Printable ammonia sensor based on organic field effect transistor

We report an organic field-effect transistor (OFET)-based sensor made from printable materials with an unusually high sensitivity of 0.5 ppm v/v for ammonia and with limit of detection on the order of 0.1 ppm v/v. The device developed has a polyethylene terephthalate (PET) substrate, bottom contacts, and poly (3,3^?$3\text{,}{3}^{?}$-didodecylquaterthiophene) (PQT-12) cast from 4 mg/mL cholorobenzene solution as active semiconductor. The fabrication process is simplified by replacing the gate electrode and dielectric deposition steps with the introduction of static charges on the back surface of the PET substrate by corona charging, a procedure that is adaptable to roll-to-roll processing. Hydrophobic polymers applied to the back surface stabilize this charge, providing evidence for their activity at that location. In the proposed sensor, these static charges are used as a static gate, reducing the OFET architecture to a chemiresistor. The sensor is selective for ammonia over common organic solvent vapors, and the response is generally reversible. The device also demonstrates memory behavior required for dosimetric sensors when kept at low temperature (4 °C to −30 °C). A converse response from an n-channel semiconductor is also reported.     

Humidity sensitive organic field effect transistor

This paper reports the experimental results for the humidity dependent properties of an organic field effect transistor.The organic field effect transistor was fabricated on thoroughly cleaned glass substrate,in which the junction between the metal gate and the organic channel plays the role of gate dielectric.Thin films of organic semiconductor copper phthalocynanine (CuPc) and semitransparent Al were deposited in sequence by vacuum thermal evaporation on the glass substrate with preliminarily deposited Ag source and drain electrodes.The output and transfer characteristics of the fabricated device were performed.The effect of humidity on the drain current,drain current-drain voltage relationship,and threshold voltage was investigated.It was observed that humidity has a strong effect on the characteristics of the organic field effect transistor.     

All-organic vertical transistor in an analogous n-semiconductor/metal/p-semiconductor trilayer structure

We report on the development and characterization of an all-organic vertical transistor, consisting of a p-type conjugated polymer, poly(bithiophene), as collector material, a poly(ethylene dioxythiophene)/poly(styrene sulfonate) layer as base material and a n-type molecule layer, Alq₃, as emitter material. The transistor is operated under direct bias in the common-emitter mode, being its operation based upon charge recombination of the injected majority carriers at the emitter–base interface. Experimental results have yielded current amplification factors up to 7. We also demonstrate that tunneling controls the transport characteristics of the device.     

Influence of oxygen on the parameters of a thin film copper phthalocyanine field effect transistor

The influence of oxygen on the electrical parameters of a copper phthalocyanine thin film field effect transistor was investigated by means of temperature‐modulated field effect spectroscopy. It was found that both the dark electrical conductivity and threshold voltage of the source–drain current versus gate voltage dependence were changed after oxygen exposure. Both effects can be effectively utilised for gas sensing. Copyright © 1999 John Wiley & Sons, Ltd.     

DNA detection with a water-gated organic field-effect transistor

A DNA sensor based on a water-gated organic field-effect transistor is described. The semiconductor is poly [3-(5-carboxypentyl)thiophene-2,5-diyl] onto which DNA probes are covalently grafted via NHS/EDC chemistry. Clear changes in the output characteristic of the device are observed upon DNA immobilization and after DNA hybridization. Experimental data point out the importance of the electrolyte Debye length that can screen negative DNA charges and impede transduction. For this reason, deionized water was used in order to increase the Debye length up to several hundreds of nanometers. In this case, a decrease in the off current was observed upon hybridization, whereas no significant change occurred when using saline solutions.     

Hexa-peri-hexabenzocoronene and diketopyrrolopyrrole based D-A conjugated copolymers for organic field effect transistor and polymer solar cells

