Low-voltage organic field-effect transistors (OFETs) with solution-processed metal-oxide as gate dielectric

Synthesis and investigation of the electrical properties of novel liquid-crystal phthalocyanines bearing triple branched alkylthia chains

The synthesis and electrical characterization of liquid crystalline and conducting properties of novel peripheral- and non-peripheral-tetra 2-(tri(hexylthio))ethoxy- and 2-(tri(octylthio))ethoxy-substituted copper(ii) phthalocyanines have been reported.

Highly Fluorinated Barium Titanate Nanoparticle Dispersion for Fabrication of Lithographically Patterned Thin Films

We report the synthesis, characterization, and photopatterning of high-k inorganic nanoparticles that are covered with highly fluorinated carboxylic acid and, as a result, are solution-processable in fluorous liquids. Barium titanate (BTO) nanoparticles, 7–8 nm in diameter, were prepared under solvothermal conditions and were surface-modified with perfluoroalkyl ether-type carboxylic acid molecules via ligand-exchange reactions. Thin films with a high dielectric constant (9.27 at 1 kHz) were achieved by spin-coating homogeneous solutions of BTO nanoparticles in a fluorous solvent (HFE-7500). Additionally, electron-beam lithography and photolithography were applied to the thin films of BTO nanoparticles, yielding BTO patterns with scales of 300 nm and 5 μm, respectively. Thus, an approach for a chemically non-damaging solution process of inorganic materials for device implementation was successfully demonstrated.

Organic Field-Effect Transistor-Based Ultrafast, Flexible, Physiological-Temperature Sensors with Hexagonal Barium Titanate Nanocrystals in Amorphous Matrix as Sensing Material

Organic field-effect transistors (OFETs) with hexagonal barium titanate nanocrystals (h-BTNCs) in amorphous matrix as one of the bilayer dielectric systems have been fabricated on a highly flexible 10 μm thick poly(ethylene terephthalate) substrate. The device current and mobility remain constant up to a bending radius of 4 mm, which makes the substrate suitable for wearable e-skin applications. h-BTNC films are found to be highly temperature-sensitive, and the OFETs designed based on this material showed ultraprecision measurement (∼4.3 mK), low power (∼1 μW at 1.2 V operating voltage), and ultrafast response (∼24 ms) in sensing temperature over a range of 20-45 °C continuously. The sensors are highly stable around body temperature and work at various extreme conditions, such as under water and in solutions of different pH values and various salt concentrations. These properties make this sensor unique and highly suitable for various healthcare and other applications, wherein a small variation of temperature around this temperature range is required to be measured at an ultrahigh speed.

Intense-pulsed-UV-converted perhydropolysilazane gate dielectrics for organic field-effect transistors and logic gates

We fabricated a high-quality perhydropolysilazane (PHPS)-derived SiO₂ film by intense pulsed UV irradiation and applied it as a gate dielectric layer in high-performance organic field-effect transistors (OFETs) and complementary inverters.

Metal-oxide assisted surface treatment of polyimide gate insulators for high-performance organic thin-film transistors

We developed a facile method for treating polyimide-based organic gate insulator (OGI) surfaces with self-assembled monolayers (SAMs) by introducing metal-oxide interlayers, called the metal-oxide assisted SAM treatment (MAST).

Achieving high mobility, low-voltage operating organic field-effect transistor nonvolatile memory by an ultraviolet-ozone treating ferroelectric terpolymer

Poly(vinylidene fluoride–trifluoroethylene) has been widely used as a dielectric of the ferroelectric organic field-effect transistor (FE-OFET) nonvolatile memory (NVM). Some critical issues, including low mobility and high operation voltage, existed in these FE-OFET NVMs, should be resolved before considering to their commercial application. In this paper, we demonstrated low-voltage operating FE-OFET NVMs based on a ferroelectric terpolymer poly(vinylidene-fluoride-trifluoroethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] owed to its low coercive field. By applying an ultraviolet-ozone (UVO) treatment to modify the surface of P(VDF-TrFE-CTFE) films, the growth model of the pentacene film was changed, which improved the pentacene grain size and the interface morphology of the pentacene/P(VDF-TrFE-CTFE). Thus, the mobility of the FE-OFET was significantly improved. As a result, a high performance FE-OFET NVM, with a high mobility of 0.8 cm²V⁻¹s⁻¹, large memory window of 15.4~19.2, good memory on/off ratio of 10³, the reliable memory endurance over 100 cycles and stable memory retention ability, was achieved at a low operation voltage of ±15 V.

