When the printing industry thinks about printed electronics—when it thinks about it at all—it has traditionally been in the context of RFID (radio frequency identification) tags, printed antennas that facilitate processes like inventory tracking. RFID never quite lived up to the potential that was forecast a decade ago, but there is a whole new set of applications for printed electronics—some of which sound downright science-fictiony.
Printed electronics systems use conductive, semiconductive, and/or dielectric ink to create a printed circuitboard. Basically, you print circuitry, said Don Carli, curator of GAAmericas Fourth Printed Electronics, Functional Printing & Intelligent Packaging Symposium, held June 23–24, 2014, at Clemson University in Clemson, S.C. This printed circuitry can, said Carli, “do more than just radiate RF, but can also store information, [and include] capacitors, supercapacitors, batteries, sensors, actuators, transducers, logic—a whole variety of components can actually be printed.”
Printing conductive inks on polymer-based substrates—typically a type of polyethylene terephthalate (PET) or, more promisingly, a new ultra-thin flexible glass called Willow Glass being developed by Corning—has advantages over traditional silicon-based circuitry. It’s more flexible (physically, not just in terms of applications), easier to produce, can be printed from rolls, is generally less constrained in terms of size, and can conceivably be produced using a “white paper in” approach à la high-volume inkjet: a blank roll of substrate goes in, all the components are laid down, and out comes a complete circuitboard.
When Carli curated his first printed electronics symposium in 2006, much of the discussion was purely theoretical and, in fact, his first keynote speaker was cyberpunk novelist Bruce Sterling. The second symposium saw early pilot projects, and the third showed how the pilots were helping people learn what to do and what not to do. Which brings us to the fourth symposium, which showcased the emergence of concrete applications and industries that have become excited by the prospects. Such as...
Tags and Labels
“Cold-chain” applications are common in food and pharmaceutical packaging and shipping. Perishable drugs and foods need to be maintained at a certain temperature, and thus need to be transported with a way of determining if there has been any variation in temperature. If there is any doubt, the drug or food must be discarded—a considerable waste and expense. Printed smart tags can log temperature continuously for up to a month, and the data can be stored and read with a smartphone using near-field communication (NFC). This can replace much more expensive ways of ensuring that the cold chain was not broken.
Sensors and Wearables
Printed electronics can incorporate sensors, which can be implanted into impact-sensing helmets, which have sports and military applications. Printed floor sensors can be installed in hospitals or nursing homes and gather data about potential pathologies detectable by changes in patients’ gaits, such as certain forms of dementia. They can also be used to predict when an elderly patient may be likely to suffer a fall.
A class of sensors referred to as wearables is also becoming a hot application. In one example, a company called Electrozyme has developed a screen-printed biosensing tattoo that is applied like any normal temporary tattoo. The tattoo communicates via NFC with a watch, armband, or other wearable monitor and can analyze the tattooee’s sweat to glean data about metabolic functions that other types of monitors can’t measure.
Any time you’re going to do a gym workout, said Carli, “slap on a tattoo and now it’s monitoring not just heart rate, but ketone levels in your blood, ammonia, hydration levels.” It has applications in sports, health and wellness, the military—any time you’re putting people in stressful situations or where cognitive function is potentially affected by hydration.
In the early 2000s, there were many companies developing flexible displays. This process involved both sending data to a polymer-based substrate as well as finding a way to have the substrate generate light so the display could be read. This led to the development of organic light-emitting polymers (OLEPs) and organic light-emitting diodes (OLEDs). After a while, some researchers decided to concentrate solely on light-generation. Much of the work in this area is printed electronics-based, with one variant utilizing LED-based inks whose pigments are actually tiny components of light-emitting diodes. When you deposit these inks on a conducting substrate, you can create a flexible light source.
“Consider the amount of energy in a building that is allocated to lighting,” said Carli. “Consider a building that has a 2x2 ceiling grid with drop-in fixtures, like fluorescents. Now imagine that the grid is just an inductive power grid that works the same way that wireless [phone] chargers work. A 2x2 tile that’s dropped in has a skin on it that is an organic light-emitting polymer. Now the tile is the light. It will last for 25 years, and it absolutely sips energy.” This has tremendous potential for transforming ambient lighting and even architecture. “It just changes the form factor of lighting.”
