Tag Archives: bendable screens

The age of the ‘nano-pixel’

As mentioned here before, ‘The Diamond Age: Or, A Young Lady’s Illustrated Primer’, a 1985 novel by Neal Stephenson featured in its opening chapter a flexible, bendable, rollable, newspaper screen. It’s one of those devices promised by ‘nano evangelists’ that never quite seems to come into existence. However, ‘hope springs eternally’ as they say and a team from the University of Oxford claims to be bringing us one step closer.

From a July 10, 2014 University of Oxford press release (also on EurekAlert but dated July 9, 2014 and on Azoanano as a July 10, 2014 news item),

A new discovery will make it possible to create pixels just a few hundred nanometres across that could pave the way for extremely high-resolution and low-energy thin, flexible displays for applications such as ‘smart’ glasses, synthetic retinas, and foldable screens.

A team led by Oxford University scientists explored the link between the electrical and optical properties of phase change materials (materials that can change from an amorphous to a crystalline state). They found that by sandwiching a seven nanometre thick layer of a phase change material (GST) between two layers of a transparent electrode they could use a tiny current to ‘draw’ images within the sandwich ‘stack’.

Here’s a series of images the researchers have created using this technology,

Still images drawn with the technology: at around 70 micrometres across each image is smaller than the width of a human hair.  Courtesy University of Oxford

Still images drawn with the technology: at around 70 micrometres across each image is smaller than the width of a human hair. Courtesy University of Oxford

The press release offers a technical description,

Initially still images were created using an atomic force microscope but the team went on to demonstrate that such tiny ‘stacks’ can be turned into prototype pixel-like devices. These ‘nano-pixels’ – just 300 by 300 nanometres in size – can be electrically switched ‘on and off’ at will, creating the coloured dots that would form the building blocks of an extremely high-resolution display technology.

‘We didn’t set out to invent a new kind of display,’ said Professor Harish Bhaskaran of Oxford University’s Department of Materials, who led the research. ‘We were exploring the relationship between the electrical and optical properties of phase change materials and then had the idea of creating this GST ‘sandwich’ made up of layers just a few nanometres thick. We found that not only were we able to create images in the stack but, to our surprise, thinner layers of GST actually gave us better contrast. We also discovered that altering the size of the bottom electrode layer enabled us to change the colour of the image.’

The layers of the GST sandwich are created using a sputtering technique where a target is bombarded with high energy particles so that atoms from the target are deposited onto another material as a thin film.

‘Because the layers that make up our devices can be deposited as thin films they can be incorporated into very thin flexible materials – we have already demonstrated that the technique works on flexible Mylar sheets around 200 nanometres thick,’ said Professor Bhaskaran. ‘This makes them potentially useful for ‘smart’ glasses, foldable screens, windshield displays, and even synthetic retinas that mimic the abilities of photoreceptor cells in the human eye.’

Peiman Hosseini of Oxford University’s Department of Materials, first author of the paper, said: ‘Our models are so good at predicting the experiment that we can tune our prototype ‘pixels’ to create any colour we want – including the primary colours needed for a display. One of the advantages of our design is that, unlike most conventional LCD screens, there would be no need to constantly refresh all pixels, you would only have to refresh those pixels that actually change (static pixels remain as they were). This means that any display based on this technology would have extremely low energy consumption.’

The research suggests that flexible paper-thin displays based on the technology could have the capacity to switch between a power-saving ‘colour e-reader mode’, and a backlit display capable of showing video. Such displays could be created using cheap materials and, because they would be solid-state, promise to be reliable and easy to manufacture. The tiny ‘nano-pixels’ make it ideal for applications, such as smart glasses, where an image would be projected at a larger size as, even enlarged, they would offer very high-resolution.

Professor David Wright of the Department of Engineering at the University of Exeter, co-author of the paper, said: ‘Along with many other researchers around the world we have been looking into the use of these GST materials for memory applications for many years, but no one before thought of combining their electrical and optical functionality to provide entirely new kinds of non-volatile, high-resolution, electronic colour displays – so our work is a real breakthrough.’

The phase change material used was the alloy Ge2Sb2Te5 (Germanium-Antimony-Tellurium or GST) sandwiched between electrode layers made of indium tin oxide (ITO).

I gather the researchers are looking for investors (from the press release),

Whilst the work is still in its early stages, realising its potential, the Oxford team has filed a patent on the discovery with the help of Isis Innovation, Oxford University’s technology commercialisation company. Isis is now discussing the displays with companies who are interested in assessing the technology, and with investors.

Here’s a link to and a citation for the paper,

An optoelectronic framework enabled by low-dimensional phase-change films by Peiman Hosseini, C. David Wright, & Harish Bhaskaran. Nature 511, 206–211 (10 July 2014) doi:10.1038/nature13487 Published online 09 July 2014

This paper is behind a paywall.

Transparent image sensor has no electronics or internal components

This shows the world's first flexible and completely transparent image sensor. The plastic film is coated with fluorescent particles. Credit: Optics Express.

