Properties Of Transistors Research Articles

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.

Improvement in Crystallinity of Large-Scale Mote2 Thin Film and Electrical Properties of Transistors by Using High-Pressure Annealing

Improvement in Crystallinity of Large-Scale Mote2 Thin Film and Electrical Properties of Transistors by Using High-Pressure Annealing

Small-signal Modeling of InP HBT based on PSO-ELM Neural Network

Extreme Learning Machine (ELM) is a new learning algorithm for single-hidden layer feedforward neural network, which has been widely used in lots of fields. However, it still has the insufficiency of randomly determining the hidden layer threshold and output weight, which leads to ill-conditioned output. In order to avoid the risk of decreasing prediction accuracy caused by this possibility, the ELM is optimized using particle swarm algorithm. A Particle Swarm Optimization (PSO) enhanced ELM algorithm is proposed to accurately model the small-signal properties of InP Heterojunction Bipolar Transistors (HBTs). PSOELM algorithm solves the problem of unstable prediction data caused by random determination of input weights in ELM. Comparing the modeling effects of the PSO-ELM model and the ELM model under different bias conditions for a 1 μm×15 μm InP HBT, it is proved that the PSO-ELM algorithm has better consistency with the measured data.

Hysteretic behavior of all CVD h-BN/graphene/h-BN heterostructure field-effect transistors by interfacial charge trap

Superior electrical transport properties of graphene field-effect transistors (FETs) can be achieved when graphene is supported by a high-quality hexagonal boron nitride (h-BN) layer. The h-BN layer can serve as a high-performance insulator for a graphene channel to achieve high carrier mobility and to minimize doping effects on graphene by screening out the interaction with a gate oxide substrate. However, chemical vapor deposition (CVD) grown h-BN can have surface defects and impurities unlike mechanically exfoliated h-BN layers, which can result in completely different electrical transport properties of graphene FETs. In this study, we fabricated all CVD h-BN/graphene/h-BN FETs to explore how surface defects and impurities on the supporting h-BN layer can influence electrical transport properties of graphene. The presence of surface defects and impurities on the supporting h-BN layer, as revealed by Raman spectroscopy analysis, resulted in significant p-doping and hysteresis in the h-BN/graphene/h-BN FETs. Hysteresis in the FETs was induced by charge carrier trapping at the surface defects and impurities of the h-BN layer, which can be controlled by modulating a back-gate voltage. Based on the charge trapping mechanism on the surface of the h-BN, electrical charge states in all CVD h-BN/graphene/h-BN can be modulated dynamically by realizing two different resistance states (‘trap’ vs. ‘release’ states), which can be utilized as memristive devices or sensors.

Surface Cleaning and Modification of Oxide Films by Atomic Hydrogen Annealing

To suppress degradation of the electrical property of field-effect transistors, the removal of C contamination without damaging oxide films is important in the semiconductor industry. In addition, to reduce bonding failure, it is necessary to remove native oxide films from metal films. To achieve this, atomic hydrogen was generated by the decomposition of H2 gas on a heated tungsten mesh. This surface treatment is referred to as atomic hydrogen annealing (AHA). The reaction of atomic hydrogen with various oxide films, such as AlOx, TiOx, CrOx, NiOx, CuOx, and SiOx, was investigated. The O concentrations in Al, Ti, and Cr slightly decreased by AHA. The thermal oxide films prepared at 400 ℃ were not changed by AHA, except for CuOx. The reduction in the reactivity of the oxide film due to atomic hydrogen depends on the metal–oxygen bond strength. In addition, although the thermal oxide film of the Si substrate prepared at 1000 ℃ was not etched, AHA resulted in the etching of the Si-rich SiOx. These findings are useful for the removal of C contamination and native oxide films and for controlling the surface properties of oxide films.

Quantitative Prediction of Charge Mobilities and Theoretical Insight into the Regulation of Site-Specific Trifluoromethylethynyl Substitution to Electronic and Charge Transport Properties of 9,10-Anthraquinone.

