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A series of thiazolothiazole–phenylene co-oligomers was synthesized and their properties, particularly as semiconductors for OFETs, were investigated. The naphthyl and biphenyl- substituted derivatives showed p-type semiconducting behavior with hole mobilities ranging from 10−2 to 10−1 cm2 V−1 s−1. The hole mobility and on/off ratio were enhanced to 0.12 cm2 V−1 s−1 and 106 on the HMDS treated substrate. The introduction of phenyl groups as end substituents was found to be favorable for charge transport and air-stability.

The syntheses and FET characteristics of perfluoropentacene and perfluorotetracene are described. Both acenes are planar and crystalline materials that adopt π-stack structures with the short interpalnar distances of 3.27 A in perfluorotetracene and 3.21 A in perfluoropentacene. The oxidation and reduction peak potentials of the perfluorinated acenes shift positively compared with those of the corresponding acenes, suggesting that the HOMO and LUMO energies are diminished by fluorine substituents. Organic field-effect transistors (OFETs) with perfluoropentacene exhibit n-type semiconducting properties with high electron mobility of 0.22 cm2/V s.

Novel anthracene derivatives were prepared as semiconductors for FETs to prove the effect of terminal groups on charge transport. The n- and p-type activities were achieved by introduction of acceptor or donor units into the anthracene structure.

Organic thin-film transistors (OTFTs)—with an active layer based on the organic semiconducting anthracene oligomers, 2,2′-bianthracene (2A), 2,6-trianthracene (3A), and their dihexyl derivatives (DH-2A and DH-3A)—were fabricated. It was found that thin films of anthracene oligomers deposited by thermal evaporation had lamellar structures with a high degree of molecular ordering. Consequently, the OTFTs based on anthracene oligomers showed high field-effect mobilities. The mobility of the OTFTs was increased by the oligomerization and the substitution of alkyl groups. DH-2A on a SiO2/Si substrate showed the highest mobility of 0.13 cm2/V s. It was also found that the electrical characteristics of the OTFTs were improved by using a Ta2O5 gate insulator.

The characteristics of pentacene-based organic thin-film transistors (OTFTs) on plastic substrates with anodized gate insulators using different electrolyte solutions were investigated. The characteristics were significantly improved by using ammonium borate as the solution. The results show a good current-saturation characteristic, field-effect mobility of 0.51 cm2/Vs and a current on/off ratio of 105 at a low drain voltage of 3 V. To investigate the reason for the improvements, the structural and electrical characteristics of OTFTs and insulators were examined using various methods such as X-ray diffraction, atomic force microscope, capacitance-voltage measurement and secondary ion mass spectroscopy. From the results of these experiments, it was found that the orientation of pentacene was improved and the concentration of impurities in the insulator decreased in the case of ammonium borate. We also examined low-voltage driving of liquid crystal devices by the OTFT, targeting its application for flexible displays. Improvement of characteristics by the solution was also confirmed in the driving.

Organic thin-film transistors (OTFTs) which use Ta2O5 as the gate insulators were fabricated on plastic substrates. The gate insulators were synthesized by anodizing the gate electrodes fabricated as stacked structures of aluminum (Al) and tantalum (Ta) at room temperature. The stacked structure suppressed the stress at the interface between the substrate and metal electrodes so that cracks on Ta could be avoided. The organic semiconductor pentacene was used as the active layer on the gate insulator. The OTFTs showed the best performance at an operating voltage of 5 V and a good field-effect mobility of 0.36 cm2/Vs on plastic substrates. The structural order of the pentacene in the film and the temperature dependence of the leakage current in the insulator were also studied to improve the device characteristics.

