The influence of gate dielectrics on a high-mobility n-type conjugated polymer in organic thin-film transistors (original) (raw)
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Japanese Journal of Applied Physics, 2007
We describe the importance of the functional group density of polymeric insulators (PI) for organic thin-film-transistors (OTFTs) in terms of the insulator processing temperature and the exposure of a linearly polarized ultraviolet (LPUV) light. The PI layers processed at lower temperatures than the boiling temperature (T b ) of the solvent have higher densities of functional groups than those processed above T b . The carrier mobility in the pentacene OTFT processed below T b increases at least by a factor of three with maintaining other electrical properties such as the threshold voltage and the current on/off ratio. Our results suggest that the preferential alignment of the pentacene molecules is not the main physical mechanism for the mobility enhancement. From the mobility anisotropy resulting from the polarization of the LPUV, the packing density of the pentacene molecules on the PI layer, dictated primarily by the density of functional groups, is found to play a critical role on the magnitude of the mobility.
Organic thin-film transistors with polymeric gate insulators
Journal of Non-crystalline Solids, 2008
Copper phthalocyanine (CuPc) thin-film transistors (TFTs) have been fabricated using spin-coated polymeric gate insulators, including polymethyl methacrylate (PMMA) and a novel poly(methylmethacrylate-co-glycidylmethacrylate) (P(MMA-co-GMA)). These devices behaved fairly well and showed satisfactory p-type electrical characteristics. The transistor with P(MMA-co-GMA) gate insulator showed higher field-effect mobility, l FET = 1.22 · 10 À2 cm 2 /V s, larger on/off current ratio, I on /I off = 7 · 10 3 and lower threshold voltage, V T = À8 V, compared with the transistor with PMMA gate insulator (l FET = 5.89 · 10 À3 cm 2 /V s, I on /I off = 2 · 10 3 and V T = À15 V). The higher mobility of CuPc on P(MMA-co-GMA) was attributed to better ordering and enhanced crystallinity within the CuPc film and the better CuPc/P(MMA-co-GMA) interface, as observed by X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) measurements. The correlation between the structural properties and the device performance of CuPc films grown on different polymeric gate insulators is discussed.
Journal of Applied Physics, 2007
This work elucidates the way polymer gate dielectrics affect the accumulation and transport of charge carriers in the active layer of organic field-effect transistors ͑OFETs͒. Incorporating a poly͑vinyl alcohol͒ polymer interfacial film and another cross-linked poly͑4-vinyl phenol͒ layer as a double-layer gate dielectric causes the pentacene-based OFETs to exhibit effective n-channel conduction of a saturated, apparent pinch-off drain-source current with the electron mobility of ϳ0.012 cm 2 V −1 s −1. The formation of an n channel in the pentacene layer is supported by the increased capacitance that is identified by the quasistatic capacitance-voltage measurements of devices with the metal-insulator-semiconductor configuration, biased at a positive gate voltage, in the n-type accumulation regime.
Cross-Linked Polymer Gate Dielectric Films for Low-Voltage Organic Transistors
Chemistry of Materials, 2009
Cross-linked polymer films were investigated as new gate dielectric materials for low-voltage thinfilm transistors. Poly(4-vinylphenol) (PVP) was cross-linked through esterification reactions with commercially available bifunctional anhydrides, acyl chlorides, and carboxylic acids. The polymer dielectric films were evaluated based on surface morphology, capacitance, leakage current, and their compatibility with organic semiconductors. Thin insulating PVP films cross-linked with dianhydrides yielded a capacitance as high as 400 nF/cm 2 with leakage currents below 10 -8 A/cm 2 . Organic thin-film transistors (OTFTs) fabricated on these gate dielectric layers exhibited charge carrier mobilities as high as 3 cm 2 / (V s) for p-channel pentacene on octadecyltriethoxylsilane (OTS)-modified PVP and 0.045 cm 2 /(V s) for n-channel perfluorinated copper phthalocyanine (FCuPc).
