Roly-Poly
Years ago we saw a mock-up of an OLED device that looked like a large pen. It had a tab that allowed the user to pull out a flexible OLED display that showed full color images and text, as if you were reading a magazine or newspaper., which you could wirelessly update or switch pages with the press of a button. As one who has spent many hours on trains commuting to and from work, the idea of such a device remained a futuristic but eminently achievable industry goal in our minds, and we have followed the display space closely ever since.
It seems that we are getting ever closer to that dream as Samsung Display (pvt) promises to show an updated version of their flexible and rollable displays at the upcoming SID show next week. The product is called Rollable Flex, and while it is similar to other SDC display products, and those of other display manufacturers, it takes the rollable concept a bit further. Typically rollable displays are able to expand their surface area by 3x by maintaining a wide circumference around a drum, or in some cases folding across the interior of a device, however the folks at SDC have come up with a display that is able to be more tightly ‘wound’ around a cylinder without damage, and is able to expand its surface area by 5x, with the show demo being 49mm (1.9”) long when rolled to 254.4mm (10.01”) long when unrolled by wrapping it tightly around a cylinder.
While rollable OLED displays exist currently, they do not have the physical characteristics to be tightly wound without showing stress and eventual more serious damage. While all of the materials in an OLED stack have their own ‘modulus of elasticity’, a fancy way of saying its resistance to being deformed, much of an OLED display’s flexibility is not determined by its substrate but by the material used to create the OLED stack’s anode. The anode must be transparent if the light from the OLED emitters is to exit the pixel, and the most common material for OLED anodes is ITO, or indium Tin Oxide, which it typically sputtered[1] onto the substrate. ITO is unusual in that it has both high electrical conductivity and optical transparency, a rare combination, along with ability to be finely etched, however the material is also brittle, the antithesis of what is needed for rollable displays, and is also permeable enough to allow oxygen and water vapor into the OLED stack, which destroys OLED materials.
In rigid OLED displays, the ITO is deposited on glass, and with a second ‘base’ glass substrate, locks the ITO and other OLED materials away from oxygen and water, however rollable displays must be built on flexible substrates which leaves the ITO and other material open to damage. The solution for this issue is ‘layer’ other impermeable but transparent materials over the ITO, a process called encapsulation, solving the contamination issue. That said, ITO’s brittleness is still an issue, and we expect SDC has come up with either an ITO substitute or modified ITO mixture that allows the material to have a higher elasticity modulus that exceeds that of current materials, and the odds are that SDC will not reveal the details of the difference from ‘normal’ and less flexible OLED stack components.
While this is all technical, it does pave the way for progressively smaller rollable devices and puts into sight the one-day pocket pen that opens into a large, full color display. Samsung has already patented a number of ‘hybrid’ devices that use a rolled OLED display and a mechanical pull-out frame that holds the display when open, but these are typically the size of smartphones when closed, still a reach from the pocket-pen newspaper.
[1] Sputtering is a process that involves the creation of plasma that ionizes the mater5ial (source) which forces the molecules out of the source and on to a target material as a thin film.
It seems that we are getting ever closer to that dream as Samsung Display (pvt) promises to show an updated version of their flexible and rollable displays at the upcoming SID show next week. The product is called Rollable Flex, and while it is similar to other SDC display products, and those of other display manufacturers, it takes the rollable concept a bit further. Typically rollable displays are able to expand their surface area by 3x by maintaining a wide circumference around a drum, or in some cases folding across the interior of a device, however the folks at SDC have come up with a display that is able to be more tightly ‘wound’ around a cylinder without damage, and is able to expand its surface area by 5x, with the show demo being 49mm (1.9”) long when rolled to 254.4mm (10.01”) long when unrolled by wrapping it tightly around a cylinder.
While rollable OLED displays exist currently, they do not have the physical characteristics to be tightly wound without showing stress and eventual more serious damage. While all of the materials in an OLED stack have their own ‘modulus of elasticity’, a fancy way of saying its resistance to being deformed, much of an OLED display’s flexibility is not determined by its substrate but by the material used to create the OLED stack’s anode. The anode must be transparent if the light from the OLED emitters is to exit the pixel, and the most common material for OLED anodes is ITO, or indium Tin Oxide, which it typically sputtered[1] onto the substrate. ITO is unusual in that it has both high electrical conductivity and optical transparency, a rare combination, along with ability to be finely etched, however the material is also brittle, the antithesis of what is needed for rollable displays, and is also permeable enough to allow oxygen and water vapor into the OLED stack, which destroys OLED materials.
In rigid OLED displays, the ITO is deposited on glass, and with a second ‘base’ glass substrate, locks the ITO and other OLED materials away from oxygen and water, however rollable displays must be built on flexible substrates which leaves the ITO and other material open to damage. The solution for this issue is ‘layer’ other impermeable but transparent materials over the ITO, a process called encapsulation, solving the contamination issue. That said, ITO’s brittleness is still an issue, and we expect SDC has come up with either an ITO substitute or modified ITO mixture that allows the material to have a higher elasticity modulus that exceeds that of current materials, and the odds are that SDC will not reveal the details of the difference from ‘normal’ and less flexible OLED stack components.
While this is all technical, it does pave the way for progressively smaller rollable devices and puts into sight the one-day pocket pen that opens into a large, full color display. Samsung has already patented a number of ‘hybrid’ devices that use a rolled OLED display and a mechanical pull-out frame that holds the display when open, but these are typically the size of smartphones when closed, still a reach from the pocket-pen newspaper.
[1] Sputtering is a process that involves the creation of plasma that ionizes the mater5ial (source) which forces the molecules out of the source and on to a target material as a thin film.
Pen-based Rollable OLED display concept - Source: Photonics.com
RSS Feed