Research at CMMPEDevices & applications — Hybrid LC electroluminescent displays

 

Since 2004 CMMPE has worked in collaboration with Pelikon (now an MFLEX Company) to develop novel electroluminescent hybrid liquid crystal displays based upon a dye-doped polymer dispersed liquid crystal (PDLC) layer and an encapsulated printed segment electroluminescent layer (PSEL). This results in a flexible display technology that is low power and operates in all light conditions. Some of the current applications of the hybrid technology (designated SmartInk) include Portable devices, such as mobile phones and MP3 players, and Home appliances, e.g. washing machines etc. An example of an early mobile phone keypad prototype in both low light and direct sunlight conditions is shown in Figure 1.

Figure 1. Prototype of the hybrid technology as a reconfigurable keypad.

Our focus at CMMPE has been on studying the PDLC layer in terms of its optical and electrical characteristics and the morphology and alignment of the liquid crystal droplets. Examples of optical microscope and scanning electron microscope images are shown in Figure 3.

Figure 3. A Polarizing microscope image of the PDLC layer and a cross-section of the layer resolved using a scanning electron microscope.

Figure 2. Modus operandi of the ELLC hybrid device.

A schematic of the device is shown in Figure 2. A voltage is applied to both layers resulting in light emission from the EL layer and the dye-doped PDLC layer becoming transparent. In the absence of a voltage the PDLC is opaque. For low ambient light conditions the light emission from the EL is viewed directly. However, for high ambient light conditions the PDLC acts as a shutter and the ambient light is reflected from the underlying EL segment, see Figure 2.

 

Further information

For more information on the technology and the related products please see the Pelikon website at http://www.pelikon.com

This work has been carried out in two Collaborative R&D projects funded by the DTI (TSB) and the Engineering and Physical Sciences Research Council (“Electroluminescent hybrid liquid crystal plastic displays” Technology Programme project 10276 & “ELLC Hybrid Displays for Automotive and Mobile Appliances” Technology Programme project M1038K).

Further reading

Novel, High Visibility Transreflective Display
Evans C.M., Fryer C.J.N., Johnston D.R., Coles H.J. and Morris S.M.
SID 2007 Digest, 38(02), 1821-1823, (2007)

Hybrid liquid crystal/electroluminescent devices: Visibility in all lighting conditions (prizewinning poster)
D.J. Gardiner, S.M. Morris, C.M. Evans, H.J. Coles
BLCS, Bristol, April 2009

 

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