P-type Organic Field-effect Transistors Research Articles

IDTI based copolymers for p-type organic field-effect transistors

Organic semiconductors received more and more attention in the past few years. Development some novel chromophore with the strong electron-deficient to construct donor–acceptor polymers plays a crucial role for the development of the organic semiconductors. A new acceptor indaceno[1,2-b:5,6-b′]dithiophene)-2,7-diylbis(methan-1-yl-1-ylidene))bis(6-bromo-indolin-2-one) (IDTI, M1), as well as a IIDT-based polymer P1 were designed in this work, and for the first time applied in the OFET. The results shows that the P1 present not only a strong aggregation, but also a suitable highest occupied molecular orbital (HOMO) energy level. As a consequent, the P1 exhibited a p-type behavior with the hole mobility up to 0.29 cm2 V−1 s−1. This work demonstrated that the IDTI chromophore is a promising electron-deficient block for the constructing donor–acceptor high performance semiconductor polymers.

Evaluating the performance of p-type organic field-effect transistor using different source–drain electrodes

Evaluating the performance of p-type organic field-effect transistor using different source–drain electrodes

Active matrix-based pressure sensor system with a 4 × 16 printed decoder designed with a flexible hybrid organic process design kit

The innovative field of printed sensor with a demand for high accuracy, sensitivity and durability has enabled a wide application area in sensing, healthcare etc. A large-area printed sensor system on a flexible foil substrate emplying p-type organic field-effect transistors (OFETs) is presented. Thereby, the OFET is fabricated through a hybrid manufacturing process, including photolithographically structured source- and drain-electrodes, ink-jet printed organic semiconductor, and spin-coated dielectric. Moreover, a dedicated device model, derived from the variable range hopping model, is developed and integrated together with process related design rules, materials properties and geometric information into a comprehensive process design kit (FH_OPDK). The FH_OPDK is integrated in a commercial electronic design automation tool and is used to design and perform post-layout simulations on logic gates, such as INV, NAND2, and NOR2 as well as circuitry such as ring oscillators and a 4 × 16 digital decoder. Several circuit topologies have been tested and evaluated in a detailed model-hardware correlation analysis. Finally we have optimized logic gates and the decoder in a PMOS only, pseudo CMOS design style. To demonstrate the feasibility of the full sensor system in hardware a 16 × 16 active matrix pressure sensor on a flexible substrate integrated with a 4 × 16 binary decoder was fabricated and tested. We have integrated our flexible hybrid sensor system with a PCB board and a microcontroller to demonstrate the hardware readout platform capable of detecting the weight of objects and visualizing a digital map of applied forces.

Solution-processable quinoidal compounds containing heterocycle for air-stable n‑type organic field-effect transistors and gas sensors

Organic field effect transistors (OFETs) have potential applications in gas sensing area, but the performance and diversity of n-type OFETs are still far behind that of p-type OFETs due to the poor stability in air atmosphere. Herein, a series of novel dicyanomethylene-terminated quinoids compounds were synthesized and characterized by using electron withdrawing aromatic heterocycles as the core structural units. The introduction of alkyl branch chain greatly improves the solubility, which is helpful to the preparation of thin film OFETs devices by low-cost solution method. These OFETs show typical n-channel FET characteristics with mobility ranging from 10−3∼10−1 cm2V−1s−1. Among them, the 3-T-TZCN based OFETs exhibit the best stability, in which the mobility decreased no more than 18 % after 90 days stored in air atmosphere, this is an outstanding performance compared with the previous researches. We further investigated the dimethyl methylphosphonate (DMMP, which is a substitute for detecting sarin) gas sensing performance of each material, the experimental results indicated that the sensitivity, recovery and stability of 3-T-TZCN are better than other materials, and the limit of detection can be lower to 10 ppb level. This general approach could offer new solution for constructing n-type OFET-based gas sensors with good stability in air atmosphere.

