Novel poly(p-phenylene ethynylene) polymers, ANT-OPPE and COU-OPPE, have been prepared, in which anthracene and coumarin sensitizer molecules are covalently attached to the conjugated polymer backbone via a flexible spacer. These polymers show efficient energy transfer from the pendent sensitizer molecule to the PPE backbone, both in dilute solution as well as in an oriented polyethylene matrix. In case of ANT-OPPE, we found that the PPE backbone adapts the orientation of the matrix and is efficiently oriented, while the anthracene moiety remains essentially isotropic, resulting in a state-of-the-art polarizing energy transfer for this system.

Thin layers of poly(dihexylfluorene-co-N-hexylcarbazole) sandwiched between ITO and aluminium electrodes show stable photoluminescence and electro-luminescence at room temperature and ambient atmosphere. I(V) and Electro-luminescence versus voltage curves present a much lower threshold than device made up of poly(dihexylfluorene) homopolymer. When using the copolymer, the barrier height for hole injection is reduced to a value close to 0.17 eV to be compared to 0.83 eV for the homopolymer. This difference in offsets has been confirmed by electrochemical investigations.

A novel family of phasmidic liquid crystals incorporating an oligo(p-phenylenevinylene) core was produced. These compounds exhibit blue luminescence in both solution and the solid state. The emission profiles are influenced by the degree of organization in the solid state. The snthesis and liquid-crystalline behavior of these compounds will be discussed. Their photophysical properties, as studied by c.w. photoluminescence excitation, emission spectroscopy, and site selective spectroscopy, as well as their optoelectronic properties will be presented.

Samples of Eu3+-activated PMMA:PAAc copolymers were prepared in order to investigate their spectroscopic properties. The densities, refractive indices, UV-Visible absorption and emission spectra and fluorescence decay times were obtained experimentally. These data were used in conjunction with Judd-Ofelt theory to calculate the spontaneous emission probabilities and branching ratios, as a function of the europium content. The range of the concentration was 0.1 to 2.5 % mol. Our results are combined with previous information on the optical properties of rare-earth activated polymers in order to get a better understanding of the role played by the Eu3+ ions on the polymerization process in our samples.

The preparation of poly(p-phenylene vinylene) (PPV) encapsulated in a mesoporous silica, MCM-41, is reported. In situ polymerization of xylylene bis(tetrahydrothiophenium chloride) yields a highly luminescent, yellow powder with a fluorescence spectrum matching that of unencapsulated PPV. Nitrogen adsorption isotherms show that the pore size of the PPV- loaded MCM-41 is significantly smaller than that of empty MCM-41 and a polymer loading of ca. 8% by weight is obtained by thermogravimetric analysis. Photoluminescence data for the encapsulated PPV are presented.

We present a study of the effects of blending electroluminescent polymers with platinum (II) octaethylporphyrin (PtOEP). We find that in the case of polymers which are measured to have HOMO and LUMO levels respectively below and above those of the PtOEP, and which have emission spectra overlapping the PtOEP absorption spectra, energy transfer occurs as expected. We find further evidence, in the form of steady state and time-resolved electroluminescence and photoluminescence measurements, which indicates additional transfer of triplet excitons between polymer and porphyrin. Where the polymers have emission spectra overlapping the absorption spectra of PtOEP, but which are measured to have a HOMO or LUMO level between those of the porphyrin, quenching of the photoluminescence efficiency occurs. We propose this is due to charge separation between the porphyrin and the polymer, and show evidence for this in the form of photoinduced absorption measurements.

Poly(p-phenylene vinylene)s (PPVs) are very promising materials for optoelectronic applications, especially for displays based on polymer light emitting diodes (PLEDs). We report here our findings concerning defect structures in this materials and the influence of the discovered irregularities on an important property of the materials, i.e. the operational life in a PLED. Recent improvements, which were deviated from this findings are presented: optimized PPVs with a lower amount of defects result in a strong increase of operational lifetime.

Two-dimensional passive photodiode matrices are hardly useful for image sensing due to the crosstalk between pixels. This crosstalk makes it difficult to recover information from individual pixels. A switching unit attached to each sensing unit has been the common solution in image sensors (such as in CMOS sensors and in TFT-PiN a-Si photosensors). A novel organic photodiode with voltage-switchable photosensitivity was developed recently. Passive photodiode matrices made with such organic photodiodes can be used for image sensing applications. This circuit simulation study demonstrates an effective scheme to extract images from passive photodiode matrices, concluding that individual photodiode parameters determine the contrast and resolution of N by M image sensors.

