High-mobility Organic Thin-film Transistors Research Articles

Achieving low-voltage operating high-mobility organic thin-film transistors by a multi-layered gate dielectric

Organic thin-film transistors (OTFTs) have attracted great attention for their inherent advantages and promising applications in emerging fields. Simultaneously realizing low-voltage operation and high-mobility in one OTFT is one of prerequisites for the commercialization, which is a huge challenge so far. An important route to address this challenge is to develop an ideal gate dielectric with a high capacitance and a low interfacial trap density at the dielectric/channel. In this Letter, we demonstrate the low-voltage operating high-mobility OTFTs by elaborately designing and processing a multi-layered gate dielectric. The gate dielectric consists of a high permittivity polymer film, a polymer buffing layer with a high surface energy, and an ultrathin long-chain alkane buffer layer. The effects of both the structures and the processes of gate dielectrics on the performances of OTFTs are investigated in detail. In addition, the relevant physical mechanisms are discussed. Finally, the optimal OTFTs exhibit high mobilities with the average and maximum values up to 5.62 and 6.74 cm2/V s, respectively, at low operating voltages below −5 V. Our findings reveal that designing and processing a reasonable multi-layered gate dielectric is a promising strategy to achieve both high-mobility and low-voltage operation in OTFTs, thereby fostering their development.

Highly stable, low-voltage operable high-mobility flexible organic thin-film transistors based on a tri-layer gate dielectric

The application fields of organic thin-film transistors (OTFTs) depend on their field-effect mobility (μ). The low-voltage operation and good operating stability are the prerequisites for the practical applications of OTFTs. To date, it is still a huge challenge to obtain low-voltage operable OTFTs with high μ and good operating stability at the same time. In this work, we elaborately design and process a tri-layer gate dielectric, for pursuing the low-voltage operable, high-performance flexible OTFTs. The effects of the gate dielectrics on the device performances and the relevant mechanisms are discussed in detail. The tri-layer gate dielectric has a large gate capacitance per unit area, and simultaneously suppresses the polarization effect of the gate dielectric and the charge trapping at the interface and bulk of the gate dielectric, by which both the μ and the operating stability are significantly improved. As a result, the flexible OTFTs exhibit excellent figures of merit at low operating voltages below 4 V, with high μ up to 2.6 cm2 Vs−1, good bias stress stability with a negligible change of the channel current for 5000 s, and good mechanical flexibility with a negligible performance degradation after the tension bending for 1000 times at small curvature radii of both 5.0 mm and 3.0 mm in sequence. Our works provide a strategy for developing the high-performance flexible OTFTs with low-voltage operation, high μ and good operating stability simultaneously.

Diketopyrrolopyrrole-based conjugated polymers synthesized by direct arylation polycondensation for anisole-processed high mobility organic thin-film transistors

DPP-based conjugated polymers were synthesized via environmentally benign direct arylation polycondensation. With these polymers, OTFTs with μe values of up to 2.79 cm2 V−1 s−1 were fabricated using a green solvent anisole.

High-mobility pentacene organic thin-film transistors achieved by reducing remote phonon scattering and surface-roughness scattering

Pentacene organic thin-film transistors (OTFTs) with very high carrier mobility have been achieved on both rigid and flexible substrates by using high-k gate dielectric and metal gate. The high-k gate dielectric with suitable thickness can reduce the surface-roughness scattering, while the metal gate can suppress the remote phonon scattering. As a result, based on NbLaO gate dielectric, OTFTs with high carrier mobility of 10.6 cm2 V−1 s−1 (7.99 cm2 V−1 s−1) with the capacitance per unit area measured at frequency of 1 kHz and small threshold voltage of −0.92 V (−0.74 V) fabricated on Pd-coated Si substrate (Pd-coated vacuum tape) are realized, though they have rougher dielectric surface and smaller pentacene grains than their counterparts fabricated on n-Si substrate. Moreover, with the addition of 13-nm SiO2 interlayer between the NbLaO gate dielectric and metal gate electrode, the carrier mobility decreases by 71% and 65% for the OTFTs on Si and V.T. substrates, respectively, highlighting the importance of the RPS.

Highly-ordered Triptycene Modifier Layer Based on Blade Coating for Ultraflexible Organic Transistors

We present a highly ordered surface modification layer for polymers based on ambient solution-processed triptycene (Trip) derivatives for high-mobility organic thin-film transistors (OTFTs). The nested packing of Trip molecules results in the formation of 2D hexagonal arrays, which stack one-dimensionally on the surface of polymer dielectrics without anchoring groups. The Trip surface was previously shown to be preferable for the growth of organic semiconductors (OSCs), and hence for enhancing the mobility of OTFTs. However, although the Trip modifier layer has been realized by thermal evaporation in a high-vacuum environment (TVE), it still has grain-boundary disorders that hinder the optimal growth of OSCs. To fabricate OTFTs with higher mobility, a disorder-free Trip layer is needed. We developed highly ordered Trip layers on polymer dielectrics via blade coating. In addition, we clarified that the highly ordered Trip modifier layer enhances the mobility of the OTFTs by more than 40%, relative to the disordered Trip layer prepared by TVE. Finally, we realized a ring oscillator composed of OTFTs with a highly ordered Trip layer.

