Roll-process technology for flexible electronics

Korean scientists have developed highly productive roll-process technology that can continuously transfer and package a range of large-scale integrated circuits (LSI), a breakthrough that could help realize the next generation of flexible electronics, including application processors, high-density memories and high-speed communication devices. With such roll-processing being seen as a core LSI technology to improve the commercialization of wearable computers, the team resolved previous challenges around the nanofabrication process for plastics and to help realize the interconnection of flexible LSI with flexible displays, batteries and other peripheral devices.

In this study, which was reported in the journal Advanced Materials [Kim et al Adv. Mater. (2016) DOI: 10.1002/adma.201602339], the team, led by Keon Jae Lee from the Korea Advanced Institute of Science and Technology, and with Jae-Hyun Kim from the Korea Institute of Machinery and Materials, fabricated NAND flash memories on bulk silicon wafer using standard processes for making semiconductors, before eliminating the thick handle wafer to leave a nanometer-thick circuit layer. They next simultaneously transferred and interconnected the ultrathin device on a printed circuit board through roll-based thermo-compression bonding using anisotropic conductive film (ACF) as a flexible packaging material. The silicon-based flexible NAND memory was able to show stable memory operations and interconnections even after undergoing severe bending, while the circuitry had significant flexibility and stable ACF interconnections.

“Our results may open up new opportunities to integrate silicon-based flexible LSIs on plastics with the ACF packing for roll-based manufacturing”Keon Jae Lee

The technology showed outstanding bonding capability for continuous roll-based transfer and excellent flexibility of interconnecting core and peripheral devices. They confirmed the reliable operation of the flexible NAND memory at the circuit level by programming and reading letters in ASCII codes. As Keon Jae Lee points out, “Our results may open up new opportunities to integrate silicon-based flexible LSIs on plastics with the ACF packing for roll-based manufacturing”.

LSI consist of over a thousand nanotransistors integrated for computing, memory and communication, and flexible LSI are key to wearable/flexible computers primarily as their main functions are mostly operated through the integration of high-speed nanoscale transistors. The devices, along with the flexible display and communication technology, can be interconnected each other for potential innovative future flexible consumer electronics such as rollable computers, wearable smart devices, and implantable small, thin, flexible, non-breakable, light biomedical devices.

The scientists are now looking at how to realize fully operational flexible electronic systems, including the integrated components of flexible LSIs, displays, batteries and other devices, to demonstrate the credibility of mass commercialization of flexible electronics.