The Air Force Bets on a Bright Future for Flexible Hybrid ElectronicsJune 12, 2020 by Gary Elinoff
With the ability to conform to any shape, flexible hybrid electronics will animate devices with unprecedented spatial adaptability.
NextFlex, a flexible hybrid electronics (FHE) manufacturing innovation institute, has secured a seven-year, $154 million grant from the Air Force Research Laboratory (AFRL) and the Office of the Secretary of Defense’s (OSD) manufacturing technology program. The aim is to support NextFlex’s efforts in developing flexible hybrid electronics innovations with particular attention to military applications.
What exactly are flexible hybrid electronics and how do they compare to flexible electronics?
What are Flexible Hybrid Electronics?
Flexible, hybrid, and printed electronics are now being designed into a wide range of products in every segment. The term “hybrid” refers to designs that have both printed components and CMOS-based components. The diagram below illustrates the idea of FHE.
The architecture of flexible hybrid electronics. Image used courtesy of NextFlex
The antenna and circuit traces are painted, while the processor and memory are CMOS.
This technology can be the basis for an inexpensive heads up display for pilots and others. And, as is so often the case in technology devised originally for the military, such a device it will undoubtedly find eventual civilian applications.
FHE may always lag behind electronics mounted on rigid boards. As the flexible substrate is bent, its possible that traces will change position in relation to each other, which will affect propagation speed and signal interference. Heat generation may be tougher to deal with, and even if the rest of the system can bend, the rigid ICs themselves, of course, won’t be able to.
Flexible Electronics and Flexible Hybrid Electronics—What’s the Difference?
Flexible electronics can be incredibly useful with wearable electronics, especially as they relate to prosthetics and medical sensing. But we seldom see flexible electronics venture beyond the realm of sensors and displays.
While CMOS fabrication processes are in the nanometer range and can operate at GHz frequencies and higher, thin-film transistors are a thousand times slower, and their fabrication processes are in the tens of micrometers.
Researchers from Arizona State University explain, however, that flexible hybrid electronics expand the application possibilities of flexible electronics by combining conventional rigid ICs with printed electronics on a flexible substrate.
Diagram of flexible hybrid electronics. Image used courtesy of Arizona State University
"This hybrid approach combines the processing and storage capabilities of silicon ICs with the physical and cost benefits of flexible electronics," the researchers explain. "Hence, FHE exhibit an inherent design trade-off between flexibility and computational efficiency (more rigid ICs)."
Because FHEs make it possible to incorporate regular ICs onto flexible substrates, designers can move beyond the severe limitations inherent to flexible electronics. The subsystems in an FHE device related to power and energy storage include energy harvesting technology, wireless power, batteries, and supercapacitors.
The Need for Improved Substrates and a Substitute for Solder
Present-day flexible printed circuitry is generally mounted on polyimide (PI), which is orange colored. This prevents its use in optical applications. It is also expensive, and worst of all, it doesn’t stretch. This latter fault precludes its use in e-textiles or wearable skin patches.
Thus, a move to such substrates as PET (polyethylene terephthalate), PEN (polyethylene naphtholate), and stretchable TPU (thermoplastic polyurethane) will be necessary. The problem is that these more desirable substrates can’t take the heat of soldering.
PI-based flexible PCB (left) and a PET substrate-based transparent printed electronics circuit (right). Image used courtesy of IDTechEx
As described in a report published by IDTechEx, expanding practical applications of FHE will hinge on developing methods to mechanically and electrically attaching ICs to newer substrates.
A similar market research study recently addressed the shortcomings—and promise—of FHEs, which may include soldering a conventional packaged rigid IC to a flexible substrate, creating flexible ICs from thinned silicon, or using natively flexible ICs made from metal oxide.
An Ongoing Partnership
The seven-year agreement between the Air Force Research Laboratory and NextFlex underscores the importance of FHE to the military. It will enable the NextFlex partnership to extend its project support for FHE manufacturing in concert with the DoD and other government entities.
Dr. Richard Vaia, Chief Scientist for the Materials and Manufacturing Directorate at AFRL, expressed promise in the partnership, especially in developing a flexible hybrid electronic manufacturing ecosystem.
“Today these technologies are not only providing component solutions to our current platforms but are revolutionizing our design concepts for future transformation capabilities for 2030," he says.
While designers encountering this new technology must consider its many limitations, devices that can be bent and shaped surely provide a unique kind of electronic utility.
What types of product innovations do think that FHE will make possible? Please share your comments below.