Thiophene and Selenophene Donor-Acceptor Polyimides as Polymer Electrets for Nonvolatile Transistor Memory Devices

We report the nonvolatile memory characteristics of n-type N,N'-bis(2-phenylethyl)perylene-3,4:9,10-tetracarboxylic diimide (BPE-PTCDI) based organic field-effect transistors (OFET) using the polyimide electrets of poly[2,5-bis(4-aminophenylenesulfanyl)selenophene-hexafluoroisopropylidenediphthalimide] (PI(APSP-6FDA)), poly[2,5-bis(4-aminophenylenesulfanyl)thiophene-hexafluoroisopropylidenediphthalimide] (PI(APST-6FDA)), and poly(4,4'-oxidianiline-4,4'-hexafluoroisopropylidenediphthalic anhydride) (PI(ODA-6FDA)). Among those polymer electrets, the OFET memory device based on PI(APSP-6FDA) with a strong electron-rich selenophene moiety exhibited the highest field-effect mobility and I-on/I-off current ratio of 10(5) due to the formation of the large grain size of the BPE-PTCDI film. Furthermore, the device with PI(APSP-6FDA) exhibited the largest memory window of 63 V because the highest HOMO energy level and largest electric filed facilitated the charges transferring from BPE-PTCDI and trapping in the PI electret. Moreover, the charge transfer from BPE-PTCDI to the PI(APSP-6FDA) or PI(APST-6FDA) electrets was more efficient than that of PI(ODA-6FDA) due to the electron-donating heterocyclic ring. The nanowire device with PI(APSP-6FDA) showed a relatively larger memory window of 82 V, compared to the thin film device. The present study suggested that the donor acceptor polyimide electrets could enhance the capabilities for transferring and store the charges and have potential applications for advanced OFET memory devices.