Asymmetric Gate Research Articles

Gate-Tunable High-Responsivity Photodiode Based on 2D Ambipolar Semiconductor

Abstract Electrically tunable homojunctions based on ambipolar two-dimensional materials have attracted widespread attention in the field of intelligent vision. These devices exhibit inherent switchable positive and negative photovoltaic properties, that effectively mimic the behavior of human retinal cells. However, the photovoltaic responsivity of most electrically tunable homojunctions remain significantly low due to the weak light absorption, making it challenging to meet the application requirements for high-sensitivity target detection in the field of intelligent vision. Here, we propose a gate-tunable photodiode based on two-dimensional ambipolar WSe2 with an asymmetric gate electrode, achieving high photovoltaic responsivity. By adjusting the gate voltage and keeping bias voltage zero, we can dynamically realize reconfigurable n--p and n--n homojunction states, as well as gate-tunable photovoltaic response characteristics that range from positive to negative. The maximum photovoltaic responsivity of the electrically tunable WSe2 homojunction is approximately 0.4 A/W, which is significantly larger than the previously reported value ~0.1 A/W in homojunction devices. In addition, the responsivity can be further enhanced to approximately 1.0 A/W when the n--p photodiode operates in reverse bias mode, enabling high-sensitivity detection of targets. Our work paves the way for developing gate-tunable photodiodes with high photovoltaic responsivity and advancing high-performance intelligent vision technology.

Cryo-EM structure of the heteromeric TRPC1/TRPC4 channel.

Transient receptor potential (TRP) ion channels have a crucial role as cellular sensors, mediating diverse physical and chemical stimuli. The formation of heteromeric structures expands the functionality of TRP channels; however, their molecular architecture remains largely unknown. Here we present the cryo-electron microscopy structures of the human TRPC1/TRPC4 heteromer in the apo and antagonist-bound states, both consisting of one TRPC1 subunit and three TRPC4 subunits. The heteromer structure reveals a distinct ion-conduction pathway, including an asymmetrically constricted selectivity filter and an asymmetric lower gate, primarily attributed to the incorporation of TRPC1. Through a structure-guided electrophysiological assay, we show that both the selectivity filter and the lower part of the S6 helix participate in deciding overall preference for permeating monovalent cations. Moreover, we reveal that the introduction of one lysine residue of TRPC1 into the tetrameric central cavity is enough to render one of the most important functional consequences of TRPC heteromerization: reduced calcium permeability. Our results establish a framework for addressing the structure-function relationship of the heteromeric TRP channels.

New paradigms of 2D layered material self-driven photodetectors.

By virtue of the high carrier mobility, diverse electronic band structures, excellent electrostatic tunability, easy integration, and strong light-harvesting capability, 2D layered materials (2DLMs) have emerged as compelling contenders in the realm of photodetection and ushered in a new era of optoelectronic industry. In contrast to powered devices, self-driven photodetectors boast a wealth of advantages, notably low dark current, superior signal-to-noise ratio, low energy consumption, and exceptional compactness. Nevertheless, the construction of self-driven 2DLM photodetectors based on traditional p-n, homo-type, or Schottky heterojunctions, predominantly adopting a vertical configuration, confronts insurmountable dilemmas such as intricate fabrication procedures, sophisticated equipment, and formidable interface issues. In recent years, worldwide researchers have been devoted to pursuing exceptional strategies aimed at achieving the self-driven characteristics. This comprehensive review offers a methodical survey of the emergent paradigms toward self-driven photodetectors constructed from 2DLMs. Firstly, the burgeoning approaches employed to realize diverse self-driven 2DLM photodetectors are compiled, encompassing strategies such as strain modulation, thickness tailoring, structural engineering, asymmetric ferroelectric gating, asymmetric contacts (including work function, contact length, and contact area), ferroelectricity-enabled bulk photovoltaic effect, asymmetric optical antennas, among others, with a keen eye on the fundamental physical mechanisms that underpin them. Subsequently, the prevalent challenges within this research landscape are outlined, and the corresponding potential approaches for overcoming these obstacles are proposed. On the whole, this review highlights new device engineering avenues for the implementation of bias-free, high-performance, and highly integrated 2DLM optoelectronic devices.

