A series of 2,3,9,10-tetrasubstituted-6,13-dialkynylpentacenes was synthesized and their properties evaluated. Various alkynes with different substituents were chosen to explore the effects of substitution on acene properties. The addition of alkyl groups to the pentacene 2,3,9,10-positions showed significant effects on the absorption, emission, and redox properties versus the non-alkylated (R = H) materials. The acenes exhibited excellent solubility in numerous solvents, and HOMO energy levels matched well with the work function of gold, an important electrode material. Crystallographic characterization of the methoxymethylene derivative showed it to adopt a 1-dimensional π-stacked arrangement, with good overlap of the aromatic faces.

We fabricated a novel type photo-FET using poly(N-vinylcarbazole) as a photosensitive gate dielectric. For the photo-FET, photo-illumination to the PVK insulator layer make the field-effect mobility μ_FET two order of magnitude higher than dark condition. In particular, under blue-light illumination condition the on-off ratio was also a few ten times higher than dark condition. We concluded that the improvement of the transistor properties resulted from effective charge accumulation at the conductive channel by photo illuminations.

The field-effect mobility in two isomers of thieno[f,f']bis[1]benzothiophene was studied as a function of structure. Both regioisomers exhibit substantial mobilities up to 0.12 cm²/Vs, a value that is at most one order of magnitude lower than the best known organic transistors based on silicon dioxide gate insulators. The devices based on these materials exhibit another phenomenon, namely a shift in the threshold voltage during operation. This shift differs from usually observed threshold voltage changes in amount and irreversibility. In this paper, we present possible explanations for the observed behavior.

We have developed and synthesized highly conductive regioregular poly(3-alkylthiophene) (rr-PAT) derivatives for use in sensor arrays on a chip. Poly(3-alkylthiophene)s are ideally suited for this application because of their excellent electrical properties, solution processability and our ability to modify their chemical structure. Here, we synthesized rr-PATs that have different side chains and different end groups. The polymers were ink-jetted onto ChemFET devices on a chip and their chemical sensing properties were tested to a variety of volatile organic compounds (VOCs). The sensors demonstrated ppm level sensitivity and selectivity to all VOCs tested, including both polar and non-polar compounds.

The development of p-type semiconducting polymers demonstrating good stability under ambient operation is of importance for the development of low cost, printed electronics. We present here the synthesis and full characterisation of two soluble terthiophene polymers, and examine the effect of introducing a fused aromatic heterocycle, thieno[2,3-b]thiophene, into a terthiophene polymer backbone. This heterocycle contains a cross-conjugated central double bond, and its inclusion was shown to have a marked influence on the optical, thermal and electrical properties of the terthiophene polymer. Transistors were fabricated from both polymers, and the operation and storage lifetime under ambient operation was compared.

We have re-investigated the negative charge carrier transport in discotic columnar phases of triphenylene derivatives and a phthalocyanine derivative by time-of-flight method in order to clarify the intrinsic nature of charge carrier transport in discotic liquid crystals. In a purified hexabutyloxytriphenylene (H4T), in which the fast hole transport was discovered previous reports, the transient photocurrents for negative carriers showed two transits in different time ranges, which were correspond to electron and ionic transports, respectively. The fast mobility corresponded to 10^-2 cm²V^-1s^-1 comparable to the hole mobility reported previously. The fast electron transports were observed in purified hexahexyloxytriphenylene (H6T), hexapentyloxytriphenylene (H5T), and hexahexylthiotriphenylene (HHTT) as well, and the electron mobilities in these materials were 10^-4, 10^-3 and 10^-1 cm²V^-1s^-1, respectively. Furthermore, even in a phthalocyanine derivative that is well known as a typical p-type organic semiconductor, i.e., octaoctylphthalocyanine (8H₂Pc), a high electron mobility of 0.3 cm²V^-1s^-1 was established, while the highest bulk hole mobility of 0.2 cm²V^-1s^-1 was reported recently. Therefore, we conclude that the slow negative charge carrier transport reported in discotic liquid crystals previously originates from impurity-induced ionic transport, and that it is very likely for the intrinsic charge carrier transport in liquid crystalline semiconductors to be electronic and ambipolar, while it is very sensitive to the purity.

