Characteristics Of Field-effect Transistors Research Articles

Electrical characterization of si nanowire GAA-TFET based on dimensions downscaling

This research paper explains the effect of the dimensions of Gate-all-around Si nanowire tunneling field effect transistor (GAA Si-NW TFET) on ON/OFF current ratio, drain induces barrier lowering (DIBL), sub-threshold swing (SS), and threshold voltage (VT). These parameters are critical factors of the characteristics of tunnel field effect transistors. The Silvaco TCAD has been used to study the electrical characteristics of Si-NW TFET. Output (gate voltage-drain current) characteristics with channel dimensions were simulated. Results show that 50nm long nanowires with 9nm-18nm diameter and 3nm oxide thickness tend to have the best nanowire tunnel field effect transistor (Si-NW TFET) characteristics.

Unscrambling for Subgap Density-of-States in Multilayered MoS2Field Effect Transistors under DC Bias Stress via Optical Charge-Pumping Capacitance-Voltage Spectroscopy

Herein, we quantitatively analyze the evolution of the subgap density of states (DOSs) for multilayered molybdenum disulfide (m-MoS2) field effect transistors (FETs) with bilayered SiNx/SiOx gate dielectrics under positive bias stress (PBS) and negative bias stress (NBS) by using optical charge-pumping capacitance-voltage spectroscopy. To decouple external gas ambient effects on device instability, hydrophobic fluoropolymers (cyclized transparent optical polymer; CYTOP) are employed for m-MoS2 FETs followed by the evaluation of subgap-DOSs in the devices for the respective PBS (or NBS). Through extraction of subgap-DOSs and their deconvolution with an analytical model of acceptor (or donor)-like states, it is shown that the device instability is closely correlated with state transitions of DOSs, corresponding to shallow (or midgap) levels for monosulfur vacancy (VS) (or disulfur vacancy ( $\text{V}_{\mathrm {S2}}$ )). Moreover, after PBS, the initial states of VS(0) (or $\text{H}_{\mathrm {S2}}$ (0)) transit toward VS (−1) (or $\text{H}_{\mathrm {S2}}(-1$ )) via electron trapping, whereas the transition toward VS (0) and $\text{H}_{\mathrm {S2}}$ (+1) during NBS is assessed from the initial $\text{V}_{\mathrm {S}}(-1$ ) and $\text{H}_{\mathrm {S2}}$ (0) states. Furthermore, technology computer-aided design (TCAD) simulation based on the extracted DOSs properly replicates the measured I-V characteristics of m-MoS2 FETs with (and without) CYTOP encapsulation. In this study, subgap-DOS characterization via optical charge pumping and validation of the quantitative evolution of subgap-DOSs suggest that this platform can be potentially beneficial for an in-depth understanding of the origins of device instability for transition metal dichalcogenide (MX2)-based FETs, where M is a transition metal and X is a chalcogenide.

Field-effect-transistor-based ion sensors: ultrasensitive mercury(II) detection via healing MoS2 defects.

The contamination of water with heavy metal ions represents a harsh environmental problem resulting from societal development. Among various hazardous compounds, mercury ions (Hg2+) surely belong to the most poisonous ones. Their accumulation in the human body results in health deterioration, affecting vital organs and eventually leading to chronic diseases, and, in the worst-case scenario, early death. High selectivity and sensitivity for the analyte of choice can be achieved in chemical sensing using suitable active materials capable of interacting at the supramolecular level with the chosen species. Among them, 2D transition metal dichalcogenides (TMDCs) have attracted great attention as sensory materials because of their unique physical and chemical properties, which are highly susceptible to environmental changes. In this work, we have fabricated MoS2-based field-effect transistors (FETs) and exploited them as platforms for Hg2+ sensing, relying on the affinity of heavy metal ions for both point defects in TMDCs and sulphur atoms in the MoS2 lattice. X-ray photoelectron spectroscopy characterization showed both a significant reduction of the defectiveness of MoS2 when exposed to Hg2+ with increasing concentration and a shift in the binding energy of 0.2 eV suggesting p-type doping of the 2D semiconductor. The efficient defect healing has been confirmed also by low-temperature photoluminescence measurements by monitoring the attenuation of defect-related bands after Hg2+ exposure. Transfer characteristics in MoS2 FETs provided further evidence that Hg2+ acts as a p-dopant of MoS2. Interestingly, we observed a strict correlation of doping with the concentration of Hg2+, following a semi-log trend. Hg2+ concentrations as low as 1 pM can be detected, being way below the limits imposed by health regulations. Electrical characterization also revealed that our sensor can be efficiently washed and used multiple times. Moreover, the developed devices displayed a markedly high selectivity for Hg2+ against other metal ions as ruled by soft/soft interaction among chemical systems with appropriate redox potentials, being a generally applicable approach to develop chemical sensing devices combining high sensitivity, selectivity and reversibility, to meet technological needs.

