Improved Electrical Properties of EHD Jet-Patterned MoS2 Thin-Film Transistors with Printed Ag Electrodes on a High-k Dielectric.

Electrohydrodynamic (EHD) jet printing is known as a versatile method to print a wide viscosity range of materials that are impossible to print by conventional inkjet printing. Hence, with the understanding of the benefits of EHD jet printing, solution-based MoS2 and a high-viscosity Ag paste were EHD jet-printed for electronic applications in this work. In particular, printed MoS2 TFTs with a patterned Ag source and drain were successfully fabricated with low-k silica (SiO2) and high-k alumina (Al2O3) gate dielectrics, respectively. Eventually, the devices based on Al2O3 exhibited much better electrical properties compared to the ones based on SiO2. Interestingly, an improvement of around one order of magnitude in hysteresis was achieved for devices after changing the gate insulator from SiO2 to Al2O3. In effect, the results of this work for the printed MoS2 and the printed Ag source and drains for TFTs demonstrate a new approach for jet printing in the fabrication of electronic devices.

Stacked printed MoS2 and Ag electrodes using electrohydrodynamic jet printing for thin-film transistors.

Transition metal dichalcogenide-based thin-film transistors (TFTs) have drawn intense research attention, but they suffer from high cost of materials and complex methods. Directly printed transistors have been in the limelight due to low cost and an environmentally friendly technique. An electrohydrodynamic (EHD) jet printing technique was employed to pattern both MoS2 active layer and Ag source and drain (S/D) electrodes. Printed MoS2 lines were patterned on a silicon wafer using a precursor solution and simple annealing, and the patterns were transferred on other SiO2 substrates for TFT fabrication. On top of the patterned MoS2, Ag paste was also patterned for S/D electrodes using EHD jet printing. The printed TFTs had a high on-off current ratio exceeding 105, low subthreshold slope, and better hysteresis behavior after transferring MoS2 patterns. This result could be important for practical TFT applications and could be extended to other 2D materials.

EHD-jet patterned MoS2on a high-kdielectric for high mobility in thin film transistor applications.

Solution synthesis of MoS2precursor followed by direct printing could be an effective way to make printed electronic devices. A linear MoS2pattern was obtained by an electrohydrodynamic (EHD)-jet printer with a sol-gel system without chemical vapor deposition. The morphology of the MoS2after a transfer process was maintained without wrinkles or cracking, resulting in a smooth surface compared with that of spin-coated films. EHD-jet printed MoS2was transferred onto high-kdielectric Al2O3and used as a semiconductor layer in thin film transistor (TFT) devices. The printed MoS2TFT has relatively good electrical characteristics, such as a linear field effect mobility, current ratio, and low subthreshold swing of 47.64 ± 2.99 cm2V-1s-1, 7.39 ± 0.12 × 106, and 0.7 ± 0.05 V decade-1, respectively. This technique may have promise for future applications.

Electrospray mechanism for quantum dot thin-film formation using an electrohydrodynamic jet and light-emitting device application.

A novel electrohydrodynamic (EHD) electrospray coating mechanism was proposed for the continuous fabrication of large-area quantum dot (QD) thin films for high-performance light-emitting diodes (LEDs). The size of QD droplets was systemically controlled using the stable EHD electrospray mode from a mixed solvent, which is a crucial factor for the formation of large and smooth QD thin films. The minimum amount of material consumption was achieved during the process by applying the unique coating system. A QD-LED device based on electrodeposited QDs showed a maximum luminance of 12,082 cd m-2, maximum current efficiency of nearly 4.0 cd A-1, and maximum EQE of 1.86%. This system demonstrates not only high reproducibility but could also pave the way for commercializing high-quality QD-LED devices.

Optimization of Quantum Dot Thin Films using Electrohydrodynamic Jet Spraying for Solution-Processed Quantum Dot Light-Emitting Diodes.