Herein, we systematically studied the electronic and conducting properties of 9,10-anthraquinone (AQ) and its derivatives and discussed the substitute-site effects on their organic field-effect transistor (OFET) properties in detail. Our calculation results show the influence of different substitute sites on the ionization potential (IP), electronic affinity (EA), reorganization energy (λ), electronic couplings (V), and anisotropic mobility (μ) of semiconducting materials, which mainly originates from the variations of the frontier molecular orbital charge distributions, the steric hindrance, and the conjugate degree. Combining quantum-chemical calculations with charge transfer theory, we simulated the intermolecular hopping rate in the organic crystals of AQ derivatives and predicted the fluctuation range of three-dimensional (3D) anisotropic charge carrier mobility for the first time. Our calculation results well reproduced the experimental observations and provided evidence for the determination of the optimal OFET conduction plane and channel direction relative to the crystal axis.

Fabrication and Properties of InGaZnO Thin-Film Transistors Based on a Sol-Gel Method with Different Electrode Patterns.

The preparation of thin-film transistors (TFTs) with InGaZnO (IGZO) channels using sol-gel technology has the advantages of simplicity in terms of process and weak substrate selectivity. We prepared a series of TFT devices with a top contact and bottom gate structure, in which the top contact was divided into rectangular and circular structures of drain/source electrodes. The field-effect performance of TFT devices with circular pattern drain/source electrodes was better than that with a traditional rectangular structure on both substrates. The uniform distribution of the potential in the circular electrode structure was more conducive to the regulation of carriers under the same channel length at different applied voltages. In addition, with the development of transparent substrate devices, we also constructed a hafnium oxide (HfO2) insulation layer and an IGZO active layer on an indium tin oxide conductive substrate, and explored the effect of circular drain/source electrodes on field-effect properties of the semitransparent TFT device. The IGZO deposited on the HfO2 dielectric layer by spin-coating can effectively reduce the surface roughness of the HfO2 layer and optimize the scattering of carriers at the interface in TFT devices.

Study of electrical transport properties of GaN-based side-gate heterostructure transistors

In this study, GaN-based side-gate heterostructure transistors (SGHTs) with two electrical operating modes were fabricated. In the first operating mode, the SGHT was utilized as a common-source voltage amplifier with low power consumption and a broad input signal range. Analysis of the main scattering mechanisms affecting the electrical transport of two-dimensional electron gas (2DEG) in the channel revealed that polar optical phonon scattering and polarization Coulomb field (PCF) scattering play dominant roles under different side-gate voltages. In addition, channel current modulation of 2DEG electron mobility is primarily attributed to PCF scattering. Due to PCF scattering, the channel width also modulates the threshold voltage in this mode of operation. Moreover, in the second operating mode, the SGHT functioned as a traditional GaN high electron mobility transistor, allowing for electrically modulated threshold voltage and transconductance.

Effects of solution-shearing process parameters on charge carrier mobility in green solvent-processed organic field-effect transistors

In this work, we explored the effect of solution-shearing processing parameters, coating speed and substrate temperature, on the electrical properties of solution-processed organic field-effect transistors (OFETs) based on 2-decyl-7-phenyl[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-C10) when green solvents are used. Organic semiconductor thin films were solution-sheared with various coating speeds and substrate temperatures and film morphologies/microstructures were investigated by atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis. Our data demonstrate that crystal growth of Ph-BTBT-C10 molecule is highly affected by the two solution shearing processing parameters and, especially, the OFET devices fabricated with cyclohexanone as green solvent exhibited the charge carrier mobility as high as 5.1 cm2/Vs with optimized processing condition. This work could further provide a guideline for process optimization for fabricating high-performance green solvent-processed OFETs.

