Single Field Effect Transistors Research Articles

Ion detection in a DNA nanopore FET device.

An ion detection device that combines a DNA-origami nanopore and a field-effect transistor (FET) was designed and modeled to determine sensitivity of the nanodevice to the local cellular environment. Such devices could be integrated into a live cell, creating an abiotic-biotic interface integrated with semiconductor electronics. A continuum model is used to describe the behavior of ions in an electrolyte solution. The drift-diffusion equations are employed to model the ion distribution, taking into account the electric fields and concentration gradients. This was matched to the results from electric double layer theory to verify applicability of the model to a bio-sensing environment. The FET device combined with the nanopore is shown to have high sensitivity to ion concentration and nanopore geometry, with the electrical double layer behavior governing the device characteristics. A logarithmic relationship was found between ion concentration and a single FET current, generating up to 200 nA of current difference with a small applied bias.

Anisotropic sensing based on single ReS2 flake for VOCs discrimination

Selective and sensitive detection of volatile organic compounds (VOCs) holds paramount importance in real-world applications. This study proposes an innovative approach utilizing a single ReS2 field-effect transistor (FET) characterized by distinct in-plane anisotropy, specifically tailored for VOC recognition. The unique responses of ReS2, endowed with robust in-plane anisotropic properties, demonstrate significant difference along the a-axis and b-axis directions when exposed to four kinds of VOCs: acetone, methanol, ethanol, and IPA. Remarkably, the responses of ReS2 were significantly magnified under ultraviolet (UV) illumination, particularly in the case of acetone, where the response amplified by 10–15 times and the detection limit decreasing from 70 to 4 ppm compared to the dark conditions. Exploiting the discernible variances in responses along the a-axis and b-axis under both UV and dark conditions, the data points of acetone, ethanol, methanol and IPA gases were clearly separated in the principal component space without any overlap through principal component analysis, indicating that the single ReS2 FET has a high ability to distinguish various gas species. The exploration of anisotropic sensing materials and light excitation strategies can be applied to a broad range of sensing platforms based on two-dimensional materials for practical applications.

ReS2-MoS2 heterojunction nanotube FET with superlattice structures for ultrasensitive detection of miRNA

Ultrasensitive detection of cancer biomarkers holds immense importance in facilitating the early diagnosis and treatment of cancer. Compared to conventional detection techniques, field-effect transistor (FET) biosensors have demonstrated substantial potential in achieving sensitive detection of cancer biomarkers. However, the ultrasensitive FET still remains great challenges due to the limited electron transport capacity and sensitivity of channel materials. Herein, we employed rhenium disulfide-molybdenum disulfide nanotube (ReS2-MoS2 NT) featuring superlattice structures as channel materials in FET biosensors for the highly sensitive detection of cancer biomarker miRNA-21. More concretely, ReS2-MoS2 NT featuring superlattice structures was synthesized using the anodic aluminum oxide (AAO) template sacrifice method and atomic layer deposition (ALD) method. The electrical properties of single ReS2-MoS2 NT FET were regulated by adjusting the total layers and number of heterojunction interfaces, and the optimal number of heterojunction interfaces of 7 was obtained. Finally, FET biosensors utilizing the network ReS2-MoS2 NT as the channel materials were fabricated and exhibited remarkable sensitivity in detecting miRNA-21 under an external light source. The linear range for detection spanned from 10 aM to 1 nM, with an exceptionally low detection limit of 2.1 aM. This study holds promise for replacing current channel materials and surpassing the detection threshold of cancer biomarkers in the future.

Thermally Driven Multilevel Non-Volatile Memory with Monolayer MoS2 for Brain-Inspired Artificial Learning.

The demands of modern electronic components require advanced computing platforms for efficient information processing to realize in-memory operations with a high density of data storage capabilities toward developing alternatives to von Neumann architectures. Herein, we demonstrate the multifunctionality of monolayer MoS2 memtransistors, which can be used as a high-geared intrinsic transistor at room temperature; however, at a high temperature (>350 K), they exhibit synaptic multilevel memory operations. The temperature-dependent memory mechanism is governed by interfacial physics, which solely depends on the gate field modulated ion dynamics and charge transfer at the MoS2/dielectric interface. We have proposed a non-volatile memory application using a single Field Effect Transistor (FET) device where thermal energy can be ventured to aid the memory functions with multilevel (3-bit) storage capabilities. Furthermore, our devices exhibit linear and symmetry in conductance weight updates when subjected to electrical potentiation and depression. This feature has enabled us to attain a high classification accuracy while training and testing the Modified National Institute of Standards and Technology datasets through artificial neural network simulation. This work paves the way toward reliable data processing and storage using 2D semiconductors with high-packing density arrays for brain-inspired artificial learning.

