The significance of wafer bonding is fundamental to the progression of electronic systems. Common fabrication techniques for Cu pillars play a crucial role in establishing resilient and efficient interconnects within semiconductor devices. It is imperative to explore the potential of nano-copper as an alternative material to overcome limitations associated with conventional copper. The use of nano copper paste in manufacturing has the potential to simplify the process, potentially reducing the number of steps compared to conventional methods. This study delves into the intricacies of wafer-level packaging (WLP), with a particular focus on hybrid bonding processes utilizing nanocopper sintering. Through the application of Finite Element Method (FEM) simulations, we investigate the stress distribution and thermal dynamics inherent in the sintering and hybrid bonding of both bulk copper and nanocopper materials. Our findings illuminate the superior mechanical and thermal properties of nanocopper, which contribute to reduced stress concentrations and enhanced mechanical integrity in semiconductor packaging. The research highlights the pivotal role of nanocopper sintering in advancing WLP technologies, offering insights into optimizing sintering and bonding parameters for improved device reliability and performance.@en

In recent years, metal crack-based stretchable flexible strain sensors have attracted significant attention in wearable device applications due to their extremely high sensitivity. However, the tradeoff between sensitivity and detection range has been an intractable dilemma, severely limiting their practical applications. Herein, we propose a laser transmission pyrolysis (LTP) technology for fabricating high-performance flexible strain sensors based on (Au) metal cracks with the microchannel array on the polydimethylsiloxane (PDMS) surface. The fabricated flexible strain sensors exhibit high sensitivity [gauge factor (GF) of 2448], wide detection range (59% for tensile strain), precise strain resolution (0.1%), fast response and recovery times (69 and 141 ms), and robust durability (over 3000 cycles). In addition, experiment and simulation results reveal that introducing a microchannel array enables the stress redistribution strategy on the sensor surface, which significantly improves the sensing sensitivity compared to conventional flat surface sensors. Based on the excellent performance, the sensors are applied to detect subtle physiological signals, such as pulse and swallowing, as well as to monitor large-scale motion signals, such as knee flexion and finger bending, demonstrating their potential applications in health monitoring, human-machine interactions, and electronic skin.

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This paper proposes and simulates research on the reverse recovery characteristics of two novel superjunction (SJ) MOSFETs by adjusting the doping profile. In the manufacturing process of the SJ MOSFET using multilayer epitaxial deposition (MED), the position and concentration of each Boron bubble can be adjusted by designing different doping profiles to adjust the resistance of the upper half P-pillar. A higher P-pillar resistance can slow down the sweep out speed of hole carriers when the body diode is turned off, thus resulting in a smoother reverse recovery current and reducing the current recovery rate (d (Formula presented.) /d (Formula presented.)) from a peak to zero. The simulation results show that the reverse recovery peak current (I (Formula presented.)) of the two proposed devices decreased by 5% and 3%, respectively, compared to the conventional SJ. Additionally, the softness factor (S) increased by 64% and 55%, respectively. Furthermore, this study also demonstrates a trade-off relationship between static and reverse recovery characteristics with the adjustable doping profile, thus providing a guideline for actual application scenarios.

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Substrate metallization is a crucial factor affecting the mechanical properties of sintered nanoparticles in microelectronics applications, as it is essential for ensuring good adhesion between the substrate and the sintered material. In this study, we investigated the influence of metallization on pressure-assisted nanocopper sintering and analyzed the related mechanism of interaction using experiments and molecular dynamics simulation. In the first session, we bonded dummy dies on various substrates, including bare Cu, and substrates with Ag or Au metallization by nanocopper pressure-assisted sintering. The mechanical properties of the bonding layers were estimated using shear strength and SEM image analysis of fracture and cross-section morphologies under different sintering conditions. We found that the group of Cu-bare Cu have better bonding strength as the sintering temperature or assisted pressure is not high enough. However, as more energy input to the bonding layer, such as higher temperature or larger sintering pressure, the mechanical performance showed a significant increase. In the second session, a sintering model, which contained a single nanoparticle and substrate, was built to illustrate the effects of metallization from the perspective of solid-state wetting. The contact angle was estimated using a creative method, and the crystallization structure evolutions under different sintering conditions were analyzed. We found that the lattice boundary generated as the Cu nanoparticle coalescence with Ag or Au substrate, which may decrease the bonding strength. However, for Ag and Au metallization, limited interface diffusion can be observed at the neck region, where a few numbers of substrate atoms transmitted toward Cu nanoparticle, and the contact area was larger than that of bare Cu substrate. Finally, a simple uniaxial stretching simulation was conducted to prove the results of sintering simulation. This study provides valuable insights into the effects of metallization on pressure-assisted nanocopper sintering, which can contribute to the optimization of mechanical properties of sintered nanoparticles in microelectronics applications.@en

