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Thin film organic field-effect transistors were grown with vapor-deposited polycrystallineoctithiophene on silicon oxide insulating layers. This component requires an ohmic source and drain contacts for ideal operation. The perfor...
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Thin film organic field-effect transistors were grown with vapor-deposited polycrystallineoctithiophene on silicon oxide insulating layers. This component requires an ohmic source and drain contacts for ideal operation. The performance of organic electronic-devices is often limited by injection. In many real situations, however and specifically in organic devices, the injection of charge carriers from metals into semiconductors is non-linear. This has an adverse impact on the performance of thin film transistors, and makes the analysis of electrical measurements a complex task because contact effects need to be disentangled from transistor properties. This paper deals with the effects of non-ohmic contacts on the modeling of organic transistors and gives specific rules on how to extract the real transistor parameters using only electrical measurements. Several methods are used in order to study the influence of the contact resistance on the performance of organic transistors. This influence appears especially on the current-voltage characteristics of organic field effect transistor. We present a first method used to extract the key parameters of OFET such as; mobility, threshold voltage and contact resistances using the fit of the transfer characteristic of the devices. The second method has been used to exploit the different functional dependences of current on gate voltage which is induced by the presence of contact resistances in the linear and in the saturation regimes. All electrical key parameters of OFETs based on octithiophene have been extracted and we demonstrate that both mobility and contact resistance depend on gate voltage and temperature.
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Organic field-effect transistors (OFETs) have attracted great interest in recent years as a potential low-cost alternative to amorphous silicon-based transistors for many applications in electronics.[1] Charge-carrier mobility in ...
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Organic field-effect transistors (OFETs) have attracted great interest in recent years as a potential low-cost alternative to amorphous silicon-based transistors for many applications in electronics.[1] Charge-carrier mobility in an OFET device is strongly related to the crystalline structure of the organic semiconductor, that is, the molecular packing mode is one of the critical factors governing the intermolecular electronic interaction and charge transport.[2] It is known that charge-carrier transport depends on being able to hop between the molecules in the region, therefore, the molecular arrangement in a good semiconductor needs to provide sufficient overlap of the p orbitals of conjugated organic molecules to enable efficient charge migration between neighbouring molecules.[2a]
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A fluorinated-graphene, 2,5,8,11,14,17-hexafluoro-hexa-peri-hexabenzocoronene (6F-HBC), has been synthesized. 6F-HBC was deposited by vacuum sublimation as an active layer in an organic field-effect transistor (OFET). The OFET wit...
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A fluorinated-graphene, 2,5,8,11,14,17-hexafluoro-hexa-peri-hexabenzocoronene (6F-HBC), has been synthesized. 6F-HBC was deposited by vacuum sublimation as an active layer in an organic field-effect transistor (OFET). The OFET with 6F-HBC performed as an n-type semiconductor, while that with hexa-peri-hexabenzocoronene (HBC) performed as a p-type semiconductor. The electron field-effect mobility and on/off ratio for 6F-HBC were 1.6 × 10~(-2) cm~2/Vs and 10~4, respectively. Hexafluoro-substituting reduces both the highest occupied molecular orbital and lowest unoccupied molecular orbital levels by 0.5 eV, which is suitable for electron injection from the electrode. 6F-HBC has a face-to-face structure which is a preferable crystal structure for carrier transport.
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We report that the pervoskite material, strontium titanate (STO) can be used as a gate dielectric layer of flexible and low voltage organic field effect transistor (OFET). The crystallinity, dielectric constant, and surface morpho...