Ambipolar Nonvolatile Memory Behavior and Reversible Type‐Conversion in MoSe2/MoSe2 Transistors with Modified Stack Interface

Abstract2D semiconductor devices have been studied due to their unique potential in architecture and properties. As one of the unique devices approaches, 2D hetero‐stack channel field‐effect transistors (FETs) have recently been reported, but homo‐stack FETs are rare to find. Here, MoSe2/MoSe2 homo‐stack transistors are rather fabricated for study. Unlike the equivalently‐thick single MoSe2 FET, homo‐stack FETs show n‐type memory behavior that originates from stack interface‐induced traps. Particularly, when their stack interfaces are engineered by surface oxidation of bottom MoSe2, more stable nonvolatile memory behavior turns out. Short‐term ultraviolet ozone (UVO)‐induced oxidation only results in n‐type memory, but 15 min‐long oxidation surprisingly enables both n‐ and p‐type nonvolatile memory behavior due to nm‐thin MoOx embedded between upper and lower MoSe2. Furthermore, by alternating gate voltage pulse to the 15 min‐long UVO‐treated FETs, channel polarity conversion appears reversible in a small gate voltage (VGS) sweep range, which means that the channel type of a transistor can be reversibly modulated via stack interface engineering. It is believed that homo‐stack interface engineering must be one of the approaches to maximize the potential of 2D devices.

2D multifunctional SiAs2/GeAs2 van der Waals heterostructure

The structural and electronic properties of two-dimensional (2D) SiAs2/GeAs2 van der Waals heterostructure (vdWH) and its applications are investigated by combing first-principles calculations and Silvaco Atlas simulations. The stable SiAs2/GeAs2 vdWH exhibits an indirect bandgap of 0.99 eV in type II band alignment for light detection and energy harvesting. The vdWH can exhibit a direct bandgap up to 0.66 eV by applying an appropriate electric field (E ext ). Due to the E ext induced charge redistribution, its band alignment can be transformed from type II to type I for light-emitting. Further simulation shows that the band alignment of SiAs2/GeAs2 vdWH can be tuned back and forth between type II and type I by gate voltage in a single field-effect transistor for multiple functional applications. These results may be useful for applications of the SiAs2/GeAs2 heterostructure in future electronic and optoelectronic devices.

Single β-Ga2O3 nanowire back-gate field-effect transistor

In this work, a normally-on single-monocrystal β-Ga2O3 nanowire (NW) back-gate field-effect transistor (FET) has been demonstrated by transferring metal-organic chemical vapor deposition-grown β-Ga2O3 NWs on sapphire onto SiO2(300 nm)/p +-Si substrate. When the gate voltage (V G) exceeds −14 V, the device is pinched off, with an on/off ratio greater than 108 and a drain leakage current density as low as ∼7.34 fA. The maximum field-effect carrier mobility for these n-doped single β-Ga2O3 NW FETs reaches ∼62.2 cm2 (V s)−1. A prompt degradation in the on/off ratio for these β-Ga2O3 NW back-gate FETs is observed as the operation temperature increased up to 400 K. With strong evidence, the temperature-dependent degradation in the performance is determined by the activation of self-trapped holes and intrinsic vacancy-related defects, both of which would lead to a rapid increase in the channel leakage current at high temperatures.

Vertically stacked multilayer atomic-layer-deposited sub-1-nm In2O3 field-effect transistors with back-end-of-line compatibility

In this work, we demonstrate vertically stacked multilayer sub-1-nm In2O3 field-effect transistors (FETs) with surrounding gate in a back-end-of-line (BEOL) compatible low-temperature fabrication process. A typical bottom-gated single layer In2O3 FET with maximum on-state current (ION) of 890 μA/μm at VDS = 0.8 V and an on/off ratio over 106 is achieved with a channel length (Lch) of 100 nm. The effects of HfO2 capping and O2 annealing are systematically studied, which is critical to realizing the multilayer FETs. Each atomically thin In2O3 channel layer with a thickness (TIO) of 0.9 nm is realized by atomic layer deposition (ALD) at 225 °C. Multilayer FETs with a number of In2O3 layers up to 4 and 1.2 nm-thick HfO2 between each individual layer are fabricated. An enhancement of on-state current (ION) from 183 μA in a single layer In2O3 FET to 339 μA in a 4 layer device with an on/off ratio of 3.4 × 104 is achieved, demonstrating the key advantage of the multilayer FETs to improve the current. Several critical features, such as large-area growth, high uniformity, high reproducibility, ultrathin body, flexibility, and BEOL compatibility, have turned ALD In2O3 into a noteworthy candidate for next-generation oxide semiconductor channel materials.

