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1.
To improve the performances of pentacene-based organic thin-film transistors (OTFTs), a TPD buffer layer was inserted between the Au metal electrode and the pentacene channel layer. As shown by the ultraviolet photoelectron spectroscopy measurement, the Au work function was increased from 4.61 eV for Au in direct contact with pentacene to 4.74 eV and 4.78 eV for the sample inserted with 2-nm-thick and 3-nm-thick TPD buffer layers, respectively, between the Au metal electrode and the pentacene channel layer. Moreover, the contact resistance was reduced from 1 MΩ to 0.1 MΩ by inserting a 2-nm-thick TPD buffer layer. Compared with the transconductance of 2.67 × 10?7 S, the field-effect mobility of 0.46 cm2/V s, and the substhreshold swing of 1.78 V/decade for the conventional pentacene-based OTFTs without TPD buffer layer, the transconductance, the field-effect mobility, and the subthreshold swing were improved to 9.77 × 10?7 S, 1.68 cm2/V s, and 1.46 V/decade, respectively, for the pentacene-based OTFTs inserted with a 2-nm-thick TPD buffer layer. By considering the trade-off between the increase of Au work function and the tunneling effect, the optimal thickness of the TPD buffer layer in the pentacene-based OTFTs was 2 nm. 相似文献
2.
《Organic Electronics》2008,9(6):1069-1075
We have studied the effect of the chemical structure of dielectrics by evaporating pentacene onto a series of polyacrylates: poly(methylmethacrylate), poly(4-methoxyphenylacrylate), poly(phenylacrylate), and poly(2,2,2-trifluoroethyl methacrylate) in organic thin-film transistors (OTFTs). In top-contact OTFTs, the polyacrylates had a significant effect on field-effect mobilities ranging 0.093 ∼ 0.195 cm2 V−1 s−1. This variation neither correlated with the polymer surface morphology nor the observed pentacene crystallite size. This result implies that the PTFMA device generates the local electric field that accumulates holes and significantly shifts the threshold voltage and the turn-on voltage to −8.62 V and 3.5 V, respectively, in comparison with those of PMMA devices. 相似文献
3.
《Organic Electronics》2008,9(5):899-902
High electronegativity of non-charged fluorinated ethylene propylene (FEP) affected the performance of pentacene organic thin film transistors (OTFTs). The threshold voltage of the OTFT shifted from −14.7 V to −12.5 V without deterioration of on–off ratio and charge mobility. The degree of shift was related to the coverage of the FEP film on an active layer. No further shift was observed upon reaching the full coverage of surface at a 3-nm thickness of FEP. Encapsulation of the FEP-covered pentacene OTFT in a multilayer of PMMA/PUA/PET protected the device from oxygen and moisture. 相似文献
4.
《Organic Electronics》2014,15(9):1990-1997
The authors report the fabrication of efficient and transparent pentacene field-effect transistors (FETs) using a graded structure of ultra-thin silver (Ag) source and drain (S–D) electrodes. The S–D electrodes were prepared by thermal evaporation with a controlled deposition rate to form Ag layer with a graded structure, leading to a reduced injection barrier and smoothing the contact surface between the electrode and the pentacene channel. The sheet resistance of such Ag electrode was found to be as low as 9 Ω/sq. In addition, a hole-only behavior of device with Ag electrode characterized by current–voltage measurement and conductive atomic-force microscopy shows the injection property of high current flowing as compared with device using Au electrode, resulting in an efficient injection condition existing at the interface of the graded Ag/pentacene. Device characterization indicates the transparent pentacene FET with a graded ultra-thin Ag electrode and organic capping layer of N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine exhibits a high transmission rate of ∼75% in the range of visible light from 400 to 550 nm, a threshold voltage of −6.0 V, an on–off drain current ratio of 8.4 × 105, and a field-effect mobility of 1.71 cm2/V s, thus significantly outperforming pentacene FETs with multilayer oxide electrodes or other transparent thin metal layers. 相似文献
5.
