Behavior Of Field-effect Transistors Research Articles

Three-dimensional Modeling of Core-structured Field Effect Transistor

Objective: In our previous publication, a core-structured field effect transistor (CoreFET) device shows field effect transistor (FET) behavior. In this work, we investigated factors such as the thickness of the film and the channel on the conductivity of the device in order to optimize the geometry to provide guidance on the fabrication of the device with the best performance. Methods: This study uses Silvaco ATLAS numerical simulation software to investigate the performance of CoreFET. The effects of the thickness of the dielectric layer, SiO2, and the distance between the drain and source (channel length) on the conductivity of the semi-conductor indium gallium zinc oxide (IGZO) have been studied. The flat FET models with the same parameters were used for comparison. Results: Our simulation results demonstrate a directed correlation between the optimized conductivity of the device and the thickness of the dielectric material, as well as the length of the channel. Enhanced sensitivity is achievable by employing a thinner dielectric layer and a narrower channel. Conclusion: According to the results, the device can achieve better performance by optimizing the thickness of the insulator and the gap distance between drain and source electrodes. The remarkable similarity between them indicates that the FET effect remained largely unaffected by variations in FET shape. This observation suggests a consistent outcome across FETs, reinforcing the notion that CoreFET exhibits comparable results as those of film FETs. This finding significantly broadens the scope of CoreFET applications.

Peculiarities of the SCLC Effect in Gate‐All‐Around Silicon Nanowire Field‐Effect Transistor Biosensors

AbstractHigh‐quality liquid gate‐all‐around (LGAA) silicon nanowire (NW) field‐effect transistor (FET) biosensors are fabricated and studied their properties in 1 mm phosphate‐buffered saline solution with pH = 7.4 using transport and noise spectroscopy. At small VDS, the conventional current behavior of FET with a linear dependence on voltage is registered in the output current‐voltage (I‐VM) characteristics with M = 1. At drain‐source voltage VDS > 0.6 V, the I‐V characteristics with stronger power M are revealed. It is shown that the current in LGAA NW FETs follows current proportional to voltage in power M = 4 dependence on small liquid gate voltages. Transport and noise spectroscopy analyses demonstrate that the obtained results are associated with the space‐charge‐limited current (SCLC) effect. Moreover, a strong two‐level random telegraph signal (RTS) is found in the region corresponding to SCLC at VDS values exceeding 0.6 V. The RTS related to single trap phenomena results in a well‐resolved Lorentzian component of noise spectra. The results demonstrate that the SCLC and two‐level RTS phenomenon are correlated effects. They should be taken into account during the development of single‐trap‐based devices, including biosensors.

Multi-Layer Palladium Diselenide as a Contact Material for Two-Dimensional Tungsten Diselenide Field-Effect Transistors.

Tungsten diselenide (WSe2) has emerged as a promising ambipolar semiconductor material for field-effect transistors (FETs) due to its unique electronic properties, including a sizeable band gap, high carrier mobility, and remarkable on-off ratio. However, engineering the contacts to WSe2 remains an issue, and high contact barriers prevent the utilization of the full performance in electronic applications. Furthermore, it could be possible to tune the contacts to WSe2 for effective electron or hole injection and consequently pin the threshold voltage to either conduction or valence band. This would be the way to achieve complementary metal-oxide-semiconductor devices without doping of the channel material.This study investigates the behaviour of two-dimensional WSe2 field-effect transistors with multi-layer palladium diselenide (PdSe2) as a contact material. We demonstrate that PdSe2 contacts favour hole injection while preserving the ambipolar nature of the channel material. This consequently yields high-performance p-type WSe2 devices with PdSe2 van der Waals contacts. Further, we explore the tunability of the contact interface by selective laser alteration of the WSe2 under the contacts, enabling pinning of the threshold voltage to the valence band of WSe2, yielding pure p-type operation of the devices.