Asymmetric Dressing of WSe2 with (Macro)molecular Switches: Fabrication of Quaternary-Responsive Transistors.

The forthcoming saturation of Moore's law has led to a strong demand for integrating analogue functionalities within semiconductor-based devices. As a step toward this goal, we fabricate quaternary-responsive WSe2-based field-effect transistors (FETs) whose output current can be remotely and reversibly controlled by light, heat, and electric field. A photochromic silane-terminated spiropyran (SP) is chemisorbed on SiO2 forming a self-assembled monolayer (SAM) that can switch from the SP to the merocyanine (MC) form in response to UV illumination and switch back by either heat or visible illumination. Such a SAM is incorporated at the dielectric-semiconductor interface in WSe2-based FETs. Upon UV irradiation, a drastic decrease in the output current of 82% is observed and ascribed to the zwitterionic MC isomer acting as charge scattering site. To provide an additional functionality, the WSe2 top surface is coated with a ferroelectric co-polymer layer based on poly(vinylidene fluoride-co-trifluoroethylene). Because of its switchable inherent electrical polarization, it can promote either the accumulation or depletion of charge carriers in the WSe2 channel, thereby inducing a current modulation with 99% efficiency. Thanks to the efficient tuning induced by the two components and their synergistic effects, the device polarity could be modulated from n-type to p-type. Such a control over the carrier concentration and device polarity is key to develop 2D advanced electronics. Moreover, the integration strategy of multiple stimuli-responsive elements into a single FET allows us to greatly enrich its functionality, thereby promoting the development for More-than-Moore technology.

Enhanced Electrical Performance of Van der Waals Heterostructure

AbstractIn this study, a novel van der Waals (vdW) heterostructure field‐effect transistor (FET) using vdW stacking as next‐generation device architecture is demonstrated. The MoS2/WS2 heterostructure FET exhibits a large improvement in the drain current and field‐effect mobility (from 43.3 to 62.4 cm2 V−1 s−1) compared with single MoS2 FET. Such significant enhancement is mainly due to the charge‐transfer effect. The vdW self‐encapsulation effect in the device channel also helps to reduce the Schottky barrier height from 120 to 52 meV at the contact interface. Finally, the WS2/MoS2/WS2 double heterostructure FETs further boosts the mobility up to 102.5 cm2 V−1 s−1 at room temperature (25 °C) and 169.7 cm2 V−1 s−1 at 30 K. The much higher mobility exhibited at the lower temperature indicates the suppression of Coulomb scattering. Thus the electrical performance of the double‐heterostructure FETs can be further enhanced.

Simultaneous Incorporation of Two Types of Azo-Groups in the Side Chains of a Conjugated D-A Polymer for Logic Control of the Semiconducting Performance by Light Irradiation.

A new design strategy for photoresponsive semiconducting polymer with tri-stable semiconducting states is reported by simultaneous incorporation of tetra-ortho-methoxy-substituted azobenzene (mAzo) and arylazopyrazole (pAzo) in the side chains. The trans-to-cis transformations for mAzo and pAzo groups can sequentially occur within the polymer thin film after sequential 560 and 365nm light irradiation. Remarkably, the trans-cis isomerization of mAzo and pAzo groups can modulate the thin film crystallinity. Accordingly, the performances of the resulting field-effect transistors (FETs) can be reversibly modulated, leading to tri-stable semiconducting states after sequential 560, 365, and 470nm light irradiation. Therefore, the device performance can be logically controlled by light irradiation at three different wavelengths. In addition, with light irradiation and device current as the input and output signals, the three-value logic gate by using single FET device can be successfully mimicked.

2D Ruddlesden–Popper Perovskite Single Crystal Field‐Effect Transistors

Abstract2D Ruddlesden–Popper perovskites (2D PVKs) have attracted huge interest because of their excellent optoelectronic properties, yet the understanding of their electrical properties is inadequate due to the difficulties in obtaining 2D PVK field‐effect transistors (FETs) with decent performance. Herein, the fabrication and characterization of 2D PVK ((BA)2(MA)n−1PbnI3n+1) single crystal FETs are reported, which exhibit reliable field effect electrical characteristics at low temperatures. Kelvin probe force microscopy (KPFM) results reveal that both ion migration and contact resistance seriously degrade device performance. While ion migration can be suppressed at low temperatures, contact resistance seems to fundamentally determine device performance. On one hand, Schottky contacts are observed to form at the metal/2D PVK interface because of Fermi level pinning, resulting in significant charge injection resistance, although this can be remarkably improved by replacing Au electrodes with Ca. On the other hand, the out‐of‐plane mobility is found to be three orders of magnitude lower than the in‐plane mobility in 2D PVKs, causing large interlayer transport resistance. Thus, a low work‐function metal and a thin crystal are important for achieving high device performance. This work provides important experimental insights into fabrication and electrical properties of 2D PVK FETs.

