Source Electrodes Research Articles

Temperature dependence of carrier mobility in hydrogenated germanane field-effect transistor with various electrode materials

Germanane, a layered material in which single-layer germanium is terminated by hydrogen atoms, was utilized as a channel material in back-gate-type FETs. Titanium, aluminum, and nickel were used as source and drain electrodes of FETs, and most of the fabricated FETs showed ambipolar characteristics. Among the three electrode materials, nickel was the best for high field-effect carrier mobility. It was also found that the mobility changes with temperature T according to the T −3/2 law below 273 K, whereas the mobility change deviates from the law of T −3/2 above 293 K.

Ultrasensitive immunosensor for monitoring of CA 19-9 pancreatic cancer marker using electrolyte-gated TiS3 nanoribbons field-effect transistor

Measuring CA 19-9 antigen level is critical for early diagnosis of pancreatic cancer, monitoring the treatment process, and predicting disease recurrence. The purpose of this research is to assess the application of novel few-layered TiS3 nanoribbons material as a channel material in electrolyte-gated field-effect transistor immunosensor for rapid detection of CA 19-9 antigen as a cancer marker. Accordingly, TiS3 nanoribbons were produced through liquid-phase exfoliation of as-synthesized TiS3 whiskers in N, N-dimethylformamide. Then, dispersed TiS3 nanoribbons were drop cast onto the FET surface to form an active channel material between source and drain electrodes. Subsequently, the channel surface was modified by utilizing 1-naphthylamine (NA) and glutaraldehyde (GA) to strengthen the binding of monoclonal antibody 19-9 to TiS3 nanoribbons. Spectroscopic and microscopic methods were utilized for comprehensive characterizations. Electrical characterization of electrolyte-gated TiS3 nanoribbons field-effect transistor represented a depletion-mode n-type behavior with field-effect mobility of 0.059 cm2/Vs, current on/off ratio of 10.88 and subthreshold swing (SS) of 450.9 mV/decade. With increasing in CA 19-9 antigen concentration from 1.0 × 10−12 U/mL to 1.0 × 10−5 U/mL, a decrease in the drain current occurred with high sensitivity of 0.04 μA/decade and a detection limit of 1.3 × 10−13 U/mL. Additionally, the proposed TiS3 nanoribbons FET immunosensor exhibited outstanding selectivity, and its good performance was compared with an enzyme-linked immunosorbent assay (ELISA) for spiked real human serum samples. The good and satisfactory obtained results of the proposed immunosensor suggest that the developed platform can be a superb candidate for cancer diagnosis and therapeutic monitoring.

A Ferroelectric Domain-Wall Transistor

On the basis of novel properties of ferroelectric conducting domain walls, the domain wall nanoelectronics emerges and provides a brand-new dimension for the development of high-density, high-speed and energy-efficient nanodevices. For in-memory computing, three-terminal devices with both logic and memory functions such as transistors purely based on ferroelectric domain walls are urgently required. Here, a prototype ferroelectric domain-wall transistor with a well-designed coplanar electrode geometry is demonstrated on epitaxial BiFeO3 thin films. For the logic function, the current switching between on/off states of the transistor depends on the creation or elimination of conducting domain walls between drain and source electrodes. For the data storage, the transistor can maintain nonvolatile on/off states after the write/erase operations, providing an innovative approach for the development of the domain wall nanoelectronics.

