Micromachines最新文献

This paper examined the reliability of complex PCB assemblies under random vibration and temperature cycling, which are two primary causes of assembly failure. A combination of finite element simulation and environmental testing was employed to investigate the effects of different reinforcement methods and solder joint morphology on assembly reliability. The linear accumulation of damage was utilized to predict assembly failure, and the predicted failure damage was compared with the damage extracted post-testing to validate the simulation analysis. The results indicate that SAC305 solder exhibits greater strength than Sn63Pb37 solder in withstanding temperature cycling fatigue, yet is weaker than Sn63Pb37 solder in withstanding random vibration fatigue. When the solder is Sn63Pb37, the temperature cycling life of the assembly with the bottom filled and the corners fixed is reduced by 92.3% and 99.3%, respectively, compared to the unreinforced method, while the random vibration life is enhanced by 84 times and 3.9 times, respectively. An increase in pad diameter is advantageous for improving the random vibration life of the assembly, but results in a decrease in the temperature cycling life. When the lower pad diameter ranges from 0.35 mm to 0.55 mm, the assembly temperature cycling life decreases by 28.83%, 82.03%, 90.66%, and 91.22% with the increase of the lower pad diameter, and the random vibration life improves by 4.8 times, 9.5 times, 20.4 times, and 33.6 times, respectively. The predicted locations of vulnerable solder joints for the assembly are consistent with the experimental results, and the failure prediction accuracy of the assembly is 88.89%.

The demand for sensors in wearable devices [...].

An all-optical single-longitudinal-mode (SLM) forward Brillouin microwave oscillator (FB-MO) with an unbalanced Fiber Mach-Zehnder interferometer (UF-MZI) for microwave photonics (MWP) generation is proposed and experimentally investigated. UF-MZI consists of an optical coupler (OC), a polarization controller (PC), and two asymmetric length arms with 5 km and 500 m single-mode fibers (SMFs), which implements two unbalanced length feedback rings that are connected to one another. One long-length ring with a forward Brillouin gain cooperates with the other short-length ring to maintain a spectral Vernier effect and improve the effective free spectral range (FSR). By contrast with traditional optoelectronic oscillators (OEOs), this design does not require any photoelectric conversion devices and additional modulation, avoids external electromagnetic interference, and side-mode suppression and linewidth are favorable. Experimental results reveal that the 3-dB linewidth of the all-optical SLM FB-MO with UF-MZI is about 140 Hz. The acoustic-mode and side-mode suppression ratios are 26 dB and 31 dB. Within 60 min of the stability experiment, the power and frequency stability fluctuation were ±1 dB and ±100 Hz. Thanks to its long main ring cavity length, our all-optical SLM FB-MO with UF-MZI maintains good phase-noise performance. The measurement shows that a phase noise as low as -120 dBc/Hz at an offset frequency of 100 kHz is achieved. This SLM MWP generation technology holds great potential for applications in radar monitoring and wireless communication systems.

Electro-Fenton chemical mechanical polishing primarily regulates the generation of hydroxyl radicals (·OH) via the Fenton reaction through an applied electric field, which subsequently influences the formation and removal of the oxide layer on the workpiece surface, thereby impacting the overall polishing quality and rate. This study employs Pin-Disk friction and wear experiments to investigate the material removal behavior of single-crystal GaN during electro-Fenton chemical mechanical polishing. Utilizing a range of analytical techniques, including coefficient of friction (COF) curves, surface morphology assessments, cross-sectional analysis, and power spectral density (PSD) measurements on the workpiece surface, we examine the influence of abrasives, polishing pads, polishing pressure, and other parameters on the electro-Fenton chemical-mechanical material removal process. Furthermore, this research provides preliminary insights into the synergistic removal mechanisms associated with the electro-Fenton chemical-mechanical action in single-crystal GaN. The experimental results indicate that optimal mechanical removal occurs when using a W0.5 diamond at a concentration of 1.5 wt% combined with a urethane pad (SH-Q13K-600) under a pressure of 0.2242 MPa.

AlN-based bulk acoustic wave (BAW) filters have emerged as crucial components in 5G communication due to their high frequency, wide bandwidth, high power capacity, and compact size. This paper mainly reviews the basic principles and recent research advances of AlN-based BAW resonators, which are the backbone of BAW filters. We begin by summarizing the epitaxial growth of single-crystal, polycrystalline, and doped AlN films, with a focus on single-crystal AlN and ScAlN, which are currently the most popular. The discussion then extends to the structure and fabrication of BAW resonators, including the basic solidly mounted resonator (SMR) and the film bulk acoustic resonator (FBAR). The new Xtended Bulk Acoustic Wave (XBAW) technology is highlighted as an effective method to enhance filter bandwidth. Hybrid SAW/BAW resonators (HSBRs) combine the benefits of BAW and SAW resonators to significantly reduce temperature drift. The paper further explores the application of BAW resonators in ladder and lattice BAW filters, highlighting advancements in their design improvements. The frequency-reconfigurable BAW filter, which broadens the filter's application range, has garnered substantial attention from researchers. Additionally, optimization algorithms for designing AlN-based BAW filters are outlined to reduce design time and improve efficiency. This work aims to serve as a reference for future research on AlN-based BAW filters and to provide insight for similar device studies.