《Organic Electronics》2008,9(3):385-395
Oriented growth of polycrystalline rubrene thin film on oriented pentacene buffer layer was investigated. The oriented pentacene buffer layer was created by thermal evaporation of pentacene on a rubbed polyvinylalcohol (PVA) surface. The pentacene layer in turn induced the oriented growth of rubrene crystals upon thermal deposition. The structures of successive layers were characterized by using grazing incidence X-ray diffraction (GIXD) and atomic force microscopy. Highly oriented rubrene crystallites with the a-axis aligning along the surface normal and the (0 0 2) plane preferentially oriented 45° away from the rubbing direction were found. In contrast, the rubrene thin film deposited on PVA or rubbed-PVA substrate without a pentacene buffer layer only gave amorphous phases. With the aligned pentacene/rubrene film as the active layer of organic field-effect transistor, anisotropic mobilities were observed. The highest field-effect mobility (0.105 cm2/V s) was observed along the direction 45° away from the rubbing direction and is ∼4 times higher than that for similar device prepared on unrubbed PVA. The direction was consistent with the GIXD observation that a large number of rubrene crystallites are having their [0 0 2] direction aligning in this direction. A favourable C–H⋯π interaction between an oriented pentacene layer and the rubrene layer on the control of molecular orientation in the conduction channel of the OFET is suggested. 相似文献
6.
Lung-Kai Mao Jenn-Chang Hwang Ting-Hao Chang Chao-Ying Hsieh Li-Shiuan Tsai Yu-Lun Chueh Shawn S.H. Hsu Ping-Chiang Lyu Ta-Jo Liu 《Organic Electronics》2013,14(4):1170-1176
Gelatin is a natural protein in the field of food, pharmaceutical and tissue engineering, which works very well as the gate dielectric for pentacene organic thin-film transistors (OTFTs). An aqueous solution process has been applied to form a gelatin thin film on poly(ethylene terephthalate) (PET) or glass by spin-coating and subsequent casting. The device performance of pentacene OTFTs depend on the bloom number (molecular weight) of gelatin. The pentacene OTFT with 300 bloom gelatin as the gate dielectric in air ambient exhibits the best performance with an average field-effect mobility (μFE) value of ca. 16 cm2 V?1 s?1 in the saturation regime and a low threshold voltage of ?1 V. The high performance of the pentacene OTFT in air ambient is attributed to the water resided in gelatin. The crystal quality of pentacene is not the key factor for the high performance. 相似文献
7.
《Organic Electronics》2008,9(5):721-726
We have studied the performance improvement of organic thin-film transistor (OTFT) with a solution based TIPS pentacene (6,13-bis(triisopropylsilylethynyl)pentacene) by inkjet printing. The TIPS pentacene with 1.0 wt.% solution in 1,2-dichlorobenzene was used for printing of an active layer of OTFT. The OTFT printed at room temperature shows a shoulder-like behavior but it disappears for the OTFT printed at the substrate temperature of 60 °C. The OTFT on plastic exhibited an on/off current ratio of ∼107, a threshold voltage of −2.0 V, a gate voltage swing of 0.6 V/decade and a field-effect mobility of 0.24 cm2/Vs in the saturation region. 相似文献
8.
Ching-Lin Fan Yu-Zuo Lin Ping-Cheng Chiu Shea-Jue Wang Win-Der Lee 《Organic Electronics》2013,14(9):2228-2232
We demonstrate a bilayer passivation method using a Teflon and SiO2 combination layer to improve the electrical reliability of pentacene-based organic thin-film transistors (OTFTs). The Teflon was deposited as a buffer layer using a thermal evaporator that exhibited good compatibility with the underlying pentacene channel layer, and can effectively protect the OTFTs from plasma damage during the SiO2 deposition process, resulting in a negligible initial performance drop in OTFTs. Furthermore, because of the excellent moisture barrier ability of SiO2, the OTFTs exhibited good time-dependent electrical performance, even after 168 h of aging in ambient air with 60–80% relative humidity. 相似文献
9.
Min Hee Choi Seung Hoon Han Sun Hee Lee Dong Joon Choo Jin Jang Soon Ki Kwon 《Organic Electronics》2009,10(3):421-425
We have studied the effect of active layer thickness on the performance and environmental stability of the 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) thin-film transistor. The organic thin-film transistors (OTFTs) were fabricated by inkjet printing using a solution based TIPS pentacene. To get thick organic semiconductor, the surface of gate insulator was treated with n-octyltrichlorosilane (OTS-C8) before jetting. The on-currents of the OTFT with ~1 μm active layer decreases a little in air, but the OTFT with 0.05 μm TIPS pentacene shows a significant degradation in drain currents. 相似文献
10.
