Performance Of Field-effect Transistors Research Articles

Ultrafast high-endurance memory based on sliding ferroelectrics.

The persistence of voltage-switchable collective electronic phenomena down to the atomic scale has extensive implications for area- and energy-efficient electronics, especially in emerging nonvolatile memory technology. We investigate the performance of a ferroelectric field-effect transistor (FeFET) based on sliding ferroelectricity in bilayer boron nitride at room temperature. Sliding ferroelectricity represents a different form of atomically thin two-dimensional (2D) ferroelectrics, characterized by the switching of out-of-plane polarization through interlayer sliding motion. We examined the FeFET device employing monolayer graphene as the channel layer, which demonstrated ultrafast switching speeds on the nanosecond scale and high endurance exceeding 1011 switching cycles, comparable to state-of-the-art FeFET devices. These characteristics highlight the potential of 2D sliding ferroelectrics for inspiring next-generation nonvolatile memory technology.

Impact of Rh, Ru, and Pd Leads and Contact Topologies on Performance of WSe2 FETs: A First Comparative Ab Initio Study.

2D field-effect transistors (FETs) fabricated with transition metal dichalcogenide (TMD) materials are a potential replacement for the silicon-based CMOS. However, the lack of advancement in p-type contact is also a key factor hindering TMD-based CMOS applications. The less investigated path towards improving electrical characteristics based on contact geometries with low contact resistance (RC) has also been established. Moreover, finding contact metals to reduce the RC is indeed one of the significant challenges in achieving the above goal. Our research provides the first comparative analysis of the three contact configurations for a WSe2 monolayer with different noble metals (Rh, Ru, and Pd) by employing ab initio density functional theory (DFT) and non-equilibrium Green's function (NEGF) methods. From the perspective of the contact topologies, the RC and minimum subthreshold slope (SSMIN) of all the conventional edge contacts are outperformed by the novel non-van der Waals (vdW) sandwich contacts. These non-vdW sandwich contacts reveal that their RC values are below 50 Ω∙μm, attributed to the narrow Schottky barrier widths (SBWs) and low Schottky barrier heights (SBHs). Not only are the RC values dramatically reduced by such novel contacts, but the SSMIN values are lower than 68 mV/dec. The new proposal offers the lowest RC and SSMIN, irrespective of the contact metals. Further considering the metal leads, the WSe2/Rh FETs based on the non-vdW sandwich contacts show a meager RC value of 33 Ω∙μm and an exceptional SSMIN of 63 mV/dec. The two calculated results present the smallest-ever values reported in our study, indicating that the non-vdW sandwich contacts with Rh leads can attain the best-case scenario. In contrast, the symmetric convex edge contacts with Pd leads cause the worst-case degradation, yielding an RC value of 213 Ω∙μm and an SSMIN value of 95 mV/dec. While all the WSe2/Ru FETs exhibit medium performances, the minimal shift in the transfer curves is interestingly advantageous to the circuit operation. Conclusively, the low-RC performances and the desirable SSMIN values are a combination of the contact geometries and metal leads. This innovation, achieved through noble metal leads in conjunction with the novel contact configurations, paves the way for a TMD-based CMOS with ultra-low RC and rapid switching speeds.

Enhancing Radio Frequency Performance of Graphene Field-Effect Transistors through Machine-Learning-Based Physical Prediction and Optimization

Enhancing Radio Frequency Performance of Graphene Field-Effect Transistors through Machine-Learning-Based Physical Prediction and Optimization

SiX2 (X = S, Se) Nanowire Gate-All-Around MOSFETs for Sub-5 nm Applications.

The gate-all-around (GAA) field-effect transistor (FET) holds great potential to support next-generation integrated circuits. Nanowires such as carbon nanotubes (CNTs) are one important category of channel materials in GAA FETs. Based on first-principles investigations, we propose that SiX2 (X = S, Se) nanowires are promising channel materials that can significantly elevate the performance of GAA FETs. The sub-5 nm SiX2 (X = S, Se) nanowire GAA FETs exhibit excellent ballistic transport properties that meet the requirements of the 2013 International Technology Roadmap for Semiconductors (ITRS). Compared to CNTs, they are also advantageous or at least comparable in terms of gate controllability, device dimensions, etc. Importantly, SiSe2 GAA FETs show superb gate controllability due to the ultralow minimum subthreshold swing (SSmin) that breaks "Boltzmann's tyranny". Moreover, the energy-delay product (EDP) of SiX2 GAA FETs is significantly lower than that of the CNT FETs. These features make SiX2 nanowires ideal channel material in the sub-5 nm GAA FET devices.

