Barrier Metal Research Articles

Demonstration of aluminum nitride metal oxide semiconductor field effect transistor on sapphire substrate

Abstract Aluminum nitride (AlN) is a promising ultrawide bandgap material with significant advantages for power electronics and optoelectronic applications due to its high breakdown voltage, mobility, and thermal conductivity. AlN Schottky barrier diodes and metal semiconductor field effect transistors have shown potential but are limited by issues such as high off-state leakage current and complex structures to achieve ohmic contacts. To address these challenges, we report on the fabrication and characterization of an AlN metal oxide semiconductor field effect transistor (MOSFET) with a recessed gate structure. The source and drain contacts were fabricated on n-doped AlN epitaxy using Ti-based contacts with a Ti/Al/Ti/Au metal stack. To evaluate the performance of these contacts, a circular transmission line model was employed, and contacts were annealed at various temperatures ranging from 750 °C to 950 °C in a nitrogen ambient. Our results reveal that unannealed Ti-based contacts on AlN showed no current conduction. However, annealing these contacts at 950 °C for 30 s significantly reduced the specific contact resistance to 0.148 Ω·cm2, achieving an ∼80% reduction compared to samples annealed at 750 °C. Utilizing these optimized contact conditions, we fabricated, to the best of our knowledge, the first AlN MOSFET. The fabricated AlN MOSFET exhibits a threshold voltage of −10.91 V, an effective mobility of 2.95 cm2 V−1 s−1, an on–off current ratio spanning two orders of magnitude, and a reverse breakdown voltage of approximately ∼250 V in air without a field plate.

Multifunctional Water Additive Enabling Stable Cycling of Chloride‐Free Magnesium Metal Batteries Based on Carbonate Electrolyte

AbstractRechargeable magnesium batteries (RMBs) face with the challenge of interphase passivation between electrolytes and Mg anodes. Compared with ether electrolytes, carbonate solvents possess the superior electrochemical stability at cathode side, but their incompatibility with Mg metal, high viscosity, and desolvation energy barrier restrict their practical utilization in RMBs. Herein, the “unwanted‐impurity” water with high concentration is revisited and employed as multifunctional additive in carbonate electrolyte to improve the reversibility of RMBs. Water additive enables the localized deep eutectic effect, reduces the viscosity of carbonate electrolyte, and improves the Mg ion conductivity. The water molecules also participate the solvation sheath of Mg ions, resulting in the reduction of Mg deposition overpotential and inhibition of parasitic reaction. Furthermore, the co‐intercalated water molecules in V2O5 cathode layers enable the stabilization of intercalation structure and supply of additional magnesiophilic sites. Cooperated with the binder‐decorated Mg powder anode, the propylene carbonate electrolyte with water additive endows Mg||Mg symmetric cells and Mg||V2O5 full cells with satisfactory cycling performance and high‐voltage stability. This work revisits the impact of impurity water and provides a practical strategy for the utilization of conventional low‐cost carbonate electrolyte family, broadening the design and formulation of electrolytes for chlorine‐free and high‐voltage RMBs.

Combating Pathogens Using Carbon-Fiber Ionizers (CFIs) for Air Purification: A Narrative Review

Airborne pathogens, though a minor fraction of airborne particles, can cause infections, intoxications, or allergic reactions through respiration, dermal contact, or ingestion. The SARS-CoV-2 pandemic has underscored the significance of mitigating airborne microbial threats. Traditional air ionization methods, such as dielectric barrier discharge and metal tip corona discharge, produce ozone, a reactive and potentially harmful byproduct. However, carbon-fiber ionizers (CFIs) generate high concentrations of ions with minimal ozone production, making them a safer alternative. Operating at voltages below 5 kV, CFIs are more efficient than their metallic counterparts. This review focuses on the antimicrobial efficacy of CFIs, which produce unipolar ions that can disrupt microbial membranes, leading to cell death. Compared to ultraviolet light sterilization, CFIs are cost-effective and suitable for small spaces. The literature review highlights the need for comprehensive studies to evaluate the real-world application and effectiveness of CFIs. Many existing studies are limited by small-scale testing and insufficient data reporting, complicating comparative analyses. Our work aims to provide a detailed perspective on CFIs, examining their impact on various microorganisms, ion efficacy, ionization outcomes, and ozone generation levels. By addressing these aspects, the review seeks to offer an updated understanding of CFIs’ antimicrobial capabilities and to identify limitations in current research, paving the way for more informed and effective air purification strategies.