Посвящается памяти В.Д. Александрова Влияние отжига в инертной атмосфере на электрические свойства кристаллических пленок пентацена

The results of a study of the effect of annealing at 150 °C in an inert atmosphere (Ar + 5% H2) on the electrical properties of organic field-effect transistors based on pentacene are presented. Crystalline pentacene films with a thickness of 95 ± 5 nm were obtained using thermal vacuum deposition. The transfer and output characteristics of field-effect transistors before and after annealing for 15 hours are investigated. It was found that as a result of heat treatment, the hole mobility in the saturation regime increased by an average of 30%, and the threshold voltage decreased approximately two times. According to the data of atomic force microscopy, annealing led to a more than twofold decrease in the surface roughness of pentacene films, as well as to a noticeable enlargement of grains, which led to a decrease in the concentration of traps for hole electric transport in the channel of the field-effect transistor.

Ultrashort Pulse Detection and Response Time Analysis Using Plasma-Wave Terahertz Field-Effect Transistors

We report on the response characteristics of plasmonic terahertz field-effect transistors (TeraFETs) fed with femtosecond and picosecond pulses. Varying the pulse width (tpw) from 10-15 s to 10-10 s under a constant input power condition revealed two distinctive pulse detection modes. In the short pulse mode (tpw << L/s, where L is the gated channel length, s is the plasma velocity), the source-to-drain voltage response is a sharp pulse oscillatory decay preceded by a delay time on the order of L/s. The plasma wave travels along the channel like the shallow water wave with a relatively narrow wave package. In the long pulse mode (tpw > L/s), the response profile has two oscillatory decay processes and the propagation of plasma wave is analogues to oscillating rod with one side fixed. The ultimate response time at the long pulse mode is significantly higher than that under the short pulse conditions. The detection conditions under the long pulse mode are close to the step response condition, and the response time conforms well to the analytical theory for the step function response. The simulated waveform agrees well with the measured pulse response. Our results show that the measurements of the pulse response enable the material parameter extraction from the pulse response data (including the effective mass, kinematic viscosity and momentum relaxation time).

Output Characteristics of Graphene Field Effect Transistors

The use of graphene, which has high mobility of charge carriers, high thermal conductivity and a number of other positive properties, is promising for the creation of new semiconductor devices with good output characteristics. The aim was to simulate the output characteristics of field effect transistors containing graphene using the Monte-Carlo method and the Poisson equation.Two semiconductor structures in which a single layer (or monolayer) of graphene is placed on a substrate formed from 6H-SiC silicon carbide material are considered. The peculiarity of the first of them is that the contact areas of drain and source were completely located on the graphene layer, the length of which along the longitudinal coordinate was equal to the length of the substrate. The second structure differed in that the length of the graphene layer was shortened and the drain and source areas were partly located on the graphene layer and partly on the substrate.The main output characteristics of field-effect transistors based on the two semiconductor structures considered were obtained by modeling. The modeling was performed using the statistical Monte Carlo method. To perform the simulation, a computational algorithm was developed and a program of numerical simulation using the Monte-Carlo method in three-dimensional space using the Poisson equation was compiled and debugged.The results of the studies show that the development of field-effect transistors using graphene layers can improve the output characteristics – to increase the output current and transconductance, as well as the limit frequency of semiconductor structures in high frequency ranges.

Gate Bias Stress Instability and Hysteresis Characteristics of InAs Nanowire Field-Effect Transistors.

