Critical Gate Voltage Research Articles

Redox gating-induced modulation of charge carrier density and lattice expansion in LaNiO3 thin films

Redox gating involves the use of reversible redox functionalities combined with ionic electrolytes to substantially alter the charge carrier density in functional condensed materials. This modification leads to the emergence of physical properties not observed in the original material. In our study, we focus on redox gating applied to a LaNiO3 (001) film within a field-effect device and identify a critical gate voltage of 0.7 V. Hall measurements indicate that redox gating markedly increases the charge carrier density in LaNiO3, reaching over 1014 cm−2. This increase is primarily due to the injection of electrons into LaNiO3, which offsets the existing hole carriers. These adjustments in the carrier concentration result in reversible lattice expansion in LaNiO3 when gate voltages are below 0.7 V. This expansion correlates well with theoretical models that consider adjustments to the Ni–O bond length, influenced by oxygen ligand holes. Conversely, at gate voltages above 0.7 V, there are significant changes in resistivity, lattice structure, and Ni valence, stemming from the formation of oxygen vacancies in the LaNiO3 film.

Gate-Tunable Critical Current of the Three-Dimensional Niobium Nanobridge Josephson Junction.

Recent studies have shown that the critical currents of several metallic superconducting nanowires and Dayem bridges can be locally tuned by using a gate voltage (Vg). Here, we report a gate-tunable Josephson junction structure constructed from a three-dimensional (3D) niobium nanobridge junction (NBJ) with a voltage gate on top. Measurements up to 6 K showed that the critical current of this structure can be tuned to zero by increasing Vg. The critical gate voltage was reduced to 16 V and may possibly be reduced further by reducing the thickness of the insulation layer between the gate and the NBJ. Furthermore, the flux modulation generated by Josephson interference of two parallel 3D NBJs can also be tuned by using Vg in a similar manner. Therefore, we believe that this gate-tunable Josephson junction structure is promising for superconducting circuit fabrication at high integration levels.

Bias Temperature Instability of Multilayer ReS2 FET with α‐MoO3 Passivation

Abstract2D semiconductors are regarded as promising candidates for channel applications in the next generation of field effect transistors (FETs) with sub‐5 nm pitch designs. Among 2D transition metal dichalcogenides (TMDs), rhenium disulfide (ReS2) is reported to have weak interaction among neighboring layers, resulting in more susceptibility to the functionalization of the surface channel. The bias temperature instability (BTI) of ReS2 FETs with α‐molybdenum trioxide (α‐MoO3) passivation that functions as a charge buffer layer is investigated. The transconductance (gm) with a passivation layer shows the saturation behavior under the critical gate voltage even with cumulative electric stress. In addition, unintentional shifts of threshold voltages (VTH) are significantly reduced, which is attributed to the effects of the α‐MoO3 passivation. The electron transfer with the passivation effect suggests a way of surface engineering for controlling the 2D devices with enhanced stabilities.

An Analytical Model for the Electrostatics of Reverse-Biased Al/SiO₂/Si(p) MOS Capacitors With Tunneling Oxide

An analytical model for the electrostatics of Al/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si(p) MOS tunnel structures under reverse bias has been proposed in this work by formulating and balancing minority carrier current equations. The model was validated by experimental and technology computer-aided design (TCAD) simulation data under a wide range of oxide thicknesses with minor deviations. Moreover, for ultrathin oxides, it manages to predict the deep depletion phenomenon, while the ordinary MOS electrostatics model does not. Collectively, an approximate closed-form expression for the critical gate voltage as the starting point of deep depletion phenomena has also been formulated. Future corrections and more delicate assumptions may help improve the model’s accuracy in accordance with experimental values of critical voltage. This model is believed to be a convenient and comprehensive approach for evaluating the electrostatics of the MOS(p) tunnel structures.

High-electric-field behavior of the metal-insulator transition in TiS3 nanowire transistors

We investigate the behavior of the metal-insulator transition (MIT) in TiS3 nanowire field-effect transistors, in the strongly nonequilibrium limit that has, thus far, largely been neglected. Under high electric fields within the TiS3 channel (≤115 kV/cm), we observe the emergence of a critical fixed point, separating insulating and metallic regions in the transfer curves of the device. The critical gate voltage that defines this fixed point evolves systematically with the drain bias (field), allowing us to map out a phase diagram that identifies the conditions for metallicity or for insulating behavior. Dependent upon the choice of the gate voltage used to tune the carrier concentration in the nanowire, the existence of the field-induced MIT allows the TiS3 to be either insulating or metallic over an extensive range of temperature. The possible connection of this strongly nonequilibrium state to some form of charge density wave is discussed.

