Channel Organic Transistors Research Articles

Potential Application of Organic Electronics in Electrical Sensing of Insects and Integrated Pest Management towards Developing Ecofriendly Replacements for Chemical Insecticides.

Synthetic insecticides are widely used against plant pest insects to protect the crops. However, many insecticides have poor selectivity and are toxic also to beneficial insects, animals, and humans. In addition, insecticide residues can remain on fruits for many days, jeopardizing food safety. For these reasons, a reusable, low-cost electronic trap that can attract, detect, and identify, but attack only the pest while leaving beneficial insects unharmed could provide a sustainable, nature-friendly replacement. Here, for the first time, research results are presented suggesting the great potential and compatibility of organic electronic devices and technologies with pest management. Electrical characterizations confirm that an insect's body has relatively high dielectric permittivity. Adaptive memcapacitor circuits can track the impedance change for insect detection. Other experiments show that printed polymer piezoelectric transducers on a plastic substrate can collect information about the weight and activity of insects for identification. The breakdown voltage of most insects´ integument is measured to be <200V. Long channel organic transistors easily work at such high voltages while being safe to touch for humans thanks to their inherent low current. This feasibility study paves the way for the future development of organic electronics for physical pest control and biodiversity protection.

Unidirectionally Aligned Donor–Acceptor Semiconducting Polymers in Floating Films for High‐Performance Unipolar n‐Channel Organic Transistors

AbstractThe orientational control of semiconducting polymers (SCPs) in floating films offers several advantages over conventional solution‐processing methods for device fabrication, and the unidirectional floating film transfer method (UFTM) has been applied to fabricate large‐area oriented p‐type SCP films. Here, UFTM can be used to prepare high‐performance n‐type SCP films of P(NDI2OD‐T2) is reported. A strong correlation between the degree of polymer orientation and the solvent used for the preparation of P(NDI2OD‐T2) floating films is observed. In particular, the size of the nanofibers aligned along the orientation direction prepared using chloroform is dramatically increased by adding a small amount of chlorobenzene. Microstructural characterization reveals that the P(NDI2OD‐T2) floating films are uniaxially aligned with edge‐on orientation, whereas the spin‐coated films are isotropic with face‐on orientation. Notably, the floating films of P(NDI2OD‐T2) prepared with solvent blending have higher electron mobility with ambipolar‐like device characteristics and high threshold voltage (VTH) of ≈25 V. Finally, using the one‐step immersion process, the introduction of an interlayer of hexa(ethylene glycol)‐dithiol between the source/drain contacts and P(NDI2OD‐T2) film results in a drastic improvement in device, giving unipolar n‐channel transistor characteristics with a VTH of ≈0 V, on/off ratio of &gt;105, and mobility reliability factor of almost 100%.

Submicrometer‐Channel Organic Transistors with MHz Operation Range on Flexible Substrates by a Low‐Resolution Fabrication Technique

AbstractIn this paper, the development of a simple and reproducible approach for the fabrication of n‐type organic field‐effect transistors with a 350 nm‐long channel on flexible substrates is reported. The critical feature of the device, the channel length, is obtained using a self‐alignment process that exploits the vertical step of a plasma‐etched thin Parylene C layer, according to the so‐called step‐edge architecture. The fabricated devices can operate in continuous mode and show an average and maximum transition frequency of 2.5 MHz and 5.5 MHz, respectively. The possibility of easily obtaining high‐performing, short channel organic transistors on flexible substrates, without the use of expensive and high‐resolution techniques, represents an interesting step toward the miniaturization of flexible circuits in the field of large‐area organic electronics.

Label free detection of miRNA-21 with electrolyte gated organic field effect transistors (EGOFETs)

We report a dual gate/common channel organic transistor architecture designed for quantifying the concentration of one of the strands of miRNA-21 in solution. The device allows one to measure the differential response between two gate electrodes, viz. one sensing and one reference, both immersed in the electrolyte above the transistor channel. Hybridization with oligonucleotide in the picomolar regime induces a sizable reduction of the current flowing through the transistor channel. The device signal is reported at various gate voltages, showing maximum sensitivity in the sublinear regime, with a limit of detection as low as 35 pM. We describe the dose curves with an analytical function derived from a thermodynamic model of the reaction equilibria relevant in our experiment and device configuration, and we show that the apparent Hill dependence on analyte concentration, whose exponent lies between 0.5 and 1, emerges from the interplay of the different equilibria. The binding free energy characteristic of the hybridization on the device surface is found to be approximately 20% lower with respect to the reaction in solution, hinting to partially inhibiting effect of the surface and presence of competing reactions. Impedance spectroscopy and surface plasmon resonance (SPR) performed on the same oligonucleotide pair were correlated to the electronic current transduced by the EGOFET, and confirmed the selectivity of the biorecognition probe covalently bound on the gold surface.

