This PDF file contains the front matter associated with SPIE Proceedings Volume 8117, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Syntheses, characterizations, and applications to organic field-effect transistors (OFETs) of four isomeric naphthodithiophenes (NDTs) are reported. The NDT cores are utilized to both small-molecular organic semiconductors for vapor-processed OFETs and polymer semiconductors for solution processed OFETs. For the vapor-processed OFETs, the linear-shaped NDT gives the best material showing mobility of up to 1.5 cm² V^-1 s^-1, whereas for the polymer-based solution-processed OFETs, the angular-shaped NDT gives better results with mobility as high as 0.77 cm² V^-1 s^-1. To understand the different trends in the mobility of the two systems, the packing structure and intermolecular orbital interaction are studied.

We report three generations of p-type dendrimer semiconductors comprised of spirobifluorene cores, carbazole branching units and fluorene surface groups for use in organic field-effect transistors (OFETs). The group of dendrimers are defined by their generation and noted as SBF-(Gx)₂, where x is the generation. Top contact-bottom gate OFETs were fabricated by spin-coating the dendrimers onto an n-octyltrichlorosilane (OTS) passivated silicon dioxide surface. The dendrimer films were found to be amorphous. The highest mobility was measured for the first generation dendrimer (SBF-(G1)₂), which had an average mobility of (6.6 ± 0.2) × 10^-5 cm²/V s and an ON/OFF ratio of 3.0 × 104. As the generation of the dendrimer was increased there was only a slight decrease in the measured mobility in spite of the significantly different molecular sizes of the dendrimers. The mobility of SBF-(G3)₂, which had a hydrodynamic radius almost twice of SBF-(G1)₂, still had an average mobility of (4.7 ± 0.6) × 10^-5 cm²/V s and an ON/OFF ratio of 2.7 × 10³. Density functional theory calculations showed that the highest occupied molecular orbital was distributed over the core and carbazole units meaning that both intra- and intermolecular charge transfer could occur enabling the hole mobility to remain essentially constant even though the dendrimers would pack differently in the solid-state.

The concept of self-asssembling monolayer formation of organic semiconductors using highly reactive chlorosilane linker groups has been extended to the phosphonic acid linker which can be handled in air. A first proof of concept using an oxidized Al-gate electrode to form a hybrid thin dielectric resulted in a low voltage field effect transistor with hole mobilities of 10^-5 cm²/Vs. PEDOT based hole-transport and conductive materials have been improved for use in organic photovoltaics and wide area devices that require Ag busbars. A novel etchant can provide an invisible pattern for conductive transparent electrodes comprised of Clevios^TM PEDOT:PSS.

Three types of alkyl-substituted vanadyl phthalocyanines (OVPcs) were synthesized and their organic thin film transistors (OTFTs) were prepared by solution casting with a bottom gate and top contact device geometry. A peripheral octaoctyl-substituted OVPc (OVPc-op-C8) showed the mobility in the order of 10^-5 cm²/V•s. Both peripheral and nonperipheral tetraalkyl-substituted OVPcs are a mixture of four isomers, and exhibited the mobility of 10^-4-10^-2 cm²/V•s, depending on the length of the alkyl chains. Four isomers of non-peripheral tetraalkyl-substituted OVPcs can be separated by common lab column chromatography. A mobility of 0.13 cm²/V•s has been demonstrated with a pure isomer.

Patternable solution-crystallized organic transistors are developed with high carrier mobility that exceeds 10 cm²/Vs. We have investigated techniques of crystallization during the fabrication of the organic semiconductor thin films from solution. Regulating direction of the crystal growth in the above process, we successfully formed crystalline films with the mobility as high as 10-12 cm²/Vs from newly developed air-stable organic semiconductor compounds of 2,7-dialkyl[1]benzothieno[3,2-b]benzothiophene (Cn-BTBT) and 2,9-dialkyl-dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (Cn-DNTT). Furthermore, comprehensive measurements of Hall-effect and temperature dependent mobility in the solution-crystallized single-crystal transistors tell us that their fundamental charge transport mechanism is band transport.