Solid‐State Homojunction Electrochemical Transistors and Logic Gates on Plastic

AbstractOrganic electrochemical transistors (OECTs) have attracted significant attention due to their unique ionic–electronic charge coupling, which holds promise for use in a variety of bioelectronics. However, the typical electronic components of OECTs, such as the rigid metal electrodes and aqueous electrolytes, have limited their application in solid‐state bioelectronics that requires design flexibility and a variety of form factors. Here, the fabrication of a solid‐state homojunction OECT consisting of a pristine polymer semiconductor channel, doped polymer semiconductor electrodes, and a solid electrolyte is demonstrated. This structure combines the photo‐crosslinking of all of the electronic OECT components with the selective doping of the polymer semiconductor. Three Lewis acids (gold (III) chloride (AuCl3), iron (III) chloride (FeCl3), and copper (II) chloride (CuCl2) ) are utilized as dopants for the metallization of the polymer semiconductor. The AuCl3‐doped polymer semiconductor with an electrical conductivity of ≈100 S cm−1 is successfully employed as the source, drain, and gate electrodes for the OECT, which exhibited a high carrier mobility of 3.4 cm2 V−1 s−1 and excellent mechanical stability, with negligible degradation in device performance after 5000 cycles of folding at a radius of 0.1 mm. Homojunction OECTs are then successfully assembled to produce NOT, NAND, and NOR logic gates.

Anisotropic etching by electrospray for reduction in parasitic resistance of organic field-effect transistors

Productive manufacturing that uses a roll-to-roll process, called printed electronics, is highly demanded for low-cost, large-area, and high-speed fabrication of organic devices. However, although most studies on the printing process have been focused on the deposition of films, few studies are reported on solution methods for anisotropic etching that are compatible with the printing process. Studying anisotropic etching by using a wet process is a matter of great importance for the further development of printed electronics. Here, we conduct anisotropic etching by using an electrospray method, one of the wet processes, on an underlying active layer beneath source and drain electrodes and demonstrate a reduction in the parasitic resistance of organic field-effect transistors. The same equipment for the etching as the deposition of films was consistently used. Therefore, this study will pave the way for sophisticating printed electronics. • TIPS pentacene/PMMA blend films and PMMA etch masks were prepared by ESD. • We conducted anisotropic etching by using an electrospray method (a wet process). • Underlying TIPS pentacene beneath source/drain electrodes was selectively etched. • We demonstrated a clear reduction in the parasitic resistance of top-contact OFETs. • The same ESD system for the etching as the deposition of films was consistently used.

Selective and non-selective modification of electrodes in organic thin film transistors by self-assembled monolayers

During the engineering of OTFT electrodes with dipolar molecular films, non-intentional modification of the common OTFT substrate can occur, affecting the crystallinity of the organic semiconductor and, consequently, the device performance.

Experimental Demonstration of Coupled Sub-Harmonic Injection Locked Oscillation in Micro-Electro-Mechanical Relays

The voltage dependence of DC-driven self-sustaining oscillation behavior of a micro-electro-mechanical (MEM) relay makes it possible to influence the phase of oscillation by coupling the gate or body, source and/or drain electrodes to other voltage signals. In this work, sub-harmonic injection locking and synchronized oscillation of electrically coupled MEM relays are experimentally demonstrated, representing a significant milestone toward achieving a MEM-oscillator-based Ising machine that can solve combinatorial optimization problems much more efficiently than conventional computer architectures.

Effects of Asymmetric Source-Drain Electrodes and Their Modifications on the Operation of Organic Phototransistors

Asymmetric source and drain (S-D) electrodes and their interfacial modifications have significant effects on the charge injection and transport in organic field-effect transistors, however their effects on the operation and performance of organic phototransistors (OPTs) are unknown. Herein, OPTs with symmetric (Ag-Ag, Au-Au) and asymmetric (Au-Ag, Au-bathocuproine (BCP)/Ag, Au/MoO3-BCP/Ag) S-D electrodes were fabricated and their performances were investigated. The results demonstrated that the devices with asymmetric S-D electrodes are superior than their counterparts with symmetric S-D electrodes. Among the three devices with asymmetric S-D electrodes Au-BCP/Ag device exhibits the highest photo responsivity of 36.6 A/W and external quantum efficiency of 7000%, meanwhile Au-BCP/Ag and Au/MoO3-BCP/Ag device exhibit significantly larger specific detectivity than Au-Ag device. The result gives an important guideline for designing high performance OPTs.

