High-Performance Nonvolatile Organic Transistor Memory Devices Using the Electrets of Semiconducting Blends

Organic nonvolatile transistor memory devices of the <i>n</i>-type semiconductor <i>N</i>,<i>N</i>′-bis­(2-phenylethyl)-perylene-3,4:9,10-tetracarboxylic diimide (BPE-PTCDI) were prepared using various electrets (i.e., three-armed star-shaped poly­[4-(diphenylamino)­benzyl methacrylate] (N­(PTPMA)₃) and its blends with 6,6-phenyl-C₆₁-butyric acid methyl ester (PCBM), 6,13-bis­(triisopropylsilylethynyl)­pentacene (TIPS-pen) or ferrocene). In the device using the PCBM:N­(PTPMA)₃ blend electret, it changed its memory feature from a write-once-read-many (WORM) type to a flash type as the PCBM content increased and could be operated repeatedly based on a tunneling process. The large shifts on the reversible transfer curves and the hysteresis after implementing a gate bias indicated the considerable charge storage in the electret layer. On the other hand, the memory characteristics showed a flash type and a WORM characteristic, respectively, using the donor/donor electrets TIPS-pen:N­(PTPMA)₃ and ferrocene:N­(PTPMA)₃. The variation on the memory characteristics was attributed to the difference of energy barrier at the interface when different types of electret materials were employed. All the studied memory devices exhibited a long retention over 10⁴ s with a highly stable read-out current. In addition, the afore-discussed memory devices by inserting another electret layer of poly­(methacrylic acid) (PMAA) between the BPE-PTCDI layer and the semiconducting blend layer enhanced the write-read-erase-read (WRER) operation cycle as high as 200 times. This study suggested that the energy level and charge transfer in the blend electret had a significant effect on tuning the characteristics of nonvolatile transistor memory devices