The authors show that source and drain electrodes made of the title metallic organic charge-transfer salt (tetrathiafulvalene)(tetracyanoquinodimethane) [(TTF)(TCNQ)] result in drastic reduction of contact resistance in organic thin-film transistors (TFTs). The contact resistance is estimated by the variable gate-length transfer-line method. Pentacene TFTs with the organic electrodes show smaller contact resistance and larger overall mobility by more than one order than those of bottom-contact Au transistors. The performance is comparable to that of top-contact Au transistors, indicating that (TTF)(TCNQ) is an excellent electrode material for bottom-contact transistors.
Thin-film transistors of dibenzotetrathiafulvalene (DBTTF) are investigated by changing the source and drain (S/D) electrode materials. Not only the mobility but also the contact resistance, estimated from the transfer line method, changes depending on the metal work functions. Nonetheless, S/D electrodes made of a metallic organic charge-transfer salt, (tetrathiafulvalene) (tetracyanoquinodimethane) [(TTF)(TCNQ)] exhibits much smaller contact resistance, which is attributed to small potential shift on the organic/organic interface compared with the organic/metal interface. A thin film of (DBTTF)(TCNQ) works as an active layer of air-stable n-channel organic transistors when (TTF)(TCNQ) is used as the S/D electrodes.
N-channel organic field-effect transistors with stable performance at ambient conditions are fabricated on the basis of an electron-accepting molecule, dimethyldicyanoquinone diimine (DMDCNQI). The transistors are investigated by varying source and drain electrode materials: Au, Ag, Cu, and a highly conducting organic charge-transfer salt, (tetrathiafulvalene)(tetracyanoquinodimethane) [(TTF)(TCNQ)]. The devices with the Au electrode show lowest contact resistance and highest electron mobility (0.011 cm 2 V À1 s À1 for bottom-contact configuration), and the performance decreases in the order of Au > (TTF)(TCNQ) > Ag > Cu. This order does not seem related to the metal work functions, but is attributed to the organic-metal interfacial potentials. DMDCNQI forms highly conducting charge-transfer complexes with Ag and Cu, but the complex layer increases the interfacial potential as well as the electron-injection barrier and also increases the off-current for short channel devices. The air stability is not determined solely by the organic semiconductor but is considerably influenced by the electrode materials.
The crystal structures, thin-film properties, and field-effect transistor (FET) characteristics of tetrathiafulvalene (TTF) derivatives with two phenyl groups are systematically investigated. The highest mobility, 0.11 cm(2) V(-1) s(-1), is observed in biphenyl-substituted TTF (1). The correlation between the crystal structures and the FET properties demonstrates that good transistor properties are associated with two-dimensional intermolecular interaction, which is achieved when the molecules are standing nearly perpendicular to the substrate. Since these TTF derivatives are strong electron donors, the use of a metallic charge-transfer salt (TTF)(TCNQ) as the source and drain electrodes has resulted in a considerable reduction of the off current (TCNQ: tetracyanoquinodimethane).
A metallic organic charge-transfer salt, (tetrathiafulvalene)(tetracyanoquinodimethane) [(TTF)(TCNQ)], is used as a source and drain contact material in n-channel organic transistors based on hexadecafluorophthalocyaninato copper (F16CuPc), and low contact resistance and good performance comparable to the Au-contact devices are observed. Ambipolar transistors are fabricated on the basis of a heterostructure of F16CuPc and copper phthalocyanine (CuPc).
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