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

Ion migration in p-type perovskite MAPbI3 films under an electric field and thin-film transistor device failure

This study demonstrated a dynamic analysis to investigate the ion migration in p-type perovskite MAPbI3 films under an electric field, revealing its detrimental effects on the electrical performance of MAPbI3-based devices. An additive strategy was proposed to suppress ion migration, thereby facilitating the fabrication of high-performance MAPbI3-based devices.

Influence of Volatile Organic Compound Adsorption on the Characteristics of Organic Field-Effect Transistors and Rules for Gas-Sensing Measurements

Owing to the advantages of organic field-effect transistors (OFETs) in the versatility of organic synthesis, multiparameter measurement, and signal amplification, sensors based on OFETs have received increasing attention for detecting volatile organic compounds (VOCs). However, false device operation and gas-sensing measurements often occur to vitiate the advantages of OFETs and even output error gas-sensing signals. In this work, by experimentally and theoretically studying the effects of VOC adsorption on the operational characteristics of the OFET, the proper operations of OFETs in gas-sensing measurements were clarified. The multiparameter measurements of OFETs showed that the source-drain current was the optimized parameter for achieving high responsivity, and other OFET parameters could be used for fingerprint analysis. By operating OFETs in the near-threshold region, the amplification effect was switched to enhance the responsivity by orders of magnitude to VOCs, while in the overthreshold region, the OFETs had a low signal-to-noise ratio. Besides, a counteraction effect and an uncertainty effect were discovered, leading to error gas-sensing signals. A theoretical study was carried out to reveal the dependency of the gas-sensing properties of OFETs on VOC adsorption. A series of rules were proposed for guiding the measurements of OFET sensors by taking full advantage of transistors in gas-sensing applications.

Dual-Gate Organic Thin-Film Transistor and Multiplexer Chips for the Next Generation of Flexible EG-ISFET Sensor Chips

Ion-sensitive field-effect transistors (ISFETs) are used as elementary devices to build many types of chemical sensors and biosensors. Organic thin-film transistor (OTFT) ISFETs use either small molecules or polymers as semiconductors together with an additive manufacturing process of much lower cost than standard silicon sensors and have the additional advantage of being environmentally friendly. OTFT ISFETs' drawbacks include limited sensitivity and higher variability. In this paper, we propose a novel design technique for integrating extended-gate OTFT ISFETs (OTFT EG-ISFETs) together with dual-gate OTFT multiplexers (MUXs) made in the same process. The achieved results show that our OTFT ISFET sensors are of the state of the art of the literature. Our microsystem architecture enables switching between the different ISFETs implemented in the chip. In the case of sensors with the same gain, we have a fault-tolerant architecture since we are able to replace the faulty sensor with a fault-free one on the chip. For a chip including sensors with different gains, an external processor can select the sensor with the required sensitivity.

Improving Environmental and Operational Stability of Polymer Field-Effect Transistors by Doping with Tetranitrofluorenone

Operational instability of organic field-effect transistors (OFETs) is one of the key limitations for applications of printed electronics. Environmental species, especially oxygen and water, unintentionally introduced in the OFET channel, can act as either dopants or traps for charge carriers, affecting the electrical characteristics and stability of devices. Here, we report that intentional doping of the benchmark p-type semiconducting polymer (DPP-DTT) with 2,4,5,7-tetranitrofluorenone (TeNF) markedly improves the operational and environmental stability of OFETs. Electrical interrogation of DPP-DTT OFETs in various environments and at variable temperatures shows suppression of electron-induced traps and increase of hole mobility in oxygen-rich environment, while the water molecules act as traps for positive charge carrier, reducing the hole mobility and significantly shifting the threshold voltage. Doping of DPP-DTT with TeNF suppresses both effects, resulting in environmentally independent performance and superior long-term stability of unencapsulated devices for up to 4 months in ambient air. Furthermore, the doped OFETs exhibit dramatically reduced hysteresis and bias-stressed current drop. Such improvement of the environmental and operational stabilities is ascribed to the mitigation of traps induced by the injected minority carrier (electrons) and the reduction of the majority carrier (hole) traps in doped polymer films due to enhanced microstructural order.

Enhanced Organic Thin-Film Transistor Stability by Preventing MoO3 Diffusion with Metal/MoO3/Organic Multilayered Interface Source-Drain Contact

The source-drain electrode with a MoO₃ interfacial modification layer (IML) is considered the most promising method to solve electrical contact issues impeding organic thin-film transistors (OTFTs) from commercialization. However, this method raises many concerns because MoO₃ might diffuse into organic materials, which causes device instability. In this work, we observed a significant device stability degradation by damaging on/off switching performance caused by MoO₃ diffusion. To prevent the MoO₃ diffusion, a source-drain electrode with a multilayered interface contact (MIC) consisting of a top-down stack of metal, MoO₃ IML, and organic buffer layer (OBL) is proposed. In the MIC device, the MoO₃ IML serves well for its intended functions of reducing contact resistance and suppressing minority carrier injection to the OTFT channel. The inclusion of OBL to the MIC helps block MoO₃ diffusion and thereby leads to better device stability and an increased on/off ratio. Through combinations with several organic compounds as a buffer layer, the MoO₃ diffusion related electrical behaviors of OTFTs are systematically studied. Key parameters related to MoO₃ diffusion such as the Fick coefficient and bias-stress stability such as carrier trapping time are extracted from numerical device analysis. Finally, we summarize a general rule of material selection for making robust source-drain contact.

Doped Vertical Organic Field-Effect Transistors Demonstrating Superior Bias-Stress Stability

Bias-stress stability is essential to the practical applications of organic field-effect transistors (OFETs), yet it remains a challenge issue in conventional planar OFETs. Here, the feasibility of achieving high bias-stress stability in vertical structured OFETs (VOFETs) in combination with doping techniques is demonstrated. VOFETs with silver nanowires as source electrodes are fabricated and the device performance is optimized by understanding the influence of device parameters on performance. Then, the bias-stress stability of the optimized PDVT-10 VOFETs is investigated and found to be superior to the corresponding planar OFETs, which is attributed to reduced trapping effects of gate dielectrics in the VOFETs. Moreover, the bias-stress stability can be further improved by doping PDVT-10 to passivate bulk traps. Consequently, the characteristic time of doped PDVT-10 VOFETs extracted from stretched exponential equation is found to be over four times larger than that of the planar PDVT-10 OFETs under the same bias-stress conditions. These results present the promising applications of VOFETs as well as an effective strategy to achieve highly bias-stress stable OFETs.