An integrate-and-fire neuron circuit made from printed organic field-effect transistors

Neuromorphic circuits that mimic the operation of nerve cells are promising approaches to interface with or emulate the operation of biological neural network. These types of electronic circuits have generally been realised by fabrication using well-established silicon technology but herein we report the fabrication of a simple neuromorphic circuit, specifically, an integrate-and-fire (I&F) circuit, using solution-processed OFETs. It consists of p-type organic field-effect transistors (OFETs) realised with parylene-dielectric, printed silver electrodes and a solution processed semiconductor on a flexible plastic substrate. As the behaviour of the fabricated I&F circuit is predictable by simulation, the reported process allows for customised circuit design and provides the basis to realise a variety of flexible neuromorphic circuit designs. • Neuromorphic circuits can mimic the electrical spiking of nerve cells. • A simple neuromorphic circuit made using printed organic field-effect transistors. • Performance of a printed integrate and fire circuit can be modelled by simulation.

Improving bias-stress stability of p-type organic field-effect transistors by suppressing electron injection

Improving bias-stress stability of p-type organic field-effect transistors by suppressing electron injection

Polyaniline Based Field Effect Transistor for Humidity Sensor

In this present research work, we presented a new Bottom Gate P-Type Organic Field Effect Transistor (OFET) humidity sensor and its applicability towards humidity has been experimentally demonstrated. P-type organic semiconductor polyaniline (PANI) has been used in a variety of applications, including logic circuit components, electromagnetic shielding, chemical sensing, and anticorrosion. Humidity sensor can be used to monitor relative humidity (RH) in various environments. We only focus on the fabrication of conducting polymer OFETs with top contact to measure humidity and verify I-V properties. The current saturation (ISat) of p-type OFETs was 0.8 μA, while the threshold voltage VTh was 2.2 V. The results of FESEM have been perform to confirm that deposited thin film grown on the substrate is purely uniform. The Proposed sensor shows that organic gate dielectrics are a low-cost alternative to inorganic gate dielectrics with good electrical performance. The proposed OFET-based sensors have a number of benefits, such as high sensitivity, low cost, quick response, and physical flexibility.

Directly Patterning Conductive Polymer Electrodes on Organic Semiconductor via In Situ Polymerization in Microchannels for High-Performance Organic Transistors.

Conductive polymers are considered promising electrode materials for organic transistors, but the reported devices with conductive polymer electrodes generally suffer from considerable contact resistance. Currently, it is still highly challenging to pattern conductive polymer electrodes on organic semiconductor surfaces with good structure and interface quality. Herein, we develop an in situ polymerization strategy to directly pattern the top-contacted polypyrrole (PPy) electrodes on hydrophobic surfaces of organic semiconductors by microchannel templates, which is also applicable on diverse hydrophobic and hydrophilic surfaces. Remarkably, a width-normalized contact resistance as low as 1.01 kΩ·cm is achieved in the PPy-contacted transistors. Both p-type and n-type organic field-effect transistors (OFETs) exhibit ideal electrical characteristics, including almost hysteresis-free, low threshold voltage, and good stability under long-term test. The facile patterning method and high device performance indicate that the in situ polymerization strategy in confined microchannels has application prospects in all-organic, transparent, and flexible electronics.

Solution-Processed Organic and ZnO Field-Effect Transistors in Complementary Circuits

The use of high κ dielectrics lowers the operating voltage in organic field-effect transistors (FETs). Polymer ferroelectrics open the path not just for high κ values but allow processing of the dielectric films via electrical poling. Poled ferroelectric dielectrics in p-type organic FETs was seen to improve carrier mobility and reduce leakage current when compared to unpoled devices using the same dielectric. For n-type FETs, solution-processed ZnO films provide a viable low-cost option. UV–ozone-treated ZnO films was seen to improve the FET performance due to the filling of oxygen vacancies. P-type FETs were fabricated using the ferroelectric polymer poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) as the dielectric along with a donor–acceptor polymer based on diketopyrrolopyrrole (DPP-DTT) as the semiconductor layer. The DPP-DTT FETs yield carrier mobilities upwards of 0.4 cm2/Vs and high on/off ratios when the PVDF-TrFE layer is electrically poled. For n-type FETs, UV–ozone-treated sol–gel ZnO films on SiO2 yield carrier mobilities of 10−2 cm2/Vs. DPP-DTT-based p- and ZnO-based n-type FETs were used in a complementary voltage inverter circuit, showing promising characteristic gain. A basic inverter model was used to simulate the inverter characteristics, using parameters from the individual FET characteristics.