Monitoring of Dynamic Processes during Detection of Cardiac Biomarkers Using Silicon Nanowire Field‐Effect Transistors

AbstractNumerous sensitive nanobiosensors are reported for various bioassay applications as a result of the development of materials science and nanotechnology. Among these sensors, nanowire (NW) field‐effect transistors (FETs) represent one of the most promising practical biosensors for ultrasensitive clinical diagnostic tools. Most studies mainly focus on how to achieve a lower detection limit but pay less attention to the long settling time effect for the detection of very small concentrations of molecules in a solution. In this study, single silicon NW FETs with long‐term stability is fabricated to investigate the settling time process at small concentrations of cardiac biomarkers relevant to myocardial diseases. It is found that the settling time strongly depends on the type of molecule, its charge state and analyte concentrations. For low concentrations, the time for measurement signals to settle down is relatively long. Therefore, it is essential to understand the settling time effect in Si NW FET‐based biosensing processes to ensure the accuracy and reliability of the detection signal. An alternative approach is demonstrated to circumvent the long measurement time by utilizing reaction kinetics parameters for the fast determination of low‐concentration detection, which also benefits the optimal balance between suitable detection time and reliable detection results.

Design of a Frequency Doubler Circuit for Suppressing Odd Harmonics

In this paper, a doubler circuit which can suppress odd harmonics is designed by using the non-linear characteristics of field effect transistor (FET) and bipolar junction transistor(BJT) devices. The frequency doubler consists of three parts: small signal full wave rectifier circuit, frequency doubler circuit and band-pass filter circuit. It realizes fundamental and third harmonics suppression by rectifying the input signal of single FET frequency doubler. Meanwhile, the output power is twice as high as that of single FET frequency doubler (3dB higher). Circuit simulation results indicate that when the input fundamental voltage amplitude is 0.5V, the output voltage amplitude of second harmonics is 0.342V, the fundamental suppression is greater than 48.85dBc, and the third harmonic suppression is greater than 34.39dBc. Compared with the traditional single FET frequency doubler, this design improves the frequency conversion efficiency.

Compact Terahertz SPICE/ADS Model

We describe a compact terahertz (THz) SPICE/advanced design system (ADS) model based on the extended Enz-Krummenacher-Vittoz (EKV) MOSFET model with channel segmentation but accounting for the new physics of the electron transport at THz frequencies. The model includes the distributed Drude inductance representing the electron inertia. The channel segmentation allows reproducing the nonuniformity in the electron density excitations and the plasmonic oscillations at THz frequencies. The model was validated by comparing the simulation results with the analytical THz detection theory and experimental data for silicon MOSFETs and FinFETs with gate lengths ranging from 60 to 800 nm. The good agreement between the simulated and analytical results and experimental data revealed the significance of the electron inertia and demonstrated the improved validity of the model at higher frequencies with an increase in the number of segments. The model was used to simulate a novel TeraFET THz spectrometer and the resonant TeraFET THz detector. These results show the model utility for device and circuit simulations at sub-THz and THz frequencies. An important application of the THz spectrometer simulation is in the design of a single field-effect transistor (FET) THz vector detector that could be extremely useful for 5G (and beyond) line-of-sight applications.

Electrical Detection of Singlet Fission in Single Crystal Tetracene Transistors.

We present the electrical detection of singlet fission in tetracene by using a field-effect transistor (FET). Singlet fission is a photoinduced spin-dependent process, yielding two triplet excitons from the absorption of a single photon. In this study, we engineered a more deterministic platform composed of an organic single crystal FET rather than amorphous or polycrystalline FETs to elucidate spin-dependent processes under magnetic fields. Despite the unipolar operation and relatively high mobility of single crystal tetracene FETs, we were able to manipulate spin dependent processes to detect magnetoconductance (MC) at room temperature by illuminating the FETs and tuning the bias voltage to adjust majority charge carrier density and trap occupancy. In considering the crystalline direction and magnetic field interactions in tetracene, we show the MC response observed in tetracene FETs to be the result of the singlet fission process.

