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Energy band diagram and current–voltage characteristics of various NVCTs a,b, Energy band diagram along the source–vacuum channel–drain direction of the NVCT for a gate voltage of 0 V (a) and high gate and drain voltages (b). A 3 × 3 emitter array is the nominal device used in the measurements. Here, q is the elementry charge, φB0 is the built-in potential barrier between metal and vacuum, EF is the Fermi energy, and EC is conduction band energy. c, Drain current versus gate voltage at a drain bias of 20 V and drain current versus drain voltage at a gate bias of 20 V. d, Gate leakage current during the measurements in c for comparing thin oxide, thick oxide FG and EG NVCTs. e,f, Drain current versus gate voltage at a drain bias of 20 V for comparing Si- and SiC-based EG NVCTs (e) and vacuum and air channel EG NVCTs (f).
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Vacuum tubes were central to the early development of electronics, but were replaced, decades ago, by semiconductor transistors. Vacuum channel devices, however, offer inherently faster operation and better noise immunity due to the nature of their channel. They are also stable in harsh environments such as radiation and high temperature. However,...
Citations
... Even with the utilization of advanced materials to address the weight-immunity trade-off, cost remains a primary concern [18,19]. Another innovative solution is the use of FETs based on the vacuum paradigm [20][21][22][23]. The fundamental concept behind radiation-immune vacuum devices involves eliminating the local cause of radiation-induced effects, which is the gate oxide and/or channel [20][21][22][23][24][25][26]. ...
... Another innovative solution is the use of FETs based on the vacuum paradigm [20][21][22][23]. The fundamental concept behind radiation-immune vacuum devices involves eliminating the local cause of radiation-induced effects, which is the gate oxide and/or channel [20][21][22][23][24][25][26]. In other words, the immunity of vacuum devices to radiation stems from the absence of a semiconductor channel and/or dielectric material, where radiation-induced multi-defects occur. ...
... In other words, the immunity of vacuum devices to radiation stems from the absence of a semiconductor channel and/or dielectric material, where radiation-induced multi-defects occur. The vacuum FETs have shown intriguing and promising performance in terms of immunity to radiation, electrical and switching behavior, and miniaturization [20][21][22][23][24][25][26][27][28][29]. ...
This paper investigates the performance of vacuum gate dielectric doping-free carbon nanotube/nanoribbon field-effect transistors (VGD-DL CNT/GNRFETs) via computational analysis employing a quantum simulation approach. The methodology integrates the self-consistent solution of the Poisson solver with the mode space non-equilibrium Green’s function (NEGF) in the ballistic limit. Adopting the vacuum gate dielectric (VGD) paradigm ensures radiation-hardened functionality while avoiding radiation-induced trapped charge mechanisms, while the doping-free paradigm facilitates fabrication flexibility by avoiding the realization of a sharp doping gradient in the nanoscale regime. Electrostatic doping of the nanodevices is achieved via source and drain doping gates. The simulations encompass MOSFET and tunnel FET (TFET) modes. The numerical investigation comprehensively examines potential distribution, transfer characteristics, subthreshold swing, leakage current, on-state current, current ratio, and scaling capability. Results demonstrate the robustness of vacuum nanodevices for high-performance, radiation-hardened switching applications. Furthermore, a proposal for extrinsic enhancement via doping gate voltage adjustment to optimize band diagrams and improve switching performance at ultra-scaled regimes is successfully presented. These findings underscore the potential of vacuum gate dielectric carbon-based nanotransistors for ultrascaled, high-performance, energy-efficient, and radiation-immune nanoelectronics.
... Vacuum transistors, based on field emission, have the potential to operate faster than solid-state transistors and last longer in harsh environments. 1,2 Various materials have been used to fabricate the cathodes in field emitters. 3 III-nitride materials, such as AlGaN and GaN, are promising candidates for the fabrication of field emitter arrays (FEAs) due to their tunable electron affinity. ...
Field emitter arrays (FEAs) have the potential to operate at high frequencies and in harsh environments. However, they have been shown to degrade under oxidizing environments. Studying the effect of O2 on FEAs can help to understand the degradation mechanisms, identify the requirements for vacuum packaging, and estimate the lifetime of the device. In this work, the effect of O2 exposure on 100 × 100 gallium-nitride-field emitter arrays (GaN-FEAs) was studied. The GaN-FEAs were operated at 6 × 10−10 Torr with a 1000 V DC anode voltage and a 50 V DC gate voltage, where the anode current was 1 μA and the gate current was ≤4 nA. The devices were exposed to 10−7, 10−6, and 10−5 Torr of O2 for 100 000 L. The anode current dropped by 50% after 300 L and 98% after 100 000 L. It was observed that the degradation depends on the exposure dose, rather than pressure. The devices mostly degrade when they are ON, confirmed by exposing the device to O2 when the gate voltage was off, and also by the relation between the degradation and duty cycle when pulsing the gate. The results of O2 exposure were compared to Ar exposure to determine whether sputtering and changes in the surface geometry were the primary cause of degradation. The results suggest that changes in the work function and surface chemistry are the cause of emission degradation of GaN-FEA induced by O2.
