Field-effect Transistor Structure Research Articles

New Insight on Terahertz Rectification in a Metal–Oxide–Semiconductor Field-Effect Transistor Structure

The use of a metal–oxide–semiconductor field-effect transistor (MOS-FET) permits the rectification of electromagnetic radiation by employing integrated circuit technology. However, obtaining a high-efficiency rectification device requires the assessment of a physical model capable of providing a qualitative and quantitative explanation of the processes involved. For a long time, high-frequency detection based on MOS technology was explained using plasma wave detection theory. In this paper, we review the rectification mechanism in light of high-frequency numerical simulations, showing features never examined until now. The results achieved substantially change our understanding of terahertz (THz) rectification in semiconductors, and can be interpreted by the model based on the self-mixing process in the device substrate, providing a new and essential tool for designing this type of detector.

Chemical pressure effect of the electron-doped FeSe films with an electric double-layer-transistor structure

We investigated chemical pressure effect of the electron-doped FeSe1−x S x and FeSe1−y Te y on LaAlO3 (x ≤ 0.25, y ≤ 0.5) with the electric double layer transistor structure. T c of all the FeSe1−x S x and FeSe1−y Te y films except y = 0.5 is increased by doping electron with gate voltage V G = +5 V. T c of the electron-doped FeSe1−x S x and FeSe1−y Te y is decreased monotonically by substituting Se for both S and Te. The behavior is similar to those of the intercalated FeSe1−x S x and FeSe1−y Te y and the electron-doped FeSe0.5Te0.5 with the solid-ion-conductor field-effect transistor structure, but quite different from that of the pristine FeSe1−x S x and FeSe1−y Te y . This difference is considered to originate from the difference of the Fermi surface topology, which suggests that the superconducting mechanism of the electron-doped FeSe is different from that of the pristine FeSe.

Doping-Dependent Nonlinear Electron Mobility in GaAs|InxGa1 –xAs Coupled Quantum-Well Pseudo-Morphic MODFET Structure

We analyze the asymmetric delta-doping dependence of nonlinear electron mobility μ of GaAs|InxGa1 –xAs double quantum-well pseudo-morphic modulation doped field-effect transistor structure. We solve the Schrodinger and Poisson’s equations self-consistently to obtain the sub-band energy levels and wave functions. We consider scatterings due to the ionized impurities (IMP), alloy disorder (AL), and interface roughness (IR) to calculate μ for a system having double sub-band occupancy, in which the inter-sub-band effects play an important role. Considering the doping concentrations in the barriers towards the substrate and surface sides as Nd1 and Nd2, respectively, we show that variation of Nd1 leads to a dip in μ near Nd1 = Nd2, at which the resonance of the sub-band states occurs. A similar dip in μ as a function of Nd1 is also obtained at Nd1 = Nd2 by keeping (Nd1 + Nd2) unchanged. By increasing the central barrier width and well width, the dip in μ becomes sharp. We note that even though the overall μ is governed by the IMP- and AL-scatterings, the dip in μ is mostly affected through substantial variation of the sub-band mobilities due to IR-scattering near the resonance. Our results of nonlinear electron mobility near the resonance of sub-band states can be utilized for the performance analysis of GaAs|InGaAs pseudo-morphic quantum-well field-effect transistors.

Photosensor Based on Split Gate TMD TFET Using Photogating Effect for Visible Light Detection

This paper reports a highly-sensitive and low power photosensor based on split gate tunnel field effect transistor (TFET) structure for visible light detection in wavelength ranging from 450-750 nm. The TFET based sensing device utilizes the photogating effect in a portion of transition metal dichalcogenide (TMD) channel. The optically tunable workfunction contrast between the two gates of dual material gate (DMG) TFET achieves significant gains in the overall device characteristics. It demonstrates high photo-to-dark current ratio of the order of 10 8 and variation in responsivity in the range between 10 3 AmW -1 to 10 -5 AmW -1 for V gs = -0.9 V. This paper further discusses the photodetector performance based on the position of the photogate on the tunneling or auxiliary side, the gate splitting ratio between the photosensing region and the metal, and the n-TFET based device design. The device performance has been analyzed using the analytical model for the optically controlled workfunction. This hybrid device consisting of an ultrathin channel sensitized with absorbing semiconductors while exploiting the characteristics of TFET leads to a new generation of highly sensitive photodetectors.