Boosting the performance of polymer field-effect transistors through fluorine atom substitutions and comparing the effect of various acceptor units and channel mobilities

Three conjugated copolymers, PDPP-2FTVT, PIID-2FTVT, and PNDI-2FTVT based on the 2,2′-(1E)-1,2-ethenediylbis[3-fluorothiophene] (2FTVT) core with varying acceptor units, diketopyrrolopyrrole (DPP), isoindigo (IID), and naphthalenediimide (NDI) were developed for organic field-effect transistors (OFETs). Combined electron-withdrawing fluorine atoms and vinyl linkage in the 2FTVT unit not only reduce the frontier molecular orbital energies but also extended the absorption profile and planarize the polymer backbone, manifesting synergetic effect on the strengthened molecular interactions and charge-carrier properties. The resulted copolymer, PDPP-2FTVT show highly reliable thin film transistor properties with highest hole mobility of 1.93 cm2 V−1 s−1 compared to PIID-2FTV and PNDI-2FTVT. PIID-2FTV copolymer show ambipolar characteristic with hole and electron mobilities of 0.71 and 0.03 cm2 V−1 s−1 respectively while PNDI-2FTVT exhibited the highest electron mobility of 0.20 cm2 V−1 s−1 among three copolymers. Thin film micro-structure characterization reveal that the three copolymers formed lamellar, edge-on molecular packing (for PDPP-2FTVT and PIID-2FTV), increased crystallinity with smaller π-π stacking distances, and strengthen the planarity after thermal annealing. These results contribute important progresses in solution-processed OFET and could provide a greater possibility of 2FTVT based copolymers for commercial application.

Origin of two-dimensional hole gas at the hydrogen-terminated diamond surfaces: Negative interface valence-induced upward band bending

The surface transfer doping model has been extensively adopted as a mechanism to account for the generation of hole accumulation layers below hydrogen-terminated diamond (H-diamond) surfaces. To achieve effective surface transfer doping, surface electron acceptor materials with high electron affinity (EA) are required to produce a high density of two-dimensional hole gas (2DHG) on the H-diamond subsurface. We have established ingenious theoretical models to demonstrate that even if these solid materials do not have a high EA value, they remain capable of absorbing electrons from the H-diamond surface by forming a negatively charged interface to act as a surface electron acceptor in the surface transfer doping model. Our calculations, particularly for the local density of states, provide compelling evidence that the effect of an interface with negative charges induces an upward band bending on the H-diamond side. Furthermore, the valence band maximum of the diamond atoms at the interface crosses the Fermi level, giving rise to strong surface transfer p-type doping. These results give a strong theoretical interpretation of the origin of 2DHG on H-diamond surfaces. The proposed guidelines contribute to further improvements in the performance of 2DHG H-diamond field effect transistors.

High-detectivity photodetectors based on CsPbCl3/Au heterostructures

Photodetector based on all-inorganic CsPbCl3 perovskite is drawing increasing interest owing to its stable chemical properties, suitable band gap and superior inherent optoelectronic properties. However, most of the perovskite detectors are fabricated from polycrystalline films with a number of grain boundaries and defects which would decline the device performance. At the same time, the performance of the device is sacrificed by the presence of a large amount of gaps between the metal electrodes and the material. Here, a high detective photodetector is demonstrated based on CsPbCl3 crystals by liquid-phase growth on pre-patterned Au electrodes. Heterojunctions fabricated by liquid-phase self-assembly synthesis form an embedded structure between metal electrodes and the material, which greatly enhances the contact area and reduces the dark current. The device serves as photodetectors with a responsivity of 62.5 μA/W and detectivity up to 1.79 × 1011 Jones. Furthermore, these devices exhibit outstanding performance of field-effect transistors with a remarkable on/off ratio of 107. These results offer novel insights for the exploration of high-performance photodetectors based on all-inorganic perovskite materials.

High-Performance Contact-Doped WSe2 Transistors Using TaSe2 Electrodes.

Two-dimensional (2D) transitional metal dichalcogenides (TMDs) have garnered significant attention due to their potential for next-generation electronics, which require device scaling. However, the performance of TMD-based field-effect transistors (FETs) is greatly limited by the contact resistance. This study develops an effective strategy to optimize the contact resistance of WSe2 FETs by combining contact doping and 2D metallic electrode materials. The contact regions were doped using a laser, and the metallic TaSe2 flakes were stacked on doped WSe2 as electrodes. Doping the contact areas decreases the depletion width, while introducing the TaSe2 contact results in a lower Schottky barrier. This method significantly improves the electrical performance of the WSe2 FETs. The doped WSe2/TaSe2 contact exhibits an ultralow Schottky barrier height of 65 meV and a contact resistance of 11 kΩ·μm, which is a 50-fold reduction compared to the conventional Cr/Au contact. Our method offers a way on fabricating high-performance 2D FETs.

