Gate Organic Field-effect Transistors Research Articles

Extended π-Conjugation and Structural Planarity Effects of Symmetrical D-π-A-π-D Naphthalene and Perylene Diimide Semiconductors on n-Type Electrical Properties.

A series of Donor-π-Acceptor-π-Donor (D-π-A-π-D) compounds based on naphthalendiimide (NDI) and perylenediimide (PDI) central cores combined with triphenylamine and phenylcarbazole donor groups have been synthesized, characterized and tested in top-contact/bottom gate organic field-effect transistors (OFETs). The results showed high electron mobilities, up to 0.3 cm2V-1s-1, in the case of NDI derivatives and moderate values of around 10-3 cm2V-1s-1 for PDI-based semiconductors. Quantum chemical calculations were performed in order to support the experimental data. The results suggest that adequate molecular characteristics and larger crystalline domains in NDI vs. PDI semiconducting films may be the reasons behind the enhanced electrical properties of NDI derivatives. Furthermore, when the lateral donor substituents are triphenylamine groups, the mobilities were slightly higher in comparison to phenylcarbazole donor groups due to an improved electron-donating character. Other characterization techniques such as AFM, X-ray diffraction or spectroelectrochemistry, among others, have been performed to analyze supramolecular order, charge carriers' nature and stability, parameters closely related to charge transport characteristics.

Carbon dots-functionalized extended gate organic field effect transistor-based biosensors for low abundance proteins.

Organic field effect transistors have emerged as promising platforms for biosensing applications. However, the challenge lies in optimizing functionalization strategies for the sensing interface, enabling the simultaneous detection of low abundance proteins while maintaining device performance. Here, we designed a carbon dots-functionalized extended gate organic field effect transistor. Leveraging the advantages of facile synthesis, tunable modification, small particle size, and cost-effectiveness of carbon dots, we implemented their integration onto the electrode surface. Through harnessing the covalent interactions of functional groups on the surface of carbon dots, we achieved effective immobilization of low abundance proteins without compromising device performance. Consequently, this biosensor exhibits a remarkably low limit of detection of 2.7 pg mL-1 and demonstrates high selectivity for the carcinoembryonic antigen. These findings highlight the superior capabilities of carbon dots in enhancing biosensor performance and emphasize their potential for early cancer detection.

Direct Comparison of the Effect of Processing Conditions in Electrolyte-Gated and Bottom-Gated TIPS-Pentacene Transistors

Among the plethora of soluble and easy processable organic semiconductors, 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-P5) is one of the most promising materials for next-generation flexible electronics. However, based on the information reported in the literature, it is difficult to exploit in field-effect transistors the high-performance characteristics of this material. This article correlates the HMDS functionalization of the silicon substrate with the electrical characteristics of TIPS-P5-based bottom gate organic field-effect transistors (OFETs) and electrolyte-gated organic field-effect transistors (EGOFETs) fabricated over the same platform. TIPS-P5 transistors with a double-gate architecture were fabricated by simple drop-casting on Si/SiO2 substrates, and the substrates were either functionalized with hexamethyldisilazane (HMDS) or left untreated. The same devices were characterized both as standard bottom-gate transistors and as (top-gate) electrolyte-gated transistors, and the results with and without HMDS treatment were compared. It is shown that the functionalization of the silicon substrate negatively influences EGOFETs performance, while it is beneficial for bottom-gate OFETs. Different device architectures (e.g., bottom-gate vs. top-gate) require specific evaluation of the fabrication protocols starting from the effect of the HMDS functionalization to maximize the electrical characteristics of TIPS-P5-based devices.

Role of diaminonaphthalene based polymers as sensors in detection of biomolecules: A review

The recent advancements in the synthetic polymer chemistry have resulted in synthesis of potentially distinct conducting polymers that have found a wide range of applications from industry to biology. Among various conducting polymers, poly (diaminonaphthalene) (PDAN) and its derivatives have emerged as promising materials in constructing bio/chemical sensors and shown potential in quantitative and qualitative assays of a variety of bioactive molecules. It is, however, surprising that in spite of having unusual physicochemical properties of this typical polymer and its monomers, no comprehensive information about their sensing properties are available in the literature either as review articles or monographs. The present review article highlights a broad scenario of diaminonaphthalene (DAN) and its polymer-based nanostructured bio/chemical sensors providing insights into their functioning, structural composition, fabrication through various polymerization routes, and eventual applications in sensing different type of biochemically active molecules. Moreover, PDAN based Dual Gate Organic Field Effect Transistor has been modeled and substantially reviewed for their applications in sensing the biomolecules. The underlying present challenges in the area of PDAN based biochemical sensors and their future prospects have been critically examined and several issues to be addressed have also been raised.

