the tunneling and blocking of charges.

The solution processing used for the preparation of most of the polymeric dielectric layers also makes it difficult to use them in flash memory due to the complexity involved in the formation of the bilayer dielectric structure, which is the key to flash memory operations.

The research team tried to overcome these hurdles and realize highly flexible flash memory by employing thin polymeric insulators grown with initiated chemical vapor deposition (iCVD), a vapor-phase growth technique for polymers that was previously shown to be promising for the fabrication of flexible TFTs. It was shown that these iCVD-based polymeric insulators when coupled with rational device design and material choice can make a significant contribution to flash memory as well.

Memory using conventional polymer insulating films has required a voltage as high as 100 volts in order to attain long memory retention. If the device is made to operate at a low voltage, the retention period of less than a month is problematic.

The KAIST team produced flash memory with programming voltages around 10 volts and a projected data retention time of over 10 years while maintaining its memory performance even at a mechanical strain of 2.8 percent. This is a significant improvement over the existing inorganic insulation layer-based flash memory that allowed only a 1 percent strain.

The team demonstrated the virtually foldable memory devices by fabricating the proposed flash memory on a 6-micrometer-thick ultrathin plastic film. In addition, it succeeded in producing them on printing paper, which opens a way for disposable smart electronic products like electronic paper and electronic business cards.

Professor Yoo said, “This study well illustrates that even highly flexible flash memory can be made to have a practically viable level of performance so that it contributes to full-fledged wearable electronic devices and smart electronic paper."

The paper on this research was published in Nature Communications.

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