Short-wave ultraviolet (also called UVC) irradiation is a well-adopted method of viral inactivation due to its ability to damage genetic material. A fundamental problem with the UVC inactivation method is that its mechanism of action on viruses is still unknown at the molecular level. To address this problem, herein we investigate the response mechanism of genome materials to UVC light by means of quantum chemical calculations. The spectral properties of four nucleotides, namely, adenine, cytosine, guanine, and uracil, are mainly focused on. Meanwhile, the transition state and reaction rate constant of uracil molecules are also considered to demonstrate the difficulty level of adjacent nucleotide reaction without and with UVC irradiation. The results show that the peak wavelengths are 248.7 nm, 226.1 nm (252.7 nm), 248.3 nm, and 205.8 nm (249.2 nm) for adenine, cytosine, guanine, and uracil nucleotides, respectively. Besides, the reaction rate constants of uracil molecules are 6.419 × 10⁻⁴⁹ s⁻¹ M⁻¹ and 5.436 × 10¹¹ s⁻¹ M⁻¹ for the ground state and excited state, respectively. Their corresponding half-life values are 1.56 × 10⁴⁸ s and 1.84 × 10⁻¹² s. This directly suggests that the molecular reaction between nucleotides is a photochemical process and the reaction without UVC irradiation almost cannot occur.

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In this article, the avalanche withstand capability and transient failure model of commercial 1200 V asymmetric trench gate SiC MOSFETs are investigated by experiment and simulation under single-pulse unclamped inductive switching (UIS) conditions. The limiting avalanche current and limiting avalanche energy of the device are determined by evaluating the voltage and current waveforms, the power dissipation, and the avalanche energy curves before and during avalanche failure. Then, by using the calibrated simulation model, the sequence between the critical electric field stress and critical thermal stress suffered by the device is revealed, and the transient failure mode of the device is proved to be the thermal runaway. Moreover, after decapping the failed device, the failure mode of the device is further confirmed by analyzing the failure point. Finally, by using the focused ion beam (FIB) technology, the failure mechanism of the device is confirmed as a structural rupture caused by avalanche thermal stress.@en

Nano copper sintering technology has great potential to be widely applied in the wide-bandgap semiconductor packaging. In order to investigate the coalescence kinetics of copper nano particles for this application, a molecular dynamic (MD) simulation was carried out at low temperature on a special model containing two substrate and multiple particles in between. Accordingly, thorough microstructure and dislocation investigation was conducted to identify the atomic-scale evolution in the system. The corresponding findings could provide evidence on the new particle-substrate sintering mechanism. Furthermore, atomic trajectories tracking method was applied to study the rotation behavior of different sized nano particles. New rotation behavior and mechanism were described. Additionally, the study on the size effect of copper particles on the sintering process and coalescence mechanism was conducted via comparing the microstructural and dislocation distribution of 3 nm, 4 nm and 5 nm models. Finally, by comparing the MSD results at low and high temperature for each model, the dominant coalescence dynamics changes were obtained.

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Cu-Ag core-shell (CS) nanoparticle (NP) is considered as a cost-effective alternative material to nano silver sintering material in die attachment application. To further reduce the cost, the thickness of the Ag shell can be adjusted. Whereas the shell thickness will also affect the thermal stability of the Cu-Ag CSNPs. In this study, molecular dynamics simulation was applied to study the thickness effect on the thermal behavior of Cu-Ag CSNPs. The melting points of CSNPs and Pure NPs can be determined by the evolutions of Potential Energy (PE), and the Lindemann index (LI) of the system. The results indicated that the melting points of CS NPs were lower than monometallic NP and the melting point of CS NP is influenced by the size of the Cu core and the number of lattice mismatches. Moreover, the distribution of atoms’ LI showed that the premelting point is independent of shell thickness. However, the fraction of atoms that occurred premelting is increased with the decrease of the shell thickness. Otherwise, we also simulated the sintering process of double CS NPs with equal size.@en

Owing to the outstanding physical properties of graphene, its biosensing applications implemented by the terahertz metasurface are widely concerned and studied. Here, we present a novel design of the graphene metasurface, which consists of an individual graphene ring and an H-shaped graphene structure. The graphene metasurface exhibits a dual-resonance response, whose resonance frequency strongly varies with the geometrical parameters of the proposed metasurface, the carrier density of graphene, and the analyte composition. The transparency window, including width and position, can be artificially controlled by adjusting the geometrical parameters or the Fermi energy. Furthermore, the sensing parameters of the graphene metasurface for cancerous and normal cells are investigated, focusing on two factors, namely cell quantity and position on the metasurface. The simulated results clearly show that the theoretical sensitivity, figure of merit, and quantity of the graphene metasurface for breast cells reach 1.21 THz/RIU, 2.75 RIU (Formula presented.), and 2.43, respectively. Our findings may open up new avenues for promising applications in the diagnosis of cancers.