Eliminating the Double-Slope Behavior of Organic Field-Effect Transistors by Functionalizing the Dielectric Surface With a High Electron Affinity Self-Assembly Monolayer

Eliminating the Double-Slope Behavior of Organic Field-Effect Transistors by Functionalizing the Dielectric Surface With a High Electron Affinity Self-Assembly Monolayer

Distinctive Behavior of Field-Effect and Redox Electrolyte-Gated Organic Transistors

Distinctive Behavior of Field-Effect and Redox Electrolyte-Gated Organic Transistors

Design of Dual-Material Gate Junctionless FinFET based on the Properties of Materials Forming Gate Electrode

This work elaborately investigates the electrical behaviour and short channel performance of Dual-Material Gate Junctionless Fin Field Effect Transistors (DMG-JLFinFETs) with multiple-gate metal pairs and varying gate metal length ratios. Rigorous analysis on the nature of DMG-JLFinFET with gate length as low as 10 nm is done using a device simulator by Silvaco, Inc. The gate material closer to the source, namely M1, has a dominating influence on the threshold voltage (V th) and tunnelling current (I tunn) than the gate material closer to the drain (named M2) in a DMG-JLFinFET. I tunn is lower when the work function of M1 (Φ M1) is greater than the work function of M2 (Φ M2). The relative change in threshold voltage is minimum for Platinum–Gold (PtAu)-DMG-JLFinFET (0.68%). Titanium–Aluminium (TiAl) and Nickel–Titanium (NiTi) gate material pairs, having the same work function difference of 0.38 eV, have the least Drain-Induced Barrier Lowering (DIBL) of 12.88 mV/V. A better Sub-threshold Swing (SS) is observed for DMG-JLFinFET having Φ M1 < Φ M2. For devices with Φ M1 > Φ M2, SS can be improved by making a length of M1 (L M1) greater than 70% of the total gate length (L g).

Molecule-induced n-type behavior of phosphorene-based field-effect transistor for highly sensitive detection of sialic acid

Low-concentration detection of sialic acid (SA) seems to be a promising method in early cancer prognosis. In this work, a phosphorene-based field-effect-transistor (Ph-FET) device has been introduced for detecting various concentrations of SA. The device was fabricated using successive hydrogen plasma treatment to start from the red phosphorus layer and to realize highly crystalline black phosphorus sheets. The morphology and crystalline quality of phosphorene sheets have been extensively examined by transmission electron microscopy, scanning electron microscopy, atomic force microscopy, and Raman spectroscopy. By utilizing this device, we can detect different concentrations of SA from 3 to 2400 μM owing to its negative charge. The detection limit of SA is as low as 2.8 μM. This technique offers a straightforward method for the fabrication of high-performance Ph-FET with no need for exfoliation or sheet transfer. We have fabricated a Ph-FET with a mobility of 10 cm2 V−1 s−1, a carrier concentration of 3.9 × 1011 cm−2, and an on/off current ratio of 103. Moreover, we have observed that exposure to SA solution would change the carrier type of the transistor from a p-type channel into an n-type channel device due to the interaction of SA molecules with the phosphorene atoms at the top of the puckered structure that weakens the P-P lattice anti-bonding orbitals and screens the trapped sites.

Humidity-dependent synaptic characteristics in gelatin-based organic transistors

Organic synaptic transistors based on gelatin gate dielectric exhibit humidity-dependent synaptic characteristics. The device showed excellent field-effect transistor behavior without hysteresis when measured in a vacuum and dry air, but clear pinched hysteresis loops appeared in a humid environment. A large difference in the hysteresis window was observed under a small scanning range of gate voltage in different humid conditions, while the difference vanished under a large scanning range of gate voltage. The excitatory postsynaptic current strongly relies on stimulus pulse width, which is more pronounced in high humidity conditions, suggesting that slow proton transportation through a sequence of hopping may be responsible for the less pronounced dependence of stimulus amplitude with a short stimulus pulse width. The simulation of an artificial neural network for handwritten digit recognition revealed that the ultimate recognition accuracy at high relative humidity is higher than that at low relative humidity due to the large nonlinearity factor resulting from inadequate and low transportation of protons in the gelatin film under ambient conditions with low relative humidity. This work provides valuable insights into the effects of humidity on the performance of gelatin-based organic synaptic transistors, which could be useful for the development of environment-dependent synaptic devices.

Distinct Contact Scaling Effects in MoS2 Transistors Revealed with Asymmetrical Contact Measurements.

