This paper reviews the research and development of micromachined accelerometers with a noise floor lower than 1 µg/√Hz. Firstly, the basic working principle of micromachined accelerometers is introduced. Then, different methods of reducing the noise floor of micromachined accelerometers are analyzed. Different types of micromachined accelerometers with a noise floor below 1 µg/√Hz are discussed. Such sensors can mainly be categorized into: (i) micromachined accelerometers with a low spring constant; (ii) with a large proof mass; (iii) with a high quality factor; (iv) with a low noise interface circuit; (v) with sensing schemes leading to a high scale factor. Finally, the characteristics of various micromachined accelerometers and their trends are discussed and investigated.

This paper describes a novel, semiautomated design methodology based on a genetic algorithm (GA) using freeform geometries for microelectromechanical systems (MEMS) devices. The proposed method can design MEMS devices comprising freeform geometries and optimize such MEMS devices to provide high sensitivity, large bandwidth, and large fabrication tolerances. The proposed method does not require much computation time or memory. The use of freeform geometries allows more degrees of freedom in the design process, improving the diversity and performance of MEMS devices. A MEMS accelerometer comprising a mechanical motion amplifier is presented to demonstrate the effectiveness of the design approach. Experimental results show an improvement in the product of sensitivity and bandwidth by 100% and a sensitivity improvement by 141% compared to the case of a device designed with conventional orthogonal shapes. Furthermore, excellent immunities to fabrication tolerance and parameter mismatch are achieved.

Anti-spring mechanisms are widely used for improving the noise performance of MEMS accelerometers due to their stiffness softening effect. However, the existing mechanisms typically require large bias force and displacement for achieving stiffness softening, leading to large device dimensions. Here, we propose a novel anti-spring mechanism composed of two pre-shaped curved beams connected in a parallel configuration, which can achieve stiffness softening without requiring large bias force and displacement. The stiffness softening effect of the mechanism is verified through theoretical modeling and finite element method (FEM) simulation. After that, the mechanism is implemented in a 4.2 mm × 4.9 mm MEMS capacitive accelerometer prototype. The experimental results reveal that the sensitivity of the accelerometer increases by 10.4% compared to the initial sensitivity; at the same time, the noise floor and bias instability decrease by 10.5% and 4.2%. The sensitivity, nonlinearity, bias instability, and noise floor after biasing are 51.1 mV/g, 0.99%, 0.24 mg, and 21.3 $${\rm{\mu }}{\rm{g}}/\sqrt{{\rm{Hz}}}$$ μ g / Hz , respectively. Thus, the proposed mechanism can enhance the performance of the accelerometer. This work provides an innovative approach for improving the performance of MEMS accelerometers while enabling miniaturization.

Topological invariants in the band structure, such as Chern numbers, are important for the understanding and classification of the topological properties of matter and dictate the occurrence of exotic behaviors, yet their direct spectroscopic determination has been largely limited to electronic bands. Here, we use inelastic neutron scattering in conjunction with ab initio calculations to identify a variety of topological phonon band crossings in MnSi and CoSi single crystals. We find a distinct relation between the Chern numbers of a band-crossing node and the scattering intensity modulation in momentum space around the node. Given sufficiently high resolution, our method can be used to determine arbitrarily large Chern numbers of topological phonon band-crossing nodes.

This paper presents a dual quantization lateral-axis capacitive electromechanical sigma-delta modulator (EM-Σ Δ M) vibratory wheel gyroscope under mode-matched condition. A symmetric wheel gyroscope structure was designed, fabricated, and wafer-level packaged under vacuum. The EM-Σ Δ M interface loop adopts a fourth-order multifeedback and local resonator Σ Δ M noise shaping structure, taking advantage of single-bit and multibit quantization in a single-loop modulator. To evaluate the influence of quantization noise, various numbers of bits of the multibit quantizator were compared and the optimal number of bits was calculated. The interface circuit system was implemented in hardware based on a low-noise front-end application-specified integrated circuit and a back-end discrete-time EM-Σ Δ M realized in a field-programmable gate array chip. The system clock was generated using a self-clocking scheme, which allows interfacing to gyroscope with a wide range of drive frequencies. Experimental evaluation indicated that the digital gyroscope system achieved a scale factor of 2073LSB(4.1 mV)/deg/s, with a nonlinearity of 0.046%, a noise floor of 3.1 m°/s/√ Hz within a bandwidth of 100 Hz, and a bias instability of 1.3 deg/hr. [2017-0081]

This paper presents a novel single-side (111)-silicon (non-SOI) fabricated tri-axis capacitive micro-accelerometer with a dual quantization electromechanical sigma-delta modulator (EM-ΣΔM) interface circuit. The fully CMOS compatible single-sided micromachining process with toroidal shaped electrical isolation structures is described. A 2.6mm×2.6mm sized tri-axis accelerometer was designed and fabricated using only the front-side of a 4-inch (111) silicon wafer. The interface circuit was based on a front-end ASIC readout circuit and a back-end dual quantization high-order EM-ΣΔM digital circuit implemented on an FPGA. The EM-ΣΔM loop adopts a multi-feedback noise shaping architecture, for which different numbers of bits for the loop quantization were analyzed. The parameters of the EM-ΣΔM loop are optimized by a genetic algorithm (GA). Acceleration sensitivities of 170mV/g (2785LSB/g), 142mV/g (2327LSB/g) and 26mV/g (426LSB/g) were measured in EM-ΣΔM closed-loop operation for the in-plane (X/Y) and out-of-plane (Z) axis, respectively. The cross-axis sensitivity was in the order of 1 to 6% and the output noise was 0.5mg to 2mg/√Hz, with a one hour bias drift of 3 to 6mg.