Researchers from the Tohoku University announced results from their work on LCD based flexible displays. Up to now, the term flexible display has been strongly related with the OLED display technology. Now the research group at Tohoku University in Sedai, Japan around Professor Hideo Fujikake and Associate Professor Takahiro Ishinabe announced that they were able to produce a flexible substrate structure capable of supporting a LCD device.
While OLEDs are thin and therefore very flexible, they have an issue with moisture and oxygen sensitivity, leading to short device lifetimes. As a consequence much research went into thin film barrier coatings that slow down water penetration, without achieving a complete success so far. As an alternative, OLED emitters resistant to water and oxygen would solve this issue as well, but so far there is nothing in the market today that would achieve this.
On the other hand, flexible LCDs have been shown many years ago but the performance was not very satisfying by the display standards back then and even less by today’s requirements. The key for a high performance LCD device is the tight control of the cell gap, among other things. Making a LCD flexible requires flexible and thinner substrates, which leads to a significant loss of cell gap control. The Tohoku University group is using a very thin polyimide film (10 micrometers) for both the upper and lower substrate.
Source: Tohoku University – Flexible LCD cross section
Using thin substrate films leads to the loss of all form stability and any LCD panel will need a stabilizing factor in order to work. As a solution the group is using polymer spacer walls that keeps the upper and lower substrate at a defined distance. In order to achieve this, they are irradiating a twisted-alignment LC layer including monomer components with a laser through the thin substrate film. This way, the thickness gets controlled without relying on the material itself. It is almost like making bubble wrap in a high tech fashion.
They succeeded in making these bonded films and were able to roll and unroll the device structure around a 3mmm radius cylinder without destroying the wall spacer.
For the next step the researchers are looking at creating actual LCD pixels in the structure and plan to improve the alignment layers (they have to be flexible too) and put a thin light guide panel on the back. They do not say how they plan to achieve the needed light polarization, unless the used films already have a sufficient polarization effect.
Analyst Comment
One thing we have learned over the last few decades of LCD development, the insistence of the LCD industry to come up with new solutions to make LCD panels better is almost limitless. When PDP threatened the use of LCD in large size TVs, the envelope of LCD manufacturing was pushed to the point where PDP could not compete anymore. I admit this is a very simple view of what actually happened, but it is certainly part of it. So the question is if we can expect this development opening up a new lifeline for LCD to compete with OLED displays in flexible applications. I wouldn’t bet against it, even though I would not give it much of a chance right now. (NH)