Electrochemically decorated gold nanoparticles on CVD graphene ChemFET sensor for the highly sensitive detection of As(III)

In this paper, we report a novel reusable receptor-free chemically sensitive field-effect transistor (ChemFET) sensor for the sensitive detection of As(III) using electrochemical doping of Au nanoparticles (AuNPs)-chemical vapour deposition (CVD) graphene (Gr) sensing film (AuNPs-Gr). The sensor consists of a single-gap gold electrode and a single layer of CVD graphene as a conducting/sensing channel decorated with a thin layer of electrochemically deposited AuNPs to catalyze the electroreduction of As(III) ions onto the sensing channel. A new detection strategy was proposed by measuring the resistance change rate of the AuNPs-Gr sensing channel modified between the source electrode and drain electrode, wherein the resistance change was caused by the electrochemical doping of As(0). The results indicated that the electrochemical doping of As(0) onto the sensing channel led to an increase in resistance through the doping interaction among As(0), AuNPs and graphene, enabling the proposed sensor to have an extraordinary detection performance with a high sensitivity. Moreover, the proposed sensor can be recycled by removing the As(0) deposited on the sensing film with the aid of a simple electrochemical oxidization process. Additionally, the mechanism of the sensing strategy based on the electrochemical n-doping of As(0) into the AuNPs-Gr sensing film was investigated using a top liquid gate electrode. The As(III) concentration detected by the AuNPs-Gr ChemFET sensor was as low as 0.001 μg/L, demonstrating that such sensors with a compatible sensing strategy can be used to detect As(III) with high sensitivity, easy fabrication, fast response and can be recycled.

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.

Mechanically robust stretchable semiconductor metallization for skin-inspired organic transistors.

Despite recent remarkable advances in stretchable organic thin-film field-effect transistors (OTFTs), the development of stretchable metallization remains a challenge. Here, we report a highly stretchable and robust metallization on an elastomeric semiconductor film based on metal-elastic semiconductor intermixing. We found that vaporized silver (Ag) atom with higher diffusivity than other noble metals (Au and Cu) forms a continuous intermixing layer during thermal evaporation, enabling highly stretchable metallization. The Ag metallization maintains a high conductivity (>104 S/cm) even under 100% strain and successfully preserves its conductivity without delamination even after 10,000 stretching cycles at 100% strain and several adhesive tape tests. Moreover, a native silver oxide layer formed on the intermixed Ag clusters facilitates efficient hole injection into the elastomeric semiconductor, which transcends previously reported stretchable source and drain electrodes for OTFTs.

N-Type Printed Organic Source-Gated Transistors with High Intrinsic Gain.

Source-gated transistors (SGTs) are emerging devices enabling high-gain single-stage amplifiers with low complexity. To date, the p-type printed organic SGT (OSGT) has been developed and showed high gain and low power consumption. However, complementary OSGT circuits remained impossible because of the lack of n-type OSGTs. Here, we show the first n-type OSGTs, which are printed and have a high intrinsic gain over 40. A Schottky source contact is intentionally formed between an n-type organic semiconductor, poly{[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (N2200), and the silver electrode. In addition, a blocking layer at the edge of the source electrode plays an important role to improve the saturation characteristics and increase the intrinsic gain. Such n-type printed OSGTs and complementary circuits based on them are promising for flexible and wearable electronic devices such as for physiological and biochemical health monitoring.

Self-Aligned Organic Metal–Semiconductor Field-Effect Transistor

We propose the design and fabrication of a coplanar electrode structure for an organic metal–semiconductor field-effect transistor (OMESFET), with the gate electrode self-aligned between the source and drain electrodes. We first used nanoimprint lithography (NIL) to define a channel area of the device on a patterned metal, and then used chemical wet etching to create the source and drain electrodes by removing the metal in the channel area. After the wet etching, the gate electrode was deposited in the channel area. The organic semiconductor was then deposited to cover the patterned electrodes. The rectifying response and the device characteristics prove that the self-aligned device is a functional OMESFET. In this experiment, we also demonstrated that the self-aligned OMESFET has lower driving voltages and smaller subthreshold swing (SS) than that of a conventional organic metal–insulator–semiconductor field-effect transistor (OMISFET). Compared with the most common OMESFET structure, this self-aligned coplanar structure effectively eliminates the overlapping area between the gate and source/drain electrodes commonly seen in currently reported OMESFETs, which means that this self-aligned device structure reduces the parasitic capacitance, theoretically allowing the transistor to have a higher cutoff frequency. These features render our proposed OMESFET devices more favorable for low-power and high-frequency organic circuit applications.