Electron Injection Improvement of n-Type Organic Field-Effect Transistors With Indium Contact Interlayer

The organic field-effect transistors (OFETs) have developed rapidly in recent years. However, compared with the p-type OFETs, the n-type devices always show poorer performance due to their hard electron injection and low stability. It is necessary to further improve the charge injection properties of n-type OFETs. In this work, indium (In) layers, as an interlayer above contacts, were adopted for electron injection improvement in the n-type poly((N, $\text{N}^{\prime }$ -bis(2-octyldodecyl)-1,4,5,8-naphthalenedicarboximide-2,6-diyl)-alt-5, $5^{\prime }$ -(2, $2^{\prime }$ -bithiophene)) (N2200) OFETs. The injection barrier, such as Schottky barrier, at the metal/semiconductor interface was effectively weakened with the In interlayers thickness ( ${T}_{In}$ ) increasing from 0 to 6 nm. The mechanism of electron injection changed from thermionic emission to tunneling, as the ${T}_{In}$ reaching 6 nm. It results in a marked improvement in electrical properties for N2200 OFETs. The mobility increased from 0.09 to 0.29 cm ${}^{2}\cdot \text{V}^{-1}\cdot \text{s}^{-1}$ while the subthreshold swing decreased from 2.7 to 0.8 $\text{V}\cdot $ dec−1 with the ${T}_{In}$ . This work provides an efficient approach for the electron injection improvement in n-type OFETs.

Improving Bias-Stress Stability of p-Type Organic Field-Effect Transistors by Constructing an Electron Injection Barrier at the Drain Electrode/Semiconductor Interfaces.

Bias-stress instability has been a challenging problem and a roadblock for developing stable p-type organic field-effect transistors (OFETs). This device instability is hypothesized because of electron-correlated charge carrier trapping, neutralization, and recombination at semiconductor/dielectric interfaces and in semiconductor channels. Here, in this paper, a strategy is demonstrated to improve the bias-stress stability by constructing a multilayered drain electrode with energy-level modification layers (ELMLs). Several organic small molecules with high lowest unoccupied molecular orbital (LUMO) energy levels are experimented as ELMLs. The energy-level offset between the Fermi level of the drain electrode and the LUMOs of the ELMLs is shown to construct the interfacial barrier, which suppresses electron injection from the drain electrode into the channel, leading to significantly improved bias-stress stability of OFETs. The mechanism of the ELMLs on the bias-stress stability is studied by quantitative modeling analysis of charge carrier dynamics. Of all injection models evaluated, it is found that Fowler-Nordheim tunneling describes best the observed experimental data. Both theory and experimental data show that, by using the ELMLs with higher LUMO levels, the electron injection can be suppressed effectively, and the bias-stress stability of p-type OFETs can thereby be improved significantly.

Non-lithographic direct patterning of carbon nanomaterial electrodes via electrohydrodynamic-printed wettability patterns by polymer brush for fabrication of organic field-effect transistor

In this study, we report a new approach for patterning of carbon nanomaterials via the solution route through wettability patterning using electrohydrodynamic (EHD) printing. Differences in wettability were successfully obtained by treating dimethylchlorosilane-terminated polystyrene (PS-brush) with the micro-dripping mode of EHD printing up to 6-μm line width and scaled fine patterns with various shapes at 6-μm printing conditions. We obtained sub-micrometer scaled carbon nanomaterial patterns, which were utilized as source and drain (S/D) electrodes for organic field-effect transistors (OFETs), without using any lithographic process. In addition, the PS-brush treatment modified the surface hydrophobicity of the substrates that served as the PS-brush and SiO2 bilayer dielectrics to guarantee high stability during the OFET operation. As a result, the OFETs employing S/D electrodes based on carbon nanomaterial patterns exhibited the electrical performance of typical p-type OFETs with negligible hysteresis. Additionally, we confirmed that a solution processing organic semiconductor forms a more suitable crystal structure than a vacuum process based organic semiconductor by several tools like CPOM, AFM, and 2D-GIXD.

High-performance n- and p-type organic single-crystal field-effect transistors with an air-gap dielectric towards anti-ambipolar transport

By combining high-performance n- and p-type single crystals with an air-gap dielectric, excellent anti-ambipolar transport with a small hysteresis was achieved.

