Capacitive Micro-accelerometer Research Articles

An experimentation of hand–arm tremor control using low-g area-changed capacitive micro-accelerometer

This paper aims to measure the human hand tremor caused by handheld device using a low-g micro-accelerometer. A novel low-g area-changed differential capacitive micro-accelerometer is designed and analyzed using microproduct design software INTELLISUITE 8.6. Thermo-electro-mechanical analysis is conducted for applied acceleration within the low-g range spans between 0 and 10 g. Existing design performances such as displacement and sensitivity are compared with new proposed design. The sensitivity of micro-accelerometer is improved by using U-shaped spring. The designed micro-accelerometer is used to find vibration that exists while using handheld device. Experimentation is done to measure vibration under dissimilar surfaces. The workers are made to drill three different surface blocks namely paver block, solid cement block, and black stone, and vibrations produced are recorded. These accelerations are intended to calculate exposure action value (EAV) and exposure limit value (ELV) for 8 hours of a working day so that worker can halt the work as soon as ELV is accomplished.

Study on the Dynamic Characteristics of a SiC-Based Capacitive Micro-Accelerometer in Rarefied Air.

In this study, we investigated the viscosity, squeeze-film damping, and a SiC-based capacitive micro-accelerometer in rarefied air. A specific expression for the effective viscosity coefficient of the air was derived, and when the air pressure drops from the standard atmospheric pressure, the viscosity of the air will decrease accordingly. Decreases in the air pressure and the viscosity of the air lead to the change in the squeeze-film air damping in the micro-accelerometer, and both the viscous damping force and the elastic damping force of the air film between the moving electrode plate and the fixed electrode plate will also decrease. The damping coefficient and relative damping ratio of the micro-accelerometer in rarefied air were calculated, which was also confirmed by simulations. The changes of the damping coefficient and the relative damping ratio of the system will directly affect the dynamic characteristics of the micro-accelerometer. When the air pressure in the working environment is below the standard atmospheric pressure, the micro-accelerometer will be in an underdamping state. With the decrease in the air pressure, the working bandwidth of the micro-accelerometer will decrease significantly, and the resonant phenomenon may appear. However, the decrease in the air pressure will not have a notable impact on the response time of the micro-accelerometer. Therefore, this work provides a theoretical basis for the study of the performance characteristics of a SiC-based capacitive accelerometer in rarefied air.

A novel capacitive micro-accelerometer made of steel using micro wire electrical discharge machining method

A new method has been proposed to design and fabricate a metallic microelectromechanical capacitive accelerometer, in this paper. The conventional MEMS fabrication methods, as well as the micro wire electrical discharge machining (WEDM) method, have been employed to fabricate the proposed accelerometer. The WEDM offers several advantages including its capability for attaining a proof mass of higher thickness, as well as using dense metals, in the accelerometers, thus providing better control over noise reduction and damping. This sensor has the proof mass of 6.8 mg which leads to the low Brownian noise of 1.2 g/. The proof mass-beam structure of the accelerometer has been made of steel, which has higher yield strength and fracture toughness than silicon, enabling the accelerometer to withstand high-amplitude accelerations. Conducted tests showed that this sensor operates in the range of 100 g. Thanks to its low noise (due to the larger proof mass) and capability to measure high-amplitude accelerations (due to the high yield strength of steel), the dynamic range of the proposed accelerometer is improved considerably in comparison with the conventional MEMS accelerometers. The presented accelerometer is also operable in the air which facilitates its packaging

A Single-Side Fabricated Triaxis (111)-Silicon Microaccelerometer With Electromechanical Sigma–Delta Modulation