Five-ring-fused asymmetric thienoacenes for high mobility organic thin-film transistors: the influence of the position of the S atom in the terminal thiophene ring

Two isomeric asymmetric thienoacenes are designed and synthesized; the syn-isomer demonstrates both μsat and μlin above 10 cm2 V−1 s−1.

Effects of tunneling-based access resistance in layered single-crystalline organic transistors

Abstract

Copolymer dielectrics with balanced chain-packing density and surface polarity for high-performance flexible organic electronics

The ever-increasing demand for flexible electronics calls for the development of low-voltage and high-mobility organic thin-film transistors (OTFTs) that can be integrated into emerging display and labeling technologies. Polymer dielectrics with comprehensive and balanced dielectric properties (i.e., a good balance between their insulating characteristics and compatibility with organic semiconductors) are considered particularly important for this end. Here, we introduce a simple but highly efficient strategy to realize this target by using a new type of copolymer as dielectrics. Benefiting from both high chain packing density guaranteeing dielectric properties and surface polarity optimizing molecular packing of organic semiconductors, this rationally designed copolymer dielectric endows flexible OTFTs with high mobility (5.6 cm2 V−1 s−1), low operating voltage (3 V) and outstanding stability. Further, their applicability in integrated circuits is verified. The excellent device performance shows exciting prospects of this molecular-scale engineered copolymer for the realization of plastic high-performance integrated electronics.

Megahertz-class printed high mobility organic thin-film transistors and inverters on plastic using attoliter-scale high-speed gravure-printed sub-5 μm gate electrodes

High performance organic thin-film transistors and inverters operating at MHz frequencies at 10V are fabricated on plastic with high throughput (printing speed up to 1.0m/s) using attoliter-scale high-speed gravure printing. The high performance of the devices is achieved using highly scaled gravure printed features (smaller than 5μm) and optimizing a high mobility organic semiconductor for the short-channel gravure printed devices (>0.5cm2/Vs) to realize record performance levels.

Low-temperature carrier dynamics in high-mobility organic transistors of alkylated dinaphtho-thienothiophene as investigated by electron spin resonance

Charge carriers in high-mobility organic thin-film transistors of alkylated dinaphtho-thienothiophene (C10-DNTT) have been directly observed by field-induced electron spin resonance (FI-ESR) down to 4 K. FI-ESR spectra of π-electron hole carriers of C10-DNTT exhibited clear anisotropy, indicating a highly organized end-on molecular orientation at the device interface. The intra-grain and inter-grain carrier motion were probed by the motional narrowing effect of the ESR spectra. The intra-grain motion was clearly observed even at 4 K, showing intrinsically high mobility of C10-DNTT crystallites. On the other hand, significantly low activation energy of ∼10 meV for inter-grain carrier hopping, compared with pristine DNTT, was observed, which shows that the alkyl substitution drastically enhances the carrier mobility of DNTT system.

High mobility organic thin-film transistors based on p-p heterojunction buffer layer

The p-p heterojunction of 5, 6, 11, 12-tetraphenylnaphthacene/vanadyl phthalocyanine, which has been used as the buffer layer, is demonstrated. The highest field-effect mobility is 5.1 cm2/Vs, which is one of the highest reported for polycrystalline rubrene thin film transistors. Current versus voltage characteristics of heterojunction diodes are utilized to investigate the charge injection mechanism, revealing the factors that bring about the improvement of carrier injection and the reduction of contact resistance. These results suggest that our approach is very promising to fabricate high performance organic thin-film transistors for practical applications in organic electronics.

High-mobility organic thin-film transistors based on a small-molecule semiconductor deposited in vacuum and by solution shearing

The small-molecule organic semiconductor 2,9-di-decyl-dinaphtho-[2,3-b:2′,3′-f]-thieno-[3,2-b]-thiophene (C10-DNTT) was used to fabricate bottom-gate, top-contact thin-film transistors (TFTs) in which the semiconductor layer was prepared either by vacuum deposition or by solution shearing. The maximum effective charge-carrier mobility of TFTs with vacuum-deposited C10-DNTT is 8.5cm2/Vs for a nominal semiconductor thickness of 10nm and a substrate temperature during the semiconductor deposition of 80°C. Scanning electron microscopy analysis reveals the growth of small, isolated islands that begin to coalesce into a flat conducting layer when the nominal thickness exceeds 4nm. The morphology of the vacuum-deposited semiconductor layers is dominated by tall lamellae that are formed during the deposition, except at very high substrate temperatures. Atomic force microscopy and X-ray diffraction measurements indicate that the C10-DNTT molecules stand approximately upright with respect to the substrate surface, both in the flat conducting layer near the surface and within the lamellae. Using the transmission line method on TFTs with channel lengths ranging from 10 to 100μm, a relatively small contact resistance of 0.33kΩcm was determined. TFTs with the C10-DNTT layer prepared by solution shearing exhibit a pronounced anisotropy of the electrical performance: TFTs with the channel oriented parallel to the shearing direction have an average carrier mobility of (2.8±0.3)cm2/Vs, while TFTs with the channel oriented perpendicular to the shearing direction have a somewhat smaller average mobility of (1.3±0.1)cm2/Vs.

