Effective Gate Research Articles

Study of the effect of circular p-GaN gate on the DC characteristics of AlGaN/GaN HEMTs

Abstract In this paper, we use Silvaco-ATLAS two-dimensional numerical simulation to calculate the performance of two different circular-gate AlGaN/GaN HEMT device models. The influence of the special circular-gate structure on the DC characteristics of the AlGaN/GaN HEMT device is studied and compared with that of conventional devices. Compared with conventional, the threshold voltage of the drain-center and source-center circular-gate devices increased from 1.1 V to 1.5 V, while the transconductance improved from 245 mS/mm to 328 mS/mm and 285 mS/mm respectively. In the on-state of devices, the maximum saturation output current increased from 536 mA/mm to 620 mA/mm and 650 mA/mm. Furthermore, the breakdown voltage of the source-center circular-gate device rose from 765 V to 870 V compared to conventional devices; however, for the drain-center circular-gate device it was only at 685 V due to concentrated electric fields outside the drain region—this limitation can be effectively addressed by increasing the drain area. Simulation results demonstrate that circular-gate AlGaN/GaN HEMT devices can avoid edge effects, improve electric field distribution, and alleviate self-heating effects.

A Cascaded Duplex Organic Vertical Memory with Learning Rate Scheduling for Efficient Artificial Neural Network Training

AbstractLearning rate scheduling (LRS) is a critical factor influencing the performance of neural networks by accelerating the convergence of learning algorithms and enhancing the generalization capabilities. The escalating computational demands in artificial intelligence (AI) necessitate advanced hardware solutions capable of supporting neural network training with LRS. This not only requires linear and symmetric analog programming capabilities but also the precise adjustment of channel conductance to achieve tunable slope in weight update behaviors. Here, a cascaded duplex organic vertical memory is proposed with the coupling of ferroelectric polarization effect and Schottky gate control on the same semiconducting channel, exhibiting adjustable‐slope conductance update with high linearity and symmetry. Therefore, in the chest X‐ray image detection, a fast‐to‐slow LRS is used for a bi‐layer ANN training, achieving a rapid, stable convergence behavior within only 15 epochs and a high recognition accuracy. Moreover, the proposed LRS training is also suitable for the Mackey Glass prediction task using long short‐term memory networks. This work integrates LRS into synaptic devices, enabling efficient hardware implementation of neural networks and thus enhancing AI performance in practical applications.

Linearly Polarized AC-Driven Perovskite Light Emitting Device with Nanoscale Metal Contact

Electroluminescent (EL) devices consisting of a single metal-semiconductor contact and a gate effect structure have garnered significant attention in the field of perovskite light-emitting devices. This interest is largely due...

Thermopower modulation analyses of effective channel thickness for Zn-incorporated In2O3-based thin-film transistors

Abstract Zn-incorporated In2O3 (IZO) thin-film transistors (TFTs) show high field-effect mobility (µFE ~40 cm2 V−1 s−1) when the IZO channel is amorphous, whereas a lower µFE (~10 cm2 V−1 s−1) is observed with polycrystalline channel. The reasons behind this difference in µFE remain unclear despite various studies on IZO TFTs. Here, we perform electric field thermopower modulation analysis on amorphous and polycrystalline IZO TFTs to measure the change in effective thickness. For amorphous channel, the effective thickness was zero when the effective gate voltage (Vg−Vth, Vg: gate voltage, Vth: threshold voltage) was zero. Furthermore, it gradually increased with Vg−Vth up to 1.6 nm, reflecting that conduction band bending occurred. By contrast, polycrystalline channel showed an initial effective thickness of 5 nm (≈ film thickness of IZO) and sharply decreased to ~1.7 nm. In amorphous channels, electron transport followed field effect theory, while factors like grain boundaries limited transport in polycrystalline channels.

