Organic thin-film transistors (OTFTs) have lived to see great improvements in recent years. This review presents new insight into conduction mechanisms and performance characteristics, as well as opportunities for modeling properties of OTFTs. The shifted focus in research from novel chemical structures to fabrication technologies that optimize morphology and structural order is underscored by chapters on vacuum-deposited and solution-processed organic semiconducting films. Finally, progress in the growing field of the n-type OTFTs is discussed in ample detail. The Figure, showing a pentacene film edge on SiO2, illustrates the morphology issue.

Organic Thin Film Transistors for Large Area Electronics

Since the discovery of highly conducting polyacetylene by Shirakawa, MacDiarmid, and Heeger in 1977, π-conjugated systems have attracted much attention as futuristic materials for the development and production of the next generation of electronics, that is, organic electronics. Conceptually, organic electronics are quite different from conventional inorganic solid state electronics because the structural versatility of organic semiconductors allows for the incorporation of functionality by molecular design. This versatility leads to a new era in the design of electronic devices. To date, the great number of π-conjugated semiconducting materials that have either been discovered or synthesized generate an exciting library of π-conjugated systems for use in organic electronics. 11 However, some key challenges for further advancement remain: the low mobility and stability of organic semiconductors, the lack of knowledge regarding structure property relationships for understanding the fundamental chemical aspects behind the structural design, and realization of desired properties. Organic field-effect transistors (OFETs) are a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals (drain, source, and gate electrodes). OFETs are not only essential building blocks for the next generation of cheap and flexible organic circuits, but they also provide an important insight into the charge transport of πconjugated systems. Therefore, they act as strong tools for the exploration of the structure property relationships of πconjugated systems, such as parameters of field-effect mobility (μ, the drift velocity of carriers under unit electric field), current on/off ratio (the ratio of the maximum on-state current to the minimum off-state current), and threshold voltage (the minimum gate voltage that is required to turn on the transistor). 17 Since the discovery of OFETs in the 1980s, they have attracted much attention. Research onOFETs includes the discovery, design, and synthesis of π-conjugated systems for OFETs, device optimization, development of applications in radio frequency identification (RFID) tags, flexible displays, electronic papers, sensors, and so forth. It is beyond the scope of this review to cover all aspects of π-conjugated systems; hence, our focus will be on the performance analysis of π-conjugated systems in OFETs. This should make it possible to extract information regarding the fundamental merit of semiconducting π-conjugated materials and capture what is needed for newmaterials and what is the synthesis orientation of newπ-conjugated systems. In fact, for a new science with many practical applications, the field of organic electronics is progressing extremely rapidly. For example, using “organic field effect transistor” or “organic field effect transistors” as the query keywords to search the Web of Science citation database, it is possible to show the distribution of papers over recent years as shown in Figure 1A. It is very clear

Semiconducting π-conjugated systems in field-effect transistors: a material odyssey of organic electronics.

At present, flexible displays are an important focus of research1,2,3 Further development of large, flexible displays requires a cost-effective manufacturing process for the active-matrix backplane, which contains one transistor per pixel One way to further reduce costs is to integrate (part of) the display drive circuitry, such as row shift registers, directly on the display substrate Here, we demonstrate flexible active-matrix monochrome electrophoretic displays based on solution-processed organic transistors on 25-μm-thick polyimide substrates The displays can be bent to a radius of 1 cm without significant loss in performance Using the same process flow we prepared row shift registers With 1,888 transistors, these are the largest organic integrated circuits reported to date More importantly, the operating frequency of 5 kHz is sufficiently high to allow integration with the display operating at video speed This work therefore represents a major step towards 'system-on-plastic'

Flexible active-matrix displays and shift registers based on solution-processed organic transistors.

Color Control in π-Conjugated Organic Polymers for Use in Electrochromic Devices

In this paper we review recent progress in materials, fabrication processes, device designs, and applications related to organic thin-film transistors (OTFTs), with an emphasis on papers published during the last three years. Some earlier papers that played an important role in shaping the OTFT field are included, and a number of previously published review papers that cover that early period more completely are referenced. We also review in more detail related work that originated at IBM during the last four years and has led to the fabrication of high-performance organic transistors on flexible, transparent plastic substrates requiring low operating voltages.

