This PDF file contains the front matter associated with SPIE Proceedings Volume 8831, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

This paper focuses on industrial aspects of the material development of DPP-Polymers for the application in solution processed field effect transistors. It is shown that optimization of processing conditions can have a significant effect on transistor performance for a certain polymer. Although the solubility of DPP-Polymers is in general much higher than that of highly crystalline polymers like Poly-3-hexylthiophene (P3HT), transforming the polymer powder into a film is still challenging. Semiconductor film morphology and thus transistor performance strongly depends on the film formation process. Aspects of device architectures and testing conditions will also be discussed.

For the development of circuits consisting of organic thin film transistors (OTFT) with satisfying yield, a stable and reliable process is necessary. This can be achieved by eliminating failure mechanisms and understanding the charge transport phenomena in the individual device. Following the way of a charge through the device, we start with the investigation of the influence of the Schottky barrier height and contact morphology on the device performance by finite-elements simulations. It could be verified that the charge injection limiting contact resistance can be decreased by two orders of magnitude by reducing the thin oxide layer at the source and drain contacts and improving the semiconductor layer morphology at their vicinity. Second, we present an analytical closed-form solution of the OTFT channel potential used for Monte-Carlo charge transport simulations and compute current-voltage and transient response characteristics out of it. In a next step, the influence of the deposition process on the layer interface is investigated. Therefore, velocity distribution measurements of the charge carriers lead to a simulation model with varying disorder, depending on the layer surfaces and deposition techniques. Afterwards, leakage currents through the gate dielectric can be described by a poor conducting semiconductor model in the finite-elements framework. Leakage currents increase power consumption in circuits and, what is more critical, can lead to a total failure of the OTFT. However, they can be influenced by the number of deposited dielectric layers and charge injection supporting self-assembled monolayers at the source and drain contacts. These findings lead to circuit building blocks for an organic device library whereupon still existing performance fluctuations can be coped with Monte-Carlo circuit simulations.

Hybrids of semiconducting polymers and single-walled carbon nanotubes (SWNT) are interesting for organic electronic devices such as solar cells, light-emitting diodes and field-effect transistors (FETs). They are easily produced by selective dispersion of SWNTs in polymer solutions by ultrasonication followed by centrifugation. We demonstrate that nanotubes at concentration levels well below the percolation limit significantly improve charge injection of both holes and electrons into semiconducting polymers in top-gate FETs. This leads to lower contact resistances and reduced threshold voltages, thus the maximum ambipolar currents and visible light emission due to electron-hole recombination are considerably enhanced. The improved injection of holes and electrons allows for a much wider range of accessible polymers for ambipolar and light-emitting transistors. The same conjugated polymers can also be used to enrich specific semiconducting SWNT and to produce high-performance ambipolar nanotube network FETs. These show efficient nearinfrared electroluminescence. Mapping the emission from these networks during a gate voltage sweep allows us to visualize preferential current paths and investigate percolation models for purely semiconducting nanotube networks.

Although state-of-the-art ambipolar polymer semiconductors have been extensively reported in recent years, highperformance ambipolar polymers with tunable dominant polarity are still required to realize on-demand, target-specific, high-performance organic circuitry. Herein, dithienyl-diketopyrrolopyrrole (TDPP)-based polymer semiconductors with engineered side-chains have been synthesized, characterized and employed in ambipolar organic field-effect transistors, in order to achieve controllable and improved electrical properties. Thermally removable tert-butoxycarbonyl (t-BOC) groups and hybrid siloxane-solubilizing groups are introduced as the solubilizing groups, and they are found to enable the tunable dominant polarity and the enhanced ambipolar performance, respectively. Such outstanding performance based on our molecular design strategies makes these ambipolar polymer semiconductors highly promising for low-cost, large-area, and flexible electronics.

In this study we investigated the influence of the deposition technique on the surface topology and the resulting device performance in organic thin film transistors (OTFT). We varied the parameters of flexographic and gravure printing for the organic semiconductor (OSC) and did multilayer gravure printing for the dielectric, respectively. Therefore, we manufactured transistors in bottom contact top gate architecture and compared them to spin coated samples. As investigation tool for OTFTs, the charge carrier velocity distribution is correlated with the optical characteristics of the printed layers. We found a dependency of the printing technique on the surface topology of the semiconductor and, due to the resulting increase of the channel length, a broadening of the charge carrier velocity distribution. For the dielectric we found a dependency on the layer thickness which seems to be independent from the deposition technique.

