Bin Zhou

Addressing the need for intrusion detection and localization in critical areas, this study develops a method for outdoor ground vibration source localization utilizing subterranean-deployed MEMS accelerometers. First, the Particle Swarm Optimization (PSO) algorithm is employed to minimize the Geometric Dilution of Precision (GDOP), thereby determining the optimal configuration of the sensor array. The acquired signals are then filtered, and a novel time delay estimation algorithm, termed the Sliding Window Derivative (SWD) algorithm, is proposed. This method utilizes a sliding window to compute the sum of squared differences between adjacent sampling points within the window, generating a time-windowed energy change signal. The derivative of this signal yields a rate-of-change curve, highlighting abrupt signal transitions. The SWD algorithm, in conjunction with the STA/LTA–AIC algorithm, precisely identifies the first arrival point of the vibration signal, determining its time of arrival at each of the four sensors. Finally, an improved two-step weighted least squares method based on Time Difference of Arrival (TDOA) is used to calculate the position of the vibration source. Experimental results demonstrate an average positional error of 0.095 m and an average directional error of 0.935 degrees, validating the efficacy of the proposed method in achieving high-precision localization in outdoor environments.

This letter presents a quantitative approach for 2.5 µm Au–Sn metallization with accurate mass calibration, which is applied to solid–liquid interdiffusion bonding of microelectromechanical systems (MEMS) wafer-level packaging (WLP) devices, particularly those that demand a micron-level gap of out-of-plane electrodes. For Au–Sn metallization, traditional deposition methods, such as electroplating, are unable to achieve micron-level thickness and accurate composition due to poor robustness to varying process conditions. In this study, we further improve the composition of the deposited Au–Sn alloy through direct mass measurement and calibration during the cosputtering process. In the experiment, a high-precision balance with a resolution of 0.1 mg was utilized to measure the mass increment of sputtered Au and Sn in the clean room. Subsequently, the sputtering rate of the Sn target was calculated and applied to calibrate the final Au–Sn composition. According to the energy-dispersive X-ray spectrum (EDS) results, the difference between the measured Au–Sn mass composition and the set value is 1.1%, which is significantly lower than the typical 5%–10% composition deviation of electroplated Au–Sn solder, demonstrating a strengthened robustness to varying conditions by the effective calibration. The test results show that the shear strength of the WLP structure reaches 31.8 MPa, and the cross-sectional EDS results of the as-bonded Au–Sn alloy are consistent with the designed Au–Sn composition. The proposed calibration method can also be applied to other alloy depositions that require precise mass composition and micron-level thickness with a better robustness to varying conditions.

This paper shows the design, fabrication, test verification, and theoretical analysis of a proposed sandwich wafer-level packaging (WLP) structure with double-sided out-of-plane electrode configuration and precise symmetry adjustment method of 5 μm out-of-plane gaps for MEMS devices requiring control and detection of out-of-plane movement. Common WLP schemes are typically fabricated based on silicon on insulator process and direct silicon bonding, which is difficult to place double-sided out-of-plane electrodes. In this paper, a glass-silicon-glass sandwich WLP scheme is designed to configure symmetrical out-of-plane electrodes on top and bottom layers. Anodic bonding and Au-Sn solid-liquid interdiffusion (SLID) bonding are used for WLP encapsulation of triple stacks. Gaps between out-of-plane electrodes and suspended mass are controlled by the height of etched silicon anchors and standoffs. Extremely thin metallization layers with a total thickness less than 3 μm is precisely deposited by a novel online calibration method to reach required Au-Sn composition for a stable liquid phase transition during bonding, matching standoffs height for out-of-plane gap control. After fabrication, capacitance is measured to evaluate double-sided symmetry of out-of-plane electrodes gaps. WLP dies with standoffs have a relative capacitance difference less than 1.77%, while WLP dies without standoffs have a relative capacitance difference of 7.82%. A theoretical symmetry analysis based on process data is carried out to resolve capacitance variance into several sources, getting a high estimation accuracy of 87.6%. The designed WLP framework is aimed at a fabrication implementation based on universal MEMS processes, without a requirement for advanced MEMS platform.

