Capacitive MEMS Accelerometer Research Articles

A Micromachined Silicon-on-Glass Accelerometer with an Optimized Comb Finger Gap Arrangement.

This paper reports the design, fabrication, and characterization of a MEMS capacitive accelerometer with an asymmetrical comb finger arrangement. By optimizing the ratio of the gaps of a rotor finger to its two adjacent stator fingers, the sensitivity of the accelerometer is maximized for the same comb finger area. With the fingers' length, width, and depth at 120 μm, 4 μm, and 45 μm, respectively, the optimized finger gap ratio is 2.5. The area of the proof mass is 750 μm × 560 μm, which leads to a theoretical thermomechanical noise of 9 μg/√Hz. The accelerometer has been fabricated using a modified silicon-on-glass (SOG) process, in which a groove is pre-etched into the glass to hold the metal electrode. This SOG process greatly improves the silicon-to-glass bonding yield. The measurement results show that the resonant frequency of the accelerometer is about 2.05 kHz, the noise floor is 28 μg/√Hz, and the nonlinearity is less than 0.5%.

Evaluation of the Diagnostic Sensitivity of Digital Vibration Sensors Based on Capacitive MEMS Accelerometers.

In recent years, there has been an increasing use of digital vibration sensors that are based on capacitive MEMS accelerometers for machine vibration monitoring and diagnostics. These sensors simplify the design of monitoring and diagnostic systems, thus reducing implementation costs. However, it is important to understand how effective these digital sensors are in detecting rolling bearing faults. This article describes a method for determining the diagnostic sensitivity of diagnostic parameters provided by commercially available vibration sensors based on MEMS accelerometers. Experimental tests were conducted in laboratory conditions, during which vibrations from 11 healthy and faulty rolling bearings were measured using two commercial vibration sensors based on MEMS accelerometers and a piezoelectric accelerometer as a reference sensor. The results showed that the diagnostic sensitivity of the parameters depends on the upper-frequency band limit of the sensors, and the parameters most sensitive to the typical fatigue faults of rolling bearings are the peak and peak-to-peak amplitudes of vibration acceleration. Despite having a lower upper-frequency range compared to the piezoelectric accelerometer, the commercial vibration sensors were found to be sensitive to rolling bearing faults and can be successfully used in continuous monitoring and diagnostics systems for machines.

Serpentine spring design technique for high sensitivity MEMS capacitive accelerometer fabricated by gold multi-layer metal technology

This paper describes a design technique for serpentine spring with the edge span beam L/2. In order to improve design accuracy, we investigate the key structure parameters influenced by the fabrication process for MEMS device, comparing finite element analysis (FEA) and analytical models. It is found that the Fedder model as the analytical model is suitable for the spring constant characteristics of FEA with the edge span beam L/2. Further, the thickness and width are found to be the key structure parameters and the dominant factor of variation regarding the serpentine spring. Based on the analysis, we propose a spring design technique. The experimental results show that the variation between the measured data of 4.46 N m−1 and the design value of 4.15 N m−1 was 7.5%, satisfying the target of ±10%. It is confirmed that the proposed technique can establish the serpentine spring for high sensitivity gold proof-mass MEMS accelerometers.

Design and performance analysis of a MEMS Based Area-Variation Capacitive Accelerometer with Readout Circuit

The structural optimization of the device is used in the present work to demonstrate the improvement of the device sensitivity for a MEMS accelerometer based on capacitive principle due to overlap area change between electrodes. The proof mass of the device is made up of a few parallel fingers those are joined together. Proof mass is supported by flexible mechanical beams that resemble springs is suspended over fixed electrodes and are fastened to the substrate. The greatest displacement that the proof mass can suffer with application of acceleration is determined for the specific construction. The connected beams' width and length were changed, and ANSYS FEA software was used to model the reaction. Sensitivity of the device is analyzed and discussed based on the findings of various device geometry measurements, and suggestions for improving sensitivity are also made. Additionally, a signal conditioning circuit that changes the capacitance to voltage as a result of the proof mass deflecting differently is described. These discoveries might help designers to create capacitive MEMS accelerometers with increased sensitivity.

