Orthogonal Lithography for Organic Electronics CNF

We introduce a new class of photo-electron-beam resists and solvents which are benign to organic electronic materials. We demonstrate that our patterning approach enables the fabrication of unique organic electronic devices, such as all organic thin film transistors, patterned light emitting diode displays and top-contact small channel length thin film transistors. Summary of Research: Organic electronics and optoelectronics are fast developing branches of modern science and technology that are aiming to replace conventional inorganic materials with light, inexpensive, flexible organic materials. One of the main issues to be solved on the route to real word application is patterning and processing of thin layer active organic materials. In collaboration with Prof. Christopher Ober’s group, we present new reliable photolithography microand nano-patterning techniques for high resolution, high throughput patterning of solution processable organic materials. We also demonstrate that the proposed approach is completely benign to a majority of organic electronic materials as well as environmental friendly and easily adopted by industry. This is achieved by utilizing environmentally benign fluorous solvents combined with specifically tailored patterning materials. Fluorous solvents are poor solvents for non-fluorinated organic materials [1]. Among the variety of fluorous solvents, segregated hydrofluoroethers (HFEs) attracted our attention because of their nonflammability, zero ozone-depletion potential and low toxicity for humans [1]. We further verified that HFE are completely benign to majority of organic electronic materials independently on their hydrophilicity/oleophilicity [2]. In order to perform the patterning, we tested three different negative tone photo-(e-beam) resists synthesized by Prof. Ober’s group. The first resist is a random copolymer, composed of 1H,1H,2H,2H– perfluorodecyl methacrylate (FDMA) and tert-butyl methacrylate (TBMA). The detail synthesis and characterization of this resist are given elsewhere [3]. The resist has resolution down to 1 μm and is processable in supercritical carbon dioxide and HFEs. We demonstrated the capabilities of the resist by fabricating patterned organic light emitting diodes (OLEDs). Figure 1 illustrates an optical micro-graph of patterned OLEDs under operation, with sizes as small as 5 μm. The operating voltage for 1 cd/ m2 is ~ 4 V while the brightness is ~ 1,000 cd/m2 at 10 V. A maximum l u m i n o u s e f f i c i e n c y of ~ 22 cd/A (co r re spond ing to ~ 8 lm/W) was obtained at a driving current of ~ 1 mA/cm2 in the device with a patterned LEP layer, without much optimization. The second resist is a semi-perfluoroFigure 1: Optical images of electroluminescence from patterned OLEDs with various feature sizes under operation. Image is reprinted from Journal of Materials Chemistry, 2008, 18, 3087 cover page.