MICROFLUIDIC ORGANIC LIGHT EMITTING DIODE (OLED) USING LIQUID ORGANIC SEMICONDUCTORS

T. Kasahara1, J. Mizuno1, S. Hirata2, T. Edura2, S. Matsunami2, C. Adachi2, and S. Shoji1 1Waseda University, Tokyo, JAPAN 2Kyushu University, Fukuoka, JAPAN

MEMS 2012, Paris, FRANCE, 29 January - 2 February 2012

Reporter-Vivek Hegde

OLED Technology Motivation Concept and Principle Experimental Procedure

Design of Prototype micro-fluidic OLEDFabrication ProcessEvaluation of Fabricated micro-fluidic OLED

Result and Discussion Conclusion

Outline

Micro fluidic devices have been developed for a wide range of applications.

OLEDs containing of solid-state organic semiconductors.

Next generation flat panel display due to their wide viewing angle, light weight and thin components.

Recently the optoelectronics devices based on the liquid emitting materials such as electro-chemiluminescence (ECL) OLEDs are also reported.

OLED Technology

The micro-channel structures are usually fabricated using MEMS technology.

Negative photo-resist SU-8 has been suitable material for the micro channel fabrication .

Transparent electrodes such as indium tin oxide (ITO) facilitate the optical microscopic observation of fluidic behaviour in the micro channels.

ITO has been widely used as an anode in OLEDs due to its high electrical conductivity.

Here Combination of micro-fluidics and liquid OLED.

Motivation

Different fresh liquid organic semiconductors are continuously injected from the inlets to the light emitting areas using the syringe pumps.

Concept And Principle

Micro-fluidic OLED, which consists of micro-channels and pairs of ITO anode and cathode.

Electroluminescence is performed in the flowed liquid organic semiconductors by the radiative recombination of electron-hole pairs with DC voltage.

Concept And Principle

The microchip has a 3 × 3 matrix of OLED array in the SU-8 micro-channels.

The micro-channels are sandwiched between the ITO anodes on a glass substrate and the polyethylene naphthalate (PEN) film with the ITO cathodes.

Depth is chosen about 6 µm for enhancement of OLED performances, widths are 1000, 1250, and 1500 µm.

Experimental Procedure-Design

ITO-anode patterned by conventional photolithography and wet etching using dilute aquarigia(a).(HCl-HNO3-H2O)

SU-8 3005 6 µm thick obtained by spun on substrate at 4000 rpm for 20 Sec and soft baked at 95ºC for 10 min(b).

For the surface modification of the SU-8 layer, the ITO anodes in the micro channels were covered by sacrificial layer of positive resist of 350 nm(c).

Fabrication Process

The ITO cathodes were fabricated by the same process as the ITO anodes.

The inlet and outlet of the microchannels were mechanically punched for injecting.

The anode and cathode substrates were separately fabricated and were bonded to form enclosed ITO electrodes embedded micro-fluidic channels.

Fabrication Process

Fabrication Process

Immersed in GOPTS-Glycidodyloxy proplyl tri methoxysilaneAPTES- Amino propyl triethoxysilane

The anode substrate was then rinsed with acetone and IPA to remove the sacrificial resist and any unbound GOPTS-SAM, while the cathode substrate was rinsed with ethanol .

Finally, the surfaces were bonded under contact pressure of 1.5 MPa at 140 °C for 5 min to form bond

To incorporate oxygen functionalities in to SU8,PEN and ITO

Fabricated OLED were investigated using scanning acoustic microscope (SAM) at 175 MHz

Two types of tests were performed : the observation of the fluidic behaviour and electroluminescence of the liquid emitter in the micro-channels, and the current density-voltage (J-V) measurement.

Evaluation of Fabricated micro fluidic OLED

The inlet and outlet nozzles were connected to the top plate. The liquid emitters introduced manually while the used liquid emitters were collected from the outlet nozzles.

The flow of the liquid emitter was detected by 365 nm UV light irradiation. Proper DC voltages were applied to the device with a source meter, and the electroluminescence was recorded with a digital camera. The J-V characteristics were measured using a semiconductor parameter analyzer

Result and Discussion

SAM image of the fabricated microfluidic OLED Demonstration

Electroluminescence in the microchannels of (b) 1000, (c) 1250 and (d) 1500 µm width under applied 70 V.

Result and Discussion

J-V Characteristics of micro-fluidic OLED

The current density increased with increasing applied voltage

The intensity increased significantly larger than 30 V

Research proposed a combination of micro-fluidic and liquid OLED, and fabricated a first prototype micro-fluidic OLED.

Optimized fabrication method was developed.

The electroluminescence was obtained in the flowed liquid emitters under the appropriate applied voltage.

The current density of 2.11 mA/cm2 was measured when 60 V was applied .

In contrast thicker emitter layer, higher driving voltage than solid state OLED.

Conclusion

Thank you

https://www.youtube.com/watch?v=9OvTLg4i2_U&playnext=1&list=PL7C0E1F21B3FB709C&feature=results_main