Stability Of Organic Field-effect Transistors Research Articles

The Importance of Grain Boundaries for the Time-Dependent Mobility Degradation in Organic Thin-Film Transistors

The relationships between organic semiconductor morphology and device stability of organic field-effect transistors (FETs) are very complex and not yet fully understood. Especially for obtaining high-performance, air-stable n-channel FETs, gaining a deep insight into possible degradation mechanisms can help improve their air stability. Here, we investigate the performance and stability of organic n-channel FETs based on solution-grown single-crystalline ribbons of the conjugated semiconductor bis(1H,1H-perfluorobutyl)-dicyano-perylene tetracarboxylic diimide (C3F7CH2−PTCDI-(CN)2). The FETs show an electron mobility of 0.25 cm2/(V s) in air and an on/off ratio up to 1 × 107. Their mobility does not significantly change when devices are stored in air for more than 5 weeks. This excellent air stability stands in contrast to FETs based on thin evaporated polycrystalline films of the same compound that degrade by more than an order of magnitude during the same 5 week period. We attribute this striking difference in air stability to the grain boundaries in the polycrystalline films and discuss different possible degradation mechanisms.

Influence of fine roughness of insulator surface on threshold voltage stability of organic field-effect transistors

We have investigated the influence of the surface roughness of an insulator on the threshold voltage shift caused by gate bias stressing in organic field-effect transistors (OFETs). Our investigation was conducted for OFETs with SiO2 insulators. We observed that the threshold voltage shift is extremely sensitive to changes in the fine roughness of the SiO2 surface; the shift increased with the roughness. The large shift in OFETs with rough SiO2 insulators can be attributed to lattice distortion in pentacene layers deposited on rough SiO2 surfaces.

Air Stability of p-Channel Organic Field-Effect Transistors Based on Oligo- p-phenylenevinylene Derivatives

We have investigated that the stability of organic field-effect transistors (OFETs) based on two oligo- p-phenylenevinylenes, 1,4-bis(4-methylstyryl)benzene (CH3-OPV) and 1,4-bis(4-dimethylaminostyryl)benzene [(CH3)2N-OPV], which is a new organic semiconductor for OFETs. The OFET fabricated using CH3-OPV with a highest occupied molecular orbital (HOMO) energy level of -5.55 eV shows good ambient stability even after storage in air for one year. On the other hand, the field-effect mobilities of organic semiconductors including (CH3)2N-OPV with the HOMO energy level ranging from -4.94 to -5.20 eV have decreased with time. The stability of CH3-OPV is suggested to be due to the relatively low HOMO energy level.

Threshold voltage stability of organic field-effect transistors for various chemical species in the insulator surface

The relationship between the threshold voltage (Vt) stability and the chemical species of the insulator surface was investigated by using organic field-effect transistors with different types of self-assembled monolayers on a SiO2 insulator. The Vt shift induced by gate bias stressing was considerably increased by the introduction of long-chain chemical species to the SiO2 surface. In order to obtain high-performance and high-stability organic transistors, insulator surfaces with short-chain chemical species that can improve transistor performance without degrading stability are required.

Air-Stable Operation of Organic Field-Effect Transistors on Plastic Films Using Organic/Metallic Hybrid Passivation Layers

We investigated the stability of organic field-effect transistors (FETs) under ambient conditions. By employing organic/metallic hybrid passivation layers, we improved the electric stability of organic FETs in air. Pentacene FETs were fabricated on plastic films and encapsulated in organic/metallic hybrid passivation layers. These FETs exhibited a high mobility of 0.6 cm2 V-1 s-1 and an on/off ratio greater than 106. When the devices were stored in air for two months, the change in mobility was less than 2%. When continuous source–drain and gate voltages of -40 V were applied to the FETs for 10 days in air, the change in saturation current was less than 5%. We performed bending and heating tests in air. The FETs retained their functionality after being bent with a bending radius of less than 1 mm, and exhibited no changes in the performance after being subjected to a number of heat cycles up to 160 °C. The organic/metallic hybrid passivation layer is also effective in reducing air degradation of n-type organic FETs.