Debat af skærmeteknologi, nutidens såvel som fremtidens. LCD, plasma, OLED samt HD, 4K, 8K, HDR mm.

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#132083
http://ing.dk/artikel/116931-foerste-fa ... nteprikker
Første farveskærm baseret på kvanteprikker

Effektforbruget er kun en femtedel af LCD i den farveskærm baseret på kvanteprikker, som Samsung har udviklet. Teknologien har potentiale til at udkonkurrere LCD, LED og OLED-teknologierne.


Af Jens Ramskov, onsdag 02. mar 2011 kl. 10:02


Samsungs forskningslaboratorium har opnået et gennembrud for farveskærme baseret på kvanteprikker.

I en artikel i Nature Photonics beskriver forskerne, hvorledes de med en ny produktionsmetode har fremstillet en fire-tommer-skærm. Det er det første konkrete skridt til at kommercialisere en teknik, der har været studeret de senere år.

»Skærme og displays baseret på kvanteprikker vil have et effektforbrug, der er en femtedel af en tilsvarende LCD-displays,« siger artiklens førsteforfatter Tae-Ho Kim til MIT-tidsskriftet Technology Review. »Og de kan produceres for mindre end halvdelen af prisen.«

Nogle få nanometer
En kvanteprik er en lille lysdiode (LED), som har en rumlig udstrækning på nogle få nanometer.

Kvanteprikker udsender lys på samme måde som andre halvledermaterialer ved, at elektroner rekombinerer med huller, hvorved energi omdannes til lys i et meget smalt frekvensbånd.

I laboratorier har man tidligere lavet monokrone kvanteprik-displays ved at hælde en opløsning med kvanteprikker ud over et roterende substrat (spin coating), hvor ved der dannes en tynd film af materialet.

I et farvedisplay skal man bruge tre forskellige kvanteprikker, der henholdsvis udsender rødt, grønt og blåt lys. Et farvedisplay baseret på kvanteprikker kan dog ikke laves med den simple teknik, da den ikke vil placere de røde, grønne og blåt kvanteprikker korrekt i forhold til hinanden.

Det er her, Samsungs forskere har opnået et gennembrud.

Kan bruges til HD-tv
Forskerne fra Frontier Research Laboratory ved Samsung Advanced Institute of Technology har udviklet en metode, hvor man først anvender spincoating-teknikken for hver af de tre farver på forskellige substrater for siden med en trykteknik at overføre dem til en fælles glasplade coated med indiumtin-oxid.

Det er lykkedes med denne metode at lave et fire-tommer-display med 320 x 240 pixels.

Det aktive område i hver pixel har en størrelse på 46 x 96 mikrometer. Forskerne bemærker i deres artikel, at denne størrelse kan anvendes til HD-tv.

I det færdig display styres hver pixel af en tyndfilmtransistor, som regulerer mængden af elektroner og huller, der finder vej til kvanteprikken, hvor de rekombinerer og giver anledning til udsendelse af lys.

Transistorerne er lavet af hafnium-indium-zink-oxid, som har en ti gange så høj elektronmobilitet som konventionelle silicum-transistorer og tilmed leverer en mere stabil strøm.

Konkurrenten er imponeret
Andre elektronikvirksomheder arbejder også med displays baseret på kvanteprikker. LG Display er bl.a. gået sammen med MIT spinoff-virksomheden QD Vision.

Teknologidirektør Seth Coe-Sullivan fra QD Vision siger til Technology Review, at metoderne, Samsung anvender, ikke er nye.

»Men Samsung har udført et godt ingeniørarbejde ved at kombinere dem på imponerende vis,« siger han.

Seth Coe-Sullivan påpeger dog, at der er mange andre problemer, der skal løses, før man kan masseproducere displays baseret på kvanteprikker. Han skønner, det vil vare mindst tre år endnu, før kvanteprik-displays finder vej til markedet.

John Rogers fra University of Illinois er også imponeret.

»Det er klart den hidtil den bedste demonstration af, hvad teknologien kan byde på,« siger han til det britiske magasin Physics World.

Han advarer dog om, at kvanteprikker kan få kamp til stregen i kampen om at blive den førende display-teknologi:

»Backlit LCD bliver fortsat bedre og bedre – og billigere og billigere,« bemærker han.

[img]http://ing.dk/modules/xphoto/cache/14/5 ... _0_0_0.jpg[/img]
Kvanteprik-display med 320 x 240 pixels - fire tommer. (Foto: Samsung)
Af Snurrerundtlyd
#132087
http://www.nature.com/news/2011/110220/ ... 1.109.html
Connect the quantum dots for a full-colour image

Nanocrystal display could be used in high-resolution, low-energy televisions.


Zeeya Merali

Ink stamps have been used to print text and pictures for centuries. Now, engineers have adapted the technique to build pixels into the first full-colour 'quantum dot' display — a feat that could eventually lead to televisions that are more energy-efficient and have sharper screen images than anything available today.

Engineers have been hoping to make improved television displays with the help of quantum dots — semiconducting crystals billionths of a metre across — for more than a decade. The dots could produce much crisper images than those in liquid-crystal displays, because quantum dots emit light at an extremely narrow, and finely tunable, range of wavelengths.

The colour of the light generated depends only on the size of the nanocrystal, says Byoung Lyong Choi, an electronic engineer at the Samsung Advanced Institute of Technology in Yongin, South Korea. Quantum dots also convert electrical power to light efficiently, making them ideal for use in energy-saving lighting and display devices.

