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Bump-shaped vertically aligned multi-walled carbon nanotubes (MWNTs) were bonded to a Au substrate by a surface activated bonding method using Ar fast atom bombardment (FAB). After carrying out Ar-FAB for 1200 s at a bonding load of 0.74 MPa, the interconnect resistance reduced to 1/1000 of the original resistance. The lowest resistance of 5.2 Ω was achieved for the bonded specimens. Torn graphite layers were observed in the MWNT that was processed by Ar-FAB for 2400 s, and the ratio of the G -band to the D -band in the Raman spectra indicated that the peaks attributable to the defects in the carbon nanotubes increased in response to the Ar-FAB process. These findings indicate that the torn graphite layers were exposed and were in contact with the Au layer, which caused the conductivity path between MWNTs and Au substrates to increase. [ABSTRACT FROM AUTHOR]

• A novel strategy of room-temperature bonding followed by high-temperature annealing to fabricate a GaN-on-diamond device with a high TBC has been proposed. • Annealing results in crystallization of amorphous Si layers and elimination of multi-interfaces, thus improving interfacial TBC • The process induces stress<30 MPa after bonding and<230 MPa after annealing, exhibiting a remarkable advantage in stress control. [Display omitted] To achieve high device performance and high reliability for the gallium nitride (GaN)-based high electron mobility transistors (HEMTs), efficient heat dissipation is important but remains challenging. Enormous efforts have been made to transfer a GaN device layer onto a diamond substrate with a high thermal conductivity by bonding. In this work, two GaN-diamond bonded composites are prepared via modified surface activated bonding (SAB) at room temperature with silicon interlayers of different thicknesses (15 nm and 22 nm). Before and after post annealing process at 800 °C, thermal boundary conductance (TBC) across the bonded interface including the interlayer and the stress of GaN layer are investigated by time-domain thermoreflectance and Raman spectroscopy, respectively. In the case of as-bonded samples, TBC of the 15 nm Si interlayer (32.4 MW/m2-K) was higher than that of the 22 nm (28.0 MW/m2-K); but after annealing, TBC of the 15 nm Si interlayer (71.3 MW/m2-K) became lower than that of the 22 nm (85.9 MW/m2-K), because the annealing is especially effective for thicker interlayer to improved interfacial TBC. The obtained stress was less than 230 MPa for both before and after the annealing, and this high thermal stability indicates that the room-temperature bonding can realize a GaN-on-diamond template suitable for further epitaxial growth or device process. [ABSTRACT FROM AUTHOR]

Abstract: Direct wafer bonding of Si–Si and Si–SiN wafers was demonstrated using a nanoadhesion layer at room temperature. The two mating surfaces were cleaned by an Ar-ion beam and simultaneously deposited with ultrathin Fe layers (known as nanoadhesion layers). The ultrathin Fe layers imparted high bond strengths to Si–Si and Si–SiN bonds without heat treatment. Transmission electron microscopy revealed that the Si–Si and Si–SiN interfaces were tightly bonded and defect free. Moreover, the formation of crystalline iron silicide across the interface was found to enhance Si–Si wafer bonding. In addition to FeSi, an amorphous layer formed at the Si–SiN interface, resulting in a high bond strength at room temperature. [Copyright &y& Elsevier]

Abstract: Fine carbon tubes “fullerene shell tubes (FSTs)” have been found among the C60 nanowhiskers heat-treated under vacuum at a temperature higher than 600°C. FSTs with open ends have been found as well as FSTs with closed spherical ends. It has been also found that the FSTs can be easily prepared by the heat treatment of the C60 whiskers prepared by using C60 powders containing (η 2-C60)Pt(PPh3)2. Since the high temperature-treated fullerene (nano)whiskers exhibit a high specific surface area and a good electrical conductivity, they are expected to be utilized as new electrode materials for fuel cells. [Copyright &y& Elsevier]