Rethinking the Characterization of Nanoscale Field-Effect Transistors: A Universal Approach.

Standard methods for calculating transport parameters in nanoscale field-effect transistors (FETs), namely carrier concentration and mobility, require a linear connection between the gate voltage and channel conductance; however, this is often not the case. One reason often overlooked is that shifts in chemical and electric potential can partially compensate each other, commonly referred to as quantum capacitance. In nanoscale FETs, capacitance is often unmeasurable and an analytical formula is required, which assumes the conducting channel as metallic and common methods of determining threshold voltage no longer couple properly into transport equations. As present and future FET structures become smaller and have increased channel-gate coupling, this issue will render standard methods impossible to use. This work discusses the validity of common methods of characterization for nanoscale FETs, develops a universal model to determine transport properties by only measuring the threshold voltage of an FET and presents a new parameter to easily classify FETs as either quantum capacitance-limited or metallic approximated charge transport. Also considered in this work is electrical hysteresis from trap states and, in combination with the proposed universal model, novel techniques are introduced to measure and remove the errors associated with these effects often ignored in literature.

(Invited) Enzymatic Metal Oxide Electrolyte-Gated Field-Effect Transistors for Non-Invasive Glucose Biosensor

Fabrication of nano-scaled biosensors with high sensing performance is essential demand for a future biological sensing system. Detection of biomolecules is conducted in terms of change in electrical properties of the biosensor so that the consideration of semiconductor material becomes more crucial. Although a lot of attractive attentions are attempted such as utilizing silicon nanowire or carbon nanotube, studies for investigating the highly reliable and biocompatible materials still have been progressed. Metal oxide material for biosensing application has an advantages of relatively high electrical characteristics and provides environmental condition for immobilizing an enzyme. InGaZnO (IGZO) has high electron mobility and reliability which leads a high sensitivity for detecting biomolecules. Adapting field effect transistor (FET) structure is additional approach to enhance the signal response of the sensor. The fundamental principle of the FET biosensor relies on its sensitive response to the variation of electric field or potential at the sensor surface resulting from the electrical interaction between the semiconductor and glucose molecules captured at the glucose oxidase (GOx). The FET biosensor also could be effectively integrated with other application circuits through conventional photolithography technologies. In addition, electrolyte-gated FET structure, utilizing an electrolyte as a gate insulator, shows a high sensitivity to the glucose concentration originated from a large capacitance of the electrolyte.IGZO based electrolyte-gated FET (IGZO-EGFET) biosensor is fabricated. The pH sensing is tested for predicting the biosensing performance of IGZO-EGFET. The pH sensitivity is measured as 52.5 mV/pH within 3 to 9 pH range, which is comparable to other nano material pH sensors. Immobilization of GOx on the IGZO surface is conducted via crosslinking modification with (3-aminopropyl)triethoxysilane (APTES) and glutaraldehyde treatment. Finally, the variation of glucose concentration is successfully identified on the GOx immobilized IGZO-EGFET. This study shows the IGZO-EGFET biosensor could lead to the applications of portable and real-time detecting sensor.

Anisotropy of charge carrier transport in PCPDTBT field-effect transistor structures

In this paper we are analyzing anisotropy of hole mobility in the organic field-effect transistor structures with an active layer of PCPDTBT (poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)]). Hole mobility and its dependence on the temperature was measured by i-CELIV and current transients methods. The combination of both techniques allowed us to obtain results of hole mobilities in perpendicular and parallel to the substrate directions. In the same temperature range differential scanning calorimetry (DSC) measurements were performed to detect morphological changes in the active layer of the field-effect transistor structure. From obtained results of mobility dependence on temperature, energetic disorder parameter of Bässler’s Gaussian Disorder Model (GDM) was estimated. DSC data and hole transport data demonstrated that the change in PCPDTBT’s morphology is responsible for the abrupt decrease of hole mobility on temperature in the field-effect transistor structure.