Electron Mobility Exceeding 10 cm(2) V(-1) s(-1) and Band-Like Charge Transport in Solution-Processed n-Channel Organic Thin-Film Transistors

Solution-processed n-channel organic thin-film transistors (OTFTs) that exhibit a field-effect mobility as high as 11 cm(2) V(-1) s(-1) at room temperature and a band-like temperature dependence of electron mobility are reported. By comparison of solution-processed OTFTs with vacuum-deposited OTFTs of the same organic semiconductor, it is found that grain boundaries are a key factor inhibiting band-like charge transport.

Low-temperature sol–gel processed AlOx gate dielectric buffer layer for improved performance in pentacene-based OFETs

An approach to achieve improved performance in pentacene-based organic field effect transistors (OFETs) using high-k AlO_x prepared by a low temperature sol–gel technique as a thin buffer layer on a SiO₂ gate dielectric was demonstrated.

Solution-Processed Ambipolar Organic Thin-Film Transistors by Blending p- and n-Type Semiconductors: Solid Solution versus Microphase Separation

Here, we report solid solution of p- and n-type organic semiconductors as a new type of p-n blend for solution-processed ambipolar organic thin film transistors (OTFTs). This study compares the solid-solution films of silylethynylated tetraazapentacene 1 (acceptor) and silylethynylated pentacene 2 (donor) with the microphase-separated films of 1 and 3, a heptagon-embedded analogue of 2. It is found that the solid solutions of (1)x(2)1-x function as ambipolar semiconductors, whose hole and electron mobilities are tunable by varying the ratio of 1 and 2 in the solid solution. The OTFTs of (1)0.5(2)0.5 exhibit relatively balanced hole and electron mobilities comparable to the highest values as reported for ambipolar OTFTs of stoichiometric donor-acceptor cocrystals and microphase-separated p-n bulk heterojunctions. The solid solution of (1)0.5(2)0.5 and the microphase-separated blend of 1:3 (0.5:0.5) in OTFTs exhibit different responses to light in terms of absorption and photoeffect of OTFTs because the donor and acceptor are mixed at molecular level with π-π stacking in the solid solution.

Synthesis, Molecular Packing, and Thin Film Transistors of Dibenzo[a,m]rubicenes

We herein report an efficient synthesis of dibenzo[a,m]rubicene, a new member of nonplanar cyclopenta-fused polycyclic aromatic hydrocarbon, and its derivatives. It is found that the conformation and molecular packing of dibenzo[a,m]rubicenes in the solid state can be tuned by the substituting groups, and the silylethynylated derivatives of dibenzo[a,m]rubicenes function as p-type organic semiconductors in solution-processed thin film transistors with field effect mobility of up to 1.0 cm(2) V(-1) s(-1).

Enhanced environmental stability induced by effective polarization of a polar dielectric layer in a trilayer dielectric system of organic field-effect transistors: a quantitative study

