PMMA-based patternable gate insulators for organic thin-film transistors

In order to prepare patternable polymer gate insulators, two methods of photo-crosslinking the polymer insulator were investigated. In the first method, poly(methyl methacrylate- co-2-hydroxyethyl methacrylate) [poly(MMA- co-HEMA)] functionalized with cinnamate groups was synthesized and photo-crosslinked. In the second method, a semi-interpenetrating PMMA network was prepared using a 25 wt% solution of PMMA/dipentaerythritol hexa-acrylate (DPEHA)/diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) by photo-crosslinking. Both of the photo-crosslinked insulator layers showed a high pattern resolution, indicating that physically and chemically stable crosslinking was accomplished. The field-effect mobilities of the pentacene-based OTFTs fabricated with the functionalized poly(MMA- co-HEMA) (60/40) and PMMA/DPEHA as gate insulators were 0.98 and 0.71 cm 2/V s, respectively. It was found that patternable polymer gate insulators having good electrical properties could be prepared by using the functionalized poly(MMA- co-HEMA) and the PMMA/DPEHA solution.