Researchers in South Korea have developed a continuous roll-processing technology that transfers and packages flexible large-scale integrated circuits (LSI), the key element in constructing the computer's brain such as CPU, on plastics to realise flexible electronics.

Highly productive roll-processing is considered a core technology for accelerating the commercialisation of wearable computers using flexible LSI. However, realising it has been a difficult challenge not only from the roll-based manufacturing perspective but also for creating roll-based packaging for the interconnection of flexible LSI with flexible displays, batteries, and other peripheral devices.

To overcome these challenges, researchers from the Korea Advanced Institute of Science and Technology (KAIST) and the Korea Institute of Machinery and Materials (KIMM) started fabricating NAND flash memories on a silicon wafer using conventional semiconductor processes, and then removed a sacrificial wafer leaving a top hundreds-nanometre-thick circuit layer. Next, they simultaneously transferred and interconnected the ultrathin device on a flexible substrate through the continuous roll-packaging technology using anisotropic conductive film (ACF).

EETA roll process 01 Figure 1: The flexible silicon NAND flash memory is attached to a 7mm diametre glass rod. (Source: KAIST)

The final silicon-based flexible NAND memory successfully demonstrated stable memory operations and interconnections even under severe bending conditions. This roll-based flexible LSI technology can be potentially utilised to produce flexible application processors (AP), high-density memories, and high-speed communication devices for mass manufacture.

“Highly productive roll-process was successfully applied to flexible LSIs to continuously transfer and interconnect them onto plastics. For example, we have confirmed the reliable operation of our flexible NAND memory at the circuit level by programming and reading letters in ASCII codes. Out results may open up new opportunities to integrate silicon-based flexible LSIs on plastics with the ACF packing for roll-based manufacturing," said KAIST Professor Keon Jae Lee.

“We employed the roll-to-plate ACF packaging, which showed outstanding bonding capability for continuous roll-based transfer and excellent flexibility of interconnecting core and peripheral devices. This can be a key process to the new era of flexible computers combining the already developed flexible displays and batteries," said KIMM Professor Jae-Hyun Kim.