Because of the excellent electrical properties, III-V semiconductor nanowires are promising building blocks for next-generation electronics; however, their rich surface states inevitably contribute large amounts of charge traps, leading to gate bias stress instability and hysteresis characteristics in nanowire field-effect transistors (FETs). Here, we investigated thoroughly the gate bias stress and hysteresis effects in InAs nanowire FETs. It is observed that the output current decreases together with the threshold voltage shifting to the positive direction when a positive gate bias stress is applied, and vice versa for the negative gate bias stress. For double-sweep transfer characteristics, the significant hysteresis behavior is observed, depending heavily on the sweeping rate and range. On the basis of complementary investigations of these devices, charge traps are confirmed to be the dominant factor for these instability effects. Importantly, the hysteresis can be simulated well by utilizing a combination of the rate equation for electron density and the empirical model for electron mobility. This provides an accurate evaluation of carrier mobility, which is in distinct contrast to the overestimation of mobility when using the transconductance for calculation. All these findings are important for understanding the charge trap dynamics to further enhance the device performance of nanowire FETs.

Prepare with care: Low contact resistance of pentacene Field-Effect transistors with clean and oxidized gold electrodes

In recent years, a number of researchers have voiced concerns regarding the increasing amount of publications which report record performance characteristics of organic field-effect transistors (OFETs). These devices often make use of elaborate architectures, ranging from surface treatment by self-assembled monolayers to contact-limited doping, injection layer introduction etc. While these techniques are claimed to improve the device performance, they often result in poorly defined device interfaces, such as that of the organic semiconductor with the dielectric and electrode surfaces, which render a rigorous theoretical description of the interface effects close to impossible. Furthermore, the effects of ambient exposure of prepared devices are often neglected during the analysis. In this work we introduce a completely high vacuum-based manufacturing and electrical characterization of OFETs using commercially available gold bottom-contact bottom-gate FET structures, which enables a rigorous exclusion of any air contact of the devices. Using the example of the prototypical and widely studied organic semiconductor pentacene, we compare various initial cleaning procedures of the FET-structures prior to the vacuum deposition of pentacene films on the device characteristics and complement the electrical in situ analysis by ex situ AFM measurements of the pentacene film morphology. We demonstrate that O 2 plasma cleaning with subsequent thermal annealing under vacuum conditions results in well-defined interfaces of the pentacene film with clean surface of gold electrodes, which exhibit a remarkably low width-normalized contact resistance of 1.19 kΩcm. Additionally, we show that the formation of gold oxide on top of the electrodes as a result of O 2 plasma cleaning without subsequent heating is beneficial for the charge carrier injection, resulting in a contact resistance of only 0.16 kΩcm – to the best of our knowledge, one of the lowest yet reported values for pentacene-gold systems. In addition, the comparative rigorous vacuum-based processing and analysis allows in particular to study also the effects of controlled exposure to ambient air – even for a short time – as well as aging under different storage conditions on the device performance. • Full HV OFET fabrication and characterization process chain is introduced. • HV process chain allows rigorous characterization of the charge carrier injection. • Reference for a PEN OFET with clean Au electrodes is demonstrated. • Gold oxide improves the charge carrier injection in PEN OFETs. • Ambient exposure and HV storage of OFETs affects the device characteristics.

Detection of Stress-Related Secretory IgA in Human Sweat Using Lectin-Immobilized Field Effect Transistor Biosensor