Abstract: Electrostatically-driven Ni curl-up microcantilever probes, which can be applied to new MEMS probe cards with contact-switching function, have been developed. MEMS probe cards are requisite to higher pad-density and smaller pad-pitch chips, and are effective in high frequency testing. If a probe card consists of an array of actuator-integrated microprobes, it could be applied to next-generation testing, for instance, a new wafer-level test/burn-in. This can be achieved as the microprobes can be used for the direct switching of the contact to reduce the number of the I/O lines of the probe card. We have designed arrays of Ni curl-up microcantilevers with a rolling-contact touch-mode electrostatic actuator and developed a micromachining process which includes the electroplating deposition of two layers having different internal stress and etching of the Al sacrifice layer. The fabricated cantilevers with a thickness of 1.0μm and a width of 50μm have successfully been driven at a pull-in voltage of approximately 100V. From the disconnection force of the fritting contact between a Ni probe and an Al film, it is estimated that the fritting contact could be disconnected by applying voltages less than 100V. [Copyright &y& Elsevier]

Abstract: A novel approach using a PZT/HfO2 multi-layered dielectric for capacitive type MEMS switches was investigated. Compared to Si3N4, PZT/HfO2 demonstrated a high equivalent dielectric constant of 79–82 and a low leakage current density of 1.58×10−6 A/cm2 after a bias stressing time of 104 s, that result in high switching isolation and very low power consumption. In addition, a finite element analysis was used to estimate actuation voltage, insertion loss and isolation performance of one-bridge and π-match switches. After manufacturing, the experimental results of the π-match switch showed an acceptable insertion loss of less than −0.5dB in a frequency band of 50MHz–20GHz and significantly high isolation of −30 to −65dB in a broad frequency band of 50MHz–57GHz. [Copyright &y& Elsevier]

Direct bonding of GaN and Si substrates at 125 °C under atmospheric conditions was investigated by different Plasma activation bonding (PAB) methods. The substrates activated by a sequential oxygen and nitrogen plasma were strongly bonded so that the fracture within GaN bulk occurred during strength measurement. A ∼3-nm-thick amorphous layer consisting of GaOx and SiOx was confirmed at the bonding interface. This plasma-assisted low-temperature direct bonding may shed light on the advanced electronic devices using the GaN-Si heterostructure. Image 1 • Direct bonding of GaN-Si surfaces was strongly formed at 125 °C by plasma activation. • Bonded sample was fractured in GaN instead of interface during strength measurement. • Oxynitride film formed by plasma supposedly promoted the interfacial adhesion. • GaN and Si were bonded with a 3-nm-thick amorphous layer consisting of Si, Ga and O. [ABSTRACT FROM AUTHOR]

• Silk fibroin coated MgZnCa alloy structure without conversion layer was achieved via a two-step plasma activation. • The two-step activation contributed to the significantly increased adhesion force compared to other coating strategies. • The corrosion resistance of coated sample by two-step activation was significantly improved, retarding pitting corrosion. Based on a two-step plasma surface activation process (O 2 followed by N 2 plasma), silk fibroin coating was prepared on Mg-Zn-Ca alloy without conversion layer to retard the corrosion. This method achieved homogenized surfaces with better hydrophilicity and increased functional groups, significantly improving the adhesion force. The corrosion resistance of coated magnesium alloy was significantly enhanced compared to that of bare samples. Nanoscratch combined with corrosion behavior indicated that the remarkably improvement of anticorrosion ability attributed to the protective layer and the increased adhesion force. Our findings provided more possibilities for corrosion protection of degradable metals. [ABSTRACT FROM AUTHOR]

Lithium niobate (LiNbO 3 ) is emerging as an appealing candidate for integrated optical applications with enhanced complexity, owing to its inherent abundant optoelectronic properties. To compensate for the inability of LiNbO 3 to generate indistinguishable single photons, the evanescent coupling heterointerface constructed between III-V compound semiconductors (e.g., InP) and LiNbO 3 through plasma activation provides a feasible solution for balancing the integration efficiency and interfacial stability while achieving sub-50 nm alignment accuracy between devices, thus offering ultracompact on-chip light sources for classical optoelectronics and quantum optics. However, a challenge remains in the formation of the InP/LiNbO 3 platform due to the huge mismatch in the coefficient of thermal expansion. Here, we demonstrate the InP/LiNbO 3 covalent heterointerface using an asymmetric plasma activation strategy. Different plasmas are used for the activation of InP and LiNbO 3 specifically, balancing the enhancement of surface functional group density with the avoidance of defect generation effectively. More importantly, combined with surface comprehensive characterizations and interface performance, we determine that the introduction of ammonia solution enables the surface hydroxyl groups to be "effective" as LiNbO 3 surface relaxation increases the chance of -OH groups' contact. Therefore, a robust covalent bond network is established across the InP/LiNbO 3 interface at 80 °C with an enhanced bonding strength of 9.7 MPa. Moreover, a hybrid quantum photonic chip based on the InP/LiNbO 3 platform is designed to compute the coupling efficiency and the impact of misalignment on it, demonstrating the potential of extending the platform to hybrid integrated quantum systems.