All‐Solid‐State Organic Schmitt Trigger Implemented by Twin Two‐in‐One Ferroelectric Memory Transistors

AbstractAlthough there have been many attempts to replace conventional inorganic electronics with organic materials that can be mass produced at low cost, few organic electronic filters to increase immunity to electrical noise have been reported thus far. Conventional Schmitt triggers or their inverters are used in many electronic circuits as versatile electronic noise filters. However, it is challenging to manufacture organic electronic systems with complex circuitry. In this study, a simple, all‐solid‐state organic Schmitt trigger consisting of twin two‐in‐one organic ferroelectric memory transistors with the same chemical compositions and device dimensions but different threshold voltages is introduced. Threshold voltages and hysteresis in the two‐in‐one devices can be controlled by polarization switching as demonstrated in a previous study. Hysteresis of a ferroelectric p‐type depletion load inverter can be achieved using twin two‐in‐one devices when the sweep voltage is higher than the critical gate voltages. This facilitates inverter characteristics at two different threshold voltages, and realizing a Schmitt trigger. Finally, based on simulation program with integrated circuit emphasis (SPICE) simulation, guidelines are proposed on how to design organic Schmitt triggers with p‐ or n‐type materials and ferroelectric or charge‐trapping mechanisms to achieve inverting or non‐inverting characteristics.

Carrier Transport Mechanisms Underlying the Bidirectional &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;${V}_{\mathrm{{TH}}}$ &lt;/tex-math&gt; &lt;/inline-formula&gt; Shift in p-GaN Gate HEMTs Under Forward Gate Stress

The threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> ) instability of p-GaN/AlGaN/GaN HEMTs was investigated under forward gate stress. A unique bidirectional V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> shift (AV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> ) with the critical gate voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> ) of 6 V was observed. The carrier transport mechanisms underlying the AV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> were extensively investigated through the voltage-dependent, timeresolved, and temperature-dependentgate current. The gate current is decomposed into electron and hole current in three distinct regions with respect to V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> , which are off-state for V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> <; 1.2 V (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> ), on-state for 1.2 V <; V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> <; 5 V and “gate-injected” region for V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> > 5 V. In off-state, the electrons were thermally activated and transport towards the gate, while electron-trapping governed by the space charge limited conduction (SCLC) in AlGaN barrier was observed in on-state and “gate-injected” region. Such an electrontrapping effect results in the positive V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> shift for V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> <; 6 V. Meanwhile, the marginal hole transport from gate by thermal activation was also captured by gate current, which features negligible impact on V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> . However, for V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> > 6 V, a drastic hole injection triggered by high V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> takes place that causes subsequent hole-trapping in AlGaN barrier and holeinjection into GaN buffer. The injected holes enhance the positive charge in the gate region and turned the positively shifted V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> into a negative shift.

Landau-Zener tunneling of qubit states and Aharonov-Bohm interferometry in double quantum wires

This paper gives a detailed description of a high-performance tunneling wire “flying qubit” for a quantum mechanical two-level system. We propose a simple double-wire interferometer setup and theoretically carry out the spectroscopy of these flying qubits. As such, we present a tight binding theoretical model which effectively mimicks the experimental setup and then compute the energy diagram and the Landau-Zener quantum tunneling probability under the effect of a sequence of magnetic pulses and gate voltages. At certain critical electrostatic gate voltages, the system exhibits a step rise in the Landau-Zener tunneling transition by playing a multi-crossing scenario in a privileged position of two geometric wires. We predict the consecutive modulations and precise the conservation of the Landau-Zener-Stückelberg-Majorana interference patterns mapped from the two-terminal of the double-wire system. A successful conversion of interferometry signals is identified within the two-path interferometer with higher intrinsic quantum correction errors. The latter is used quantitatively and qualitatively to achieve high-precision measurements beyond the standard Landau-Zener limit. The obtained results confirm the possibility of the construction of Aharonov-Bohm interferometers following the proposed model.

Ultra-Efficient Superconducting Dayem Bridge Field-Effect Transistor.

