Modeling of mobility in organic thin-film transistor based octithiophene (8T)

Thin-film organic field-effect transistor was made with vapor-deposited polycrystalline octithiophene on silicon oxide insulator layers. In conventional field-effect transistors, the extracted mobility does not take into account the distribution of charge carriers. However, in disordered organic field-effect transistors, the local charge carrier mobility decreases from the semiconductors/insulator interface in to the bulk, due to its dependence on the charge carrier density. It is demonstrated that the conventional field-effect mobility is a good approximation for the local mobility of the charge carriers at the interface. In this paper we present a new approach to the mobility in organic thin-film transistor (OTFTs), and with a new procedure we extract the electrical parameters of organic TFTs that possible to reproduce very well the device characteristic and mobility.     

9,10-Bis(phenylethynyl)anthracene-based organic semiconducting molecules for annealing-free thin film transistors

New anthracene-containing conjugated molecules have been synthesized through Stille coupling reaction. 2,6-Dibromoanthracene-9,10-dione was reacted with ethynylbenzene or 1-ethynyl-4-hexylbenzene to yield 2,6-dibromo-9,10-bis(phenylethynyl)anthracene 4 and 2,6-dibromo-9,10-bis((4-hexylphenyl) ethynyl)anthracene 5. Tributyl(5-hexylthiophen-2-yl)stannane was coupled through Stille reaction to generate two anthracene-based X-shaped molecules. They exhibit good solubility in common organic solvents and good self-film-forming properties. The semiconducting properties of the two molecules were evaluated in organic thin film transistors (OTFTs). Two conjugated molecules 7 and 8 exhibit fairly high charge carrier mobilities—as high as 0.010–0.014 cm² V^?1 s^?1 (I_on/I_off = 1.27 × 10⁷ to 4.38 × 10⁶) without thermal annealing process. The X-shaped molecules result in easy crystallization and densely cover the surface of a dielectric layer. This helps in attaining good network interconnection for the carrier transport channel, which is responsible for the relatively high carrier mobility in solution-processed OTFT.     

Spin-coated conductive polymer film resistivity measurement using the TLM method

Organic conductors such as PEDOT:PSS are commonly used for the fabrication of OLEDs or OTFT transistors. Conductivity measurement is mandatory to improve both material composition and process parameters, and to allow device and circuit modeling. Film deposition using spin-coating on circular TLM electrode structures is a straightforward method for extracting both the film resistance and the contact resistivity, providing an accurate model is used. A practical measurement procedure is described in detail and applied to the measurement of PEDOT:PSS solutions.     

Effect of postfabrication thermal annealing on the electrical performance of pentacene organic thin-film transistors

We report the results of a systematic investigation of the electrical and physical modifications to pentacene organic thin-film transistors (OTFT) that result from postfabrication thermal annealing. The thermally induced electrical modifications of the performance of the pentacene OTFTs were explored, and the morphology and structure of the pentacene films were investigated using atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. We found that postfabrication thermal annealing at 50 °C significantly improved the mobility, from 0.19 to 0.36 cm²/Vs, and increased the on/off ratio to almost twice that of the non-annealed device. We also found that annealing increased the pentacene grain size and enhanced the 0 0 1 peak intensity in the XRD pattern, indicating greater molecular ordering. At postfabrication thermal annealing temperatures of 70 °C and above, the pentacene films lose their crystallinity and the OTFT performance is decreased.     

低介微波介质陶瓷基板材料研究进展

低介电常数能减小基板与电极之间的交互耦合损耗并提高电信号的传输速率,高品质因数有利于提高器件工作频率的可选择性和简化散热结构设计,近零的谐振频率温度系数有助于提高器件的频率温度稳定特性。特别在工作频率逐渐提高的情况下,介电损耗不断增大,器件发热量迅速增加,材料的热导率成为一个需要重点考虑的因素。由于陶瓷材料的热导率是有机材料的20倍左右,因此,低介电常数微波介质陶瓷成为制备高性能基板的理想材料。此外,基板材料还需具备高强度和优越的表面／界面特性等综合性能。鉴于此,首先评述了介电常数小于15的低介微波介质陶瓷材料体系的研究进展情况,在此基础上,介绍了降低基板材料介电常数的方法和表面致密化措施,最后指出了在高性能低介微波介质陶瓷基板材料研制过程中面临的问题及今后的发展方向。     