A time-domain analog weighted-sum calculation circuit using ferroelectric-gate field-effect transistors for artificial intelligence processors

Time-domain analog computing with transient states (TACT) approaches have been proposed to realize high performance artificial intelligence (AI) processors, which have over 100 times higher energy efficiency than the latest digital AI processors. Such approaches require analog memory devices that can hold and control very high resistance on the order of giga-ohms to tera-ohms, with nonvolatility and rectification. Memory devices with a field-effect transistor (FET) structure can operate in a subthreshold region to realize such high resistance, and can also rectify the current using FET operation. In this paper, we propose using ferroelectric-gate FETs (FeFETs) as a candidate for such devices. We design crossbar circuit architectures for using them, and show measurement results for device characteristics as analog memory devices with pulse control based on TACT approaches, and evaluation results for weighted-sum calculation operation in proof-of-concept FeFET circuits.

Field effect transistor with thin AlOxNy film as gate dielectric

PurposeThe purpose of this study is to directly measure and determine the Si/SiO2/AlOxNy interface state density on metal insulator semiconductor field effect transistor (MISFET) structures. The primary advantage of using aluminum oxynitride (AlOxNy) is the perfectly controlled variability of the properties of these layers depending on their stoichiometry, which can be easily controlled by the parameters of the magnetron sputtering process. Therefore, a continuous spectrum of properties can be achieved from the specific values for oxide to the specific ones for nitride, thus opening a wide range of applications in high power, high temperature and high frequency electronics, optics and sensors and even acoustic devices.Design/methodology/approachThe basic subject of this study is n-channel transistors manufactured using silicon with 50-nm-thick AlOxNy films deposited on a silicon dioxide buffer layer via magnetron sputtering in which the gate dielectric was etched with wet solutions and/or dry plasma mixtures. Furthermore, the output, transfer and charge pumping (CP) characteristics were measured and compared for all modifications of the etching process.FindingsAn electrical measurement of MISFETs with AlOxNy gate dielectrics was conducted to plot the current-voltage and CP characteristics and examine the influence of the etching method on MISFET parameters.Originality/valueIn this report, a flat band and threshold voltage and the density of interface traps were determined to evaluate and improve an AlOxNy-based MISFET performance toward highly sensitive field effect transistors for hydrogen detection by applying a Pd-based nanocrystalline layer. The sensitivity of the detectors was highly correlated with the quality of the etching process of the gate dielectrics.

Amorphous IGZO field effect transistor based flexible chemical and biosensors for label free detection

Flexible chemical sensors and biosensors are of interest in different industry sectors and have advantages for being shape-friendly, lightweight, with potential of low cost. The performance factors such as fast response and label free detection makes field effect transistors an attractive platform for such sensors. While there is a large body of literature on ion sensitive field effect transistors using rigid substrates, limited studies are reported on flexible substrates. Electrolytic gated field effect transistors, a class of ion sensitive field effect transistors, have a further advantage as no gate dielectrics are needed (with the electrolytic solution itself acting as the gate dielectric) and need lower operating voltages; there are no reports yet of electrolytic gated field effect transistor with amorphous indium gallium zinc oxide as the semiconductor as well as a sensing layer on flexible substrates and this is the subject of the present work, where fully flexible electrolytic gated field effect transistors are demonstrated on flexible polyethylene terephthalate substrates for pH sensing and for detection of prostate specific antigen. Bottom contact electrolytic gated field effect transistors structures with indium tin oxide as the source and drain were fabricated on flexible polyethylene terephthalate substrates with amorphous indium gallium zinc oxide as the semiconductor deposited over indium tin oxide at room temperature. Materials and electrical characterizations (in a low operating voltage range of −1–1.5 V) were conducted. A pH sensitivity of 20 ± 2 mV pH−1 was demonstrated. Stability studies and bending tests were also conducted. Label-free bio-sensing for prostate specific antigen was demonstrated in the concentration range 1 pg ml−1–10 ng ml−1 in phosphate buffer saline. This learning can be utilized to fabricate wearable sensors for healthcare monitoring at low cost.