We report a concept fabrication method that helps to improve the performance and stability of copper phthalocyanine (CuPc) based organic field-effect transistors (OFETs) in ambient. The devices were fabricated using a trilayer dielectric system that contains a bilayer polymer dielectrics consisting of a hydrophobic thin layer of poly(methyl methacrylate) (PMMA) on poly(vinyl alcohol) (PVA) or poly(4-vinylphenol) (PVP) or polystyrene (PS) with Al2O3 as a third layer. We have explored the peculiarities in the device performance (i.e., superior performance under ambient humidity), which are caused due to the polarization of dipoles residing in the polar dielectric material. The anomalous behavior of the bias-stress measured under vacuum has been explained successfully by a stretched exponential function modified by adding a time dependent dipole polarization term. The OFET with a dielectric layer of PVA or PVP containing hydroxyl groups has shown enhanced characteristics and remains highly stable without any degradation even after 300 days in ambient with three times enhancement in carrier mobility (0.015 cm(2)·V(-1)·s(-1)) compared to vacuum. This has been attributed to the enhanced polarization of hydroxyl groups in the presence of absorbed water molecules at the CuPc/PMMA interface. In addition, a model has been proposed based on the polarization of hydroxyl groups to explain the enhanced stability in these devices. We believe that this general method using a trilayer dielectric system can be extended to fabricate other OFETs with materials that are known to show high performances under vacuum but degrade under ambient conditions.

Molecular packing and n-channel thin film transistors of chlorinated cyclobuta[1,2-b:3,4-b′]diquinoxalines

Introduction of chlorine substituents into cyclobuta[1,2-b:3,4-b′]diquinoxaline leads to tunable molecular packing motifs and n-type organic semiconductors with a field effect mobility of up to 0.42 cm² V⁻¹ s⁻¹ in thin film transistors.

Self-assembled monolayers of cyclohexyl-terminated phosphonic acids as a general dielectric surface for high-performance organic thin-film transistors

A novel self-assembled monolayer (SAM) on AlOy /TiOx is terminated with cyclohexyl groups, an unprecedented terminal group for all kinds of SAMs. The SAM-modified AlOy /TiOx functions as a general dielectric, enabling organic thin-film transistors with a field-effect mobility higher than 5 cm(2) V(-1) s(-1) for both holes and electrons, good air stability with low operating voltage, and general applicability to solution-processed and vacuum-deposited n-type and p-type organic semiconductors.

Low-voltage graphene field-effect transistors based on octadecylphosphonic acid modified solution-processed high-k dielectrics

In this study, a solution-processed bilayer high-k dielectric (Al2O(y)/TiO(x), abbrev. as ATO) was used to realize the low-voltage operation of graphene field-effect transistors (GFETs), in which the graphene was grown by atmospheric pressure chemical vapor deposition (APCVD). Upon modifying the interface between graphene and the dielectric by octadecylphosphonic acid (ODPA), outstanding room-temperature hole mobility up to 5805 cm(2) V(-1) s(-1) and electron mobility of 3232 cm(2) V(-1) s(-1) were obtained in a small gate voltage range from -3.0 V to 3.0 V under a vacuum. Meanwhile, an excellent on/off current ratio of about 8 was achieved. Our studies demonstrate an effective route in which utilizing the low-temperature solution-processed dielectrics can achieve low-voltage and high performance GFETs.

Low-temperature facile solution-processed gate dielectric for combustion derived oxide thin film transistors

An improved hydrophilic aluminum nitrate solution was designed to spin coat robust dielectric layers for thin film transistors.

Insights into the interfacial properties of low-voltage CuPc field-effect transistor

The interfacial transport properties and density of states (DOS) of CuPc near the dielectric surface in an operating organic field-effect transistor (OFET) are investigated using Kelvin probe force microscopy. We find that the carrier mobility of CuPc on high-k Al2Oy/TiOx (ATO) dielectrics under a channel electrical field of 4.3 × 10(2) V/cm reaches 20 times as large as that of CuPc on SiO2. The DOS of the highest occupied molecular orbital (HOMO) of CuPc on the ATO substrate has a Gaussian width of 0.33 ± 0.02 eV, and the traps DOS in the gap of CuPc on the ATO substrate is as small as 7 × 10(17) cm(-3). A gap state near the HOMO edge is observed and assigned to the doping level of oxygen. The measured HOMO DOS of CuPc on SiO2 decreases abruptly near E(V(GS) = V(T)), and the pinning of DOS is observed, suggesting a higher trap DOS of 10(19)-10(20) cm(-3) at the interface. The relationships between DOS and the structural, chemical, as well as electrical properties at the interface are discussed. The superior performance of CuPc/ATO OFET is attributed to the low trap DOS and doping effect.