Multilevel nonvolatile transistor memories using a star-shaped poly((4-diphenylamino)benzyl methacrylate) gate electret

Abstract

Multilevel nonvolatile transistor memories were fabricated using star-shaped poly((4-diphenylamino)benzyl methacrylate) (star-PTPMA) electret dielectric for charge storage and N,N′-bis(2-phenylethyl)perylene-3,4,9,10-bis(dicarboximide) (BPE-PTCDI) as an n-type semiconductor. Charges were controllably stored by applying a negative voltage bias, detected by shifting the threshold voltage, and this device retained the digital states even when the supplied voltage was removed. The multilevel data storage characteristics obtained by applying different gate voltages suggested that the device possessed nonvolatile write-many-read-many (WMRM) memory behaviors. The electronic charges were transferred and permanently accumulated in the gate electret from the restricting region of the star-PTPMA with well-defined charge trapping elements, but not in the case of linear-PTPMA. P-type pentacene was also used as a semiconductor layer to clarify the operating mechanism under a gate electric field. Our results demonstrated the significance of the architecture effect of the polymer electrets for nonvolatile organic transistor memory devices and their potentials in high-density data storage. Nonvolatile transistor memories combine the functionality of transistors in microchips with memory elements that are able to store information even if the power is turned off. As such they have great promise for the construction of next-generation computers. Wen-Chang Chen from National Taiwan University and colleagues from National Central University in Taiwan and Hokkaido University in Japan have now developed an organic multilevel nonvolatile transistor memory. The transistor element of the device is constructed from a polymer and a polymer electret - a dielectric material that has a quasi permanent electric charge. In this system current is generated by a combination of an applied external voltage and the charge stored in the electret - variation of which controls the overall current. Such polymer memory devices are of particular interest for potential applications in flexible electronics. Multilevel nonvolatile transistor memories were fabricated with inserted electret dielectric of star-shaped poly((4-diphenylamino)benzyl methacrylate). The devices could be controllably charged and retain the digital states even when the supply voltage was removed. The multilevel data storage characteristics by applying different gate voltages suggested novel ‘write-many-read-many memory’ behaviors.