... Vacuum electron devices are sublime contender for high power and high frequency electronics because of their radiation hardness and ballistic electron transport. 1,2 Metallic and silicon field emitters improved a lot in terms of performance and reliability in recent years [3][4][5][6][7] thanks to the improvement in fabrication technology. III-Nitride materials (semiconductors) show possibilities of an improved field emission performance due to their electron affinities which can be tuned. ...
We are exploring the potential of gallium nitride (GaN) field emitter arrays in vacuum channel transistors. This study investigated the impact of ultraviolet (UV) light on the emission properties of large arrays of GaN field emitters. Arrays of 150 × 150 emitters were analyzed before and after UV exposure. With a constant collector voltage of 200 V DC, gate voltage sweeps from 0 to 60 V were applied. The initial I–V measurements showed a rapid increase in emission current, indicating a conditioning effect, settling at a stable value of 1.25 μA after three to five sweeps. Remarkably, exposure to UV light resulted in a fivefold increase in the maximum field emission current, reaching an impressive 6 μA. This significant enhancement highlights the potential of UV treatment for improving the performance of GaN-based field emitters. This surge in current can be attributed to the desorption of water vapor caused by the UV light. To compare with the heating-based water desorption technique, another array of 150 × 150 emitters was characterized before and after heating at 400 °C. While the collector voltage remained constant at 200 V DC, the gate voltage was systematically increased from 0 to 75 V in this experiment. This controlled sweeping of the gate voltage provided a precise method for characterizing the field emission properties of the GaN emitters. The I–V measurements revealed that, similar to the UV exposure case, collector current increased by approximately four times after heat treatment at 400 °C for 10 min. This resulted in a maximum field emission current of around 10 μA at 75 V. As with the UV case, this increase can also be attributed to surface desorption, primarily of water.
... Advances in electronic devices demand ever-increasing miniaturization, which in turn leads to ever-higher heat fluxes. By facilitating heat dissipation, materials with high thermal conductivity are crucial to ensuring operational reliability and efficiency. 1 Semiconductors such as gallium nitride, 2-4 silicon carbide, [5][6][7] and boron arsenide (BAs) [8][9][10][11][12] have higher thermal conductivity than silicon and have shown great potential as materials for high electron mobility transistors. In particular, BAs stand out for possessing the highest room temperature thermal conductivity (900-1,300 W/m-K [meter-Kelvin]), [9][10][11] an appropriate band gap (1.5-2.1 eV) [13][14][15] and an unusually high ambipolar mobility ($1,400 and $2,100 cm 2 /V-s [volt second] for electrons and holes, respectively), [16][17][18] making it the ideal semiconductor. ...
Boron arsenide, considered an ideal semiconductor, inevitably introduces arsenic defects during crystal growth. Here, we develop a unified neural network interatomic potential with quantum-mechanical precision that accurately describes phonon transport properties in both perfect and defective boron arsenides. Through molecular dynamics simulations, we quantitatively explore the degree of phonon localization in boron arsenide caused by arsenic vacancies. We confirm that this localization primarily affects vibration modes within the frequency range of 2.0–4.0 THz, which is a challenge for conventional first-principles approaches. In addition, we examine the fluctuation of the heat flux autocorrelation function, which reveals the extent of phonon phase disruption resulting from arsenic voids and lattice anharmonicity from a more fundamental perspective. Our study highlights the applicability of molecular dynamics simulations in conjunction with neural network interatomic potential for defective systems, laying the theoretical groundwork for phonon engineering in real semiconductor crystals.
... A planar nanoscale vacuum channel transistor (NVCT) with a dimension that can be compared with a modern-day field effect transistor was demonstrated recently [10]. In these structures, electron transport takes place using quantum tunneling [11], where drift-diffusion is the primary mode of electron transportation in traditional semiconductors [12]. Recent work also suggested that these devices can be operated at a voltage as low as 15 V [13]. ...
... Recent work also suggested that these devices can be operated at a voltage as low as 15 V [13]. Also, scattering or collision loss is negligible thanks to the short vacuum channel length, which is a few hundred nm [12]. These virtues make these VTs a perfect candidate for harsh environment electronics [9]. ...
