Organic non‐volatile memory (ONVM) based on pentacene field‐effect transistors (FETs) has been fabricated using various chargeable thin polymer gate dielectrics—termed electrets—onto silicon oxide insulating layers. The overall transfer curve of organic FETs is significantly shifted in both positive and negative directions and the shifts in threshold voltage (VTh) can be systemically and reversibly controlled via relatively brief application of the appropriate external gate bias. The shifted transfer curve is stable for a relatively long time—more than 105 s. However, this significant reversible shift in VTh is evident only in OFETs with non‐polar and hydrophobic polymer electret layers. Moreover, the magnitude of the memory window in this device is inversely proportional to the hydrophilicity (determined from the water contact angle) and dielectric polarity (determined from the dielectric constant), respectively. Memory behaviors of ONVM originate from charge storage in polymer gate electret layers. Therefore, the small shifts in VTh in ONVM with hydrophilic and polar polymers may be due to very rapid dissipation of transferred charges through the conductive channels which form from dipoles, residual moisture, or ions in the polymer electret layers. It is verified that the surface or bulk conductivities of polymer gate electret layers played a critical role in determining the non‐volatile memory properties.
Many attempts have been made to realize a universal memory, [1] that is, an ideal memory device comprising new, fast, non-volatile, inexpensive methods for storing information. Compared to its inorganic counterparts, organic memory has attracted a great deal of interest because of its remarkable progress in organic electronics and its unique advantages: it is inexpensive, lightweight, and capable of printing ubiquitous components onto plastic substrates. [2][3][4] In an attempt to create a novel organic memory, several types of memory devices based on organic and polymeric materials have been evaluated, including organic electrical bistable devices, [5] organicinorganic hybrid memory using a polymeric fuse, [6] and organic field-effect transistors (OFETs) based on ferroelectric gate insulators and chargeable gate dielectrics. [7][8][9][10][11] Among these types of organic memory devices, a memory element based on FETs is especially attractive because of its non-destructive readout and single-transistor applications. [12] In this case, the functionality arises from the field-effect modulation by the spontaneous polarization that occurs in ferroelectrics or the trapped charges in chargeable dielectrics, which are referred to as electrets.While an OFET memory has many potential advantages, state-of-the-art results of OFET memory devices are in a less favorable position, compared to other types of organic memories. [7][8][9][10][11] With respect to the case of organic ferroelectrics, Naber et al. recently demonstrated an on/off ratio of 10 4 with a programming time of 0.3 ms and a memory effect stability of more than one week. [8] However, when compared to ferroelectrics, only a small amount of attention has been given to electret-charged OFET memory, in spite of the similar field-effect modulation. Moreover, the characteristics of OFET memory based on electrets are less well understood than those of ferroelectric-based OFET memory devices due to a lack of research. Katz et al. demonstrated an OFET memory with a polarizable gate insulator that induced a floating-gate-like behavior, [9] and Singh et al. also demonstrated an OFET memory using poly(vinyl alcohol) as a gate electret.[10] However, these devices still do not sufficiently satisfy the criteria demanded in order to compete with other types of memory devices. [13] Furthermore, details of the operating mechanisms of these devices are not well understood. Therefore, the mechanism should be further investigated to successfully develop a high-performance OFET memory based on electrets.In this Communication, we report on OFET memory devices built on silicon wafers and based on films of pentacene and an SiO 2 gate insulator that are separated by a thin layer of poly(a-methylstyrene) (PaMS), which acts as a polymeric gate dielectric. This OFET memory device displayed reversible shifts in the threshold voltage (V Th ) when an appropriate gate voltage (V g ) was applied above a certain threshold via a relatively short switching time. Based on these reversible shifts in...
Highly sensitive thin-film organic phototransistors: Effect of wavelength of light source on device performance J. Appl. Phys. 98, 074505 (2005); 10.1063/1.2061892High-photosensitivity p -channel organic phototransistors based on a biphenyl end-capped fused bithiophene oligomer Appl. Phys. Lett. 86, 043501 (2005);The effect of light irradiation on the characteristics of organic field-effect transistors containing sexithiophene ͑6-T͒ and pentacene was examined. Organic phototransistors ͑OPTs͒ in which 6-T and pentacene were incorporated were fabricated. Their response behaviors were investigated under conditions of irradiation by either modulated or continuous ultraviolet light with various intensities. Both devices showed two distinguishable responses, i.e., fast and slow responses from photoconductive and photovoltaic effects, respectively. The fast response is mainly the result of the generation of mobile carriers by the absorption of a photon energy higher than the band gap energy of the semiconductor and, subsequently, an increase in conductance via a greater flow of photogenerated mobile carriers into the channel layer. On the other hand, the slow response, which was confirmed by a light induced shift in the threshold voltage ͑V th ͒ or the switch-on voltage ͑V O ͒, is the result of a slow release of accumulated and trapped electrons in the semiconductor-gate dielectric interface. The V O is defined as the flatband voltage of devices. Below the V O , the channel current with the gate voltage is off current, and the channel current increases with the gate voltage above the V O . The speed of release of the accumulated charge was dependent on the type of semiconductor used. Pentacene OPTs showed a particularly long retention time. Even after storage for ten days, the shifted V O ͑or V th ͒ for the pentacene OPTs by light irradiation was not restored to the original value of the fresh devices. We conclude that this long sustained V th shift renders them attractive for use in "light-addressable nonvolatile memory devices."
[reaction: see text] A new curable arylamine containing a perfluorocyclobutane (PFCB) structure without an acidic group was synthesized. The material was thermally cured on ITO after spin-coating. The polymer showed excellent solvent resistance, high thermal stability, high transparency, and good surface smoothness.
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