Impact of underlap layer on DC and RF/analog performance of asymmetric junctionless dual material double gate MOSFET for low-power analog amplifier design

Impact of underlap layer is analytically investigated on asymmetric junctionless dual material double gate MOSFET (AJDMDG) to reduce subthreshold slope and threshold voltage, which are two essential requirements with shrinking device dimensions to avoid short channel effects. The model utilizes two-dimensional Poisson’s equation with parabolic approximation for determining electrical parameters where dimensional ranges are kept within fabrication limit. Excellent accuracy is found for the obtained analytical outcome, when compared with results obtained from TCAD ATLAS simulator. Comparative study is extended for conventional junctionless DMDG (JDMDG) and underlap asymmetric junctionless single material DGFET (UAJDG) device, having identical dimensional parameters and biasing ranges; where the present structure exhibits superior performance in terms of threshold voltage, subthreshold slope and DIBL of 34.57%, 62.85% and 69.85% respectively compared to JDMDG and 12.50%, 26.08% and 40.25% respectively w.r.t UAJDG structure. Supremacy of the proposed architecture is further established with RF/analog Figures of Merit (FOMs), which are essential for designing low power analog amplifier.

Investigation of Analog/RF behaviour of Asymmetrical Gate Tunnel FET at Cryogenic temperatures

Investigation of Analog/RF behaviour of Asymmetrical Gate Tunnel FET at Cryogenic temperatures

RF linearity and improved transconductance of ScAlN/GaN HEMT with novel inverse L-shaped gate structure

In this study, we investigate the enhancement of effective transconductance and gain linearity in submicrometer gate AlGaN-barrier-based transistors utilizing ScAlN/GaN coupling-channel structures. A novel asymmetric gate design, incorporating an AlGaN cap on ScAlN/GaN HEMT, is proposed. This configuration demonstrates a flat transconductance profile and significantly reduced transconductance derivative, thereby improving the linearity of GaN-based transistors. For transistors with a gate length of 0.5 μm, both the current gain cut-off frequency and power gain cut-off frequency are measured at 53.52 GHz and 72.98 GHz, respectively. These values represent a more than threefold increase from the corresponding frequencies of conventional devices. Moreover, the theoretical Output Third-Order Intercept value of the proposed structure has increased by 7.5 dBm compared to conventional HEMTs. This superior linear performance can be attributed to the combined effect of AlGaN cap layer and air cavity. Furthermore, the introduction of the ScAlN layer results in a substantial impact, including a decrease in electron concentration from 4.96 × 1019/cm3 to 1.98 × 1019/cm3 and an increase in electron velocity from 4.5 × 107 to 7.6 × 108 cm/s. These findings underscore the potential of the proposed device for high-frequency applications requiring superior linearity.

Terahertz-frequency plasmonic-crystal instability in field-effect transistors with asymmetric gate arrays

We present a theory for plasmonic crystal instability in a semiconductor field-effect transistor with a dual grating gate array, designed with strong asymmetry in the elementary cell of this “crystal”. We demonstrate that, under the action of a dc current bias, the Bloch plasma waves in the plasmonic crystal formed in this transistor develop the Dyakonov–Shur instability. By calculating the energy spectrum and instability increments/decrements—which govern the growth/decay of excitations within the plasmonic crystal—we analyze the dependence of the latter on the electron drift velocity and the extent of the structural asymmetry. In contrast with the corresponding problem for gate arrays with symmetric unit cells, the presence of finite plasma instability increments across the entire Brillouin zone is established. This important difference points to the possibility of exciting sustained, radiating, non-linear electron plasma oscillations in the instability endpoint of the asymmetric array. These structures should be readily implementable in common semiconductor heterostructures, using standard nanofabrication techniques, enabling operation at room temperature. Long-range coherence of the unstable plasma oscillations, generated in the elementary cells of the crystal, should dramatically increase the radiated THz electromagnetic power, making this approach a promising pathway to the generation of THz signals.

Supercurrent in the Presence of Direct Transmission and a Resonant Localized State.

We study the current-phase relation (CPR) of an InSb-Al nanowire Josephson junction in parallel magnetic fields up to 700mT. At high magnetic fields and in narrow voltage intervals of a gate under the junction, the CPR exhibits π shifts. The supercurrent declines within these gate intervals and shows asymmetric gate voltage dependence above and below them. We detect these features sometimes also at zero magnetic field. The observed CPR properties are reproduced by a theoretical model of supercurrent transport via interference between direct transmission and a resonant localized state.

Terahertz Detection by Asymmetric Dual Grating Gate Bilayer Graphene FETs with Integrated Bowtie Antenna.

