Nesibe Lakhani EECS 277A Prof. Richard Nelson OLED Fabrication Nesibe Lakhani EECS 277A Prof. Richard Nelson

OLED Structure OLEDs are light emitting devices that have a thin film of organic compounds as its emissive electroluminescent layer.

Fabrication Methods Physical Vapor Deposition Screen Printing Ink Jet Printing In-line Fabrication

OLED Fabrication Steps

Physical Vapor Deposition (PVD)

Physical Vapor Deposition Thermal vapor evaporation of small molecules occurs in environment of 10e(-6) Torr or higher It is usually carried out on glass substrate Multicolor displays are made using properly matched shadow masks for depositing RGB emitting materials

Advantages of PVD Thickness can be easily controlled 2-dimensional combinatorial arrays of OLEDs can be easily fabricated in a single deposition procedure PVD uses the generally available vacuum equipment that exists in the semiconductor industry

Disadvantages of PVD Expensive Not flexible Has no control to direct the materials to deposit on the desired areas Inefficient use of materials

Screen Printing Used in low information content displays such as logos and signs Thin films achieved Elements of screen printing: screen, stencil, squeegee, ink, press bed, and substrate Mesh materials can vary from polyester to stainless steel

Screen Printing Steps The mesh material is stretched across a frame Hole transport layer prepared using a solution of diamine, polycarbonate, and rubrene. Squeegee is used to wipe solution through the open mesh Resulting film covers entire surface of ITO Electron transport layer (ETL) and cathode are deposited by PVD

Screen Printing For patterned hole transport layer (HTL) devices: cathode is deposited in a block larger than the HTL pattern For non-patterned HTL: cathode is deposited through a mask to create emitting regions of known area for device output measurement

Advantages of Screen Printing Simple Lower cost Great reduction in materials usage because materials are only directed to the printed areas Faster than inkjet printing More versatile

Ink Jet Printing OLEDs are sprayed onto substrates like ink sprayed on paper during printing Advantages: Reduced cost Allows OLEDs to be printed on very large films

Ink Jet Printing Ink jet printing to define and pattern RGB emitting subpixels

In-Line Fabrication Mass production technique Vertical in-line tool operates with continuous substrate flow Linear sources of depositing organic and metallic materials

In-Line Fabrication Excellent thickness homogeneity Cheaper mass production technique Excellent thickness homogeneity Excellent deposition stability Complicated stack structures possible High deposition rates/high throughput High material usage Large substrate handling

OLED Fabrication Roadmap

References Ghassan E. Jabbour et al., Screen Printing for the Fabrication of Organic Light-Emitting Devices, IEEE 7:5, 2001 Joseph Shinar, Organic Light-emitting Devices. http://www.ewh.ieee.org/soc/cpmt/presentations/cpmt0401a.pdf http://www.opera2015.org/deliverables/MONA_CD-ROM/4_Symposium%20Presentations/04-scholles2752.pdf Muhamad Mat Salleh, et.al., Fabrication of Organic Light Emitting Diodes. http://optics.org/cws/article/research/24299