Room temperature wafer bonding is a desirable approach for the packaging and assembly of diverse electronic devices. The formation of [Formula: see text] layer at the bonding interface is crucial for a reliable wafer bonding as represented by conventional bonding techniques such as hydrophilic bonding and glass frit bonding. This paper reports a novel concept of room temperature wafer bonding based on the conversion of polysilazane to [Formula: see text] at the bonding interface. As polysilazane is converted to [Formula: see text] by hydrolysis, in this work, adsorbed water is introduced to the bonding interface by plasma treatment, thereby facilitating the formation of [Formula: see text] at the wafer bonding interface. The experimental results indicate that the adsorbed water from the plasma treatment diffuses into the polysilazane layer and facilitates its hydrolysis and conversion. The proposed method demonstrates the successful wafer bonding at room temperature with high bond strength without interfacial voids. This technique will provide a new approach of bonding wafers at room temperature for electronics packaging., (© 2024. The Author(s).)

Cu-Cu direct interconnects are highly desirable for the microelectronic industry as they allow for significant reductions in the size and spacing of microcontacts. The main challenge associated with using Cu is its tendency to rapidly oxidize in air. This research paper describes a method of Cu passivation using a self-assembled monolayer (SAM) to protect the surface against oxidation. However, this approach faces two main challenges: the degradation of the SAM at room temperature in the ambient atmosphere and the monolayer desorption technique prior to Cu-Cu bonding. In this paper, the systematic investigation of these challenges and their possible solutions are presented. The methods used in this study include thermocompression (TC) bonding, X-ray photoelectron spectroscopy (XPS), shear strength testing, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The results indicate nearly no Cu oxidation (4 at.%) for samples with SAM passivation in contrast to the bare Cu surface (27 at.%) after the storage at -18 °C in a conventional freezer for three weeks. Significant improvement was observed in the TC bonding with SAM after storage. The mean shear strength of the passivated samples reached 65.5 MPa without storage. The average shear strength values before and after the storage tests were 43% greater for samples with SAM than for the bare Cu surface. In conclusion, this study shows that Cu-Cu bonding technology can be improved by using SAM as an oxidation inhibitor, leading to a higher interconnect quality.

The wafer-scale single-crystal GaN film was transferred from a commercial bulk GaN wafer onto a Si (100) substrate by combining ion-cut and surface-activated bonding. Well-defined, uniformly thick, and large-scale wafer size ReS 2 multilayers were grown on the GaN substrate. Finally, ReS 2 photodetectors were fabricated on GaN and sapphire substrates, respectively, and their performances were compared. Due to the polarization effect of GaN, the ReS 2 /GaN photodetector showed better performance. The ReS 2 /GaN photodetector has a responsivity of 40.12 A/W, while ReS 2 /sapphire has a responsivity of 0.17 A/W. In addition, the ReS 2 /GaN photodetector properties have reached an excellent reasonable level, including a photoconductive gain of 447.30, noise-equivalent power of 1.80 × 10 -14 W/Hz 1/2 , and detectivity of 1.21 × 10 10 Jones. This study expands the way to enhance the performance of ReS 2 photodetectors., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Minimally invasive biosensing using microneedles (MNs) is a desirable technology for continuous healthcare monitoring. Among a wide range of MNs, porous MNs are expected to be applied for sampling of interstitial fluids (ISF) by connecting the internal tissue to external measurement devices. In order to realize a continuous measurement of biomarkers in ISF through porous MNs, their integration with a microfluidic chip is a promising approach due to its applicability to micro-total analysis system (μTAS) technology. In this study, we developed a fluidic system to directly interface porous MNs to a microfluidic chip consisting of a capillary pump for the continuous sampling of ISF. The porous and flexible MNs made of PDMS are connected to the microfluidic chip fabricated by standard microelectro-mechanical system (MEMS) processes, showing a continuous flow of phosphate buffered saline (PBS). The developed device will lead to the minimally invasive and continuous biosampling for long-term healthcare monitoring., (© 2021. Controlled Release Society.)

