With the advancement of semiconductor manufacturing technology, thin film structures were widely used in MEMS devices. These films played critical roles in providing support, reinforcement, and insulation in MEMS devices. However, due to their microscopic dimensions, the sensitivity of their parameters and performance to thermal stress increased significantly. In this study, a Pirani gauge sample with a multilayer thin film structure was designed and fabricated. Based on this sample, finite element modeling analysis and thermal stress experiments were conducted. The finite element modeling analysis employed a combination of steady-state and transient methods to simulate the deformation and stress distribution of the device at room temperature (25 °C), low temperature (-55 °C), and high temperature (125 °C). The thermal stress test involved placing the sample in a temperature cycling chamber for temperature cycling tests. After the tests, the resonant frequency and surface deformation of the device were measured to quantitatively evaluate the impact of thermal stress on the deformation and resonant frequency parameters of the device. After the experiments, it was found that the clamped-end beams made of Pt were a stress concentration area. Additionally, the repetitive thermal load caused the cantilever beam to move cyclically in the Z direction. This movement altered the deformation of the film and the resonant frequency. The suspended film exhibited concavity, and the overall trend of the resonant frequency was downward. Over time, this could even lead to the fracture of the clamped-end beams. The variation of mechanical parameters derived from finite element simulations and experiments provided an important reference value for device design improvement and played a crucial role in enhancing the reliability of thin film devices.

The effect of sand and dust pollution on the sensitive structures of flow sensors in microelectromechanical systems (MEMS) is a hot issue in current MEMS reliability research. However, previous studies on sand and dust contamination have only searched for sensor accuracy degradation due to heat conduction in sand and dust cover and have yet to search for other failure-inducing factors. This paper aims to discover the other inducing factors for the accuracy failure of MEMS flow sensors under sand and dust pollution by using a combined model simulation and sample test method. The accuracy of a flow sensor is mainly reflected by the size of its thermistor, so in this study, the output value of the thermistor value was chosen as an electrical characterization parameter to verify the change in the sensor's accuracy side by side. The results show that after excluding the influence of heat conduction, when sand particles fall on the device, the mutual friction between the sand particles will produce an electrostatic current; through the principle of electrostatic dissipation into the thermistor, the principle of measurement leads to the resistance value becoming smaller, and when the sand dust is stationary for some time, the resistance value returns to the expected level. This finding provides theoretical guidance for finding failure-inducing factors in MEMS failure modes.

Exploring interfacial thermal transport of a heterojunction interface is crucial to achieving advanced thermal management for gallium nitride-based high electron mobility transistor devices. The current research primarily focuses on material enhancements and microstructure design at the interfaces of epitaxial layers, buffer layers, and substrates, such as the GaN/SiC interface and GaN/AlN interface. Yet, the influence of different concentrations of Al/Ga atoms and interface roughness on the interfacial thermal conductance (ITC) of AlGaN/GaN interface, the closest interface to the hot spot, is still poorly understood. Herein, we focus on the rough AlGaN/GaN interface and evaluate the changes in ITC under different Al-Ga atomic concentrations and interface roughness using atomistic simulations. When the interface is completely smooth and AlGaN and GaN are arranged according to common polarization characteristic structures, the ITC gradually increases as the proportion of Al atoms decreases. When the proportion of Al atoms is reduced to 20%-30%, the impact of the interface structure on heat transfer is almost negligible. For interface models with different roughness levels, as the interface roughness increases, the ITC drops from 735.09 MW m−2K−1 (smooth interface) to 469.47 MW m−2K−1 by 36.13%. The decrease in ITC is attributed to phonon localization induced by rough interfaces. The phonon modes at the interface are significantly different from those in bulk materials. The degree of phonon localization is most pronounced in the frequency range that contributes significantly to heat flux. This work provides valuable physical insights into understanding the thermal transfer behaviors across the rough AlGaN/GaN interfaces. © 2024 Author(s).

