Polymeric thin-film transistors (TFTs) have been proposed for several applications including displays, electronic paper, chemical sensors, and radio-frequency identification (RFID) tags. One important technical hurdle that has to be overcome for using organic transistors in RFID tags is for these devices to operate at RF frequencies (typically 13.56 MHz) in the front end. It was long thought that conjugated polymer transistors are too slow for this. In this presentation we will demonstrate that polymer transistor based full-wave rectifier circuits utilizing a polythiophene, a p-channel semiconductor, can operate at this frequency with a useful efficiency. In order to achieve such high-frequency operation, we make use of the non-quasi static (NQS) state of the transistors. Bottom gate and top gate structures are explored and a comparison is made between the observed electrical properties. These circuits are fabricated on PEN (polyethylenenapthalate) or PET (polyethylene-terepthalate) substrates using a spin on dielectric. Gate, source and drain contacts are defined photolithographically using evaporated gold as the metal. Field-effect mobilities in the range of 0.02 and 0.2 cm2/Vs that equal or exceed the highest reported among the ones employing similar geometries on plastic substrates are easily obtained in these systems. In order for NQS based rectification to take place the carrier velocity in a 2 micrometer channel length device needs to be more than 2×104 cm/s. This would correspond to a mobility of 0.1cm2/V-s at a field of 105 V/cm. The rectifiers were based on a 4-transistor full-wave design. A coil (transformer secondary) drives the AC inputs in differential mode. The lower diode connected transistors in a manner similar to the half-wave rectifier define the DC voltage level of the two AC input signals. The two upper transistors are connected as switches and are used to move current from the AC inputs to the positive DC output. The capacitor is used to hold the peak voltage level supplied by the coil through the switch-connected devices. The voltage rectification efficiency is relatively high being as much as 45% at 13.56 MHz. This is among the fastest polymer transistor circuit of any kind demonstrated to date.

We report the failure mode observed in polymer EL blue device. Such modes were analyzed by non-destructive and destructive ways. As a non-destructive way, investigation of mobility changes of hole and electron, measuring transient EL corresponding to life curve, had been done. We also observed compositional and morphological variation using TEM-EDX, STM, FT-IR, TOF-SIMS and reverse engineering method as a destructive way. Electron mobility has a higher dependency on life curve, which fact could be reflected on the formation of insoluble layer inside emitting layer on anode side. And such insoluble layer showed relatively ordered surface morphology, and might be a cross-linked layer through C-O-C bond cleavage process while EL operation. But, contrary to sulfur migration mechanism into insoluble layer insisted by CDT, we did confirm no obvious difference of sulfur composition between insoluble and emitting layers. Rather, there's some degree of Ba diffusion into emitting layer from decomposition of BaF2, but, which dose not have a major effect on device degradation.

In this paper we report the heteroepitaxial growth and the structural evolution of hexakis-dodecyl-peri-hexabenzocoronene (HBC-C12) adsorbed on a template monolayer (n-C50H102). STM measurements at the liquid/solid interface made it possible to follow in real time the early stage of deposition of the HBC-C12 molecules. Additionally, molecule manipulations were realized using the tip of the STM. Our measurements give direct evidence of two successive phase transitions occurring in the upper HBC monolayer weakly bonded to the underlying template layer.

Control of film morphology is widely recognized as one of the limiting factors in the development of conjugated polymers for photonic and electronic applications. Surface polymerization by ion-assisted deposition (SPIAD) is shown to drive film morphology. A wide variety of structures form in the SPIAD polythiophene films, including islands, lamellar structures, nanoscale crystallites, and fractal-like growth patterns. Density functional theory-molecular dynamic simulations are utilized to illustrate the manner in the incident ions affect polymerization, bond dissociation, and other chemical events in SPIAD. These ion-assisted events mediate thermal processes such as neutral deposition, sublimation, diffusion, and dewetting. However, these thermal processes are on longer timescales that cannot be directly studied by the computational techniques reported here.

