Single Proof Mass Research Articles

A comprehensive modeling of a 6-axis single proof mass MEMS-based piezoelectric IMU

A comprehensive modeling of a 6-axis single proof mass MEMS-based piezoelectric IMU

Design and simulation of a novel MEMS-based single proof mass three-axis piezo-capacitive accelerometer

Design and simulation of a novel MEMS-based single proof mass three-axis piezo-capacitive accelerometer

Graphene Coated Liquid Metal Droplet‐Enabled Dual‐Axis Integrated Accelerometer

AbstractThis paper presents the design, optimization, fabrication, and characterization of a novel accelerometer consisting of a graphene‐coated liquid metal proof mass integrated with laser‐induced graphene (LIG) resistive sensing elements. The sensor utilizes the unique electromechanical properties of eutectic gallium‐indium (EGaIn) liquid metal by confining an EGaIn droplet within a graphene‐patterned 3D pyramid cavity. The pyramid base structure imposes a restoring force on the droplet enabling continuous and simultaneous sensing in two directions using a single proof mass. Coating EGaIn droplet with graphene forms an interpenetrated protective shell around the droplet, enhancing its mobility and mechanical robustness. Design optimization of the sensing microelectrodes is performed to improve the sensor performance. The accelerometer performance is evaluated and characterized, demonstrating a sensitivity of ≈9.5 kΩ g−1 (978 Ω m−1 s2) and a cross‐axis sensitivity of ≈3 % with excellent repeatability (over 120 000 cycles). The sensor is fabricated using a scalable laser writing technique and integrated with a programmable system on a chip (PSoC) to function as a stand‐alone system for real‐time wireless motion monitoring and virtual game control. The developed Graphene/Liquid metal droplet‐based sensor is promising for applications of inertial sensors, inertial switches, and soft liquid metal robots with attractive electromechanical properties.

Effect of various shapes of single proof mass and multiple proof masses on piezoelectric energy harvester for powering mobile phone devices

In this work, Type I and II Piezoelectric structures are analyzed with the effect of the single and multiple shapes of proof masses (two proof mass and three proof mass). Eight different shapes of proof masses are considered in this study. The main objective of the work is to determine the maximum power generated by the piezoelectric harvester at a lower frequency for powering mobile phone devices. A comparison analysis is carried out for Type I and II structures, in which the Type II structure with multiple proof mass-three proof mass, generates maximum power at lower frequency (121mW, 78 Hz) respectively.

A Low-g MEMS Accelerometer with High Sensitivity, Low Nonlinearity and Large Dynamic Range Based on Mode-Localization of 3-DoF Weakly Coupled Resonators.

This paper presents a new design of microelectromechanical systems (MEMS) based low-g accelerometer utilizing mode-localization effect in the three degree-of-freedom (3-DoF) weakly coupled MEMS resonators. Two sets of the 3-DoF mechanically coupled resonators are used on either side of the single proof mass and difference in the amplitude ratio of two resonator sets is considered as an output metric for the input acceleration measurement. The proof mass is electrostatically coupled to the perturbation resonators and for the sensitivity and input dynamic range tuning of MEMS accelerometer, electrostatic electrodes are used with each resonator in two sets of 3-DoF coupled resonators. The MEMS accelerometer is designed considering the foundry process constraints of silicon-on-insulator multi-user MEMS processes (SOIMUMPs). The performance of the MEMS accelerometer is analyzed through finite-element-method (FEM) based simulations. The sensitivity of the MEMS accelerometer in terms of amplitude ratio difference is obtained as 10.61/g for an input acceleration range of ±2 g with thermomechanical noise based resolution of 0.22 and nonlinearity less than 0.5%.

A Novel Design of High Resolution MEMS Gyroscope Using Mode-Localization in Weakly Coupled Resonators