(Invited) Reduction of Contact Resistance through the Application of Cylindrical Contacts to WSe2

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) are gaining attention as the next-generation semiconductor materials instead of silicon, owing to their atomic thickness and thickness-dependent energy bandgap. Moreover, because of their atomic thickness, TMDs show effective electrostatic gate modulation, thereby short channel effects can be suppressed. Among various TMDs, tungsten diselenide(WSe2) has an ambipolar conductivity which can be tuned to n- or p-type via various processing and shows excellent electrical properties and mechanical stability. However, achieving Ohmic contact in 2D material-metal junction is challenging due to high Schottky barrier and Fermi-level pinning. Therefore, research on the improvement of contact resistance is crucial to maximizing the full potential of 2D materials and utilizing their superior electrical properties. Edge contact, where the junction is formed on the edge of the 2D material layers, has been researched as an effective method to minimize the contact resistance in 2D materials. Unlike the traditional surface contact method, which results in high tunnel barrier and out-of-plane current flow, the edge contact method provides strong orbital overlap and allows in-plane current flow through a narrower tunnel barrier, offering advantages in terms of carrier transport at the contact interface [1]. Yang et al. demonstrated conventional edge contacts to MoS2 using hexagonal boron nitride (h-BN) to encapsulate the surface of the MoS2. This method ensures that current flows only between the edge of the MoS2 and metal [2]. However, this approach necessitates additional process that requires h-BN to completely cover the entire upper part of the contact area and cannot control the area of the edge contact.In this work, edge contact using cylindrical contacts of WSe2 transistors is demonstrated. WSe2 flakes were fabricated through mechanical exfoliation and were dry-transferred on Si/SiO2 substrates. Spin-coating of electron-beam resist and electron-beam lithography (EBL) was performed to prepare the etch mask for cylindrical etching at the contact areas of WSe2. Reactive ion etching was conducted using 15 sccm of Ar, 15 sccm of SF6 with 20 W for 20 s. Spin-coating and EBL process was performed again to define the area for ultraviolet (UV)-ozone treatment and deposition of Pt/Au electrodes. UV-ozone treatment oxidizes the top few layers of WSe2 into WOx, resulting in the p-doping of the underlying WSe2 layer of the contact area. Pt/Au contact metal was deposited by electron-beam evaporation.The fabricated WSe2 FETs shows p-type dominant characteristic and Ohmic behavior, as shown in Fig. 1. Cylindrical contact and UV-ozone treatment process for WSe2 FETs enabled low contact resistance (4 kΩ·μm), high field-effect mobility (149 cm2/V·s) and high on-off ratio (>107). As the perimeter of the cross-sectional circle of the etched cylinder increases, the area of the edge contact becomes larger. The WSe2 FETs with cylindrical contacts exhibited decrease in the contact resistance and increase in the field-effect mobility as the ratio of the etched perimeter to the top contact area increased (Table 1). P-type WSe2 FETs with low contact resistance and high field-effect mobility were demonstrated using cylindrical contacts. With this fabrication, edge contact area can be controlled with the variation of the etched perimeter and electron transport can be improved using both top contact and edge contact.Reference:[1] J. Kang, W. Liu, D. Sarkar, D. Jena, K. Banerjee, Phys. Rev. X 2014,4, 1.[2] Z. Yang, C. Kim, K. Y. Lee, M. Lee, S. Appalakondaiah, C.-H. Ra, K.Watanabe, T. Taniguchi, K. Cho, E. Hwang, J. Hone, W. J. Yoo,Adv.Mater.2019,31, 1808231 Figure 1

Chemogenetic Breakdown of the Dentate Gate Causes Seizures and Spatial Memory Deficits.

