Enhanced field-effect mobility in pentacene based organic thin-film transistors on polyacrylates (original) (raw)
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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.
Journal of Electronic Materials, 2020
In this study, we present two regioregular poly(3-hexylthiophene-2,5-diyl) (rr-P3HT)-based top-gate bottom-contact configured organic thin-film transistors (OTFTs) using poly(a-methyl acrylate) (PMA) and poly(methyl methacrylate) (PMMA) polymers separately as gate insulators for comparison. In order to compare only the performance of the dielectrics, the other parts of the devices were kept qualitatively and quantitatively identical. Unlike PMMA, PMA is flexible, and flexibility is a desirable property for an OTFT. Thus, utilizing PMA can be advantageous if it supports higher performance of the transistor. In this respect, the electronic parameters of the fabricated devices were extracted from transfer and output characteristics to determine the performance of PMA in OTFT applications. Results showed that the mobility of the OTFT with PMA (PMA-OTFT) was nearly three times greater than that of the OTFT with PMMA (PMMA-OTFT), while the PMA-OTFT threshold voltage (V TH) was slightly less than that of the PMMA-OTFT, which was likely because of the greater effective capacitance (C EFF) of the PMA layer compared to that of the PMMA layer. This is the main advantage of the PMA. On the other hand, the major downside is found in the reduced onto off current (I ON /I OFF) and increased subthreshold swing originating from a huge off-current (I OFF), implying the existence of a large gate leakage current. Increasing the thickness of the PMA layer could reduce such large gate leakage current. However, this would lead to additional increase in the OTFT operating voltage. Therefore, further studies are required to improve the insulating property of the PMA polymer in order to substitute it for the PMMA.
Pramana, 2008
Organic thin film transistors (OTFTs) were fabricated using pentacene as the active layer with two different gate dielectrics, namely SiO2 and poly(methyl methacrylate) (PMMA), in top contact geometry for comparative studies. OTFTs with SiO 2 as dielectric and gold deposited on the rough side of highly doped silicon (n + -Si) as gate electrode exhibited reasonable field effect mobilities. To deal with poor stability and large leakage currents between source/drain and gate electrodes in these devices, isolated OTFTs with reduced source/drain contact area were fabricated by selective deposition of pentacene on SiO 2/PMMA through shadow mask. This led to almost negligible leakage currents and no degradation in electrical performance even after 14 days of storage under ambient conditions. But, the field effect mobilities obtained were lower than 10 −3 cm 2 V −1 s −1 , whereas by using PMMA as gate dielectric with chromium deposited on the polished side of n + -Si as gate electrode, improved field effect mobilities (>0.02 cm 2 V −1 s −1 ) were obtained. PMMA-based OTFTs also exhibited lower leakage currents and reproducible output characteristics even after 30 days of storage under ambient conditions.
Journal of Non-crystalline Solids, 2004
Pentacene thin-film transistors using polymethyl methacrylate as a gate dielectric have been fabricated. A bottom gate, inverted staggered structure was selected to study the influence of the dielectric on the device performance. Crystalline silicon wafers and polyethylenenaphtalate polymer foils were used as substrates. Pentacene thin-films were deposited by thermal evaporation in a highvacuum system. The maximum process temperature was 170°C, corresponding to the baking of polymethyl methacrylate. These devices showed satisfactory p-type electrical characteristics with on/off ratios exceeding 10 3 for V GS ranging from )30 to 30 V. The field-effect mobility and threshold voltage were around 0.01 cm 2 V À1 s À1 and )14 V, respectively. The polymethyl methacrylate dielectric also seems to provide some advantages of the so-called self-assembling monolayers.
Electrical characterization of pentacene thin-film transistors with polymeric gate dielectric
Synthetic Metals, 2004
Pentacene thin films obtained by thermal evaporation at room temperature have been incorporated as the active layer in bottom-gate thin-film transistors (TFTs). The dielectric was spin-cast polymethyl methacrylate (PMMA) baked at only 170 • C. Crystalline silicon wafers and polyethylenenaphtalate (PEN) polymer foils were used as substrates. These devices were electrically characterised by measuring the output and transfer characteristics at different temperatures. Both the channel conductance and field-effect mobility evidenced similar thermal activation energies around 0.15 eV. These results could indicate that electrical transport is mainly controlled by trapping and thermal release of carriers from localised states.
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.
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.
Pentacene thin-film transistors with polymeric gate dielectric
Organic Electronics, 2004
Pentacene thin-film transistors have been obtained using polymethyl methacrylate as a gate dielectric. The maximum process temperature was 170°C, which corresponds to the baking of the polymeric gate dielectric. These devices presented good electrical performances with field-effect mobilities of 0.01 cm 2 V À1 s À1 and low threshold voltages ()15 V). Atomic force microscopy studies reveal that the microstructure of pentacene layers is strongly conditioned by the surface morphology of the dielectric.
Influence of organic gate dielectrics on the performance of pentacene thin film transistors
Synthetic Metals, 2005
The electronic transport of polycrystalline pentacene thin film transistors is investigated. The thermally evaporated pentacene films prepared on organic dielectrics like benzocyclobutane exhibit mobilities comparable with inorganic dielectrics like thermal oxide and plasma enhanced chemical vapor deposited silicon nitride. To gain insights in the electronic transport behavior of the organic thin film transistors (TFTs) the I/V characteristics were simulated by a one-dimensional density-of-states transistor model. The experimental data can be described by using a broad distribution of acceptor-like states deep in the bandgap and a narrow distribution of donor-like states close to the valance band. The influence of the different dielectrics on the defect distribution and the electronic transport will be discussed.