This paper presents a novel silicon-based piezoresistive pressure sensor composed of a silicon layer with sensing elements and a glass cover for hermetic packaging. Unlike conventional designs, this study employs numerical simulation to analyze the influence of varying roughness levels of the sensitive membrane on the sensor’s output response. Simulation results demonstrate that pressure sensors with smoother sensitive membranes exhibit superior performance in terms of sensitivity (5.07 mV/V/MPa), linearity (0.67% FS), hysteresis (0.88% FS), and repeatability (0.75% FS). Furthermore, an optimized process for controlling membrane roughness was achieved by adjusting the concentration of the etchant solution. Experimental results reveal that a membrane roughness of 35.37 nm was attained under conditions of 80 °C and 25 wt% TMAH. Additionally, the fabrication process of this piezoresistive pressure sensor was significantly simplified and cost-effective due to the adoption of a backside wet etching technique. The fabricated sensor demonstrates excellent performance metrics, including a sensitivity of 5.07 mV/V/MPa, a full-scale (FS) output of 101.42 mV, a hysteresis of 0.88% FS, a repeatability of 0.75% FS, and a nonlinearity of 0.67% FS. These results indicate that the proposed sensor is a promising tool for precise pressure measurement applications, offering both high performance and cost efficiency. This study not only advances the understanding of the impact of membrane roughness on sensor performance but also provides a practical and scalable fabrication approach for piezoresistive pressure sensors.

To address the limitations of the traditional long-vector model, which cannot adequately preserve the inherent orthogonal structure among channels in the signal processing of a single vector hydrophone, three minimum variance distortionless response (MVDR) direction-of-arrival estimation algorithms based on the quaternion model are proposed for a single MEMS vector hydrophone. Compared with the traditional long-vector model, the quaternion can retain the structural relationship between channels in a more compact data representation form. First, based on the output characteristics of the sound pressure and dual-channel vibration velocity of the two-dimensional MEMS vector hydrophone, three quaternion signal models—namely Q-VV, Q-PVV, and Q-PV—are constructed. Subsequently, the corresponding MVDR spatial spectra are derived in the quaternion domain. To enhance the direction-of-arrival resolution performance under low-signal-to-noise-ratio (SNR) conditions, the algorithms are then improved by incorporating subspace decomposition theory. The simulation results show that the three proposed quaternion-based MVDR algorithms can all realize effective direction-of-arrival estimation for a single target. When the signal-to-noise ratio is greater than −4 dB, the direction estimation error is less than 1°. The results of dynamic bearing trajectory tests and fixed-point direction-of-arrival estimation experiments indicate that the proposed method can realize the continuous and stable tracking of the target azimuth. Among the involved algorithms, Q-PV-MVDR can effectively suppress false targets, with an average relative angle orientation error of 0.5°.

To improve the stability of ohmic contacts for SiC sensor chips operating at 600 °C, SiC/Ti/TaSi₂/Pt ohmic contact stacks were fabricated on n-type 4H-SiC in this work. The effects of the Ti/TaSi₂/Pt thickness ratio and annealing conditions on electrode performance were systematically investigated, and the resulting electrodes were characterized via SEM, XRD and AES. The results show that a lower specific contact resistivity (SCR) (7.16 × 10⁻⁵ Ω·cm²) is obtained after the Ti/TaSi₂/Pt ratio of 1:3:2 (50/150/100 nm) is rapidly annealed at 1050 °C. The SCR remains 3.05 × 10⁻⁴ Ω·cm² after 20 h of atmospheric aging at 600 °C, and the electrode surface remains flat enough for the subsequent processes. Taken together, the XRD and AES results suggest that the formation of well-crystallized TiC/TaC and Si-enriched titanium silicides lowers the specific contact resistance, and that the thermally stable phases, such as TaC, hinder oxygen ingress, which is consistent with the observed high-temperature stability. In contrast, oxygen penetrates into the contact interface and forms TiO₂, an insulating oxide that increases the contact resistance and thereby degrades the contact performance. The results provide a basis for the design of ohmic contacts for high-temperature silicon carbide sensors.