Organic thin-film transistors: a review of recent advances

Electrically (and, possibly, mechanically) active patterns are applied using a colloidal suspension of nanoparticles that exhibit a desired electrical characteristic. The nanoparticles are surrounded by an insulative shells that may be removed by therefrom by application of energy (e.g., in the form of electromagnetic radiation or heat). The nanoparticle suspension is applied to a surface, forming a layer that is substantially insulative owing to the nanoparticle shells. The applied suspension is exposed to energy to remove the capping groups and fuse the particles into cohesion. If the nanoparticle suspension was deposited as a uniform film, the energy is applied in a desired pattern so that unexposed areas remain insulative while exposed areas exhibit the electrical behavior associated with the nanoparticles. If the nanoparticle suspension was deposited in a desired pattern, it may be uniformly exposed to energy. Additional layers may be applied in the same manner, one over the other, to form a multilayer device.

Methods and apparatus for manufacturing electronic and electromechanical elements and devices by thin-film deposition and imaging

An all-additive method for direct fabrication of nanometer-scale planar and multilayer structures utilizes the tip of a scanning probe microscope and a material reservoir. True “pick-and-place” retrieval and deposition of materials with a wide range of electrical, chemical, and mechanical properties is thereby facilitated.

Method and apparatus for direct fabrication of nanostructures

Fabrication and arrangement of nanoparticles into one-dimensional linear chains is achieved by successive chemical reactions, each reaction adding one or more nanoparticles by building onto exposed, unprotected linker functionalities. Optionally, protecting groups may be used to control and organize growth. Nanoparticle spheres are functionalized in a controlled manner in order to enable covalent linkages. Functionalization of nanoparticles is accomplished by either ligand exchange or chemical modification of the terminal functional groups of the capping ligand. Nanoparticle chains are obtained by a variety of connectivity modes such as direct coupling, use of linker molecules, and use of linear polymeric templates. In particular, a versatile building block system is obtained through controlled monofunctionalization of nanoparticles.

Nanoparticle chains and preparation thereof

PROBLEM TO BE SOLVED: To prevent the occurrence of sedimentation caused by particle flocculation in an electromotive display device. SOLUTION: The electrophoretic display device is provided with substantially two- dimensional arrangement of microcapsules and a potential generating means. Each of the microcapsules has electrophoresis formulation that is constituted of dielectric fluid and suspended particles. The particles are visually contrastive with respect to the dielectric fluid and have surface electric charges. The potential generating means generates a potential difference between a pair of electrodes. At least one of the electrodes is visually transparent, placed on the arrangement of the microcapsules and covers both sides of the arrangement. The means moves the particles toward one of the electrodes using the potential difference. The device is supplied with electricity by one or equal to or greater than two piezoelectric elements. These elements are also suitable to supply electricity to other types of non radiative display devices. COPYRIGHT: (C)2004,JPO

Non radiative display device and supply of piezoelectric power for the device

An application-ready electrophoresis material includes a carrier and a dispersion of microcapsules therein, the microcapsules each containing a plurality of phases therein. At least some of the phases contrast visually and exhibit differential responsiveness to an electric field, such that application of the field determines the visual appearance of the microcapsules. The material exhibits stability such the visual appearance persists despite removal of the field. In one aspect, the invention provides for enhanced stability of the visual appearance. In another aspect, the reflectivity of at least one of the phases is enhanced. In another aspect, one of phases is particulate in nature and emits visible radiation.

Joseph M. Jacobson

Papers

Methods and apparatus for manufacturing electronic and electromechanical elements and devices by thin-film deposition and imaging

Method and apparatus for direct fabrication of nanostructures

Nanoparticle chains and preparation thereof

Non radiative display device and supply of piezoelectric power for the device

Electrophoretic material and electrophoretic device