The ability to measure the structural development of organic semiconductor films and correlate it to the electrical characteristics of organic devices such as thin film transistors (OTFTs) is needed to facilitate the commercialization of this technology. Synchrotron-based Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy is a powerful tool that meets this need because it can non-destructively reveal both the structure and chemistry of thin organic films. The density of bonds involving Carbon, Nitrogen, Oxygen, and Fluorine can be quantified, a depth profile can be developed, and bond orientation can be determined. Here, we outline the principles of NEXAFS experimentation and data analysis with an emphasis on their application to organic semiconductor thin films. NEXAFS spectra of model organic semiconductors such as pentacene and poly(3-hexylthiophene) (P3HT) are used to demonstrate how NEXAFS can enhance understanding of the complex processing-structure relationships of semiconductor film formation and identify processing methods that may optimize device performance.

We studied how the underlying grain boundary morphology in the first pentacene monolayer affects the "macroscopic" mobility of the 40 nm thick OTFT film. Through manipulating surface properties of a SiO₂ dielectric layer using self assembled monolayers (SAMs), we controlled the crystalline domain morphology of pentacene films that have thicknesses ranging from sub-monolayer to 40 nm. Atomic force microscopy (AFM) and two-dimensional grazing incidence X-ray diffraction are employed to characterize the morphology and crystalline structure of pentane films. In addition, the spatial variation of charge carriers in the first few layers was investigated using conducting AFM (C-AFM). In particular, faceted or dendritic island morphology has been observed in the first pentacene layer mainly depending on surface morphology of hydrophobic SAMs, and C-AFM supported that the faceted islands showed larger current flow than the dendritic islands. This C-AFM current tendency correlates with the "macroscopic" charge mobility in OTFT. Because the faceted morphology should represent the single crystal-like pentacene island, faceted islands have fewer internal crystal defects and the higher current flow than the dendritic islands.

In this work, we report on the study of pentacene field effect transistors with a polymer (PMMA) on a high-k oxide (Ta₂O₅) two-layer gate dielectric, in order to combine low voltage operating devices and stability. Two-layer dielectric devices were compared to single layer (Ta₂O₅ or PMMA) gate insulators. To assess the importance of the structural quality of the Ta₂O₅, two deposition processes (e-beam evaporation and anodization) are studied. In order to evidence the relation between the electrical performances and behavior and the structural quality of the organic thin film, X-ray diffraction and AFM measurements were carried out to determine the pentacene morphology and ordering on the different dielectrics. Devices with bilayer gate dielectric present the best mobility, up to 0,6cm²/V/s, the pentacene film being well ordered in large grains on PMMA with or without high-k under layer. The transistors operate at 15V and show reduced polarisation effect compared to devices with only Ta₂O₅.

During the deposition of Pentacene on a Si-SiO₂ gate structure with Au bottom contacts for source and drain, the film growth was monitored with simultaneous in situ macro Raman spectroscopy and drain current measurements of the OFET device. The deposition of the active layer was carried out under UHV conditions at a growth rate of 0.65 Å/min. The purpose of the in situ characterization was to determine the minimum nominal thickness of the Pentacene layer required for efficient charge transport through the OFET circuit. At a thickness around 1.5 nm nominal coverage, the first percolation paths through the first organic monolayer develop, resulting in a sharp rise of the drain current. Up to a nominal film thickness of 30 nm, a subsequent slower increase of the drain current can be observed, revealing that the percolation of the first monolayer continues on a slower pace up to rather thick organic layers. These in situ measurements were complemented by ex situ isothermal deep level transient spectroscopy (charge QTS).