The dentate gyrus has often been posited to act as a gate that dampens highly active afferent input into the hippocampus. Effective gating is thought to prevent seizure initiation and propagation in the hippocampus and support learning and memory processes. Pathological changes to DG circuitry that occur in temporal lobe epilepsy (TLE) can increase DG excitability and impair its gating ability which can contribute to seizures and cognitive deficits. There is evidence that TLE pathologies and seizures may independently contribute to learning and memory deficits in TLE through distinct mechanisms. These two factors are difficult to untangle since TLE pathologies can drive seizures, and seizures can worsen TLE pathologies. Here we assessed whether chemogenetically increasing dentate granule cell (DGC) excitability was enough to break down the dentate gate in the absence of TLE pathologies. We found that increasing excitability specifically in DGCs caused seizures in non-epileptic mice. Importantly, due to the modulatory nature of DREADD effects, seizures were driven by intrinsic circuit activity rather than direct activation of DGCs. These seizures resulted in a spatial memory deficit when induced after training in the spatial object recognition task and showed stereotypical patterns of activity in miniscope calcium recordings. Our results provide direct support for the dentate gate hypothesis since seizures could be induced in non-epileptic animals by artificially degrading the dentate gate with chemogenetics in the absence of epilepsy pathologies.

Mitigating Pass Gate Effect in Buried Channel Array Transistors Through Buried Oxide Integration: Addressing Interference Phenomenon Between Word Lines

As semiconductor devices become smaller, their performance and integration density improve, but new negative effects emerge due to the reduced distance between structures. In DRAM, these effects can lead to data loss or require additional refresh cycles, causing performance degradation. Specifically, in the 6F2 DRAM structure, activating a word line (WL) lowers the energy barrier of adjacent WLs, leading to the Pass Gate Effect (PGE). This study investigates the use of buried oxide beneath the WL to mitigate the PGE through simulation. Using SILVACO TCAD, we analyzed the impact of varying the size and position of the buried oxide on the PGE. The results showed that increasing the oxide size or reducing the distance to the WL effectively reduced the PGE. However, the presence of interface traps, which increase with the addition of buried oxide, was found to exacerbate the PGE, indicating that minimizing interface traps is crucial when incorporating buried oxide.

High-performance cold-source field-effect transistors based on Cd3C2/ boron phosphide heterojunction

To overcome the short-channel effect and large gate leakage current in the field-effect transistors (FETs), some cold-source materials have been suggested as alternative materials. We explore the performance of FET based on the cold-source material Cd3C2 using the ab initio quantum transport method. It is shown that the figure of merits (FOMs) of Cd3C2/ Boron phosphide (BP) FET satisfies the requirements of ITRS2028 HP for UL=2 and UL=3nm. The performance of Cd3C2/BP FET is improved when Cd3C2 is p-type doped. Doping causes a super-exponential decrease in carrier concentration, thus the cold-source FET based on Cd3C2/BP is formed. When the doping concentration reaches 10.0 × 1013cm−2, the device satisfies the requirements of ITRS2028 HP. More importantly, at the doping concentration of 10.0 × 1013cm−2 for UL=2 and 3 nm, the subthreshold swings are 52.32 and 56.84 mV/dec, which are lower than 60 mV/dec. This work proposes a new cold-source FET based on Cd3C2/BP, whose excellent performance can make it a competitive candidate in future electronic devices.

Improved breakdown voltage and dynamic Ron characteristics in normally-off GaN-based HEMTs featuring fully-recessed and bilayer-dielectric gate structure

Abstract The degradation of dynamic on-resistance (Ron) is a major challenge in GaN-based high electron mobility transistors (HEMTs), which seriously affects their performance and reliability. The degradation area of dynamic Ron mainly comes from two aspects. One is the region below the gate that also affects the threshold voltage (Vth) of the devices. And the other one is the interface region of the gate to drain access. The optimal device exhibits a Vth of 0.97 V, a small Vth hysteresis of only 20 mV, a high current density of 723 mA/mm, and a breakdown voltage (BV) of 760 V which could be further boosted when additional field plate design is employed. It is found that when high voltage drain stress is applied, a positive Vth shift is induced, leading to the decrease of the effective gate driving voltage, and thus the dynamic Ron of the devices is increased. Of particular concern is the effects of dielectric layer and/or interface of the access region on the dynamic Ron degradation, which can be alleviated by removing the dielectric layer of the access region.