Superconducting field-effect transitor (SuFET) and Josephson field-effect transistor (JoFET) technologies take advantage of electric-field-induced control of charge-carrier concentration to modulate the channel superconducting properties. Despite the fact that the field-effect is believed to be ineffective for superconducting metals, recent experiments showed electric-field-dependent modulation of the critical current ( IC) in a fully metallic transistor. However, the grounding mechanism of this phenomenon is not completely understood. Here, we show the experimental realization of Ti-based Dayem bridge field-effect transistors (DB-FETs) able to control the IC of the superconducting channel. Our easy fabrication process for DB-FETs show symmetric full suppression of IC for applied critical gate voltages as low as VGC ≃ ±8 V at temperatures reaching about the 85% of the record critical temperature, TC ≃ 550 mK, for titanium. The gate-independent TC and normal-state resistance ( RN) coupled with the increase of resistance in the superconducting state ( RS) for gate voltages close to the critical value ( VGC) suggest the creation of field-effect induced metallic puddles in the superconducting sea. Our devices show extremely high values of transconductance (| gmMAX| ≃ 15 μA/V at VG ≃ ±6.5 V) and variations of Josephson kinetic inductance ( LK) with VG of 2 orders of magnitude. Therefore, the DB-FET appears as an ideal candidate for the realization of superconducting electronics, superconducting qubits, and tunable interferometers as well as photon detectors.

Fermi-level pinning of bilayer graphene with defects under an external electric field

The electronic structure of bilayer graphene, where one of the layers possesses monovacancies, is studied under an external electric field using density functional theory. Our calculations show that Fermi-level pinning occurs in the bilayer graphene with defects under hole doping. However, under electron doping, the Fermi level rapidly increases at the critical gate voltage with an increasing electron concentration. In addition to the carrier species, the relative arrangement of the gate electrode to the defective graphene layer affects the Fermi energy position with respect to the carrier concentration. Because the distribution of the accumulated carrier depends on the electrode position, the quantum capacitance of bilayer graphene with defects depends on the electrode position.

Effect of dose loss of phosphorus on capacitance-voltage characteristics of n-type poly-Si junctionless thin-film transistors

This study examines the effects of the dose loss of phosphorus on the capacitance-voltage characteristics of an n-type polycrystalline silicon junctionless (JL) transistor using experimental, analytical and simulated analyses. It clearly demonstrates that the gate voltage increases as the doping concentration in the channel of the JL transistor decreases, maintaining constant capacitance because the depletion region is easily formed at the surface of the channel with a low doping concentration. The critical gate voltage (VGC) is defined as the applied gate voltage that induces the gate capacitance at the kink of the C-V curve. The simulated results clearly suggest that the critical gate voltage increases linearly with the percentage of dose loss of phosphorus.

Controlling charge current through a DNA based molecular transistor

Molecular electronics is complementary to silicon-based electronics and may induce electronic functions which are difficult to obtain with conventional technology. We have considered a DNA based molecular transistor and study its transport properties. The appropriate DNA sequence as a central chain in molecular transistor and the functional interval for applied voltages is obtained. I–V characteristic diagram shows the rectifier behavior as well as the negative differential resistance phenomenon of DNA transistor. We have observed the nearly periodic behavior in the current flowing through DNA. It is reported that there is a critical gate voltage for each applied bias which above it, the electrical current is always positive.

Josephson coupling between superconducting islands on single- and bi-layer graphene

We study the Josephson coupling of superconducting (SC) islands through the surface of single-layer graphene (SLG) and bilayer graphene (BLG) in the long-junction regime, as a function of the distance between the grains, temperature, chemical potential and external (transverse) gate-voltage. For SLG, we provide a comparison with existing literature. The proximity effect is analyzed through a Matsubara Green’s function approach. This represents the first step in a discussion of the conditions for the onset of a granular superconductivity within the film, made possible by Josephson currents flowing between superconductors. To ensure phase coherence over the 2D sample, a random spatial distribution can be assumed for the SC islands on the SLG sheet (or intercalating the BLG sheets). The tunable gate-voltage-induced band gap of BLG affects the asymptotic decay of the Josephson coupling-distance characteristic for each pair of SC islands in the sample, which results in a qualitatively strong field dependence of the relation between Berezinskii–Kosterlitz–Thouless transition critical temperature and gate voltage.

Analysis of threshold voltage instability in AlGaN/GaN MISHEMTs by forward gate voltage stress pulses

We report on the investigation of the Vth drift behaviour of AlGaN/GaN MISHEMTs upon forward gate voltage stress in dependence of stress bias and stress time. The pulsed measurements allow for the evaluation of the operational regime for optimum device efficiency. We compared the effect of two different high‐κ gate dielectric materials with similar equivalent oxide thickness ϵ0ϵr/thigh‐κ on the Vth instability in order to separate the influence of the heterojunction design and the high‐κ/GaN‐cap interface from the bulk high‐κ. The matched gate capacitance coupling of the studied Al2O3 and HfO2 gate dielectric results in an nearly identical critical forward gate voltage, where the AlGaN barrier potential is lowered and severe threshold voltage shift (ΔVth) into the positive voltage direction is induced. Beyond this critical forward voltage, detailed time‐dependent stress pulse measurements from 1 µs to 1000 s revealed an immediate electron injection and trapping at the oxide/GaN interface for stress pulses with tstress ≥ 1 µs. The presented results of Vth drift analysis demonstrate the limits of the maximum tolerable forward gate voltage of the investigated Al2O3 and HfO2 MISHEMTs, although the excellent low‐leakage currents of the insulated gate would imply a potentially higher gate‐overdrive.