We present a comprehensive study of short channel effects in organic field-effect transistors by measuring the electrical characteristics of devices with fixed channel width and varying channel length. Our studies are conducted on a p-type organic semiconductor, (E,E-2,5-bis-{4'-bis-(4''-methoxy-phenyl)amino-styryl}-3,4-ethylenedioxy-thiophene that is spin-coated from solution to form bottom contact organic field-effect transistors. Drain-source currents from transistors with a channel length of 50 μm show excellent agreement with the square law equations derived for crystalline Si MOSFETs in both the linear and saturation regimes. As the channel length is incrementally reduced to 1 μm, device characteristics such as saturation regime channel conductance, sub-threshold current and threshold voltage, behave in a manner similar to Si MOSFETs of decreasing channel length. Results of these studies indicate the presence of non-destructive current punch-through and in addition, both channel-length modulation and threshold-voltage roll-off, neither of which have previously been reported in OFETs.

Potentiometry with a Kelvin probe atomic force microscope is used to investigate the contact resistances of pentacene OFETs, so that the injection of the charges at the source contact and their extraction at the drain contact can be distinguished from the influence of trap states on the charge transport through the accumulation channel. The samples consist of Au bottom contacts on a SiO₂ gate dielectric with a channel length of L=10- 15 μm and a channel width of W=100 μm. The gate oxide is first treated by an oxygen plasma before depositing about 30 nm of pentacene under high vacuum conditions. The output characteristics are measured as a function of temperature in an evacuated cryostat, revealing temperature-activated hole transport. The potentiometry measurements are performed ex situ under atmospheric conditions after storing the samples in air for several weeks. At room temperature, the pentacene OFETs are dominated by the resistance at the injection contact, so that the mobility in the channel region as deduced from potentiometry is about one order of magnitude higher than the value obtained from the output characteristics. The measurements are interpreted with microscopic model calculations for the temperature-activated currents.

The field-effect mobility in crystalline organic FETs is known to be an order of magnitude larger than the mobility observed in thin-film OFETs. We have shown for state-of-the-art crystalline pentacene that the density of gap states, and hence the field-effect mobility, is still limited by residual impurities and disorder in the material. We use photoconductivity and space-charge-limited current (SCLC) in pentacene single crystals to extract the density of states in the HOMO-LUMO bandgap. We find that purified crystals still possess band tails broader than those typically observed in inorganic amorphous solids. Results on field effect transistors (FETs) fabricated from similar crystals imply that the gap state density is much larger within 5-10 nm of the gate dielectric. We also have observed a defect generation phenomenon that is new to organic semiconductors. We use SCLC to study a defect in pentacene single crystals that can be created by bias stress and persists at room temperature for an hour in the dark but only seconds with 420nm illumination. The defect gives rise to a hole trap at E_v + 0.38eV and causes metastable transport effects at room temperature. Creation and decay rates of the hole trap have a 0.67eV activation energy with a small (10⁸ sec^-1) prefactor, suggesting that atomic motion plays a key role in the generation and quenching process. Clearly, such defect reactions could be a factor in the stability of pentacene OFETs.

The electrical stability of metal insulator semiconductor (MIS) capacitors and field effect transistor structures based in organic semiconductors were investigated. The device characteristics were studied using steady state measurements AC admittance measurements as well as techniques for addressing trap states. Temperature-dependent measurements show clear evidence that an electrical instability occurs above 200 K and is caused by an electronic trapping process. It is suggested that the trapping sites are created by a change in the organic conjugated chain, a process similar to a phase transition.

Solution-processed pentacene thin films could be prepared directly from pentacene solution without using precursor molecules. The solution-processed pentacene films showed highly oriented and highly crystalline structure. It appeared that large crystal-like platelets grown in the films, and it was assumed that crystalline size of solution-processed films was larger than that of sublimed films determined by in grazing incidence X-ray diffraction method and powder X-ray diffraction method. FETs formed with solution-processed films exhibited good switching properties with the mobility of 0.8cm²/Vs and on/off ratio above 10⁵. Maximum carrier mobility above 1cm²/Vs was confirmed. The solution-processed film transistors showed lower threshold voltage due to lower carrier density in the films compared with sublimed films. It was confirmed that the solution-processed transistors showed more stable properties for the storage for months than sublimed film transistors. These aspects of transistor performance could be explained by structural difference between solution-processed and sublimed films. Transistors of solution-processed films of pentacene were fabricated by printing technique using a temperature controllable dispenser and the switching operations of isolated transistors were confirmed.

