A Phase-Separated Polymer Blocking Layer for Enhancing Data Retention in Flexible Printed Nonvolatile Organic Memories

In this work, we present enhanced data retention characteristics of flexible printed organic nonvolatile thin-film transistor (TFT) memories using a phase-separated polymer blocking layer. The memory devices are configured in a bottom-gate bottom-contact TFT structure with a bilayer dielectric layer consisting of a high-k insulator poly(vinylidene fluoride-co-trifluoroethylene) and a low-k chargeable polymer Parylene at the bottom and top, respectively. All the functional layers are solutionprocessed or printed except for the Parylene film. The blend ink containing a small-molecule semiconductor 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) and insulating polymer polystyrene (PS) are printed on the TFT active area. As dried, the printed ink leaves the phase-separated layers of PS and TIPS-pentacene due to the density difference. The bottom PS performs as a blocking layer to the charge stored in the electret Parylene beneath. The printed nonvolatile memory with the phase-separated PS exhibited significantly improved data retention time of over 10 years, compared with that of the pristine TIPS-pentacene memory devices (only few hours). We believe these results suggest a facile way to fabrication of printed organic memories that have long data retention characteristics.