《Organic Electronics》2014,15(7):1672-1677
In this paper organic thin film transistors (OTFTs) are directly fabricated on fabric substrates consisting of Polyethylene Terephthalate (PET) fibers. A key process is coating the polymer layers on the fabric in order to reduce the large surface roughness of the fabric substrate. Two polymers, i.e. polyurethane (PU) and photo-acryl (PA), are used to reduce the large surface roughness and simultaneously improve the process compatibility of the layers with the subsequent OTFTs processes while also retaining the original flexibility of the fabric. The surface roughness of the PU/PA-coated fabric is significantly reduced to 0.3 μm. Furthermore, the original flexibility of the PET fabric remained after coating of the PU/PA polymer layers. The mobility of the OTFTs fabricated on the PU-PA coated fabric substrate is 0.05 ± 0.02 cm2/V s when three PA layers and 90 nm thick pentacene layer were used. The performance does not vary even after 30,000 bending test. 相似文献
11.
In this study, we have successfully explored the potential of a new bilayer gate dielectric material, composed of Polystyrene (PS), Pluronic P123 Block Copolymer Surfactant (P123) composite thin film and Polyacrylonitrile (PAN) through fabrication of metal insulator metal (MIM) capacitor devices and organic thin film transistors (OTFTs). The conditions for fabrication of PAN and PS-P123 as a bilayer dielectric material are optimized before employing it further as a gate dielectric in OTFTs. Simple solution processable techniques are applied to deposit PAN and PS-P123 as a bilayer dielectric layer on Polyimide (PI) substrates. Contact angle study is further performed to explore the surface property of this bilayer polymer gate dielectric material. This new bilayer dielectric having a k value of 3.7 intermediate to that of PS-P123 composite thin film dielectric (k ∼ 2.8) and PAN dielectric (k ∼ 5.5) has successfully acted as a buffer layer by preventing the direct contact between the organic semiconducting layer and high k PAN dielectric. The OTFT devices based on α,ω-dihexylquaterthiophene (DH4T) incorporated with this bilayer dielectric, has demonstrated a hole mobility of 1.37 × 10−2 and on/off current ratio of 103 which is one of the good values as reported before. Several bending conditions are applied, to explore the charge carrier hopping mechanism involved in deterioration of electrical properties of these OTFTs. Additionally, the electrical performance of OTFTs, which are exposed to open atmosphere for five days, can be interestingly recovered by means of re-baking them respectively at 90 °C. 相似文献
12.
Youngjun Yun Christopher Pearson Duncan H. Cadd Richard L. Thompson Michael C. Petty 《Organic Electronics》2009,10(8):1596-1600
The electrical characteristics of pentacene organic thin-film transistors (OTFTs) using cross-linked poly(methyl methacrylate) (PMMA) as the gate dielectric are reported. Ultra-thin films of cross-linked PMMA could be obtained by spin-coating and subsequent irradiation using a 1.515 MeV 4He+ ion beam. The resulting film, with a thickness of 33 nm, possessed a low leakage current density of about 10?6 A cm?2 for fields up to 2 MV cm?1. OTFTs incorporating the cross-linked dielectric operated at relatively low voltages, <10 V, and exhibited a mobility of 1.1 cm2 V?1 s?1, a threshold voltage of ?1 V, a sub-threshold slope of 220 mV per decade and an on/off current ratio of 1.0 × 106. 相似文献
13.