An asymmetric dual-grating gate bilayer graphene-based field effect transistor (ADGG-GFET) with an integrated bowtie antenna was fabricated and its response as a Terahertz (THz) detector was experimentally investigated. The device was cooled down to 4.5 K, and excited at different frequencies (0.15, 0.3 and 0.6 THz) using a THz solid-state source. The integration of the bowtie antenna allowed to obtain a substantial increase in the photocurrent response (up to 8 nA) of the device at the three studied frequencies as compared to similar transistors lacking the integrated antenna (1 nA). The photocurrent increase was observed for all the studied values of the bias voltage applied to both the top and back gates. Besides the action of the antenna that helps the coupling of THz radiation to the transistor channel, the observed enhancement by nearly one order of magnitude of the photoresponse is also related to the modulation of the hole and electron concentration profiles inside the transistor channel by the bias voltages imposed to the top and back gates. The creation of local n and p regions leads to the formation of homojuctions (np, pn or pp+) along the channel that strongly affects the overall photoresponse of the detector. Additionally, the bias of both back and top gates could induce an opening of the gap of the bilayer graphene channel that would also contribute to the photocurrent.

Control-gate-free reconfigurable transistor based on 2D MoTe2 with asymmetric gating

As transistor footprint scales down to the sub-10 nm regime, the process development for advancing to further technology nodes has encountered slowdowns. Achieving greater functionality within a single chip requires concurrent development at the device, circuit, and system levels. Reconfigurable transistors possess the capability to transform into both n-type and p-type transistors dynamically during operation. This transistor-level reconfigurability enables field-programmable logic circuits with fewer components compared to conventional circuits. However, the reconfigurability requires additional polarity control gates in the transistor and potentially impairs the gain from a smaller footprint. In this paper, we demonstrate a 2D control-gate-free reconfigurable transistor based on direct modulation of out-of-plane conduction in an ambipolar MoTe2 channel. Asymmetric electrostatic gating at the source and drain contacts is employed in the MoTe2 transistor resulting in different Schottky barrier widths at the two contacts. Consequently, the ambipolar conduction is reduced to unipolar conduction, where the current flow direction determines the preferred carrier type and the transistor polarity. Temperature dependence of the transfer characteristics reveals the Schottky barrier-controlled conduction and confirms that the Schottky barrier widths at the top contact are effectively tuned by electrostatic gating. Without the complexity overhead from polarity control gates, control-gate-free reconfigurable transistors promise higher logic density and lower cost in future integrated circuits.

PH-Stimulated Response Gating for Mimic Cytochrome C Transport on Biomimetic Asymmetric Nanochannels.

Proteins are vital components in cells, biological tissues, and organs, playing a pivotal role in growth and developmental processes in living organisms. Cytochrome C (Cyt C) is a class of heme proteins found in almost all life and is involved in cellular energy metabolic processes such as respiration, mainly as electron carriers or terminal reductases. It binds cardiolipin in the inner mitochondrial membrane, leading to apoptosis. It is a challenge to design a simple and effective artificial system to mimic the complex Cyt C biological transport process. In this paper, an asymmetric biomimetic pH-driven protein gate is described by introducing arginine (Arg) at one end of an hourglass-shaped nanochannel. The nanochannel shows a sensitive protonation-driven protein gate that can be "off" at pH = 7 and "on" at pH = 2. Further studies show that differences in the binding of Arg and Cyt C at different levels of protonation lead to different switching behaviors within the nanochannels, which in turn lead to different surface charges within the nanochannels. It can be used for detecting Cyt C and as an excellent and robust gate for developing integrated circuits and nanoelectronic logic devices.

Asymmetric Gate and SiC Substrate Grooved InGaN Back‐Barrier AlGaN/GaN HEMTs for High‐Power RF Applications

We report high‐power InGaN back‐barrier AlGaN/GaN high electron mobility transistors with the gate placed closer to the source with an Au‐filled groove in the SiC substrate near the drain end. An InGaN back‐barrier is known to reduce short‐channel effects at high drain‐to‐source (VDS) voltage. However, the improvement is realized at the cost of reduced two‐dimensional electron gas density (ns) and saturation drain‐to‐source (IDS,SAT) current. Here, we demonstrate that bothnsandIDS,SATare recovered when the gate is appropriately delineated near the source. The junction temperature increases at higherVDS,which tends to deteriorate the power performance and suppress the benefits from higherIDS,SAT. This problem is contained by further thinning down the SiC substrate near the drain by creating a backside groove using deep reactive‐ion‐etching and filling it with Ti/Au. An enhanced thinned‐down substrate distributes the lateral electric field uniformly near the drain end, compounding its benefits with an asymmetric gate and lower junction temperature. The proposed device shows an output power ofPout = 6.7 W mm−1atVDS = 28 V at 15 GHz for a 200 nm gate length (LG).