MEMS capacitive accelerometer: A review

Micro-electro-mechanical systems sensors are integrated systems used in many fields such as consumer electronics, the automobile industry, and biomedical, and their dimensions change between micrometers and millimeters. MEMS capacitive accelerometers are the most widely used sensor type among MEMS accelerometer sensors. As a result of the external force applied to the capacitive accelerometer sensor, the proof mass inside the sensor moves, and the capacitive change is measured as an electrical signal using reading circuits. In this review paper, general information about MEMS sensors is given, and a comprehensive review is made of MEMS capacitive accelerometers. In the study, the dynamic circuit of the MEMS capacitive accelerometer is given, and the calculation of the important values for the mechanical and electronic structure during the design of the capacitive MEMS accelerometer is explained. In addition, information about the readout circuits used to convert the capacitive change to voltage is given. Finally, the fabrication processes used to produce the final product are explained, and the studies on sample fabrication processes found in the literature are mentioned.

Analysis of the Frequency-Dependent Vibration Rectification Error in Area-Variation-Based Capacitive MEMS Accelerometers.

The presence of strong ambient vibrations could have a negative impact on applications such as high precision inertial navigation and tilt measurement due to the vibration rectification error (VRE) of the accelerometer. In this paper, we investigate the origins of the VRE using a self-developed MEMS accelerometer equipped with an area-variation-based capacitive displacement transducer. Our findings indicate that the second-order nonlinearity coefficient is dependent on the frequency but the VRE remains constant when the displacement amplitude of the excitation is maintained at a constant level. This frequency dependence of nonlinearity is a result of several factors coupling with each other during signal conversion from acceleration to electrical output signal. These factors include the amplification of the proof mass's amplitude as the excitation frequency approaches resonance, the nonlinearity in capacitance-displacement conversion at larger displacements caused by the fringing effect, and the offset of the mechanical suspension's equilibrium point from the null position of the differential capacitance electrodes. Through displacement transducer and damping optimization, the second-order nonlinearity coefficient is greatly reduced from mg/g2 to μg/g2.

Impact of Thermal Variations and Soldering Process on Performance and Behavior of MEMS Capacitive Accelerometers

Impact of Thermal Variations and Soldering Process on Performance and Behavior of MEMS Capacitive Accelerometers

A novel design of capacitive MEMS multi-range accelerometer; FEM and numerical approach

Sensing the acceleration with high dynamic range follows space and size limitations and many errors and inconveniences caused by using multiple accelerometers on a single structure. A novel MEMS capacitive accelerometer with a dual-spring system has been proposed to address this issue. Such a design is a single device with two sensitivities in different sensing ranges. It increases the dynamic range of the sensing by incorporating the supporting springs at high accelerations. Therefore, the sensor can sense a more comprehensive dynamic range while maintaining the required resolution in different ranges. The design parameters of the sensor, such as the thickness of the structural layer, the size of the sensor, and the width of the spring beams, have been investigated. The mechanical sensitivity in the first range is 0.082 μm g−1. For the second range, it is 0.0015 to 0.0091 μm g−1 depending on the supportive springs’ width. Moreover, the natural frequency of the device is 1740 Hz. The capacitance change of the proposed sensor is 7 fF g−1 on average for the first range and 0.08 to 0. 48 fF g−1 for different configurations in the second range. Utilizing such sensors with changeable stiffness in different ranges can reduce the sensor footprint and fabrication cost and increase reliability.

The High-Efficiency Design Method for Capacitive MEMS Accelerometer.