Electret-Based Vertical Organic Synaptic Transistor With MXene for Neural Network-Based Computation

Organic synaptic transistors with excellent solution processability and biocompatibility have emerged as artificial electronic synapses. Regular organic synaptic transistors suffer from slight conductance variation and asymmetric conductance tuning, limiting the development of the model perception accuracy of the organic neuromorphic systems. Here, we first develop an electret-based vertical organic synaptic transistor (EVOST) with Mxene as the source electrode. The EVOST achieves linear conductance tuning by leveraging the nanoscale carrier transport channel length and high conductivity of MXene. Moreover, we develop an artificial neural recognition system composed of EVOSTs for recognizing the random images from the database, which achieves outstanding perception accuracy of 94.9%. The EVOST provides an alternative way for neuromorphic computing networks.

窒化ガリウム高電子移動度トランジスタの内部構造評価

Improving the performance of power devices is necessary to perform highly efficient power conversion. Therefore, better power devices made of wide bandgap semiconductors have come to be used. However, most of the complicated structures of GaN-HEMT as high-speed operating devices have not been analyzed in detail. In this study, we clarified the structures of GaN-HEMT by analyzing with the SEM, TEM, EDS, and the multifunctional SPM. We have clarified the existence of fine electrodes and p-type GaN layers near the source and drain electrodes by using SEM. We have clarified the composition of the superlattice strain relief layer of about 5 nm and the AlGaN layer for carrier generation of about 20 nm by using TEM and EDS. We have clarified the dopant polarity of a p-type GaN layer with a thickness of about 300 nm under the gate electrode for normally-off function by using the multifunctional SPM.

High Efficiency and Uniform Emission in Micropixelated Inorganic/Organic Hybrid Vertical Light-Emitting Transistors and Displays

Vertical light-emitting transistors (VLETs) fabricated by integrating organic vertical transistors and organic light-emitting diodes (OLEDs) have been proposed as a prospective building block for display technologies. However, organic vertical transistors normally have non-ohmic injection and a low-mobility channel, resulting in low VLET performance compared to the pristine OLED. The difficulty of fine patterning the source electrode and organic layer in a stacked VLET geometry has also been a technical issue limiting industrial applications. This paper reports on a simple approach to realize a high-performance, miniaturized VLET by using a highly conductive, well-designed inorganic transistor. Here, we investigate the ZnO transistor configured with an insulator-encapsulated source electrode to confine the current pathway in the VLET, which can be easily fabricated and integrated with various solution-processed or vacuum-sublimed inverted OLEDs (IOLEDs). This ZnO transistor exhibits ohmic contact and a high electron mobility of >10 cm2/(V s) that enables effective electron injection and lateral transport in the VLET, forming a millimeter-scale density gradient (channel depth) for strong surface emission. Furthermore, the high mobility of ZnO facilitates the design of a simple source pattern with a large aperture ratio on the ZnO area to control the current density and distribution and thus the VLET output. From a systematic study of the source design, we show that the ZnO transistor can be optimized to achieve homogeneously high conductivity in the ON state and yield the best VLET performance with maximum emission intensity and efficiency close to those of the IOLED, while the emission can be spatially uniform and precisely defined by the ZnO pattern. Finally, we implement a micropixelated VLET-based active matrix panel to demonstrate the prospect of high-resolution display applications.

Recovery of gold from e-waste via food waste byproducts

Global materials’ and energy constraints and environmental issues call for a holistic approach to waste upcycling. We propose a chemically rational, cost-effective and environmentally friendly recovery of non-leaching gold from e-waste using aqueous chemistry with hydrogen peroxide, an environmentally benign oxidant, and lactic acid, a food chain byproduct. The oxidation of the base metals enables the release of gold in its metallic state in the form of flakes subsequently separated via filtration. Our main byproduct is a precursor of Cu2O, a relevant metal oxide for solar energy conversion applications. The recovered gold was characterized by scanning electron microscopy, energy dispersive spectroscopy and x-ray photoelectron spectroscopy to gain insight into the morphology of the flakes and their chemical composition. Furthermore, recovered gold was used to successfully fabricate the source and drain electrodes in organic field-effect transistors.