Demonstration of a Ternary Inverter Based on the Novel TDDFET with Dual-Doped Source and Asymmetric Gates

Demonstration of a Ternary Inverter Based on the Novel TDDFET with Dual-Doped Source and Asymmetric Gates

11.2 W/mm power density AlGaN/GaN high electron-mobility transistors on a GaN substrate

In this letter, high power density AlGaN/GaN high electron-mobility transistors (HEMTs) on a freestanding GaN substrate are reported. An asymmetric Γ-shaped 500-nm gate with a field plate of 650 nm is introduced to improve microwave power performance. The breakdown voltage (BV) is increased to more than 200 V for the fabricated device with gate-to-source and gate-to-drain distances of 1.08 and 2.92 μm. A record continuous-wave power density of 11.2 W/mm@10 GHz is realized with a drain bias of 70 V. The maximum oscillation frequency (f max) and unity current gain cut-off frequency (f t) of the AlGaN/GaN HEMTs exceed 30 and 20 GHz, respectively. The results demonstrate the potential of AlGaN/GaN HEMTs on free-standing GaN substrates for microwave power applications.

Moiré synaptic transistor with room-temperature neuromorphic functionality.

Moiré quantum materials host exotic electronic phenomena through enhanced internal Coulomb interactions in twisted two-dimensional heterostructures1-4. When combined with the exceptionally high electrostatic control in atomically thin materials5-8, moiré heterostructures have the potential to enable next-generation electronic devices with unprecedented functionality. However, despite extensive exploration, moiré electronic phenomena have thus far been limited to impractically low cryogenic temperatures9-14, thus precluding real-world applications of moiré quantum materials. Here we report the experimental realization and room-temperature operation of a low-power (20 pW) moiré synaptic transistor based on an asymmetric bilayer graphene/hexagonal boron nitride moiré heterostructure. The asymmetric moiré potential gives rise to robust electronic ratchet states, which enable hysteretic, non-volatile injection of charge carriers that control the conductance of the device. The asymmetric gating in dual-gated moiré heterostructures realizes diverse biorealistic neuromorphic functionalities, such as reconfigurable synaptic responses, spatiotemporal-based tempotrons and Bienenstock-Cooper-Munro input-specific adaptation. In this manner, the moiré synaptic transistor enables efficient compute-in-memory designs and edge hardware accelerators for artificial intelligence and machine learning.

Design and Development of Cascaded Current Control in DC Motor Variable Speed Drive using dSPACE

Even today, DC motors are still used in variety of applications, including home appliances, transportation, as well as industrial crane and rolling machine. However, achieving precise speed and torque control in DC drives at industry level could be challenging, as instability and reduced efficiency remains at large. This project focuses on developing a cascaded control system for a Separately Excited Brushed DC motor using dSPACE platform. The cascaded control system, designed using MATLAB Simulink, incorporates a proportional-integral (PI) controller at the speed loop and a Hysteresis controller at the current loop to improve robustness and dynamic performance. The experimental setup utilizes the dSPACE 1104 platform, an asymmetric bridge converter board, gate driver, and electrical load. Speed measurement is done using an incremental encoder, while current is measured using the ACS712 current sensor. The drive system was tested in alternate low and high speed cycle on various load level to test for stability, robustness and dynamic performance. The proposed control system was compared with PI-closed-loop control and open-loop control determine the best drive performance. Experimental results showed significant improvement in term of transient response and ripple reduction of speed and current for proposed cascaded current control over the closed-loop design.

Asymmetric gating of a human hetero-pentameric glycine receptor

Hetero-pentameric Cys-loop receptors constitute a major type of neurotransmitter receptors that enable signal transmission and processing in the nervous system. Despite intense investigations into their working mechanism and pharmaceutical potentials, how neurotransmitters activate these receptors remains unclear due to the lack of high-resolution structural information in the activated open state. Here we report near-atomic resolution structures resolved in digitonin consistent with all principle functional states of the human α1β GlyR, which is a major Cys-loop receptor that mediates inhibitory neurotransmission in the central nervous system of adults. Glycine binding induces cooperative and symmetric structural rearrangements in the neurotransmitter-binding extracellular domain but asymmetrical pore dilation in the transmembrane domain. Symmetric response in the extracellular domain is consistent with electrophysiological data showing cooperative glycine activation and contribution from both α1 and β subunits. A set of functionally essential but differentially charged amino acid residues in the transmembrane domain of the α1 and β subunits explains asymmetric activation. These findings provide a foundation for understanding how the gating of the Cys-loop receptor family members diverges to accommodate specific physiological environments.