The heat-transfer process described in this paper will be useful for controllably and selectively doping polymer films used to make hyperfine full-color polymer electroluminescent (EL) displays. A polymer receiver film is placed in direct contact with a dye-dispersed polymer film coated onto an efficient photo-absorbing substrate to permit heat-transfer dye diffusion. The widely used heat-mode magneto-optical storage material, TbFeCo was used as the photo-absorbing material. We irradiated it with a laser in order to generate heat. This method can be used to control the lateral and vertical dopant distributions in polymer films for EL devices. We demonstrated that coumarin 6 and Nile red can be doped into the rather thermally stable polymer poly( N -vinylcarbazole) containing the electron-transporting 2-(4-biphenylyl)-5-(4- tert -butyl-phenyl)-1,3,4-oxadiazole from a viewpoint of luminescent properties. The diffusion power and time for about 1-mm 2 doping area were 1.2 W and about 10 s.

Thermal degradation of acrylonitrile–butadiene–styrene terpolymer (ABS) in bean oil has been carried out in the temperature 350 and 370°C. The degradation products have been investigated by means of gel permeation chromatography (GPC) and fourier transform infra-red spectrometry (FTIR). With the presence of bean oil, ABS thermally degrades into asphalt-like degradation residue, which is soluble in common organic solvent such as tetrahydrofuran (THF), instead of monomer and oligomers that are usually generated in direct pyrolysis of ABS. Moreover, for the system of ABS/bean oil the cross-linking reaction of ABS with bean oil takes place and forms a polymer network before the decomposition of ABS. Between the two reaction stages, the polymerization or oligomerization of sequence of adjacent nitrile groups occurs. The thermal degradation of ABS in bean oil was believed to be a radical process, which is dependent on the reaction condition, especially the concentration of bean oil, reaction temperature and time.

Three surfactants, p-bis(2-dodecyloxymethyl-3-oxa-6-sodiosulfonatohexyloxy)benz ene (BDSB) having two sulfonate groups and two lipophilic chains, disodium 10-dodecanoyl-5,15-bis(dodecyloxymethyl)-10-aza-4,7,13,16-tetra oxa-1,19-nonadecanedisulfonate (DDBTN) having two sulfonate groups and three lipophilic chains and disodium 4,11-bis(dodecyloxymethyl)-3,6,9,12-tetraoxa-1,14-tetrade canedionate (DBTT) having two carboxylate groups and two lipophilic chains, were used in micellar electrokinetic chromatography (MEKC). Eight naphthalene derivatives were baseline separated at 10 mM BDSB or 5 mM DBTT, and five flavone derivatives at 5 mM BDSB, DDBTN or DBTT. The elution order of the naphthalene derivatives in MEKC with BDSB was identical with that with DDBTN. However, this elution order was different from that found with DBTT. In the case of the flavone derivatives, BDSB, DDBTN and DBTT produced the identical elution order. These double- and triple-chain surfactants exhibited different selectivity when compared with widely used sodium dodecyl sulfate.

Blue emitting Sr2Ga2S5:Ce phosphor thin film has been first grown by multisource deposition. The evaporating source materials are Sr metal and Ga2S3 compound, and the dopant is CeCl3. This polycrystalline thin film shows the single orientation of (004). The SrS thin film is a buffer layer underneath the Sr2Ga2S5 thin film and is necessary for growth. The photoluminescence spectrum by excitation of the UV light at 290 nm is a broad band with two peaks at 443 and 484 nm, that is originated from 2D–4F5/2,7/2 transitions of Ce3+ ion. The emission is a saturated blue color and the Commission International de l’Eclairage chromaticity coordinates are x=0.15 and y=0.12.

Flexible displays using plastic film substrates are key devices for ubiquitous and universal services of digital broadcasting because of their mobile characteristics, low cost productivity, and flexibility of viewing style and so on. Polymer organic light-emitting devices (P-OLED) and ferroelectric liquid-crystal (FLC) films composed of ferroelectric liquid crystal and polymer network are promising display devices and materials for reproduction of TV images, where gray-scale and high-speed response characteristics are required. Both prototype flexible displays of P-OLED using phosphorescence materials and A4-sized FLC have been fabricated. Performances of these displays showed substantial potential for ubiquitous and universal digital broadcasting services.

