Since the first description of their use as potential elements for electronic devices, [1] in 1987, organic thin-film transistors (OTFTs) have been intensively studied, due to their potentially lower cost, higher performance, and higher compatibility with flexible electronic applications, as compared to conventional silicon technology. [2][3][4][5] Recently, new functions of OTFTs and their integrated circuits have been being considered, in an attempt to take advantage of organic electronic devices in different applications, such as memory, [6,7] radio-frequency identification (RFID), [8] and sensors. [9][10][11][12] For functional organic devices, organic smart materials with ferroelectric, piezoelectric, and pyroelectric properties can be directly integrated into the OTFT device structure. Good candidates are poly(vinylidene fluoride) (PVDF) and its copolymer with trifluoroethylene, P(VDF-TrFE). The piezo-and pyroelectricity of PVDF and P(VDF-TrFE) were studied in depth, [13][14][15][16][17][18][19][20][21][22] and have been successfully applied in many research fields, [23] but the applications of these properties in OTFTs are limited to external sensing modules. [9,11] On the other hand, there have been both theoretical and experimental reports of memory applications based on the ferroelectricity of P(VDF-TrFE) in OTFTs. [6,7,[24][25][26] High current on-off ratio and fast switching dipoles, which imply a small remnant polarization, are the key aspects in this case. In applications making use of the pyroelectric and piezoelectric properties of P(VDF-TrFE), however, the switching of small remnant polarization should be avoided, and a stable large polarization is required instead. Thus, physical models based on the assumption of small and easy-to-switch remnant polarizations [24][25][26] are not appropriate in interpreting the experimental observation in this work, showing a very large remnant polarization, and need to be modified in order to accurately interpret the experimental information.In this report, we present for the first time the direct use of a highly crystalline P(VDF-TrFE) material with a very large remnant polarization as a pyroelectric gate-insulator layer in an OTFT structure for temperature-sensing applications. This has the advantage of a simpler fabrication process compared to external sensing modules. A poling strategy based on step-wise poling process [20] was required to enhance the effects of the pyroelectricity on the transistor performance (see Experimental). The output characteristics of the OTFTs were changed so as to exhibit a linear current-voltage relationship, thus providing evidence of their large polarization. We introduced a modified transistor equation to fully explain this phenomenon and related problems, such as the effect of the geometry on poling. The thermal behavior of the functional OTFT was also investigated, and the results showed a linear response below the phase transition temperature of P(VDF-TrFE). The temperature response of the device was primarily attributed t...

The incorporation of an ultrathin, atomic layer deposited HfO2 layer in between the spin-coated poly-4-vinyl phenol (PVP) organic layers in the laminated multilayer gate dielectric for pentacene organic thin film transistors on a flexible substrate reduced the gate leakage current by three to four orders of magnitude and thereby significantly enhanced the current on/off ratio up to ≅104-fold. Cyclic bending testing indicated that the electrical characteristics of the device with the PVP∕HfO2∕PVP trilayer gate dielectric stack were superior to those of the device with the single PVP gate dielectrics due to the improved mechanical and electrical stabilities of the gate dielectric.

Improvement of dispersion of the Al 2 O 3 nanoparticles in the poly͑4-vinyl phenol͒ ͑PVP͒ matrix by coupling agent treatment resulted in a reduction of the leakage current density of the nanocomposite gate dielectric in organic thin-film transistor ͑OTFT͒ devices, which, in turn, improved the device performance compared to that of the device with the pure PVP gate dielectric. Under repetitive cyclic bending, the leakage current density of the nanocomposite layer was not changed, while that of the PVP layer was increased significantly. The nanocomposite gate dielectric layer provided the flexible OTFT device with improved mechanical and electrical stabilities.During the past few years, flexible organic thin-film transistors ͑OTFTs͒ have been extensively studied for various applications such as radio-frequency identification, 1,2 low-cost sensors, 3,4 and flexible displays. 5-7 Achieving the electrical reliability of flexible OTFTs under repetitive mechanical deformation requires good mechanical flexibility and stability of the electrical properties. Therefore, gate dielectric, electrode, and semiconductor layers possessing good mechanical flexibility, with no cracking or delamination, and whose electrical properties remain stable in the device during repetitive mechanical bending, need to be developed for flexible devices.One of the important materials determining the performance of OTFTs is the gate dielectric layer. 8 Inorganic gate dielectric layers, such as SiO , and lead zirconate titanate, etc., 8 can provide a higher capacitance with a smaller thickness due to their large dielectric constant ͑k͒ and low-leakage characteristics. However, cracking during repetitive mechanical deformation can cause an increase in the leakage current. In the case of low-k organic gate dielectrics such as poly͑4-vinyl phenol͒ ͑PVP͒, poly͑vinyl alcohol͒, polyimide ͑PI͒, and benzocyclobutane, 8,9 the required large thickness of the gate dielectric layer due to the high leakage current lowers the gate capacitance. Furthermore, although organic gate dielectric layers are known to be mechanically flexible, their electrical stability is unknown. One way of overcoming the problems of inorganic and organic gate dielectrics would be to develop mechanically flexible nanocomposite gate dielectrics. Nanocomposite gate dielectrics in OTFTs have been studied for the purpose of increasing the gate capacitance and thereby improving device performance. 10-13 However, their leakage characteristics of the nanocomposite gate dielectrics and their electrical stability under repetitive mechanical deformation has not been reported.In this work, Al 2 O 3 /PVP nanocomposite layers with good dispersion of the Al 2 O 3 nanoparticles were obtained by treating the surface of the nanoparticles with a coupling agent ͑CA͒. A mechanically flexible, low-leakage, and high-capacitance nanocomposite gate dielectric layer was obtained and successfully applied to OTFT devices. ExperimentalAl 2 O 3 particles with the average size of Х50 nm ͑Sigma Aldrich͒ were surface...

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