A novel SOI MESFET to spread the potential contours towards the drain

ABSTRACT This paper presents a new structure of Metal Semiconductor Field Effect Transistor (MESFET) for high power applications. One of the problems that we face in the design of the MESFET devices is that in most cases, the increase of breakdown voltage is accompanied by a decrease in the saturation drain current. Our aim to propose this structure is to improve these two parameters simultaneously. Using the insulator region under the sides of the gate (IR) and the hide field plate (HFP) in the buried oxide (BOX) are the fundamental solution for improving these parameters. We named the proposed structure as spread potential contours towards the drain MESFET (SPC-MESFET). By applying the proposed structure, the drain current and the breakdown voltage improve 20 and 27 percent compared to a conventional structure (C-MESFET), respectively. Therefore, the proposed device has a higher maximum power density than the C-MESFET structure. Also, this idea reduces the gate capacitance and thus the frequency characteristics such as cut off frequency (fT), maximum oscillation frequency (fmax), and Maximum Available Gain (MAG) improve in comparison with the C-MESFET structure.

Novel Quantum Structure of an III-V Tunneling Field-Effect Transistor with Source and Channel Heterojunction

In this work, an III-V tunneling field-effect transistor (TFET) with source and channel heterojunctions is proposed and introduced. Proposed structure combine the high tunneling efficiency induced by heterojunction material and the high mobility of III-V material. The III-V TFETs based on either source heterojunction and channel heterojunctions have been intensively researched due to their excellent subthreshold-swing characteristics. However, compared with conventional III-V TFETs, the III-V TFETs with source and channel heterojunctions have both shorter tunneling distance and two transmission resonances that significantly improve the on-current. The transfer characteristics affected by gate length were also evaluated. The results show that on-current, off-current, and on-current/off-current ratio and subthreshold-swing of III-V TFETs with source and channel heterojunctions are about 10-3 A/?m, 10-13 A/?m, 10-10 and 30 mV/decade, respectively.

Design study of the gate-all-around silicon nanosheet MOSFETs

The gate-all-around (GAA) silicon nanosheet (SiNS) metal-oxide-semiconductor field-effect transistor (MOSFET) structures have been recognized as excellent candidates to achieve improved power performance and area scaling compared to the current FinFET technologies. Specifically, SiNS structures provide high drive currents due to wide effective channel width (Weff) while maintaining short-channel control. In this paper, we fabricate a GAA SiNS MOSFET fully surrounded by a gate with a gate length (LG) of 22 nm, a SiNS width (WNS) of 23 nm, and SiNS thickness (TNS) of 6 nm. In addition, the fabricated GAA SiNS MOSFETs were evaluated for electrostatic characteristics and short-channel effects (SCEs) according to various channel length and width dimensions. We confirmed that the GAA SiNS MOSFET showed similar short-channel controllability regardless of WNS due to the extremely thin TNS. In addition, we analyzed SCEs of GAA SiNS MOSFETs with different TNS through simulation.