Low-power logic computing realized in a single electric-double-layer MoS2 transistor gated with polymer electrolyte

Due to its mechanical flexibility, large bandgap and carrier mobility, atomically thin molybdenum disulphide (MoS2) has attracted widespread attention. However, it still lacks a facile route to fabricate a low-power high-performance logic gates/circuits before it gets the real application. Herein, we reported a facile and environment-friendly method to establish the low-power logic function in a single MoS2 field-effect transistor (FET) configuration gated with a polymer electrolyte. Such low-power and high-performance MoS2 FET can be implemented by using water-soluble polyvinyl alcohol (PVA) polymer as proton-conducting electric-double-layer (EDL) dielectric layer. It exhibited an ultra-low voltage (1.5 V) and a good performance with a high current on/off ratio (Ion/off) of 1 × 105, a large electron mobility (µ) of 47.5 cm2/V s, and a small subthreshold swing (S) of 0.26 V/dec, respectively. The inverter can be realized by using such a single MoS2 EDL FET with a gain of ∼4 at the operation voltage of only ∼1 V. Most importantly, the neuronal AND logic computing can be also demonstrated by using such a double-lateral-gate single MoS2 EDL transistor. These results show an effective step for future applications of 2D MoS2 FETs for integrated electronic engineering and low-energy environment-friendly green electronics.

Junctionless Diode Enabled by Self-Bias Effect of Ion Gel in Single-Layer MoS2 Device.

The self-biasing effects of ion gel from source and drain electrodes on electrical characteristics of single layer and few layer molybdenum disulfide (MoS2) field-effect transistor (FET) have been studied. The self-biasing effect of ion gel is tested for two different configurations, covered and open, where ion gel is in contact with either one or both, source and drain electrodes, respectively. In open configuration, the linear output characteristics of the pristine device becomes nonlinear and on-off ratio drops by 3 orders of magnitude due to the increase in "off" current for both single and few layer MoS2 FETs. However, the covered configuration results in a highly asymmetric output characteristics with a rectification of around 103 and an ideality factor of 1.9. This diode like behavior has been attributed to the reduction of Schottky barrier width by the electric field of self-biased ion gel, which enables an efficient injection of electrons by tunneling at metal-MoS2 interface. Finally, finite element method based simulations are carried out and the simulated results matches well in principle with the experimental analysis. These self-biased diodes can perform a crucial role in the development of high-frequency optoelectronic and valleytronic devices.

Multiple Schottky Barrier-Limited Field-Effect Transistors on a Single Silicon Nanowire with an Intrinsic Doping Gradient.

In comparison to conventional (channel-limited) field-effect transistors (FETs), Schottky barrier-limited FETs possess some unique characteristics which make them attractive candidates for some electronic and sensing applications. Consequently, modulation of the nano Schottky barrier at a metal-semiconductor interface promises higher performance for chemical and biomolecular sensor applications when compared to conventional FETs with ohmic contacts. However, the fabrication and optimization of devices with a combination of ideal ohmic and Schottky contacts as the source and drain, respectively, present many challenges. We address this issue by utilizing Si nanowires (NWs) synthesized by a chemical vapor deposition process which yields a pronounced doping gradient along the length of the NWs. Devices with a series of metal contacts on a single Si NW are fabricated in a single lithography and metallization process. The graded doping profile of the NW is manifested in monotonic increases in the channel and junction resistances and variation of the nature of the contacts from ohmic to Schottky of increasing effective barrier height along the NW. Hence multiple single Schottky junction-limited FETs with extreme asymmetry and high reproducibility are obtained on an individual NW. A definitive correlation between increasing Schottky barrier height and enhanced gate modulation is revealed. Having access to systematically varying Schottky barrier contacts on the same NW device provides an ideal platform for identifying optimal device characteristics for sensing and electronic applications.

Current relation of single energy level Graphene through considering defects and energy broadening

Graphene consist of sheet of carbon atoms bonded in sp2 manner of hexagonal lattice structure offers a number of uses in electronic application with number of desirable properties (like as large thermal conductivity, large Young’s modulus). In this paper we have modelled I-V characteristics for single energy level GNR FET (grapheme nanoribbon field effect transistor) by considering disorder in graphene sheet. Gaussian distribution function is used to show potential distribution because of this disorder at Dirac point. It is convoluted with homogeneous density of states of grapheme to get DOS for disordered graphene. Homogeneous DOS is considered for linear band structure of graphene. Then by putting this disordered DOS in defined relation I-V expression is achieved for disordered grapheme sheet. In addition energy broadening of channel (due to spilling of states from electrodes to channel and vice-versa) has been considered in this paper to get optimum result.