Indium tin oxide (ITO) is a commonly used material for transparent conductive electrodes (TCE) in optoelectronic applications. On the other hand, graphene has superior electrical conductivity and exceptional mechanical flexibility, which makes it a promising candidate as a TCE material. This work proposes a CVD graphene/ITO hybrid electrode enhanced by doping with silver nanowires (Ag-NWs). The study aims to improve the performance of the electrode by optimizing two key parameters during the fabrication process: the thermal annealing time after the transfer of graphene on ITO and the Ag-NWs doping conditions. The annealing treatment is fundamental to reducing the residues on the surface of graphene and increasing the interface contact between graphene and ITO. The correct coverage and distribution of the dopant on graphene is obtained by controlling the concentration of the Ag-NWs and the spin coating speeds. The results indicate a substantial improvement in the optical and electrical performance of the Ag-NWs/graphene/ITO hybrid electrode. A remarkably low sheet resistance of 42.4 Ω/sq (±2 Ω/sq) has been achieved while maintaining a high optical transmittance of 87.3% (±0.5%).

The vibration of porous Al-Al₂O₃ micro-cantilever sandwich beams in fluids was studied utilizing the modified couple stress theory and the scale distribution theory (MCST and SDT). Four types of porosity distributions were defined; the uniform distribution of pores was defined as U-type, while O-type, V-type and X-type represented non-uniform distributions of pores. The material properties of different porous sandwich beams were calculated. The properties of the micro-cantilever sandwich beams were adjusted to account for scale effects according to MCST. With the fluid driving force taken into consideration, the amplitude-frequency response, and resonant frequencies of the FGM sandwich beams in three different fluids were calculated using the Euler-Bernoulli beam theory. The computational studies showed that the presence of gradient factor p and the pores in the micro-cantilever sandwich beams affect the temperature field distribution and amplitude-frequency response in fluids. Increasing gradient factor p leads to a more obvious thermal concentration of the one-dimensional temperature field and migrates the resonance peaks to lower frequencies. In contrast to the uniform distribution type, the non-uniformly distributed pores also cause a decrease in the resonance frequency.

Monolithic micro LED display arrays show potential for application in small-area display modules, such as augmented reality (AR) displays. Due to the short distance between micro LEDs and the monolithic transparent substrate, a light crosstalk phenomenon exists between adjacent micro LED pixels, decreasing the array's display definition. In this paper, a 64 × 64 GaN micro LED monolithic display array was fabricated on a silicon-based drive circuit. The micro LED size was 20 μm × 20 μm, and the pitch between micro LEDs was 28 μm. To suppress the optical crosstalk between adjacent micro LEDs in the array, we etched a photonic crystal structure using a focused ion beam (FIB) on the micro LED sapphire substrate. Measurements of the micro LED nearfield electroluminescence (EL) and finite element method (FEM) calculations demonstrated that the light expansion was confined in the photonic crystal micro LED with a thinner substrate. The presented work provides references regarding the fabrication of monolithic micro LED arrays and the control of crosstalk in displays.

This paper presents a novel multi-layer, dual-band antenna array designed for WLAN and X-band applications, incorporating several innovative features. The design employs a pentagon-shaped radiating element with parasitic strips to enable dual-band operation. A dual-transformed feed network with chamfered feed strip corners minimizes radiation distortion and cross-polarization while introducing orthogonal phase shifts to achieve circular polarization (CP) at the X-band. A Fabry-Pérot structure, strategically placed above the array, enhances gain in the WLAN band. The antenna demonstrates an impedance bandwidth of 1.8 GHz (S₁₁ < -10 dB) at the WLAN band, with 36% fractional bandwidth, and 4.3 GHz at the X-band, with 43% fractional bandwidth. Measured peak gains are 7 dBi for the WLAN band and 6.8 dBi for the X-band, with favourable S₁₁ levels, omni-directional radiation patterns, and consistent gain across both bands. Circular polarization is achieved within 8.5-10.4 GHz. Experimental results confirm the array's significant advancements in multi-band performance, making it highly suitable for diverse wireless communication applications.

The integrated imaging of LWIR cameras and SAR is one of the important directions of multi-sensor integration. In order to reduce the structural complexity of LWIR cameras and SAR-integrated imaging antenna, a dual-polarized metasurface-integrated antenna (MIA) is designed in this paper. It is composed of a microwave metasurface antenna and an optical metalens, and the metalens is embedded in the center of the metasurface antenna. The MIA uses the powerful electromagnetic wave control ability to simplify the optical and microwave signal transmission paths and reduce the number of devices. At the same time, in order to expand the function of the MIA, based on the principle of metasurface, the dual-linearly polarized and dual-circularly polarized MIAs are designed and simulated, respectively. The results show that the designed dual-polarized MIA has good performance. This paper provides a new scheme for the integrated imaging system of LWIR cameras and SAR with simple structure, diverse functions and easy integration.