The electrohydrodynamic (EHD) jet spraying process is a good method for making quantum dot (QD) layers in light-emitting diodes (LEDs). However, controlling the morphology and large-scale fabrication of the QD layers are critical for realizing all-solution-processed QD-LEDs with high performance. Three spraying techniques were used with the EHD jet spraying technique: a big circular film method, a spiral-line method, and a straight-line method. These techniques were used to obtain QD films with good uniformity. The straight-line spray showed the most promise to obtain a uniform QD layer with large area, and QD-LEDs made with this method showed better performance with a low turn-on voltage of 3.0 V, a luminance of 7801 cd/m2, and a maximum current efficiency of 2.93 cd/A.

Patterning of High-Viscosity Silver Paste by an Electrohydrodynamic-Jet Printer for Use in TFT Applications.

Electrohydrodynamic (EHD) jet printing has a variety of benefits compared to conventional inkjet techniques, such as high resolution and the ability to work with high-viscosity pastes. In this work, Ag nanoparticles with 4000 cPs were chosen because they are printable on various substrates for electronic devices. The effects of additive on the high-viscosity Ag paste formulation were investigated, and pattern lines narrower than 100 µm were achieved by EHD-jet printing with an average sheet resistance of 0.027 Ω â–¡-1. Furthermore, solution-processed oxide TFTs were fabricated with EHD jet-printed Ag electrodes for the first time. The electrical properties obtained were a current ratio of 1.5 × 106, a mobility of approximately 1 cm2 V-1 s-1, a threshold voltage of 21.5 V, and a subthreshold slope of 3.05 V dec-1.

Chemical vapor deposition-free solution-processed synthesis method for two-dimensional MoS2 atomic layer films.

In this study, a solution-processed synthesis method was developed and successfully synthesized large-scale and uniform MoS2 thin films without using chemical vapor deposition. The MoS2 precursor solution was formulated by a sulfur-dissolving method to obtain uniform coating properties. MoS2 thin film was prepared by simple spin-coating and a one-step annealing method. The solution-synthesized MoS2 thin films were characterized to examine the 2H MoS2 structure. The various atomic layers could be controlled with the precursor concentrations. For example, two layers were obtained with 0.0070 M, three layers were obtained with 0.0125 M, and five layers were obtained with 0.025 M of MoS2 in the precursor solution, which were confirmed by scanning transmission electron microscopy.

Optimization of a Solution-Processed Quantum-Dot Light-Emitting-Diode with an Inverted Structure.

Colloidal quantum-dot based light-emitting diodes (QD-LEDs) are attractive for use in display devices because of the remarkable electrical and optical characteristics of colloidal quantum dots. An inverted structure may be one method to achieve the necessary multilayer device structures in QD-LEDs. In this study, each layer of an inverted-structure QD-LED was optimized. The effect of the solvent on the hole transfer layer was investigated, along with the effect of the concentration of the electron transfer layer, the effect of the co-solvent on the hole transfer layer, and the effect of the concentration and solvent of quantum dot layer. The quantum dots and ZnO NPs were synthesized as the emitting layer and carrier transporting layer using a solution-mediated process. The inverted QD-LED device showed a luminance of 3,762 cd/m², current efficiency of 1.86 cd/A, and EQE of 1.18%.

A mixed solution-processed gate dielectric for zinc-tin oxide thin-film transistor and its MIS capacitance.

Solution-processed gate dielectrics were fabricated with the combined ZrO2 and Al2O3 (ZAO) in the form of mixed and stacked types for oxide thin film transistors (TFTs). ZAO thin films prepared with double coatings for solid gate dielectrics were characterized by analytical tools. For the first time, the capacitance of the oxide semiconductor was extracted from the capacitance-voltage properties of the zinc-tin oxide (ZTO) TFTs with the combined ZAO dielectrics by using the proposed metal-insulator-semiconductor (MIS) structure model. The capacitance evolution of the semiconductor from the TFT model structure described well the threshold voltage shift observed in the ZTO TFT with the ZAO (1:2) gate dielectric. The electrical properties of the ZTO TFT with a ZAO (1:2) gate dielectric showed low voltage driving with a field effect mobility of 37.01 cm(2)/Vs, a threshold voltage of 2.00 V, an on-to-off current ratio of 1.46 × 10(5), and a subthreshold slope of 0.10 V/dec.