Novel pi-electron systems with trifluoromethylphenyl groups and/or a thiazolothiazole unit were developed as n-type semiconductors for OFETs. They showed excellent n-type performances with high electron mobilities. The trifluoromethylphenyl group was found to be very effective in inducing n-type behavior. The thiazolothiazole unit was favorable for forming stacking structures leading to efficient intermolecular pi-pi interactions.

We report the synthesis and characterization of perfluoropentacene as an n-type semiconductor for organic field-effect transistors (OFETs). Perfluoropentacene is a planar and crystalline material that adopts a herringbone structure as observed for pentacene. OFETs with perfluoropentacene were constructed using top-contact geometry, and an electron mobility of 0.11 cm2 V-1 s-1 was observed. Bipolar OFETs with perfluoropentacene and pentacene function at both negative and positive gate voltages. The improved p−n junctions are probably due to the similar d-spacings of both acenes. Complementary inverter circuits were fabricated, and the transfer characteristics exhibit a sharp inversion of the output signal with a high-voltage gain.

Organic thin film transistors (OTFTs) that operate at low voltage were fabricated using a tantalum oxide (Ta2O5) gate insulator on plastic substrates. The Ta2O5 insulator was prepared by anodizing a Ta gate electrode. The high dielectric constant of the Ta2O5 enabled the OTFTs to operate at a lower voltage than those of previous devices. The OTFTs exhibited a high field-effect mobility of 0.35 - 0.51 cm2/Vs, and a current on/off ratio of 105-106 at gate voltages of less than 5 V. The threshold voltage of -1.1 V and the subthreshold slope of 0.2 V/decade were the best among those reported to date. We also demonstrated operation of a phosphorescent organic light-emitting device (OLED) with the OTFT operating at a low voltage.

Novel thiazole oligomers and thiazole/thiophene co-oligomers with trifluoromethylphenyl groups were developed as n-type semiconductors for OFETs. They showed excellent n-type performances with high electron mobilities. A 5,5'-bithiazole with trifluoromethylphenyl groups forms a closely packed two-dimensional columnar structure leading to a high performance n-type FET. The electron mobility was enhanced to 1.83 cm2/Vs on the OTS-treated substrate.

Novel mixed five-membered heterocyclic (furan, thiophene, and thiazole) oligomers containing a thiazolothiazole ring system have been investigated as active materials of organic field-effect transi...

A pentacene thin-film transistor (TFT) was fabricated on a SiO2 gate insulator treated with β-phenethyltrichlorosilane (β-PTS). Employing β-PTS for the surface treatment of SiO2, large grains were present in the initial stage of pentacene crystal growth. The field effect mobility was as high as 1.5cm2∕Vs and the on/off ratio was over 106. The surface treatment dramatically improved the stability in air of the pentacene-TFT’s electrical characteristics. A field effect mobility of over 1cm2∕Vs and on/off ratio of over 105 were maintained after scanning the gate voltage 2000 times in air. This result indicates that the surface treatment with β-PTS not only improved TFT performance but also significantly suppressed the device’s degradation.

A fast-response flexible ferroelectric liquid crystal (FLC) display panel driven by organic TFT (OTFT) was successfully developed. The fabricated OTFT with Ta2O5 gate insulator showed a mobility of 0.3 cm2/Vs and a current on/off ratio of 107 with a low operating drain voltage of −5 V. We obtained fast responses of less than 1 msec and contrast ratio of 14:1 with gray-scale display capability from a 16×16 pixel FLC panel.

We report on n-channel organic thin-film transistors (OTFTs) based on the novel n-type organic semiconductor, perfluoropentacene. The transistor exhibits excellent electrical characteristics, with a high electron mobility of 0.22 cm2/(V s) and a good current on/off ratio of 105. The electron mobility is comparable to the hole mobility of a pentacene OTFT. By combining the n-type perfluoropentacene and the p-type pentacene, we have fabricated ambipolar OTFTs and complementary inverter circuits. The OTFTs with heterostructures of the p- and n-type organic semiconductors can operate as an ambipolar device with high electron and hole mobilities of 0.042 and 0.041 cm2/(V s). The complementary inverter using an n-channel perfluoropentacene OTFT and a p-channel pentacene OTFT exhibits excellent transfer characteristics with a voltage gain of 45. A complementary inverter using the ambipolar OTFTs is also demonstrated.

