A Resonant Microaccelerometer With High Sensitivity Operating in an Oscillating Circuit
13 Sep 2010-IEEE\/ASME Journal of Microelectromechanical Systems (IEEE)-Vol. 19, Iss: 5, pp 1140-1152
TL;DR: In this article, a micromachined uniaxial silicon resonant accelerometer characterized by a high sensitivity and very small dimensions is presented, which is based on the frequency variations of two resonating beams coupled to a proof mass.
Abstract: A new micromachined uniaxial silicon resonant accelerometer characterized by a high sensitivity and very small dimensions is presented. The device's working principle is based on the frequency variations of two resonating beams coupled to a proof mass. Under an external acceleration, the movement of the proof mass causes an axial load on the beams, generating opposite stiffness variations, which, in turn, result in a differential separation of their resonance frequencies. A high level of sensitivity is obtained, owing to an innovative and optimized geometrical design of the device that guarantees a great amplification of the axial loads. The acceleration measure is obtained, owing to a properly designed oscillating circuit. In agreement with the theoretical prediction, the experimental results show a sensitivity of 455 Hz/ ( g being the gravity acceleration) with a resonant frequency of about 58 kHz and a good linearity in the range of interest.
Citations
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TL;DR: In this paper, an acceleration sensing method based on two weakly coupled resonators (WCRs) using the phenomenon of mode localization was reported. But the proposed mode localization with the differential perturbation method leads to a sensitivity enhancement of a factor of 2 than the common single perturbations method.
Abstract: This paper reports an acceleration sensing method based on two weakly coupled resonators (WCRs) using the phenomenon of mode localization. When acceleration acts on the proof masses, differential electrostatic stiffness perturbations will be applied to the WCRs, leading to mode localization, and thus, mode shape changes. Therefore, acceleration can be sensed by measuring the amplitude ratio shift. The proposed mode localization with the differential perturbation method leads to a sensitivity enhancement of a factor of 2 than the common single perturbation method. The theoretical model of the sensitivity, bandwidth, and linearity of the accelerometer is established and verified. The measured relative shift in amplitude ratio ( $\sim 312162$ ppm/g) is 302 times higher than the shift in resonance frequency ( $\sim 1035$ ppm/g) within the measurement range of ±1 g. The measured resolution based on the amplitude ratio is 0.619 mg and the nonlinearity is $\sim 3.5$ % in the open-loop measurement operation. [2015-0247]
136 citations
Cites background or result from "A Resonant Microaccelerometer With ..."
...To enhance the sensitivity of resonant accelerometers, various designs with differential resonators [11], multistage leverage mechanism [13] and flexible resonant beams [4] have been reported....
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...Furthermore, the sensitivity based on the amplitude ratio is also ∼40 times higher than that of the resonant accelerometers reported in [4] (7845 ppm/g)....
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01 Aug 2008
TL;DR: In this article, a double-ended tuning-fork (DETF) accelerometer is used to measure the acceleration of a single-axis accelerometer with a measured sensitivity of 3.4 Hz/G and resolution of 0.9 mG/radicHz.
Abstract: This paper describes the development of aluminum nitride (AlN) resonant accelerometers that can be integrated directly over foundry CMOS circuitry. Acceleration is measured by a change in resonant frequency of AlN double-ended tuning-fork (DETF) resonators. The DETF resonators and an attached proof mass are composed of a 1-mum-thick piezoelectric AlN layer. Utilizing piezoelectric coupling for the resonator drive and sense, DETFs at 890 kHz have been realized with quality factors (Q) of 5090 and a maximum power handling of 1 muW. The linear drive of the piezoelectric coupling reduces upconversion of 1/f amplifier noise into 1/f 3 phase noise close to the oscillator carrier. This results in lower oscillator phase noise, -96 dBc/Hz at 100-Hz offset from the carrier, and improved sensor resolution when the DETF resonators are oscillated by the readout electronics. Attached to a 110-ng proof mass, the accelerometer microsystem has a measured sensitivity of 3.4 Hz/G and a resolution of 0.9 mG/radicHz from 10 to 200 Hz, where the accelerometer bandwidth is limited by the measurement setup. Theoretical calculations predict an upper limit on the accelerometer bandwidth of 1.4 kHz.
83 citations
01 Jan 2017
TL;DR: In this article, a temperature-compensated differential accelerometer fabricated in a wafer-scale encapsulation process is presented, which utilizes a pair of ultra-stable, high quality factor (>50,000) resonant beams as a strain gauge.
Abstract: This work demonstrates a unique temperature-compensated differential resonant accelerometer fabricated in a wafer-scale encapsulation process. By utilizing a pair of ultra-stable, high quality factor (>50,000) resonant beams as a strain gauge, we show differential operation with a scale factor of 427Hz/g and a bias instability of 0.16μg at 21s integration time. Furthermore, matched temperature coefficients of frequency (TCf) of the two beams provide a first order cancellation of temperature drift, resulting in a scale factor stability of 0.38% over the temperature range from −20°C to 80°C.
64 citations
Cites background from "A Resonant Microaccelerometer With ..."
...Prior work on resonant accelerometers [2,3] employs differential sensing schemes, but exhibits stress coupling instability from multiple anchor designs....