Microfluidic heat sinks are regarded as an efficient cooling solution in micro-electronic systems. However, as the hydraulic diameter of the microfluidic heat sinks shrinks, the blockage problem may occur due to the particles caused by cooling components’ abrasion, which limits the application in long-term operation. This paper proposes an unconstrained microfluidic heat sink (UCMFHS) with high anti-blockage capacity for multiple hotspot systems, which aims to solve the blockage problem. The position and shape of the micro pin fins in UCMFHS are optimized by the CFD model. According to the test requirements of anti-blockage capacity and cooling performance, the test platform is built, which adopts the thermal test chips as heat source array. The results show that when the coolant particle concentration is 0.5%, the pressure drop variation is less than 0.3 kPa in UCMFHS, which is 99.43% lower than the control sample. The average temperature and temperature non-uniformity coefficient of 16 hotspots under the condition of 1200 W/cm2 and 125 mL per minute are 141.1 ℃ and 0.049, respectively. Therefore, the UCMFHS has both anti-blockage capacity and cooling capacity and is considered to have a high application prospect in long-term multi-hotspot cooling. © 2024 Society of Thermal Engineers of Serbia. Published by the Vinča Institute of Nuclear Sciences, Belgrade, Serbia. This is an open access article distributed under the CC BY-NC-ND 4.0 terms and conditions.

This letter reports a wide band linearly polarized(LP) and orbital angular momentum (OAM) mode reconfigurable magneto-electric (ME) dipole antenna array. A switchable microstrip balanced feed structure (MBFS), which can provide a stable phase difference of 180-degree in the whole operating frequency band, is employed in the design of ME dipole element. By using two orthogonal MBFS, two high-isolation LP modes with switchable 180-degree phase shifting characteristics can be generated, enabling the reconstruction of LP modes through polarization synthesis. By manipulating the states of the reconfigurable feed network and the four ME dipole elements, the polarization can be altered among two orthogonal LP states and the OAM mode can be reconfigured between l=-1,0,and+1.The measurement results indicate that the proposed ME dipole array exhibits good reflection coefficient in the frequency range of 3.0-4.0 GHz (|S11| IEEE

Diamond substrate with superior thermal conductivity has been the most promising heat sink to solve the heat dissipation issues in GaN-based power electronics. The phonon transport behaviors across the GaN-diamond interface crucially determine the thermal performance and still remain largely unexplored especially considering the presence of pre-interface vacancies. Herein, the influence of localized high-concentration Ga/N atomic vacancies on phonon transport across the GaN-diamond interface is fully investigated using non-equilibrium molecular dynamics. The calculated interface thermal resistance (ITR) of the perfect GaN-diamond interface at room temperature is approximately 1.5 m2·K/GW, consistent with prediction of the diffusion mismatch model. After introducing the Ga/N vacancies at a concentration of 30%, the existence of vacancy-phonon scattering increases the interfacial thermal resistance (ITR) by up to 67%. Analyzing the phonon density of states and the spectral heat current, the heat flux contributed by GaN high-frequency phonons decreases after introducing vacancy defects. This is attributed that the vacancy-phonon scattering in GaN enhances anharmonic phonon scattering, and the phonon energy is redistributed among different phonon modes. Moreover, the collective vibration of propagation phonons is disrupted randomly by the vacancy-phonon scattering. This work aims to understand the influence of vacancy-phonon scattering on the phonon transport across GaN-diamond interface and provide helpful guidance to engineering such interface for better heat dissipation performance. © 2023 Elsevier Ltd

Subject to intense high-energy particle irradiation, various effects manifest within a material. Specifically, when high-energy particles collide with lattice atoms in a crystal material, a sequence of interactions is set in motion, initiating irradiation effects. Using GaAs solar cells as an example, this study investigates how potential barriers in different directions of atoms in sphalerite structures affect atomic displacement and establishes a probability model for lattice atomic displacement under proton irradiation. By combining Markov chains, changes in displacement threshold energy with different crystal orientations are described, and a damage model for cascading collision relationships that cause irradiation effects is established. Finally, the new model is compared to classical models, and differences in defects caused by proton impacts at several energies on GaAs crystals are simulated.