In this research, a high-efficiency design method of the capacitive MEMS accelerometer is proposed. As the MEMS accelerometer has high precision and a compact structure, much research has been carried out, which mainly focused on the structural design and materials selection. To overcome the inconvenience and inaccuracy of the traditional design method, an orthogonal design and the particle swarm optimization (PSO) algorithm are introduced to improve the design efficiency. The whole process includes a finite element method (FEM) simulation, high-efficiency design, and verification. Through the theoretical analysis, the working mechanism of capacitive MEMS accelerometer is clear. Based on the comparison among the sweep calculation results of these parameters in the FEM software, four representative structural parameters are selected for further study, and they are le, nf, lf and wPM, respectively. le and lf are the length of the sensing electrode and fixed electrode on the right. nf is the number of electrode pairs, and wPM is the width of the mass block. Then, in order to reduce computation, an orthogonal design is adopted and finally, 81 experimental groups are produced. Sensitivity SV and mass Ma are defined as evaluation parameters, and structural parameters of experimental groups are imported into the FEM software to obtain the corresponding calculation results. These simulation data are imported into neural networks with the PSO algorithm. For a comprehensively accurate examination, three cases are used to verify our design method, and every case endows the performance parameters with different weights and expected values. The corresponding structural parameters of each case are given out after 24 iterations. Finally, the maximum calculation errors of SV and Ma are 1.2941% and 0.1335%, respectively, proving the feasibility of the high-efficiency design method.

Impurity analysis of electroplated gold components with multi-layered structures by thermal desorption spectrometry toward application in gold Micro electro mechanical system capacitive accelerometers

Au-based micro-electro-mechanical-system (Au-MEMS) capacitance accelerometers show high sensitivity by suppressing the mechanical noise because of the high mass density of gold (ρ = 19.3 g/cm3). On the other hand, their long-term reliability suffers from drift phenomena induced by the impurities incorporated in the key component during their fabrication process, such as the gold electroplating step. Herein, impurities in electroplated Au-based components for MEMS capacitive accelerometers are evaluated by thermal desorption spectrometry (TDS) measurements. The TDS measurement reveals that dominant desorption gases from the Au-based component are molecular hydrogen (H2) and water (H2O). These desorption gases are derived from impurities in the electroplated Au-based component, and the amount of these gases is significantly suppressed by a thermal treatment step. In conclusion, this study demonstrates that the electroplated Au-based component contains impurities originated from the fabrication process, and these impurities could be removed by a thermal treatment step.

Empirical model for substrate resistivity influence on MEMS capacitive accelerometer performance

Empirical model for substrate resistivity influence on MEMS capacitive accelerometer performance

The Use of Shape Accel Array for Deformation Monitoring and Parameter Inversion of a 300 m Ultrahigh Rockfill Dam

The global construction of rockfill dams has now surpassed the 300 m height level. Despite great achievements in dam design and construction, monitoring techniques have lagged behind the development of high rockfill dams. Existing deformation monitoring techniques are ill-suited to the high earth and water pressures, and extended monitoring periods are required for ultrahigh rockfill dams. This study introduces, for the first time, the use of a shape accel array (SAA) to monitor internal displacement in a 300 m high earth core rockfill dam. The SAA employs a rope-like array of capacitive MEMS accelerometers for deformation measurement. Compared to conventional monitoring techniques, SAA is a data-intensive monitoring technique. Based on the intensive data obtained from SAA, we employed a parameter inversion method, utilizing multiobjective optimization algorithm, the nondominated sorting genetic algorithm-III (NSGA-III), to inverse the constitutive model parameters of the rockfill dam. The multiobjective parameter inversion method maximizes the use of multisource monitoring data for predicting rockfill dam deformation.