n-channel organic thin film transistors (OTFTs) with field-effect mobility comparable to that typically reported for p-channel pentacene TFTs were fabricated on oxidized silicon wafers using N,N'-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C₁₃H₂₇) as the semiconductor. Au, Cr, Al, and LiF/Al source and drain contacts were studied. Accumulation mode n-channel transistor operation was demonstrated for all contact metals despite the large differences in their work functions. High field effect mobility near 0.6 cm²/Vs and large I_on/I_off of 10⁷ were achieved for the best device which compares favorably with the best reported performance for OTFTs fabricated using this class of material. Despite the impressive performance significant device instability was observed. n-channel TFT performance was sufficient to demonstrate pentacene/PTCDI-C₁₃H₂₇ TFT complementary inverters with a high gain of 140.

Behaviors of charge transportation in organic heterojunction consisted of p-type CuPc and n-type F₁₆CuPc have been studied. Conductivity parallel to heterojunction interface is higher than that of each single layer is observed. It has been confirmed that the higher conductivity is originate from accumulation of positive and negative mobile charges. Based on this phenomenon, a novel heterojunction organic field-effect transistor (OFET) having two conducting channels has been demonstrated. The heterojunction OFETs, with either p-type layer or n-type layer connected to the insulator, can operate in mode of normally-on (depletion-accumulation). In addition, ambipolar electrical properties with mobility of 0.04cm²/Vs and balanced charge transportation, and CMOS inverter comprising unique ambipolar transitor have been optimised based on the heterojunction OFET.

In this paper, we introduce our recent results on organic thin-film transistor (TFT) technologies; self-aligned self-assembly process and a high-resolution color active-matrix LCD panel driven by organic TFT. First, a novel process for fabricating alignment-free, printable, organic thin-film transistors is presented. This process exploits a self-assembly phenomenon in which soluble nanomaterials such as metal nanoparticles and organic molecules are self-assembled into a device structure. Solution-processed source and drain electrodes were self-aligned to a gate electrode by using a hydrophobic self-assembled monolayer optically patterned onto the gate electrode with a back-substrate exposure technique. An organic semiconductor film deposited on the patterned SAM was selectively ordered and substantially self-aligned to the gate electrode. A field-effect mobility of 0.15 cm²/Vs and on/off current ratio of 10⁵ were experimentally demonstrated when pentacene molecules were used as the semiconductor and silver nanoparticles were used as electrode materials. Second, a full-color twisted-nematic type liquid crystal display (TN-LCD) of 1.4-inch diagonal size driven by organic TFT has been fabricated. This TN-LCD has 80 x 80 x 3 (RGB) pixel arrays addressed by pentacene TFT with a channel width of 50 μm. The contact resistance between the pentacene film and the source/drain electrodes has been reduced by steepening the side slope of the electrodes. In addition, a solution-processed passivation film with a novel structure, consisting of organic and inorganic stacked layers, has been developed to protect the TFT against degradation induced by integration with TN-LCD devices. Consequently, the organic-TFT-driven TN-LCD is capable of displaying full-color moving images at a resolution of 80 pixels per inch.