Easier said than done

Attempts to commercialize the technology have been hampered because it is difficult to make large quantum-dot displays without compromising the quality of the image. The dots are usually layered onto the material used to make the display by spraying them onto the surface — a technique similar to that of an ink-jet printer. But the dots must be prepared in an organic solvent, which "contaminates the display, reducing the brightness of the colours and the energy efficiency", says Choi.

Choi and his colleagues have now found a way to bypass this obstacle, by turning to a more old-fashioned printing technique — details of which appear today in Nature Photonics¹. The team used a patterned silicon wafer as an 'ink stamp' to pick up strips of dots made from cadmium selenide, and press them down onto a glass substrate to create red, green and blue pixels without using a solvent.

The idea may sound simple, but getting it to work was not easy, Choi explains. "It took us three years to get the details right, such as changing the speed and the pressure of the stamp to get a 100% transfer."

The team has now produced a 10-centimetre full-colour display. The pixels ware brighter and more efficient than in quantum dot displays made by rival methods, says Choi. For example, "the maximum brightness of the red pixels is about 50% better," he says. The maximum power efficiency for the red pixels is about 70% better.

Around the bend

Bending the screen did not greatly affect the display's performance, which means that the displays can be rolled up for portability, or used to make flexible lighting, says Choi.

Paul O'Brien, an inorganic chemist who studies quantum dots at the University of Manchester, UK, commends the group's achievement. He notes that quantum dots are "robust", so their efficiency will not quickly degrade. "For televisions, where you want a long lifetime, quantum dots are appealing," he adds.

Seth Coe-Sullivan, the chief technology officer of QD Vision, a company in Watertown, Massachusetts, that produces devices with lighting based on quantum dots, notes that Choi and his team's method is cheap. "We all have our eyes on making large-screen televisions, and this fabrication technique seems to be cost-effective," he says.

But Coe-Sullivan adds that it may take some time to commercialize quantum-dot displays for big items. "I can imagine that we will have small cell-phone displays using this technology within around three years," he says. "For the rest, there may be more of a wait."

References

1. Kim, T.-H. et al. Nature Photonics doi:10.1038/NPHOTON.2011.12 (2011).
Af Snurrerundtlyd
#132097
http://www.technologyreview.com/computing/32407
The First Full-Color Display with Quantum Dots

Samsung's new four-inch display could eventually lead to flexible screens.


TUESDAY, FEBRUARY 22, 2011BY PRACHI PATEL

Researchers at Samsung Electronics have made the first full-color display that uses quantum dots. Quantum-dot displays promise to be brighter, cheaper, and more energy-efficient than those found in today's cell phones and MP3 players.

Samsung's four-inch diagonal display is controlled using an active matrix, which means each of its color quantum-dot pixels is turned on and off with a thin-film transistor. The researchers have made the prototype on glass as well as on flexible plastic, as reported in Nature Photonics this week. "We have converted a scientific challenge into a real technological achievement," says Jong Min Kim, a fellow at the Samsung Advanced Institute of Technology.

Quantum dots are semiconductor nanocrystals that glow when exposed to current or light. They emit different colors depending on their size and the material they're made from. Their bright, pure colors and low power consumption make them very appealing for displays. Most computer monitors and TVs use power-hungry liquid-crystal displays (LCDs). Organic light-emitting diode (OLED) displays are more brilliant and energy-efficient, but are confined to small gadgets because they are too expensive for TV screens, and their organic materials have limited lifetimes.

Quantum-dot displays would consume less than a fifth of the power of LCDs, says Samsung researcher Tae-Ho Kim. They promise to be brighter and longer-lasting than OLEDs. What's more, they could be manufactured for less than half of what it costs to make LCD or OLED screens.

This potential has caught the attention of big display manufacturers other than Samsung. LG Display is partnering with MIT spinoff QD Vision to develop quantum-dot displays.

To make their prototype, the Samsung researchers start by coating a solution of quantum dots on a silicon plate and evaporating the solvent. Then they gently press a rubber stamp with a ridged surface into the quantum-dot layer, peel it off, and then press it on the desired glass or plastic substrate. This transfers stripes of quantum dots onto the substrate.

In a color display, each pixel contains red, green, and blue subpixels. These colors are combined in varying intensities to produce millions of colors. By using their stamping technique over and over, the researchers can create a repeated pattern of red, green, and blue stripes.

They transfer the stripes directly onto an array of thin-film transistors. The transistors are made of amorphous hafnium-indium-zinc oxide, which provide higher, more stable current than conventional amorphous-silicon transistors. The resulting display has subpixels that are about 50 micrometers wide and 100 micrometers long, small enough for use in cell-phone screens.

"This is a powerful demonstration," says Seth Coe-Sullivan, cofounder and chief technology officer of QD Vision. "The individual technology elements aren't necessarily new. Samsung definitely did a lot of good engineering to put all the pieces together in an impressive way."

He cautions, though, that there are many more research and engineering issues to be solved, and that quantum-dot displays are still at least three years away from commercialization. The best quantum-dot devices are still not as power-efficient as OLEDs. They also need to last longer—right now, they start losing their brightness after about 10,000 hours. Finally, researchers will have to develop ways to manufacture them at low cost and large scale.


Billede
Bright and bendy: Color quantum dots and oxide thin-film transistors work together in this new active matrix display prototype.
Credit: Byoung Lyong Choi, Samsung Electronics