Enhanced Electrical Transport Properties of Molybdenum Disulfide Field-Effect Transistors by Using Alkali Metal Fluorides as Dielectric Capping Layers.

The electronic properties of 2D materials are highly influenced by the molecular activity at their interfaces. A method was proposed to address this issue by employing passivation techniques using monolayer MoS2 field-effect transistors (FETs) while preserving high performance. Herein, we have used alkali metal fluorides as dielectric capping layers, including lithium fluoride (LiF), sodium fluoride (NaF), and potassium fluoride (KF) dielectric capping layers, to mitigate the environmental impact of oxygen and water exposure. Among them, the LiF dielectric capping layer significantly improved the transistor performance, specifically in terms of enhanced field effect mobility from 74 to 137 cm2/V·s, increased current density from 17 μA/μm to 32.13 μA/μm at a drain voltage of Vd of 1 V, and decreased subthreshold swing to 0.8 V/dec The results have been analytically verified by X-ray photoelectron spectroscopy (XPS) and Raman, and photoluminescence (PL) spectroscopy, and the demonstrated technique can be extended to other transition metal dichalcogenide (TMD)-based FETs, which can become a prospect for cutting-edge electronic applications. These findings highlight certain important trade-offs and provide insight into the significance of interface control and passivation material choice on the electrical stability, performance, and enhancement of the MoS2 FET.

Lead ions detection using CVD-grown ReS2-FET with the facilitation of a passivation layer

Field-effect transistor (FET)-based heavy-metal detection is garnering attention due to its heightened sensitivity, affordability, convenient fabrication, and portability. Flower-like rhenium disulfide (ReS2) offers potential for high-performance FET sensors, but direct exposure of channel materials to the ionic solution without a passivation layer results in multiple signals arising from the ionic transmission, doping impact, and gating effect. Introducing a passivation layer to the channel surface enhances sensor sensitivity without compromising device performance, ensuring conductance changes are primarily due to the gating effect. Here, a large surface area of Chemical Vapor Deposition (CVD)-grown vertically aligned ReS2 is employed in the FET-based sensor, and the utilization of the HfO2 layer is to isolate analytes from the elements of the conducting channel. For real-time lead monitoring in a water environment, it exhibits strong electrical stability, an impressive LoD (≈2 nM), a rapid response time (≈1.1 sec), and notable selectivity. Additionally, sensing operations are characterized by developing a unique amplifier circuit by integrating the fabricated sensor, contributing to advancements in sensor integration to detect hazardous metals in industrial electronics. These results underscore the potential for enhancing the performance of ion-sensitive FETs through structural optimization and improvements to the fundamental sensor mechanism.

Enhancing Stability and Performance in Tin-Based Perovskite Field-Effect Transistors Through Hydrogen Bond Suppression of Organic Cation Migration.

Ion migration poses a substantial challenge in perovskite transistors, exerting detrimental effects on hysteresis and operational stability. This study focuses on elucidating the influence of ion migration on the performance of tin-based perovskite field-effect transistors (FETs). It is revealed that the high background carrier density in FASnI3 FETs arises not only from the oxidation of Sn2+ but also from the migration of FA+ ions. The formation of hydrogen bonding between FA+ and F- ions efficiently inhibits ion migration, leading to a reduction in background carrier density and an improvement in the operational stability of the transistors. The strategy of hydrogen bond is extended to fluorine-substituted additives to improve device performance. The incorporation of 4-fluorophenethylammonium iodide additives into FETs significantly minimizes the shift of turn-on voltage during cyclic measurements. Notably, an effective mobility of up to 30 cm2 V-1 s-1 with an Ion/off ratio of 107 is achieved. These findings hold promising potential for advancing tin-based perovskite technology in the field of electronics.

Ferroelectric Based Low Power MOSFET for DC/RF Applications: Machine Learning Assisted Statistical Variation Analysis

The analog/radio-frequency (RF) performance of a ferroelectric-based substrate metal oxide semiconductor field effect transistor (FE-MOSFET) with dielectric spacer was designed and proposed. The utilization of gate side wall spacers aims to mitigate short-channel effects (SCEs), and improve overall device performance. Simulation results demonstrate enhanced performance metrics, including improved transconductance (80%), reduced gate leakage (95.4%), and enhanced cutoff frequency (25%), making this design a promising candidate for next-generation high-performance analog and RF applications. Additionally, a novel machine learning (ML)-assisted approach is proposed for investigating the spacer-based FE-MOSFET to reduce the computational cost of numerical TCAD device simulations with the help of conventional- artificial neural network (C-ANN). This method is reported for the first-time ML-based C-ANN for Fe-based low-power MOSFET, matches the similar accuracy of physics-based TCAD with the fastest learning rate and fastest computational speed (in 95–100 s). An ML-based prediction replacement for physics-based TCAD is developed to save around 8–10 h of runtime for each iteration. Because ML predictions can never be 100% accurate, it is essential to ensure approximately zero mean-square error in the final results.