Applications of an all-polymer solution-processed high-performance,transistor

Low cost production and a simple manufacturing process are desired for organic field effect transistors, OFETs, even though this usually significantly lowers device performance. We report on applications and characterization of a high performance polymer field effect transistor that utilizes a hygroscopic insulator. The latter enables the device to be used as a sensor element to detect the presence of various solvents. We show a drastic change in conductivity and current modulation for some organic solvents. Furthermore, the use of the device in electric circuits is demonstrated by combining hygroscopic insulator field effect transistor (HIFET) devices in an inverter/amplifier circuit.     

Polymer charge-transfer complexes for opto-electronic applications

The formation of charge-transfer (CT) complex to increase the conductivity has been the subject of intense research activity for the past decades. Those CT complexes have been used as organic semiconductors in field effect transistors (FETs), charge injection and transport materials in organic light-emitting diodes (OLEDs) and organic photovoltaic (OPV) cells. In this paper, a serials of new CT complexes with polymers as donor and TCNQ as acceptor were prepared. The polymers are polycarbazoles with various content of carbazole moiety in the back chain. The X-ray crystal structure of the model compound 4,4′-bis (N-carbazolyl)-1,1′-biphenyl(CBP)/TCNQ complex showed the formation of 2:1 stack structure (with 1:1 carbazole moiety: TCNQ ratio). The polycarbazole/TCNQ complexes form uniform films by spin-coating. Devices with the structure of ITO/polycarbazole:TCNQ complex/Mg:Ag were fabricated. The current–voltage characteristics showed that the devices exhibit much higher conductivity compared to their analogy ITO/polycarbazole/Mg:Ag structure devices. Devices with different polycarbazole:TCNQ ratios were fabricated and the current–voltage results showed that the conductivity increases as the ratio of polycarbazole:TCNQ increases. The conductivity reaches the maximum at the ratio of 1:1. These polymer complexes can be low-temperature processed on large area flexible substrates and are of potential use for low-cost printed electronics.     

Charge transfer effects in organic field-effect transistors containing a donor/acceptor heterojunction

Heterojunction organic field-effect transistors (OTFTs) based on copper phthalocyanine (CuPc) as p-type and on copper hexadecafluorophthalocyanine (F₁₆CuPc) or 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) as n-types were fabricated and studied. They were shown to operate in unipolar mode where hole current was recorded with values approaching those of CuPc-based single-layer device. However, due to a charge transfer phenomenon between CuPc and F₁₆CuPc, the occurrence of a build-in electrical field at the CuPc/F₁₆CuPc interface is shown to influence the transport properties at low drain-source voltages and to induce a non-ideal ohmic behavior in OTFT characteristics. This effect is not observed in the case of CuPc/TCNQ because of a larger energy difference between HOMO and LUMO energy levels of CuPc and TCNQ, respectively.     

Memory mechanism of printable ferroelectric TFT memory with tertiary structured polypeptide as a dielectric layer

Printable nonvolatile memory devices have been attracting considerable interest because of their application to flexible large-area devices. In order to fabricate such memory devices, it is necessary to discover a new ferroelectric material and to develop an efficient process for its preparation. We have previously reported that poly(γ-methyl-L-glutamate) (PMLG) functions as a ferroelectric layer of an organic thin-film transistor (OTFT) memory device [S. Uemura, A. Komukai, R. Sakaida, M. Yoshida, S. Hoshino, T. Kodzasa, T. Kamata, Synth. Met. 153 (2005) 405]. Further, ferroelectricity is observed when α-helical PMLG molecules are aligned in a direction parallel to the film surface. In this study, we investigate the effect of the tertiary structure of PMLG molecules on the hysteresis of OTFT memory devices, i.e., memory performance. From the results, we conclude that the hysteresis of the OTFT is strongly affected by the helical tertiary structure of PMLG molecules, similar to the structure of a cholesteric liquid crystal phase.     