This paper presents a novel single-side (111)-silicon (non-SOI) fabricated triaxis capacitive microaccelerometer with a dual quantization electromechanical sigma–delta modulator (EM- $\Sigma \Delta {\mathrm{ M}}$ ) interface circuit. The fully CMOS compatible single-sided micromachining process with toroidal shaped electrical isolation structures is described. A 2.6 mm $\times2.6$ mm sized triaxis accelerometer was designed and fabricated using only the front side of a 4-in (111) silicon wafer. The interface circuit was based on a front-end ASIC readout circuit and a back-end dual quantization high-order EM-SDM digital circuit implemented on an FPGA. The EM- $\Sigma \Delta {\mathrm{ M}}$ loop adopts a multifeedback noise shaping architecture, for which different numbers of bits for the loop quantization were analyzed. The parameters of the EM- $\Sigma \Delta {\mathrm{ M}}$ loop are optimized by a genetic algorithm. Acceleration sensitivities of 170 mV/g (2785 LSB/g), 142 mV/g (2327 LSB/g), and 26 mV/g (426 LSB/g) were measured in EM- $\Sigma \Delta {\mathrm{ M}}$ closed-loop operation for the in-plane (X/Y) and out-of-plane (Z) axes, respectively. The cross-axis sensitivity was in the order of 1%–6% and the output noise was 0.5 mg–2 mg/ $\surd $ Hz, with a 1-h bias drift of 3–6 mg.

A closed-loop interface for capacitive micro-accelerometers with pulse-width-modulation force feedback

This paper presents an electromechanical closed-loop interface for the high performance capacitive micro-accelerometer. To overcome the problem that the linearity of the traditional analogue force feedback scheme is sensitive to the mismatch in the MEMS transducer, a pulse-width-modulation (PWM) force feedback method is developed in this paper. Elaborate non-linearity analysis of the PWM force feedback and a comparison with traditional analog feedback method is presented. A prototype interface circuit is designed and fabricated in a standard 0.35 μm CMOS process which measures 6.25 mm2. The noise floor of the system is 10 μg/√Hz and the signal bandwidth is 1.2 kHz, respectively. The system shows a DC nonlinearity of 1.6‰ without extra linearization circuit with an input range of ± 1.4 g when interface to a commercial accelerometer device.

A High-Voltage Closed-Loop SC Interface for a ± 50 g Capacitive Micro-Accelerometer With 112.4 dB Dynamic Range

A low-noise high-linearity switched capacitor interface implemented in a 0.35$\mu \text {m}$ 3.3 V/15 V CMOS process is presented in this paper for a ±50g capacitive micro-accelerometer. The sensing element is enclosed in an optimized closed loop with proportional-integral compensation, improving the linearity significantly. In order to suppress the flicker noise of the front-end at the lowest cost, a novel switched capacitor PI controller combined with a charge sensitive amplifier using correlated double sampling is proposed. Furthermore, a detailed noise analysis of the proposed CSA-PIC combination with a final goal of achieving 120 dB dynamic range is also presented. The theoretical analysis is verified by the consistency between calculated results and PNoise simulation results. The sensor output can be read in analogue domain from a sample-and-hold buffer or in digital domain from a back-end 2-1 MASH $\Sigma$ -$\Delta$ ADC. The fabricated prototype circuit measures 11.75 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and operates under 15-V and 3.3-V supplies at a sampling clock of 111 KHz. Meanwhile, a sensitivity of 99.7 mV/g is achieved with a dynamic range of 112.4 dB over a 200-Hz bandwidth. The accelerometer has a DC nonlinearity of 0.623 in the range of -18 g to +14 g measured in self-test mode and the bias instability is 200 $\mu \text {g}$ .

Improving the dynamic performance of capacitive micro-accelerometer through electrical damping

Damping ratio and natural frequency are key design parameters to improve the dynamic performance of a micro-accelerometer. Considering the difficulty of improving the dynamic performance of current micro-accelerometers by adjusting the mechanical damping, in this paper, an electrical damping based on a proportional-integrative (PI) controller is introduced into the readout circuit to improve the dynamic performance of a capacitive micro-accelerometer. An equivalent mathematical model is established to describe the overshoot and setting time, and the proportional constant (P) ant the integrative constant (I) are derived to obtain a rational damping ratio and natural frequency. The dynamic response of a bulk micromachined silicon accelerometer is experimentally measured and the results agree with the numerical simulations, indicating that the stability and the response speed can be improved by a proper combination of P and I of the controller.