Non-volatile memory characteristics of flexible ferroelectric field-effect transistors consisting of Sm-doped BiFeO3 thin films

This study investigates the impact of Sm doping on the structural, electrical, and functional properties of BiFeO3 (BFO) thin films. The aim is to improve their non-volatile memory characteristics for use in flexible ferroelectric field-effect transistors (FeFETs). We fabricated Sm-doped BFO (SBFO) thin films on flexible mica substrates with Sm concentrations ranging from 0 to 15 %. The FeFET device structures, which include MoS2 monolayer channels and SBFO thin films with Pt bottom electrodes, were analyzed. The SBFO thin films displayed a (111) preferential orientation due to the influence of underlying Pt electrodes. Notably, the SBFO thin film doped with a 10 % Sm concentration showed optimal enhancements, including a reduction in leakage current density and an increase in remanent polarization to 55.8 μC/cm2, compared to undoped thin film (35.5 μC/cm2). Furthermore, the thin film exhibited superior fatigue resistance for up to 1012 switching cycles and maintained stable values under significant bending stress for ferroelectric polarizations. On the other hand, SBFO thin film with 15 % Sm doping displayed relaxor antiferroelectric behavior, highlighting the importance of doping concentration. Therefore, for non-volatile memory application reliability, the FeFET device featuring a 10 % Sm-doped SBFO thin film not only enhanced the memory window but also showed superior fatigue characteristics over 1012 switching cycles, compared to its undoped counterpart. These findings demonstrate the effect of Sm doping in customizing the properties of BFO thin films for advanced, flexible non-volatile memory devices, offering a novel insight to optimize ferroelectric field-effect transistor performance.

Evaluating the performance of p-type organic field-effect transistor using different source–drain electrodes

Evaluating the performance of p-type organic field-effect transistor using different source–drain electrodes

Anti-ambipolar transport and logic operation in two-dimensional field-effect transistors using in-series integration of GeAs and SnS2

Germanium arsenide (GeAs) from the IV–V semiconductor family has drawn attention for its anisotropic optical and electrical characteristics as a robust p-type semiconductor with high mobility. Despite its potential, the scope of applications for two-dimensional (2D) GeAs remains limited. In this study, we investigate the in-series integration of GeAs and SnS2 for complementary inverter operation, a crucial element in logic circuits. Moreover, the resulting in-series field-effect transistors reveal a previously undocumented anti-ambipolar behavior in this configuration, with a peak-to-valley ratio exceeding 5000 at a drain-source bias of 2 V. This anti-ambipolar characteristic operates regardless of the direction of current flow, which is rarely seen in conventional anti-ambipolar transistors built with hetero-stacked p–n junctions. Moreover, the in-series structure demonstrates stable operation as a complementary inverter, highlighting the versatile potential of p-type 2D GeAs in diverse optoelectronic applications. This work contributes insights into the transport characteristics of GeAs and its interconnected arrangement with SnS2, offering valuable implications for the development of advanced 2D material-based devices.

Investigation of thermal stress effects on subthreshold conduction in nanoscale p-FinFET from Multiphysics perspective

The rising temperature due to a self-heating or thermal environment not only degrades the subthreshold performance but also intensifies thermal stress, posing a severe challenge to device performance and reliability design. The thermal stress effects on the ON-state performance of the p-type fin field-effect transistor were previously studied. However, as far as we know, how thermal stress affects its subthreshold conduction remains unclear, which is studied in this manuscript. The impact of thermal stress due to the self-heating of adjacent devices on subthreshold conduction is investigated by solving the quantum transport, thermal conduction, and force balance equations for ballistic transport and dissipative transport with phonon scattering. Then, the thermal stress effects at different ambient temperatures are further discussed and analyzed. The simulation results show that the OFF-state leakage current can be reduced by thermal stress, even up to 9.28% for the (110)/[001] device operating at an ambient temperature of 550 K, and its reduction is the comprehensive result of the thermal stress effects on the band structure, potential profile, carrier distribution, and source-to-drain tunneling. In addition, the thermal stress has no significant effects on subthreshold swing although it can change the magnitude of the subthreshold current. Moreover, the effect of thermal stress on subthreshold conduction is highly dependent on the thermal environment of the device and the crystal orientation of the channel semiconductor material.

