Single-crystal Transistors Research Articles

Self-Assemble Monolayer Dependent Field Effect Transistor’s Performance Based On Tetracene Single-Crystal

Organic field effect transistors with an active layer based on the tetracene single-crystal were fabricated. It was found that organosilane self-assemble monolayer (SAM) modified device with tetracene single-crystals gave higher mobility and on/off ratio rather than untreated device. SAM modified tetracene single-crystal transistors with parylene gate insulator showed the highest mobility of 0.66 cm2 V-1 s-1 and high on/off ratio of ~104. This finding demonstrates that SAM treatment decrease the charge leakage between source and drain which help to decrease the off current with greater extent and increase the on current slightly of the tetracene single-crystal field-effect transistors. Journal of Bangladesh Chemical Society, Vol. 25(2), 194-199, 2012 DOI: http://dx.doi.org/10.3329/jbcs.v25i2.15086

High‐Performance Air‐Stable Single‐Crystal Organic Nanowires Based on a New Indolocarbazole Derivative for Field‐Effect Transistors

A new indolocabazole derivative possessing an extended aromatic core and solubilizing long aliphatic chains effectively self-assembles and crystallizes within the nanoscale channels to form single-crystal nanowires via a direct printing method from an ink solution. Single-crystal organic nanowire transistor arrays based on the π-extended indolocarbazole derivative exhibit an excellent hole mobility of 1.5 cm² V⁻¹ s⁻¹ and outstanding environmental stability.

High-speed organic single-crystal transistors gated with short-channel air gaps: Efficient hole and electron injection in organic semiconductor crystals

Short-channel, high-mobility organic filed-effect transistors (OFETs) are developed based on single crystals gated with short-channel air gaps. The high hole mobility of 10cm2/Vs for rubrene, and high electron mobility of 4cm2/Vs for PDIF-CN2 crystals are demonstrated even with a short channel length of 6μm. Such performance is due to low contact resistance in these devices estimated to be as low as ∼0.5kΩ cm at gate voltage of −4V for rubrene. With the benefit of the short channel length of 4.5μm in a new device architecture with less parasitic capacitance, the cutoff frequency of the rubrene air–gap device was estimated to be as high as 25MHz for drain voltage of −15V, which is the fastest reported for p-type OFETs, operating in ambient conditions.

From organic single crystals to solution processed thin-films: Charge transport and trapping with varying degree of order

We have fabricated single crystal, thermally evaporated, and spin-coated thin-film transistors (TFTs) from the same organic semiconductor N,N′-1H,1H-perfluorobutyl dicyanoperylene carboxydiimide (PDIF-CN2) using various combinations of deposition methods and gate dielectrics to investigate how the charge transport properties vary with the degree of crystalline order. Never before has a semiconductor been studied in such a wide variety of processing methods, allowing cross-comparison of the microscopic factors influencing the charge transport, and in particular the trap density of states (DOS). Excellent transistor performance was achieved for PDIF-CN2 single crystals in combination with Cytop as a dielectric layer resulting in a mobility of up to 6 cm2/Vs, an on/off-ratio exceeding 108, and a subthreshold swing of 0.45 V/dec. Furthermore, gate-bias-stress effects are not present in these transistors and we observed low stress effects in the evaporated TFTs with Cytop as the gate dielectric. These findings are reflected in the trap DOS. The single crystal field-effect transistor with Cytop has a low trap DOS, whereas in evaporated TFTs, the trap DOS is higher by 2–3 orders of magnitude. Surprisingly, the trap DOS of the spin-coated TFT is similar to that in evaporated TFTs, except for additional discrete trap states centered around 0.24 eV below the conduction band.

Solvent-Dispersed Benzothiadiazole-Tetrathiafulvalene Single-Crystal Nanowires and Their Application in Field-Effect Transistors

A new organic semiconductor (BT-TTF) based on molecular moieties of benzothiadiazole and tetrathiafulvalene was designed and synthesized, and its structure, molecular packing and charge-transporting properties were determined. Thermal properties, electrochemical behaviors, and optical absorption of this molecule were studied by using differential scanning calorimetry/thermal gravimetric analysis, cyclic voltammetry, and ultraviolet-visible spectroscopy, respectively. Its bulk and nanowire single crystals were prepared and characterized by X-ray crystallography, scanning electron microscopy, transmission electron microscopy, and field-effect transistors. It is found that short intermolecular S···S (3.41 Å), S···C (3.49 Å), and S···N (3.05 Å) contacts define the solid-state structure of BT-TTF single crystals which π-stack along the [100] with interplanar distances of 3.49 Å. Solvent-cast single-crystal nanowire transistors showed mobilities as large as 0.36 cm2/(V s) with current on/off ratios of 1×10(6). This study further illustrates the impact of molecular design and a demonstration of high-performance single-crystal nanowire transistors from the resulting semiconductor.