A capacitor that basically consists of two parallel metal plates with dielectric materials in between, can store charge at the two inner surfaces of the metal plates when a voltage bias is applied. As the thickness of the metal-plate electrodes decrease to nanometers range, we find an interesting physical phenomenon, i.e., the stored charges can modify the physical properties of the semiconductor layer coated on top of it. This discovery leads us to demonstrate a whole-new concept field-effect transistor, a vertical organic transistor with a novel device structure by stacking gate-source-drain vertically. This vertical stack consists of an active cell (drain/organics/source) on top of a capacitor cell (source/dielectrics/gate). When the gate (capacitor) is biased, charges are stored in the capacitor cell. As the thickness of the source electrode is thin enough, typically in the nanometer range, the active cell can also sense the stored charges within the capacitor cell, and, subsequently, modulate the charge injection from the source into the organics. This unique device structure provides an extremely short "channel length" and large channel conduction area. As a result, we achieved organic transistors with low working voltage (less than 5 V), high current output (up to 10 mA or 4 A/cm²), and high ON/OFF ratio (up to 4×10⁶). This device solves two long-standing issues with organic transistors, high working voltages and low current output. This novel device with its enhanced operating characteristics opens new directions for organic transistors and their applications. The device operation mechanism is different from traditional field effect transistors, where we proposed an injection-controlled mechanism, which can basically explain the observed electrical phenomenon of our vertical transistors.

To reduce the operating voltage of organic thin film transistors (TFTs) to a few volts (similar to state of the art silicon integrated circuits), a molecular thin film transistor concept based on an ultra thin molecular self assembled monolayer (SAM) gate dielectric in combination with a high mobility organic semiconductor is presented. Having a gate dielectric thickness of 2.5 nm, these TFTs can be operated with supply voltages of less than 2 V. The TFTs have a carrier mobility up to 1 cm²/Vs, an on/off current ratio of 10⁶, and a subthreshold swing of 100 mV/decade. Owing to the excellent insulation properties of the SAM dielectric, the TFTs have lower gate leakage than silicon MOSFETs with a thermally grown SiO₂ dielectric of similar thickness. Results on the first integrated circuits (inverters and ring oscillators) with molecular gate dielectrics, manufactured on glass and on flexible polymeric substrates, demonstrate the practicability of the molecular dielectric approach for applications.

Light-emitting organic field-effect transistors (LEOFETs) based on Poly [2-methoxy, 5-(2'-ethyl-hexoxy)-1, 4-phenylenevinylene] (MEH-PPV), α-sexithiophene (α-6T) and N,N'-Ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13) were prepared on a SiO₂ gate insulator. The LEOFETs based on MEH-PPV and α-6T showed a p-type semiconducting behavior whereas PTCDI-C13 operated in n-type FET. Asymmetric electrodes of Au-Al were prepared by twice of photolithography and lift-off techniques, and by electroplating of Au onto Al electrode to improved device performances. The emission efficiency of the devices with Au/Cr-Al was approximately 20 times higher than that of the device with Au/Al-Au/Al electrodes at the gate and drain voltages of -100 V. The emission region was observed with an optical microscope. The emission region was found to be very homogeneous along the drain electrode, and it did not shift when the gate and drain voltages changed. Although the carrier injection was improved by using asymmetric electrodes, the number of the carriers injected from the drain electrode was still lower than that from the source electrode in the unipolar devices.

A low temperature high quality gate dielectric process for bottom gate organic thin film transistors (OTFT) is introduced which is compatible to plastic substrates. The Al₂O₃ dielectric is grown from the aluminum gate electrode by anodic oxidation at room temperature and exhibits an exceptionally good electrical performance even for thin layers of 50nm. Finding an electrolyte which significantly reduces dielectric charges was instrumental for the desired OTFT application. The electrolyte and substrate dependent behaviour was characterized and compared to different dielectrics to point out the advantages of anodic oxidized aluminum. The characteristics of pentacene bottom contact OTFTs realized with anodized Al₂O₃ gate dielectric on glass and plastic substrates are presented.