Improving device performance of p-type organic field-effect transistor using butterfly like triarylamines

Facile and economic strategy to create a controlled self-structured architecture of semiconducting molecules is very crucial in the accomplishment of carbon electronic devices. A series of new unsymmetrically functionalized butterfly type triarylamines with electron donating/withdrawing substituents were synthesized. Simple and efficient solution based method was used as a successful strategy for OFET with improved characteristics. Binary solvent system with chloroform and toluene (7:3) has improved inter/intra molecular communication in the active layer. The morphology of the films was analyzed by SEM reveals the uniform packing. In addition post thermal annealing has enhanced the crystallinity with minimal grain boundaries. HOMO values -5.1 to -5.4 eV obtained from cyclic voltammetry ensure that these molecules can efficiently transport holes. OFET devices were fabricated in bottom gate top contact (BGTC) architecture by spin coating. Molecules exhibited typical p -channel transistor behavior with mobility up to 1 cm 2 V −1 s −1 with 10 6 I on/off current ratio. Density functional theory (DFT) visualized the packing and interaction of molecules and supported the efficient mobility. Our investigation gives insight into the role of solvents to control the film architecture in solution processing OFET device construction. • New functionalized triarylamines are designed, synthesized and scrutinised for OFET applications. • HOMO level (-5.2–-5.4 eV) ensures efficient hole injection and transport. • Band gap tuned with respect to the electron donating and withdrawing substituents. • OFETs with bottom gate top contact architecture is fabricated by spin coating from a binary solvent mixture. • Exhibited higher melting points ensures the device durability with higher mobility up to 1 cm 2 V −1 s −1 with 10 6 I on/off current ratio.

Influence of Al2O3 nanoparticles incorporation on the dielectric properties of solution processed PVA films for organic field effect transistor applications

We report, the influence of Al2O3 nanoparticles (NP) incorporation on the dielectric properties of solution processed polyvinylalcohol (PVA) films for organic field effect transistor applications. It was observed typical p-type organic field effect transistors. Devices processed using employing PVA films blended with 70 wt% of Al2O3 NP as gate dielectric layers demonstrated higher field effect mobility, better saturation behavior and reduced hysteresis phenomenon compared to the devices based on pure PVA films. Al2O3 NP:PVA blends based dielectric films with 0, 3, 5, 10, 20, 50 and 70 wt% concentrations of Al2O3 NP compared to the weight of PVA were prepared. Dielectric parameters such as dielectric constant and dielectric strength of the Al2O3 NP:PVA films were analyzed. It was found that real dielectric constant as well as dielectric strength of the films increase with increase of Al2O3 NP concentration. Cole–Cole plots of the films demonstrated depressed semi-circles which points non-Debye type behavior. We presume that the devices being investigated with promising results, may be utilized for some industrial applications such as large area sensor arrays in future.

π-Extended Phosphepines: Redox and Optically Active P-Heterocycles with Nonplanar Framework.

In this letter, we present the synthesis of a new family of π-extended dithieno[ b, f]phosphepines. The Pd-catalyzed direct arylation allows the introduction of various substituents, which tune the absorption/emission in the visible range as well as the redox properties. All those modifications were rationalized through DFT calculations. The physical properties of ambipolar phosphepine with diphenylamino substituents inspired us to use it as a semiconductor in p-type organic field-effect transistors (OFETs).

(Invited) 3D Monolithic Integration in Flexible Organic Printed Transistors

Despite the significant enhancements in material properties such as carrier mobility, few attempts have been made to print organic integrated circuits (ICs). The relatively large size of printed features (typically 10 μm – 100 μm) have limited the implementation of organic ICs with reasonable transistor densities. To overcome the limitation, we introduce three-dimensional (3D) integration of inkjet-printed organic transistors and circuits. We fabricated a p-type organic field-effect transistor that is inkjet-printed on top of an n-type organic field-effect transistor with a shared gate joining the two transistors. Based on the common-gate transistor-on-transistor structure, a complementary inverter array is fabricated with a high static noise margin and reliable characteristics. We have further developed 3D integration of a dual-gate NAND technology fabricated by printing technique with a demonstration of flexible logic circuits. The vertical stacking of independent-gate controlled dual gate transistors offers enhanced on-current, lowered sub-threshold swing, increased device stability and density. The present study fulfills the essential requirements for the fabrication of organic printed complex ICs, and the findings can be applied to realize more complex digital/analogue ICs and intelligent devices

Acceptor Percolation Determines How Electron-Accepting Additives Modify Transport of Ambipolar Polymer Organic Field-Effect Transistors.