We report a non-volatile, write-once-read-many times (WORM) memory device based on a simple organic-inorganic heterojunction. The organic film used is 9, 9-dihexylfluorene and Eu-complexed benzoate (PF6Eu (DBM)), which contains both electron-donor (9, 9-dihexylfluorene) and electron-acceptor (europium complex) groups. The inorganic n-type silicon substrate is used as the bottom electrode, while the Al is used as the top electrode. Under current-voltage testing, the device is able to switch from one initial non-conducting state (OFF) to a conducting state (ON) once a threshold voltage is reached under the first positive sweep. The “OFF” state is not recoverable with subsequent negative sweep after the device is turned “ON”. The ON/OFF current ratio is around 4×104. Diode rectifying characteristics is also observed for the turned-on device with a current ratio of 7×104, which is essential to address one memory cell in large passive matrix circuits. Reliability test is carried out and the device is able to sustain its “ON” state for at least 12 hours without any external bias.

Preliminary development towards passive matrix Electrochromic (EC) device in conjugated EC polymer system is discussed. High contrast ratio of dark and bleached pixels is obtained by modification of counter and working electrode capacitance ratio and spacer geometry. Mask patterning and laminar electropolymerization for multicolor EC system application is discussed.

We designed and synthesized a dendritic architecture in which three branches of the NLO-active component consisting of push-pull type conjugated structure were linked onto its core. Chemical structure of the dendritic nonlinear optical (NLO) chromophore was verified by NMR spectroscopy, which clearly showed that the conjugated bridge had a trans-conformation. The dendrimer exhibited that the broad absorption band centered at around 608 nm extending to 760 nm. It was thermally stable up to 275 °C in the nitrogen atmosphere. Polymer film was prepared by spincoating the solution of mixture of amorphous polycarbonate (APC) and the dendritic chromophore, which exhibited an electro-optic coefficient of 19 pm/V at 1.55 μm wavelength.

Intrinsic charge transport of copper phthalocyanine single-crystal field-effect transistors is measured as function of temperature up to above 100°C. The conduction of the accumulated carriers shows hopping-type transport, so that the field-effect mobility increases with temperature following activation-type temperature dependence throughout the measured temperature region. Due to excellent material stability at the high temperature, the mobility values are precisely reproduced after the heat cycles.

We report Hall effect of charge carriers accumulated in organic field-effect transistors. Rubrene (C42H28) single crystals are shaped in to the Hall-bar congiguration in the devices so that the Hall signal is appropriately detected in external magnetic fields. It turned out that inverse Hall coefficient, having a positive sign, is close to the amount of electric-field induced charge upon the hole accumulation. The observation of the normal Hall effect means that the electromagnetic character of the surface charge is not of hopping carriers but resembles that of a two-dimensional hole-gas system. The direct access to the density of mobile charge carriers provides a tool to understand nontrivial features of organic field-effect transistors such as gate electric field dependent mobility.

Polyfluorenes (PFs) have emerged as a promising family of blue polymer light-emitting diodes (PLED) due to their high electroluminescence quantum yield. Metal-insulator-semiconductor (MIS) diodes are the two terminal analogues of thin film transistors sharing the same basic layer structure. We have investigated two different structures based on poly [9,9'-(di 2-ethylhexyl)fluorene] (PF2/6), a MIS diode and a hole-only PLED. The MIS diodes were fabricated with the PF2/6 layer on p+ Si /Al2O3 substrates, and were characterized by means of capacitance-voltage (C-V) measurements as a function of frequency. From C-V measurements, the unintentional doping density is evaluated as ∼5.7×1017 cm−3 at frequencies above 20 kHz. The interface trap density is estimated as ∼7.2×1011 eV−1cm−2 at 10 kHz. Current-voltage measurements of PF2/6-based PLEDs shows a shallow trap space-charge-limited conduction from which the energy of the traps and hole mobilities are estimated.

