Field-effect Mobility Of Organic Thin-film Transistors Research Articles

Poly(3-hexylthiophene)-Based Organic Thin-Film Transistors with Virgin Graphene Oxide as an Interfacial Layer.

We fabricated and characterized poly(3-hexylthiophene-2, 5-diyl) (P3HT)-based Organic thin-film transistors (OTFTs) containing an interfacial layer made from virgin Graphene Oxide (GO). Previously chemically modified GO and reduced GO (RGO) were used to modify OTFT interfaces. However, to our knowledge, there are no published reports where virgin GO was employed for this purpose. For the sake of comparison, OTFTs without modification were also manufactured. The structure of the devices was based on the Bottom Gate Bottom Contact (BGBC) OTFT. We show that the presence of the GO monolayer on the surface of the OTFT's SiO2 dielectric and Au electrode surface noticeably improves their performance. Namely, the drain current and the field-effect mobility of OTFTs are considerably increased by modifying the interfaces with the virgin GO deposition. It is suggested that the observed enhancement is connected to a decrease in the contact resistance of GO-covered Au electrodes and the particular structure of the P3HT layer on the dielectric surface. Namely, we found a specific morphology of the organic semiconductor P3HT layer, where larger interconnecting polymer grains are formed on the surface of the GO-modified SiO2. It is proposed that this specific morphology is formed due to the increased mobility of the P3HT segments near the solid boundary, which was confirmed via Differential Scanning Calorimetry measurements.

Pentacene organic thin-film transistors on flexible paper and glass substrates

Pentacene-based organic thin-film transistors (OTFTs) were fabricated on several types of flexible substrate: commercial photo paper, ultra-smooth specialty paper and ultra-thin (100 μM) flexible glass. The transistors were fabricated entirely through dry-step processing. The transconductance and field-effect mobility of OTFTs on photo paper reached values of ∼0.52 mS m−1 and ∼0.1 cm2 V −1 s−1, respectively. Preliminary results on the lifetime of OTFTs on photo paper yielded stable transconductance and mobility values over a period of more than 250 h. The comparable characteristics of OTFTs fabricated on widely available, low cost paper and high quality expensive liquid crystal display glass indicate the potential importance of cellulose-based electronic devices.

Electronic properties of dioctylterthiophene-based organic thin-film transistors: A Kelvin probe force microscopy study

It appeared in the past decades that semi-conducting organic liquid crystals could be used as the active layer in organic thin film transistors (OTFTs). They can be processed by simple methods such as inkjet printing, which paves the way to applications for cheap plastic electronics such as electronic tags, biosensors, and flexible screens. However, the measured field-effect mobility in these OTFTs is relatively low compared to inorganic devices. Generally, such low field-effect mobility values result from extrinsic effects such as grain boundaries or imperfect interfaces with source and drain electrodes. It has been shown that reducing the number of grain boundaries between the source and drain electrodes improves the field effect mobility. Therefore, it is important to understand the transport mechanisms by studying the local structure and electronic properties of organic thin films within the channel and at the interfaces with source and drain electrodes in order to improve the field-effect mobility in OTFTs. Kelvin probe force microscopy (KPFM) is an ideal tool for that purpose since it allows to simultaneously investigate the local structure and the electrical potential distribution in electronic devices. In this work, the structure and the electrical properties of OTFTs based on dioctylterthiophene (DOTT) were studied. The transistors were fabricated by spin-coating DOTT on the transistor structures with untreated and treated (silanized) channel silicon oxide. The potential profiles across the channel and at the metal-electrode interfaces were measured by KPFM. The effect of surface treatment on the electrical properties, charge trapping phenomenon and hysteresis effects is demonstrated and analyzed.

Oligothiophene-Based Organic Thin-Film Transistors: A Kelvin Probe Force Microscopy Study of the Electronic Properties

ABSTRACTIn the past decades organic thin film transistors (OTFTs) have been notably studied due to their interesting properties. Not only they can be processed by simple methods such as inkjet printing but also open the doors to new applications for cheap plastic electronics including electronic tags, biosensors, flexible screens,… However, the measured field-effect mobility in OTFTs is relatively low compared to inorganic devices. Generally, such low field-effect mobility values result from extrinsic effects such as grain boundaries or imperfect interfaces with source and drain electrodes. It has been shown that reducing the number of grain boundaries between the source and drain electrodes improves the field effect mobility.1-3 Therefore, it is important to understand the transport mechanisms by studying the structure of organic thin films and local electrical properties within the channel and at the interfaces with source and drain electrodes in order to improve the field-effect mobility in OTFTs. Kelvin probe force microscopy (KPFM) is an ideal tool for that purpose since it allows to simultaneously investigation of the local structure and the electrical potential distribution in electronic devices. In this work, the structure and the electrical properties of OTFTs based on dioctylterthiophene (DOTT) were studied. The transistors were fabricated by spin-coating of DOTT on the transistor structures with treated (silanized) and untreated channel oxide. The potential profiles across the channel and at the metal-electrode interfaces were measured by KPFM. The effect of surface treatment on hysteresis effects was also studied. Smaller crystals and a lower threshold voltage were observed for the silanized devices. Hysteresis effects appeared to be less important in modified devices compared to the untreated ones.