The design considerations of stray inductance for power modules with parallel-connected IGBT chips for a digital gate driver control

This paper aims to clarify the effect of asymmetric gate inductance Lg and emitter inductance Le inside power modules with two parallel-connected IGBTs on switching characteristics when a three-step digital gate driver is employed. Five types of IGBT modules with different Lg and Le were fabricated to implement double pulse tests by conventional gate driving and digital gate driving with three-step vectors. Under the conventional gate driving, the asymmetric Le introduced an imbalanced current during on-stage, and the asymmetric Lg introduced gate voltage spike Vg_spike and an imbalanced current during the turn-off interval. Large Lg introduced large Vg_spike. From the miller plateau in the turn-off, the current started to concentrate on the IGBT whose Lg is small. In the turn-on interval, the asymmetric Le made current share in two IGBTs become imbalanced, and the occurred large Vg_spike is positively corresponding to the difference of emitter current Ie flowing through two IGBTs. Under digital gate driving, it was found that the tradeoff between switching loss and voltage/current overshoots can be improved. And, the difference of Eoff between two IGBT chips, which results from asymmetric Le mainly, could be decreased more than that in conventional gate driving. In the turn-on interval, the large Vg_spike can be suppressed by a small vector number at the second step, and the difference of turn-on loss Eon could be also decreased. According to the above switching characteristics, the design considerations of power modules with parallel-connected IGBTs were proposed as the digital gate driver is applied.

Device and circuit level performance assessments of gate engineered Ge/GaAs heterojunction doping less TFET

AbstractRecently, the doping‐less tunnel FET has gained popularity due to its lower process complexity than conventional TFETs with heavily doped source and drain regions. In this literature, we have introduced a symmetric gate Ge/GaAs heterojunction doping‐less TFET(SG HJ DL TFET) using 4.6 eV work function for both the top gate and bottom gate and an asymmetric gate Ge/GaAs heterojunction doping‐less TFET (AG HJ DL TFET) using 3.9 eV work function as top gate and 4.6 eV work function as a bottom gate. A comparative study has been performed between these two devices. The back gate misalignment engineering in the AG HJ DL TFET induces higher charge plasma near the source‐channel junction which will enhance the drain current. Due to a larger drain current, an improved ratio (11.8 times), and steeper SS (37%) are achieved in optimized AG HJ DL TFET than SG HJ DL TFET. Furthermore, the Analog/Radio Frequency and linearity performance parameters have been examined, and a significant improvement is noticed in the optimized AG HJ DL TFET. The impact of different interface trap charges (ITCs) on device performances is also investigated and it is found that AG HJ DL TFET shows more immunity to ITCs than SG HJ DL TFET. Finally, the Verilog‐A‐based model has been developed for the AG HJ DL TFET to utilize its circuit‐level behavior. The optimized device‐based Common Source amplifier (CS amplifier) has been simulated in the Cadence Virtuoso tool. The AG HJ DL TFET‐based CS amplifier offers a 6.83% improvement in voltage gain over the other reported work.

Nonlinear intensity dependence of ratchet currents induced by terahertz laser radiation in bilayer graphene with asymmetric periodic grating gates

We report on the observation of a nonlinear intensity dependence of the terahertz radiation-induced ratchet effects in bilayer graphene with asymmetric dual-grating gate lateral lattices. These nonlinear ratchet currents are studied in structures of two designs with dual-grating gates fabricated on top of boron nitride encapsulated bilayer graphene and beneath it. The strength and sign of the photocurrent can be controllably varied by changing the bias voltages applied to individual dual-grating subgates and the back gate. The current consists of contributions insensitive to the radiation’s polarization state, defined by the orientation of the radiation electric field vector with respect to the dual-grating gate metal stripes, and the circular ratchet sensitive to the radiation helicity. We show that intense terahertz radiation results in a nonlinear intensity dependence caused by electron gas heating. At room temperature, the ratchet current saturates at high intensities of the order of hundreds to several hundreds of kW cm−2. At T=4 K, the nonlinearity manifests itself at intensities that are one or two orders of magnitude lower; moreover, the photoresponse exhibits a complex dependence on the intensity, including a saturation and even a change of sign with increasing intensity. This complexity is attributed to the interplay of the Seebeck ratchet and the dynamic carrier-density redistribution, which feature different intensity dependencies and nonlinear behavior of the sample’s conductivity induced by electron gas heating. The latter is demonstrated by studying the THz photoconductivity. Our study demonstrates that graphene-based asymmetric dual-grating gate devices can be used as terahertz detectors at room temperature over a wide dynamic range, spanning many orders of magnitude of terahertz radiation power. Therefore, their integration together with current-driven read-out electronics is attractive for the operation with high-power pulsed sources.