The interface between the semiconducting polymer and the gate dielectric is one of the most critical regions of a polymeric thin film transistor. For polymeric TFTs, it is difficult to disaggregate the contributions of the electronic structure of the semiconductor and that of the dielectric because, in part, the microstructure of thin films of semiconducting polymers is strongly affected by the chemical functionality at the surface of the dielectric. We have developed a lamination technique that can be used to transfer semiconducting films formed on surfaces that yield films with high mobility to other dielectrics. We have studied films of semiconducting polymers, such as poly[5,5'-bis(3-dodecyl-2-thienyl)-2,2'-bithiophene] and poly(3-hexylthiophene) using this method. The effects of self-assembled monolayers (SAMs) formed on inorganic dielectrics on device performance are discussed. Our results suggest that mobility is mainly controlled by the structure of the semiconducting film and that the threshold voltage of TFTs may be modified through the use of SAMs.

Printed electronics is attractive as a pathway towards the realization of ultra-low-cost RFID tags for replacement of conventional optical barcodes. While this application has received tremendous attention in recent years, it also represents one of the most challenging applications for organic transistors, based on both the performance requirements and the process complexity and cost implications. Here, we report on our progress in developing materials and processes for the realization of printed transistors for low-cost RFID applications. Using inkjet printing of novel conductors, dielectrics, and organic semiconductors, we have realized printed transistors with mobilities >0.1cm²/V-s, which is approaching the requirements of certain RFID applications. We review the performance of these devices, and discuss optimization strategies for achieving the ultimate performance goals requisite for realizing printed RFID.

An effective method for detecting a trace amount of chemical impurity, e.g., a few ppm or less, that degrades the charge carrier transport properties in smectic liquid crystalline (SmLC) semiconductors was investigated with a model system i.e., a 2-phenylnaphthalene derivative of 2-(dodecyloxy)-6-(4-octylphenyl)naphthalene (8-PNP-O12) and a terthiophene derivative of 2,5-bis(5-hexylthiophene-2-yl)thiophene (6-TTP-6). A transient photocurrent measurement could detect a chemical impurity of a few ppm or less that conventional analytical methods such as high-performance liquid chromatography (HPLC) and gas chromatography (GC) failed to detect: the slow transit induced by drift of ionized impurity molecules allowed us to detect it, which was clearly distinguished from the fast transit induced by the electronic conduction in the host SmLC semiconductor. This systematic study provided a semiquantitative basis for evaluating the contamination of chemical impurity.

Significant progress has been made in the area of p-type organic field-effect transistors while progress in developing n-type materials and devices has been comparatively lacking, a limiting factor in the pursuit to develop complementary organic electronic circuits. Given the need for n-type organic semiconductors we have carried out studies using two different fullerene molecules, C₆₀ and C₇₀. Here, we report mobilities for C₆₀ ranging from 0.02 cm²/Vs up to 0.65 cm²/Vs (depending on channel length), and mobilities from 0.003 cm²/Vs up to 0.066 cm²/Vs for C₇₀. All devices were fabricated with organic films deposited under high vacuum but tested at ambient pressures under nitrogen.

Copper Phthalocyanine (CuPc) has been attracted particular attention recently due to its outstanding chemical stability and photo/electrical properties. An all-organic field-effect transistor (OFET) based on ordered CuPc was investigated. Ideal transistor behavior was observed in the OFET using copper phthalocyanine (CuPc) as the semiconductor layer and polymethylmethacrylate as the insulator layer. The ordered CuPc layer was evaporated by previous method (Thin Solid Films 347 (1999) 299). The results of the OFET demonstrated that the channel carrier mobility and switching ratio were at about 0.008 cm²V^-1s^-1 and 10³, respectively.

We report on the surface-induced molecular order and the optical anisotropy of the pentacene thin film on a photoaligning buffer layers. The photopolymer, showing an anchoring transition from the vertical alignment to the planar alignment by the exposure of a linearly polarized ultraviolet light, was used as a buffer layer to control the structural order of the pentacene molecules. The atomic force microscopic images revealed the recovery of void sites and the enlargement of the grain size in the pentacene film grown on the photoaligning buffer layer. It was found that the grain size and the optical anisotropy of the pentacene film were strongly correlated with each other.