Study and analysis of a dielectric-modulated vertical tunnel FET biosensor using dual material gate

A bimetal gate heterogeneous dielectric vertical tunnel field-effect transistor (BG-HD-VTFET) biosensor has been investigated in this paper for the first time using engineered-gate concept, where nanogaps are introduced under tunnel gate (TG) to detect biomolecules near the device surface. To improve the detection performance of BG-HD-VTFET, an overlap is designed between source and pocket region, and the sensing ability of BG-HD-VTFET with and without overlap is compared in details. Further, an auxiliary gate (AG) is added for the proposed two devices to optimize the electrical characteristics, and the y composition of GaAsySb1-y in pocket region is optimized to enhance ON-state current, and then different neutral and charged biomolecules are considered to simulate device-level gate effects. In addition, the influence of different dielectric constant at fixed charge density is studied and the length of overlap is optimized. Simulation results show that the maximum sensitivity of BG-HD-VTFET with and without overlap can reach 3.3 × 103 and 1.9 × 103, respectively.

The Effect of Gate Drive Resistance on the CM EMI Performance of the Balanced Inverter With Asymmetrical Parasitic Impedance Distribution

The Effect of Gate Drive Resistance on the CM EMI Performance of the Balanced Inverter With Asymmetrical Parasitic Impedance Distribution

Hydrogel-based fluorescence assay kit for simultaneous determination of ceftazidime and avibactam

Monitoring the concentration of antibiotics rapidly and cost-effectively is crucial for accurate clinical medication and timely identification of drug-induced illnesses. Here, we constructed a novel fluorescent assay kit to monitor Zavicefta, an effective antibiotic composed of avibactam (AVI) and ceftazidime (CFZ) to treat carbapenem-resistant gram-negative bacteria infections. AVI can emit fluorescence, but CFZ cannot. To enable simultaneous measurement of both in one kit, we designed molecularly imprinted polymer (MIP) modified quantum dots (QDs) for CFZ determination. MIPs have received significant attention as an artificial antibody due to their exceptional specificity for various targets, particularly drugs with small molecular weight. Under the excitation wavelength of 350 nm, the detection process involves a decrease in QDs’ fluorescence signal at 600 nm owing to the “gate effect” between MIP and CFZ and the internal filtration effect between CFZ and QDs. Simultaneously, a fluorescence emission characteristic peak at 420 nm for AVI emerges. In addition, to simplify the operation procedure and improve determination throughput, the detection agents were incorporated into a hydrogel and placed in a 96-well plate, enabling concurrent quantification of AVI and CFZ within the respective range of 80–1000 μM and 1–1000 μM. The developed assay kit successfully determined AVI and CFZ in human serums and therapeutic drug monitoring in a live rabbit model. Recoveries of AVI and CFZ were 92.7–114%, with relative standard deviations below 6.0%. Moreover, a smartphone was employed to read the fluorescence signals, which was beneficial for cost reduction and out-of-lab analysis. This study will deliver a pragmatic resolution to developing high-throughput assay kits for drug determination.Graphical

Ultrasensitive aflatoxin B1 detection based on vertical organic electrochemical transistor

Herein, we presented an ultrasensitive Aflatoxin B1 (AFB1) detection platform based on vertical organic electrochemical transistor (vOECT) first time. Chitosan-graphene nanosheets nanocomposites and AFB1 antibodies were modified on commercial electrodes as immunosensors, in series with gate electrodes of vOECT, operated at enhancement mode with ultrahigh transconductance gm 94 mS to amplify current signals. When AFB1 is added, the impedance of the immunosensors increased due to antigen-antibody immune binding, resulting in a potential decrease in reaction cell. Then, the potential decrease leads to an effective gate voltage VGeff increase, contributing to a significant drain-source current IDS decrease as a consequence of ultrahigh gm of vOECT. As a result, the presented vOECT platform exhibited an ultrahigh sensitivity of ∼1 mA/dec, and an ultralow detection limit of 0.01 fg/mL (S/N = 3), superior to all previous reported values. Furthermore, the platform exhibited satisfactory stability and specificity, and was applied to detect AFB1 in corn samples.