This paper presents a novel design for a high resolution microelectromechanical systems (MEMS) technology based resonant gyroscope using the mode-localization effect in weekly coupled resonators (WCRs) as a mechanism for sensing the input angular rate. The design consists of a single proof mass with two three degree-of-freedom (3-DoF) WCRs systems attached on either side. The MEMS gyroscope is designed according to the microfabrication constraints of the foundry process, silicon-on-insulator multi-user MEMS process (SOIMUMPs). The shift in the resonance frequency values, amplitude ratios of the WCRs, and amplitude ratios difference of two sets due to electrostatic stiffness perturbation, corresponding to the input angular rotation, are discussed as an output metric for the measurement of angular rate. The results show that the amplitude ratio difference as an output metric allows to achieve a linear output response and large dynamic range in comparison to the shift in the amplitude ratio and resonance frequency in 3-DoF WCRs in a single set. The dynamic range and resolution of the MEMS gyroscope in terms of maximum allowed resonators amplitude and noise floor is discussed. The proposed MEMS gyroscope design has a sensitivity of 62830 ppm/°/s based on a difference in the amplitude ratios of resonators in two 3-DoF WCRs systems and a dynamic range of ±100 °/s. The resolution of the MEMS gyroscope is 31.09 × 10-6 °/s which is significantly higher than existing MEMS gyroscopes and is comparable to traditional bulky ring laser gyroscopes. This high resolution makes the proposed MEMS gyroscope design suitable for use in applications such as earth rotation rate measurement for gyrocompassing and high precision robotics.

Meandering-trapezoidal shaped MEMS structure for low frequency vibration based energy harvesting applications

In this study, we explore the design of new two highly symmetric springs of Meandering-Trapezoidal shaped microelectromechanical system (MEMS) structure based biosensor application with a single proof mass for low frequency vibration based energy harvesting applications. The related harvester design and output were obtained and validated by means of finite elements analysis (FEA) and finite element method (FEM) simulations. We use four different kind of piezoelectric material such as PZT-5A, ZnO, AlN, PVDF on the same dimension of Meandering-Trapezoidal shaped springs and analyze the FEA and FEM output. The maximum output power using PZT-5A, ZnO, AlN, PVDF piezoelectric materials are 117.55 nW, 44.37 nW, 10.58 nW, 0.55 nW over 35.9 Hz, 40.7 Hz, 49.7 Hz, 29.7 Hz resonant frequency, respectively at input acceleration of 0.1 g. From the comparative study, we obtain that piezoelectric material PZT-5A on Meandering-Trapezoidal spring design imply better potential generation.

Capacitive‐Type Two‐Axis Accelerometer with Liquid‐Type Proof Mass

AbstractUtilizing the advantages of a liquid metal (LM) (i.e., mercury) and its electro‐mechanical properties (i.e., high density, high surface tension, and high electrical conductivity), a novel capacitive‐type two‐axis accelerometer is proposed. The device employs a liquid‐type proof mass (i.e., liquid metal droplet) and is located in a cone‐shaped guiding channel. The Laplace pressure induced by the guiding channel and the LM droplet in the device acts as a spring due to the high surface tension of LM. To accurately set the spring constant of the device, a 2D mathematical model is established. Based on this mathematical model, the influence of the channel shape on device sensitivity is analyzed. Despite measuring the two‐axis accelerations using a single proof mass, the accelerometer yields a cross‐axis sensitivity of less than 1% for the x‐ and y‐axes. The accelerometer demonstrates an output similar to that of a reference accelerometer for a randomly applied acceleration. Owing to the nature of the liquid‐type proof mass, even if it is destroyed, its functionality is recovered by simply shaking the accelerometer. Finally, a 1.4% change in the accelerometer output is observed in the 15 000‐cycle test, and the device is applied to a maze escape game for verification.

Duplex mode tilt measurements based on a MEMS biaxial resonant accelerometer

This paper firstly reports the duplex mode tilt measurements (biaxial tilt measurement with small angle range and uniaxial tilt measurement with large angle range) based on a micro electromechanical system (MEMS) biaxial resonant accelerometer. For the accelerometer, two pairs of double-ended tuning fork (DETF) resonators are the sensing elements and they are integrated with a single proof mass. The two-stage microleverage mechanisms, possessing higher amplification factor, amplify and translate the weight component to the resonators. The adoption of decoupling beams lower the cross impact and allow the simultaneous differential measurement of tilt angles acting along two orthogonal axes. Based on the biaxial sensing structure, the biaxial tilt measurement is realized on the two orthogonal sensing axes. By the combination of the four DETFs resonant frequencies at each angular position, the linear range of uniaxial tilt measurement is extended. For the biaxial tilt measurement with small angle range, the experiments demonstrate a high sensitivity (X-axis: 4.351 Hz/deg and Y-axis: 5.257 Hz/deg) and a low cross-axis sensitivity (X-axis: 0.180 Hz/deg and Y-axis: 0.202 Hz/deg) for a ±40° biaxial tilt angle range. For the uniaxial tilt measurement with large angle range, the device shows an average sensitivity of 3.973 Hz/deg for a ±90° range. In addition, the close-loop self-oscillation is realized and the minimum Allan deviation of 68 ppb is obtained. The performance makes the device a potentially attractive option for compact, multi-functional and highly-sensitive tilt measurements.