Overall enhancement of electrical properties of indium oxide thin-film transistors by surface doping

Doping is a powerful tool for modulating the charge carrier density in metal oxide thin-film transistors (TFTs). However, one crucial limitation is the disruption of microstructure after doping of crystalline semiconductors, which dramatically decreases the charge carrier mobility. Here, we report on a surface doping method that utilizes organic acceptor molecules to efficiently modulate the carrier concentration without disrupting the lattice of thin indium oxide channel layers. For the first time, we achieve electron transfer from indium oxide channel to the organic layer, instead conventional strategy of organic to metal oxide, to control the intrinsic carrier concentration and enhance the electrical performance of the indium oxide TFTs. Moreover, we use a complementary tool based on spectroscopic techniques to prove the fundamental charge transfer processes between metal oxide semiconductors and organic molecular dopants. The results indicate that surface doping is a simple and effective way to improve the performance of oxide TFTs and suitable for potential applications in large-area electronics. • Indium oxide TFTs were fabricated by solution process method. • Surface doping modulates the carrier concentration of the channel layer. • The electrical performances of the devices were enhanced by surface doping.

Effect of Humidity on Properties of Aqueous-Processed Tb-Doped Indium Oxide Thin-Film Transistors

Aqueous route is readily for fabricating oxide thin-film transistors (TFTs), but the relative humidity (RH) impacts evolution of oxide thin films. Herein, the effect of RH on the electronic performance and bias stability of aqueous-processed Tb-doped indium oxide (Tb:In2O3) TFTs is investigated. The mobility is sensitive to RH. By tuning the RH for desirable thickness and density of the obtained Tb:In2O3 films, the TFTs present optimized mobility of 13.0 cm2/Vs, with high ON/OFF ratio of 108. Notably, low threshold voltage shift of −0.35 V and 0.42 V under negative and positive gate bias stress are simultaneously obtained with a fabricating RH of 40%. Moreover, dry ambience (RH <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\le23$ </tex-math></inline-formula> %) affords to abundant nanopores and defects, resulting in inferior performance and stability of the aqueous-processed oxide TFTs. And high humid ambience easily ruins the uniform of precursor films. This work indicates the strategy to fabricate highly stable oxide TFTs with high performance.

Preparation and electrical properties of Ni-doped InZnO thin film transistors

In this work, Ni-doped InZnO (IZO: Ni) thin film transistors (TFTs) with staggered bottom-gate structure were fabricated on SiO2/Si substrates by radio frequency (RF) magnetron sputtering, and IZO: Ni thin films severed as active layer, Al electrodes were used as the source and drain electrodes. X-ray Diffraction (XRD) results showed that IZO: Ni film was amorphous structure. Transmittance of the deposited sample was higher than 80% in the visible range. Secondary ion mass spectroscopy (SIMS) exhibited a uniform distribution of all the elements in the film. Field emission scanning electron micrograph (FESEM) and Atom force microscopy (AFM) results revealed that the film had a smooth surface and a root-mean-square (RMS) roughness of 0.225 nm. The TFTs annealed at 265 °C in nitrogen atmosphere showed the excellent electrical performance with a high saturation mobility (μSAT) of 37.2 cm2V−1s−1, a low threshold voltage (VTH) of 2.5 V, a low subthreshold swing (SS) of 0.39 V/dec, and a high on/off current ratio (Ion/Ioff) of 4.1 × 108.

Characterization of the electric transport properties of black phosphorous back-gated field-effect transistors

We use thin layers of exfoliated black phosphorus to realize back-gated field-effect transistors in which the Si/SiO2 substrate is exploited as gate electrode. To prevent the detrimental effect of the air exposure the devices are protected by Poly(methyl methacrylate). We report the observation of an improved contact resistance at the interface between the layered material and the metal contact by electrical conditioning. We also demonstrate the existence of a hysteresis in the transfer characteristics that improves by increasing the gate voltage sweep range. Finally, we prove the suitability of such transistors as memory devices.

Organic Vapor Sensing Mechanisms by Large-Area Graphene Back-Gated Field-Effect Transistors under UV Irradiation.