A field effect transistor (FET) biosensor is a promising device for various applications such as medical diagnosis and environmental monitoring. Because characteristics of FET biosensors are directly influenced by the change of gate-insulator surface potential induced by the adsorption of charged molecules, FET biosensors could provide the rapid and label-free biomolecular detection. Recently, mental stress-related diseases, such as integration disorder syndrome and depression, affect people's health, resulting that simple stress monitoring is expected for early stage detection of the disease. Previously, the relation between concentration of stress markers and mental stress has been reported [1], and the monitoring of circadian concentration of the markers is found to be important for prediction of the stress condition. Especially, secretory immunoglobulin A (s-IgA), which is an immunity-related molecule present in the human mucus, is one of the candidates to be monitored as a stress marker. However, conventional methods for measuring concentration of s-IgA are restricted in daily use due to complex protocol, time-consuming and expensive equipment.Nowadays, we have investigated sensitive detection method for various targets by using the FET biosensor [2,3]. To achieve improvement of the sensitivity, small receptors have been applied to increase electrical responses owing to the effective use of a charge-recognition region from FET gate surface, Debye length [4,5]. In this study, we selected a small plant lectin, jacalin (66 kDa), which specifically binds glycan of hinge region of IgA, as a receptor. Additionally, jacalin was inexpensive compared with antibody due to the purification from jackfruits seeds. From these points, jacalin-immobilized FET biosensor was worth to be investigated to realize a simple, sensitive and low-cost stress monitoring device for stress marker. Thus, we investigated the usefulness of the jacalin as a FET receptor.The SiO2 gate insulator of the FET was exposed to O2 plasma (200 W for 1 min) for introduction of hydroxyl groups reacting with triethoxysilane groups of self-assembled monolayer (SAM). Then, the FET chip was immersed in toluene solvent including 1%(v/w) 3-aminopropyltriethoxysilane in an argon atmosphere (60ºC for 7 min.). Following by the cross-linking by glutaraldehyde, jacalin was immobilized on FET gate surfaces. Finally, ethanolamine capping was performed to prevent the non-specific adsorption of contaminating molecules in analyzed samples, resulting in the fabrication of the jacalin-immobilized FET biosensor. The FET characteristics were measured by sweeping the gate-voltage (V g) from -2.0 V to 0 V with 0.1 V drain voltage (V d) in 0.01 × phosphate buffered saline (pH 7.4). Then, the electrical responses (ΔV g) were analyzed from the FET characteristics before and after the addition of analyte to gate surface.To evaluate the specificity of jacalin-immobilized FET biosensor, ΔV g caused by the addition of s-IgA and human serum albumin (HSA) were measured. The FET charactristics was shifted in a positive direction (+53 mV) due to the adsorption of negative-charged s-IgA (Figure 1a), while the responses related with HSA addition were scarcely observed. Thus, specific capture of the s-IgA molecules by the jacalin-immobilized surface was indicated. Moreover, to evaluate the advantage of jacalin, we compared ΔV g with FET functionalized by antigen binding fragment (Fab), which was obtained by cleaving the anti-s-IgA antibody. An electrical response of Fab-immobilized FET was +24 mV (Figure 1b). The change in ΔV g values for these two FET sensors using jacalin or Fab could be discussed as follows. Jacalin could capture more s-IgA molecules within Debye length from the gate surface of FET. In addition, the jacalin-immobilized FET responded linearly to s-IgA in a concentration range from 0.1 μg/mL to 100 μg/mL. Finally, sweat samples collected from healthy persons were examined with the developed jacalin-immobilized FET biosensor, and clear responses were obtained. From these results, jacalin was found to be useful as a receptor for FET biosensors to achieve a sensitive, simple and non-invasive detection of s-IgA.[1] K. Obayashi, Clin. Chim. Acta, 425, 196-201 (2013).[2] S. Hideshima, M. Kobayashi, T. Wada, S. Kuroiwa, T. Nakanishi, N. Sawamura, T. Asahi, T. Osaka, Chem. Commun., 50, 3476-3479 (2014).[3] S. Hideshima, K. Fujita, Y. Harada, M. Tsuna, Y. Seto, S. Sekiguchi, S. Kuroiwa, T. Nakanishi, T. Osaka, Sens. Bio-Sens. Res., 7, 90–94 (2016).[4] S. Cheng, K. Hotani, S. Hideshima, S. Kuroiwa, T. Nakanishi, M. Hashimoto, Y. Mori, T. Osaka, Materials, 7, (4), 2490-2500 (2014).[5] S. Hideshima, H. Hayashi, H. Hinou, S. Nambuya, S. Kuroiwa, T. Nakanishi, T. Momma, S.-I. Nishimura, Y. Sakoda, T. Osaka, Sci. Rep., 9, 11616 (2019).Figure 1 V g-I d characteristics of (a) jacalin or (b) Fab-immobilized FET biosensor before and after the addition of 100 μg/mL s-IgA. Figure 1

