Implantable Flexible Integrated Circuits Demonstrated by Korean Researchers

Silicon-based flexible large scale integrated circuits (LSI) which can be used for in vivo (implanted) bio-medical wireless communication were successfully developed and tested by a team led by Professor Keon Jae Lee from the Department of Materials Science and Engineering at KAIST, Korea Advanced Institute of Science and Technology.

Silicon-based semiconductors have played significant roles in signal processing, nerve stimulation, memory storage, and wireless communication in implantable electronics. However, the rigid and bulky LSI chips have limited uses in in vivo devices due to incongruent contact with the curvilinear surfaces of human organs. As an example, the researchers say that the artificial retinas recently approved by the U.S. Food and Drug Administration require extremely flexible and slim LSI to incorporate it within the cramped area of the human eye.

Professor Keon Jae Lee's team fabricated radio frequency integrated circuits (RFICs) interconnected with thousand nano-transistors on silicon wafer by state-of-the-art CMOS process, and then they removed the entire bottom substrate except top 100 nm active circuit layer by wet chemical etching. The flexible RF switches for wireless communication were monolithically encapsulated with biocompatible liquid crystal polymers (LCPs) for in vivo bio-medical applications. Finally, they implanted the LCP encapsulated RFICs into live rats to demonstrate the stable operation of flexible devices under in vivo circumstances.

Professor Lee said, "This work could provide an approach to flexible LSI for an ideal artificial retina system and other bio-medical devices. Moreover, the result represents an exciting technology with the strong potential to realize fully flexible consumer electronics such as application processor (AP) for mobile operating system, high-capacity memory, and wireless communication in the near future."

Flexible integrated circuits (ICs, dozens of interconnected transistors) on plastics are not new and have been demonstrated by a number of research teams, but their inaccurate nano-scale alignment on plastics has restricted the demonstration of flexible nano-transistors and their large scale interconnection for in vivo LSI applications such as main process unit (MPU), high density memory and wireless communication. Professor Lee's team previously demonstrated fully functional flexible memory using ultra-thin silicon membranes (Nano Letters, Flexible Memristive Memory Array on Plastic Substrates), however, its integration level and transistor size (over micron scale) have limited functional applications for flexible consumer electronics.

This result was published in the May online issue of the American Chemical Society's journal, ACS Nano (In vivo Flexible RFICs Monolithically Encapsulated with LCP). They are currently engaged in commercializing efforts of roll-to-roll printing of flexible LSI on large area plastic substrates.