Micropatterned Single-Walled Carbon Nanotube Electrodes for Use in High-Performance Transistors and Inverters

We demonstrated the solution-processed single-walled carbon nanotube (SWNT) source–drain electrodes patterned using a plasma-enhanced detachment patterning method for high-performance organic transistors and inverters. The high-resolution SWNT electrode patterning began with the formation of highly uniform SWNT thin films on a hydrophobic silanized substrate. The SWNT source–drain patterns were then formed by modulating the interfacial energies of the prepatterned elastomeric mold and the SWNT thin film using oxygen plasma. The SWNT films were subsequently selectively delaminated using a rubber mold. The patterned SWNTs could be used as the source–drain electrodes for both n-type PTCDI-C8 and p-type pentacene field-effect transistors (FETs). The n- and p-type devices exhibited good and exactly matched electrical performances, with a field-effect mobility of around 0.15 cm² V^–1 s^–1 and an ON/OFF current ratio exceeding 10⁶. The single electrode material was used for both the n and p channels, permitting the successful fabrication of a high-performance complementary inverter by connecting a p-type pentacene FET to an n-type PTCDI-C8 FET. This patterning technique was simple, inexpensive, and easily scaled for the preparation of large-area electrode micropatterns for flexible microelectronic device fabrication

Ladder-Type Silsesquioxane Copolymer Gate Dielectrics for High-Performance Organic Transistors and Inverters

A ladder-type poly­(phenyl-<i>co</i>-methacryl silsesquioxane) (PPMSQ) copolymer was developed for use as a gate dielectric in high-performance organic field-effect transistors (OFETs). The ladder-type PPMSQ copolymer was synthesized via the hydrolysis of two types of monomers, methacryloxypropyltrimethoxysilane and phenyltrimethoxysilane, followed by a condensation polymerization. The phenyl groups in one monomer were introduced to enhance the structural ordering of the overlying organic semiconductors, whereas the methacryloxypropyl groups in the other monomer were introduced to cross-link the polymer chains via thermal- or photocuring. The curing process enhanced the electrical strength of the gate dielectric layer due to the formation of a network structure with a reduced free volume. Thermal curing reduced the surface energy of the gate dielectrics, which improved the structural order of the overlying organic semiconductors and promoted the formation of large grains. The ladder-type PPMSQ was used as a gate dielectric to produce benchmark p- and n-channel OFETs based on pentacene and <i>N</i>,<i>N</i>′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C₈), respectively. The resulting OFETs exhibited excellent electrical performances, including a high carrier mobility (0.53 cm² V^–1s^–1 for the p-type pentacene OFET and 0.17 cm² V^–1s^–1 for the n-type PTCDI-C₈ OFET) and a high ON/OFF current ratio exceeding 10⁴. The photocured patterned PPMSQ film was successfully used to fabricate complementary OFET-based inverters that yielded high gains. The use of the ladder-type PPMSQ gate dielectrics provides a novel approach to realizing next-generation organic electronics

High Crystalline Dithienosilole-Cored Small Molecule Semiconductor for Ambipolar Transistor and Nonvolatile Memory

We characterized the electrical properties of a field-effect transistor (FET) and a nonvolatile memory device based on a solution-processable low bandgap small molecule, Si1TDPP-EE-C6. The small molecule consisted of electron-rich thiophene-dithienosilole-thiophene (Si1T) units and electron-deficient diketopyrrolopyrrole (DPP) units. The as-spun Si1TDPP-EE-C6 FET device exhibited ambipolar transport properties with a hole mobility of 7.3 × 10^–5 cm²/(V s) and an electron mobility of 1.6 × 10^–5 cm²/(V s). Thermal annealing at 110 °C led to a significant increase in carrier mobility, with hole and electron mobilities of 3.7 × 10^–3 and 5.1 × 10^–4 cm²/(Vs), respectively. This improvement is strongly correlated with the increased film crystallinity and reduced π–π intermolecular stacking distance upon thermal annealing, revealed by grazing incidence X-ray diffraction (GIXD) and atomic force microscopy (AFM) measurements. In addition, nonvolatile memory devices based on Si1TDPP-EE-C6 were successfully fabricated by incorporating Au nanoparticles (AuNPs) as charge trapping sites at the interface between the silicon oxide (SiO₂) and cross-linked poly­(4-vinylphenol) (<i>c</i>PVP) dielectrics. The device exhibited reliable nonvolatile memory characteristics, including a wide memory window of 98 V, a high on/off-current ratio of 1 × 10³, and good electrical reliability. Overall, we demonstrate that donor–acceptor-type small molecules are a potentially important class of materials for ambipolar FETs and nonvolatile memory applications