Proof-of-principle demonstration of vertical-gravity-gradient measurement using a single-proof-mass double-loop atom interferometer

We demonstrate a proof-of-principle of direct Earth gravity gradient measurement with an atom interferometer-based gravity gradiomter using a single proof mass of cold 87 rubidium atoms. The atomic gradiometer is implemented in the so-called double-loop configuration, hence providing a direct gravity gradient dependent phase shift insensitive do DC acceleration and constant rotation rate. The atom interferometer (AI) can be either operated as a gravimeter or a gradiomter by simply adding an extra Raman $\pi$-pulse. We demonstrate gravity gradient measurements first using a vibration isolation platform and second without seismic isolation using the correlation between the AI signal and the vibration signal measured by an auxilliary classical accelerometer. The simplicity of the experimental setup (a single atomic source and unique detection) and the immunity of the AI to rotation-induced contrast loss, make it a good candidate for onboard gravity gradient measurements.

Monolithic Multi Degree of Freedom (MDoF) Capacitive MEMS Accelerometers.

With the continuous advancements in microelectromechanical systems (MEMS) fabrication technology, inertial sensors like accelerometers and gyroscopes can be designed and manufactured with smaller footprint and lower power consumption. In the literature, there are several reported accelerometer designs based on MEMS technology and utilizing various transductions like capacitive, piezoelectric, optical, thermal, among several others. In particular, capacitive accelerometers are the most popular and highly researched due to several advantages like high sensitivity, low noise, low temperature sensitivity, linearity, and small footprint. Accelerometers can be designed to sense acceleration in all the three directions (X, Y, and Z-axis). Single-axis accelerometers are the most common and are often integrated orthogonally and combined as multiple-degree-of-freedom (MDoF) packages for sensing acceleration in the three directions. This type of MDoF increases the overall device footprint and cost. It also causes calibration errors and may require expensive compensations. Another type of MDoF accelerometers is based on monolithic integration and is proving to be effective in solving the footprint and calibration problems. There are mainly two classes of such monolithic MDoF accelerometers, depending on the number of proof masses used. The first class uses multiple proof masses with the main advantage being zero calibration issues. The second class uses a single proof mass, which results in compact device with a reduced noise floor. The latter class, however, suffers from high cross-axis sensitivity. It also requires very innovative layout designs, owing to the complicated mechanical structures and electrical contact placement. The performance complications due to nonlinearity, post fabrication process, and readout electronics affects both classes of accelerometers. In order to effectively compare them, we have used metrics such as sensitivity per unit area and noise-area product. This paper is devoted to an in-depth review of monolithic multi-axis capacitive MEMS accelerometers, including a detailed analysis of recent advancements aimed at solving their problems such as size, noise floor, cross-axis sensitivity, and process aware modeling.

A low-g MEMS inertial switch with a novel radial electrode for uniform omnidirectional sensitivity

A low-g MEMS inertial switch with uniform omnidirectional sensitivity is designed and fabricated for automotive airbags in this paper. The design objective acceleration of the switch is about 38g. By adopting the combination of Archimedes’ spirals and a single circular proof mass as the mass-spring system, the switch can sense the applied accelerations from any radial directions in XOY plane. To obtain a good omnidirectional performance, a novel radial electrode with a spherical contact surface and novel serpentine springs is designed, and limitation blocks are beside it. The omnidirectional response of the switch is simulated and analyzed by ANSYS software. The simulated result indicates that the novel radial electrodes are conducive to achieve the uniform thresholds in all sensitive directions, and the switch can reach a reliable contact because of the novel serpentine spring. The switch is fabricated based on non-silicon surface micromachining technology. To decrease the deviation of threshold acceleration induced by fabrication errors of crucial dimensions, a new method of “thickness compensation” is proposed. The fabricated prototypes were tested by the centrifuge device and dropping hammer. The switch can be triggered under an acceleration of about 40g from any directions in XOY plane and has an excellent anti-overload performance.

