Application of micro transfer stamping technique on the fabrication of organic thin-film transistor
Date Issued
2010
Date
2010
Author(s)
He, Huei-Wun
Abstract
Soft electronics devices based on organic thin-film transistors (OTFTs) possess a lot of advantages, such as flexibility, light weight and portability. The key to fabricate organic thin-film transistors on plastic substrate is one of the biggest challenges. Micro-transfer stamping technique is a simple and low-cost process to directly fabricate microstructure without residual layer. This study develops the micro-transfer stamping technique for the fabrication of OTFTs, including: 1. Investigation and fabrication of stamping mold; 2. Development of micro-transfer stamping process; 3. Implementation of complete process for fabrication of organic thin-film transistors.
First, in the topic of “Investigation and fabrication of stamp mold”, we used dry-film photoresist to rapidly define the interdigitated micro-patterns on the PET substrates, and after developing, the microstructured dry-film photoresist was used as the master mold for casting PDMS mold. The PDMS mold has faithful duplication of micro-patterns in the master mold with smooth bottom surface.
Second, in the topic of “Development of micro-transfer stamping process”, we investigated the effect of surface energy of materials and developed mechanism for effective stamping. The real deformation of PDMS mold was observed using optical microscopy. We demonstrated the micro-transfer stamping technique can be used to transfer conductive silver paste on PMMA substrate, and with different process conditions (pressure, temperature and transfer time), the stamping results can be obtained. It was found that: Under low temperature, the silver paste cannot be adequately heated and the viscosity is too low; but if the temperature is too high, the solvent will quickly evaporate causing the silver paste adhere to PDMS mold. Too low pressure fails to ensure the PDMS in uniform contact with the substrate, while excessive pressure will lead to severe deformation of PDMS mold, crumbling the contour of silver paste. PDMS will fail to be in complete contact with the substrate if the transfer time is too short; on the other hand, if the duration is too long, the silver paste will attach to PDMS mold causing the transfer failure. Under proper process parameters, we have succeeded in directly patterning the interdigitated electrode of silver paste without residual layer.
In the last topic of “Fabrication of organic thin-film transistors (OTFTs)”, the PMMA was spin coated for the dielectric layer on the ITO/PET flexible film that serve as gate/substrate, and the characteristics of dielectric such as capacitance and leakage under various conditions were discussed. We also proved that the stamping technique can apply to directly transferring source/drain structure of OTFTs. The P3HT semiconductive layer was then coated on source/drain electrode by drop casting to complete the fabrication of OTFTs.
Subjects
soft electronics
micro-transfer stamping
silver paste
OTFTs
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