Enhancement-mode β-Ga2O3 U-shaped gate trench vertical MOSFET realized by oxygen annealing

Vertical metal–oxide–semiconductor field effect transistor (MOSFET) is essential to the future application of ultrawide bandgap β-Ga2O3. In this work, we demonstrated an enhancement-mode β-Ga2O3 U-shaped gate trench vertical metal–oxide–semiconductor field effect transistor (UMOSFET) featuring a current blocking layer (CBL). The CBL was realized by high-temperature annealing under oxygen ambient, which provided electrical isolation between the source and drain electrodes. The CBL thicknesses of different annealing temperatures were derived from C–V measurements and the Fermi level position of the sample surfaces of different annealing temperature was characterized by x-ray photoelectron spectroscopy measurements, indicating good process controllability. Furthermore, photoluminescence spectra were measured to study the effect of oxygen annealing. The fabricated UMOSFET showed normally off with a Vth of 11.5 V, an on-state resistance of 1.48 Ω cm2, a maximum on-state current of 11 A/cm2, an on–off ratio of 6 × 104, and a three-terminal breakdown voltage over 100 V. This work paves a way to form a CBL and broadens the design space for high-power β-Ga2O3 vertical transistors.

Selective electrical stimulation of low versus high diameter myelinated fibers and its application in pain relief: a modeling study.

Electrical stimulation of peripheral nerve fibers has always been an attractive field of research. Due to the higher activation threshold, the stimulation of small fibers is accompanied by the stimulation of larger ones. It is therefore necessary to design a specific stimulation theme in order to only activate narrow fibers. There is evidence that stimulating Aδ fibers can activate endogenous pain-relieving mechanisms. However, both selective stimulation and reducing pain by activating small nociceptive fibers are still poorly investigated. In this study, using high-frequency stimulation waveforms (5-20kHz), computational modeling provides a simple framework for activating narrow nociceptive fibers. Additionally, a model of myelinated nerve fibers is modified by including sodium-potassium pump and investigating its effects on neuronal stimulation. Besides, a modified mathematical model of pain processing circuits in the dorsal horn is presented that consists of supraspinal pain control mechanisms. Hence, by employing this pain-modulating model, the mechanism of the reduction of pain by activating nociceptive fibers is explored. In the case of two fibers with the same distance from the point source electrode, a single stimulation waveform is capable of blocking one large fiber and stimulating another small fiber. Noteworthy, the Na/K pump model demonstrated that it does not have a significant effect on the activation threshold and firing frequency of fiber. Ultimately, results suggest that the descending pathways of Locus coeruleus may effectively contribute to pain relief through stimulation of nociceptive fibers, which will be beneficial for clinical interventions.

Submicron Vertical Channel Organic Electrochemical Transistors with Ultrahigh Transconductance

AbstractOrganic electrochemical transistors (OECTs) belong to the class of electrolyte gated organic transistors (EGOTs) that offer a smooth interface with biology in combination with high transconductance values of typically a few mS. Fabrication‐wise, though, most of the up‐to‐date reported devices are limited to two dimensional structures, where the transistor channel is patterned on the same plane as the source and drain electrodes. Here, a method is introduced for the fabrication of integrated vertical channel OECTs (vOECTs) with submicron channel length. By employing electrodeposition, a vertical channel sandwiched between the source and drain electrodes is created. Channel lengths down to 60 nm are demonstrated, giving rise to ultrahigh transconductance of up to 275 mS. Accounting for the voltage loss on the device connection tracks, an intrinsic transconductance of vOECTs of 500 mS is found. The vOECTs are three‐dimensional transistors finding relevant application in “organ‐on‐a‐chip” and implantable devices, where high amplification and small footprint are demanded.