Recent advances in salivary cancer diagnostics enabled by biosensors and bioelectronics.

There is a high demand for a non-invasive, rapid, and highly accurate tool for disease diagnostics. Recently, saliva based diagnostics for the detection of specific biomarkers has drawn significant attention since the sample extraction is simple, cost-effective, and precise. Compared to blood, saliva contains a similar variety of DNA, RNA, proteins, metabolites, and microbiota that can be compiled into a multiplex of cancer detection markers. The salivary diagnostic method holds great potential for early-stage cancer diagnostics without any complicated and expensive procedures. Here, we review various cancer biomarkers in saliva and compare the biomarkers efficacy with traditional diagnostics and state-of-the-art bioelectronics. We summarize biomarkers in four major groups: genomics, transcriptomics, proteomics, and metabolomics/microbiota. Representative bioelectronic systems for each group are summarized based on various stages of a cancer. Systematic study of oxidative stress establishes the relationship between macromolecules and cancer biomarkers in saliva. We also introduce the most recent examples of salivary diagnostic electronics based on nanotechnologies that can offer rapid, yet highly accurate detection of biomarkers. A concluding section highlights areas of opportunity in the further development and applications of these technologies.

Electrohydrodynamic jet-printed zinc-tin oxide TFTs and their bias stability.

Zinc-tin oxide (ZTO) thin-film transistors (TFTs) were fabricated using an electrohydrodynamic-jet (EHD-jet) printing technique at annealing temperatures ranging from 300 to 500 °C. An EHD-jet-printed ZTO active layer was patterned with a 60 µm width using a 100 µm inner diameter metal nozzle. The electrical properties of an EHD-jet-printed ZTO TFT showed a mobility of 9.82 cm(2)/(V s), an on-off current ratio of 3.7 × 10(6), a threshold voltage of 2.36 V, and a subthreshold slope of 0.73 V/dec at 500 °C. Significantly improved properties were obtained compared to the spin-coated and inkjet-printed ones. Better hysteresis behavior and positive bias stability of the ZTO TFTs were also achieved using EHD-jet printing technology.

Materials and optimized designs for human-machine interfaces via epidermal electronics.

Thin, soft, and elastic electronics with physical properties well matched to the epidermis can be conformally and robustly integrated with the skin. Materials and optimized designs for such devices are presented for surface electromyography (sEMG). The findings enable sEMG from wide ranging areas of the body. The measurements have quality sufficient for advanced forms of human-machine interface.

Inkjet-printed In(2)O(3) thin-film transistor below 200 °C.

High-performance In2O3 thin-film transistors could be prepared by an inkjet-printing method below 200 °C with a single precursor and solvent formulation. The self-combustion reaction took place with the electrical properties of In2O3 at a low temperature of 147 °C, which was confirmed by X-ray photoelectron spectroacopy and thermal analysis. The electrical properties after postannealing at 200 °C were as follows: a mobility of 3.98 cm(2)/V·s, a threshold voltage of 1.83 V, a subthreshold slope of 0.4 V/dec, and an on-to-off current ratio of 10(8), which are the best properties by an inkjet process thus far. The positive bias stability was much improved by postannealing, and good negative bias stability was obtained.

Solution-processed flexible ZnO transparent thin-film transistors with a polymer gate dielectric fabricated by microwave heating.

We report the development of solution-processed zinc oxide (ZnO) transparent thin-film transistors (TFTs) with a poly(2-hydroxyethyl methacrylate) (PHEMA) gate dielectric on a plastic substrate. The ZnO nanorod film active layer, prepared by microwave heating, showed a highly uniform and densely packed array of large crystal size (58 nm) in the [002] direction of ZnO nanorods on the plasma-treated PHEMA. The flexible ZnO TFTs with the plasma-treated PHEMA gate dielectric exhibited an electron mobility of 1.1 cm(2) V(-1) s(-1), which was higher by a factor of approximately 8.5 than that of ZnO TFTs based on the bare PHEMA gate dielectric.