Design of serial linkage-type vibration energy harvester with three resonant frequencies

This paper presents a new design method of a planar 3 degrees-of-freedom(DOF) serial linkage-type vibration energy harvester with a single proof mass. The harvester is designed to generate electrical power at equally spaced three target resonant frequencies which can be chosen arbitrarily. For given target frequencies and a proof mass, the design method involves (1) the determination of the stiffness matrix, (2) the synthesis of the stiffness by means of a parallel connection of three line springs and (3) its conversion into a 3DOF device connected serially by torsional springs. The torsional springs are realized by the flexible hinge joints and the polyvinylidene fluoride(PVDF) films are attached on the joints. Upon determination of the desired stiffness matrix, the SQP algorithm is utilized to find the optimum locations and spring constants of the serial hinge joints for the minimum difference among three electrical power peaks. The FEM analysis and experiments are conducted to verify the proposed design method. Three measured resonant power peaks occur at 24.7, 30.4 and 33.6 Hz comparing to the target frequencies of 25, 30 and 35 Hz. The normalized maximum power of is generated at 24.7 Hz. The experimental results also demonstrate that the harvester can generate at least 18.6% of the peak power throughout the frequency range from 23.1 to 36.5 Hz, which ensures consistently acquirable power within the operating frequency range by virtue of the coupled effect of a serial linkage-type structure.

Double-Comb-Finger Design to Eliminate Cross-Axis Sensitivity in a Dual-Axis Accelerometer

We present a dual-axis accelerometer with zero cross-axis sensitivity. In general, multiaxis accelerometers with single proof-mass have multiple degrees of freedom, making them susceptible to high cross-axis sensitivity. In this article, a novel differential capacitive finger scheme is presented, which fully eliminates the in-plane cross-axis sensitivity at the device level. The proposed accelerometer is highly sensitive and has a differential capacitance scale factor of 80.97 fF/g (g = 9.8 m/s 2 ) over + 10 g range with a pull-in voltage of 6 V. Additionally, the out-of-plane motion due to acceleration in the Z-axis direction is significantly suppressed due to the high-spring constant in that direction. The device is fabricated in a compact footprint of 1.6 mm x 1.6 mm using GlobalFoundries' Inertial Measurement Unit (IMU) platform.

Design and simulations of a resonant accelerometer

A resonant accelerometer was designed and simulated in detail. The structure was composed of external frame and internal structure. The internal structure consists of a single proof mass, a pair of resonators and elastic beams. Structure design is implemented by taking advantage of the finite element analyses. From the simulation results we can see that the design of external frame, should ensure that the frame in line with the “beam” characteristics, and increase its stiffness under this condition. The design of internal structure, should ensure that the resonant beam stiffness, sensitivity, vertical vibration and range. Moreover, simulation results reveal the resonant accelerometer linearity is better under the condition of |F| < 5 N, the range is ±25 g and the sensitivity is 272.5 Hz/g. All these simulations above can verify the high performance accelerometer by simple and optimized structure design.

A high-sensitivity biaxial resonant accelerometer with two-stage microleverage mechanisms

This paper presents a design and experimental evaluation of a micro-electro-mechanical system biaxial resonant accelerometer with two-stage microleverage mechanisms. The device incorporates two pairs of double-ended tuning fork resonators coupled to a single proof mass. The two-stage microleverage mechanisms possess a higher amplification factor than single-stage microleverage mechanisms, so that the proposed accelerometer has a high level of sensitivity. In addition, a low level of cross-axis sensitivity is realized because of the decoupling beams. The accelerometer is theoretically analyzed and then simulated in the system level by the finite element method. The device is fabricated in a silicon-on-insulator wafer. The experimental results demonstrate that the average differential sensitivity of the resonant accelerometer is 275 Hz g−1 at a resonant frequency of 290 kHz under a polarization voltage of 5 V. The measured cross-axis sensitivity is lower than 3.4%.