Kwang-Suk Jang Hye Jung Suk Won Soo Kim Taek Ahn Jae-Won Ka Jinsoo Kim Mi Hye Yi 《Organic Electronics》2012,13(9):1665-1670
We have developed photo-sensitive, low-temperature processable, soluble polyimide (PSPI) gate insulator with excellent resistance to the photo-patterning process. The PSPI was synthesized through one-step condensation polymerization of monomers 5-(2,5-dioxytetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride (DOCDA) and 3,5-diaminobenzyl cinnamate (DABC). PSPI thin film, fabricated at 160 °C, has a dielectric constant of 3.3 at 10 kHz, and leakage current density of <1.7 × 10?10 A/cm2, while biased from 0 to 100 V. PSPI could be easily patterned by selective UV-light exposure and dipping into γ-butyrolactone. To investigate the potential of the polyimide as the photo-patternable gate insulator, we fabricated pentacene OTFTs and confirmed the PSPI’s resistance to the photo-patterning process. The photo-patternable polyimide shows promise as gate dielectrics for OTFTs. 相似文献
14.
Contact doping was conducted by iodine in a top contact configuration in a pentacene organic thin film transistor (OTFT), to investigate its effects on contact resistance and the resulting electrical performance. Iodine doping in the pentacene film caused the change of pentacene structure, thus leading to an increase in electrical anisotropy, i.e. ratio of lateral to vertical resistivity. The two resistive components of doped pentacene film underneath the Au contacts were major contributors to the contact resistance, and a model to explain the dependence of contact resistance on iodine doping was presented. Finally, OTFTs fabricated on iodine doped source/drain contacts exhibited high mobility of 1.078 cm2/V s, two times that of OTFTs with undoped contacts, due to the low contact resistance. 相似文献
15.
《Organic Electronics》2008,9(1):30-38
A multilayer organic light-emitting device (OLED) has been fabricated with a thin (0.3 nm) lithium fluoride (LiF) layer inserted inside an electron transport layer (ETL), aluminum tris(8-hydroxyquinoline) (Alq3). The LiF electron injection layer (EIL) has not been used at an Al/Alq3 interface in the device on purpose to observe properties of LiF. The electron injection-limited OLED with the LiF layer inside 50 nm Alq3 at a one forth, a half or a three forth position assures two different enhancing properties of LiF. When the LiF layer is positioned closer to the Al cathode, the injection-limited OLED shows enhanced injection by Al interdiffusion. The Al interdiffusion at least up to 12.5 nm inside Alq3 rules out the possible insulating buffer model in a small molecule bottom-emission (BE) OLED with a thin, less than one nanometer, electron injection layer (EIL). If the position is further away from the Al cathode, the Al diffusion reaches the LiF layer no longer and the device shows the electroluminescence (EL) enhancement without an enhanced injection. The suggested mechanism of LiF EL efficiency enhancer is that the thin LiF layer induces carrier trap sites and the trapped charges alters the distribution of the field inside the OLED and, consequently, gives a better recombination of the device. By substituting the Alq3 ETL region with copper phthalocyanine (CuPc), all of the electron injection from the cathode of Al/CuPc interface, the induced recombination at the Alq3 emitting layer (EML) by the LiF EL efficiency enhancer, and the operating voltage reduction from high conductive CuPc can be achieved. The enhanced property reaches 100 mA/cm2 of current density and 1000 cd/m2 of luminance at 5 V with its turn-on slightly larger than 2 V. The enhanced device is as good as our previously reported non-injection limited LiF EIL device [Yeonjin Yi, Seong Jun Kang, Kwanghee Cho, Jong Mo Koo, Kyul Han, Kyongjin Park, Myungkeun Noh, Chung Nam Whang, Kwangho Jeong, Appl. Phys. Lett. 86 (2005) 213502]. 相似文献
16.
《Organic Electronics》2008,9(2):191-197
We report on the realization of fully flexible and transparent n-type and ambipolar all-organic OFETs. A double layer, pentacene-C60 heterojunction, was used as the semiconductor layer. The contacts were made with poly(ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) and patterned by means of Soft Lithography MicroContact Printing (μCP). Interestingly, as demonstrated by atomic force microscopy and X-ray diffraction investigations, growing C60 on a pre-deposited pentacene buffer layer leads to a clear improvement in the morphology and crystallinity of the deposited film allowing to obtain n-type conduction despite the very high electron injection barrier at the interface between PEDOT:PSS and C60. As a result, it was possible to realize n-type and ambipolar all-organic OFETs by optimizing the thicknesses of the pentacene buffer layer. All devices, measured in air, worked in accumulation mode with mobilities up to 1 × 10−2 cm2/V s and 3.5 × 10−4 cm2/V s for p-type and n-type regimes, respectively. This is particularly interesting because it demonstrates, also for n-type and ambipolar transistors, the possibility of avoiding problems normally associated to metal contacts: the lack of mechanical robustness, flexibility, and the unfeasibility of realizing contacts with low cost techniques like printing or soft lithography. These results confirm the importance of the substrate properties for the ordered growth of organic semiconductors, which determines the transport properties of organic materials. 相似文献
17.
