Printed and flexible electronics: highlights from 2020

Flexible silicon

An especially exciting technical development is fully flexible thinned silicon integrated circuits (ICs). These support capabilities such as Bluetooth previously associated with packaged ICs to be mounted on flexible/curved substrates, enabling a wide range of novel form factors. The flexible ICs are produced by grinding down a convention silicon die to as thin as 3um before encapsulating it in polyimide, and can have a bending radius as low as 1mm.

Flexible mounted components are key components of the emerging manufacturing trend known as ‘Flexible Hybrid Electronics’ (FHE). FHE seeks to resolve some of the compromises inherent in printed electronics by combining mounted components (such as flexible ICs) with printed conductive traces on a flexible substrate. While wearable electronics and smart packaging are forecast to be the most promising applications, FHE can be applied across many sectors.

Advances in OLED materials

Turning to OLED materials, the dominant technical trend is the emergence of a new class of materials that promise lower-costs, high efficiency, and a wider colour gamut. Known as triplet activated delayed fluorescent (TADF) materials, they represent an entirely new approach to ensuring that all the incoming charges are utilised in producing light.

Orange emitters, using materials developed by Japanese film Kyulux, have already been commercialised for small displays, with other colours set to follow in 2021.

Additionally, we were especially impressed this year by a novel approach to the host materials, which generally receive less research effort than their emissive counterparts. Developed by early-stage US firm Molecular Glasses, this innovative host material increases the solubility of dopant molecules, be they fluorescent, phosphorescent or TADF, while retaining charge transport capabilities.

This is achieved by making the host material from a wide range of subtly different chemical structures, known as an isomeric mixture. As such, crystallisation of the host material is prevented and emissive dopant molecules are more evenly dispersed, thus avoiding aggregation. This in turn reduces interaction between charges and excitons prior to light emission, improving luminescent efficiency.

Alternatives to particle based conductive inks

Another exciting and innovative technology, again material based, is an alternative to stretchable conductive inks. Rather than combining silver flakes with elastomeric binders, early-stage company Liquid Wire use a metal gel based on a gallium/indium alloy that is liquid at room temperature. As such, this stretchable conductor does not fatigue following repeated stretching.

Furthermore, as a gel it avoids the difficulties in attaching rigid components with different thermal and mechanical properties to the stretchable, polymeric substrate. The circuits are constructed by embedding the metal gel within stacked sheets of stencilled TPU.

Liquid Wire’s metal gel and associated component attachment technology is initially targeted at wearable applications, such as monitoring electrical signals inside the body. Wearable electronics are a rapidly growing area, with applications in healthcare, therapeutics, and fitness.

Impact of COVID-19 on printed and flexible electronics

In 2020 some companies have pivoted to providing solutions to address the COVID-19 pandemic. For example, within wearable electronics, remote patient monitoring, including electronic skin patches has seen strong interest for monitoring a patient’s temperature remotely, the benefit being that the patient does not need to come into contact with healthcare professionals to take their temperature which may expose them to the virus. Furthermore, conductive ink has been used in sensor test systems as part of a system to detect infections, including COVID-19.

In other areas materials such as nano copper have been developed for their anti-viral benefits, with equipment providers 3D printing the material onto surfaces such as door handles. In retail environments, printed force sensors have been applied into mats to alert shoppers where they are standing too close to each other.

Overall, 2020 has been an exciting year for printed electronics, with an increased focus on the aspects, such as flexible hybrid electronics, that bring a real value proposition to manufacturers and ultimately consumers. IDTechEx expect printed/flexible/hybrid electronics to be increasingly adopted in commercial applications including smart packaging, wearables, automotive interiors, and consumer goods over the next few years.