Organic thin film technologies have opened a new range of interest into the optoelectronics industry. Nevertheless the physics and devices modeling still present a lack of accuracy. In order to provide designers with the latest performances of our organic CMOS technology, we have compared the performances of a behavioral model to the public a-Si TFT model in terms of accuracy on device modeling and basic circuit simulations. Fully printed organic CMOS devices and circuits have been processed and characterized in order to validate our device models. In particular, measurements have been carried out on several digital circuits like inverters and ring oscillators. Analog circuits such as current mirrors and differential pairs have also been measured. Simulations of these circuits have been performed using the device behavioral model and the a-Si TFT one under common EDA commercial tools. We show that both kinds of models enable to reproduce the different simple CMOS circuits performances in static as well as in dynamic modes which can open the way for designing a wide range and more complex digital and analog organic applications.

The combination of organic semiconductors and emerging solution-dispersible metal and metal oxide nanoparticles and nanowires enables the fabrication of electronic devices that are fully built from solution. This establishes a new device-processing platform that, in turn allows integration of functionality in systems not feasible in any conventional semiconductor technology. Examples of novel applications and systems enabled by this include: large-area, ultra light and flexible power harvesting, logic-integrated sensing and memory technologies. In this paper we discuss the use of organic Thin Film Transistors (TFTs) based on printed solution-processed materials for displays and memory applications. Polarizable solution-processed dielectrics and polymer semiconductors were integrated in the fabrication of non-volatile analog memory arrays. The stability of memory TFTs over 7 days was studied and characterized, and a stable process to achieve all printed TFTs is presented.

Patterned Electrode Vertical Organic Field Effect Transistor (PE-VOFET) operational behavior is examined in this work with the use of self-consistent numerical model and experimental measurements. The device is described as a single carrier type diode where one of its electrode's electrical properties could be altered under the gate influence, switching the current regime between the Contact Limited (CL) and the Space Charge Limited (SCL) regimes. Here we show that two distinct mechanisms can play a role in the switching process; inducing the formation of virtual contacts for the ideal Schottky barrier-based device or inducing a potential barrier which eliminates charge extraction for the non-ideal ohmic contact-based device. The latter is further examined by varying the Patterned Electrode (PE) thickness which alters the sub-threshold swing performances, determining the gate bias required to turn off the device. We further provide optimization rules regarding the active layer thickness (channel length), which hold for the 'ideal' performances of the single layer PE-VOFET. Based on the aforementioned models and optimization rules, we provide guidelines for the ideal PE-VOFET structure and future challenges in its fabrication.

We demonstrate the performance of thin film transistor devices based on a solution processable organic semiconductor with a field effect mobility of up to 2.5cm²V^-1s^-1. The performance of the material is demonstrated in a top gate, bottom contact device architecture operational in air without the requirement for device encapsulation. From a device performance aspect, we also highlight the influence that contact resistance has on the mobility.

Cleaved rubrene crystals offer reproducible and unoxidized surfaces ideal for investigation of the environmental dependence of the charge transport properties. Using atomic force microscopy (AFM), we found that the ambient environment induces molecular reorganization on a cleaved rubrene surface. Nanoscale beads and molecular fingers are formed on new surfaces exposed to the atmospheric environment. The bead formation is found to be suppressed in the argon environment. Studied by conductive AFM, the beads show insulating behavior. The observations suggest that the bead formation process is related to oxidation and charge transport modification of the rubrene surface.

The carrier behaviors in pentacene based organic field-effect transistor (OFET) were investigated by impedance spectroscopy measurement (IS). We clearly observed the carrier injection from the electrode and accumulation at the pentacene/insulator interface. We propose the measurement circuit for IS in transistor operation by using battery source for drain voltage. In this method, an additional structure where capacitance gradually increases is observed between injection and accumulation processes. From the comparison this result and the analyzed curve which reflects the injection properties from the electrode, we conclude that this additional structure originates from the charge sheet spreading into channel region. This technique enables us to observe the carrier injection to the channel region and investigate the charge sheet formation from off-state to on-state and vice versa of OFETs.