Amyloid-beta peptide detection via aptamer-functionalized nanowire sensors exploiting single-trap phenomena

New highly sensitive direct methods for the early detection of peptides involved in Alzheimer's disease (AD) are required in order to prolong effective and healthy memory and thinking capabilities and also to stop the factors resulting in AD. In this contribution, we report the successful demonstration of a label-free approach for the detection of amyloid-beta (Aβ) peptides by highly selective aptamers immobilized onto the SiO2 surface of the fabricated sensors. A modified single-stranded deoxyribonucleic acid (ssDNA) aptamer was specially designed and synthesized to detect the target amyloid beta-40 sequence (Aβ-40). Electrolyte–insulator–semiconductor (EIS) structures as well as silicon (Si) nanowire (NW) field-effect transistors (FETs) covered with a thin SiO2 dielectric layer have been successfully functionalized with Aβ-40-specific aptamers and used to detect ultra-low concentrations of the target peptide. The binding of amyloid-beta peptides of different concentrations to the surface of the sensors varied in the range from 0.1 pg/ml to 10 μg/ml resulting in a change of the surface potential was registered by the fabricated devices. Moreover, we show that the single-trap phenomena observed in the novel Si two-layer (TL) NW FET structures with advanced characteristic parameters can be effectively used to increase the sensitivity of nanoscale sensors. The obtained experimental data demonstrate a highly sensitive and reliable detection of ultra-low concentrations of the Aβ-40 peptides. This opens up prospects for the development of real-time electrical biosensors for studying and understanding different stages of AD by utilizing Si TL NW FET structures fabricated on the basis of cost-efficient CMOS-compatible technology.

Core-Shell Junctionless Nanotube Tunnel Field Effect Transistor: Design and Sensitivity Analysis for Biosensing Application

In this paper, the structure of Core-Shell Junctionless Nanotube Tunnel Field Effect Transistor is proposed and investigated to minimize the fabrication steps and fabrication complexity of the device. The proposed junctionless device is implemented as a biosensor. The core-source metal and shell gate electrode are created using suitable work function. The p-type source region is created by using metal of work function 5.93eV and the shell gate is created by using a metal of work function 4.5eV, over the silicon surface. For biosensing application, a nano cavity is introduced between core-source metal and source region. The device is vertically aligned which provides stability to the biomolecules within the structure. For the investigation of biosensing application, three biomolecules of different dielectric constants, streptavidin (k = 2.1), 3-aminopropyltriethoxysilane (k = 3.57), and protein (k = 8), are used. The performance of the device for biosensing application is analyzed for both neutral and charged biomolecules. To examine the efficiency of the device, various characteristics are studied based on parametric variations, the effect of charged biomolecules, and sensitivity of the device and so on. The motivation behind our work is to design a device having optimum performance attributes without sacrificing the performance parameters of the device such as the ON-state current, subthreshold slope, ION/IOFF ratio, etc.

Analytical Prediction of Highly Sensitive CNT-FET-Based Sensor Performance for Detection of Gas Molecules

In this study, a set of new analytical models to predict and investigate the impacts of gas adsorption on the electronic band structure and electrical transport properties of the single-wall carbon nanotube field-effect transistor (SWCNT-FET) based gas sensor are proposed. The sensing mechanism is based on introducing new hopping energy and on-site energy parameters for gas-carbon interactions representing the charge transfer between gas molecules (CO2, NH3, and H2O) and the hopping energies between carbon atoms of the CNT and gas molecule. The modeling starts from the atomic level to the device level using the tight-binding technique to formulate molecular adsorption effects on the energy band structure, density of states, carrier velocity, and I-V characteristics. Therefore, the variation of the energy bandgap, density of states and current-voltage properties of the CNT sensor in the presence of the gas molecules is discovered and discussed. The simulated results show that the proposed analytical models can be used with an electrical CNT gas sensor to predict the behavior of sensing mechanisms in gas sensors.

Investigation of Charge Plasma Enhanced Tunnel Field Effect Transistor for Hydrogen Gas Sensing Application

In this letter, a transducer sensor is introduced that is based on the principle of charge plasma-enhanced tunnel field-effect transistor (CPE-TFET) structure for catalytic metal gate based electrochemical hydrogen (H2) gas detection using numerical device simulation. In the proposed sensor, the induced charge plasma at the source region is exploited for realizing a superior gate control over tunneling junction electrostatics that leads to a drain current sensitivity improvement near an order of magnitude over the conventional (Conv) TFET. The underlying physics of the proposed sensor is explored from a detailed electrostatic analysis of the tunneling junction in the context of gas molecule adsorption. In this effect, the sensitivity is estimated for the different gate and drain biases, and the suitable biasing range of operation is indicated. Furthermore, extensive structural optimization is performed to achieve a design-level understanding of CPE-TFET. Finally, the comparative performance analysis with Conv-TFET and mosfet establishes the inherent superiority of CPE-TFET for H2 gas sensing at different partial gas pressures and temperatures.