Effects of insertion of an h-AlN monolayer spacer in Pt-WSe2-Pt field-effect transistors

The growth of two-dimensional hexagonal aluminum nitride (h-AlN) on transition metal dichalcogenide (TMD) monolayers exhibits superior uniformity and smoothness compared to HfO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document} on silicon substrate. This makes an h-AlN monolayer an ideal spacer between the gate oxide material and the WSe2 monolayer in a two-dimensional field effect transistor (FET). From first principles approaches, we calculate and compare the transmission functions and current densities of Pt–WSe2–Pt nanojunctions without and with the insertion of an h-AlN monolayer as a spacer in the gate architecture. The inclusion of h-AlN can alter the characteristics of the Pt–WSe2–Pt FET in response to the gate voltage (Vg\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$V_\ ext {g}$$\\end{document}). The FET without (or with) h-AlN exhibits the characteristics of a P-type (or bipolar) transistor: an on/off ratio of around 2.5×106\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2.5 \ imes 10^{6}$$\\end{document} (or 1.7×106\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1.7 \ imes 10^{6}$$\\end{document}); and an average subthreshold swing (S.S.) of approximately 109 mV/dec.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {dec.}$$\\end{document} (or 112 mV/dec.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {dec.}$$\\end{document}), respectively. We observe that Vg\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$V_\ ext {g}$$\\end{document} shifts the profile of the transmission function by an energy of α(eVg)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha (e V_{\ ext {g}})$$\\end{document}, where α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha$$\\end{document} represents the gate-controlling efficiency. We observed that αin=83%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha _{\ ext {in}}=83\\%$$\\end{document} and αout=33%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha _{\ ext {out}}=33\\%$$\\end{document}, corresponding to whether the Fermi energy is located inside or outside the band gap. Therefore, we construct an effective gate model based on the Landauer formula, with the transmission function at Vg=0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$V_\ ext {g}=0$$\\end{document} as the baseline. Our model generates results that are consistent with those obtained through first principles calculations. The relative error in current densities between model and first-principles calculations is within [ln(10)S.S.]|ΔVGeff|\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$[\\frac{ln(10)}{S.S.}] | \\Delta V_{\ ext {G}}^{\ ext {eff}} |$$\\end{document}. The 2D atomistic FETs show excellent device specifications and the ability to compete with existing transistors based on traditional silicon technology. Our findings could help advance the design of TMD-based FETs.

Large-Scale Green Method for Synthesizing Ultralong Uniform Tellurium Nanowires for Semiconductor Devices.

This study presents a large-scale green approach for synthesizing ultralong tellurium nanowires with diameters around 13 nm using a solution-based method. By adjusting key synthesis parameters such as the surfactant concentration, temperature, and reaction duration, we achieved high-quality, ultralong Te NWs. These nanowires exhibit properties suitable for use in semiconductor applications, particularly when employed as channel materials in thin-film transistors, displaying a pronounced gate effect with a high switch of up to 104 and a mobility of 0.9 cm2 V-1s-1. This study underscores the potential of solvent-based methods in synthesizing large-scale ultralong Te NWs as a critical resource for future sustainable nanoelectronic devices.

Molecular Beam Epitaxy of Homogeneous Topological HgTe on Doped InAs Substrate

AbstractHgTe has been considered to be one of the most versatile topological materials. Depending on the in‐plane strain, Weyl and Dirac semi‐metal, as well as topological insulator phases, are feasible. Here, for the first time it is reported, that an InAs:S substrate promotes an initial 2D growth of a ZnTe thin layer and subsequent high crystalline quality ZnTe/CdTe superlattices serve as a smooth and continuous virtual substrate for the growth of (Cd,Hg)Te/HgTe/(Cd,Hg)Te heterostructures with unstrained quantum well HgTe (topological insulator) and compressively strained bulk HgTe (Weyl semimetal) by molecular beam epitaxy. Compared with the superlattices previously grown on GaAs substrates, the quantum well and bulk heterostructures exhibit homogeneous surfaces with root mean square roughnesses of 0.88–0.93 nm, which is three times lower than those observed for 3D islands (2.7–3.4 nm) on GaAs substrates. Additionally, magnetotransport measurements confirm high electronic quality and demonstrate that the S‐doped InAs substrate can be used as an effective back gate. These results manifest a (big) step forward toward the improvement of micro‐ and nanometer‐sized top‐ and back‐gated device fabrication on topological materials.