This shows the world’s first flexible and completely transparent image sensor. The plastic film is coated with fluorescent particles. Credit: Optics Express.

Stunning isn’t it? The work is from researchers at the Johannes Kepler University Linz in Austria and is featured in an article being published in Optics Express. From the Feb. 20, 2013 news release about the Optics Express article on EurekAlert,

Digital cameras, medical scanners, and other imaging technologies have advanced considerably during the past decade. Continuing this pace of innovation, an Austrian research team has developed an entirely new way of capturing images based on a flat, flexible, transparent, and potentially disposable polymer sheet. The team describes their new device and its possible applications in a paper published today in the Optical Society’s (OSA) open-access journal Optics Express.

The new imager, which resembles a flexible plastic film, uses fluorescent particles to capture incoming light and channel a portion of it to an array of sensors framing the sheet. With no electronics or internal components, the imager’s elegant design makes it ideal for a new breed of imaging technologies, including user interface devices that can respond not to a touch, but merely to a simple gesture.

The news release goes on to describe the technology,

The sensor is based on a polymer film known as a luminescent concentrator (LC), which is suffused with tiny fluorescent particles that absorb a very specific wavelength (blue light for example) and then reemit it at a longer wavelength (green light for example). Some of the reemitted fluorescent light is scattered out of the imager, but a portion of it travels throughout the interior of the film to the outer edges, where arrays of optical sensors (similar to 1-D pinhole cameras) capture the light. A computer then combines the signals to create a gray-scale image. “With fluorescence, a portion of the light that is reemitted actually stays inside the film,” says Bimber. [Oliver Bimber of the Johannes Kepler University Linz in Austria, co-author of the Optics Express paper] “This is the basic principle of our sensor.”

For the luminescent concentrator to work as an imager, Bimber and his colleagues had to determine precisely where light was falling across the entire surface of the film. This was the major technical challenge because the polymer sheet cannot be divided into individual pixels like the CCD camera inside a smartphone. Instead, fluorescent light from all points across its surface travels to all the edge sensors. Calculating where each bit of light entered the imager would be like determining where along a subway line a passenger got on after the train reached its final destination and all the passengers exited at once.

The solution came from the phenomenon of light attenuation, or dimming, as it travels through the polymer. The longer it travels, the dimmer it becomes. So by measuring the relative brightness of light reaching the sensor array, it was possible to calculate where the light entered the film. This same principle has already been employed in an input device that tracks the location of a single laser point on a screen.

The researchers were able to scale up this basic principle by measuring how much light arrives from every direction at each position on the image sensor at the film’s edge. They could then reconstruct the image by using a technique similar to X-ray computed tomography, more commonly known as a CT scan.

“In CT technology, it’s impossible to reconstruct an image from a single measurement of X-ray attenuation along one scanning direction alone,” says Bimber. “With a multiple of these measurements taken at different positions and directions, however, this becomes possible. Our system works in the same way, but where CT uses X-rays, our technique uses visible light.”

Currently, the resolution from this image sensor is low (32×32 pixels with the first prototypes). The main reason for this is the limited signal-to-noise ratio of the low-cost photodiodes being used. The researchers are planning better prototypes that cool the photodiodes to achieve a higher signal-to-noise ratio.

By applying advanced sampling techniques, the researchers can already enhance the resolution by reconstructing multiple images at different positions on the film. These positions differ by less than a single pixel (as determined by the final image, not the polymer itself). By having multiple of these slightly different images reconstructed, it’s possible to create a higher resolution image. “This does not require better photodiodes,” notes Bimber, “and does not make the sensor significantly slower. The more images we combine, the higher the final resolution is, up to a certain limit.”

The researchers discuss applications,

The main application the researchers envision for this new technology is in touch-free, transparent user interfaces that could seamlessly overlay a television or other display technology. This would give computer operators or video-game players full gesture control without the need for cameras or other external motion-tracking devices. The polymer sheet could also be wrapped around objects to provide them with sensor capabilities. Since the material is transparent, it’s also possible to use multiple layers that each fluoresce at different wavelengths to capture color images.

The researchers also are considering attaching their new sensor in front of a regular, high-resolution CCD sensor. This would allow recording of two images at the same time at two different exposures. “Combining both would give us a high-resolution image with less overexposed or underexposed regions if scenes with a high dynamic range or contrast are captured,” Bimber speculates. He also notes that the polymer sheet portion of the device is relatively inexpensive and therefore disposable. “I think there are many applications for this sensor that we are not yet aware of,” he concludes.

Here’s a citation and a link,

“Towards a transparent, flexible, scalable and disposable image sensor using thin-film luminescent concentrators,” A. Koppelhuber and O. Bimber, Optics Express, Vol. 21, Issue 4, pp. 4796-4810 (2013) (link: http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-21-4-4796).