Vacuum transistors (VTs) are promising candidates in electronics due to their fast response and ability to function in harsh environments. In this study, several oscillator and logic gate circuit simulations using VTs are demonstrated. Silicon-gated field emitter arrays (Si-GFEAs) with 1000 × 1000 arrays were used experimentally to create a VT model. First, transfer and output characteristics sweeps were measured, and based on those data, an LTspice vacuum transistor (VT) model was developed. Then, the model was used to develop Wein and Ring oscillator circuits. The circuits were analytically simulated using LTspice, where the collector bias voltage was 200 V DC, and the gate bias voltage was 30–40 V DC. The Wein oscillator circuit produced a frequency of 102 kHz with a magnitude of 26 Vpp. The Ring oscillator produced a frequency of 1.14 MHz with a magnitude of 4 Vpp. Furthermore, two logic circuits, NOR and NAND gates, were also demonstrated using LTspice modeling. These simulation results illustrate the feasibility of integrating VTs into functional integrated circuits and provide a design approach for future on-chip vacuum transistors applied in logic or radio-frequency (RF) devices.
... Old vacuum tube technology can point toward a direction to resolve these issues. 3,18 A vacuum is one of the ideal tunneling barriers, and it is almost free from defects. Due to the absence of trap sites and electron interference in the ideal vacuum, the vacuum device exhibits ballistic transport properties. ...
A nano vacuum tube which consists of a vacuum transistor and a nano vacuum chamber was demonstrated. For the device, a vacuum region is an electron transport channel, and a vacuum is a tunneling barrier. Tilted angle evaporation was studied for the formation of the nano level vacuum chamber structure. This vacuum tube was ultraminiaturized with several tens of 10–18 L scale volume and 10–6 Torr of pressure. The device structure made it possible to achieve a high integration density and to sustain the vacuum state in various real operations. In particular, the vacuum transistor performed stably in extreme external environments because the tunneling mechanism showed a wide range of working stability. The vacuum was sustained well by the sealing layer and provided a defect-free tunneling junction. In tests, the high vacuum level was maintained for more than 15 months with high reliability. The Al sealing layer and tube structure can effectively block exposed light such as visible light and UV, enabling the stable operation of the tunneling transistor. In addition, it is estimated that the structure blocks approximately 5 keV of X-ray. The device showed stable operating characteristics in a wide temperature range of 100–390 K. Therefore, the vacuum tube can be used in a wide range of applications involving integrated circuits while resolving the disadvantages of a large volume in old vacuum tubes. Additionally, it can be an important solution for next-generation devices in various fields such as aerospace, artificial intelligence, and THz applications.
... Through experimentation, we observed that optimizing the electrode structure not only reduced the turn-on voltage but also greatly increased the switching speed. We offer an explanation using field emission theory [23], [24], [25], [26], modified Paschen's law [27], [28], [29], [30], and the switching speed limitation theory [13]. Moreover, we investigated the impact of electrode structure design and reduced device gap on the working voltage of the device in submicrometer gaps. ...
Recent advances in micro-and nano-processes have resulted in substantial advancements in micro/nano plasma devices, resulting in superior properties such as picosecond switching speed, high output power beyond that of conventional electronic devices, and exceptional tolerance to high temperature radiation. Despite this progress, certain issues such as high working voltage, electrodes susceptible to damage, and limited reliability have hindered their further practical applications. In this article, we propose a novel approach based on the design of the device electrode structure with a submicrometer gap, aiming to reduce the working voltage by optimizing the device’s surface electric field. Compared to traditional techniques, such as gap reduction or gate structure addition, this approach offers advantages including lower production costs, better consistency, and the ability to achieve wafer-level fabrication. More importantly, the approach improves the device’s switching speed significantly. Experimental results show that this method has the potential to reduce the working voltage by 34 V and increase the switching speed by nearly double, up to a maximum of 3.19 V/ps. We elaborate on the optimization mechanism and demonstrate the potential of this approach, providing new ideas for further enhancing the performance and reliability of micro/nano plasma devices.
... Field emitters are now widely discussed as an electron source for nanovacuum channel transistors. [1][2][3][4][5] In field emitters, emission of electrons takes place by quantum mechanical tunneling from a micro-or nanometer scale tip by applying a positive potential on a gate electrode that surrounds the tip. [6][7][8][9] During the operation of these devices, high vacuum is required to reduce the gas-electron collision probability between the electrodes. ...