Modulating Electrical Double Layers: Facile Approach for Promoting Noncovalent Interactions between Boron Nitride Nanosheets and Gold Nanoparticles.

Electrical double layer (EDL) plays a crucial role in colloidal chemistry, which can be modified by changing the pH and ionic strength of a solution. Even though EDL is well-recognized, there are limited studies exploring interactions between two-dimensional (2D) and zero-dimensional nanoparticles. Herein, we demonstrate a simple pH-based approach to control the EDL of boron nitride nanosheets (BNNSs) and gold nanoparticles (AuNPs) that plays a crucial role in their interaction, displaying a one-way gate effect. We observed that as the EDL decreases, AuNPs can come into closer interaction with BNNSs, and this also resulted in a deceleration of the aggregation process of AuNPs when functionalized with l-cysteine. This work provides a fundamental understanding of how modulation of the EDL of 2D nanomaterials can be achieved through functionalizing strategies.

Integration of Vertical Graphene Onto a Tunnelling Cathode for Digital X-Ray Imaging.

As an alternative to thermionic X-ray generators, cold-cathode X-ray tubes are being developed for portable and multichannel tomography. Field emission propagating from needle structures such as carbon nanotubes or Si tips currently dominates related research and development, but various obstacles prevent the widespread of this technology. An old but simple electron emission design is the planar tunnelling cathode using a metal-oxide-semiconductor (MOS) structure, which achieves narrow beam dispersion and low supplying voltage. Directly grown vertical graphene (VG) is employed as the gate electrode of MOS and tests its potential as a new emission source. The emission efficiency of the device is initially ≈1% because of unavoidable fabrication damage during the patterning processes; it drastically improves to >40% after ozone treatment. The resulting emission current obeys the Fowler-Nordheim tunnelling model, and the enhanced emission is attributed to the effective gate thickness reduction by ozone treatment. As a proof-of-concept experiment, a clustered array of 2140 cells is integrated into a system that provides mA-class emission current for X-ray generation. With pulsed digital excitations, X-ray imaging of a chest phantom, demonstrating the feasibility of using a VG MOS electron emission source as a new and innovative X-ray generator is realized.

High-performance electrolyte-gated amorphous InGaZnO field-effect transistor for label-free DNA sensing

Accurate, convenient, label-free, and cost-effective biomolecules detection platforms are currently in high demand. In this study, we showcased the utilization of electrolyte-gated InGaZnO field-effect transistors (IGZO FETs) featuring a large on-off current ratio of over 106 and a low subthreshold slope of 78.5 mV/dec. In the DNA biosensor, the modification of target DNA changed the effective gate voltage of IGZO FETs, enabling an impressive low detection limit of 0.1 pM and a wide linear detection range from 0.1 pM to 1 μM. This label-free detection method also exhibits high selectivity, allowing for the discrimination of single-base mismatch. Furthermore, the reuse of gate electrodes and channel films offers cost-saving benefits and simplifies device fabrication processes. The electrolyte-gated IGZO FET biosensor presented in this study shows great promise for achieving low-cost and highly sensitive detection of various biomolecules.

