Organic Light Emitting Diode

Thin Film Packaging

Several problems must be solved before flexible OLEDs can become a reality. The extreme sensitivity of OLEDs to water and oxygen requires an extremely low gas permeability of the substrates that is far from what any known transparent polymeric substrate can achieve. Unlike OLED on rigid glass, the encapsulation for flexible OLED is neither rigid metal sheet or glass caps. An advanced thin film encapsulation technique for FOLED applications is needed. Such an encapsulation scheme demands low gas permeability and "thick" enough to eliminate the dust effect. Besides, the film(s) must prohibit the crack propagation during bending. In fact, exploration of the possible potential of thin films for encapsulation is challenging and 'product-ready' encapsulation has not been achieved yet. Single-layer structure or multilayered structure can be the winner. CityU aims at developing a thin film packaging technique which consists of single layer or multi-layers of nano-scale organic and inorganic thin films, which act as a barrier to protect the electrode and active region from water and oxygen permeation. The films are prepared by magnetron sputtering and chemical vapor deposition. The factors to be noted here are the control of low substrate temperature (< 100oC) and ion bombardment damage so as to minimize damages to the EL organic layer already deposited.

The Structure of Thin Film Packaging for FOLED
The Structure of Thin Film Packaging for FOLED

P1/C1 Structures P1/C2 Structures
SEM Micrographs Showing the P1/C1 and P1/C2 Structures

Highlight of Cyclic Bending Test

Plastic Substrate Thickness (mm) Passivation Unit Coupling Layer No. of Unit Bending cycles
PET/PEN 50 - 75 - C1 (150nm) 1 250
PET/PEN 50 - 75 P1 (75nm) C1 (150 nm) 1 1000
PEN 100 p1 (75nm) C1 (150nm) 1 300
PC 120 - 200 p1 (75nm) C1 (150nm) 1 1 - 2
PET/PEN 50 - 75 P1 (75nm) C1 (150nm) 3 250
PET/PEN 50 - 75 P1 (25nm) C1 (50nm) 3 1200
PET/PEN 50 - 75 P1 (25nm) C1 (50nm) 4 800
PET/PEN 50 - 75 P1 (75nm) C2 (150nm) 1 850
PET/PEN 50 - 75 p1 (25nm) C2 (50nm) 3 1000
A Summary of Cyclic Bending Test
Appearance of Cracks After the Cyclic Bending Test
Appearance of Cracks After the Cyclic Bending Test

  1. Only plastic substrates thinner than 75m m passed the cyclic bending test!
  2. Critical total thickness of barrier films < 225nm!
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