《Organic Electronics》2007,8(4):455-459
The interfacial interactions between semiconductors and gate dielectrics have a profound influence on the device characteristics of field effect transistors (FETs). This paper reports on the concept of introducing a sol–gel SiO2 as inorganic capping layer to significantly improve device characteristics of pentacene-based FETs. The smoother film surfaces of sol–gel SiO2 (1.9 Å root-mean-square) induced larger pentacene grain sizes, and led to hole mobilities of 1.43 cm2/Vs, on–off ratio of 107, and a subthreshold swing of 102 mV/decade when operating at −20 V. 相似文献
18.
《Microelectronics Journal》2007,38(4-5):509-512
Top contact organic thin-film transistors (TC OTFTs) based on pentacene are fabricated. For improving the contact characteristics between the organic semiconductor thin-film and gold electrodes, we doped the starburst molecular 4,4′,4″-tris{N,(3-methylpheny)-N-phenylamino}-triphenylamine) (m-MTDATA), which is an excellent hole injection material for the organic light-emitting devices (OLEDs), into the interlayer contact with the electrodes. Compared with conventional TC OTFT, the performances of the organic transistor with the doped interlayer are improved. The field-effect mobility increases from 0.16 to 0.51 cm2/V s, and threshold voltage downshifts from –11 to –2.8 V for the linear region. The on/off current ratio is more than 104 when the gate voltage varies from 0 to –20 V. We ascribe the improvements to the doped interlayer for which the contact resistance is reduced and the hole injection is enhanced. 相似文献
19.
《Organic Electronics》2007,8(5):552-558
We report on the fabrication and characterization of dual-gate pentacene organic thin-film transistors (OTFTs) with plasma-enhanced atomic-layer-deposited (PEALD) 150 nm thick Al2O3 as a bottom-gate dielectric and PEALD 200 nm thick Al2O3 as a top-gate dielectric. The Vth of dual-gate OTFT has changed systematically with the application of voltage bias to top-gate electrode. When voltage bias from −10 V to 10 V is applied to top gate, Vth changes from 1.95 V to −9.8 V. Two novel types of the zero drive load logic inverter with dual-gate structure have been proposed and fabricated using PEALD Al2O3 gate dielectrics. Because the variation of Vth due to chemical degradation and the spatial variation of Vth are inherent in OTFTs, the compensation technology by dual-gate structure can be essential to OTFT applications. 相似文献
20.
《Organic Electronics》2007,8(6):690-694
Contact resistance between indium–tin oxide (ITO) electrode and pentacene was studied by transmission line method (TLM). Organic solvent cleaned, inorganic alkali cleaned, and self-assembled monolayer (with OTS: octadecyltrichlorosilane) modified ITO electrode structures were compared. Pentacene layer of 300 Å thickness was vacuum deposited on patterned ITO layer at 70 °C with a deposition rate of 0.3 Å/s. Alkali cleaned and SAM modified ITO gave a lower contact resistance of about 6.34 × 104 Ω cm2 and 1.88 × 103 Ω cm2, respectively than organic solvent cleaned ITO of about 6.58 × 105 Ω cm2. Especially with the SAM treatment, the work function of ITO increased closer to the highest occupied molecular orbital (HOMO) level of pentacene, which lowers the injection barrier between ITO and pentacene. It was also believed that pentacene morphology was improved on SAM modified ITO surface due to the lowering of the surface energy. We could obtain the low contact resistance with SAM treatment which is comparable to the measured value of gold–pentacene contact, 1.86 × 103 Ω cm2. This specific contact resistance is still much higher than that of amorphous silicon thin film transistor (0.1–30 Ω cm2). 相似文献