Multiple-Degree-of-Freedom Modeling and Simulation for Seismic-Grade Sigma–Delta MEMS Capacitive Accelerometers

The high-order mechanical resonances of the sensing element in a high-vacuum environment can significantly degrade the noise and distortion performance of seismic-grade sigma–delta MEMS capacitive accelerometers. However, the current modeling approach is unable to evaluate the effects of high-order mechanical resonances. This study proposes a novel multiple-degree-of-freedom (MDOF) model to evaluate the noise and distortion induced by high-order mechanical resonances. Firstly, the MDOF dynamic equations of the sensing element are derived using the principle of modal superposition and Lagrange’s equations. Secondly, a fifth-order electromechanical sigma–delta system of the MEMS accelerometer is established in Simulink based on the dynamic equations of the sensing element. Then, the mechanism through which the high-order mechanical resonances degrade the noise and distortion performances is discovered by analyzing the simulated result. Finally, a noise and distortion suppression method is proposed based on the appropriate improvement in high-order natural frequency. The results show that the low-frequency noise drastically decreases from about −120.5 dB to −175.3 dB after the high-order natural frequency increases from about 130 kHz to 455 kHz. The harmonic distortion also reduces significantly.

A 63 μg/√Hz Noise Floor and 14 pJ Power Efficiency Open-Loop MEMS Capacitive Accelerometer Using Closed-Loop Hybrid Dynamic Amplifier

MEMS capacitive accelerometer for the Internet of Things (IoT) applications is designed with open-loop structure rather than close-loop structure to achieve low power consumption. In the open-loop structure, voltage control readout technique is preferred for low cost. However, voltage control readout technique suffers from poor noise performance and low power efficiency (in terms of FoM). In this paper, the weak feedback oversampling successive approximation readout circuit which merges the closed-loop hybrid dynamic amplifier with noise reduction technique is proposed to achieve low noise floor, high power efficiency and high accuracy. The proposed WFB-OSA based readout circuit is fabricated in a commercial <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.18\mu \text{m}$ </tex-math></inline-formula> 1.8V CMOS process. The measurement result shows that the circuit has achieved a noise floor of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$63\mu g/\surd Hz$ </tex-math></inline-formula> and an FoM of 14pJ.

An accurate Verilog-A based model for MEMS capacitive accelerometer

This paper presents an accurate macro model for a capacitive micro accelerometer using Verilog-A tool. For this purpose, first the accelerometer is simulated in COMSOL software. Then, considering the simplified physics of the accelerometer, a preliminary Verilog-A model is derived, which is not accurate enough. This initial model has been modified by using mathematical tools and adapting to the results of COMSOL. Furthermore, a switched-capacitor based capacitance to voltage converter (CVC) is used as a readout circuit to validate the proposed model. The CVC is designed, simulated and optimized in the Cadence software by using a 65 nm CMOS technology. In order to reduce low-frequency non-idealities such as flicker noise and DC offsets, a chopper-stabilization technique is used. The power consumption for a 1.2 V supply is 140 μW. Simulation results show a good agreement between COMSOL results and simulation of the proposed model in the Cadence.

An aerosol deposition based MEMS piezoelectric accelerometer for low noise measurement

Potentially applied in low-noise applications such as structural health monitoring (SHM), a 1-axis piezoelectric MEMS accelerometer based on aerosol deposition is designed, fabricated, simulated, and measured in this study. It is a cantilever beam structure with a tip proof mass and PZT sensing layer. To figure out whether the design is suitable for SHM, working bandwidth and noise level are obtained via simulation. For the first time, we use aerosol deposition method to deposit thick PZT film during the fabrication process to achieve high sensitivity. In performance measurement, we obtain the charge sensitivity, natural frequency, working bandwidth and noise equivalent acceleration of 22.74 pC/g, 867.4 Hz, 10–200 Hz (within ±5% deviation) and 5.6 mu {{{rm{g}}}}/sqrt{{{{rm{Hz}}}}} (at 20 Hz). To demonstrate its feasibility for real applications, vibrations of a fan are measured by our designed sensor and a commercial piezoelectric accelerometer, and the results match well with each other. Moreover, shaker vibration measurement with ADXL1001 indicates that the fabricated sensor has a much lower noise level. In the end, we show that our designed accelerometer has good performance compared to piezoelectric MEMS accelerometers in relevant studies and great potential for low-noise applications compared to low-noise capacitive MEMS accelerometers.