2D semiconducting materials have immense potential for future electronics due to their atomically thin nature, whichenables better scalability. While the channel scalability of 2D materials has been extensively studied, the current understanding of contact scaling in 2D devices is inconsistent andoversimplified. Here physically scaled contacts and asymmetrical contact measurements (ACMs) are combined to investigate the contact scaling behavior in 2D field-effect transistors. The ACMs directly compare electron injection at different contact lengths while using the exact same MoS2 channel, eliminating channel-to-channel variations.Theresults show that scaled source contacts can limit the drain current, whereas scaled drain contacts do not. Compared to devices with long contact lengths, devices with short contact lengths (scaled contacts) exhibit larger variations, 15% lower drain currents at high drain-source voltages, and a higher chance ofearly saturation and negative differential resistance. Quantum transport simulations reveal that the transfer length of Ni-MoS2 contacts can be as short as 5nm. Furthermore,it isclearly identified that the actual transfer length depends on the quality of the metal-2D interface. The ACMs demonstrated here will enable further understanding of contact scaling behavior at various interfaces.

Scalable Fabrication of Edge Contacts to 2D Materials: Implications for Quantum Resistance Metrology and 2D Electronics

We report a reliable and scalable fabrication method for producing electrical contacts to two-dimensional (2D) materials based on the tri-layer resist system. We demonstrate the applicability of this method in devices fabricated on epitaxial graphene on silicon carbide (epigraphene) used as a scalable 2D material platform. For epigraphene, data on nearly 70 contacts result in median values of the one-dimensional (1D) specific contact resistances ρc ∼ 67 Ω·μm and follow the Landauer quantum limit ρc ∼ n–1/2, consistently reaching values ρc < 50 Ω·μm at high carrier densityn. As a proof of concept, we apply the same fabrication method to the transition metal dichalcogenide (TMDC) molybdenum disulfide (MoS2). Our edge contacts enable MoS2 field-effect transistor (FET) behavior with an ON/OFF ratio of >106 at room temperature (>109 at cryogenic temperatures). The fabrication route demonstrated here allows for contact metallization using thermal evaporation and also by sputtering, giving an additional flexibility when designing electrical interfaces, which is key in practical devices and when exploring the electrical properties of emerging materials.

Temperature dependent black phosphorus transistor and memory

We studied the temperature dependent transport properties and memory behaviour of ultrathin black phosphorus field-effect transistors. The devices show electrical conductance and field-effect mobility that decreases with the rising temperature. The field effect mobility, which depends also on the gate voltage sweep range, is 283 cm2V−1s−1 at 150 K and reduces to 33 cm2V−1s−1 at 340 K, when the voltage gate sweep range is 50 V. The transfer characteristics show a hysteresis width that increases with the temperature and is exploited to enable non-volatile memories with a wider programming window at higher temperatures.

Моделирование поведения полевых транзисторов при воздействии радиации

The paper deals with the behavior of field-effect transistors under the influence of radiation. The structure of tunnel field-effect transistors, the principle of operation, various effects from exposure to ionization radiation from outer space, and the results of experimental studies of resistance are presented. Field-effect transistors based on single-layer materials such as graphene and MoS2 are also considered. The behavior of field-effect transistors based on graphene is simulated. The paper presents current-voltage characteristics before and after irradiation, at positive and negative voltage at the transistor gate, etc., the analysis of which showed that there were significant changes in the electrical characteristics of transistors and the surface morphology of a single-layer material. The appearance of defects is associated with the heating of the material in the center of the particle track. Similarly, the simulation of the behavior of transistors based on nanotubes, when exposed to radiation, single events appear, was carried out.

Metallization considerations for carbon nanotube device optimization

As a one-dimensional structure with atomically thin sidewalls, charge transport in carbon nanotubes can be regarded as a surface phenomenon. As such, perturbations from the surrounding environment can have a dramatic impact on transport and consequently on the device behavior of carbon nanotube field-effect transistors (CNTFETs). Importantly, this includes effects from device fabrication processes like contact metallization. With this as motivation, several aspects of contact metallization are investigated herein. First, it is found that ON current in n-type CNTFETs is enhanced to the level of p-type CNTFETs through the utilization of titanium as an adhesion layer, a result of improved wetting. Effects of different metallization techniques, namely, thermal and electron-beam evaporation, are also explored in p-type devices using titanium/palladium/gold contacts. It is found that thermal metallization consistently produces devices with higher ON current. In-depth analysis of the transfer characteristics reveals that this is due to radiation effects encountered during electron-beam processing, resulting in channel scattering and a decreased transconductance in the devices. This effect is particularly severe upon gold processing, and attempts to heal this device degradation through annealing proved unsuccessful. All studies presented here are conducted through the analysis of a large number of nanotube devices, giving a degree of confidence to the average results. Additionally, only device parameters that can be directly extracted from the transfer characteristics are analyzed. Assumptions including nanotube diameter, capacitance, and nanotube number per device are not made. Results from this study provide recommendations for optimizing CNTFET performance as it relates to contact metallization.