A novel σ-conjugated hyperbranched polysilane is presented, and it has good solubility in common organic solvents. The photoluminescence (PL) emission spectrum of it exhibits an emission maximum at 425nm, which indicates that the polymer emits blue light. The resulting polymer also has good thermal stability and high glass transition temperature. Therefore, it demonstrates a promising application in blue light emitting diodes.

ICP-MS is a well established analytical technique in the semiconductor industry for essential trace metal characterization in chemical reagents and silicon wafers. Tetracene, Antracene, Pentacene and Rubrene are among the most interesting organic semiconductors for use in molecular electronic devises such as single-crystal Organic Field Effect Transistors (OFETs). One of the most important parameter for fabrication of single-crystal OFETs is the purity of the starting material. As the crystal growth process also results in the chemical purification of the material, several re-growth cycles may be required for improving the field-effect mobility, with the grown crystals used as the starting material for the subsequent re-growth. The number of required re-growth cycles depends strongly on the purity of starting material. We report the application of ICP-MS for impurity analysis in the organic semiconductors. The ICP plasma, where samples are atomized and ionized, generates strong ion current, which is instrumental in achieving exceptional detection limits. Some elements can be measured down to part per trillion range. This study can provide a better characterization of the trace metal impurities in starting material.

Recently, several studies have been done by various groups to understand the memory effects behind organic materials, which include understanding in terms of conformation changes, conjugation modification and oxidation-reduction process. In this paper, a WORM (write-once read-many times) memory device using a new polymer material 2-(9H-carbazol-9-yl)ethyl methacrylate (PCz) containing carbazole donor group has been demonstrated. The device uses a MIM (metal-insulator-metal) structure with ITO coated glass as bottom electrode, the synthesized polymer material PCz as the active layer and Al as the top electrode. The toluene solution of PCz was spin-coated on the ITO, followed by solvent removal in a vacuum chamber. Finally, Al was thermally evaporated through shadow mask onto the PCz film.

The memory effect of PCz was observed in the I-V characteristic of the MIM structure. The as-fabricated device is found to be in its OFF state, and can be programmed to ON state which is not reversible. The WORM device exhibits a high ON/OFF current ratio of up to 106, and shows a good retention time for both the ON and OFF states which can be sustained within a 24 h timeframe, and extrapolated to sustain for another 10 years. The effect of continuous read pulse on the ON and OFF states was evaluated and no resistance degradation is observed for read cycles up to 107 times. By comparing the electrical characteristics of PCz and PVK as well as their optimized geometry simulation corresponding to their minimized energy states, the memory effect or bi-stable states of PCz can be attributed to the long linker between the carbazole groups and backbone present in PCz which play a part in the conduction mechanism.

1,4-Distyrylbenzenes with terminal dialkylamino groups and a central 2,5-disubstitution with electron-accepting groups were prepared via twofold Horner-olefination. These chromophores with a quadrupolar donor-acceptor-donor substitution and C2-symmetry absorb in the violet to green region of the visible spectrum exhibit large two-photon-absorption cross-sections when irrdiated in the NIR. Whereas a variation of the solvent polarity only slightly alters the absorption spectra, the fluorescence appears to be highly responsive. Besides a positive solvatochromism, the emission is very sensitive towards protonation. Quenching or appearance of new emitting species depends on the substitution pattern and is controlled by the concentration of the acid.

Organic semiconductors are under investigation for radiation sensors at Sandia National Laboratories. The wide band gaps, high resistivities, low dielectric constants, and high dielectric strengths of conjugated polymers suggest these materials may be suitable for solid-state particle counting detectors. A range of solution cast materials have been evaluated for this application, including polythiophenes and poly(p-phenylene vinylene)s, or PPVs.