Programmable Graphene e-Nose Sensor Arrays for Fast, Sensitive, and Label-Free Identification of Chemical Vapors

Conventional nanoelectronic chemical vapor sensors are mostly based on charge transfer mechanisms. The presence of vapor molecules interacts with the sensing material, resulting in changes in charge density in the channel; the resulting conductance change can subsequently be detected as changes in the current signals. This charge transfer-based mechanism naturally requires strong molecule-sensor interaction in order to achieve high sensitivity. However, the strong binding of analytes to the sensor surface will inevitably lead to slow response time and slow sensor recovery, making it unsuitable for applications requiring rapid monitoring of chemical vapors.To address this challenge, our groups previously demonstrated a new type of fast, sensitive, and broad-spectrum electronic vapor sensor by exploiting the fringing field capacitance effect in the graphene field-effect transistor (GFET). The typically trivial fringing field capacitance change due to analyte absorption is greatly amplified by both the graphene transistor and a micro-flow channel covering the surface of graphene. Different from the charge-transfer process in traditional sensors, when molecules of analytes flow through the surface of the graphene transistor, its local dielectric environment is altered which results in changes in the fringing capacitance. This molecular fringing gate effect can be amplified intrinsically by the large transconductance of the GFET. Instead of using AC spectroscopy, this capacitance change can be measured conveniently as a peak in DC current.1 In this work, a programmable graphene e-nose sensor array with electrical gates design and enhanced packaging will be demonstrated to achieve true label-free sensing and identification of chemical vapors. Individual graphene sensors within the 1D sensor array (up to 1 x 9) can be optimized to offer sensitive (down to picogram) and fast (sub-second) detection toward a variety of analytes. Figure 1 demonstrates the prototype of the graphene sensor array. Each sensor chip consists of two parts: an array of nine GFETs with a dimension of 15mm by 15mm (Figure 1(A)), and a 40cm long micro-column chip with a column width of 20-60 μm fabricated on a silicon wafer with 200nm of SiO2 by using DRIE (Deep Reactive Ion Etching) (Figure 1(B)). These two components were then bonded by epoxy and the assembled sensor chip is shown in Figure 1(C). The graphene transistor array was fabricated by transferring CVD graphene onto a silicon substrate with 200nm of thermally grown SiO2. Individual gold metal back gates were fabricated underneath the graphene film with 200nm Al2O3 deposited by ALD (atomic layer deposition) as the gate dielectric. Devices with single or multi-layer (up to 4 layers) graphene films were fabricated and tested.The fabricated graphene sensors have near-perfect device yield and a resistance range within 2 ~ 10 kΩ. Figure 1(D) and 1(E) shows the DC current signal changes of a typical sensor within the array when vapor-phase analytes of different masses were injected through a benchtop gas chromatography (GC) setup. 9 ng and 6 ng of Hexanal injection generated current peaks with peak heights of 0.8 μA and 0.5 μA, and peak width (full width at half maximum) of 1.8 seconds and 2 seconds, respectively. The high signal-to-noise ratio (~ 80 to 1) and the short response time demonstrate the high sensitivity and fast detection capability of the graphene sensor. Figure 1(E) shows a detailed sensitivity test from the injections of hexanal vapor of five different masses. The graphene sensor exhibits good linearity with a sensitivity of 79nA per nanogram of Hexanal and a 3σ detection limit of 380 picograms.We further tested the electrical gate tunability of the graphene sensor’s response. In order to eliminate the effect of graphene conductance modulation by the gate voltage, we normalize the peak height with the baseline current. As shown in Figure 1(F), when the gate voltage is programmed from -10V to +10V, the hexanal peak height is strengthened by approximately 30 percent. Similar gate voltage tuning is also observed on other analytes, such as acetone and hexanol.Our results clearly show the gate voltage tunability of the graphene sensor, suggesting a novel graphene sensor array using electrical programming rather than chemical functionalization to achieve selectivity. Combined with advanced data analysis tools, the graphene e-nose array has the potential to offer label-free chemical vapor sensing without the need to individually functionalize each sensor as in traditional e-nose devices. Furthermore, we will discuss the integration of the graphene e-nose sensor array with a micro-gas chromatography chip and a smartphone-sized custom PCB board for programming, readout, and Bluetooth data communication. W. Zang et al., Nano Lett., 21, 10301–10308 (2021). Figure 1