The electrical properties of layer-by-layer films of poly(o-methoxyaniline) (POMA) alternated with poly(vinylsulfonic acid) (PVS) have been investigated as a function of the surrounding atmosphere, in order to probe the sensitivity of POMA/PVS as a gas sensor. The POMA films have their conductivity increased with increasing humidity, near to one order of magnitude higher for 100% relative humidity when compared to nitrogen. The d.c. applied field may affect the POMA films, for these films become practically insulating if the field is applied for a prolonged time (typically 10-20 h) in humid air. In order to circumvent this problem, a.c. impedance measurements were conducted. For samples in nitrogen, oxygen and carbon dioxide, the real part of the complex impedance increases only when the frequency is lowered below 10 kHz. In a humid atmosphere, the onset for the real part occurs at higher frequencies than for dry atmospheres. Furthermore, at a fixed frequency in the range from 10 to 100 kHz this impedance component increases with the relative humidity.

We propose new poly-Si TFT's with selectively doped region in the center of channel in order to reduce large leakage current. In proposed TFT's, the selectively doped region redistributes total induced electric field in the channel. For VGS<0, VDS> 0 in the n-channel proposed TFT's, most of the high electric field applies in the depletion regions which exist the drain/undoped region and undoped region/selectively doped region which faces to the source. Comparing with conventional TFT's, the electric field induced near the drain junction reduces to about 1/2, therefore, electron-hole pairs generated in drain junction are considerably reduced. Furthermore, the ON-current of proposed TFT's is the same or slightly lower than that of conventional ones. Consequently, the experimental data show the considerable improvement of the ON/OFF current ratio.

We fabricated a new device, which employs counter-doped lateral body terminal (CLBT) in order to suppress kink effects and improve the device stability. Proposed device also employs a buried channel (BC), which increases ON-current and operating frequency. Although LDD structure is not employed in the proposed device, low OFF-current is successfully obtained due to elimination of minority carrier through CLBT. We have measured the dynamic properties of poly-Si TFT device and circuit. The reliability of TFT and circuits after AC stress is also discussed in our paper.

The proposed poly-Si TFT has high ON-current and low OFF-current compared with conventional 3-terminal poly-Si TFT. The 4-terminal device characteristics were measured with source and CLBT shorted. The proposed device exhibits superior performance to conventional device in ON-current because BC prevents carrier scattering to gate oxide. We have performed bias and high temperature stress test of ring oscillator in order to investigate dynamic reliability between conventional poly-Si TFT and proposed 4-terminal poly-Si TFT. Our experimental results show that BC enables the device to have high mobility and switching frequency (33MHz at VDD=15V). The minority carrier elimination of CLBT suppresses kink effects and makes superb dynamic reliability of CMOS circuit.

Controlled oxidation of polycrystalline and single crystal silicon has been carried out at temperatures < 100 °C using microwave excited, plasma assisted anodisation. Oxide thicknesses up to 30 nm have been obtained in times ∼ 15 minutes. The growth kinetics are similar for both types of Si. The results of infrared absorption measurements clearly indicate that the anodic oxides have a network structure significantly different to that of high temperature, thermally grown oxides and this is partly due to ultra-violet radiation present in the plasma during growth. Electrical measurements (CV, IV) are underway on simple MOS capacitors. The results indicate that the plasma oxides have acceptable levels of fixed oxide charge but that the breakdown electric fields are presently low. Preliminary data suggests that these very low temperature oxides are suitable for TFT applications though some technical problems need to be addressed. Given these reservations the processing of large area flat panel displays using this type of plasma assisted oxidation is perfectly feasible.

Initial N-channel self aligned polycrystalline silicon gate transistors fabricated on 1.5μm -2μm single crystal Silicon-O-Glass(SOG) layers exhibited poor transfer characteristics. Measured threshold voltages and On/Off current ratios were in the order of -8V and 10 respectively. This is due to the presence of fixed charge at the bond interface introducing back gate effects which degrade and distort device performance. These back gate effects were suppressed by implantation of boron into the silicon substrate prior to oxidation and bonding, with energy 40keV and dose 7.4×1012cm−2. This resulted in an improvement in device performance with a threshold voltage of-0.54V. On/Off current ratio increased to 1840 and field effect mobility increased from 274cm2/Vs to 357cm2 Vs

The fabrication of large-area thin-film transistor (TFT) arrays on thin flexible plastic substrates requires deposition of thin film layers at relatively low temperatures since the upper working temperature of low-cost plastic films should not exceed ∼200°C. In this paper, we report a fabrication process of a-Si:H TFTs at 120°C on flexible polyimide substrates for large-area imaging applications.

