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Optoelectronics/Displays  

Has flexible OLED cleared its last hurdle?

Posted: 19 Nov 2014     Print Version  Bookmark and Share

Keywords:OLED  flexible  Kateeva  display 

There is a new method that promises to protect flexible displays from the environment. Kateeva Inc. announced that it has solved the last remaining hurdle to flexible, bendable, rollable OLED displays allowing designers to create myriad devices that can bend, flex and conform to almost any shape over and over without damage.

Organic Light Emitting Diodes (OLEDs) enable displays whose colours are richer, whose manufacturing is simpler, and which can be deposited on flexible substrates for all the wearables, smart-watches, smartphones, and other gadgets that would like to have a flexible, bendable, rollable form factor. Many of these devices have been prototyped already, but their lifetimes would be too short for commercialisation since the oxygen and moisture would eventually penetrate into the OLED level spoiling it.

Last year, Menlo Park, California-based Kateeva released its ink-jet roll-to-roll printing presses that could create OLED panels as large as G8-sizes (98in x 86in). However, even though they were flexible, they still has to be encased in glass and metal to keep out the oxygen and moisture, allowing curved displays, but ones that were fixed at those angles once they were sold to consumers.

Kateeva

Kateeva's roll-to-roll process mass produced OLED displays with complete protection from the oxygen and moisture that washes out the colours and limits the lifetime of flexible OLED. (Source: Kateeva)

Now Kateeva is announcing that it has invented a way of encapsulating their OLED panels within a flexible substrate, permitting designers to realise their dreams of electronic devices that can conform to different shapes at the will, even whim, of the end-user. It is called the YieldJet Flex.

The thin-film encapsulation (TFE) method Kateeva has invented is novel in that is mixed very thin inorganic layers atop of very conformable organic layers, resulting in a unique hybrid material that Kateeva's president and cofounder, Conor Madigan, claimed solves the oxygen and moisture penetration problem once and for all.

"The TFE process works by coating a continuous TFE stack over the entire display area. This stack is patterned to have a precise edge between the active area and the electrical contacts surrounding the display (that provide the connection to the drive electronics). The stack itself is a multi-layer structure of alternating inorganic films (typically 1 micron or less in thickness) and organic films (typically 6 microns or more in thickness). The inorganic layer provides the primary barrier to oxygen and moisture protecting the OLED device. The organic layer serves to planarise and smooth the display surface (coating over the circuit and pixel structures on the surface as well as particles) so that the next inorganic layer can be deposited onto a smooth, flat, clean surface. By having a smooth, flat, clean surface for deposition, the quality of the inorganic layer is dramatically improved, enabling the TFE structure of have high yield and reliability even after undergoing repeated flexing and bending," Madigan told EE Times.

YieldJet Flex

Kateeva's YieldJet Flex alternates thin inorganic layers with thicker organic layers to guarantee that no moisture or oxygen reaches the delicate OLED layer. (Source: Kateeva)

The YieldJet Flex released by Kateeva to deposit the alternating organic/inorganic layers uses standard semiconductor techniques for the deposition of well-known materials.

"These inorganic layers are typically silicon nitride or aluminium oxide. They are deposited by one of three techniques: Plasma Enhanced Chemical Vapor Deposition (PECVD), Sputtering Type Physical Vapor Deposition (PVD), or Atomic Layer Deposition (ALD). Each of these three techniques have different pros and cons. The Kateeva solution is agnostic to the inorganic layer type or deposition method—we can work with all three approaches. Currently, the PECVD technique appears to be the most mature for mass production, but as the technologies improve, it is always possible that this could change in the future. We will follow the requirements of the customer and ensure our system interfaces effectively with whatever approach the customer selects," Madigan explained.

Kateeva so far has a single customer (in Asia) to which it will ship the first YieldJet Flex this month. It predicts that its customers will build devices never seen before, such as pocket-sized trifold smartphones that unfurl to provide immersive viewing; flexible and comfortable smart-watches almost completely covered by a flexible display; and surface-conforming displays for automobiles, aircraft, and other more novel devices.

- R. Colin Johnson
  EE Times





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