Efficient Copper Extraction from Industrial Dilute Solutions Using Air-Assisted Solvent Extraction

ABSTRACT The growing demand for valuable metals in recent decades has heightened the economic significance of extracting them from dilute solutions. This research carefully assesses the extraction efficiency of the air-assisted solvent extraction (AASX) process for effectively recovering copper from industrial dilute solutions, such as the raffinate of the solvent extraction (SX) plant and heap leach solutions. The results clearly showed that increasing the frother dosage to 50 mg/L improved the Cu extraction from 83.5% to 90.2%, but increasing the frother dosage beyond 50 mg/L did not change this response significantly. Although varying the extractant concentration and silicone oil dosage in the studied range did not affect Cu extraction, it noticeably led to an increase in the barrier metals recovery. Furthermore, a nine-step AASX system was applied to comprehensively evaluate the extraction efficiency of Cu from dilute heap leach solution. Moreover, an impressive 95.1% of Cu recovery (from a solution containing 890 mg/L Cu, 12.32 g/L Fe, 2.64 g/L Zn, and 4.1 g/L Mn) was achieved with selectivity ratios of 149.6, 153.0, and 93.5, for Cu/Fe, Cu/Zn, Cu/Mn, respectively. It could be concluded that the AASX process is an efficient and promising method for extracting Cu from industrial dilute solutions derived from secondary resources, low-grade ores, and acid mine drainages.

High-Quality 4H-SiC Homogeneous Epitaxy via Homemade Horizontal Hot-Wall Reactor

In this paper, using a self-developed silicon carbide epitaxial reactor, we obtained high-quality 6-inch epitaxial wafers with doping concentration uniformity less than 2%, thickness uniformity less than 1% and roughness less than 0.2 nm on domestic substrates, which meets the application requirements of high-quality Schottky Barrier Diode (SBD) and Metal–Oxide–Semiconductor Field-Effect Transistor (MOSFET) devices. We found that increasing the carrier gas flow rate can minimize source gas depletion and optimize the doping uniformity of the 6-inch epitaxial wafer from over 5% to less than 2%. Moreover, reducing the C/Si ratio significantly can suppress the “two-dimensional nucleation growth mode” and improve the wafer surface roughness Ra from 1.82 nm to 0.16 nm.

Analytical modeling of threshold voltage and on-resistance in multi-barrier E-mode MISHEMT with gate-recess and field-plates

This work presents an analytical model for threshold voltage and On-resistance of multi barrier Metal–Insulator–Semiconductor High-Electron-Mobility-Transistor (MISHEMT) with gate-recess and field-plates. The device featuring a high two-dimensional electron-gas (2DEG) density in the channel region. The primary objectives of this device are to achieve a high threshold voltage (Vth) and enhance electron mobility with specific low ON-resistance (Ron_sp) by mitigating the degradation effects arising from scattering and interface-charges. Also, a physics based analytical model for Vth and 2DEG charge density at upper and lower channels is presented. This model is validated by comparing with TCAD numerical simulations and are well matched. The proposed MISHEMT demonstrates improved electron mobility in the lower channel of 1260 cm2/V.s, Vth of ∼2.6 V and Ron_sp is minimized by 33 % in contrast with a conventional MISHEMT. Additionally, the proposed MISHEMT becomes a promising device for achieving both high threshold voltage and mobility which are required for power semiconductor devices.