New method of driving an OLED with an OTFT

We present a new method of driving an organic light-emitting diode (OLED) with an organic thin-film transistor (OTFT). The OTFT and the OLED were fabricated on separate substrates, namely on Si for the OTFT and on glass for the OLED and both devices were laminated with silver paste. After driving a 2 mm × 2 mm OLED with an OTFT devices, we obtained 105 cd/m² from the green OLED with a drain current of 60 μA, a drain voltage of −50 V and a gate voltage of −40 V. For the white OLED (WOLED), we obtained 260 cd/m² with a drain current of 108 μA, a drain voltage of −60 V and a gate voltage of −60 V.     

Synthesis and electromagnetic characterization of polyaniline nanorods using Schiff base through ‘seeding’ polymerization

Two kinds of Schiff base, m-phenylenediamine-glyoxal (Schiff base A) and p-phenylenediamine-glyoxal (Schiff base B), were used as ‘seed’ to induce the polymerization of aniline and hence prepare polyaniline (PANI) nanorods. The different preparation conditions including the Schiff base structure, dosage and acidity of the reaction medium, were investigated to discuss the influence of these conditions on the conductivity of the resulting samples through two-probe method at room temperature. The products were also characterized by Fourier transform infrared (FTIR), ultraviolet–visible (UV–vis), scanning electro microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) techniques. The results implied that these conditions play an important role in the formation of PANI nanorods. Moreover, the resulting PANI nanorods exhibited an unusual electromagnetic loss at the microwave frequency (f = 8.2–12.4 GHz) arose from order arrangement of polaron as charge carrier caused by a nanorods morphology and can be used for the potential application as microwave absorbing materials.     

Moisture measurements in building materials with microwaves

The method requires two parallel boreholes in the specimen in which two microwave antennae can be moved. The moisture content in the material can be calculated from the microwave intensity transmitted between the two boreholes. Moisture profiles along the boreholes can be obtained by moving the antennae in steps along the length of the boreholes and taking measurements at each step.The microwave frequencies used in the laboratory measurements ranged from 8 to 16.5 GHz in steps of 0.5 GHz. The diameters of the antennae were between 7 and 9 mm, and of the boreholes between 8 and 12 mm. The microwave method produced measurement uncertainties between 0 and 2% by volume for all the materials studied in this report.     

Top gate copper phthalocyanine thin film transistors with laser-printed dielectric

Dielectric layers involved in top gate organic thin film transistors (TG-OTFTs) have been fabricated by using laser induced forward transfer (LIFT) technique. Poly(methyl methacrylate) (PMMA) as insulating polymer was spin-coated on a quartz substrate and transferred by laser on an acceptor substrate to form a dielectric layer on top of an organic semiconducting layer and source/drain contacts both previously vapour phase deposited. Copper phthalocyanine (CuPc) has been chosen to form p-type organic active layers. The nature of transferred patterns and the efficiency of LIFT confirm the important potential of a laser printing technique in the development of plastic microelectronics. Electrical characterizations in TG configuration demonstrated that transistors are fully operative with hole mobility up to 8.6 × 10^?3 cm²/V s. A comparative study with others dielectric layers in bottom gate transistors (BG-OTFTs), as PMMA spin-coated and silicon dioxide SiO₂, points out more precisely the limiting parameters to an efficient charge transport in the conducting channel created at the interface between PMMA and CuPc.     

功能型氟硅聚合物涂层的研究进展

氟硅聚合物涂层是一种以有机硅、氟改性有机硅或有机氟为基体的材料,具有表面能低、稳定性高、易加工等特点,广泛应用于国防军事、轻工、机械、化工、医学等领域。综述了近年来氟硅聚合物常用的合成方法,如原子转移自由基聚合（ATRP）法、阴离子开环聚合法、硅烷偶联剂法、硫醇–烯点击法等,采用上述方法合成的氟硅聚合物,因其有序的氟/硅–碳排列,使得制备的涂层材料具有润湿性低和稳定性高等特点,在防污、抗菌等领域有着巨大的应用前景。同时,综述了不同维度材料修饰的氟硅聚合物涂层的研究进展,如一维材料（纳米线、纳米管等）、二维材料（片状硫化铜、石墨烯、MXene、氮化硼等）和三维材料（CeO₂、SiO₂、Fe₃O₄等颗粒及微胶囊）。对不同维度材料在防覆冰、抗菌、导电、导热、红外隐身、光催化、自修复等领域的应用和作用机制进行了分析。此外,综述了有机链段（聚氨酯、环氧树脂、聚甲基丙烯酸甲酯等）改性的氟硅聚合物涂层在医学、防污、自修复等领域的应用,并对其作用机制进行了分析。最后,对氟硅聚合物涂层研究中存在的问题进行了归纳,并对...     