Reduction in leakage current through interface between Ga2O3 epitaxial layer and substrate by ion implantation doping of compensating impurities

Strong accumulation of Si impurities has been observed at a Ga2O3 epilayer/substrate interface. The highly Si-doped region around the interface typically becomes a current conduction path, causing buffer leakage for lateral Ga2O3 field-effect transistors (FETs). To overcome the drawback, we performed Mg- or Fe-ion implantation doping into a Ga2O3 substrate prior to the subsequent molecular-beam epitaxy growth to compensate the accumulated Si donors at the interface. The Mg implantation doping showed a minimal effect on reduction in the interface leakage, irrespective of its concentration. On the other hand, the Fe doping with a high density of 2 × 1019 cm−3 provided a significant decrease in the leakage and decent FET characteristics.

Characteristics and Applications of CAAC-IGZO FET with Gate Length of 13nm

A field-effect transistor (FET) using CAAC-IGZO, a crystalline oxide semiconductor having a c-axis alignment, is considered for application to various circuits. In particular, its extremely low off-state leakage current[1,2] enables design of non-volatile memory and analog memory devices[3], allowing AI tasks to be run in non-von-Neumann architectures. Furthermore, CAAC-IGZO FET can be applied to use cases other than memory, such as RF applications. CAAC-IGZO FET can be integrated in the back-end-of-line processes of CMOS technologies[4], and allows higher power supply voltages than conventional CMOS devices[4]. This may contribute to reduced chip area, which can create smaller packages, which are demanded for IoT endpoints.As there are not many applications that currently use scaled CAAC-IGZO FET, CAAC-IGZO FET is not yet applied to quasi-millimeter-wave applications. In addition, circuit design for high-frequency applications of CAAC-IGZO FETs will require extraction of FET characteristics that will be utilized in this application. Compact models are available for large IGZO FETs [5], but not for scaled CAAC-IGZO FETs.For this work, we have prototyped and evaluated scaled CAAC-IGZO FETs (Fig. 1(a)) that are suitable for high-frequency applications in addition to memory applications. From network measurements, it was found that the CAAC-IGZO FET exhibits a cutoff frequency of 60 GHz (Fig. 1(b)) and a maximum oscillation frequency of 16 GHz, which is promising for quasi-millimeter-wave designs.In addition, we have designed equivalent circuits of the scaled CAAC-IGZO FET using linear devices. This circuit shows not only the characteristics of the scaled CAAC-IGZO FET, but also the potential for circuit designs with the device.This work compiles the characteristics of the scaled CAAC-IGZO FET, and proposes a novel circuit application for the device.Fig. 1 (a) L-direction cross section of the scaled CAAC-IGZO FET.(b) Network measurment result of the scaled CAAC-IGZO FET References [1] N. Kimizuka and S. Yamazaki, “Physics and Technology of Crystalline Oxide Semiconductor CAAC-IGZO FUNDAMENTALS,” WILEY, 2017.[2] S. Yamazaki and M. Fujita, “Physics and Technology of Crystalline Oxide Semiconductor CAAC-IGZO Application to LSI,” WILEY, 2017.[3] Y. Kurokawa et al., JJAP, vol. 59, pp. (SGGB03-1)-(SGGB03-11), 2020.[4] H. Kunitake et al., J-EDS, vol. 7, pp.495-502, 2019.[5] L. J. Giacoletto et al., JSSC, vol. 4, issue 2, pp.80-83, 1969. Figure 1

Investigation of electrical characteristics of flexible CMOS devices fabricated with thickness-controlled spalling process

Processing techniques for the thickness-controlled layer separation of a single-crystalline semiconductor have been actively developed for manufacturing complementary metal–oxide–semiconductor (CMOS)-technology-based flexible devices. A mechanical separation process for thin semiconductor layers, called the spalling technique, has recently attracted much attention because of its process simplicity, thickness controllability, and kerf-less layer separation. In this paper, we show that the thickness of separated device layers and the residual stress in the layers are critical factors to determine the performance of flexible CMOS devices fabricated with the spalling process. We investigated the electrical characteristics of flexible field-effect transistors (FETs) and CMOS inverters under various stress conditions. The results show that the excessive stress induced in the device layers can cause a severe performance mismatch between n- and p-channel FETs that results in the malfunction of flexible silicon CMOS devices. In addition, we verified that the unrelaxed stress remaining in the device layer after the spalling/transfer process is a major factor degrading the CMOS performance. The results also show that the residual stress induced by the spalling/transfer process as well as the external stress by mechanical bending are significantly dependent on the thickness of the separated device layers.