Utilizing H2S to sulfurize transition metal and oxide barriers for suppressing resistivity scaling of ruthenium metallization

Ruthenium is of great potential for use as next-generation interconnect metallization but still suffers from resistivity scaling at nanoscale linewidths due to the severe interface scattering of electrons. In this study, a thin sulfurized layer was hence formed on titanium-tantalum and titanium-tantalum oxide barriers by utilizing hydrogen sulfide gas for interface modification. The microstructure, chemical composition, bonding configuration and interfacial adhesion of the sulfurized barriers and ruthenium films were investigated, and the resistivity scaling of the ruthenium films on the barriers was evaluated. Experimental results indicate that an amorphous sulfide layer of only several nanometers thick was uniformly formed on the top surface of the barriers and changed the resistivity and binding state of the metal and oxide barriers. Attributed to the formation of the sulfide layer, the specular scattering of electrons at the ruthenium/barrier interface was enhanced, effectively suppressing the resistivity scaling of the ruthenium films, and the interfacial adhesion strength was also markedly improved.

Dual operation modes of the Ge Schottky barrier metal–oxide–semiconductor field-effect transistor

A germanium p-channel Schottky barrier metal–oxide–semiconductor field-effect transistor (SB-MOSFET) with germanium–platinum Schottky contacts is demonstrated experimentally. The fabrication process has a low thermal budget of 450° C and requires neither intentional doping nor ion implantation. At a temperature of 4 K, the p-channel SB-MOSFET turns on at a gate voltage of −1.6 V and shows a peak mobility of 500 cm2/V s at a carrier density of 3 × 1012 cm–2. Under high drain–source bias voltages, the device operates in an unconventional mode where the current is limited by the source contact. Injection of carriers from the source contact to the germanium channel is controlled by the gate bias, which modulates the Schottky barrier capacitively. The transconductance in this mode deviates from and is significantly higher than the value expected for a conventional MOSFET with the same geometry, mobility, and capacitance. Based on four-point current–voltage measurements, we present a theoretical band diagram of the device and give a physical picture for the observed high currents and transconductances.

양자점 디스플레이 분야에서의 원자층증착법 응용

Atomic layer deposition (ALD) is gaining traction in the semiconductor industry due to its ability to meet the demands of high aspect ratios and densities. This is attributed to its excellent step coverage and uniformity, which are based on the self-limiting deposition process. Its applications have expanded to include various components such as memory device capacitors, gate oxides, metal barriers, and charge transport channels. Moreover, ALD is being explored for diverse purposes not only within the semiconductor field but also in displays and optoelectronics. This review aims to explore the versatility of ALD deposition methods, widely utilized in the semiconductor industry, and their potential applications in the display and optoelectronics sectors. Additionally, we present future prospects for ALD applications in display based on current approaches.

Comparative Cryogenic Investigation of FD-SOI Devices with Doped Epitaxial and Metallic Source/Drain

Defects induced by the source/drain process have a significant impact on the scattering mechanism of PMOS at cryogenic temperatures. Here, the cryogenic characteristics of FD-SOI devices with heavily doped epitaxial source/drain (Epi FD-SOI devices) and metallic Schottky barrier source/drain (SB FD-SOI devices) were investigated from 300 K down to 6 K. The doping profile along the channel was analyzed by TCAD simulation analysis. Experimental comparison of transistor performance at cryogenic temperatures was carried out for these devices with gate lengths (L G ) of 100 nm and 40 nm. The I-V characteristics of the FD-SOI devices were measured with a liquid helium cooling environment. The cryogenic effect of the two types of devices on Key parameters including transconductance (G m ), field effect mobility (μ FE ), threshold voltage (V th ) and subthreshold slope (SS) were systematically analyzed. The doping distribution of the heavily doped epitaxial SiGe source/drain structure were subjected to more Coulomb scattering at cryogenic temperatures, whereas the doping distribution of the Schottky-barrier source/drain structure dictates that the device is mainly subjected to phonon scattering at cryogenic temperatures.