Organic single crystals: Addressing the fundamentals of organic electronics

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Electrolyte gated single-crystal organic transistors to examine transport in the high carrier density regime

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Substitution effects on the electrical tranporting properties of tetrathia[22]annulene[2,1,2,1]: experimental and theoretical investigations

Tetrathia[22]annulene[2,1,2,1] and its derivatives are p-type organic semiconductors possessing relatively high mobilities in thin film field-effect transistors. To get a full understanding of the relationship between the molecular structures and transporting properties of these macrocyclic molecules, the single crystal structures of three meso-substituted tetrathia[22]annulene[2,1,2,1]s were determined by X-ray diffraction, and the electrical properties were investigated by single crystal transistor characterization and quantum simulations. The observed relationship between the mobilities of different crystals was strongly corroborated by calculations of both the molecular reorganization energies and the maximum intermolecular transfer integrals.

Strategies for Fabricating Nanogap Single-Crystal Organic Transistors

Nanotechnology is an emerging technology for fabricating nanostructures where at least one dimension is smaller than 100 nm. This paper explains how single-crystal organic transistors of channel length down to just 7 nm can be fabricated without damaging the organic material. Single crystals of C60, rubrene, and pentacene have been chosen in our structures, but the same process can be used for a wide variety of organics. The method combines high-resolution electron-beam lithography and vacuum device assembly with piezo manipulators. As modern devices are typically designed with short semiconducting channel length, this type of fabrication methods allows downscaling of organic electronic devices for research purposes.

High-speed solution-processed organic single crystal transistors using a novel triisopropylsilylethynyl anthracene derivative

A high-quality organic single crystal transistor (OSCT) was fabricated via solution-processing using a novel anthracene derivative (TIPsAntNE). The OSCT fabricated on a surface-modified high-capacitance ZrOx substrate provided a transistor that operated at low voltages with a high mobility up to 4.1 cm2/Vs and negligible hysteresis (a Vth shift of <20 mV). Importantly, the TIPsAntNE OSCT functioned under a high-frequency AC signal with a gate bias as high as 30 kHz. These are crucial operational requirements for commercial applications of organic transistors. The photoresponsivity (>1 A/W) of the TIPsAntNE single crystal was high over a wide range across the visible spectrum.

Surface Selectively Deposited Organic Single-crystal Transistor Arrays with High Device Performance

A method for patterning organic single-crystal transistor arrays via surface selective deposition is presented. Solvent-vapor annealing is applied for the formation of organic crystals under ambient conditions. The devices are fabricated with a dual-gate structure, which allows the investigation of device performances of bottom-gate/top-contact (BG/TC) and top-gate/top-contact (TG/TC) structures based on the same crystals. The resulting BG/TC devices exhibit the field-effect mobility (μFET) up to 3.5 cm2/Vs. And μ FET is influenced by the contact resistance, resulting in large variation in device performance. On the other hand, TG/TC structure exhibits better performance with smaller variation. The highest μ FET is 7.4 cm2/Vs.

Current‐Confinement Structure and Extremely High Current Density in Organic Light‐Emitting Transistors

Extremely high current densities are realized in single-crystal ambipolar light-emitting transistors using an electron-injection buffer layer and a current-confinement structure via laser etching. Moreover, a linear increase in the luminance was observed at current densities of up to 1 kA cm(-2) , which is an efficiency-preservation improvement of three orders of magnitude over conventional organic light-emitting diodes (OLEDs) at high current densities.

Organic single crystal transistor characteristics of single-crystal phase pentacene grown by ionic liquid-assisted vacuum deposition

Organic transistor characteristics of single-crystal phase pentacene were investigated. Ionic liquids (ILs) were used as not only a gate dielectric material in the transistors but also a crystallization solvent in vacuum deposition of pentacene. The crystal sizes reached 200 μm and their surface exhibits a molecularly step-and-terrace structure. There was no sign of IL molecules inside the crystal, and the impurity level of 6,13-pentacenequinone was also reduced. The average value of the field-effect mobility was not so inferior to those for the conventional pentacene single crystals, and the highest value exceeded 5 cm2/Vs, with the on/off current ratio of 104.

On the fabrication of crystalline C60 nanorod transistors from solution

Flexible and high-aspect-ratio C60 nanorods are synthesized using a liquid–liquid interfacial precipitation process. As-grown nanorods are shown to exhibit a hexagonal close-packed single-crystal structure, with m-dichlorobenzene solvent molecules incorporated into the crystalline structure in a C60:m-dichlorobenzene ratio of 3:2. An annealing step at 200 °C transforms the nanorods into a solvent-free face-centred-cubic polycrystalline structure. The nanorods are deposited onto field-effect transistor structures using two solvent-based techniques: drop-casting and dip-coating. We find that dip-coating deposition results in a preferred alignment of non-bundled nanorods and a satisfying transistor performance. The latter is quantified by the attainment of an electron mobility of 0.08 cm 2 V −1 s −1 and an on/off ratio of > 104 for a single-crystal nanorod transistor, fabricated with a solution-based and low-temperature process that is compatible with flexible substrates.