Effect of quantum confinement on the defect-induced localized levels in 4H-SiC(0001)/SiO2 systems

In the present study, we characterize the nature of interface states in silicon carbide (SiC) metal–oxide–semiconductor (MOS) systems by analyzing the electrical characteristics of MOS field effect transistors (MOSFETs) based on the results of numerical calculations. In the calculation, the potential distributions and energy sub-bands were calculated by solving Poisson and Schrödinger equations, respectively. As a result, we demonstrate that the defect-induced localized levels in the bandgap are subjected to quantum confinement at the inversion layer, leading to the increase in their energy levels. The result implies that the conventional interface defects (e.g., near-interface oxide traps), which create defect states at certain energy levels measured from the vacuum level, are unlikely to be the major origin of the interface states in SiC MOS systems. The interface state density is almost uniquely determined by the oxide formation process (as oxidation or interface nitridation) and independent of the acceptor concentration (3 × 1015–1 × 1018 cm−3). It is also suggested that the drain current decrease observed in heavily doped MOSFETs is mainly due to the decrease in the drift mobility rather than that in the free carrier density.

Compensation for the Nonlinearity of the Drain–Gate I–V Characteristic in Field-Effect Transistors with a Gate Length of ~100 nm

The nonlinearity of the gate–drain current–voltage characteristics in classical Schottky transistors and two-dimensional electron gas field-effect transistors based on AlGaAs/InGaAs/GaAs and InGaAs/GaAs compounds is analyzed. The carrier velocity-overshoot effect in the transistor channel is analyzed for various doping profiles of the structures under study.

Observation of trap-related phenomena in electrical performance of back-gated MoS2 field-effect transistors

Trap-related phenomena in the electrical performance of back-gated mechanical exfoliated MoS2 field-effect transistors are investigated in terms of the super linear increase in the drain current under positive gate bias and the shift of transfer curves with gate voltage stress. The super linear increase in drain current is only observed for the MoS2 field-effect transistors in the electron accumulation regime under positive gate bias, which can be attributed to a trap-assisted tunneling effect with S vacancies at the contact interface between metal Ti and MoS2. After thermal annealing of the devices in vacuum at 300 °C for 2 h, the almost complete metallization of Ti contacting with the MoS2 layer leads to the variation of the drain current relationship with drain voltage from a super linear to a linear increase, thus screening the efficacy of the mechanism of defect level assisted electron tunneling. The shift of transfer curves with gate voltage stress (denoted as hysteresis) is attributed to the defects near the interface between MoS2 and SiO2, which is slightly impacted by thermal annealing. The hump effect caused by parasitic transistors is also observed in back-gated mechanical exfoliated MoS2 field-effect transistors. These results further enrich the knowledge of the complex electrical characteristics of MoS2 field-effect transistors.

Influence of the Self-Heating Effect on the I–V Characteristics of Field Transistors on a Silicon-on-Insulator Structure at High Temperatures

An approach is discussed to study the effect of self-heating on the current–voltage (I–V) characteristics of submicron field-effect transistors on a silicon-on-insulator (SOI) structure in ambient temperatures of 225 to 350°C. The approach consists of combining the experimental data and numerical simulation results. It is shown that with an increase in the ambient temperature the contribution of the self-heating mechanism gradually decreases. Different dynamics of the drop in current of the n- and p-transistors are noted, which is significant for analog applications and must be taken into account when designing high-temperature circuits. The proposed methodology makes it possible to critically evaluate the effect of self-heating on the I–V characteristics of transistors in a wide range of high temperatures and control voltages.

Effects of Water and Different Solutes on Carbon-Nanotube Low-Voltage Field-Effect Transistors.