The interface electronic structure of pentacene and C₆₀ layer was investigated in detail by using ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy. The magnitudes of measured interface dipole were 0.11 eV and 0.07 eV for the C₆₀ deposited on pentacene (C₆₀/pentacene) and the pentacene deposited on C₆₀(pentacene/C₆₀), respectively. The obtained C 1s spectra on pentacene/C₆₀ and C₆₀/pentacene indicate no significant chemical bonds existing at the interface. The offsets of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) at the C₆₀-pentacene interface were 1.29 eV and 0.89 eV for C₆₀/pentacene/Au while it were 1.5 eV and 1.1 eV for pentacene/C₆₀/Au. This resulted in that the HOMO and LUMO offset depend on the deposition order of the organic layers. We fabricated the ambipolar OTFTs used the favorable structure of pentacene and C₆₀, and obtained the field effect mobilities were 0.017 cm²/Vs and 0.007 cm²/Vs for p-channel and n-channel operations.

Organic field effect transistors are expected to be applicable for low-cost, large-area electronic applications, e.g. the incorporation as active-matrix into displays based on organic light emitting diodes (OLED). There are two major challenges which have to be tackled. As the low charge carrier mobility allows only for comparatively low saturation currents, the ratio of channel width and length has to increase by several orders of magnitude, compared to poly-Si-technology. Furthermore, as organic semiconductor devices usually degrade upon exposure to solvents, standard photolithography cannot be applied once the organic materials have been deposited. Therefore, the definition of single pixels has to occur before the deposition of organic materials. We prepared OFETs employing a bottom-Al-gate, an 50 nm thick anodized Al-oxide gate dielectric and a inter-digital drain-source-structure (Au), topped with 30 nm of pentacene as active layer. By applying an inter-digital structure we increased the W/L-ratio to 4340. For the given configuration, a saturation current of 4 mA could be observed at -20 V drain-source- and -20 V gate-source-voltage. The drain-source-contacts enclosed a predefined ITO-anode shorted to drain and acting as OLED-anode. For preventing shortcuts between the OLED-cathode and the OFET, poly-vinyl-alcohol (PVOH) was spin-coated from an aqueous solution and structurized by photolithography. When the OFET characteristics were measured afterwards the field-effect- mobility dropped by two orders of magnitude but recovered due to desorption of residual water. Afterwards, the organic layers and a Al/LiF-cathode were deposited. The area covered by the OLED was 1.33mm². Applying an operating bias of 11 V between cathode and source, allows for switching of the OLED by changing the gate-source-voltage from +2.5 V to -5 V. The on-state-brightness is 850 cd/m² and the on-off-ratio 950. Considering a realistic filling factor of 40% the values observed may be sufficient for active-matrix display-applications.

Recently conjugated polymers and conjugated organic molecules have drawn a great deal of attention, since they are uniquely suited for thin film, large area, mechanically flexible devices. On the other hand, polymer/inorganic nanocomposite have also been pursued to deliver unique electronic properties in various device applications such as organic light-emitting diodes, organic thin film transistors, and solar cells. Here we demonstrate a nanocomposite based on polyaniline nanofibers decorated with gold nanoparticles and apply this composite into memory devices. The electronic property shows an electric bistable effect in a two terminal sandwiched structure. These two bistable states have different conductivities by three orders of magnitude. The mechanism is likely involving electric-field induced charge transfer between the polymer and nanoparticles. This nanocomposite material provides a unique functionality and possibility to open a new direction for future organic electronics.

Metal organic pentacene based low voltage organic thin film transistors with field effect mobility as large as 0.8 cm²/V^-1.s^-1 and on/off current ratio larger than 10⁶ have been fabricated. Thin films deposited by evaporation at different deposition rate has different morphology which leads to a difference in transistor characteristics. The films with a deposition rate of 2A/sec has better morphology and also the transistor behavior. AFM (atomic force microscope) and STM (scanning tunneling microscope) were used to understand the morphology and ordering of the molecules on the silicon surface which helps the transistor to operate at low voltages. The results presented here show a strong correlation between molecular ordering and the need of well-ordered films for the performance of organic thin film transistors (OTFT's).