Germanium Twin-Transistor Nonvolatile Memory With FinFET Structure

Germanium is a promising alternative material for use in advanced technology nodes because it exhibits symmetrical mobility of holes and electrons. Embedded nonvolatile memory (NVM) is essential in electronic devices with integrated circuit (IC) technology, including future Ge-based technology. In this paper, we demonstrate Ge twin-transistor NVM with a fin field-effect transistor (FinFET) structure. This Ge twin-transistor NVM exhibits high programming and erasing speeds and satisfactory reliability. Moreover, the masks and fabrication process of this Ge twin-transistor NVM are identical to those of Ge-channel FinFETs. Thus, Ge twin-transistor NVM is a promising candidate for embedded NVM applications in future high-performance Ge complementary metal–oxide–semiconductor technology (CMOS).

Doping-Dependent Nonlinear Electron Mobility in GaAs|In-=SUB=-x-=/SUB=-Ga-=SUB=-1-x-=/SUB=-As Coupled Quantum-Well Pseudo-Morphic MODFET Structure

We analyze the asymmetric delta-doping dependence of nonlinear electron mobility μ of GaAs|InxGa1-xAs double quantum-well pseudo-morphic modulation doped field-effect transistor structure. We solve the Schrodinger and Poisson's equations self-consistently to obtain the sub-band energy levels and wave functions. We consider scatterings due to the ionized impurities (IMP), alloy disorder (AL), and interface roughness (IR) to calculate μ for a system having double sub-band occupancy, in which the inter-sub-band effects play an important role. Considering the doping concentrations in the barriers towards the substrate and surface sides as Nd1 and Nd2, respectively, we show that variation of Nd1 leads to a dip in μ near Nd1=Nd2, at which the resonance of the sub-band states occurs. A similar dip in μ as a function of Nd1 is also obtained at Nd1=Nd2 by keeping (Nd1+Nd2) unchanged. By increasing the central barrier width and well width, the dip in μ becomes sharp. We note that even though the overall μ is governed by the IMP- and AL-scatterings, the dip in μ is mostly affected through substantial variation of the sub-band mobilities due to IR-scattering near the resonance. Our results of nonlinear electron mobility near the resonance of sub-band states can be utilized for the performance analysis of GaAs|InGaAs pseudo-morphic quantum-well field-effect transistors. Keywords: asymmetric double quantum wells, GaAs|InxGa1-xAs structures, nonlinear electron mobility, pseudo-morphic HEMT structures, resonance of sub-band states.

Field Effect Transistor-Type Devices Using High-κ Gate Insulator Stacks for Neuromorphic Applications

With ability to process data in an energy-efficient way, neuromorphic computing is suggested to overcome the issues of a traditional von Neumann computing system. Neuromorphic computing is composed of two crucial features of neurons and synapses, in which neurons integrate all the charges while synapses retain these charges. In this paper, we fabricate and analyze devices for mimicking neurons and synapses in a single Si-based metal-oxide-semiconductor field-effect transistor (MOSFET) structure. We fabricate and analyze Al2O3/Si3N4 (A/N) and Al2O3/HfO2/Si3N4/SiO2 (A/H/N/O) devices to suggest that an A/N device could be used as a neuron device due to its fast charge emission characteristics, while the A/H/N/O device could be used as a synaptic device as added tunneling SiO2 causes the device to retain its charges for a long-period of time. We suggest the possibility of fabricating both neurons and synapses by adopting different gate insulator stack structures in MOSFETs.