Hemispherical resonator gyroscope (HRG) is a high precision inertial sensor for measurement of rate and attitude angle, and the fused silica hemispherical resonator is key component of HRG which the ultra-low frequency split is required. During the entire fabrication process of the resonator, the imperfects of the resonators should be trimmed by evaluating the quality-factor and frequency split in real-time. Therefore, the high-precision balance method based on synchronous trimming system has been proposed in this paper, and the quality-factor, frequency split and principle-axis angle could be identified at the same time in a single test. At first, the high precision orbital parameter identification algorithm based on nonlinear least square method has been adopted, which shows the identification error of frequency split and stiffness-axis-angle is less than 3.58×10 ^-7 Hz and 0.0207° respectively. Then, the hardware of trimming system including vacuum chamber with ion mill and neutralizer, fiber optic interferometer and FPGA control board with the proposed identification algorithm has been implemented. Finally, the focus ion beam (FIB) etching experiment has been carried out to verify the proposed trimming method. The experimental result shows that the proposed method has excellent performance, which can reduce the frequency split of all resonators under 0.0005Hz and the best result can achieve 0.00005Hz.

In this paper, a capacitive angle encoder monitored and sensed by ASIC with a sensitive structure fabricated by MEMS technology is proposed. The sensitive structure with a 27.5mm outer diameter is designed and optimized in a limited footprint to realize higher accuracy. After being fabricated by MEMS technology, it is integrated with an ASIC, realizing high fabrication accuracy and a small footprint at the same time. The ASIC is designed in an analog-digital hybrid architecture to achieve low power consumption as well as a small footprint. The analog part of the ASIC consists of a charge to voltage converter with capacitance cancellation array and a sigma-delta modulator (SDM) with a 3-bit quantizer. In the digital part of ASIC, the processor based on Cortex-M3 core is designed to perform angle calculation. The measurement result of the proposed angle sensor reveals that the power consumption is 250 mW from a single 5V supply, the bandwidth is over 130Hz, the resolution is 0.002° and the accuracy over the full range is 0.024°, indicating that the encoder has considerable potential for use in high-precision applications.

In this paper, a novel electrodes design for in-plane measurement of single-structure quadruple mass multi-axis MEMS inertial devices is proposed to achieve the closed-loop x/y-axis acceleration measurement. The designed 45 ° tilting comb electrodes combine synovial comb electrodes and laminated comb electrodes and meet the same electrostatic force coefficient on quadruple mass, with structural symmetry design ensured. Theoretical formula is analyzed in detail, which provides guidance for simulation and design.

High-precision microelectromechanical system (MEMS) gyroscopes are significant in many applications. Bias instability (BI) is an important parameter that indicates the performance of a MEMS gyroscope and is affected by the 1/f noise of the MEMS resonator and readout circuit. Since the bandgap reference (BGR) is an important block in the readout circuit, reducing its 1/f noise is key to improving a gyroscope’s BI. In a traditional BGR, the error amplifier is applied to provide a virtual short-circuit point, but it introduces the main low-frequency noise sources. This paper proposes an ultralow 1/f noise BGR by removing the error amplifier and applying an optimized circuit topology. In addition, a simplified but accurate noise model of the proposed BGR is obtained to optimize the BGR’s output noise performance. To verify this design, the proposed BGR has been implemented in a 180 nm CMOS process with a chip area of 545 × 423 μm. The experimental results show that the BGR’s output integrated noise from 0.1 to 10 Hz is 0.82 μV and the thermal noise is 35 nV/√Hz. Furthermore, bias stability tests of the MEMS gyroscope fabricated in our laboratory with the proposed BGR and some commercial BGRs are carried out. Statistical results show that reducing the BGR’s 1/f noise can nearly linearly improve the gyroscope’s BI.

Monitoring X-ray radiation in the gastrointestinal tract can enhance the precision of radiotherapy in patients with gastrointestinal cancer. Here we report the design and performance, in the gastrointestinal tract of rabbits, of a swallowable X-ray dosimeter for the simultaneous real-time monitoring of absolute absorbed radiation dose and of changes in pH and temperature. The dosimeter consists of a biocompatible optoelectronic capsule containing an optical fibre, lanthanide-doped persistent nanoscintillators, a pH-sensitive polyaniline film and a miniaturized system for the wireless readout of luminescence. The persistent luminescence of the nanoscintillators after irradiation can be used to continuously monitor pH without the need for external excitation. By using a neural-network-based regression model, we estimated the radiation dose from radioluminescence and afterglow intensity and temperature, and show that the dosimeter was approximately five times more accurate than standard methods for dose determination. Swallowable dosimeters may help to improve radiotherapy and to understand how radiotherapy affects tumour pH and temperature.