Characterization of Short Channel OTFTs Fabricated Using Ink Jet Print and Imprint Process

We fabricated short channel organic thin film transistors on polyethersulphone (PES) substrate using ink jet printing combined with an imprint method. The channel lengths of organic thin film transistors (OTFTs) which were defined by imprinting Ag/PES film were 2.5 um, 3.8 um and 6.4 um, respectively. 6,13-bis(triisopropylsilylethynyl) (TIPS) pentacene and Polyvinyl alcohol (PVA) were used as an active material and as a gate insulator, respectively. The physical properties were obtained using Alpha step, SPM, and SEM. The gate transfer characteristics and drain family curves were measured using Keithley-4200. The field-effect mobility of OTFT was about 0.25 cm2/Vs in the saturation region, and the threshold voltage of OTFT was -2.5 V.

Organic thin-film transistors of pentacene films fabricated from a supersonic molecular beam source

Top-contact organic thin-film transistors (OTFTs) of pentacene have been fabricated on bare SiO2 and SiO2 modified with hexamethyldisilazane (HMDS) and octadecyltrichlorosilane (OTS). The pentacene films were deposited from a supersonic molecular beam source with kinetic energy of incident molecules ranging from 1.5 to 6.7 eV. The field-effect mobility of OTFTs was found to increase systematically with increasing kinetic energy of the molecular beam. The improvements are more important on HMDS- and OTS-treated surfaces than on bare SiO2. Tapping mode atomic force microscopy images reveal that pentacene thin films deposited at high kinetic energy form with significantly larger grains—independent of surface treatment—than films deposited using low-energy beams.

Preparation and characterization of pentacene-based organic thin-film transistors with PVA passivation layers

High-mobility organic thin-film transistors (OTFT) were fabricated with pentacene active layers and passivated by polyvinyl acetate (PVA) in this study. The organic pentacene film showed a single phase structure with the interplanar spacing of 1.54 nm corresponding to the (001) diffraction. The initial field effect mobility of OTFT was 4.4 × 10 − 2 cm 2/Vs without the passivation. After the PVA passivation, the device exhibited an improved field-effect mobility of 1.0 × 10 − 1 cm 2/Vs. It was decreased to 8.0 × 10 − 2 cm 2/Vs after 35 days. The on/off current ratio has been at the order of 10 6. The device durability was also examined by 80° bending cycle tests in tension. The transistors exhibited lower on/off ratio and higher turn-on voltage after 2500 bending cycles. The lifetime of the passivated OTFT was improved to more than 2 months in air. It has been suggested that the PVA passivation layer could effectively protect the pentacene-based OTFT from moisture and oxygen permeation.

Correlation between Potential Barrier and FTIR Spectra in SiOC Film with the C-O Bond of sp3Structure

carbonRecently, the semiconducting c onjugated organic materials have been studied because of th eir many applications such as displays, smart cards or microelectroniscs. The field effect mobility of OTFTs (organic thin film transistors) depends on the chemical properties of the surface on gate insulator.

Influence of gate dielectrics on charge transport in copper phthalocyanine thin-film transistors

Copper phthalocyanine organic thin-film transistors (OTFTs) were fabricated with top-gate geometry and the effects of different gate dielectrics on the transport properties in OTFTs were studied. The mobility was found to be gate voltage dependent and the results showed that besides the charge density in the accumulation layer, the energetic disorder induced by gate dielectrics played an important role in determining the field-effect mobility in OTFTs.

The Improvement of Electrical Characteristic of Solution Processed Triisopropylsilyl Pentacene Organic Thin-Film Transistors Employing Hexamethyldisilazane Treatment

The field-effect mobility of triisopropylsilyl (TIPS) pentacene organic thin-film transistors (OTFTs) is increased considerably by employing hexamethyldisilazane (HMDS) treatment on poly-4-vinylphenol (PVP) gate insulator. A simple spin coating of HMDS on PVP gate insulator of OTFTs suppressed the void formation significantly and improved structural morphology of pentacene film. The field-effect mobility of OTFT where the TIPS pentacene was spin coated was increased from 0.01 cm2V-1s-1 to 0.1 cm2V-1s-1 after HMDS treatment. The threshold voltage was decreased from -2.8V to -2.0V. We have also fabricated ink-jet printed OTFTs and investigated the effect of HMDS treatment on ink-jet printed OTFTs. The field- effect mobility of OTFT was not increased significantly by HMDS treatment while the threshold voltage of the device was reduced considerably. The threshold voltage of untreated OTFT was +11.1V while that of HMDS treated OTFT was -3.0V. Our experiment results suggest that the HMDS treatment improved the characteristics of OTFTs.

An organic thin-film transistor of high mobility by dielectric surface modification with organic molecule

Organic thin-film transistors (OTFTs) based on pentacene semiconductor are elaborated on the plastic substrates through a four-level mask process without photolithographic patterning to yield a simple fabrication process. Octadecyltrimethoxysilane (OTMS) as an organic molecule for self-assembled monolayers is deposited on the surface of zirconium oxide dielectric layer. The effect of OTMS interlayer with gate dielectric surface modification on the field effect mobility of OTFTs has been examined and these prototype organic transistors showed excellent electrical characteristics with field effect mobility >0.66cm2∕Vs and Ion∕Ioff>10.5

Oligophenyl-based organic thin film transistors

Organic thin film transistors (TFTs) have been fabricated using thermally evaporated films of the oligophenyls p-quaterphenyl (p-4P), p-quinquephenyl (p-5P), and p-sexiphenyl (p-6P). The field-effect mobility of these TFTs ranges from 10−2 cm2/V s for p-4P to 10−1 cm2/V s for p-6P with on/off current ratio from 105 to 106. These values are comparable to those achieved using the more widely studied organic semiconductors alpha-sexithienyl (α-6T) and pentacene. X-ray diffraction reveals a high degree of molecular ordering, believed to be important for obtaining high field-effect mobility in organic TFTs.