Hexa-peri-hexabenzocoronene (HBC) is a disc-shaped conjugated molecule with strong π-π stacking property, high intrinsic charge mobility and good self-assembly property. But for a long time, the organic photovoltaic (OPV) solar cells based on HBC small organic molecules demonstrated low power conversion efficiencies (PCEs). In this study, a series of polymers named as PHBCDPPC20, PHBCDPPC8, PHBCDPPF and PHBCDPPDT were designed and synthesized through copolymerization of HBC with bulky mesityl substituents and strong electron-withdrawing diketopyrrolopyrrole (DPP) with different alkyl side chains and various π-bridges. Introduction of DPP unit into the HBC derivatives broadened the absorption spectra and lowered the band gaps. Bulky mesityl substituents attached to periphery of HBC prevented polymers from self-aggregating into too large domain size in the blend films of photovoltaic devices. The different π-bridges have significant effect on the structure conformation of the polymers. The polymer PHBCDPPDT with bithiophene π-bridges demonstrated the broadest absorption for its extensive π-conjugation and more coplanar conformation compared with the thiophene π-bridge one. PHBCDPPC20, PHBCDPPC8, PHBCDPPF and PHBCDPPDT gave field-effect hole mobilities of 1.35 × 10⁻³, 2.31 × 10⁻⁴, 2.79 × 10⁻⁴ and 8.60 × 10⁻³ cm² V⁻¹ s⁻¹, respectively. The solar cells based on these polymers displayed PCEs of 2.12%, 2.85%, 1.89% and 2.74%. To our knowledge, 2.85% is the highest PCE for the HBC-based photovoltaic materials till now.     

UV assisted non-volatile memory behaviour using Copper (II) phthalocyanine based organic field-effect transistors

In this report, we have demonstrated the optical non-volatile memory characteristics using CuPc OFET. The memory operation was comprehensively demonstrated with different programming conditions. It was found that the programming of CuPc OFET with an electric pulse at the gate terminal under UV-light photo-illumination compared to other programming conditions, could substantially increase the memory window due to massive charge trapping in the polymer electret layer, which causes shift in the device transfer characteristics from low-conduction state (“OFF state”, or logic 0) to high conduction state (“ON state”, or logic 1) at V_GS = 0V. From device operation at −50V, a memory window of greater than 45V could be achieved by applying a programming voltage of +70 V at the gate terminal under UV-light photo-illumination. Moreover, it was completely erased by applying −100 V at the gate terminal in dark.     

Fast detection of blood gases by solution gated organic field effect transistors

We characterize the electrochemical stability of the organic semiconductor Dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) in aqueous solutions. Electrochemical stability of DNTT in solution is validated by cyclic voltammetry and demonstrated by solution gating of DNTT organic field effect transistors (OFETs). Then, we investigate the response time of DNTT OFETs to ammonia, a common blood gas. For bare OFETs, the response time to ammonia is 1–2s only. The exact response time depends on the DNTT film morphology; the fastest response is obtained for pronounced 3D (Volmer-Weber) growth. By comparing OFETs with and without a semipermeable parylene-C encapsulation layer, the influence of the capping on the response time is investigated. An encapsulation layer of 86 nm prolongs the response time to 100s, indicating that parylene-C acts as an efficient diffusion barrier for ammonia.     

Progress of power field effect transistor based on ultra-wide bandgap Ga2O3 semiconductor material

As a promising ultra-wide bandgap semiconductor, gallium oxide(Ga_2O_3) has attracted increasing attention in recent years. The high theoretical breakdown electrical field(8 MV/cm), ultra-wide bandgap(～ 4.8 eV) and large Baliga's figure of merit(BFOM) of Ga_2O_3 make it a potential candidate material for next generation high-power electronics, including diode and field effect transistor(FET). In this paper, we introduce the basic physical properties of Ga_2O_3 single crystal, and review the recent research process of Ga_2O_3 based field effect transistors. Furthermore, various structures of FETs have been summarized and compared, and the potential of Ga_2O_3 is preliminary revealed. Finally, the prospect of the Ga_2O_3 based FET for power electronics application is analyzed.     

Bottom-contact small-molecule n-type organic field effect transistors achieved via simultaneous modification of electrode and dielectric surfaces

Low-voltage, n-type organic field effect transistors (OFETs) with simultaneously modified bottom-contact (BC) electrodes and dielectric were compared to their top-contact (TC) counterparts. The devices modified with 6-phenoxyhexylphosphonic acid (Ph6PA) self-assembled monolayer (SAM) showed similar performance, morphology, and contact resistance. Electron mobility of C₆₀ devices were 0.212 and 0.320 cm² V⁻¹ s⁻¹ and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) devices were 0.04 and 0.06 cm² V⁻¹ s⁻¹ for TC and BC devices, respectively. Low contact resistance between 11 and 45 kΩ cm was found regardless of device architecture or n-type semiconductor used. This work shows it is possible to fabricate solution processable low-voltage bottom-contact devices with performance that is similar or better than their top-contact counterparts without the addition of complex and time-consuming processing steps.     

