Here, market research firm IDTechEx shares its insight on the evolution of FHE whereby an integrated circuit is combined with multiple other elements such as printed sensors, an antenna, a thin film battery and even thin film PV.
Fundamental to FHE is mounting an integrated circuit (IC), manufactured separately using photolithography, onto a flexible substrate and linking it to printed interconnects. This presents some technological challenges: firstly, silicon dies are rigid, and thus have a completely different form factor and thermal expansion coefficient to the underlying flexible substrate; secondly, alternative semiconductors to silicon, such as metal oxides and organic semiconductors, have much lower mobilities and are difficult to manufacture with sufficiently high yields. These technical challenges and possible solutions, along with other technologies required for FHE circuits, are identified and comprehensively evaluated in the new IDTechEx report: “Flexible Hybrid Electronics 2020-2030: Applications, Challenges, Innovations and Forecasts”.
Packaged ICs: a temporary solution
An interim strategy is to solder a conventional packaged rigid IC to a (usually stiffened) flexible substrate. Such circuits are generally referred to as flexible printed circuits (FPCBs) despite having etched interconnects. Unfortunately, mounting a packaged IC substantially impedes flexibility and removes the possibility of R2R manufacturing.
One solution is to use bare dies, a strategy that has been employed for years in RFID tags. These have a very small (< 1 mm2) IC attached at two points using a conductive adhesive to an antenna. However, this application avoids two of the difficulties associated with adding larger, more capable ICs. Firstly, the ICs are so small that their flexibility is almost irrelevant at any realistic bending radius. Secondly, large attachment pads are viable since only two electronic connections are needed.
However, as the ICs become more capable (for example those that incorporate Bluetooth or memory) and hence larger, difficulties begin to arise. Firstly, their lack of flexibility becomes a problem for FHE applications since they cannot conform to the underling substrate.