The gas sensing properties of graphene back-gated field-effect transistor (GFET) sensors toward acetonitrile, tetrahydrofuran, and chloroform vapors were investigated with the focus on unfolding possible gas detection mechanisms. The FET configuration of the sensor device enabled gate voltage tuning for enhanced measurements of changes in DC electrical characteristics. Electrical measurements were combined with a fluctuation-enhanced sensing methodology and intermittent UV irradiation. Distinctly different features in 1/f noise spectra for the organic gases measured under UV irradiation and in the dark were observed. The most intense response observed for tetrahydrofuran prompted the decomposition of the DC characteristic, revealing the photoconductive and photogating effect occurring in the graphene channel with the dominance of the latter. Our observations shed light on understanding surface processes at the interface between graphene and volatile organic compounds for graphene-based sensors in ambient conditions that yield enhanced sensitivity and selectivity.

Physical Insights into Vacancy-Based Memtransistors: Toward Power Efficiency, Reliable Operation, and Scalability.

Memtransistors that combine the properties of transistor and memristor hold significant promise for in-memory computing. While superior data storage capability is achieved in memtransistors through gate voltage-induced conductance modulation, the lateral device configuration would not only result in high write bias, which compromises the power efficiency, but also suffers from unsuccessful memory reset that leads to reliability concerns. To circumvent such performance limitations, an advanced physics-based model is required to uncover the dynamic resistive switching behavior and deduce the key driving parameters for the switching process. This work demonstrates a self-consistent physics-based model which incorporates the often-overlooked effects of lattice temperature, vacancy dynamics, and channel electrostatics to accurately solve the interaction between gate potential, ions, and carriers on the memristive switching mechanism. The completed model is carefully calibrated with an ambipolar WSe2 memtransistor and hence enables the investigation of the carrier polarity effect (electrons vs holes) on vacancy transport. Nevertheless, the validity of the model can be extended to different materials by a simple material-dependent parameter modification. Building upon the existing understanding of Schottky barrier height modulation, our study reveals three key insights─leveraging threshold voltage shifts to lower write bias; optimizing lattice temperature distribution and read bias polarity to achieve successful memory state recovery; engineering contact work function to overcome the detrimental parasitic current flow in short channel ambipolar memtransistors. Therefore, understanding the significant correlation between the switching mechanisms, different material systems, and device structures allows performance optimization of operating modes and device designs for future memtransistors-based computing systems.

Electrical properties of cerium hexaboride gate hydrogen-terminated diamond field effect transistor with normally-off characteristics

Fabrication of hydrogen-terminated (H-terminated) diamond field effect transistor (FET) with low work function cerium hexaboride (CeB6) gate material has been successfully performed. For the 8 μm gate length device, the threshold voltage (VTH) is extracted to be −0.46 V, demonstrating a normally-off characteristics. The maximum drain source current density (IDmax) is −83.8 mA/mm, and the competitive IDmax may be ascribed to the undamaged two-dimensional hole gas channel. The interface state density (Dit) is evaluated to be 1.93 × 1012 cm−2·eV−1, and the relatively low value may be attributed to the uncontaminated interface in gate material. This work provides a promising strategy to realize normally-off H-terminated diamond FET for fail-safety and energy-efficient power electronic devices.

Experimental and theoretical insights into electronic properties of oxygen-doped MoTe2 field effect transistor

Modulating the electrical and photo-electrical properties is essential to enlighten the potential application in the case of field-effect transistors and other electronic devices. Molybdenum ditelluride (MoTe2), which has a limited energy gap and shows spin-orbit coupling, has piqued curiosity among two-dimensional (2D) transition metal dichalcogenides (TMDCs) and has appeared as a significant material with innovative electronic applications. In this work, we have reported the electrical modulation of multilayer MoTe2-FETs by gas doping under deep ultra-violet (DUV) light. After DUV treatment, the device characteristics were also investigated with oxygen doping. A shift in threshold voltage was observed from negative to positive back-gate voltage (Vbg), revealing a p-type doping effect. This doping effect is further confirmed through the Raman peaks, A1g and E12g were shifted towards higher wavenumbers. For pristine to 30-min doping intervals, the current ON/OFF ratio increased from 104 to 106 and the mobility of the device is enhanced from 22.36 cm2/V.s to 102.43 cm2/V.s. In addition, we used density functional theory (DFT) to investigate the impact of oxygen doping on the electrical and optical properties of MoTe2. The electronic bandgap was determined to be 0.8 eV, which can be a promising material for lower energy devices. The oxygen-doped MoTe2-based field-effect transistors are predicted to be a promising contender for low and high-temperature applications based on the highly intense peak of absorption spectra in the ultra-violet and visible regions of electromagnetic spectra.