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Recent reports focus on the hydrogenation engineering of monolayer boron phosphide and simultaneously explore its promising applications in nanoelectronics. Coupling density functional theory and finite element method, we investigate the bowtie triangle ring microstructure composed of boron phosphide with hydrogenation based on structural and performance analysis. We determine the carrier mobility of hydrogenated boron phosphide, reveal the effect of structural and material parameters on resonance frequencies, and discuss the variation of the electric field at the two tips. The results suggest that the mobilities of electrons for hydrogenated BP monolayer in the armchair and zigzag directions are 0.51 and 94.4 cm2·V−1·s−1, whereas for holes, the values are 136.8 and 175.15 cm2·V−1·s−1. Meanwhile, the transmission spectra of the bowtie triangle ring microstructure can be controlled by adjusting the length of the bowtie triangle ring microstructure and carrier density of hydrogenated BP. With the increasing length, the transmission spectrum has a red-shift and the electric field at the tips of equilateral triangle rings is significantly weakened. Furthermore, the theoretical sensitivity of the BTR structure reaches 100 GHz/RIU, which is sufficient to determine healthy and COVID-19-infected individuals. Our findings may open up new avenues for promising applications in the rapid diagnosis of COVID-19.@en

The wide-bandgap semiconductors represented by GaN have a broad application prospect because of their high service temperature and high switch frequency. Quad-Flat-No-Lead (QFN) Package is currently one of the mainstream packaging methods due to its low cost and high efficiency. However, the low reliability of QFN used in GaN devices is still a crucial problem caused by elevated temperatures and the thermal stress induced by the mismatch of coefficient of thermal expansion (CTE). Therefore, it is necessary to control the temperature inner the package and increase the mechanical property of the bonding layer. In this paper, the finite element method (FEM) with thermal-mechanical coupling is performed to optimize the reliability of the bonding layer by adopting sinter nano Cu and silver. Based on the conventional QFN package module, we tried to add different metallization on the bonding surface to decrease the influence of CTE mismatch. We should note that the Anand viscoplastic model was used in the materials of Sintered Ag and lead-free solder paste presented by SAC305, which were the most commonly used in die-attachment. The results showed that the utilization of nano copper/silver paste could hardly facilitate thermal performance although sintered Ag had excellent thermal conductivity. Since the Anand modules of Ag and SAC305 were different, there were some impacts on the stress distribution and deformation. During the bonding process, a large thermal stress generated between die-attachment layer and Package or the PCB. The die-attachment layer formed by nano Ag paste suffered the smaller thermal stress because its CTE is comparable to that of thermal pad. In terms of sintered Ag, the bonding layer generated more elastic strain. As the deformation recovered to initial stage, the stress decreased because of the elastic strain. And we also found that the Ag metallization could decreased the maximum stress of model at heating stage. But Ag metallization suffered larger thermal stress as the temperature decreased. The selection of connection materials and metallization are a crucial part of design the structure of electronic package. And this paper could provide a reference for optimize the package structure to further improve their reliability in future works.

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This paper studied the behaviors of sintering between Ag nanoparticle (NP) and nanoflake (NF) in the same size by molecular dynamics simulation. Before the sintering simulation, the melting simulation of NF was carried out to calculate the melting points of NFs and investigate the thermostability of NF. The Lindemann index and potential energy showed that the melting points of NF were significantly size-dependent. During the heating process, the sharp corner of NF transformed to the round corner and could bend spontaneously lower than melting points. In sintering simulation, the sintering process of NF-NP showed a metastable stage before equilibrium. Under low sintering temperature (500 K), the degree of plasticity sintering mechanism of NF-NP was more prominent, which generated more defects, such as amorphous atoms, dislocations, and stacking faults, than NP-NP. The sintered products of NF-NP also presented a better neck size and shrinkage than NP-NP in the same size. A new sintering behavior was observed: NF was bent toward the NP during the sintering. The bending curvature of NF increased as the thickness or the length/width decreased. For the NF with the ratio of length/width to thickness of 5:1, bending could further significantly facilitate neck growth. At 700 K, the plasticity mechanism dominated both the sintering processes of NF-NP and NP-NP. And NF-NP showed a larger diffusivity than NP-NP. At last, we investigated the effects of crystal misorientation, and found that a tilted grain boundary generated in the neck. The NF had the trend of rotation to decrease the crystal misorientation.

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