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We report that the pervoskite material, strontium titanate (STO) can be used as a gate dielectric layer of flexible and low voltage organic field effect transistor (OFET). The crystallinity, dielectric constant, and surface morphology of STO films can be controlled by the engineering of the growth condition. Under optimized growth condition, amorphous films of STO show a much better gate dielectric compared to other gate dielectrics used to date, with very small leakage current density for flexible and low voltage (<5 V) OFETs. The amorphous STO film decreases the interface trap density at organic/dielectric interface substantially. Pentacene transistors with amorphous STO gate dielectric show high mobility of 2 cm(2)/(V s), on/off ratio of 10(6), subthreshold swing of 0.3 V/dec and low interface trap density. Similarly excellent performance has been obtained in copper phthalocyanine (CuPc) based OFETs with on/off ratio, similar to 10(5) and carrier mobility, similar to 5.9 X 10(-2) cm(2)/(V s). Moreover, the operating voltage (similar to 5 V) has been reduced by more than one order of magnitude. It has been demonstrated that the low processing temperature of amorphous STO makes it the most suitable gate dielectric for flexible and transparent organic devices to operate under low voltage.
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Piezoelectric sensors are useful for a range of applications, but passive arrays suffer from crosstalk and signal attenuation, which have complicated the development of array-based polyvinylidene difluoride (PVDF) sensors. We have...
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Piezoelectric sensors are useful for a range of applications, but passive arrays suffer from crosstalk and signal attenuation, which have complicated the development of array-based polyvinylidene difluoride (PVDF) sensors. We have used organic field-effect transistors, which are compatible with the low Curie temperature of a flexible piezoelectric polymer, i.e., PVDF, to monolithically fabricate transimpedance amplifiers directly on the sensor surface and convert the piezoelectric charge signal into a current signal, which can be detected even in the presence of parasitic capacitance. The device couples the voltage generated by the PVDF film under strain into the gate of organic thin-film transistors using an arrangement that allows the full piezoelectric voltage to couple to the channel while also increasing charge-retention time. A bipolar detector is created using ultraviolet–ozone treatment to shift the threshold voltage and increase the current of the transistor under both compressive and tensile strain. An array of devices that maps the strain field on a PVDF film surface is demonstrated.
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The photoluminescence and electroluminescence of two devices made from naphthyl end-capped oligothiophenes are investigated based on an organic light-emitting field-effect transistor (OLEFET) configuration. A novel method to light...
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The photoluminescence and electroluminescence of two devices made from naphthyl end-capped oligothiophenes are investigated based on an organic light-emitting field-effect transistor (OLEFET) configuration. A novel method to light up an active organic layer using a sinusoidal alternating current (AC) gate voltage is examined. The electroluminescence spectra from both materials are very similar to their photoluminescence spectra indicating that the light emission is caused by the same electronic transitions. The intensity of the electroluminescence emission increases with increasing frequency of the AC gate voltage, and it is non-linearly dependent on the amplitude of the AC gate voltage. Moreover, light emission on both sides of the charge transporting channel is revealed by an optical microscope when the channel is appropriately wide, e.g. 10 μm. A simple model involving sequential injection of both charge-carrier types from one electrode into the organic material explains the results.
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Increasing the alignment of thin films, which leads to anisotropy, is an attractive way to improve the performance of organic devices. A highly controllable and reproducible method to fabricate organic field effect transistors wit...
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Increasing the alignment of thin films, which leads to anisotropy, is an attractive way to improve the performance of organic devices. A highly controllable and reproducible method to fabricate organic field effect transistors with large anisotropic ratios was proposed in this paper. The surface of the dielectric layer was etched to form patterns through conventional semiconductor processing. Transistors having current direction perpendicular to or parallel to the direction of the patterns were fabricated and characterized. The mobilities of these two kinds of transistors arc 0.016 and 0.001 cm~2/Vs respectively, which means the anisotropic ratio is 16.
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1,2,3,4-Tetrafluoropentacene is prepared from a soluble precursor containing a carbonyl bridge across the central benzene ring. It underwent dimerization readily in solution, yet displayed a high stability in the solid state. Whil...
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1,2,3,4-Tetrafluoropentacene is prepared from a soluble precursor containing a carbonyl bridge across the central benzene ring. It underwent dimerization readily in solution, yet displayed a high stability in the solid state. While fabricated into OFET devices, it exhibited an ambipolar charge transport characteristic. Its spectral and electronic properties are described.
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