Ultra-Low Power Schottky Barrier TFT-Based Neurotransmitter Detection and Regenerative Studies

There is limited work on understanding Schottky barrier (SB) field-effect transistor (FET) behavior, and subsequent evolution of sensitivity metrics under wet detection conditions for neurotransmitter sensing applications. In this work, we report low-power deep subthreshold (DST) characteristics of SB InGaZnO₄ (IGZO) thin film transistors (TFTs) and implement this regime for sensitive and selective <i>ex vivo</i> detection of Dopamine against Adenosine Triphosphate (ATP). Device regeneration was performed under liquid solution environment over 34 days and sensor response was observed to drift less than two orders of magnitude. Nevertheless, the quantified trends due to buffer solution baseline versus target conjugation were virtually preserved across the TFTs. Widely improved detection metrics were extracted from the detection tests, namely the limit of detection (LoD) in the 100fM-100pM range, a binding affinity (<inline-formula> <tex-math notation="LaTeX">$k_{D}$ </tex-math></inline-formula>) between <inline-formula> <tex-math notation="LaTeX">$2.03\times 10^{-11}$ </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">$3.02\times 10^{-9}\text{M}$ </tex-math></inline-formula> limits, and high sensitivity around 31-42mV/decade of target concentration. Although a steady drift with clear, repeatable differences between the device state at the start and end of the 34-day period were obtained, these devices were functional even after the regeneration test period. Such results can be used to estimate the regenerative lifetime of TFT biosensors under aptamer-immobilized solution environment detection conditions.

Review-Hysteresis in Carbon Nano-Structure Field Effect Transistor.

In recent decades, the research of nano-structure devices (e.g., carbon nanotube and graphene) has experienced rapid growth. These materials have supreme electronic, thermal, optical and mechanical properties and have received widespread concern in different fields. It is worth noting that gate hysteresis behavior of field effect transistors can always be found in ambient conditions, which may influence the transmission appearance. Many researchers have put forward various views on this question. Here, we summarize and discuss the mechanisms behind hysteresis, different influencing factors and improvement methods which help decrease or eliminate unevenness and asymmetry.

Analysis of static behavior of ion sensitive field effect Transistor for pH measurements

The Ion-Sensitive Field-Effect Transistor (ISFET) is one of the most popular pH sensors traditionally using to measure hydrogen ion concentration (pH) of the electrolytic solutions. It is developed from Metal Oxide Semiconductor Field-Effect Transistor (MOSFET) by replacing gate electrode with an electrolytic solution to be tested, and a reference metal electrode immersed in that solution. Basic principle of ISFET operation is based on that of standard NMOS structure in conjunction with the insulator-electrolyte capacitor as described in this paper. The site-binding theory (generalized to two kinds of binding sites), together with the Gouy-Chapman-Stern model for the potential profile in the electrolyte, is coupled to the MOS physics. As a result, an approximate analytical model which completely describes static behavior of the ISFET is obtained. The developed description can serve as useful tool for understanding many contemporary biosensors based on original ISFET structure which has broad application in bio-medicine, biological, chemistry and environmental areas.

Electronic transport via DTF-NEGF at bipyridine junctions with 1D organic electrodes

In this work, we study the properties of electronic transport in molecular junctions formed by bipyridine isomers as central region coupled at electrodes of carbyne wires. Through calculations of first principles , based on Density Functional Theory (DFT), combined with Non-Equilibrium Green’s Functions (NEGF), we obtain important properties such as electric current , differential conductance, transmission, and eigenchannels. The results showed that the presence of nitrogen atoms in the molecule–electrode interface strongly affects the coupling of the junction, providing better electronic conduction; this is corroborated by the transmission eigenchannels. The transport properties analyzed revealed that in bipyridine bridges, devices with carbyne electrodes, presented better performance when compared to other works that used metallic electrodes (Au, Ag, and Cu) or graphene nanoribbons electrodes. The devices proposed showed a Field Effect Transistor (FET) behavior when are formed by symmetric isomers, whereas for asymmetric systems we obtained characteristics of Molecular Diode (MD).