Design and simulations of a new biaxial silicon resonant micro-accelerometer

This paper presents a new biaxial silicon resonant micro-accelerometer. The device basically consists of a single proof mass, four pairs of decoupled beams, four lever mechanisms and two pairs of resonators, which provides 2-D in-plane acceleration measurement with the decoupled two pairs of resonators. Structure optimization is implemented by taking advantage of the finite element analyses. From the simulation results we can see that the effective frequencies of two acceleration sensitive modes are 1010.18 and 1010.13 Hz respectively, and the undesired modes and effective modes are isolated apparently. Additionally, high linear relationship between the input acceleration and the resonant frequency shifts of resonators are demonstrated by the input---output characteristic simulation. Moreover, simulation results reveal the scale factor for the x-axis is 180.03 Hz/g, and the scale factor for y-axis is 180.75 Hz/g, while the cross-axis sensitivity for x-axis is 0.046 Hz/g, and the cross-axis sensitivity for y-axis is 0.027 Hz/g. The high sensitivity and low cross-axis sensitivity are thus adequately confirmed. By the way, the simulation of temperature dependent characteristics demonstrate that the differential scheme can effectively suppress the influence of temperature variation, and the thermal analysis shows that the device can bear the thermal stress induced by temperature change. All these simulations above can verify the feasibility of the structure design.

Micromachined Tri-Axis Capacitive Accelerometer Based on the Single Mass

A novel micromachined tri-axis capacitive accelerometer based on the single mass is proposed in this paper. The presented accelerometer contains a single proof mass acting as the sensitive element which is suspended by two flexible beams above the substrate, and an array of movable and fixed electrodes is utilized. To match the sensitivity design requirement, the differential capacitive detection is utilized, and the cross-sensitivity problem of three orthogonal axes is avoided ideally. The accelerometer structure is based on the EPI-poly process to realize the 18 microns thickness. Thus the detection capacitance, sensitivity and reliability are improved, the mechanical noise is decreased. To reduce the thermomechanical stress’ effect on the offset, a special anchor-middle structure is designed. Simulation results show that the offset is insensitive to the thermomechanical stresses and the sensor has a good consistency in three axes which has been validated by the testing results.

A Three-Axis Single-Proof-Mass CMOS-MEMS Piezoresistive Accelerometer with Frequency Outp

Accelerometers have been used in a wide range of applications such as automobiles, mobile phones, and game controllers. In this paper, we present a monolithic complementary metal-oxide-semiconductor micro-electromechanical systems (CMOSMEMS) accelerometer with frequency output. The output oscillation frequency can be converted to a digital code by using a counter so that the sensor can be easily integrated with digital signal processing units on the same chip. The accelerometer is composed of a single proof mass suspended by four suspension beams. Polysilicon piezoresistors are placed at the ends of the beams to sense the displacement of the proof mass. The piezoresistors are used in RC oscillators whose oscillation frequencies vary owing to the change in resistance upon application of an external acceleration. Acceleration components in three axes can be obtained by the proper combination of signals from the piezoresistors at different locations. The accelerometer was fabricated by standard CMOS processes followed by backside and frontside dry etching postprocessing. The measured mechanical resonant frequency is 464 Hz. The oscillation frequency of the z-axis oscillator is about 70 MHz. The measured absolute sensitivity, relative sensitivity, and resolution along the z-axis are 198 kHz/g, 2.8×10−3 ∆f/f0/g, and 10.9 mG/ Hz , respectively, for a sampling rate of 400 Hz and acceleration of 6 g at 27 Hz.

A Three-Axis CMOS-MEMS Accelerometer Structure With Vertically Integrated Fully Differential Sensing Electrodes

This study presents a novel CMOS-microelectromechanical systems (MEMS) three-axis accelerometer design using Taiwan Semiconductor Manufacturing Company 0.18-μm one-poly-Si six-metal/dielectric CMOS process. The multilayer metal and dielectric stacking features of the CMOS process were exploited to vertically integrate the in-plane and out-of-plane capacitive sensing electrodes. Thus, the three-axis sensing electrodes can be integrated on a single proof mass to reduce the footprint of the accelerometer. Moreover, the fully differential gap-closing sensing electrodes among all three axes are implemented to increase the sensitivities and decrease the noise. The in-plane and out-of-plane sensing gaps are respectively defined by the minimum metal line width and the thickness of one metal layer by means of the metal wet-etching post-CMOS process. Thus, the capacitive sensitivities are further improved. The fully differential gap-closing sensing electrodes also bring the advantage of reduced cross talks between all three axes. As a result, the footprint of the presented three-axis accelerometer structure is only 400 × 400 μm2. Compared with existing commercial or CMOS-MEMS studies, the size is significantly reduced. The measured sensitivities (nonlinearities) are 14.7 mV/G (3.2%) for the X-axis, 15.4 mV/G (1.4%) for the Y-axis, and 14.6 mV/G (2.8%) for the Z-axis.