Deformable Organic Nanowire Field‐Effect Transistors

Deformable electronic devices that are impervious to mechanical influence when mounted on surfaces of dynamically changing soft matters have great potential for next‐generation implantable bioelectronic devices. Here, deformable field‐effect transistors (FETs) composed of single organic nanowires (NWs) as the semiconductor are presented. The NWs are composed of fused thiophene diketopyrrolopyrrole based polymer semiconductor and high‐molecular‐weight polyethylene oxide as both the molecular binder and deformability enhancer. The obtained transistors show high field‐effect mobility >8 cm² V^?1 s^?1 with poly(vinylidenefluoride‐ co ‐trifluoroethylene) polymer dielectric and can easily be deformed by applied strains (both 100% tensile and compressive strains). The electrical reliability and mechanical durability of the NWs can be significantly enhanced by forming serpentine‐like structures of the NWs. Remarkably, the fully deformable NW FETs withstand 3D volume changes (>1700% and reverting back to original state) of a rubber balloon with constant current output, on the surface of which it is attached. The deformable transistors can robustly operate without noticeable degradation on a mechanically dynamic soft matter surface, e.g., a pulsating balloon (pulse rate: 40 min^?1 (0.67 Hz) and 40% volume expansion) that mimics a beating heart, which underscores its potential for future biomedical applications.     

High‐Performance Vertical Organic Transistors

Vertical organic thin‐film transistors (VOTFTs) are promising devices to overcome the transconductance and cut‐off frequency restrictions of horizontal organic thin‐film transistors. The basic physical mechanisms of VOTFT operation, however, are not well understood and VOTFTs often require complex patterning techniques using self‐assembly processes which impedes a future large‐area production. In this contribution, high‐performance vertical organic transistors comprising pentacene for p‐type operation and C₆₀ for n‐type operation are presented. The static current–voltage behavior as well as the fundamental scaling laws of such transistors are studied, disclosing a remarkable transistor operation with a behavior limited by injection of charge carriers. The transistors are manufactured by photolithography, in contrast to other VOTFT concepts using self‐assembled source electrodes. Fluorinated photoresist and solvent compounds allow for photolithographical patterning directly and strongly onto the organic materials, simplifying the fabrication protocol and making VOTFTs a prospective candidate for future high‐performance applications of organic transistors.     

Thin‐Film Transistors

Thin‐film transistors (TFTs) matured later than silicon integrated circuits, but in the past 15 years the technology has grown into a huge industry based on display applications, with amorphous and polycrystalline silicon as the incumbent technology. Recently, an intense search has developed for new materials and new fabrication techniques that can improve the performance, lower manufacturing cost, and enable new functionality. There are now many new options – organic semiconductor (OSCs), metal oxides, nanowires, printing technology as well as thin‐film silicon materials with new properties. All of the new materials have something to offer but none is entirely without technical problems.     

Micrometer‐ and Nanometer‐Sized Organic Single‐Crystalline Transistors

The use of micrometer and nanometer‐sized organic single crystals to fabricate devices can retain all the advantages of single crystals, avoid the difficulties of growing large crystals, and provide a way to characterize organic semiconductors more efficiently. Moreover, the effective use of such “small” crystals will be beneficial to nanoelectronics. Here we review the recent progress of organic single‐crystalline transistors based on micro‐/nanometer‐sized structures, namely fabrication methods and related technical issues, device properties, and current challenges.     

Bottom‐Up Single‐Electron Transistors

As the downscaling of conventional semiconductor electronics becomes more and more challenging, the interest in alternative material systems and fabrication methods is growing. A novel bottom‐up approach for the fabrication of high‐quality single‐electron transistors (SETs) that can easily be contacted electrically in a controllable manner is developed. This approach employs the self‐assembly of Au nanoparticles forming the SETs, and Au nanorods forming the leads to macroscopic electrodes, thus bridging the gap between the nano‐ and microscale. Low‐temperature electron‐transport measurements reveal exemplary single‐electron tunneling characteristics. SET behavior can be significantly changed, post‐fabrication, using molecular exchange of the tunnel barriers, demonstrating the tunability of the assemblies. These results form a promising proof of principle for the versatility of bottom‐up nanoelectronics, and toward controlled fabrication of nanoelectronic devices.     

Self‐Assembled Monolayer Transistors

Self‐assembled monolayers of organic, conjugated molecules can be used as active components of field‐effect transistors. The length of the molecule can define critical device dimensions with high precision on the nanometer scale. Transistor effects on the molecular‐scale as well as in devices consisting of single active molecules have been demonstrated. The observed device performance indicates that such transistors might be useful for switching and amplifying electrical signals in logic circuits. Moreover, functionalizing the organic molecules reveals that different parts of the molecule can act as gate insulator or the active component of transistors. Such research might pave the way to molecular electronic applications.