Retraction Note: A new structure and modeling of a three-axis MEMS capacitive accelerometer with high dynamic range and sensitivity

Retraction Note: A new structure and modeling of a three-axis MEMS capacitive accelerometer with high dynamic range and sensitivity

Long-Term Degradation Evaluation of the Mismatch of Sensitive Capacitance in MEMS Accelerometers.

During long-term use, MEMS accelerometers will experience degradation, such as bias and scale factor changes. Bias of MEMS capacitive accelerometers usually comes from the mismatch of parasitic capacitance and sensitive capacitance. This paper focuses on the mismatch of sensitive capacitance and analyzes the mechanism of long-term degradation of MEMS accelerometers. Firstly, the effect of sensitive capacitance mismatch on the performance of a MEMS accelerometer was investigated. Secondly, a method of measuring the mismatch of sensitive capacitance was proposed, and the validation experiment shows that the accuracy of this measurement can be less than 1.10×10-5 of the sensitive capacitance. For the samples in this experiment, the measurement error of this method can be less than 0.36 fF. Finally, a high-temperature acceleration experiment was performed. The mismatch of the sensitive capacitance during the experiment was monitored based on the proposed method, and the experimental results are analyzed. The experimental result demonstrates that the mismatch of sensitive capacitance varies linearly with time. The change rates of sensitive capacitance mismatch for the two samples are 2.95×10-7&amp;nbsp;C0/h and 2.66×10-7&amp;nbsp;C0/h in the high-temperature acceleration experiment at 145 °C, respectively. The change in sensitive capacitance mismatch seems small, but it is not to be ignored during long-term use. The rate of change is similar for the same batch of samples. This could imply that the adverse effects due to the mismatch of sensitive capacitance changes can be reduced by compensating for this variation.

Simulation and analysis of suspension based single axis mems capacitive accelerometer

This paper reports a comparison of different types of springs used in MEMS based capacitive accelerometers. In this work MEMS based Single-axis accelerometers are designed using different Suspension systems. Analysis of the structure is done for resonant frequency of 2kHz. Analytical modeling of the different suspensions is presented for the specified frequency. Stress, displacement and capacitive analysis of the accelerometer is done. The sensitivity of the accelerometer with parallel beam suspension is 70nm/g, 50nm/g for folded beam suspension and 35nm/g for serpentine beam suspension. Hence parallel beam suspension has 0.7 times improved sensitivity than folded beam and 2 times better than serpentine suspension accelerometer. Whereas the stress obtained for folded beam is better than the other two. Hence Parallel beam suspension is preferred for higher sensitivity and accuracy whereas Folded beam suspension is preferred for greater structural stability By comparing these devices, it is concluded that a compromise on certain parameters is required in order meet the requirements. If there is higher displacement sensitivity then there is lower mechanical stability and vice versa. The simulations are carried out using COMSOL Multiphysics.

MEMS İvme Ölçerler için Analog Yapay Sinir Ağı Temelli Kontrolcü Tasarımı

Bu çalışmada tek eksenli kapasitif MEMS ivme ölçer için yeni bir analog yapay sinir ağı temelli bir kontrolcü önerilmektedir. Bu kontrolcü giriş katmanında bir, gizli katmanda altı ve çıkış katmanında iki nöron olacak şekilde tasarlanmıştır. Bu kontrolcü, AMI C5N 0,6 μm CMOS üretim teknolojisi kullanılarak Electric serim editörü ile tasarlanmıştır. Tasarlanan kontrolcünün başarısı çeşitli bilgisayar benzetimleriyle PID kontrolcüyle karşılaştırılmıştır. Benzetim sonuçları önerilen kontrolcünün tepki süresi, aşım ve ölçüm aralığı açısından PID kontrolcüden daha başarılı olduğunu göstermiştir.