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...[2,3,4], this device adopts a single-point anchor design to eliminate frequency fluctuations due to external and package stress, which may otherwise be dominant error sources....
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TL;DR: In this article, a double-ended-tuning fork resonator accelerometer was proposed for low-frequency, low-g acceleration measurement with a scale factor of 1153.3 and bias stability of 58 ppb.
Abstract: According to their inherent characteristics, MEMS resonant accelerometers are suitable for low-frequency, low-g acceleration measurement. In this paper, we report a MEMS accelerometer based on double-ended-tuning fork resonators. The scale factor of our sensor is 1153.3 Hz/g and the bias stability of the oscillator is 58 ppb (parts per billion) for an averaging time of 1 s. The static test showed that the resolution of our sensor was 13.8 μg. The dynamic performance was demonstrated by single-frequency and hybrid-frequency vibration tests, and the results showed that our device is suitable for detecting low-frequency vibration (0.5–5 Hz). The cross-axis sensitivity is 1.33%. Compared with a standard charge accelerometer, our device showed its superiority in mixed acceleration measurement, which makes it a potentially attractive option for geophone or seismometer applications.
58 citations
TL;DR: In this paper, the authors investigated the energy loss through the anchor of a hemispherical shell resonator using a numerical approach and found that anchor loss strongly depends on the shell, stem, and substrate properties.
Abstract: Micromachined hemispherical shell resonators (HSRs) can be used in high accuracy vibratory gyroscopes. These resonators need to have very low energy loss to achieve very high quality factor. Energy might be lost through the anchor, fluid-structure interaction, thermoelastic dissipation, phonon-phonon and phonon-electron interactions, and the resonator surface. This paper investigates energy loss through the anchor of HSRs using a numerical approach. To numerically determine wave radiation from the anchor to the infinite substrate, a perfectly matched layer is used around a finite substrate. Anchor loss investigations in HSRs are classified into four categories. First, the effects of shell properties-material, geometry, and imperfections-are investigated. Second, the relationships between anchor loss and properties of the stem, such as material, geometry, and stemshell misalignments, are studied. Third, the effects of substrate characteristics-substrate material, attachment material between the stem and substrate, and attachment configuration of the substrate and stem-are investigated. Finally, the effects of external motions, such as shock and rotation, are analyzed. It is found that anchor loss in HSRs strongly depends on the shell, stem, and substrate properties. This study also shows that any imperfection in the shell or any misalignment between the shell and stem increases anchor loss by orders of magnitude.
56 citations
Cites methods from "A Resonant Microaccelerometer With ..."
...MEMS RESONATORS are used in different applications such as accelerometers [1], [2], gyroscopes [3], [4], timing references [5], [6], infrared detectors [7], [8], and RF components [9], [10]....
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548 citations
"A Resonant Microaccelerometer With ..." refers methods in this paper
...The accelerometers are packed at low pressure (1 mbar) with getter to maintain degassing in the MEMS cavity, thus limiting fluid damping and ensuring a reasonably high quality factor on the order of 200....
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TL;DR: In this article, a monolithic high-Q oscillator, fabricated via a combined CMOS plus surface micromachining technology, is described, for which the oscillation frequency is controlled by a polysilicon micromechanical resonator with the intent of achieving high stability.
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"A Resonant Microaccelerometer With ..." refers background in this paper
...2, one can observe that the optimal position for the resonator is very close to the anchor point of the spring at about one-sixtieth of its length....
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TL;DR: In this article, the authors analyzed the nonlinear effects of single-crystal silicon micro-resonators with the focus on mechanical nonlinearities and showed that the higher energy density attainable with the silicon resonators can partially compensate for the small microresonator size.
Abstract: Nonlinear effects in single-crystal silicon microresonators are analyzed with the focus on mechanical nonlinearities. The bulk acoustic wave (BAW) resonators are shown to have orders-of-magnitude higher energy storage capability than flexural beam resonators. The bifurcation point for the silicon BAW resonators is measured and the maximum vibration amplitude is shown to approach the intrinsic material limit. The importance of nonlinearities in setting the limit for vibration energy storage is demonstrated in oscillator applications. The phase noise calculated for silicon microresonator-based oscillators is compared to the conventional macroscopic quartz-based oscillators, and it is shown that the higher energy density attainable with the silicon resonators can partially compensate for the small microresonator size. Scaling law for microresonator phase noise is developed.
403 citations
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332 citations
TL;DR: In this paper, the authors describe the operation of a vacuum packaged resonant accelerometer subjected to static and dynamic acceleration testing and show that it exhibits a noise floor of 40 /spl mu/g/g//spl radic/(Hz) for an input acceleration frequency of 300 Hz.
Abstract: This paper describes the operation of a vacuum packaged resonant accelerometer subjected to static and dynamic acceleration testing. The device response is in broad agreement with a new analytical model of its behavior under an applied time-varying acceleration. Measurements include tests of the scale factor of the sensor and the dependence of the output sideband power and the noise floor of the double-ended tuning fork oscillators as a function of the applied acceleration frequency. The resolution of resonant accelerometers is shown to degrade 20 dB/decade beyond a certain characteristic acceleration corner frequency. A prototype device was fabricated at Sandia National Laboratories and exhibits a noise floor of 40 /spl mu/g//spl radic/(Hz) for an input acceleration frequency of 300 Hz.
319 citations