Increasing power density and miniaturization in three-dimensional (3D) packaged power electronics demand innovative thermal management. Yet, the thermal performance of electrically insulated packages for power electronics is currently limited by the ultralow thermal conductivity of conventional thermal interface materials (TIMs) and their poor ability of directing heat current to heat sink. Herein, we have prepared a highly thermally conductive and electrically insulating TIM composite based on boron nitride nanobars (BNNB). The polar characteristics of the B-N bond in the BNNB outer tube wall-derived h-BN nanosheets facilitate the adsorption of magnetic particles. Modulating the arrangement of 3D-BNNB by an external magnetic field improves the thermal conductivity of composite up to 3.3 W m-1 K-1 at a concentration of 40 wt %, 17.8 times higher than the pure epoxy and also exhibiting significant anisotropy. Moreover, the composite shows a high stiffness of 510 MPa and a high resistivity of 27.2 M omega center dot cm, demonstrating excellent mechanical and electrical insulating characteristics. Infrared thermography results show that the surface temperature of the composite depends on the orientation of BNNB and its interfacial interaction with the epoxy resin. The magnetic field-oriented modulation of 3D-BNNB can offer a promising solution to achieve efficient thermal management of 3D-integrated power packaging.

The degradation of power converter performance is one of the most critical issues of complex system with the improvement of power capacity and density. Power converter bears severe electrical and thermal stress, resulting in an increase in the probability of failure and significant economic losses. Most research addresses performance evaluation either through reliability theory without physical understanding or through data-driven methods requiring high experimental cost. Few studies focus on predicting system-level performance degradation, which is technically difficult as many components degrade randomly. Identifying the parameters of electronic components based on sensor data has become possible with the development of neural networks and computational power. Therefore, this paper proposes a novel system-level power degradation predicting framework, which combines the advantages of neural networks in nonlinear fitting and empirical knowledge to predict the degradation of power converter. In addition, a comprehensive and improved feature parameter screening method is proposed to identify the most critical feature parameters of the power converter systems. Furthermore, the neural network parameter identification method based on SSA-Elman NN (Sparrow Search Algorithm - Elman Neural Network) is introduced to improve prediction accuracy. Finally, the result shows that the proposed method can accurately predict the degradation of the system by using a DC-DC converter as an example.

The electromigration behavior of microbumps is inevitably altered under bidirectional currents. Herein, based on a designed test system, the effect of current direction and time proportion of forward current is investigated on Cu Pillar/Ni/Sn-1.8 Ag/Cu microbumps. Under thermo-electric stressing, microbumps are found to be susceptible to complete alloying to Cu6Sn5 and Cu3Sn. As a Ni layer prevents the contact of the Cu pillar with the solder, Sn atoms mainly react with the Cu pad, and the growth of Cu3Sn is concentrated on the Cu pad sides. With direct current densities of 3.5 × 104 A/cm2 at 125 °C, the dissolution of a Ni layer on the cathode leads to a direct contact reaction between the Cu pillar and the solder, and the consumption of the Cu pillar and the Cu pad shows an obvious polarity difference. However, with a bidirectional current, there is a canceling effect of an atomic electromigration flux. With current densities of 2.5 × 104 A/cm2 at 125 °C, as the time proportion of the forward current approaches 50%, a polarity structural evolution will be hard to detect, and the influence of the chemical flux on Cu-Sn compounds will be more obvious. The mechanical properties of Cu/Sn3.0Ag0.5Cu/Cu are analyzed at 125 °C with direct and bidirectional currents of 1.0 × 104 A/cm2. Compared with high-temperature stressing, the coupled direct currents significantly reduced the mechanical strength of the interconnects, and the Cu-Sn compound layers on the cathode became the vulnerable spot. While under bidirectional currents, as the canceling effect of the electromigration flux intensifies, the interconnect shear strength gradually increases, and the fracture location is no longer concentrated on the cathode sides. © 2023 by the authors.