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]

An Acceleration Sensing Method Based on the Mode Localization of Weakly Coupled Resonators

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.

A Resonant Microaccelerometer With High Sensitivity Operating in an Oscillating Circuit

An analysis of the dynamic characteristics of pull-in for parallel-plate and torsional electrostatic actuators is presented. Traditionally, the analysis for pull-in has been done using quasi-static assumptions. However, it was recently shown experimentally that a step input can cause a decrease in the voltage required for pull-in to occur. We propose an energy-based solution for the step voltage required for pull-in that predicts the experimentally observed decrease in the pull-in voltage. We then use similar energy techniques to explore pull-in due to an actuation signal that is modulated depending on the sign of the velocity of the plate (i.e., modulated at the instantaneous mechanical resonant frequency). For this type of actuation signal, significant reductions in the pull-in voltage can theoretically be achieved without changing the stiffness of the structure. This analysis is significant to both parallel-plate and torsional electrostatic microelectromechanical systems (MEMS) switching structures where a reduced operating voltage without sacrificing stiffness is desired, as well as electrostatic MEMS oscillators where pull-in due to dynamic effects needs to be avoided.

Dynamic pull-in of parallel plate and torsional electrostatic MEMS actuators.

We report a new silicon Microelectromechanical systems (MEMS) accelerometer based on differential frequency modulation (FM) with experimentally demonstrated thermal compensation over a dynamic temperature environment and $\mu g$ -level Allan deviation of bias. The sensor architecture is based on resonant frequency tracking in a vacuum packaged silicon-on-insulator (SOI) tuning fork oscillator. To address drift over temperature, the MEMS sensor die incorporates two identical tuning forks with opposing axes of sensitivity. Demodulation of the differential FM output from the two simultaneously operated oscillators eliminates common mode errors and provides an FM output with continuous thermal compensation. The first SOI prototype with quality factor of 350000 was built and characterized over a temperature range between 30 °C and 75 °C. Temperature characterization of the FM accelerometer showed less than a 0.5% scale-factor change throughout a temperature range from 30 °C to 75 °C, without any external compensation. This is enabled by an inherently differential frequency output, which cancels common-mode influences, such as those due to temperature. Allan deviation of the differential FM accelerometer revealed a bias instability of $6\,\, \mu \text{g}$ at 20 s, along with an elimination of any temperature drift due to increases in averaging time. After comparing the measured bias instability with the designed linear range of 20 g, the sensor demonstrates a wide dynamic range of 130 dB. A second design iteration of the FM accelerometer, vacuum-sealed with getter material, was created to maximize $Q$ -factor, and thereby frequency resolution. A $Q$ -factor of 2.4 million was experimentally demonstrated, with a time constant of >20 min.

High Quality Factor Resonant MEMS Accelerometer With Continuous Thermal Compensation

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.

Post-CMOS Compatible Aluminum Nitride Resonant MEMS Accelerometers.

A microelectromechanical detection structure (1; 1') for a MEMS resonant biaxial accelerometer (16) is provided with: an inertial mass (2; 2'), anchored to a substrate (30) by means of elastic elements (8) in such a way as to be suspended above the substrate (30), the elastic elements (8) enabling inertial movements of detection of the inertial mass (2; 2') along a first axis of detection (x) and a second axis of detection (y) that belong to a plane (xy) of main extension of said inertial mass (2; 2'), in response to respective linear external accelerations (a x , a y ); and at least one first resonant element (10a) and one second resonant element (10b), which have a respective longitudinal extension, respectively along the first axis of detection (x) and the second axis of detection (y), and are mechanically coupled to the inertial mass (2; 2') through a respective one of the elastic elements (8) in such a way as to undergo a respective axial stress (N 1 , N 2 ) when the inertial mass moves respectively along the first axis of detection (x) and the second axis of detection (y).

Resonant biaxial accelerometer structure of the microelectromechanical type

The present invention relates to a microelectromechanical structure, and more specifically relates to a system, device and method which employ and adjust an elastic element used for connecting a movable testing mass to an anchoring part to compensate the thermodynamic stress The testing mass makes a response to the acceleration through moving or inclining in relative to a rotation axial line of a movable mass block The thermodynamic stressaccumulates in the manufacturing, packaging and assembling process or in the entire life of a structure The stress contributes to the displacement of the mass block A plurality of elastic elements are connected to form a supporting testing mass The geometric shapes and structures of the elastic elements are adjusted to reduce the displacement caused by the thermodynamic stress

Microelectromechanical structure having low sensitivity on thermodynamic stress

In a microelectromechanical device (1), a mobile mass (2) is suspended above a substrate (3) via elastic suspension elements (5), and is rotatable about said elastic suspension elements (5), a cover structure (10) is set above the mobile mass (2) and has an internal surface (10a) facing the mobile mass (2), and a stopper structure (12, 14) is arranged at the internal surface (10a) of the cover structure (10) and extends towards the mobile mass (2) in order to stop a movement of the mobile mass (10) away from the substrate (3) along an axis (z) transverse to the substrate (3). The stopper structure (12, 14) is arranged with respect to the mobile mass (2) so as to reduce an effect of reciprocal electrostatic interaction, in particular so as to minimize a resultant twisting moment of the mobile mass (2) about the elastic suspension elements (5).

Vertical movement microelectromechanical device with stopper structure

A microelectromechanical sensor that in one embodiment includes a supporting structure, having a substrate and electrode structures anchored to the substrate; and a sensing mass, movable with respect to the supporting structure so that a distance between the sensing mass and the substrate is variable. The sensing mass is provided with movable electrodes capacitively coupled to the electrode structures. Each electrode structure comprises a first fixed electrode and a second fixed electrode mutually insulated by a dielectric region and arranged in succession in a direction substantially perpendicular to a face of the substrate.

Barbara Simoni

Papers

Resonant biaxial accelerometer structure of the microelectromechanical type

Microelectromechanical structure having low sensitivity on thermodynamic stress

Vertical movement microelectromechanical device with stopper structure

Microelectromechanical sensor with out-of-plane sensing and process for manufacturing a microelectromechanical sensor

Multi-scale simulation of shock-induced failure of polysilicon MEMS