The future of touchscreens revealed: bigger, cheaper, bendier
18th Aug 2013 | 07:00
Silver is becoming the gold standard for touchscreen technology
At CES this year, we were writing about "monster" 20-inch touchscreens. But by this Christmas, 23-inch and 27-inch touchscreens will be available on the high street, ready to fold down and use for painting or family board games.
Touch is undeniably going big, but it's still held back by the high prices of adding the touch layer to the screen. There is an answer, though - and tech companies are going for silver to find it.
Touchscreens are made up of multiple layers: the top layer of glass with anti-scratch coating, a layer of clear adhesive and then two or even three layers of indium tin oxide (ITO) either side of more layers of glass comprising the touch sensor, then another clear adhesive layer to hold the touch sensor down onto the LCD underneath.
ITO is the critical ingredient. It's a good conductor and it's transparent, but it's also expensive. It also requires both fragile materials and expensive multi-stage manufacturing processes, and although it can be recycled when supplies are limited, its mostly mined in China in conditions that are far from green.
The ITO powder is "sputtered" over the glass in multiple layers in a vapour deposition chamber, baked onto the glass and then etched into a sensor circuit. Sometimes the glass layer is chemically hardened first, but either way, the layers have to be carefully lined up to work.
The silver solution
But there is a cheaper and less environmentally harmful alternative, developed by MIT biochemist Dr Angela Belcher and inspired by the multi-layered formation of abalone shells. It uses silver nanowires scattered over a sheet of plastic.
Take two layers of plastic coated with very long, very thin silver strands (or even one sheet coated on both sides) and you have a capacitive touch sensor that's thinner, lighter, more flexible and much easier to manufacture than the ITO sensors.
You can't see through silver, but you don't need very much of it either. Silver is the same price as ITO, but it's a hundred times more conductive - it's even more conductive than gold (so remember that next time someone tries to upsell you on gold-coated connectors).
Because the nanowires connect in a mesh, you can get a full-screen sensor and still have 99% of the screen area clear. That lets through more light than an ITO sensor, so the LCD doesn't need to be as bright. And given that powering the screen takes 60% of the battery life in most devices, what you get is a thinner, cheaper screen and longer battery life.
The random structure of the nanowire also is harder to see than the regular patterns of other metal meshes, and you don't have to match it up to the pixel pattern of the LCD to avoid a distracting moiré effect. And because the sensor is thinner, you don't get as much parallax distortion - what you see on screen is closer to where the pixels are physically placed, so you can touch things more accurately.
Making silver nanowires starts with silver nitrate. Chemists (and alchemists) have been making this since the 13th century and silver has been used in photography since the 1800s. There are plenty of factories with the machinery to deposit silver onto large rolls of paper which can be re-used for depositing silver nanowires onto plastic sheets.
Sri Peruvemba of silver nanowire producer Cambrios told TechRadar that, after it's been made in a cleanroom, the silver nanowire solution (called ClearOhm) ships to the factory in a bucket.
It's then sprayed onto the touchscreen glass like ink. "Enough silver nanowire 'ink' to fill a water bottle is enough to make a couple of hundred thousand phone screens," say Peruvemba.
There are half a dozen other touch sensor replacements being developed, using graphene, carbon nanobuds and other exotic materials. But few of them let through as much light as silver nanowire, or conduct as effectively.
And silver nanowire doesn't just work for touch in the lab: it's already in several shipping products, and we couldn't spot the nanowire mesh at all with the naked eye.
Cambrios' nanowires power the touchscreen in NEC's high-end Media X N-07D smartphone on the Japanese Docomo network, and the much cheaper Huawei Ascend phone on the US Sprint network. It's used in Gvision's 15-inch touchscreens that are designed to be used as paypoints on petrol pumps - which suggests it's pretty hardwearing.
LG used it for the 23-inch touchscreen V325 all-in-one that launched with Windows 8, as well as two touchscreen monitors. Intel has also used it in its 13.3-inch reference design for OEMs, which should introduce Cambrios to a wider market.
Wired for speed
LG also discovered that silver nanowires allowed it to cut out several of the usual manufacturing stages for assembling touchscreens. John LeMoncheck, CEO of Cambrios, explains that initially LG was etching the rolls of coated film as it would with an ITO sensor. However, once it realised the the nanowire solution could be sprayed on in the right pattern to start with, it was possible to reduce costs even further.
The manufacturing cost of silver nanowire touch sensor is already less than $4 per inch. With scale and shortcuts like that, LeMoncheck hopes it will drop to $3.50 or even $3 an inch next year.
Saving $1 an inch on a 5-inch smartphone screen might not make much difference to the ultimate retail price, but it could take $30-50 off bigger displays. LeMoncheck is hoping giant touchscreens like Microsoft's Perceptive Pixel monster will get much more affordable - and that they'll all be made with his silver nanowires.
But there other things you could do with silver nanowires. You could coat a layer of plastic or Lucite and use that as the top layer of a really cheap screen. You can't do that with ITO because the heat needed to bake it in place would melt the plastic, but the drying oven used to fix the silver nanowires in place doesn't need to be nearly as hot (a mere 120 degrees rather than 600-plus).
It will work on an e-ink screen too. It needn't be limited to flat surfaces: you could coat a curved object like a car dashboard. You could even use silver nanowires on a flexible display, where brittle ITO would crack. Japanese touch sensor manufacturer Nissha will have 3D touch sensors this year and the company has been testing how well silver nanowire touch will work on a flexible screen.
"The coating changes in resistance. As you stretch and bend it, it goes up - but then it goes back down and comes back to normal," explained Peruvemba. So touch wouldn't work while you're bending a flexible screen, but then you probably wouldn't be trying to tap or scroll when you're folding it back up to put in your pocket.
Nissha tested a 3mm thick silver nanowire touch sensor. After bending it around a 180-degree angle 100,000 times, it was still worked every time. Add that to something like AUO's flexible e-ink screen and we're one step closer to a tablet you can roll up and put in your pocket. Bigger, slimmer and bendier: that's why the future could well be silver.