Detailed Investigation of Plasticized PMMA Dielectric for Improved Performance of Organic Field-Effect Transistors

Detailed Investigation of Plasticized PMMA Dielectric for Improved Performance of Organic Field-Effect Transistors

Design and application of germanium based complementary TFET devices with step tunneling paths

Expanding tunneling has consistently been one of the approaches to enhance the on-state current (Ion) and performance of Tunnel Field-Effect Transistor (TFET). This paper proposes a novel structure for TFET called Step Tunneling Path TFET (STP TFET). The stepped tunneling path is achieved by preparing majority carrier channel and introducing pocket doping layers and lightly doped channel extension regions in the channel. Taking Germanium TFET as an example, the complementary structures, electrical parameters, DC and analog characteristics of STP TFET are investigated. Simulation results demonstrate that, compared to normal TFET, STP TFET exhibits significant improvements in Ion (n-TFET∼18/p-TFET∼45 times), cut-off frequency (n-TFET∼6/p-TFET∼16 times), Gain Bandwidth Product enhancement (n-TFET∼22/p-TFET∼16 times), and Transconductance Frequency Product enhancement (n-TFET∼3/p-TFET∼15 times). Furthermore, in the C-TFET inverter, the transient rise and fall times have decreased by 149 and 199 ns, respectively, while the voltage gain has increased by 6.7 times. The proposed device shows promising potential for applications in high-speed and low-power circuit designs.

Anisotropic phonon properties in SiP2 monolayer: A first-principles study

Recently, the micromechanical exfoliation method has effectively separated the two-dimensional (2D) SiP2 flake, which exhibits superior performance in field-effect transistors and photodetectors. In this paper, first-principles calculations were utilized to investigate the phononic properties of a SiP2 monolayer, which would be significant to explain the thermal deformation of 2D SiP2-based devices. We found that the acoustic phonon branches of SiP2 monolayer demonstrate significant in-plane anisotropy. The anisotropic ratios for the group velocities are 2.41 and 1.66 for the longitudinal and transverse acoustic modes, respectively. Meanwhile, the anisotropic ratio of the negative thermal expansion coefficient only considering the contribution from acoustic phonons is 0.14, while this ratio is ∼0.279 occurs at 120 K when both acoustic and optical phonons are taken into account. For the Raman-active optical phonons, the largest Grüneisen constant of these Raman-active phonons reaches 22.76, while the largest anisotropic ratio of phonon frequency is up to 2.16. To interpret this significant in-plane anisotropy, we calculated the electron density distribution, crystal orbital Hamilton populations (COHP) and interatomic force constants (IFCs), and found the maximal IFC in the x-direction is 5.79 times greater than y-direction, suggesting it as a major origin of the phononic anisotropy.

Enhanced N-type Semiconducting Performance of Asymmetric Monochlorinated Isoindigo-based Semiregioregular Polymers under Dynamic Forces.

The asymmetric monochlorination strategy not only effectively addresses the steric issues in conventional dichlorination but also enables the development of promising acceptor units and semiregioregular polymers. Herein, monochlorinated isoindigo (1CIID) is successfully designed and synthesized by selectively introducing single chlorine (Cl) atoms. Furthermore, the 1CIID copolymerizes with two donor counterparts, centrosymmetric 2,2'-bithiophene (2T) and axisymmetric 4,7-di(thiophen-2-yl)benzo[1,2,5]thiadiazole (DTBT), forming two polymers, P1CIID-2T and P1CIID-DTBT. These polymers exhibit notable differences in backbone linearity and dipole moments, influenced by the symmetry of their donor counterparts. In particular, P1CIID-2T, which contains a centrosymmetric 2T unit, demonstrates a linear backbone and a significant dipole moment of 10.20 D. These properties contribute to the favorable film morphology of P1CIID-2T, characterized by highly ordered crystallinity in the presence of fifth-order (500) X-ray diffraction peaks. Notably, P1CIID-2T exhibits a significant improvement in molecular alignment under dynamic force, resulting in over 8-fold improvement in the performance of organic field-effect transistor (OFET) devices, with superior electron mobility up to 1.22 cm2 V-1 s-1. This study represents the first synthesis of asymmetric monochlorinated isoindigo-based conjugated polymers, highlighting the potential of asymmetric monochlorination for developing n-type semiconducting polymers. Moreover, our findings provide valuable insights into the relationship between the molecular structure and properties.