High mobility multibit nonvolatile memory elements based organic field effect transistors with large hysteresis

High mobility multibit nonvolatile memory elements based on organic field effect transistors with a thin layer of polyquinoline (PQ) were reported. The devices show a high mobility of 1.5 cm² V⁻¹ s⁻¹ in the saturation region which is among the best reported for nonvolatile organic memory transistors. The multibit nonvolatile memory elements can be operated at voltage less than 100 V with good stability under continuous operation condition and show long retention time. The different initial scanning positive gate voltages to −100 V result in several ON states, while the scanning gate voltage from −100 V to positive voltage leads to same OFF state. The charge trapping model of electrons into the PQ layer was used to explain the origin of the memory properties.     

基于场效应管的光电式电流传感器

提出一种新型光电式电流传感器。利用电流取样电阻将被测电流转换为电压,并利用场效应管(FET)的转移特性和发光二极管(LED)将被测电流信号转换为光强度信号,再将光信号由塑料光纤(POF)传输到光电探测器(PD),可以实现直流电流(DC)、方波脉冲电流(PC)以及工频交流电流(AC)的光学传感。综合利用FET的转移特性和PD的开路电压,并合理选择FET的静态工作点,可以实现DC的线性传感。在0.03～17.00A范围内,DC测量的非线性误差低于0.44%;方波脉冲电流响应的延迟时间约为160ns。本文提出的传感器具有响应速度快、结构简单、成本低和可实现绝缘测量等优点。     

Air stable C60 based n-type organic field effect transistor using a perfluoropolymer insulator

Air stable n-type organic field effect transistors (OFETs) based on C₆₀ are realized using a perfluoropolymer as the gate dielectric layer. The devices showed the field-effect mobility of 0.049 cm²/V s in ambient air. Replacing the gate dielectric material by SiO₂ resulted in no transistor action in ambient air. Perfluorinated gate dielectric layer reduces interface traps significantly for the n-type semiconductor even in air.     

Fabrication of a planar water gated organic field effect transistor using a hydrophilic polythiophene for improved digital inverter performance

A planar water gated OFET (WG-OFET) structure is fabricated by patterning gate, source and drain electrodes on the same plane at the same time. Transistor output characteristics of this novel structure employing commercial regioregular poly(3-hexylthiophene) (rr-P3HT) as polymer semiconductor and deionized (DI) water as gate dielectric show successful field effect transistor operation with an on–off current ratio of 43 A/A and transconductance of 2.5 μA/V. These output characteristics are improved using P3HT functionalized with poly(ethylene glycol) (PEG) (P3HT-co-P3PEGT), which is more hydrophilic, leading to on–off ratio of 130 A/A and transconductance of 3.9 μA/V. Utilization of 100 mM NaCl solution instead of DI water significantly increases the on–off ratio to 141 A/A and transconductance to 7.17 μA/V for commercial P3HT and to 217 A/A and to 11.9 μA/V for P3HT-co-P3PEGT. Finally, transistors with improved transconductances are used to build digital inverters with improved characteristics. Gain of the inverters employing P3HT and P3HT-co-P3PEGT are measured as 2.9 V/V and 10.3 V/V, respectively, with 100 mM NaCl solution.     

基于量子模型的碳纳米管场效应晶体管电子输运特性

采用量子输运模型和NEGF理论,自洽求解薛定谔方程和泊松方程,对类MOS-碳纳米管场效应晶体管的电子输运特性建模。考察了沟道长度Lg为5~25 nm时,其对器件的导通电流、阈值电压、关态泄漏电流、电流开关比、亚阈值摆幅等性质的影响。结果表明:当Lg≥15 nm时,MOS-CNTFET没有量子尺寸效应;当Lg<15 nm时,器件出现短沟道效应;Lg<10 nm时短沟道效应更加明显。     

Low operational voltage and high performance organic field effect memory transistor with solution processed graphene oxide charge storage media