The ultrawide band gap, high breakdown electric field, and large-area affordable substrates make β-Ga 2 O 3 promising for applications of next-generation power electronics, while its thermal conductivity is at least 1 order of magnitude lower than other wide/ultrawide band gap semiconductors. To avoid the degradation of device performance and reliability induced by the localized Joule-heating, proper thermal management strategies are essential, especially for high-power high-frequency applications. This work reports a scalable thermal management strategy to heterogeneously integrate wafer-scale monocrystalline β-Ga 2 O 3 thin films on high thermal conductivity SiC substrates by the ion-cutting technique and room-temperature surface-activated bonding technique. The thermal boundary conductance (TBC) of the β-Ga 2 O 3 -SiC interfaces and thermal conductivity of the β-Ga 2 O 3 thin films were measured by time-domain thermoreflectance to evaluate the effects of interlayer thickness and thermal annealing. Materials characterizations were performed to understand the mechanisms of thermal transport in these structures. The results show that the β-Ga 2 O 3 -SiC TBC values are reasonably high and increase with decreasing interlayer thickness. The β-Ga 2 O 3 thermal conductivity increases more than twice after annealing at 800 °C because of the removal of implantation-induced strain in the films. A Callaway model is built to understand the measured thermal conductivity. Small spot-to-spot variations of both TBC and Ga 2 O 3 thermal conductivity confirm the uniformity and high quality of the bonding and exfoliation. Our work paves the way for thermal management of power electronics and provides a platform for β-Ga 2 O 3 -related semiconductor devices with excellent thermal dissipation.

The wide bandgap, high-breakdown electric field, and high carrier mobility makes GaN an ideal material for high-power and high-frequency electronics applications, such as wireless communication and radar systems. However, the performance and reliability of GaN-based high-electron-mobility transistors (HEMTs) are limited by the high channel temperature induced by Joule heating in the device channel. Integration of GaN with high thermal conductivity substrates can improve the heat extraction from GaN-based HEMTs and lower the operating temperature of the device. However, heterogeneous integration of GaN with diamond substrates presents technical challenges to maximize the heat dissipation potential brought by the ultrahigh thermal conductivity of diamond substrates. In this work, two modified room-temperature surface-activated bonding (SAB) techniques are used to bond GaN and single-crystal diamond. Time-domain thermoreflectance (TDTR) is used to measure the thermal properties from room temperature to 480 K. A relatively large thermal boundary conductance (TBC) of the GaN/diamond interfaces with a ∼4 nm interlayer (∼90 MW/(m 2 K)) was observed and material characterization was performed to link the interfacial structure with the TBC. Device modeling shows that the measured TBC of the bonded GaN/diamond interfaces can enable high-power GaN devices by taking full advantage of the ultrahigh thermal conductivity of single-crystal diamond. For the modeled devices, the power density of GaN-on-diamond can reach values ∼2.5 times higher than that of GaN-on-SiC and ∼5.4 times higher than that of GaN-on-Si with a maximum device temperature of 250 °C. Our work sheds light on the potential for room-temperature heterogeneous integration of semiconductors with diamond for applications of electronics cooling, especially for GaN-on-diamond devices.