Automotive and Aerospace
If you look at the dashboard of your car, you’ll notice a wide array of lights, buttons, switches, and knobs. Automotive manufacturers such as BMW and Ford, said Carli, “see printed electronics giving them the opportunity to eliminate bulbs and switches and wiring harnesses, so now the surface is capable of being one big switch.” A surface can also be subdivided into individual touch controls that activate different functions. There are similar applications in aerospace—aircraft controls, for example.
The Cyber House Rules
Printed electronics is also said to be a precursor to what has been called “the Internet of things,” or embedding tags or sensors in the objects in our daily lives so they are interconnected via the Internet. Or, to use the lingo, parts of cyber-physical systems.
“The biggest challenge remains, how do you get sensors deployed widely and cheaply enough?” said Carli. “Printing them may be the way, and [printed electronics’] potential to produce sensors at incredibly low costs in very large volumes is going to be required for the Internet of things.”
This all begs the question: what’s in it for the commercial printing industry?
How Green Is My Field?
“The first year I did this symposium, it was basically a shot across the bow to an industry that saw itself in decline, bemoaning their fate,” said Carli. “I was saying, ‘Well, maybe if you think about printing more broadly, you might find that there are markets that are growing at double digits year over year, that could become multi-billion-dollar industries within the next five to 10 years.’ You might want to get yourself oriented toward entering that field.”
Printed electronics is not the kind of thing—like, say, wide-format printing—that an offset or digital printing shop can just add in a corner of the shop floor. “This requires a ‘greenfield,’” said Carli. A greenfield, Wikipedia tells us, is “a project that lacks any constraints imposed by prior work.” Meaning, added Carli, “there is no way you bolt this onto an existing printing company.” One success story in this area is Taylor Corporation, a large commercial printer which in 2005 created a greenfield printed electronics company called Soligie, which is still in business.
The rub is that getting into printed electronics is less about adding equipment and more about seeking out the right technical expertise. “You do need materials scientists and industrial engineers,” said Carli. “People with advanced degrees, and maybe a few PhDs.” Which is exactly what Taylor had done. “It’s an order of magnitude more extreme a leap than was the case for commercial printers thinking, ‘I’ll get into digital printing.’”
Speaking of equipment, just what type of presses are we talking about? Offset and electrostatic presses by their very properties are not well-suited for printed electronics applications. As it turns out, however, gravure is. “You can create circuit traces that have incredibly detailed geometries,” said Carli. “Using electron-beam and laser engraving techniques, you can create circuit traces that have very high edge acutance and feature sizes on the order of 10 to 50 microns without difficulty.”
If you know what any of that means, maybe there is a future for you in printed electronics.
Anyway, gravure has another advantage: it supports just about any ink you might need to use—solvent-based, water-based, you name it.
Inkjet is also used for certain aspects of printed electronics, especially prototyping.
Then there are presses that are configurable to support any kind of printing process. Omet manufactures a reconfigurable press that allows users to swap printing units in and out as they’re needed. For example, “you can configure your press with two gravure units, two flexo units, and 2 inkjet units,” said Carli. “That’s kind of attractive. If you’re printing an antenna, maybe you do want rotary screen. On the other hand, you may need fine traces for doing logic, so you’d use gravure.”
At the End of the Day
“If you wait until you hear the revolution outside your door, it’s usually too late,” said Carli.
While it’s true that much of the promise of printed electronics is still in the sci-fi novel phase (take, for example, the concept of energy harvesting, whereby you can conceivably have a mobile phone that is powered by “sucking” ambient energy—the WiFi, cellular, radio, and other transmissions—around it. Don’t look for this feature in the next iPhone, but perhaps some day), some are in fact here today.
At present, the printers who have been the most interested in printed electronics are packaging printers, and “smart packages” are a top application in this area. Smart packages, in essence, are those that have an ability “sense” their environment, such as temperature, motion, magnetic fields, light, heat, x-rays, UV light—whatever they are required to sense. And the value is accessing and analyzing this data.
The difference between what we think of as “printing” and printed electronics is that the former can be considered “the graphic embellishment of surfaces” while the latter is “the functional enhancement of surfaces.”
At the end of the day, it’s really just printing—applying an ink to a substrate. But the devil is in the details.