A low-distortion ΣΔ capacitive microaccelerometer with self-test circuit

A low-distortion ΣΔ capacitive microaccelerometer with self-test circuit

Hand arm vibration measurement using micro-accelerometer in different brick structures

Hand-Arm Vibration Syndrome (HAVS) is a group of diseases caused by exposure of the hands to vibration while operating the hand held power tools such as road breaker, drilling machine, demolition hammer in construction works. In this paper, area-changed capacitive micro-accelerometer is designed to measure the vibration exposure on worker\'s hand when operating a drilling machine on various blocks such as clay block, paver block and solid cement block. The design process includes mathematical modelling of micro-accelerometer and simulations are done using INTELLISUITE 8.6. Experimental results are taken for various blocks surfaces using conventional and micro-accelerometer. Comparisons show that usage of area-changed micro-accelerometer for Hand-arm vibration monitoring provides better sensitivity, which in turn reduces the risk of HAVS in workers.

High-Performance Closed-Loop Interface Circuit for High-Q Capacitive Microaccelerometers

High-Q sensory microsystems are desirable especially in low noise applications. However this makes implementation of the closed-loop control a great challenge. An in-depth investigation into high-performance closed-loop interface circuit design for high-Q capacitive microaccelerometers is presented. Focus is placed on an analogue force feedback scheme with proportional-derivative compensation. Such an approach is differing from the commonly used electromechanical Δ Σ technique, since the latter one often suffers severe problems in balancing between the loop stability and other essential characteristics in the presence of high-Q sensing element. A comprehensive analysis concerning the system linearity and bandwidth is conducted, aiming for performance optimization. The adverse impact arising from several electronic noise sources in the system is studied in order for minimization. Accordingly, a prototype interface circuit is designed and fabricated in a commercial 0.35-μm CMOS process. The chip measures 2.5×2.5 mm2 and operates from a single 5 V supply. The quiescent current is about 10 mA. The test results show that it offers a full scale acceleration of ±1.2 g correspondingly with integrated non-linearity (INL) of 6.6%, wide-band noise equivalent acceleration of nearly 1 μg/√Hz over a signal bandwidth of about 1.2 kHz.

Structure Design of a Novel Triaxial Micro-Accelerometer

This paper reports a new capacitive triaxial micro-accelerometer which consists of four identical dual beam-mass structure. Considering the temperature characteristic, beam consistency and zero bias and other factors of the accelerometer, the arrangement and anchor position, as well as matching capacitor are studied using ANSYS software to complete the design of the overall structure of the accelerometer. The research methed having been uesd is significant for optimizing structure of the micro-accelerometer.

Review and Prospect for the Land Seismic Data Acquisition System

Essential characteristics of the seismic data acquisition system should make it capable of measuring high fidelity Seismic data，which can be used for geophysicists to fulfill a geological task. New developments of high technology in Micro-electronics and computer industries, including the extremely low-noise capacitive micro-accelerometer sensor, 24 bits A/D conversion, new generation wireless data transmission, etc. are introduced to the seismic data acquisition system to meet the requirement for global oil and gas exploration. New type of acquisition system faces the new exploration techniques, methods and tasks.

Multi-Fields Simulation Model for Micro-Machined Capacitive Accelerometer

To cope with the multi-physics fields simulation in MEMS device, based on PSPICE software, a multi-fields simulation model of capacitive micro-accelerometer is proposed, in which the mechanics, thermal and electric fields are included. Through the comparison of maximum step and pulse acceleration response under large displacement condition, which are obtained by simulation model and classic formula respectively, it is indicated that the difference between them is less than 3%. Furthermore, the comparison has been done with sensitivity test results in open loop mode. The comparison results show that the difference is less than 5% for large displacement situation and 3% for little displacement situation. Hence, the model could basically accomplish multi-physics fields simulation in MEMS device and be helpful in further research.

Design, modeling and analysis of highly reliable capacitive microaccelerometer based on circular stepped-plate and small-area touch mode

A novel capacitive microaccelerometer is designed which can operate reliably under high load. The movable structure of the microaccelerometer is a stepped circular plate which is fully compliant. Touch mode is introduced into the microaccelerometer, and small-area touch mode as a novel touch mode for MEMS is developed without the use of dielectric layer. A switch electrode is located on the substrate to prevent the short circuit of variable capacitor’s electrodes. Accurate, time saving and memory space saving models are developed with a new numerical method and validated with finite element method and boundary element method. Electrostatic force is taken into account, so the touch analysis includes an electromechanical coupling analysis. Internal mechanical force such as thermal stress and residual stress which will induce abnormal operation also is taken into account. The novel microaccelerometer’s performance is analyzed, verifying the device’s reliability, verifying the developed models’ availability for performance analysis over full measurement range.