Low turn-on voltage and 2.3 kV β -Ga2O3 heterojunction barrier Schottky diodes with Mo anode

In this work, we propose combining a low work function anode metal and junction barrier Schottky structure to simultaneously achieve low turn-on voltage (Von) and high breakdown voltage (BV), which alleviates the dilemma that high BV requires high Schottky barrier height (SBH) and high Von. Molybdenum (Mo) is used to serve as the anode metal to reduce the SBH and facilitate fast turn-on to achieve a low Von. To resolve the low SBH related low BV issue, a p-NiO/n-Ga2O3-based heterojunction structure is used to enhance β-Ga2O3 sidewall depletion during the reverse state to improve the BV. With such a design, a low Von = 0.64 V(@1A/cm2) and a high BV = 2.34 kV as well as a specific on-resistance (Ron,sp) of 5.3 mΩ cm2 are demonstrated on a 10 μm-drift layer with a doping concentration of 1.5 × 1016 cm−3. β-Ga2O3 JBS diodes with low Von = 0.64 V and a power figure of merit of 1.03 GW/cm2 show great potential for future high-voltage and high-efficiency power electronics.

Influences of faulty AC underground power cables on the neighbouring metallic gas pipelines

In this paper the impacts of faulty underground power cables on their neighboring metallic buried pipelines have been investigated, specifically in the event of line to ground faults of these cables, as well as the use of barrier mediums to reduce this effect. In this paper, the conduction current generated in metal pipeline as a result of faults in underground cables is studied.To reduce the induction voltages affecting the metallic pipelines, it is proposed to use a barrier between the cable and the metallic gas pipes. The effects of the type of barrier material, its thickness, and its distance from the cable on both the induction voltages and currents generated in the metal pipes are investigated. It is found that the use of XLPE barrier with thickness of 5 mm at 600 mm space from the pipeline reduces the induced voltage to be 40.02 % - 40.6 % of its value when concrete barrier is employed and 98.6 % - 98.5 % with the use of copper barrier respectively. Similar results proved that the increase of the barrier thickness is effective in reducing the induction voltage. The metal barrier has proven to be the best in reducing the effect of the induction voltage resulting from the line to ground faulty underground power cable on the neighboring metal pipes.

Metallic barrier layer for Ag2S1−xSex inorganic ductile thermoelectric materials

Metallic barrier layer is a key component in thermoelectric (TE) devices, but it is rarely investigated for the recently discovered inorganic ductile TE materials. In this work, we demonstrate that tungsten (W) is the excellent metallic barrier layer for Ag2S1−xSex ductile thermoelectric materials. The phase composition, microstructure, adhesive strength, and interfacial contact resistivity (ρC) of the W/Ag2S1−xSex joint have been systematically investigated. The sputtered W film has high adhesive strength and little interdiffusion/reaction with Ag2S1−xSex. The ρC decreases with increasing the Se content, which can be understood by the Thermionic-field Emission model. This work would guide the development of high-performance flexible TE devices based on ductile TE materials.

Experimental Observation of Surface Wave States at the Gold–Silver Interface

We demonstrate that a gradual interface between gold and silver supports the propagation of a novel kind of surface electromagnetic wave, which is different from the more well-known surface plasmon polaritons. The existence of such surface waves leads to a paradoxical situation in which a continuous metal barrier which does not have any pinholes may exhibit considerably increased light transmission if the barrier is made of two different metals. A spectroscopic study of this effect is reported.

Improvement of Ga2O3 vertical Schottky barrier diode by constructing NiO/Ga2O3 heterojunction

The high critical electric field strength of Ga2O3 enables higher operating voltages and reduced switching losses in power electronic devices. Suitable Schottky metals and epitaxial films are essential for further enhancing device performance. In this work, the fabrication of vertical Ga2O3 barrier diodes with three different barrier metals was carried out on an n–-Ga2O3 homogeneous epitaxial film deposited on an n+-β-Ga2O3 substrate by metal−organic chemical vapor deposition, excluding the use of edge terminals. The ideal factor, barrier height, specific on-resistance, and breakdown voltage characteristics of all devices were investigated at room temperature. In addition, the vertical Ga2O3 barrier diodes achieve a higher breakdown voltage and exhibit a reverse leakage as low as 4.82 ×10−8 A/cm2 by constructing a NiO/Ga2O3 heterojunction. Therefore, Ga2O3 power detailed investigations into Schottky barrier metal and NiO/Ga2O3 heterojunction of Ga2O3 homogeneous epitaxial films are of great research potential in high-efficiency, high-power, and high-reliability applications.

