The researchers developed the method combining screen-printable composite and metallic inks. The devices can be mounted on various supports, including nonplanar surfaces, and the team believes they could enable many IoT (Internet of Things) applications.
Next-generation technology such as automotive radars for self-driving cars, smart buildings and wearable sensors will depend more heavily on the high-frequency millimetre-wave band, including 5G.
To date, large-scale manufacturing approaches to making foldable electronics have focused on developing metallic inks and printing conductive patterns and have overlooked dielectric substrates.
Barriers to the use of substrates such as paper and some polymer films in foldable electronics include constraining and complex fabrication processes that cannot produce multi-layered or ultra-thin flexible devices. These substrates also have a dielectric loss that exceeds requirements for millimetre-wave devices.
Led by Atif Shamim, the KAUST team now claims to have devised a composite ink composed of ceramic particles dispersed in the polymer acrylonitrile-butadiene-styrene (ABS).
According to the researchers, they used the new ink to generate ‘extremely flexible’ large-area dielectric substrates with tuneable lateral dimensions, thickness and permittivity. They screen-printed the ink onto glass and, after drying, peeled off the substrates from the support.
The substrates presented a minimum thickness of a few microns that could be increased through successive printing passes, the team said, as well as exhibiting a low dielectric loss at 28GHz.
After screen-printing a silver nanowire-based ink on the dielectric substrates to build conductive patterns, researchers found that the patterned films maintained high and stable electrical performance when rolled or folded in half — a result of the polymer binder present in the ink.
Furthermore, they retained their performance when incorporated into a four-layer circuit consisting of alternating metal-patterned and dielectric layers. This suggests that the screen-printable inks can be used in multi-layer structures such as printed circuit boards and automotive radars.
For proof-of-concept, the team screen-printed a flexible quasi-Yagi antenna on a dielectric substrate to show that the device performed well in the millimetre-wave band when bent or folded.
“Our approach will be beneficial for novel 5G antennas and accelerate the implementation of 5G,” said KAUST postdoc Weiwei Li.
The team is now exploring potential applications of the approach to other electronic devices. Li said that both inks are compatible with roll-to-roll processing, which could help to meet the demand for wearable sensors at low costs. According to Shamim, fabrication costs will be ‘extremely low’ to the point that devices will become disposable.
Their paper is published in Advanced Materials Technologies.