Real-space numerical renormalization group computation of transport properties in side-coupled geometry

A real-space formulation of the numerical renormalization group (NRG) procedure is introduced. The real-space construction, dubbed eNRG, is more straightforward than the NRG discretization, and allows a faithful description of the coupling between quantum dots and conduction states even if the design of the couplings is intricate. General features of the two procedures are discussed comparatively. A more specific comparison is then developed, based on computations of the zero-bias transport properties for an Anderson-model description of a quantum wire side-coupled to a single quantum dot. An eNRG computation is shown to reproduce accurately the temperature-dependent electrical conductance for the uncorrelated model in the continuum limit, while significant deviations mark the corresponding NRG computation for thermal energies comparable to the conduction bandwidth. A combination of analytical and numerical results for the transport properties of the correlated model then provides a more exacting check on the accuracy of the eNRG procedure. A recent NRG analysis mapping the transport properties of a single-electron transistor onto universal functions of the temperature scaled by the Kondo temperature is extended to the side-coupled device, on the basis of eNRG reasoning. Numerical results for the electrical conductance, thermopower, and thermal conductance in side-coupled geometry are then shown to agree very well with the mappings. The numerical results are also checked against the thermal dependence of the thermopower measured by K\"ohler et al. [Phys. Rev. B 77, 104412 (2008)] in ${\mathrm{Lu}}_{0.9}^{\phantom{\ifmmode\dagger\else\textdagger\fi{}}}{\mathrm{Yb}}_{0.1}^{\phantom{\ifmmode\dagger\else\textdagger\fi{}}}{\mathrm{Rh}}_{2}^{\phantom{\ifmmode\dagger\else\textdagger\fi{}}}{\mathrm{Si}}_{2}^{\phantom{\ifmmode\dagger\else\textdagger\fi{}}}$, and the remarkably accurate, recent conductance measurements by Xu et al. [Chin. Phys. Lett. 38, 087101 (2021)].

Beyond the 2D Field‐Effect Charge Transport Paradigm in Molecular Thin‐Film Transistors

AbstractOrganic field‐effect transistors (OFETs) are considered almost purely interfacial devices with charge current mainly confined in the first two semiconducting layers in contact with the dielectric with no active role of the film thickness exceeding six to eight monolayers (MLs). By a combined electronic, morphological, structural, and theoretical investigation, it is demonstrated that the charge mobility and source–drain current in 2,20‐(2,20‐bithiophene‐5,50‐diyl)bis(5‐butyl‐5H‐thieno[2,3‐c]pyrrole‐4,6)‐dione (NT4N) organic transistors directly correlate with the out‐of‐plane domain size and crystallite orientation in the vertical direction, well beyond the dielectric interfacial layers. Polycrystalline films with thickness as high as 75 nm (≈30 MLs) and 3D molecular architecture provide the best electrical and optoelectronic OFET characteristics, highlighting that the molecular orientational order in the bulk of the film is the key‐enabling factor for optimum device performance. X‐ray scattering analysis and multiscale simulations reveal the functional correlation between the thickness‐dependent molecular packing, electron mobility, and vertical charge distribution. These results call for a broader view of the fundamental mechanisms that govern field‐effect charge transport in OFETs beyond the interfacial 2D paradigm and demonstrate the unexpected role of the out‐of‐plane domain size and crystallite orientation in polycrystalline films to achieve optimum electronic and optoelectronic properties in organic transistors.

Synthesis, Characterization, and Field-Effect Transistor Properties of Naphthalene Diimide-Based Conjugated Polymers with Fluorine-Containing Branched Side Chains

Synthesis, Characterization, and Field-Effect Transistor Properties of Naphthalene Diimide-Based Conjugated Polymers with Fluorine-Containing Branched Side Chains