Geometry Control of Source/Drain Electrodes in Organic Field-Effect Transistors by Electrohydrodynamic Inkjet Printing.

In this work we study the influence of dielectric surface and process parameters on the geometry and electrical properties of silver electrodes obtained by electrohydrodynamic inkjet printing. The cross-section and thickness of printed silver tracks are optimized to achieve a high conductivity. Silver overprints with cross-section larger than 4 μm2 and thickness larger than 90 nm exhibit the lowest resistivity. To fabricate electrodes in the desired geometry, a sufficient volume of ink is distributed on the surface by applying appropriate voltage amplitude. Single and multilayer overprints are incorporated as bottom contacts in bottom gate organic field-effect transistors (OFETs) with a semiconducting polymer as active layer. The multilayer electrodes result in significantly higher electrical parameters than single layer contacts, confirming the importance of a careful design of the printed tracks for reliable device performance. The results provide important design guidelines for precise fabrication of electrodes in electronic devices by electrohydrodynamic inkjet printing.

Naphthalene diimide based near-infrared luminogens with aggregation-induced emission characteristics for biological imaging and high mobility ambipolar transistors

Organic conjugated materials combining high conductivity with strong solid-state emission are highly desired for organic electronic applications, yet still rather rare. Herein, a novel luminogen (TEN) comprised by linking naphthalene diimides and tri-phenyl ethylene with vinyl bridges is reported. TEN exhibits aggregation-induced emission (AIE) behavior of a strong near-infrared fluorescence over 700 nm and the efficiency above 60.5% in the solid state, while also shows promising application in vivo bio-imaging with good permeability and extremely low background. Single crystal of TEN reveals intra- and inter-molecular C–H···O hydrogen bonds, contributing to an inclined molecular stacking along the a -axis of the cell, creating a 1D charge carrier transporting channel under a short π-π interaction distance of 3.42 A, which might benefit the solid emission and charge transport ability simultaneously. Solution processed bottom contact, top gate organic field effect transistors based on TEN reveal a high ambipolar charge transport ability with the hole mobility up to 0.13 cm2 V−1 s−1 and electron mobility up to 0.010 cm2 V−1 s−1. Further atomic force microscopy and X-ray diffraction analysis on TEN thin film confirm the existence of the 1D π-π stacking channel, suggesting the stacking geometry revealed in crystal crucial for facilitating high charge carrier mobility while preserving the strong solid emission at the same time.

Performance Investigation of Pentacene Based Organic Double Gate Field Effect Transistor and its Application as an Ultrasensitive Biosensor

In this paper, the electrical performance of double gate organic field effect transistor (DG-OFET) are thoroughly investigated and feasibility of the device as an efficient biosensor is comprehensively assessed. The introduced device provides better gate control over the channel, yielding better charge injection properties from source to channel and providing higher on-state current in comparison with single gate devices. The susceptibility of fundamental electrical parameters with respect to the variation of design parameters is thoroughly calculated. In particular, standard deviation and average value of main electrical parameters signify that metal gate workfunction, channel thickness and gate oxide thickness are fundamental design measures that may modify the device efficiency. The insensitivity of off-state current to the change of channel length and drain bias confirms feasibility of the device in nanoscale regime. Next, a nano cavity is embedded in the gate insulator region for accumulation of biomolecules. The immobilization of molecules with different dielectric constants in the gate insulator hollow alters the gate capacitance and results in the drain current deviation with respect to the air- filled cavity condition. It is shown that by the occupancy of whole volume of the nanogap, a maximum range of on-state current variation can be achieved.

