Current Issue : January-March Volume : 2025 Issue Number : 1 Articles : 6 Articles
Ultrasound is widely applied in diverse domains, such as medical imaging, non-destructive evaluation, and acoustic communication. Piezoelectric micromachined ultrasonic transducers (PMUTs) capable of generating and receiving ultrasonic signals at the micrometer level have become a prominent technology in the field of ultrasound. It is important to enrich the models of the PMUTs to meet the varied applications. In this study, a series of PMUT devices featured with various top electrode configurations, square, circular, and doughnut, were designed to assess the influence of shape on the emission efficacy. It was demonstrated that the PMUTs with a circular top electrode were outperformed, which was calculated from the external acoustic pressure produced by the PMUTs operating in the fundamental resonant mode at a specified distance. Furthermore, the superior performance of PMUT arrays were exhibited through computational simulations for the circular top electrode geometries. Conventional microelectromechanical systems (MEMS) techniques were used to fabricate an array of PMUTs based on aluminum nitride (AlN) films. These findings make great contributions for enhancing the signal transmission sensitivity and bandwidth of PMUTs, which have significant potential in non-destructive testing and medical imaging applications....
Low light extraction efficiency (LEE) remains a critical bottleneck in the performance of contemporary micro-light-emitting diodes (micro-LEDs). This study presents an innovative approach to improve the LEE of Gallium nitride (GaN)-based thin-film flip-chip (TFFC) micro-LEDs by integrating an inclined sidewall with photonic crystals (PhCs). Three-dimensional finite-difference time-domain (FDTD) simulations reveal that the inclined sidewall design significantly increases the escape probability of light, thereby improving LEE. Additionally, the PhCs’ structure further improves LEE by enabling more light to propagate into the escape cones through diffraction. Optimal results are achieved when the inclined sidewall angle (θ) is 28◦ and the PhCs exhibit a period (a) of 220 nm, a filling factor (f ) of 0.8, and a depth (d) of 3 μm, resulting in a maximum LEE of 36.47%, substantially surpassing the LEE of conventional planar TFFC micro-LEDs. These results provide valuable design guidelines for the development of high-efficiency GaN-based micro-LEDs....
The 3.3 kV SiC MOSFETs are essential for traction applications, so it is important to investigate the reliability of the recently developed high voltage MOSFETs and power modules as they are believed to be more susceptible to the effects of basal plane dislocations (BPDs). This paper presents measurement results and analysis of bipolar degradation and threshold voltage instability in 3.3 kV SiC MOSFETs having two distinct kinds of integrated diode, conventional body diode and embedded Schottky Barrier Diode (SBD). No bipolar degradation was observed both in MOSFET with conventional body diode and with embedded SBD after accumulated test with 100 hours each of 200%, 400% and 600% rated current stress in the 3rd quadrant of operation. However, the output characteristics show 1% (~0.2 m) and 2% (~0.4 m) increase in on resistance (RDS(on)) and 11% (0.23 V) and 5% (0.1 V) increase in threshold voltage (VTH), respectively, after total bipolar degradation test in the case of the MOSFET with conventional body diode and up to 74 hrs of 600% rated current stress in the case of the MOSFET with embedded SBD at 70°C. A rapid large negative VTH shift was obse rved in the MOSFETs with embedded SBD after ~ 74 hrs of 600% rated current stress. After accumulated Bias Temperature Instability (BTI) test at 150°C, the VTH value at 25°C has increased by 9.7% (0.14 V) and 14.5% (0.2 V) for the MOSFET with conventional body diode and with embedded SBD, respectively, while RDS(on) increased by 1m at 25°C and by 5m at 150°C, for both types of MOSFETs....
A picowatt CMOS voltage reference with dual outputs is proposed and simulated in this paper based on a standard 65 nm process. To compensate for the leakage current caused by parasitic reverse-biased PN junctions, an approach employing gate leakage transistors is proposed. Maintaining a maximal temperature coefficient (TC) of 20.40 ppm/◦C across an extended temperature range of −10∼155 ◦C is achieved. Additionally, a voltage divider consisting of diode-connected NMOS transistors is introduced to obtain a lower voltage output without shunting the original branch or utilizing operational amplifiers. Moreover, a novel trimming block is utilized to optimize TC across different process corners. Simulation results demonstrate that a minimum power consumption of only 53.83 pW is achieved and the line sensitivity is 0.077%/V with 0.45 V to 2.5 V supply. The power supply rejection ratio of −76.70 dB at 10 Hz and VDD = 1.8 V is obtained....
As a prominent focus in high-voltage power devices, SiC MOSFETs have broad application prospects in the aerospace field. Due to the unique characteristics of the space radiation environment, the reliability of SiC MOSFETs concerning single-event effects (SEEs) has garnered widespread attention. In this study, we employed accelerator-heavy ion irradiation experiments to study the degradation characteristics for SEEs of 1.2 kV SiC MOSFETs under different bias voltages and temperature conditions. The experimental results indicate that when the drain-source voltage (VDS) exceeds 300 V, the device leakage current increases sharply, and even single-event burnout (SEB) occurs. Furthermore, a negative gate bias (VGS) can make SEB more likely via gate damage and Poole– Frenkel emission (PF), reducing the VDS threshold of the device. The radiation degradation behavior of SiC MOSFETs at different temperatures was compared and analyzed, showing that although high temperatures can increase the safe operating voltage of VDS, they can also cause more severe latent gate damage. Through an in-depth analysis of the experimental data, the physical mechanism by which heavy ion irradiation causes gate leakage in SiC MOSFETs was explored. These research findings provide an essential basis for the reliable design of SiC MOSFETs in aerospace applications....
As artificially engineered subwavelength periodic structures, terahertz (THz) metasurface devices exhibit an equivalent dielectric constant and dispersion relation akin to those of natural materials with specific THz absorption peaks, describable using the Lorentz model. Traditional verification methods typically involve testing structural arrays using reflected and transmitted optical paths. However, directly detecting the dielectric constant of individual units has remained a significant challenge. In this study, we employed a THz time-domain spectrometer-based scattering-type scanning near-field optical microscope (THz-TDS s-SNOM) to investigate the near-field nanoscale spectrum and resonant mode distribution of a single-metal double-gap split-ring resonator (DSRR) and rectangular antenna. The findings reveal that they exhibit a dispersion relation similar to that of natural materials in specific polarization directions, indicating that units of THz metasurface can be analogous to those of molecular structures in materials. This microscopic analysis of the dispersion relation of artificial structures offers new insights into the working mechanisms of THz metasurfaces....
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