Effects of gases on field emission performance were measured using silicon-gated field emitter arrays. Gas was injected into a vacuum chamber with a 1000 × 1000 tip array, which was driven by a DC gate and collector voltages. The collector voltage was fixed at 200 V while the gate voltage was swept to 40 V. For the gas exposure study, N2, He, and Ar were used. The sets of partial pressures, 5 × 10−6, 5 × 10−5, and 5 × 10−4 Torr, were used for the experiment. It was observed that N2 had the least effect and Ar had the worst effect on emission current performance. The degradation of collector current at 5 × 10−4 Torr pressure for Ar was ≈65% where for the N2, at the same level of pressure, the degradation was ≈41%. However, further experiments with high purity Ar gas showed that it was the water vapor present in the gas itself that was the primary cause of reduction in emission current and not the gas itself. The results expressed in reduction in emission current versus Langmuir exposure versus the current clearly showed the effect of water vapor. After the vacuum was recovered, the work function again restored partially to its original value. After ultraviolet light cleaning, the emission current was restored completely to the original state.
... Remarkably, field emission physics remains highly important to solid-state devices in the post-vacuum tube era because of its critical role in the interfacial charge injection process across the metal/insulator and metal/semiconductor interfaces, 22 which are omnipresent in modern electronic and optoelectronic devices. Due to its technological importance in both vacuum 23 and solid-state device technology, the FN theory has been continually refined over the recent decades. [24][25][26][27][28][29][30][31][32][33][34] For quantum 2D materials, the validity of FN based models needs to be scrutinized since the foundational bases of such theories, particularly the assumption of a 3D quasi-free electron gas with parabolic dispersion, are fundamentally incompatible with the physical properties of 2D materials. ...
We present the theory of out-of-plane (or vertical) electron thermal-field emission from two-dimensional (2D) semimetals. We show that the current-voltage-temperature characteristic is well captured by a universal scaling relation applicable for broad classes of 2D semimetals, including graphene and its few-layer, nodal point semimetal, Dirac semimetal at the verge of topological phase transition, and nodal line semimetal. Here, an important consequence of the universal emission behavior is revealed: In contrast to the common expectation that band topology shall manifest differently in the physical observables, band topologies in two spatial dimension are indistinguishable from each other and bear no special signature in electron emission characteristics. Our findings represent the quantum extension of the universal semiclassi-cal thermionic emission scaling law in 2D materials and provide theoretical foundations for the understanding of electron emission from cathode and charge interface transport for the design of 2D-material-based vacuum nanoelectronics.
... 4 A recent approach that showed the combination of nanoscale vacuum channel with recent semiconductor processing proposed a novel vacuum nano-channel transistor with high frequency, fast switching time, and reliable performance. [4][5][6] More importantly, the vacuum transistor (VT) has proven to be high temperature (400°C) 7 and ionizing radiation 4,8,9 compatible. Han et al. 10 demonstrated a planar nanoscale vacuum channel transistor (NVCT) with a comparable structure to the traditional field effect transistor (FET), in which the electrons transport by quantum tunneling 11 instead of the semiconductor drift-diffusion method. ...
... Han et al. 10 demonstrated a planar nanoscale vacuum channel transistor (NVCT) with a comparable structure to the traditional field effect transistor (FET), in which the electrons transport by quantum tunneling 11 instead of the semiconductor drift-diffusion method. 6 Ding et al. 12 also demonstrated an NVCT working at less than 15 V showing its intrinsic advantages over conventional vacuum tubes in terms of power consumption and response time. Moreover, collisions or scattering during the electron transport is minimal due to the short vacuum channels (few hundreds of nm long 6 ). ...
... 6 Ding et al. 12 also demonstrated an NVCT working at less than 15 V showing its intrinsic advantages over conventional vacuum tubes in terms of power consumption and response time. Moreover, collisions or scattering during the electron transport is minimal due to the short vacuum channels (few hundreds of nm long 6 ). In addition, optimization of electrode materials such as 2D materials like graphene, 13 or metals, 14 could enable VTs for on-chip integration. ...
Silicon gated field emitter arrays have been used as a vacuum transistor to demonstrate a 152 kHz Colpitts oscillator. The transfer and output characteristics of the 1000 × 1000 silicon arrays were measured using a collector placed ≈ 1 mm away with a gate voltage up to 40 V and a collector voltage up to 200 V. The data were used to establish an LTspice transistor model based on a field emission tip model and a collector current model that fit the characteristics. Then, the LTspice model was used to design a low frequency Colpitts oscillator. Furthermore, experiments were carried out to successfully demonstrate the oscillation. Oscillation frequency was 152 kHz with a peak to peak voltage of 25 V for a tip to ground series resistance value of 10 kΩ at 50 V on the gate and 210 V on the collector. Further, the oscillator was also tested at 50, 100, 200, 300, and 400 °C. It was observed that frequency shifts for each temperature which is due to the change in the overall capacitance of the test setup. This type of device could be used as a temperature sensor in harsh environments.