Organic thin-film transistor (OTFT)-driven 5×5 polymer-dispersed liquid crystal (PDLC) display cells on a flexible plastic substrate have been developed. It is necessary to increase the maximum usable gate voltage of OTFT to obtain a high contrast ratio. We propose a stacked gate insulator that consists of polyvinylphenol and anodized Ta2O5 for decreasing the gate leakage current and increase the maximum voltage. The OTFT with the insulator showed a field-effect mobility of 0.4 cm2/(V s), a current on/off ratio of 105, a low threshold voltage of 1.1 V, and a subthreshold slope of 0.2 V/decade. Leakage current was successively decreased up to a gate voltage of 15 V, maintaining a low-voltage operation of OTFT. Double passivation layers using polyvinylalcohol and photosensitive acrylic material are also proposed to prevent the degradation of OTFT by liquid crystal. The bending characteristics of OTFT on plastic substrates were also measured for various radiuses of curvature. The OTFT can operate at a radius of curvature exceeding 20 mm. On the fabricated display cells, we confirmed a good display operation with a contrast ratio of 10:1 with a low driving voltage of 12–13 V.

p-Channel OFETs using thiophene/thiazolothiazole co-oligomers as active layers have been successfully fabricated, and the field-effect mobilities for these oligomers were higher than those for thiophene/thiazole co-oligomers.

We have investigated the compositional and structural properties of blue emitting BaAl2S4:Eu electroluminescent thin films fabricated by switching electron-beam evaporation using two targets. The use of X-ray photoelectron spectroscopy (XPS) revealed that the ratio of barium to sulfur in thin films is 1.0:2.0, which is identical to the stoichiometry of BaAl2S4. The X-ray diffraction (XRD) peaks from the thin film were assigned to those of a BaAl2S4 crystal. The photoluminescence (PL) spectrum shows emission from the 4f65d→4f7 transition of the activated Eu2+ ions in BaAl2S4 crystals. These results indicate that the crystalline phase in thin films is only BaAl2S4. The thin films also contain a large amount of oxygen impurities, which result in the formation of an Al2O3 layer and amorphous barium aluminate.

The relation between growth temperature and ordered structures in Ga0.5In0.5P grown using organometallic vapor phase expitaxy is investigated using transmission electron diffraction, electroreflectance, and Raman scattering measurements. It is found that generation of the ordered structure is not related to the immiscibility of this alloy and that the ordered structures do not simply represent ‘‘sublattice ordering.’’ The anomalous band gap may be a consequence of the variation in the atomic arrangement of neighboring atoms, but not of the long‐range ordered structure itself.

We have measured the electroreflectance spectra of ordered Ga0.5In0.5P alloys grown on GaAs by organometallic vapor phase epitaxy. As a result, it has been found that there exist anomalous structures in the region of the E0 and E1 band edges of this material. These anomalous structures are closely related to the recently reported ordered phase in this alloy, since these structures have never been observed with disordered Ga0.5In0.5P alloys such as bulk crystals and epitaxial layers grown by liquid phase epitaxy.

The temperature dependence of the photoluminescence spectrum of Ga0.5 In0.5 P/GaAs grown by organometallic vapor phase epitaxy is measured. Samples with a highly long‐range ordered structure show anomalous behavior, where peak energy changes with temperature exhibiting Z‐shape dependence. In the range between 100 and 30 K, peak energy decreases monotonously with decreasing temperature, and below 30 K, begins to increase, splitting into two peaks. The most probable cause of this behavior is crystal defects related to the long‐range ordered structure.