Ultrasonic Through-Metal Communication Based on Deep-Learning-Assisted Echo Cancellation.

Ultrasound is extremely efficient for wireless signal transmission through metal barriers due to no limit of the Faraday shielding effect. Echoing in the ultrasonic channel is one of the most challenging obstacles to performing high-quality communication, which is generally coped with by using a channel equalizer or pre-distorting filter. In this study, a deep learning algorithm called a dual-path recurrent neural network (DPRNN) was investigated for echo cancellation in an ultrasonic through-metal communication system. The actual system was constructed based on the combination of software and hardware, consisting of a pair of ultrasonic transducers, an FPGA module, some lab-made circuits, etc. The approach of DPRNN echo cancellation was applied to signals with a different signal-to-noise ratio (SNR) at a 2 Mbps transmission rate, achieving higher than 20 dB SNR improvement for all situations. Furthermore, this approach was successfully used for image transmission through a 50 mm thick aluminum plate, exhibiting a 24.8 dB peak-signal-to-noise ratio (PSNR) and a about 95% structural similarity index measure (SSIM). Additionally, compared with three other echo cancellation methods-LMS, RLS and PNLMS-DPRNN has demonstrated higher efficiency. All those results firmly validate that the DPRNN algorithm is a powerful tool to conduct echo cancellation and enhance the performance of ultrasonic through-metal transmission.

F‐Doped Calcium Silicate Enabling Fast Ion Deposition Kinetics for Highly Reversible Zinc Metal Batteries

AbstractAqueous zinc ion batteries (AZIBs) are subject to various unwanted side reactions, including dendrite growth, hydrogen evolution, and corrosion passivation, due to the highly active Zn anode. While constructing an artificial interface layer (AIL) can address these problems, the compromise in Zn deposition kinetics is considerable. Herein, F‐doped modified hydrated calcium silicate (F‐CSH) nanosheets are designed to enhance Zn2+ ion deposition kinetics. Combined with theoretical calculations, it is verified that the F‐doped contributes to higher interface adsorption energy with Zn metal and lower ion diffusion barrier, favoring faster charge transfer compared to non‐F‐doped counterparts. Additionally, the strong interaction between zincophilic F and Zn facilitates rapid desolvation of Zn2+ and promotes the deposition between the Zn metal and F‐CSH interphases. As a result, the F‐CSH layer maintains the stability on the Zn surface, enabling fast and reversible Zn deposition. The F‐CSH@Zn anode exhibits a long lifespan of over 2800 h at 5 mA cm−2, while running more than 2500 cycles at a ≈100% Coulombic efficiency. This work highlights the importance of constructing AIL with strong interaction with Zn2+/Zn in improving the interphase kinetics of zinc anode for realizing the stability of AZIBs.

(Invited) Ru Selective Metal Deposition for Hybrid Metallization in Nano-Interconnect Applications