Films were prepared by novel solution casting and mechanical stretching methods. Device structures including interdigital metal electrodes on glass and thin film transistors on SiO2 on silicon were fabricated by drop casting from solution and lamination of solid films. Transient and DC responses were recorded and analyzed. Experiments include laser stimulus for photoconductive pulse response, and field effect transistor testing. Mechanical stretching was shown to dramatically alter electrical properties of polymer films.

Future work will analyze the feasibility of single particle detection and analyze various geometries for optimization. The effects of traps and methods for reduction of trapping effects will be analyzed.

A variety of α, α'-subtituted quaterthiophenes containing ester, amide and polymerizable side chains have been synthesized and fully characterized. The self-assembly properties of these oligothiophenes were studied as function of the side chain. Introduction of amide functionalities highly promotes the self-assembly via π-stacking and hydrogen bond interactions, while the lack of amides prevent aggregate formation. Initial experiments show that by introducing a sorbyl moiety as a polymerizable group it is possible to achieve covalent fixation of the oligothiophene units in the self-assembled state.

We have succeeded in developing a simple solution process of pentacene thin films without particular precursor materials. High crystallinity and large plate-like grains of the solution-processed thin films were observed with several analyses. The solution-processed pentacene thin-film transistors (TFTs) were also fabricated and exhibited good transfer characteristics with maximum carrier mobility above 1 cm2/Vs. The solution-processed TFTs also indicated a steep subthreshold swing and high stability of the threshold voltage against the storage in the atmosphere. The trap states and the bulk carrier density in the films were evaluated from the transfer characteristics by using the analytical model. We considered that these good properties could be attributed to the high crystallinity and the large grains of the solution-processed thin films.

In this work, we here developed a conductive ink which contains silver nano-particles from which the electrodes for organic thin film transistor were directly patterned by ink-jet printing. Nano-sized silver particles having ∼ 20nm diameter was used for the direct metal printing. Silver conductive ink was printed on the heavily doped n-type silicon wafer with 200-nm thick thermal SiO2 layer as a substrate. To achieve a high line resolution and smooth conductive path, the printing conditions such as the inter-drop distance, stage moving velocity and temperature of the pre-heated substrates were optimized. After the heat-treatment at temperatures of about 100 ∼ 300 ° for 30 min, the printed silver patterns exhibit metal-like appearance and the conductivity. To fabricate a coplanar type TFTs, an active material of semiconducting polymer, which was dissolved in a proper solvent, was deposited between the ink-jet printed silver electrodes by solution process. The output and transfer characterization was measured in air. The OTFT with the ink-jetted source/drain electrodes show a mobility of 1.3 × 10−3 cm2 V−1 s−1 in the saturation regime and on/off current ratio over 103 and a threshold voltage of about −13 V.

We have studied the carrier transport in regio-regular polythiophene field effect transistors (FETs) by four-probe measurements of the steady-state channel conductance from room temperature to 4.2 K. At high gate voltage (constant total carrier density, n = 5×1012 cm−2) and at low temperatures, we demonstrate that the gate voltage and source-drain voltage combine to induce the insulator-to-metal transition. In the insulating regime, the carrier transport is well described by phonon assisted hopping in a disordered Fermi Glass (with Coulomb interactions between the hopping charge carrier and the charge left behind). At the highest gate voltages and at sufficiently high source-drain voltages, the data imply a zero-temperature transition from disordered insulator to metal.

A top gate pentacene TFT employing vapor deposited polyimide as a gate dielectric was fabricated. Polyimide was co-evaporated from 6FDA and ODA monomers and annealed at 150 °C in vacuum. The degree of imidization was verified by FT-IR. A breakdown voltage of 0.9 MV/cm of polyimide film was measured by MIM structure. A top gate pentacene TFT with W/L=25 has 0.01 cm2/Vs as a mobility, about 103 as an on-off ratio (In/off), −7.5V as a threshold voltage and 9 V per decade as a sub-threshold slope.