Organic field-effect transistors (OFETs) that utilize ambipolar polymer semiconductors can benefit from the ability of both electron and hole conduction, which is necessary for complementary circuits. However, simultaneous hole and electron transport in organic field-effect transistors result in poor ON/OFF ratios, limiting potential applications. Solution processing methods have been developed to control charge transport properties and transform ambipolar conduction to hole-only conduction. The electron-acceptor phenyl-C61-butyric acid methyl ester (PC61BM), when mixed in solution with an ambipolar semiconducting polymer, can reduce electron conduction. Unipolar p-type OFETs with high, well-defined ON/OFF ratios and without detrimental effects on hole conduction are achieved for a wide range of blend compositions, from 95:5 to 5:95 wt % semiconductor polymer:PC61BM. When introducing the alternative acceptor N, N'-bis(1-ethylpropyl)-3,4:9,10-perylenediimide (PDI), high ON/OFF ratios are achieved for 95:5 wt % semiconductor polymer:PDI; however, electron conduction increases for 50:50 and 5:95 wt % semiconductor polymer:PDI. As described within, we show that electron conduction is practically eliminated when additive domains do not percolate across the OFET channel, that is, electrons are "morphologically trapped". Morphologies were characterized by optical, electron, and atomic force microscopy as well as X-ray scattering techniques. PC61BM was substituted with an endohedral Lu3N fullerene, which enhanced contrast in electron microscopy and allowed for more detailed insight into the blend morphologies. Blends with alternative, nonfullerene acceptors further emphasize the importance of morphology and acceptor percolation, providing insights for such blends that control ambipolar transport and ON/OFF ratios.

Fabrication of p-type Organic Field Effect Transistor using PMMA:TiO2 as Nanocomposite Dielectric Layer

This paper report on the fabrication of p-type organic field effects transistor (OFET) using low temperature spin coating deposition technique. The p-type OFETs were fabricated using poly (3-hexylthiophene-2,5-diyl) (P3HT) and poly (methyl methacrylate):titanium dioxide (PMMA:TiO2) nanocomposite material were used as semiconductor and the gate dielectric, respectively. The electrical and structural properties of OFETs were analysed using current-voltage (I-V), atomic force microscopy (AFM) and RAMAN spectroscopy. Results from I-V show that the fabricated p-type OFET has moderate performance with threshold voltage, VTH is -3V and mobility, μ is 2.01 cm2 V-1s.

Intrinsic charge carrier mobility in single-crystal OFET by “fast trapping vs. slow detrapping” model

Abstract This study investigates the gate stress-induced mobility discrepancy in p-type single-crystal organic field-effect transistors (OFETs) on an octyltrichlorosilane (OTS)-modified SiO2/Si substrate. During measurements in atmosphere, anti-clockwise hysteresis was observed in the transfer curve, and the mobility calculated from the forward sweep was smaller than that calculated from the reverse sweep. Hysteresis has often been observed for OFETs but the mobility discrepancy has not been clearly understood. We formulated a “fast trapping vs. slow detrapping” model and suggested that the mobility values calculated from the reverse sweep represent the intrinsic property of the material. To verify the validity of this model, we investigated mobility anisotropy of an air-stable organic semiconductor, 2,7-bis(4-methoxyphenyl)benzo[b]benzo[4,5]thieno[2,3-d]thiophene (DBOP-BTBT). By measuring the single-crystal OFET characteristics of many crystals with different orientations, we observed anisotropic hole mobility calculated from the reverse sweep. The mobility along the b-axis, which corresponds to the π-π stacking direction, was 13.9 cm2 V−1 s−1, and that along the a-axis was 6.2 cm2 V−1 s−1. However, we did not see clear anisotropy when mobility was calculated from the forward sweep due to a variation in the data. The threshold voltage from the reverse and the forward sweeps showed isotropic characteristics within the range from −60 to −70 V and from −50 to −60 V, respectively. These results indicate that the numbers of filled traps were different between the reverse and the forward sweeps at the interface, and confirm the validity of our model.