Investigation of charge transport properties of [1]Benzothieno[3,2-b][1]-benzothiophene single-crystals in field-effect transistor configuration

Abstract Single-crystals of unsubstituted [1]Benzothieno[3,2-b][1]-benzothiophene (BTBT) were prepared by physical vapor transport deposition (VTP). The packing structure and morphology of the crystals were studied by X-ray diffraction (XRD), polarized optical microscopy (POM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The charge transport properties of BTBT single-crystals were also investigated via bottom contact/bottom gate (BC/BG) organic field-effect transistors (OFETs) on both SiO2 and n-octadecyltrichlorosilane (OTS) treated surfaces. A maximum hole mobility value of 0.032 cm2V−1s−1 was measured on the OTS substrate. In addition, single-crystal OFETs with ion gel top gate (TG) configuration were also investigated for low voltage operation. This work represents the first investigation of charge carrier mobility of a simple BTBT in transistor configuration and highlights the essential role of the BTBT substitution in charge transport properties.

Static Polystyrene Gate Charge Density Modulation of Dinaphthothienothiophene with Tetrafluorotetracyanoquinodimethane Layer Doping: Evidence from Conductivity and Seebeck Coefficient Measurements and Correlations

We relate the static charging of organic field effect transistor (OFET) gate dielectric polymers, the resulting change in threshold voltage shift, and the modulation of thermoelectric properties of the transistor semiconductor. We utilize a bottom gate OFET structure with cross-linkable polystyrene and plain polystyrene (XLPS/PS) bilayer dielectrics and dinaphthothienothiophene (DNTT) organic molecular semiconductor with tetrafluorotetracyanoquinodimethane (F4TCNQ) doping layer. The conductivity and Seebeck coefficient are measured before and after charging. We find that the conductivity increases significantly, while the Seebeck coefficient decreases correspondingly in a trend of S ∝ ln(σ) after the dielectrics were negatively charged, resulting in an average of 5-fold increase in power factor at the maximum charging level. Additionally, temperature-dependent conductivity measurements show that the activation energy decreases with the increasing conductivity. We calculate the Seebeck coefficient based on the activation energy and find the result is consistent with the Mott mobility edge model. This work confirms the charging mechanism in our previous published work, including the location of static charges in the bulk of the dielectric, and demonstrates modulation and enhancement of the thermoelectric properties of organic thermoelectric materials by adjacent chargeable dielectrics without changing the molecular microstructure or applying external gate voltage during operation.

Contact Resistance Effects in Ni Drain-Source P3HT/PVA OFETs

Ni bottom contacts and Al top gate organic field effect transistors of Poly 3-hexylthiophene and cross-linked Poly Vinyl Alcohol with different channel lengths (5 μm, 10 μm, 20 μm and 40 μm) were made on glass substrates, using standard photolithography and oxygen plasma etching. The transistors presented good charge mobility, high ION/IOFF and excellent environmental and temporal stability. The Shockley model and the Transmission Line Method (TLM) were applied to characterize the transistors. Mobility was extracted by both methods, and the differences were discussed. The shorter the channel length and the higher the conductivity of the semiconductor, the greater the impact of the contact resistance. In such cases, the use of TLM for parameter extraction becomes essential.

Influence of relative humidity on the electrical response of PEDOT:PSS based organic field-effect transistor

Abstract We have investigated the influence of relative humidity on the electrical response of a bottom gate organic field-effect transistor (OFET) with poly(3,4-ethylenedioxythiophene)/poly(4-styrene sulfonate) (PEDOT:PSS) as an active channel material. For sensor fabrication, the organic polymer PEDOT:PSS has been spun-cast on highly doped n-Si wafer with preliminary thermally deposited gold, source and drain electrodes. The structural characterization and surface morphology study of active layer has been performed by XRD and FESEM, respectively. From the transfer characteristic curve, the p-type hole conductivity in PEDOT:PSS thin film is confirmed. Whereas from the output current-voltage (I–V) characteristic of the OFET, the Ion/Ioff ratio has been measured to be ∼2.6, when operated at relative humidity (RH) ∼60%. The humidity sensing characteristics of the OFET have further been investigated by exposing the proposed OFET to varied RH levels (40–80% RH) at room temperature (26.2 °C). Within the humidity range examined, the channel current has been observed to amplify by nearly 29.4 times of its magnitude.

