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Printed Electronics: How 1950s Inkjet Technology is Reshaping our Future

“I have successfully checked in for my upcoming flight” and with that a dusty plastic relic imprisoned in the far corner of the home office whirs suddenly back to life. The sounds of repetitious friction and subtle clicking is a reminder of days past before – smartphones and tablets, when taking information mobile meant recording it to paper rather than swiping through an app. I can’t help but wonder if the days of printing at home are numbered, but it’s clear to me that this patriarch of inkjet technology is inspiring a whole new generation of product innovation. 

The notion of printing through the controlled flow of ink dates back to the late nineteenth century, but the race to perfect this technology didn’t heat up until the 1950s – with the introduction of the first commercial computers. Pioneers at Canon, Hewlett-Packard, Epson, and IBM discovered that vaporizing ink formed tiny bubbles that propel it onto the paper. With improved electro-mechanical controls, the first commercial inkjet printers were marketed throughout the late 1970s and 1980s. By 1990, homes everywhere were replacing their low quality dot-matrix dinosaurs with brand new, quiet color inkjets.

Fast forward to today: two-thirds of the articles in my news feed contain the words wearable or flexible. It seems that consumers are enamored with the idea of everyday technology disappearing from view while simultaneously magnifying its impact on our lives. Maybe we’re finally getting the ubiquitous invisible design that decades of science fiction have promised. But what enablers are at the heart of that transition?

 

Flexible Circuits

The worlds of fashion and electronics are converging. Technology giants like Google and Samsung are now designing high-tech eyewear, watches, and bracelets. Meanwhile, Apple announced last month that they hired Angela Ahrendts away from her wildly successful post as CEO of luxury fashion brand Burberry. The message is clear: Today’s devices will be hiding inside tomorrow’s trendy accessories.

Traditional circuit boards (PCBs) are rigid and flat multi-layered platforms for connecting electronic components. They simply cannot fit into compact, fashionable new form factors. Our next generation electronics need a thin, flexible circuit that can be stuffed into tiny, irregular, and even bendable cavities.

Flexible circuits are made by printing conductive paths onto one or more layers of thin, flexible polymer. Today, screen printing – squeezing conductive ink through a template – and photolithography – using light to cure conductive ink onto the surface of the substrate – are the most commonly used printing processes. But as the complexity and component density of flexible circuits increase, more and more manufacturers will rely on updated inkjet printing technologies to apply and cure micro-doses of conductive ink in ultra-precise patterns.

 

Organic LED Displays

Electronic displays are universal as our primary interface to intelligent devices; grids of tiny colored pixels visually speak to us and integrated touch sensors capture our commands. Today, these flat, thick, rectangular screens dictate the size and shape of our electronic devices. If product form factors are evolving, how will displays keep up?

Organic light-emitting diode – or OLED – displays create their own light by passing current through electro-luminescent organic material and when a charge is applied, the carbon-based compound glows. Since they don’t need a backlight they use less power and take up less space while improving the image’s brightness, contrast, refresh rate, and viewing angle.

Construction of newer active matrix OLED displays starts with a thin polymer substrate eliminating the need for thicker rigid and fragile glass used in LCD displays. Then, an organic field-effect transistor (OFET or organic alternative to a silicon thin-film transistor TFT) backplane is inkjet-printed onto the surface to control the flow of current through each pixel. A layer of electro-luminescent organic compounds is patterned into colored shapes on top of an additional layer of thin polymer. In some cases the compound is applied through organic vapor jet printing (OVJP, an inkjet like technology that sprays evaporated molecules carried by an inert gas) or etched into the substrate with an inkjet solvent printing technique. Finally, a cathode layer allows the current to flow out of the display.

When combined with newer on-cell touch technology – applying touch sensitive film directly to the display – all of the glass layers have been removed, and the few remaining polymer layers are significantly thinner, lighter, and more flexible. On top of these size, weight, and image quality enhancements, OLED screens are now more durable and introduce totally new bendable, foldable, and roll up display form factors.

As my boarding pass finishes printing, I set my smartphone next to it, and the bright OLED display comes to life. It reminds me of a front-porch swing scene where a weathered grandfather tells an anxious little boy about the way things were. Who would have thought when the first inkjet patents were filed in 1957 that the same technology could be used to change the face of electronics some 55 years later? That augmented reality glasses and intelligent jewelry would be an everyday part of lives? Or that the collective knowledge of that generation could be indexed on a digital piece of rolled up paper?

What lies ahead for today’s innovations? How will they be reimagined by future generations?

 

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