Derivatives of [1]benzothieno[3,2-b]benzothiophene (BTBT) are attracting much attention as a highly soluble, highmobility semiconductor material for thin-film transistor applications. These small molecules are known to organize themselves into a single crystalline structure after spin coating or drop casting. Charge transport in a single crystal material is anisotropic in nature. Hence, it is desired to control its orientation during growth or recrystallization so that the source and drain electrodes of a transistor are to be placed along a faster transport direction. We propose to generate temperature gradient in a heated liquid crystalline thin film to induce lateral recrystallization. In experiment, we tried two methods. First, an aluminum plate with two narrow ridges was inserted between a temperature-controlled stage and a square silicon substrate with a 200nm-thick SiO₂ and a spin-coated C₈-BTBT film. We raised the temperature of the stage to 120oC and let it cool gradually. During cooling at around 105oC , the color of the sample started to change, indicating a phase change. This change proceeded from the corners of the film and in about 30 seconds, darker regions merged at the center of the substrate. Second, the sample was placed at the edge of the stage. In this case, the color change started from the protruding corner of the sample and proceeded toward the other end. Micrograph observation revealed that cracks were formed in these films and they were perpendicular to the direction of the phase change.

Flexible transistor active matrix array is fabricated on PEN substrate using all screen-printed gate, source and drain electrodes. Parylene-C and DNTT act as gate dielectric layer and semiconductor, respectively. The transistor possesses high mobility (0.33 cm2V^-1 s^-1), large on/off ratio (< 106) and low leakage current (~10 pA). Active matrix array consists of 10×10 transistors were demonstrated. Transistors exhibited average mobility of 0.29 cm2V-1s-1 and on/off ratio larger than 104 in array form. In the transistor array, we achieve 75μm channel length and a size of 2 mm × 2 mm for each element in the array which indicates the current screen-printing method has large potential in large-area circuits and display applications.

In this paper we present a 2D analytical model for the potential and the electric eld in bottom-contact organic eld-e ect transistors (OFETs) and an approach for calculation of the tunneling and thermionic source and drain injection current. The electrostatics are analytically calculated by solving the Poisson equation via the conformal mapping technique, based on that the currents were computed. Typical OFET behaviors like nonlinear injection and s-like shape are clearly visible. The model is compared with devices simulated by TCAD Sentaurus for various geometrical parameters.

We have fabricated the transistor memory devices based on SiO₂ and polystyrene (PS) hybrid dielectric. The trap states densities with different semiconductors have been investigated and a maximum 160V memory window between programming and erasing is realized. For DNTT based transistor, the trapped electron density is limited by the number of mobile electrons in semiconductor. The charge transport mechanism is verified by light induced V_th shift effect. Furthermore, in order to meet the low operating power requirement of portable electronic devices, we fabricated the organic memory transistor based on AlOx/self-assembly monolayer (SAM)/PS hybrid dielectric, the effective capacitance of hybrid dielectric is 210 nF cm^-2 and the transistor can reach saturation state at -3V gate bias. The memory window in transfer I-V curve is around 1V under +/-5V programming and erasing bias.

Organic and polymeric semiconductors are among the alternatives to silicon being considered for sensing devices and circuitry. Their synthesis is now well established, and some performance metrics such as charge carrier mobility and optoelectronic quantum yield exceed those of inorganic counterparts such as amorphous silicon. The best fit for organic semiconductors is in applications where inherent capabilities such as rational modification of carrier energy levels and covalent connection between charge channels and surface receptors are leveraged. This presentation will describe newly synthesized organic molecular solids and polymer films where these attributes are emphasized. For example, addition of a borane to a semiconductor enhances response to ammonia, and introduction of highly electron donating tetrathiafulvalenes into moderately electron-rich polymers enhances response to electron-poor analytes (for example, TNT), for the development of chemical sensors. Carrier energy levels are markedly and predictably altered by static charge embedded in polystyrene films adjacent to organic semiconductors, for multiple device activities to be obtained from a single device layout using one semiconductor, and also the avoidance of powering gate electrodes to set optimal sensor sensitivities during operation.

Light emission of 2-(2,6-bis((E)-4-(diphenylamino)styryl]-4H-pyran-4-ylidene}malononitrile (TPA-DCM) is weakened by aggregate formation. Attaching tetraphenylethene (TPE) units as terminals to TPA-DCM dramatically changes its emission behavior: the resulting fluorogen 2-(2,6-bis((E)-4-(phenyl(4’-(1,2,2-triphenylvinyl)-[1,1’-biphenyl]-4- yl)amino)styryl)-4H-pyran-4-ylidene)malononitrile (TPE-TPA-DCM) is more emissive in the aggregate state, showing a novel phenomenon of aggregation-induced emission (AIE). Formulation of TPE-TPA-DCM using bovine serum albumin (BSA) as the polymer matrix yields uniformly sized protein nanoparticles (NPs) with high brightness and low cytotoxicity. Applications of the fluorogen-loaded BSA NPs for in vitro and in vivo far-red/near-infrared (FR/NIR) bioimaging are successfully demonstrated using MCF-7 breast cancer cells and a murine hepatoma-22 (H₂₂) tumorbearing mice model, respectively. The AIE-active fluorogen-loaded BSA NPs show excellent cancer cell uptake and prominent tumor targeting ability in vivo due to the enhanced permeability and retention effect.