Robustness of MW-Level IGBT modules against gate oscillations under short circuit events

The susceptibility of MW-level IGBT power modules to critical gate voltage oscillations during short circuit events has been evidenced experimentally. This paper proposes a sensitivity analysis method to better understand the oscillating behavior dependence on different operating conditions (i.e., collector–emitter voltage, gate-emitter voltage and temperature). A study case on 1.7kV/1kA IGBT power modules is presented. The proposed study helps to understand the oscillation mechanism by revealing its relationship with different working conditions. Moreover, the study can be helpful to understand the oscillation phenomenon, as well as to further improve the device performance during short circuit.

A gate current 1/f noise model for GaN/AlGaN HEMTs

This work presents a theoretical and experimental study on the gate current 1/f noise in AlGaN/GaN HEMTs. Based on the carrier number fluctuation in the two-dimensional electron gas channel of AlGaN/GaN HEMTs, a gate current 1/f noise model containing a trap-assisted tunneling current and a space charge limited current is built. The simulation results are in good agreement with the experiment. Experiments show that, if Vg < Vx (critical gate voltage of dielectric relaxation), gate current 1/f noise comes from the superimposition of trap-assisted tunneling RTS (random telegraph noise), while Vg > Vx, gate current 1/f noise comes from not only the trap-assisted tunneling RTS, but also the space charge limited current RTS. This indicates that the gate current 1/f noise of the GaN-based HEMTs device is sensitive to the interaction of defects and the piezoelectric relaxation. It provides a useful characterization tool for deeper information about the defects and their evolution in AlGaN/GaN HEMTs.

SEGR in SiO${}_2$–Si$_3$N$_4$ Stacks

This paper presents experimental Single Event Gate Rupture (SEGR) data for Metal-Insulator-Semiconductor (MIS) devices, where the gate dielectrics are made of stacked SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> structures. A semi-empirical model for predicting the critical gate voltage in these structures under heavy-ion exposure is first proposed. Then interrelationship between SEGR cross-section and heavy-ion induced energy deposition probability in thin dielectric layers is discussed. Qualitative connection between the energy deposition in the dielectric and the SEGR is proposed.

Gate-voltage-dependent Landau levels in AA-stacked bilayer graphene

The effects of gate voltage Vg on the Landau levels (LLs) of the AA-stacked bilayer graphene are investigated by the Peierls tight-binding model. A uniform perpendicular magnetic field (B0) produces two groups of LLs. Vg can raise the threshold LL energies, increase the quantum numbers of the LLs nearest to the chemical potential, and modify the LL spacing. An energy gap is induced by B0, and it has an oscillatory dependence on Vg and B0. There exist semiconductor-semimetal transitions at certain critical gate voltages. Some carriers are transferred between similar sublattices on the two different layers. On the other hand, the main features of the Landau wave functions remain unchanged.

Cooperative charging in a nanocrystal assembly gated by ionic liquid

In order to make a densely packed assembly of undoped semiconductor nanocrystals conductive, it is usually gated by a room temperature ionic liquid. The ionic liquid enters the pores of the super-crystal assembly under the influence of an applied voltage. We study the capacitance of such a device as a function of the gate voltage. We show that, counter-intuitively, the capacitance of the system is the sum of delta-functions located at a sequence of critical gate voltages. At each critical voltage every nanocrystal acquires one additional electron.

Direct detection of the relative strength of Rashba and Dresselhaus spin-orbit interaction: Utilizing the SU(2) symmetry

We propose a simple method to detect the relative strength of Rashba and Dresselhaus spin-obit interactions in quantum wells (QWs) without relying on the directional-dependent physical quantities. This method utilize the asymmetry of critical gate voltages that leading to the remarkable signals of SU(2) symmetry, which happens to reflect the intrinsic structure inversion asymmetry of the QW. We support our proposal by the numerical calculation of in-plane relaxation times based on the self-consistent eight-band Kane model. We find that the two different critical gate voltages leading to the maximum spin relaxation times [one effect of the SU(2) symmetry] can simply determine the ratio of the coefficients of Rashba and Dresselhaus terms. Our proposal can also be generalized to extract the relative strengths of the spin-orbit interactions in quantum wire and quantum dot structures.