Design and Simulation of a Capacitive Biaxial Microaccelerometer

This paper presents a capacitive biaxial microaccelerometer with a single proof mass. The theoretical analysis results are confirmed by finite element analysis. The experimental results indicate the biaxial accelerometer with uniform axial sensitivities, good linearity and high cross-axis sensitivity immunity to the z-axis input.

Research on Low Power Sigma-Delta Interface Circuit used in Capacitive Micro-accelerometers

Accelerometers have a wide range application in many fields, such as airbag deployment system and electronic stability control system in vehicles, and inertial navigation system in aircrafts and rockets. As Micro-Electro-Mechanical System (MEMS) technology advances, accelerometers are made smaller and smaller, often integrated in a single chip, with lower implementation costs and power consumptions. Modern MEMS accelerometers can be used in portable devices such as cell phones, RFID tags and even integrated in other sensors. This paper presents chip-level design and implementation of a second order sigma-delta interface circuit used in capacitive micro-accelerometers. The interface circuit provides 1-bit data stream and operates at a sampling frequency of 2.5MHz. The system model considers non-ideal factors in the circuit such as nonlinear distortion and noises. These non-ideal factors have been discussed through system level simulation in MATLAB. The micro-accelerometer, which is a highly integrated MEMS device, is then designed and implemented in silicon-on-insulator (SOI) substrate. Finally, the chip-level layout of interface circuit is implemented. Results have shown the chip with area of 1.32mm 2 and power consumption of about 5mW.

Genetic Algorithm Based Multidisciplinary Design Optimization of MEMS Accelerometer

Multidisciplinary design optimization of a biaxial capacitive micro-accelerometer with the crab-leg flexural suspension is discussed. Considering the influence of microstructure design, fabrication process and detection circuit, as well as the constraints of fabrication limitations, damp design and adhesion factor, a multidisciplinary optimization model is developed by global criterion method. Furthermore, genetic algorithm is applied to obtain the multi-objective optimum of the proposed multidisciplinary design model.

A High–G Metal Capacitive Microaccelerometer with Round Proof Mass Supported by Multi-Beam

In this paper, differential capacitors sandwiched structure of a high-G capacitive microaccelerometer with round metal proof mass supported by multi-beam and its characteristic are presented. The operation principle and built-in self-calibration and self-test functions are described. The fabrication process and the fabricated chip of the microaccelerometer based on UV-LIGA technology are reported. The detection and closed-loop control circuits of the microaccelerometer are designed and calibrated. The range of the detection channel is ±6pF, the sensitivity is 89.3mV/pF, and the linearity is 2.59%.

A Biaxial Capacitive Microaccelerometer with a Single Proof-Mass

This work focuses on the development of a biaxial fully differential capacitive microaccelerometer with a single proof-mass. Its design, optimization and fabrication are discussed in detail. Structure and geometric parameters are optimized by multidisciplinary design optimization, enabling ±1g operating range, 1182Hz resonant frequency, 97 fF/g sensitivity, 4.1mg resolution and 0.68 damping ratio. Silicon-on-glass (SOG) bulk micromachining and inductively coupled plasma (ICP) etching technologies are adopted to fabricate this accelerometer.

Design and Implementation of SOI Based Capacitive Microaccelerometers Without Notching Effects

We report our efforts towards designing and fabricating capacitive microaccelerometers with flat bottom surfaces free from the notching effects of Deep Reactive Ion Etching (DRIE) based on SOI process. The substrate layer under the device structure is etched and a metal film is deposited to the backside of moving structure for protecting the bottom surfaces so that the stiction problem and notching effects are avoided. The test results demonstrate that SOI accelerometers have been released successfully. The measured sensitivity is 169.1mV/g and the linearity of output is within 0.202%.