Canada’s Queen’s University strikes again with its ‘paper’ devices

Roel Vertegaal at Queen’s University (Ontario, Canada) has released a ‘paper’ tablet. Like the bendable, flexible ‘paper’ phone he presented at the CHI 2011 meeting in Vancouver, Canada (my May 12, 2011 posting), this tablet offers some intriguing possibilities but is tethered. The Jan. 9, 2013 news item on phys.org provides more information about the new ‘paper’ device (Note: Links have been removed),

Watch out tablet lovers – a flexible paper computer developed at Queen’s University in collaboration with Plastic Logic and Intel Labs will revolutionize the way people work with tablets and computers.

The PaperTab tablet looks and feels just like a sheet of paper. However, it is fully interactive with a flexible, high-resolution 10.7-inch plastic display developed by Plastic Logic and a flexible touchscreen. It is powered by the second generation I5 Core processor developed by Intel.

Vertegaal and his team have produced a video demonstrating their ‘paper’ tablet/computer:

The Jan. 8, 2013 Queen’s University news release, which originated the news item, provides descriptions (for those who don’t have time to watch the video),

“Using several PaperTabs makes it much easier to work with multiple documents,” says Roel Vertegaal, Director of Queen’s University’s Human Media Lab. “Within five to ten years, most computers, from ultra-notebooks to tablets, will look and feel just like these sheets of printed color paper.”

“We are actively exploring disruptive user experiences. The ‘PaperTab’ project, developed by the Human Media Lab at Queen’s University and Plastic Logic, demonstrates novel interactions powered by Intel processors that could potentially delight tablet users in the future,” says Intel’s Experience Design Lead Research Scientist, Ryan Brotman.

PaperTab’s intuitive interface allows users to create a larger drawing or display surface by placing two or more PaperTabs side by side. PaperTab emulates the natural handling of multiple sheets of paper. It can file and display thousands of paper documents, replacing the need for a computer monitor and stacks of papers or printouts.

Unlike traditional tablets, PaperTabs keep track of their location relative to each other, and to the user, providing a seamless experience across all apps, as if they were physical computer windows.

“Plastic Logic’s flexible plastic displays allow a natural human interaction with electronic paper, being lighter, thinner and more robust compared with today’s standard glass-based displays. This is just one example of the innovative revolutionary design approaches enabled by flexible displays,” explains Indro Mukerjee, CEO of Plastic Logic.

The partners are saying that ‘paper’ tablets may be on the market in foreseeable future  according to Emma Wollacott’s Jan. 8, 2013 article for TG Daily,

The bendy tablet has been coming for quite a while now, but a version to be shown off today at CES [Consumer Electronics Show] could be ready for the market within three years, say its creators.

You can find out more about the Human Media Lab at Queen’s University here, Plastic Logic here, and Intel Core I5 Processors here.

Folding screens at University of Toronto and EPD (electronic paper display) with LG

University of Toronto researchers recently announced a breakthrough with regard to organic light-emitting diodes (OLEDs) and flexible screens. From the March 29, 2012 news item by Allyson Rowley on physorg.com,

Michael Helander and Zhibin Wang, PhD candidates in the Faculty of Applied Science and Engineering, are members of a research team that has developed the world’s most efficient organic light-emitting diodes (OLEDs) on flexible plastic. Good news for manufacturers and consumers alike, the discovery means a less costly, more efficient and environmentally friendly way to build brighter flat-panel displays on a thinner, more durable and flexible surface.

The students had been cleaning sheets of indium tin oxide – a material used in all flat-panel displays – when they noticed that devices built using their cleaned sheets had become much more efficient than expected, using less energy to achieve much higher brightness. After some investigation, they determined that this greater efficiency was the result of molecules of chlorine picked up from their cleaning solvent. With this surprising discovery, the two students engineered a prototype for a new kind of OLED device, which is both simpler in construction and more efficient.

According to Rowley’s University of Toronto March 26, 2012 news release,

Over time, though, OLED devices became more complex – the original two layers of molecules became many layers, which raised manufacturing costs and failure rates.

“Basically, we went back to the original idea – and started again,” said Wang. The team’s findings were published, and in December, Helander and Wang, together with Lu [ Professor Zheng-Hong Lu.who supervises both Helander and Wang] and another U of T grad student, launched OTI Lumionics, a startup that will take the next steps toward commercializing the technology.

While OTI Lumionics is taking its next steps, the company, LG Display based in Korea has announced production of a plastic electronic paper display (EPD). From the March 30, 2012 news item by Nancy Owano on physorg.com,

LG Display has set the production clock ticking for a plastic EPD (electronic paper display) product which in turn is expected to set e-book marketability fast-forward. In an announcement Thursday, Korea-based LG Display, which manufactures thin film transistor liquid crystal display, said it has already started up mass production of EPD for e-books.

Amar Toor’s March 29, 2012 item for engadget features the company’s news release, as well as, this detail,

The plan going forward is to supply the display to ODMs [original design manufacturer] in China, in the hopes of bringing final products to Europe by “the beginning of next month.” [May 2012?]

Apparently, the screen resolution is 1024 x 768 and it has a range of 40 degrees when bent from the centre.