Semiconducting single-walled carbon nanotubes (swCNTs) are a promising class of materials for emerging applications. In particular, they are demonstrated to possess excellent biosensing capabilities, and are poised to address existing challenges in sensor reliability, sensitivity, and selectivity. This work focuses on swCNT field-effect transistors (FETs) employing rubbery double-layer capacitive dielectric poly(vinylidene fluoride-co-hexafluoropropylene). These devices exhibit small device-to-device variation as well as high current output at low voltages (<0.5 V), making them compatible with most physiological liquids. Using this platform, the swCNT devices are directly exposed to aqueous solutions containing different solutes to characterize their effects on FET current-voltage (FET I-V) characteristics. Clear deviation from ideal characteristics is observed when swCNTs are directly contacted by water. Such changes are attributed to strong interactions between water molecules and sp2 -hybridized carbon structures. Selective response to Hg2+ is discussed along with reversible pH effect using two distinct device geometries. Additionally, the influence of aqueous ammonium/ammonia in direct contact with the swCNTs is investigated. Understanding the FET I-V characteristics of low-voltage swCNT FETs may provide insights for future development of stable, reliable, and selective biosensor systems.

Effect of depolarization field on steep switching characteristics in negative capacitance field effect transistors

A theoretical model for describing the effect of depolarization field (Ed) in the negative capacitance (NC) field effect transistor (FET) was derived. Based on this model, the electrical properties of the metal-ferroelectric-insulator-semiconductor (MFIS) field effect transistor including the relationship between the depolarizing field and the gate voltage (Vg), Ed and silicon surface potential, and the drain-source current of NC-FET and Vg (transfer characteristics) were theoretically investigated. The computing results demonstrated that the surface potential amplification and the steep subthreshold slope characteristics happened at the gate voltage of about 0.4 V, results from the steep increase of Ed dependent on Vg in the NC-FETs. It is expected that the derived results may provide some insight into the design and performance improvement for the NC-MFIS-FET.

Evaluation of polarization characteristics in metal/ferroelectric/semiconductor capacitors and ferroelectric field-effect transistors

In this study, we propose a measurement technique for evaluating ferroelectric polarization characteristics in ferroelectric field-effect transistors (FeFETs). Different from standard metal/ferroelectric/metal capacitors, the depletion and inversion phenomena in semiconductor substrates have to be carefully taken into account when evaluating the ferroelectric properties using fast voltage sweep as input. The non-equilibrium deep depletion is found to be the limiting factor for the accurate evaluation of ferroelectric properties in metal/ferroelectric/semiconductor capacitors. By connecting the source, the drain, and the substrate of the FeFET together during the polarization measurement, the deep depletion can be suppressed and the ferroelectricity of the ferroelectric gate can be accurately evaluated. The present technique is a powerful method for capturing the polarization states in FeFETs, enabling new approaches for device characterization and fundamental study, and overcomes the limitation found in the conventional polarization measurement on two-terminal metal/ferroelectric/semiconductor capacitors.

Characteristics of Cl-doped MoS2 field-effect transistors

MoS2 is among the two-dimensional (2D) transition metal dichalcogenides (TMD) and has been studied as a potential semiconductor material for various devices. To increase the performance of MoS2-based devices, contact engineering of metal to TMD materials has recently become an area of focus. The doping method is one way to reduce resistance, and molecular doping is a suitable doping method for MoS2 with a very thin layer structure. We demonstrate controllable molecular doping on MoS2 transistors using 1,2 dichloroethane (DCE) solution. Chloride molecules contained within the DCE solution act as an n-type dopant and increase the carrier density. The doping effects were confirmed by Raman spectroscopy, X-ray photoelectron spectroscopy, and current-voltage characteristics. We observed that the threshold voltages shifted toward the negative direction, implying electron doping of MoS2 after Cl-doping. Additionally, the field-effect mobility and the carrier densities were enhanced from 11.9 cm2·V−1·s−1 to 72.8 cm2·V−1·s−1 and from 3.62 × 1011 cm-2 to 1.37 × 1012 cm-2, respectively, by increasing the molar concentration of 1,2-dichloroethane solution to 12.6 M.