Organic molecular sensors have the advantage of being used through an easy, fast, economical and reliable optical method for detecting toxic metal ions in our environment. In this work, we present a simple but highly specific organic ligand compound 5-Chloro-2-((E)-((E)-3-(4-(dimethylamino)phenyl)allylidene)amino)phenol (L1) that acts as a colorimetric sensor for ions in a mixture of acetonitrile/water (ratio 10:1, v:v). Binding interaction between L1 and various metal-ions has been established by ultraviolet-visible spectroscopic measurements that indicate favorable coordination of the ligand with selective metal ions, particularly, with copper. These results showed that the electronic transition band shape of L1 change after binding with copper in aqueous solution. L1 exhibited binding-induced color changes from yellow to pink one detected by the naked eye. This new sensor presented 2.5 × 10^-6 M as limit detection, even under the presence of other metal ions.

For the emerging fields of biomedical diagnostics and environmental monitoring, where sensor platforms for in-situ sensing of ions and biological substances in appropriate aqueous media are required, electrolyte-gated organic fieldeffect transistors (EGOFETs) seem to be the transducers of choice. Due to the formation of an electric double layer at the electrolyte/organic semiconductor interface, they exhibit a very high capacitance allowing for low-voltage and waterstable operation. In combination with the outstanding properties of organic devices like biocompatibility, lowtemperature processability on flexible substrates, as well as the possibility to tune the physical and chemical properties enhancing the selectivity and sensitivity, EGOFET-based sensors are a highly promising novel sensor technology. In order to obtain a reliable sensor response, a stable device operation is crucial. Within this context, we present a combined study of poly(3-hexylthiophene)–based EGOFETs on various substrates. In particular, the influences of different concentrations of NaCl in the electrolyte and various gate electrode materials, to tune the threshold voltage have been investigated. Furthermore, the limits of the stable operational window are evaluated and the effects when abandoning the latter are discussed.

A high performance proximity sensor that integrates a front semitransparent organic photodiode (OPD) and an organic light-emitting diode (OLED) is demonstrated. A 0.3-nm-thick plasma-polymerized fluorocarbon film (CFX)-modified thin silver interlayer, serving simultaneously as a semitransparent cathode for the OPD and an anode for OLED, is used to vertically connect the functional organic electronic components. A microcavity OLED is formed between a semitransparent Ag/CFX interlayer and the rear Al cathode enhancing the forward electroluminescence emission in the integrated device. The semitransparent-OPD/OLED stack is designed using an optical admittance analysis method. In the integrated sensor, the front semitransparent OPD component enables a high transmission of light emitted by the integrated OLED unit and a high absorption when light is reflected from objects, thereby to increase the signal/noise ratio. The design and fabrication flexibility of an integrated semitransparent-OPD/OLED device also has cost benefit, making it possible for application in organic proximity sensors.

Ferroelectric material supports both pyro- and piezoelectric effects that can be used for sensing pressures on large, bended surfaces. We present PyzoFlex, a pressure-sensing input device that is based on a ferroelectric material (PVDF:TrFE). It is constructed by a sandwich structure of four layers that can easily be printed on any substrate. The PyzoFlex foil is sensitive to pressure- and temperature changes, bendable, energy-efficient, and it can easily be produced by a screen-printing routine. Even a hovering input-mode is feasible due to its pyroelectric effect. In this paper, we introduce this novel, fully printed input technology and discuss its benefits and limitations.

This lecture focuses on the challenging design and realization of new materials for creating unconventional electronic circuitry. Fabrication methodologies to achieve these goals include high-throughput, large-area printing techniques. Materials design topics to be discussed include: 1. Rationally designed high-mobility p- and n-type organic semiconductors for printed organic CMOS, 2. Polycrystalline and amorphous oxide semiconductors for transparent and mechanically flexible electronics, 3) Self-assembled and printable high-k nanodielectrics enabling ultra-large capacitance, low leakage, high breakdown fields, minimal trapped interfacial charge, and device radiation hardness. 4) Combining these materials sets to fabricate a variety of high-performance thin-film transistor-based devices.