Organic Electronics, 2010
Pentacene-based organic field-effect transistors (OFETs) with different polymer gate dielectrics, such as polyvinyl alcohol (PVA), poly 4-vinyl phenol (PVP), and polystyrene (PS), are fabricated to study the influence of polymer dielectrics on the formation of the n-type conduction (electron) channel in the pentacene active layer. The output characteristics of OFETs and capacitance-voltage measurements indicate that the formation of ntype conduction channel in the active layer is hindered by the electron traps at the contact interface with PVP dielectric layers, probably due to the high dissociation constant of protons of the hydroxyl groups in PVP. The dissociated protons at PVP dielectric layer form the electron traps and restrict the formation of n-type conduction channel. In comparison, OFETs applying PVA of relatively lower dissociation constant than that of PVP as the gate dielectric present the decent n-type output characteristics. The appropriate work function of source-drain electrodes as well as a trap-free dielectric layer are essentially important to determine the performance of pentacene-based n-type OFETs. The pentacene-based OFETs applying calcium as the source-drain electrodes and PS as the dielectric layer has the electron mobility of 0.077 cm 2 s À1 V À1 in this study.
Applied Physics Letters, 2005
High-performance pentacene organic thin-film transistors with double layers of the terpolymer electret poly͑vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene͒ and the polymer poly͑vinyl cinnamate͒ as a gate dielectric are reported. The electret is a high-k dielectric polymer with a static dielectric constant of = 14. The transistors show an intrinsic field-effect mobility in the range of i =1 cm 2 / V s and an onto off-current ratio of about 10 5. High-k polymer gate dielectrics seem promising for organic nonvolatile memory and sensor field-effect transistors.
Materials Science in Semiconductor Processing, 2017
In this work, we present a method to increase the performance in solution processed organic field effect transistors (OFET) by using gel as dielectric and molecular doping to the active organic semiconductor. In order to compare the performance improvement, Poly (methylmethacrylate) (PMMA) and Poly (3-hexylthiophene-2,5diyl) P3HT material system were used as a reference. Propylene carbonate (PC) is introduced into PMMA to form the gel for using as gate dielectric. The mobility increases from 5.72×10 −3 to 0.26 cm 2 V s-1 and operation voltage decreases from −60 to −0.8 with gel dielectric. Then, the molecular dopant 2,3,5,6-tetrafluoro-7,7,8,8tetracyanoquinodimethane (F4-TCNQ) is introduced into P3HT via co-solution. The mobility increases up to 1.1 cm 2 V s-1 and the threshold voltage downs to −0.09 V with doping. The increase in performance is discussed in terms of better charge inducing by high dielectric properties of gel and trap filling due to the increased carrier density in active semiconductor by molecular doping.
The application of a high-k polymer in flexible low-voltage organic thin-film transistors
Although much progress has been made in the study of high-mobility organic semiconductors in recent years, one major challenge for organic thin film transistors (OTFTs) in real applications is the relatively high operating voltage, which is mainly related to the gate dielectric of the OTFT. Here we show the application of a high-k poly(vinylidene fluoride-trifluoroethylene-chlorofloroethylene) (P(VDF-TrFE-CFE)) as the gate dielectric of flexible low-voltage pentacene OTFTs for the first time. The performance of the OTFTs is optimized by modifying the surface of P(VDF-TrFE-CFE) films with various thin polymer films by a solution process. The flexible OTFTs show excellent performance at the operating voltage of 4 V and good stability after 1000 bending tests. It is expected that P(VDF-TrFE-CFE) is a suitable gate dielectric for low-voltage OTFTs based on various small-molecule organic semiconductors because P(VDF-TrFE-CFE) terpolymer films can be easily modified with different thin polymer films by a solution process.
Physical Review B, 2006
The long-term target of producing all-organic devices requires custom-designed dielectric materials able to be applied and patterned with a wide range of new and fast deposition and patterning methods. Inorganicorganic hybrid polymers such as organic modified ceramics ͑ORMOCERs͒ have recently gained considerable attention in polymer electronics. Consisting of organically functionalized inorganic-oxidic units, their material properties can be tuned over a wide range and, in addition, their processing is very flexible providing good compatibility to many materials and substrates and allowing for direct patterning. A study on the application of different ORMOCER systems as gate dielectric layers in organic thin-film transistors ͑OTFTs͒ with pentacene as the organic semiconductor and directly structured contact holes is presented. Depending on the chemistry of the underlying ORMOCER system, different morphologies of the thermally evaporated pentacene were observed and correlated to the electrical characteristics of the transistor devices. In some cases, OTFTs with excellent electrical performance were achieved, showing intrinsic field-effect mobility values up to 1 cm 2 /V s. Based on the high charge-carrier mobility of the pentacene-ORMOCER interface and the good dielectric, passivating, and patterning properties of the ORMOCER materials, these devices lay the foundation for a new generation of high-quality, fast, processable low-cost organic electronics.