Comparative Study of Charge-Transport Behavior of Edge-on- and Face-on-Oriented Diketopyrrolopyrrole-Based Conjugated Copolymers Bearing Chalcogenophene Units

Herein, we present comparative device analyses that help understand the charge-transport behavior in polymer field-effect transistors (PFETs) in which synthesized diketopyrrolopyrrole-based (DPP-based) conjugated copolymers bearing chalcogenophene units are used as semiconducting channel materials. The copolymer backbone orientations were successfully modified by tailoring the spacer units of the conjugated copolymers to be face-on-oriented for DPP-based copolymers bearing methylthiophene-furan-methylthiophene units (PDPP-MT-F-MT) and edge-on-oriented for the corresponding thiophene (PDPP-MT-T-MT)- and selenophene (PDPP-MT-Se-MT)-containing copolymers. Higher backbone planarity and higher field-effect mobilities were expected for the edge-on-oriented DPP-based copolymers (PDPP-MT-T-MT and PDPP-MT-Se-MT) based on density functional theory calculations; however, the face-on-oriented PDPP-MT-F-MT-based PFET exhibited superior electrical performance in terms of field-effect mobility. Charge-transport analyses based on the Gaussian disorder model, focusing on the charge-transport behavior of the disordered (amorphous) domains in the DPP-based polymer films, revealed that the localized states in the disordered domains of the face-oriented PDPP-MT-F-MT become more delocalized than those of the edge-oriented PDPP-MT-T-MT and PDPP-MT-Se-MT polymers when a gate bias is applied to their PFETs. Therefore, we attribute the electrical performance of a DPP-based PFET to the degree of delocalization of the disordered domains of its DPP-based polymer, which has a significant impact on the charge-transport behavior.

Ultrathin Al‐Assisted Al2O3 Passivation Layer for High‐Stability Tungsten Diselenide Transistors and Their Ambipolar Inverter

Abstract2D transition metal dichalcogenides (TMDs) have recently received significant attention owing to their superior electrical, optical, and mechanical properties. However, most previous research on TMDs has not focused on their stability against bias and illumination stress. Here, high‐stability tungsten diselenide (WSe2) field‐effect transistors (FETs) are introduced with an ultrathin Al‐assisted alumina (Al2O3) passivation. Through the Al‐assisted Al2O3 passivation, the transport behavior of the WSe2 FETs is converted from p‐type to ambipolar owing to the n‐type doping effect of Al2O3 passivation. Furthermore, the stability of the WSe2 FETs is highly improved against gate bias and illumination stress owing to the effect of Al2O3 film quality on WSe2 by ultrathin Al predeposition (≈1 nm). To compare the stress effect on the electrical characteristics, three types of devices: 1) pristine WSe2 FETs, 2) WSe2 FET with Al2O3 passivation layer, and 3) WSe2 FETs with Al‐assisted Al2O3 passivation layer, are systematically tested with positive gate bias stress (PBS) and positive gate bias illumination stress (PBIS). Finally, an ambipolar inverter composed of Al‐assisted Al2O3 passivated WSe2 FETs is demonstrated. This study proposes a promising approach that improves the stability of TMD‐based FETs for next‐generation logic applications.

Defects Induced Charge Trapping/Detrapping and Hysteresis Phenomenon in MoS2 Field-Effect Transistors: Mechanism Revealed by Anharmonic Marcus Charge Transfer Theory

One critical problem inhibiting the application of MoS2 field-effect transistors (FETs) is the hysteresis in their transfer characteristics, which is typically associated with charge trapping (CT) and charge detrapping (CDT) induced by atomic defects at the MoS2-dielectric interface. Here, we propose a novel atomistic framework to simulate electronic processes across the MoS2-SiO2 interface, demonstrating the distinct CT/CDT behavior of different types of atomic defects and further revealing the defect type(s) that most likely cause hysteresis. An anharmonic approximation of the classical Marcus theory is developed and combined with state-of-the-art density functional theory to calculate the gate bias-dependent CT/CDT rates. All the key electronic quantities are calculated with Heyd-Scuseria-Ernzerhof hybrid functionals. The results show that single Si-dangling bond defects are active electron trapping centers. Single O-dangling bond defects are active hole trapping centers, which are more likely to be responsible for the hysteresis phenomenon due to their significant CT rate and apparent threshold voltage shift. In contrast, double Si-dangling bond defects are not active trap centers. These findings provide fundamental physical insights for understanding the hysteresis behavior of MoS2 FETs and provide vital support for understanding and solving the reliability of nanoscale devices.