Kapton HN (DuPont) films 50 and 125 μm thick and 3 inches in diameter, were used as substrates. Both sides of the polyimide substrate were first covered with 0.5 μm thick a-SiNx. The TFT structure includes: 120 nm thick room-temperature sputtered Al gate, 250 nm thick PECVD deposited a-SiNx for the gate dielectric, 50 nm thick a-Si:H deposited by PECVD from silane-hydrogen gas mixture, 50 nm thick n+ a-Si:H source- and drain contacts, and roomtemperature sputtered Al top contact metallization. We used dry etching for all layers except for the gate and top metal, which were patterned using wet etchants. For purpose of TFT performance comparison, Coming 7059 glass substrates were used.

The performance of the fabricated TFT and its improvement with use of optimized a-Si:H and a-SiNx quality will be presented along with a discussion of the intrinsic mechanical stress in the thin film layers will also be discussed.

The mechanics of thin film-substrate couples indicates that mechanical stress in the active electronic layer can be reduced when films are deposited onto thinner substrates. To explore the question of just how thin a substrate can be, a-Si:H TFTs are fabricated on thin steel foil substrates of various thickness, and performance metrics from devices on each of the substrates are measured and compared.

We describe a new technique for making copper lines by printing a precursor pattern that is converted to copper, at a maximum process temperature of 200°C. We formed copper metallization patterns on 80 μm thick Coming 0211 glass substrates by jet printing. Continuous lines of copper with resistivity of 10 μΩcm have been obtained. We successfully applied this technique to the direct printing of copper source and drain contacts for amorphous silicon thinfilm transistors. The TFTs are bottom gate back-channel etched structures, with the silicon stack made by RF excited PE-CVD. The TFT process uses only printing for all masking steps, by employing laser-printed toner etch masks, and using the printed copper as the mask for the back channel etch. The transistor ON/OFF current ratio is 105. The process for copper printing represents a further step toward an all-printed TFT technology.

Tin Oxide transparent conductive oxide(TCO) films of less than 20nm in thickness was developed as a substrate for pen touch screens. The films were deposited using APCVD method by hydrolytic decomposition of stannic chloride. Electrical properties and stability to heat treatment were studied in relation to deposition conditions. We found the both properties depends mainly on fluorine concentration in the films. The stability was much improved at reduced fluorine concentration. The film which showed the stability to heat treatment at 600°C heat treatment was attained at the thickness of 20nm.

In203 films were deposited on YSZ (001) single crystal surface at 800°C at an oxygen pressure of 14 Pa by pulsed laser deposition (PLD) method. A heteroepitaxial relationship between the film and the substrate was seen in TEM photographs and X-ray diffraction measurements. The w locking curve full width of half maximum (FWHM) of the In203 (004) x-ray diffraction was 0.06°. Film conductivities were ∼10 S/cm or less, while carriers on the order of lO18/cm3 were generated.

We have investigated the polymeric insulators benzocyclobutene (BCB), parylene C and polyimide for use as gate dielectrics in pentacene organic thin film transistors (TFTs). Atomic force microscopy (AFM) was used to examine the surface roughness of the polymeric dielectrics and the morphology of pentacene films deposited onto them. X-ray diffraction was used to examine the molecular ordering of pentacene films deposited onto the polymeric dielectrics. We find a correlation between the surface roughness of the gate dielectric and the grain size in deposited pentacene films, with smooth surfaces yielding larger, more dendritic grains. Despite significant changes in film morphology, pentacene TFTs using BCB, parylene C, or polyimide as the gate dielectric have performance comparable to devices using SiO2 as the gate dielectric. These results suggest that there is not a strong correlation between pentacene film grain size and field-effect mobility for these devices. Pentacene TFTs using BCB as the gate dielectric had field-effect mobility as high as 0.7 cm2/V-s, on/off ratio > 107, subthreshold slope less than 2 V/decade, and negative threshold voltage, making them an attractive candidate for use in organic-based large-area electronic applications on flexible substrates.

A new class of precursor polymers, as first described by Louwet et al. [1], was used to make organic LEDs. Device properties are relatively independent from the side chain to be eliminated. However introduction of two methyl groups onto the phenyl ring introduces significant changes in absorption, photoluminescence (PL) emission, PL quantum efficiency and electroluminescence spectra. From XRD there is an indication that this effect might be related to a different packing of the polymer chains.