High‐Hole‐Mobility Field‐Effect Transistors Based on Co‐Benzobisthiadiazole‐Quaterthiophene

High-mobility organic thin film transistors based on a benzobisthiadiazole-containing polymer are presented together with their morphological and optical properties. A very tight packing pattern of "edge-on" orientated polymer chains is observed in their thin films after annealing, and the hole mobility of this polymer is up to 2.5 cm(2) V(-1) s(-1) .

High mobility organic thin-film transistors on plastic substrate

We have fabricated organic thin-film transistors (OTFTs) based on di-n-decyldinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (C10-DNTT) on a polyimide gate dielectric coated on a polycarbonate substrate with a bottom-gate, top-contact configuration. Mobilities of the C10-DNTT-based TFTs were as high as 2.4 cm2 V−1 s−1, which are much better than those of the parent dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT)-based TFTs (mobility ∼ 0.5 cm2/V) fabricated on the same substrate. Compared to the C10-DNTT-TFTs on the conventional Si/SiO2 substrate, the present mobility of C10-DNTT-TFTs are somewhat reduced, which can be attributed to reduced crystallinity on the polyimide gate dielectric, although the crystalline phase on the polyimide is the same as on the Si/SiO2 substrate.

Air-stable and high-mobility organic thin-film transistors of poly(2,5-bis(2-thienyl)-3,6-dihexadecyltheino[3,2-b]thiophene) on low-surface-energy self-assembled monolayers

Air-stable and high-mobility polymer-based organic thin-film transistors are developed by employing low-surface-energy self-assembled monolayers and prolonged post-annealing. Carrier mobility in spin-coated thin films of a high-ionic-potential polymer semiconductor poly(2,5-bis(2-thienyl)-3,6-dihexadecyltheino[3,2-b]thiophene) reaches (0.08–0.17 cm 2/V s with decyltriethoxysilane monolayers and 0.4–0.8 cm 2/V s with (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane monolayers. The values become higher with longer annealing above the glass-transition temperature. The mobility, threshold voltage and on–off ratio are stable in humid air during the whole period of the experiment for more than 2 weeks. The high-performance and the air-stability demonstrated in the polymer thin-film transistors have enhanced their applicability in large-area, low-cost and flexible electronic devices.

Fabrication of high-mobility poly(3-hexylthiophene) transistors at ambient conditions

We report on the fabrication of high-mobility organic thin-film transistors (OTFTs) made and tested under ambient conditions. A bottom gate, bottom contact architecture was used with a layer of poly(3-hexylthiophene) deposited on a 50 nm thick Al 2O 3 dielectric with pre-patterned Au source and drain electrodes. Fluoroalkyl trichlorosilane treatment of the Al 2O 3 dielectric was found to significantly improve device performance. The field-effect hole mobility reproducibly reached 0.2 cm 2 V −1 s −1 (best device 0.29 cm 2 V −1 s −1) with an on/off ratio of 10 4. Electrical and synchrotron X-ray scattering characterization shows that an interaction at the FOTS/P3HT interface is responsible for the high performance of these devices. The fabrication method described here is carried out under ambient conditions and does not require any post-deposition annealing or vacuum drying steps for the organic film; therefore it can simplify the manufacturing of OTFTs.

Free-electron-like Hall effect in high-mobility organic thin-film transistors

Free-electron-like Hall effect in high-mobility organic thin-film transistors

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.

Polymer gate dielectrics with self-assembled monolayers for high-mobility organic thin-film transistors based on copper phthalocyanine

Organic thin-film transistors based on polycrystalline copper phthalocyanine (CuPc) were fabricated by using poly(vinyl alcohol) as gate dielectric. After treatment of the gate dielectric using an octadecyltrichlorosilane self-assembled monolayer, a mobility of up to 0.11 cm2/V s was achieved, which is comparable to that of single-crystal CuPc devices (0.1–1 cm2/V s). The surface morphology was analyzed and the possible reasons for the enhanced mobility are discussed.

High-mobility spin-cast organic thin film transistors

We report high-mobility organic thin film transistors (OTFTs) with good uniformity using the small molecule organic semiconductor 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TESADT). diF-TESADT was spin cast to form OTFTs with a carrier mobility of more than 1.5cm2∕Vs and shows a useful differential microstructure on or near pentaflorobenzenethiol (PFBT) treated Au source/drain electrodes compared to untreated Au or gate dielectric areas with improved molecular order observed on PFBT treated Au electrodes. For short channel length devices diF-TESADT crystal grains extend between the source and drain electrodes, resulting in increasing OTFT field effect mobility for decreasing gate length.