Low voltage organic field effect memory transistors are demonstrated by adapting a hybrid gate dielectric and a solution processed graphene oxide charge trap layer. The hybrid gate dielectric is composed of aluminum oxide (AlO_x) and [8-(11-phenoxy-undecyloxy)-octyl]phosphonic acid (PhO-19-PA) plays an important role of both preventing leakage current from gate electrode and providing an appropriate surface energy to allow for uniform spin-casting of graphene oxide (GO). The hybrid gate dielectric has a breakdown voltage greater than 6 V and capacitance of 0.47 μF/cm². Graphene oxide charge trap layer is spin-cast on top of the hybrid dielectric and has a resulting thickness of approximately 9 nm. The final device structure is Au/Pentacene/PMMA/GO/PhO-19-PA/AlO_x/Al. The memory transistors clearly showed a large hysteresis with a memory window of around 2 V under an applied gate bias from 4 V to −5 V. The stored charge within the graphene oxide charge trap layer was measured to be 2.9 × 10¹² cm⁻². The low voltage memory transistor operated well under constant applied gate voltage and time with varying programming times (pulse duration) and voltage pulses (pulse amplitude). In addition, the drain current (I_ds) after programming and erasing remained in their pristine state after 10⁴ s and are expected to be retained for more than one year.     

A novel sub 20 nm single gate tunnel field effect transistor with intrinsic channel forultra low power applications

We propose a nanoscale single gate ultra thin body intrinsic channel tunnel field effect transistor using the charge plasma concept for ultra low power applications. The characteristics of TFETs (having low leakage) are improved by junctionless TFETs through blending advantages of Junctionless FETs (with high on current). We further improved the characteristics, simultaneously simplifying the structure at a very low power rating using an InAs channel. We found that the proposed device structure has reduced short channel effects and parasitics and provides high speed operation even at a very low supply voltage with low leakage. Simulations resulted in I_OFF of ～ 9 × 10^-16A/μm, I_ON of ～20 μA/μm, I_ON/I_OFF of ～2 × 10¹⁰, threshold voltage of 0.057 V, subthreshold slope of 7 mV/dec and DIBL of 86 mV/V for PolyGate/HfO₂/InAs TFET at a temperature of 300 K, gate length of 20 nm, oxide thickness of 2 nm, film thickness of 10 nm, low-k spacer thickness of 10 nm and V_DD of 0.2 V.     

Holography and plasma oxidation for uniform nanoscale two dimensional channel formation of vertical organic field-effect transistors with suppressed gate leakage current

Vertical organic field-effect transistors (VOFETs) with nanoscale channel openings have been fabricated using pentacene as an active layer material. To achieve uniform nanoscale two-dimensional channel openings, a laser holography lithography has been introduced. Uniformly distributed and well-aligned holes with 250 nm diameter were successfully obtained with the laser holography lithography. VOFET devices with these channel openings have shown high on/off ratio of about 10³ without any further treatment. Gate leakage current was also decreased with an additional insulating layer generated on the gate electrode sidewall via plasma oxidation.     

基于BAlq的有机电致发光器件的磁效应

研究了ITO/NPB(40nm)/BAlq(60nm)/BCP(5nm)/LiF(0.8nm)/AI有机电致发光器件(OLED)的磁效应.实验结果表明,磁场在10mT时,器件的效率最大增加了34%,这一结果是由于三线态激子与三线态激子间的相互淬灭产生激发单线态激子从而使单线态激子比率增加,致使电致发光(EL)增强.当磁...     

Locking the morphology with a green,fast and efficient physical cross-linking approach for organic electronic applications

Molecular packing and stability play crucial roles in determining the performance of organic electronic devices. To optimize the morphology of active layer, thus to improve the performance, especially the stability of devices, cross-linking technique is a viable approach that has been extensively applied to stabilize the morphology. In this work, we demonstrate a green, fast and efficient physical approach using hyperthermal hydrogen induced cross-linking (HHIC) to lock the morphology of organic electronic materials. By controlling the kinetic energy of the hyperthermal hydrogen (H₂) molecules, we can efficiently cleave the C–H bonds and induce cross-linking in a conjugated polymer. The cross-linking can be achieved in 1 min at room temperature, and the cross-linked films have excellent thermal stability and high resistance to organic solvents. Organic field effect transistors fabricated with HHIC treated poly (3-hexylthiophene) (P3HT) has comparable charge carrier mobility and superb stability than the untreated devices. Compared to the conventional chemically driven cross-linking approach, HHIC does not require additional modification in molecular structure, and the fast and non-destructive advantages have high potential for wide applications of highly stable organic electronic devices.