Sang Il Shin

Organic thin film transistors using 6,13-bis(tri-isopropylsilylethynyl)pentacene embedded into polymer binders

The active channel material of an organic thin film transistor (OTFT), 6,13-bis(tri-isopropylsilylethynyl)pentacene (TIPS pentacene), is a functionalized pentacene designed to enhance both the solubility and solid-state packing of the pentacene. In this work, in order to improve device performance, three types of polymer binders—poly(α-methylstyrene) (PAMS), poly(4-vinylbiphenyl) (PVBP), and poly(triarylamine) (PTAA)—were employed to fabricate OTFT devices with organic soluble TIPS pentacene. These binders improved film formation in a large area uniformly and helped the TIPS pentacene to form a stronger binding between source/drain electrodes onto dielectric layer. Thus, device performance was highly improved due to improvement of interfacial contact and an increase in the charge transfer in the active channel. OTFTs using TIPS pentacene with PAMS, PVBP, and PTAA for field effect mobilities in the saturation regime have 5×10−3, 8×10−3, and 2.7×10−2 cm2/V s, respectively.

Solution-processed 6,13-bis(triisopropylsilylethynyl) (TIPS) pentacene thin-film transistors with a polymer dielectric on a flexible substrate

The authors report the fabrication of solution-processed 6,13-bis(triisopropylsilylethynyl) (TIPS) pentacene thin-film transistors with a cross-linked poly-4-vinylphenol (PVP) dielectric on a polyethersulphone (PES) substrate. The device exhibited useful electrical characteristics, including a saturation field effect mobility of 2.08 × 10−2 cm2 V−1 s−1, a current on/off ratio of 105, a threshold voltage of −2 V and an excellent subthreshold slope of 0.86 V/dec. It was demonstrated that the significant improvement in the subthreshold slope of TIPS-pentacene TFTs could be attributed to a decreased carrier trap density at the PVP/TIPS-pentacene film interface. Furthermore, a 1,2,3,4-tetrahydronaphthalene (Tetralin) solvent used in this study had a high boiling point, which had a positive effect on the morphology and the molecular ordering of the TIPS-pentacene film.

A 6,13-bis(Triisopropylsilylethynyl) Pentacene Thin-Film Transistor Using a Spun-On Inorganic Gate-Dielectric

We present the latest results of the use of soluble materials such as organic semiconductors (OSCs) or gate-dielectrics for simplified processing of organic thin-film transistors (OTFTs). In this paper, we described our fabrication of a solution-processed OTFT with 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) as the OSC and siloxane-based spin-on glass (SOG) as the inorganic gate-dielectric. Also, synthesized TIPS-pentacene and SOG were examined for use as the OSC and gate-dielectric in an OTFT. From electrical measurements, we obtained device performance characteristics such as charge carrier mobility, threshold voltage, current ON/OFF ratio, and subthreshold swing, which were 6.48 times 10-3 cm2/V ldr s, -13 V, ~100, and 1.83 V/dec, respectively.

A zinc-oxide thin-film transistor using a spun-on dielectric and gate electrode

This paper presents an organic–inorganic hybrid transparent thin-film transistor (TTFT) with an active channel of zinc-oxide (ZnO). The solution-processed stagger type device consists of methyl-siloxane-based spin-on glass (SOG) and poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT : PSS) for the dielectric and gate electrode, respectively. The TTFT, fabricated by this method, has an optical transmittance of 67.4%, and it displays a field effect mobility of 20.65 cm2 V−1 s−1, an on/off ratio of >104, a threshold voltage of 6.9 V and a subthreshold swing of 1.02 V/decade when the drain voltage (VDS) is 20 V.

Carbon nanotube and conducting polymer dual-layered films fabricated by microcontact printing

We report carbon nanotube/conducting polymer dual-layered film (CPDF) electrodes fabricated by microcontact printing for flexible transparent electrodes of organic thin film transistors (OTFTs). The CPDFs show ∼1000 Ω/sq surface resistivity and ∼93% transmittance at an extremely low loading of single-walled carbon nanotubes, and can be self-aligned with a precision of 20 μm. The CPDFs are applied as the source and drain electrodes in OTFTs without any supplementary alignment process, which leads to a mobility and a current on/off ratio of approximately 0.02 cm2 V−1 s−1 and ∼104, respectively.

A Flexible Amorphous Bi5Nb3O15 Film for the Gate Insulator of the Low-Voltage Operating Pentacene Thin-Film Transistor Fabricated at Room Temperature

The amorphous Bi(5)Nb(3)O(15) film grown at room temperature under an oxygen-plasma sputtering ambient (BNRT-O(2) film) has a hydrophobic surface with a surface energy of 35.6 mJ m(-2), which is close to that of the orthorhombic pentacene (38 mJ m(-2)), resulting in the formation of a good pentacene layer without the introduction of an additional polymer layer. This film was very flexible, maintaining a high capacitance of 145 nF cm(-2) during and after 10(5) bending cycles with a small curvature radius of 7.5 mm. This film was optically transparent. Furthermore, the flexible, pentacene-based, organic thin-film transistors (OTFTs) fabricated on the poly(ether sulfone) substrate at room temperature using a BNRT-O(2) film as a gate insulator exhibited a promising device performance with a high field effect mobility of 0.5 cm(2) V(-1) s(-1), an on/off current modulation of 10(5), and a small subthreshold slope of 0.2 V decade(-1) under a low operating voltage of -5 V. This device also maintained a high carrier mobility of 0.45 cm(2) V(-1 )s(-1) during the bending with a small curvature radius of 9 mm. Therefore, the BNRT-O(2) film is considered a promising material for the gate insulator of the flexible, pentacene-based OTFT.

Organization of Pentacene Molecules on Anisotropic Ultrathin HfO2 / Al2O3 Templates for Organic Thin-Film Transistors Using an Ion-Beam Treatment

This article investigates improving organic thin-film transistor (OFT) characteristics by using an alignable high dielectric constant film to control the self-organization of pentacene molecules. The process, based on the growth of a pentacene film with high vacuum sublimation, is a method of self-organization that uses ion-beam (IB) bombardment of the HfO 2 /Al 2 O 3 surface that serves as the gate dielectric layer. X-ray photoelectron spectroscopy indicates that the IB increases the structural anisotropy of the HfO 2 /Al 2 O 3 film, and X-ray diffraction patterns show that increasing the anisotropy may lead to the self-organization of pentacene molecules in the first polarized monolayer. An effective mobility of 2.3 × 10- 3 cm 2 V ―1 s ―1 was achieved, which is significantly different from the mobility in pentacene films that are not aligned. The proposed OTFT devices with an ultrathin HfO 2 structure as the gate dielectric layer were operated at a gate voltage lower than 5 V.

Hysteresis Effects by Source/Drain Interdigitated-Finger Geometry in 6,13-Bis(triisopropylsilylethynyl)pentacene Thin-Film Transistors

This work reports on the fabrication of organic thin-film transistors (OTFTs) with a solution-based 6,13-bis(triisopropylsilylethynyl)pentacene by a drop-casting method, and the determination of the electrical properties of OTFTs having different source/drain interdigitated-finger electrodes. The results show that the hysteresis in transfer characteristics of the OTFTs depends on the variation of contact fingers. These hystereses lead to changes in threshold voltage, which originates from charge trapping/detrapping at or near the organic semiconductor/dielectric interface. These related phenomena also influence the device parameters such as the field-effect mobility, the on/off current ratio, and the gate current.