Low-Voltage pH Sensor Tag Based on All Solution Processed Organic Field-Effect Transistor

By reducing the sub-gap density of states at the channel, an all solution processed low-voltage organic field-effect transistor (OFET) was realized on a micrometer-thick SU8 gate dielectric layer. The device exhibits excellent operational stability under continuous bias stress. An integrated pH sensor tag was fabricated based on this low-voltage OFET, using an extended gate OFET for sensing and the other OFET as the load to convert the current signal to a voltage output for easy design of the subsequent readout circuit. With the low-voltage operation behavior and excellent operational stability of the OFET, the sensor tag was demonstrated to be operated in a 3.3 V battery powered electronic system for reliable pH sensing.

Thieno[3,4-c]Pyrrole-4,6-Dione and Dithiophene-Based Conjugated Polymer for Organic Field Effect Transistors: High Mobility Induced by Synergic Effect of H-Bond and Vinyl Linkage.

Here, a conjugated polymer VTTPD based on thieno[3,4-c]pyrrole-4,6-dione (TPD) and dithiophene with vinyl as linker is synthesized and characterized. Electrochemical and optical studies indicate the LUMO and HOMO energies of the polymer are -3.70 and -5.39 eV. Theoretical calculation with density functional theory suggests that H-bonds are formed between the TPD carbonyl (O) and its neighboring vinyl (H) which benefit the planarity and π-conjugation of the polymer backbone. Bottom contact bottom gate organic field effect transistor devices based on VTTPD are fabricated and examined in air. After annealing at 160 °C, the devices exhibit excellent performance of μh = 0.4 cm(2) V(-1) s(-1) , Ion/off = 10(6) , Vth within -10 V to -5 V. Thin film morphologies before and after the annealing process are also investigated with XRD and AFM.

Synthesis and Photophysical Studies of Thiadiazole[3,4-c]pyridine Copolymer Based Organic Field-Effect Transistors.

A novel thiadiazolo[3,4-c]pyridine]based donor-acceptor (D-A) copolymer, poly[4,8-bis(triisopropylsilylethynyl)benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-[4,7-bis(4-(2-ethylhexyl)thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-c]pyridine] (PTBDTPT), containing triisopropylsilylethynyl(TIPS)benzo[1,2-b:4,5-b']dithiophene as a donor is synthesized by Stille polymerization reaction. All the important photo physical prerequisites for organic field-effect transistor (OFET) application such as strong and broad optical absorption, thermal stability, and compatible HOMO-LUMO levels can be accomplished and combined on one macromolecule. Optical band gap of the polymer was found to be 1.61eV as calculated from its film onset absorption edge. The hole mobility of bottom gate OFET using the synthesized polymer as an active channel is found to be 1.92 X 10(-2)cmV(-1)s(-1) with the On/Off ratio of 25. The photophysical study suggests that PTBDTPT is promising candidate for future large area organic electronic applications.

Grain Size and Interface Dependence of Bias Stress Stability of n-Type Organic Field Effect Transistors.

The effect of grain size and interface dependence of bias stress stability of C60-based n-type organic field effect transistors (OFETs) has been studied. It has been realized that, with increasing grain size of C60, the bias stress induced threshold voltage shift can be controlled and this effect is mainly attributed to the mechanism of charge trapping at grain boundaries. It is further studied that the growth of C60 on the surface of parylene at elevated substrate temperature leads to the creation of radicals at the interface between the active layer and the gate dielectric. These radicals help to improve the bias stress stability of C60-based n-type OFETs. For achieving the bias stress stability, we have presented a procedure of creation of radicals at the interface between C60 and parylene in single gate OFETs instead of dual gate OFETs.

Surface Analytical Characterization of P3HT-Streptavidin Bilayers for Biosensing Applications

ABSTRACTUltrasensitive biosensors based on bottom gate organic field-effect transistors can be developed by depositing a functional biological (protein) interlayer directly on the silicon oxide gate dielectric and underneath the organic semiconductor film. However, the deposition methods for assembling the protein biological recognition layer can affect the biosensor analytical performances for the target analyte detection. Here, spin-coating and layer-by-layer techniques were considered as different approaches for streptavidin protein deposition. X-ray photoelectron spectroscopy (XPS) was systematically used in the non-destructive parallel angle resolved mode to characterize the multilayer device at each step of its assembly to gain information on elemental depth profiles. Scanning electron and scanning Helium ion microscopies gave information about stacked layer structure and morphology corroborating XPS results.