Thermal stability of organic transistors with short channel length on ultrathin foils

We demonstrate an effective design for fabrication of short channel organic transistors (<3μm channel length) on ultrathin 1μm thick substrates that exhibit excellent thermal stability. For short channel transistors, we demonstrate durability up to 170°C, with a theoretical cutoff frequency above 100kHz, and stable performance in cyclic heating tests up to 120°C. We fabricate inverter circuits to investigate their behavior upon heating and show that inverter gain can be improved by 150%. Device performance and topology changes were systematically analyzed after annealing steps to gain better understanding on the mechanism behind the performance change. This report on the thermal stability of short channel transistors on ultrathin films shows good durability at elevated temperatures and paves the way for high frequency imperceptible electronics.

Nanoimprint assisted inkjet printing to fabricate sub-micron channel organic field effect transistors

Solution processed poly(3-hexylthiophene) organic field effect transistors with channel lengths down to 750nm were fabricated by nanoimprint assisted inkjet printing. The nanoimprint lithography was used to define sub-micron channels into a resist because of its high resolution. A silver-containing ink was inkjet-printed onto a pre-patterned resist layer to form a metallic film, which acts as source and drain electrodes after lift-off. This process replaces the expensive vacuum evaporation of gold electrodes. The transistor short channel effect was suppressed successfully by constant field downscaling. However, samples with inkjet-printed silver electrodes have limited current density. They also have lower effective charge mobility due to higher charge injection barrier, as well as the rough metal surface. Gold nanoparticles were added into the silver ink to modify its work function and therefore reduce the contact resistance between electrodes and polymer. This emphasizes the importance of the metal-semiconductor contact especially for short channel organic transistors.

Micro-imprinted prism substrate for self-aligned short channel organic transistors on a flexible substrate

Using a simple micro-imprinting process on flexible substrates, we demonstrate fabrication of self-aligned short channel organic thin film transistors (OTFTs) with significantly reduced parasitic capacitance. The surface topology resulting from the imprinted prism-like structures enables accurate alignment of both the gate and source-drain electrodes. The parasitic overlap capacitance was reduced by 80%, which enables twice higher transition frequency (fT = 10.1 kHz) compared with conventional top-contact OTFT devices. The prism-OTFTs were applied to both p-type (pentacene) and n-type (C60) organic semiconductors to implement low voltage complementary inverters.

High-performance short channel organic transistors using densely aligned carbon nanotube array electrodes

We report high-performance short channel pentacene field effect transistor (FET) using carbon nanotube aligned array electrodes. The devices show field effect mobility of up to 0.65 cm2/Vs and current on-off ratio of up to 1.7 × 106, which is the best for sub-micron pentacene FETs. The calculated cutoff frequency (fc) of the devices is up to 211 MHz which is among the best reported fc for organic transistors. The high performance of our short channel FET is attributed to improved charge injections from the aligned array carbon nanotube electrodes into the pentacene.

Top-Contact Organic Thin-Film Transistors Fabricated by Picoliter and Sub-Femtoliter Inkjets

Employing inkjet technologies with picoliter and sub-femtoliter droplet volumes, we have successfully manufactured high-quality top-contact organic thin-film transistors. Silver fine lines were directly patterned by two inkjet systems on the pentacene channel layer without the need for any photolithographic pre patterning or any surface pretreatment. The lines were calcinated at 130 {degree sign}C to form source and drain electrodes. The minimum width of silver lines was 25 µm with the picoliter inkjet system, while that was 2µm with the sub-femtoliter inkjet system. We have manufactured p-type channel and n-type channel organic transistors with source/drain contacts prepared by the sub-femtoliter inkjet to fabricate complimentary inverter circuits.

Current transport in short channel top-contact pentacene field-effect transistors investigated with the selective molecular doping technique

The contact doping profile is controlled in the top-contact configuration to clarify a transistor operation based on a current injection process from the metal contact to the organic channel in a submicron channel pentacene field-effect transistor. The molecular doping in the pentacene film underneath the metal contact, in which a thin layer of iron (III) chloride was introduced, drastically changes transistor characteristics. The doping profile control directly revealed the resistive part for current injection. A model to explain the saturation behavior of the top-contact short channel organic transistor is presented.

Novel applications of organic based thin film transistors

An overview of the main developments in the field of organic based thin film transistors is presented, and their operation is described, both when n-type and p-type channel organic transistor materials are employed as active layers. Perspective applications in gas sensors are discussed as well.