Influence of organic gate dielectrics on the performance of pentacene thin film transistors

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.     

Characterization of metal—oxide—semiconductor field-effect transistor (MOSFET) for polypyrrole and poly (N-alkylpyrrole)s prepared by electrochemical synthesis

In this study, films of the polypyrrole series, polypyrrole (PPy), poly(N-methylpyrrole) (PNMePy) and poly(N-ethylpyrrole) (PNEtPy), are prepared at room temperature by electrochemical polymerization of the corresponding monomer in acetonitrile, utilizing p-toluenesulfonic acid monohydrate (p-TSA) as a supporting electrolyte. The results show that the thermodecomposition temperature, interchain spacing, electrical conductivity and optical absorption peak wavelength decrease with an increase in the alkyl side chain length. On the other hand, the semiconductor characteristics of these conjugated conducting polymers are utilized in the metal—oxide—semiconductor field-effect transistor (MOSFET) fabrication by electrochemical synthesis. The MOSFETs of Au/p-TSA doped PPy (PNMePy, PNEtPy)/SiO₂/Si/Au exhibit ideal field-effect characteristics. The channel current, carrier mobility and transconductance of MOSFETs increase dramatically after adequate heat treatment. The carrier mobilities of the PPy and PNEtPy MOSFETs can reach about 1.7 cm² V⁻¹ s⁻¹, which is close to those of amorphous silicon inorganic transistors (0.1–1.0 cm² V⁻¹ s⁻¹ used extensively at present.     

Impact of side-chain length on alternating current mobility of charge carriers in regioregular poly(3-alkylthiophene) films

The charge carrier mobility in films of regioregular polythiophenes substituted by n-alkyl side-chains, of butyl, hexyl, octyl, decyl, and dodecyl, was investigated by flash-photolysis time-resolved microwave conductivity (FP-TRMC), and transient photoabsorption spectroscopy excited at 355 nm. The charge carrier concentration was estimated from inspecting radical anions of perylenecarboxydiimide (PDI), which also acts as an efficient electron acceptor to improve the yield of photocarrier generation. We discuss the dependence of side-chain length in terms of decay dynamics, quantum yield of charge carrier generation, and alternating current (ca. 9 GHz) mobility, which exceeded 0.12 cm²/(V s).     

Electrochemical performance of C-La~(3+) codoped LiFePO_4 synthesized by microwave heating

La3+ was selected to elevate the lattice electronic conductivity of LiFePO4,and LiFePO4/(C+La3+) cathode powders were synthesized by microwave heating using a domestic microwave oven for 35 min. The microstructures and morphologies of the synthesized materials were investigated by XRD and SEM. The electrochemical performances were evaluated by galvanostatic charge-discharge. The electrochemical performance of LiFePO4 with different La3+ contents was studied. Results indicated that the initial specific disch...     

Eu掺杂对LiNiPO_4导电性的影响(英文)

采用Pechini方法制备了掺杂Eu和未掺杂Eu的LiNiPO4化合物,通过热重分析和差热分析(TG/DTA)来确定LiNiPO4的生成温度。粉末X射线衍射谱证实所得到的化合物为具有正交结构的纯LiNiPO4。采用复合阻抗谱技术分析样品在不同的温度和频率下的电导率和模量谱。采用Almond和West公式计算导电性能参数,如离子跃迁频率、电荷载体浓度。掺杂1.0%Eu的LiNiPO4的离子电导率增加了一个数量级。电模量谱分析表明LiNiPO4化合物中存在非德拜类型的弛豫。