Anisotropic Strain Effect on Electron Transport in C60Organic Field Effect transistors

ABSTRACTMechanical flexibility is one of the key advantages of organic semiconducting films in applications such as wearable-electronics or flexible displays. The present study is aimed at gaining deeper insight into the effect of strain on charge transport properties of the organic semiconductor films. We have fabricated high performance C60top gate organic field effect transistors (OFET) on flexible substrates and characterized the devices by curling the substrates in concave and convex manner, to apply varying values of compressive and tensile strain, respectively. Electron mobility is found to increase with compressive strain and decrease with tensile strain. The observed strain effect is found to be strongly anisotropic with respect to the direction of flow of current. This observation on mobility is quantified using an Extended Gaussian Disorder Model (EGDM) for the hopping charge transport. We suggest that the observed strain dependence of the electron transport is dominated by a change in the effective charge hopping distance over the grain boundaries in polycrystalline C60films.

Influence of the Contact Thickness on Electrical Performance of Staggered and Planer <i>p</i>-Channel Organic Field Effect Transistors

The influence of contact thickness on electrical performance of bottom gate Organic Field Effect Transistor (BG-OFET) with staggered and planer structures is studied in this paper. Two dimensional device simulation is performed with identical dimensions for both devices which show a good agreement between simulated and measured results. Contact thickness is varied from 0nm to 20nm for planer and staggered structures. The electrical characteristics are strongly affected by the contact thickness variation. With increasing contact thickness, the threshold voltage shifts from negative to positive. The simulation results indicate that saturation current value of staggered structure is higher than that of planer. Although the current does not increase in staggered structure due to its increasing contact thickness, while the current in planer structure increases up to three times. However, current in planer is still below the current in staggered structure. The extracted field effect mobility and current on-off ratio at 20nm electrode thickness for staggered structure is 0.67 cm2/V.s and 108, respectively. It has been observed that the field effect mobility, threshold voltage, sub-threshold slope, transconductance and current on-off ratio can be modified by varying contact thickness. Analysis of the results clearly demonstrates the significance of controlling the contact thickness in planer and staggered OFETs. It even offers a way to control OFETs parameters.

Modeling the effect of top gate voltage on the threshold of a double gate organic field effect transistor

In this paper we have investigated theoretically the effect of top gate voltage on the threshold voltage of a double gate organic field effect transistor. We have solved the 1-D Poisson's equation in organic semiconductor active layer of this structure. Using the calculated local potential profile in the active layer, the total surface charge density was obtained. By considering the linear variation of this charge quantity with bottom gate voltage, the modulation of threshold voltage was studied as a function of different top gate voltages. It appears that the shielding effect of the top gate charges attenuates the effect of top gate voltage on the threshold voltage. In situations where shielding charges do not exist, the top gate voltage drastically affects the threshold voltage.

Atomic force microscopy analysis of morphology of thin pentacene films deposited on parylene-C and benzocyclobutene

This paper reports on an atomic force microscopy (AFM) investigation of the surface of pentacene films deposited onto parylene-C and benzocyclobutene (BCB), two polymers dedicated to organic field effect transistors (OFETs). A thorough grain analysis was carried out by power spectral density (PSD) on pentacene films of different thicknesses (ca. 15–60nm). PSD spectra of experimental AFM images were analyzed by using fractal, ABC and superstructure models. These approaches permitted to explain the difference of the pentacene morphology on the two substrates and to illustrate structural specificities related to change in the growth mode. Superstructures larger for the pentacene on BCB than for the pentacene on parylene were revealed. On both substrates, larger superstructures occurred for 30nm thick pentacene layers. This thickness also corresponded to the highest field effect mobility in top gate OFETs parylene/pentacene deposited on BCB. The superstructure model applied on the PSD curves showed that the increase of mobility for a 30nm thickness was not related to an increase of the grain size but to an increase of the island size.