The connection of semiconductor devices happens through metal interconnects at the back end of line (BeOL) in integrated circuits. The BeOL consists of multiple metal levels that are vertically connected through small contact holes, or so-called vias. Especially at the lower metal levels, the vias are becoming much smaller in critical dimension, which increases their resistance significantly while more of these vias are needed to make the more complex connections in future device architectures. For these reasons, the vias resistance is becoming the dominating part of the total resistance of the stack and may become the limiting factor in keeping resistance-capacitance delay under control.In this work, the metal-on-metal area selective metal deposition is studied to make low resistive vias. The via is first prefilled with the Ru before performing the Cu metallization of the remainder of the vias and wires. Ru is chosen as the preferred metal [1] because it can be used without a metal barrier (it does not electromigrate) and this provides a large resistance benefit as compared to the Cu metallization which needs a TaN barrier combined with a Co liner. The combination of the different metals for the via (here Ru) and the metallization of wires (here Cu), is called a hybrid metallization scheme.We will discuss the challenges for the Ru selective deposition on the metal (growth area) towards different dielectrics as the non-growth area. The selectivity studies to optimize the Ru chemical vapour deposition (CVD) recipe and surface treatments are performed on blanket level (non-patterned wafers). A small molecule inhibitor dimethylamino-trimethylsilane (DMA-TMS) is used to passivate the dielectric surface which makes the dielectrics less reactive towards the Ru deposition improving thereby the selectivity of the CVD process (see also Fig.a).[2] We demonstrate that the growth rate and selectivity of Ru ASD depend on the CVD process conditions (type of co-reactant and process temperature) and the type of nanopattern (line spaces or via holes).[3]The most selective Ru process found with the line-space pattern (45/45nm line-space width) was also tested in nanoscale patterns with via holes of ~10.5nm.[4] It was found that the Ru growth rates in the patterned structures are enhanced as compared to the blanket substrates. The CVD Ru growth rates are ~ 1.3x higher in line-space nanopatterns as compared to flat metal substrates, and up to 3x higher in the small contact holes.[4] The growth enhancement of the CVD process is beneficial for the technological implementation of the process. The results show that the growth rate and the selectivity are different from the behavior on blankets and are also pattern dependent, which is consistent with a growth mechanism that is based on diffusion in addition to adsorption.[2] Therefore, the metal-on-metal selective deposition process may need to be optimized and adjusted to the patterned structure used in the interconnect application.[1] D. Gall et al, J. Appl. Phys. 2016, 119, p.085101.[2] F. Grillo and J. Soethoudt et al, Chem. Mater. 2020, 32, 22, 9560–9572.[3] A. Kumar Mandal et al, “Ruthenium Area-Selective Deposition for Nano-interconnect Structures: Process and nanopattern dependent selectivity and growth rate” Manuscript in submission 2023.[4] M.H. van der Veen et al, Proc. of the IITC 2021, S7-2.. Figure 1

Microstructural Stability of a Metallic Thermal Barrier Coatings for Rocket Engine

Metallic thermal barrier coatings (TBCs) consisting of a bond coating and a top coating have been extensively utilized for protecting the walls of rocket combustion chambers. However, standard coating systems often encounter failures due to the significant differences in coating composition and thermal expansion coefficient compared to the substrate under high heat flux conditions. To protect liquid rocket combustion chamber walls, a novel metallic multilayer TBC system applied with atmospheric plasma spraying is developed in the present work. It attempted to deposit dense Ni-based alloy and Cu-based bonding coatings with low oxide contents achieved by introducing boron as a deoxidizer element through atmospheric plasma spraying. The structural stability of the TBC was assessed through high temperature thermal exposure experiments, while the thermal cycle life is evaluated using laser thermal shock. Results show that the NiCrCu2B and CuNi2B bonding coatings prepared through in situ deoxygenation effect of boron exhibit dense structures, low oxide content, and excellent bonding quality. The high temperature thermal exposure experiment reveals that the multilayer structural TBC can withstand 850 °C for 10 hours without the formation of Kirkendal effect pores. Moreover, the thermal cycling life results indicate that the multilayer structural TBC designed in this study, employing a composition gradient transition and the in situ deoxygenation effect of boron, possesses a significantly improved thermal cycle lifetime compared to traditional structural TBCs.

Traces of the action of ball lightning as material for studying its structure

According to observations, at the site of the ball lightning disappearance there are no traces left except a cloud of vapor. This reduces the number of materials for its formation in nature to air and water molecules. It is shown that, using these materials, it is possible to create a model of ball lightning with an energy reserve with a density up to 1010 J/m3. Ball lightning has an electrical charge and mass. It is capable of heating water, tearing off bark from trees, jumping on the ground, cutting discs in glass, and melting holes in metal barriers. An explanation for this behavior of ball lightning is given.