Band-like transport in solution-crystallized organic transistors

Patternable solution-crystallized organic transistors are developed with high carrier mobility that exceeds 10 cm2/V. We have investigated techniques of crystallization during the fabrication of organic semiconductor thin films from solution. Regulating direction of the crystal growth in the process, we successfully formed crystalline films with the mobility as high as 10–12 cm2/V from newly developed air-stable organic semiconductor compounds of 2,7-dialkyl[1]benzothieno[3,2-b]benzothiophene (Cn-BTBT) and 2,9-dialkyl-dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (Cn-DNTT). Furthermore, comprehensive measurements of Hall-effect and temperature dependent mobility for solution-crystallized single-crystal transistors tell us that their fundamental charge-transport mechanism is band transport.

High Mobility, Air Stable, Organic Single Crystal Transistors of an n‐Type Diperylene Bisimide

Recently, some impressive progress has been made by functionalization of (hetero-)acenes, thiophenes, and arylenes with electron-defi cient constituents. [ 3–5 ] However, the development of air-stable, high mobility, n-type organic semiconductors for organic electronics is still highly emergent. The mobility of organic semiconductors depends on the effi ciency of charge transport from one molecule to another. Hence, some organic semiconductors with dense molecule packing always give high mobility. [ 6 ] As to the stability of organic compounds, it is believed that the highest occupied molecular orbital (HOMO) of p-type organic semiconductors should be more negative than –5.0 eV, e.g., locating at –5.0 to –6.0 eV, and the lowest unoccupied molecular orbitals (LUMO) of n-type organic semiconductors are best located between –4.0 and –4.5 eV, for anti-oxidation in air. [ 2 , 7 ] We have acknowledged these requirements and believe that perylene bisimides (PBIs) will fi t as candidates because of their reasonable electron acceptor ability, [ 8 ] and have been focusing on the expansion of the chemistry of perylene bisimides (PBIs) by a combination of Ullmann coupling and C–H transformation for some time, and have developed a facile strategy to synthesize fully conjugated, triply linked, diperylene bisimides, [ 8 ] conferring the expanded

Novel triethylsilylethynyl anthracene-based organic semiconductors for high performance field effect transistors

A series of triethylsilylethynyl anthracene (TESAN) derivatives, end-capped with bithiophene and thienothiophene, were synthesized by Suzuki coupling. The thermal, optical, electrochemical, and crystalline properties of the TESAN derivatives were reported and correlated with charge transport behavior measured via both a thin film transistor and a single crystal transistor. The TESAN derivative substituted with bithiophene exhibited more efficient π electron delocalization over the molecule compared to the derivative substituted with fused thienothiophene, and consequently gave the highest FET mobility, 1.28 cm2 V−1 s−1, from single crystal transistors with negligible hysteresis and almost zero turn-on voltage. The discrepancy of charge carrier mobility between the thin film transistor and single crystal transistor and the solvent annealing effects are discussed in conjunction with morphological and structural analyses.

Short-channel and high-mobility p- and n-type organic single-crystal transistors with air-gap structures

ABSTRACTIn an effort to realize high-speed organic logic components, p- and n-type single-crystal organic field-effect transistors (SC-OFETs) were fabricated using air-gap structures with channel lengths as short as several μm. High carrier mobility of about 10 cm2/Vs is demonstrated in rubrene SC-OFETs even with the short channel length of 6 μm, using Si-based microstructures. The contact resistance is estimated to be 450 Ohm cm, which is only 5% of the total channel resistance between source and drain electrodes. Performances of n-type air-gap devices based on PDIF-CN2 are also demonstrated exhibiting electron transport with the carrier mobility of about 2 cm2/Vs. Furthermore, micron-scale air-gap structures are fabricated using insulating materials on glass substrates to reduce parasitic gate capacitance. The cut-off frequency of this rubrene air-gap device is measured to be as high as 8 MHz with applied drain voltage VD of 15 V. These techniques are promising to be applicable to next-generation organic high-speed logic circuits.

An asymmetric oligomer based on thienoacene for solution processed crystal organic thin-film transistors

A novel thienoacene-based conjugated oligomer, i.e.BTTT-T-C12, was designed and synthesized. Its highly asymmetric structural feature enables the preparation of two-dimensional single-crystalline thin films in millimetre size and ~100 nm thick by a solution processing method directly on the Si/SiO(2) substrate. Single crystal organic thin film transistors exhibit a mobility of 0.70 cm(2) V(-1) s(-1) and an on/off ratio of 5.7 × 10(4).

High performance n-type single crystalline transistors of naphthalene bis(dicarboximide) and their anisotropic transport in crystals

High-performance n-type organic single crystal transistors of a naphthalene diimide are demonstrated. The accomplished transistors exhibit electron mobility as high as 0.7 cm(2) V(-1) s(-1). The anisotropic charge transport in the elongated hexagonal crystals of the naphthalene diimide is also explored. The transport anisotropy along different directions is at least 1.6 (mobility ratio).