High-power GaN-based electronics are limited by high channel temperatures induced by self-heating, which degrades device performance and reliability. Increasing the thermal boundary conductance (TBC) between GaN and SiC will aid in the heat dissipation of GaN-on-SiC devices by taking advantage of the high thermal conductivity of SiC substrates. For the typical growth method, there are issues concerning the transition layer at the interface and low-quality GaN adjacent to the interface, which impedes heat flow. In this work, a room-temperature bonding method is used to bond high-quality GaN to SiC directly, which allows for the direct integration of high-quality GaN with SiC to create a high TBC interface. Time-domain thermoreflectance is used to measure the GaN thermal conductivity and GaN-SiC TBC. The measured GaN thermal conductivity is larger than that of grown GaN-on-SiC by molecular beam epitaxy. High TBC is observed for the bonded GaN-SiC interfaces, especially for the annealed interface (∼230 MW m -2 K -1 , close to the highest value ever reported). Thus, this work provides the benefit of both a high TBC and higher GaN thermal conductivity, which will impact the GaN-device integration with substrates in which thermal dissipation always plays an important role. Additionally, simultaneous thermal and structural characterizations of heterogeneous bonded interfaces are performed to understand the structure-thermal property relation across this new type of interface.

Au⁻Au surface activated bonding is promising for room-temperature bonding. The use of Ar plasma vs. O₂ plasma for pretreatment was investigated for room-temperature wafer-scale Au⁻Au bonding using ultrathin Au films (<50 nm) in ambient air. The main difference between Ar plasma and O₂ plasma is their surface activation mechanism: physical etching and chemical reaction, respectively. Destructive razor blade testing revealed that the bonding strength of samples obtained using Ar plasma treatment was higher than the strength of bulk Si (surface energy of bulk Si: 2.5 J/m²), while that of samples obtained using O₂ plasma treatment was low (surface energy: 0.1⁻0.2 J/m²). X-ray photoelectron spectroscopy analysis revealed that a gold oxide (Au₂O₃) layer readily formed with O₂ plasma treatment, and this layer impeded Au⁻Au bonding. Thermal desorption spectroscopy analysis revealed that Au₂O₃ thermally desorbed around 110 °C. Annealing of O₂ plasma-treated samples up to 150 °C before bonding increased the bonding strength from 0.1 to 2.5 J/m² due to Au₂O₃ decomposition.

Single-crystal cubic silicon carbide has attracted great attention for MEMS and electronic devices. However, current leakage at the SiC/Si junction at high temperatures and visible-light absorption of the Si substrate are main obstacles hindering the use of the platform in a broad range of applications. To solve these bottlenecks, we present a new platform of single crystal SiC on an electrically insulating and transparent substrate using an anodic bonding process. The SiC thin film was prepared on a 150 mm Si with a surface roughness of 7 nm using LPCVD. The SiC/Si wafer was bonded to a glass substrate and then the Si layer was completely removed through wafer polishing and wet etching. The bonded SiC/glass samples show a sharp bonding interface of less than 15 nm characterized using deep profile X-ray photoelectron spectroscopy, a strong bonding strength of approximately 20 MPa measured from the pulling test, and relatively high optical transparency in the visible range. The transferred SiC film also exhibited good conductivity and a relatively high temperature coefficient of resistance varying from -12 000 to -20 000 ppm/K, which is desirable for thermal sensors. The biocompatibility of SiC/glass was also confirmed through mouse 3T3 fibroblasts cell-culturing experiments. Taking advantage of the superior electrical properties and biocompatibility of SiC, the developed SiC-on-glass platform offers unprecedented potentials for high-temperature electronics as well as bioapplications.

A technical bottleneck to the broadening of applications of glass nanofluidic chips is bonding, due to the strict conditions, especially the extremely high temperatures (~1000 °C) and the high vacuum required in the current glass-to-glass fusion bonding method. Herein, we report a strong, nanostructure-friendly, and high pressure-resistant bonding method, performed at room temperature (RT, ~25 °C) for glass nanofluidic chips, using a one-step surface activation process with an O(2)/CF(4) gas mixture plasma treatment. The developed RT bonding method is believed to be able to conquer the technical bottleneck in bonding in nanofluidic fields.

The air-gap structure between integrated LiNbO(3) optical modulators and micromachined Si substrates is reported for high-speed optoelectronic systems. The calculated and experimental results show that the high permittivity of the Si substrate decreases the resonant modulation frequency to 10 GHz LiNbO(3) resonant-type optical modulator chips on the Si substrate. To prevent this substrate effect, an air-gap was formed between the LiNbO(3) modulator and the Si substrate. The ability to fabricate the air-gap structure was demonstrated using low-temperature flip-chip bonding (100 °C) and a Si micromachining process, and its performance was experimentally verified., (© 2011 Optical Society of America)