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Two methods for limiting the oscillation amplitude in micromechanical resonators, typically used in many kinds of MEMS sensors, are discussed and compared. First, it is shown how the presence of parasitic capacitances sets several constraints on the design of the oscillating circuit gain and bandwidth. The paper specifically focuses on the case of a transimpedance based oscillator coupled to a clamped-clamped beam, that forms the sensing element of a resonant accelerometer. Experimental results then show that the oscillating amplitude can be limited either using an electronic limiting stage, or exploiting the mechanical nonlinearities of the beam for large displacements. Though the latter approach is advantageous in terms of power dissipation, it is shown that the sensitivity of the resonant accelerometer is strongly compromised.

This work presents novel Capacitive Micromachined Ultrasonic Transducers (CMUTs) and their characterization in terms of ultrasound directionality. The devices are formed by 27 membranes, integrated on the same die and connected in parallel, featuring a 1 μm gap between the membrane and the bottom electrode, and directly coupling to air at 2.23 MHz. Exploiting the information on the amplitude and delay of the received ultrasonic waves, a directionality profile showing a 14° full width at half maximum (FWHM) and a 0.5-5 cm distance operative range are demonstrated. Object localization experiments show a 2D relative position reconstruction error around 5%.

This paper reports the theoretical and experimental characterization of the dynamic behavior of torsional resonators that can be applied to inertial sensors. For the correct operation of the devices it is necessary to model the dynamic behavior of the electrostatically actuated torsional resonators both in the linear and nonlinear range. A complete analytical model is developed in this work including nonlinear terms in the electrostatic stiffness. This provides clear quantitative information about the available linear range of operation and opens the way to exploit the nonlinear range. The model is validated through comparison with experimental data on two 22 µm thick polysilicon resonators having different distances from the underlying electrodes.

In the past years we conceived and developed the concept of spectrally tunable direct color sensors, based on the principle of the Transverse Field Detector. In this work we analyze the performance of a 64x64 (x3 colors) matrix of such a sensor built in a 150-nm CMOS standard technology for demonstrative purposes. The matrix is mounted on an electronic board that provides the biasing; the board is inserted into a suitably arranged film back slot (magazine) of a Hasselblad 500C camera. The camera is aligned in front of a transparency Macbeth Color Checker uniformly illuminated by an integrating sphere. Electrical, noise and colorimetric performance are the object of the ongoing analysis. In particular, the color reconstruction results will be compared to those obtainable through large-area devices based on the same concept.

Fringe-field capacitive sensing has a potential interest for the inertial MEMS community as it decouples the sensing direction from the pull-in direction, and it is therefore intrinsically immune from this issue. This paper presents a MEMS accelerometer based on fringe-field sensing, that exploits a surface micromachining process with very thin planar interconnections (

This paper discusses the constraints in the design of circuits for microelectromechanical systems (MEMS) resonant sensors in consumer applications, presents a novel integrated circuit implementation, and shows that this approach can be competitive with respect to the mostly used capacitive readout. From a circuit design perspective, it is shown how the large equivalent resistance typical of MEMS resonators, their operation close to mechanical nonlinearity, and the effect of feedthrough capacitances on the oscillating loop constrain the power requirements of the driving/readout electronics. As a case study, a resonant accelerometer built in an industrial process is coupled to a suitably designed transimpedance amplifier with a low-power “hard limiter.” The performance shown in terms of linearity across the measurement range (±8 g), minimum measurable acceleration (1 mg with a readout bandwidth of 100 Hz), and power consumption (≈ 100 μW per axis) is comparable to those of state-of-the-art capacitive inertial sensors.

A low-power very compact Pierce oscillator for resonant accelerometers is presented in this paper. The resonator of a surface micro-machined uniaxial resonant accelerometer is embedded in the oscillating loop as a frequency selective filter. External accelerations cause a shift of the resonator resonance frequency resulting in the frequency modulation of the oscillator output signal. The proposed circuit exploits two sub-threshold operated FETs as the amplitude limiting control (ALC) network, capable of driving the resonator in its linear region of operation. The low power dissipation and the very compact 5 transistor (5T) architecture are the clear advantages of this oscillator. Experimental results demonstrate that the oscillation amplitude can be effectively limited to a desired value and that consumer grade performance can be achieved: an acceleration noise density of 360μg/VHz for a power dissipation of 21.6μW is demonstrated.

In this paper it is presented a study on two key parameters of MEMS resonant accelerometers, resolution and start-up dynamics. A uniaxial differential accelerometer, built in the surface micromachining ThELMA process of ST Microelectronics, is used in the tests together with a discrete components readout circuit. The implemented circuit is an oscillator constituted by a Transimpedance stage (TIA) followed by a gain stage and an amplitude-limiting circuit (ALC). In the present work, it is shown how the sensor resolution can be related to the phase noise of the oscillator output signal and how the start-up dynamics depends on the biasing voltage of the resonator. A sensing resolution of 98µg/√Hz is demonstrated through experimental measurements and a well-defined relationship between the resonators biasing voltage and the start-up time is observed.

This paper presents a biaxial silicon resonant microaccelerometer characterized by a high sensitivity and a low cross-axis sensitivity. The device has a detection structure with a single inertial mass and two pairs of resonating beams allowing for the simultaneous differential measurement of acceleration acting along two different axes. The design of the accelerometer and in particular the geometrical configuration of the resonating elements is analytically optimized and finalized through finite element simulations. Experimental results on a fabricated device demonstrate a mean differential sensitivity of 250 Hz g−1 at a polarization voltage of 4 V, around a resonance frequency of 84 kHz.

This paper reports the theoretical and experimental characterization of a new z-axis silicon resonant micro accelerometer fabricated by the THELMA© surface micromachining technique, characterized by differential sensing and very small dimensions. The working principle of this device is based on the variation of the electrostatic stiffness of two torsional resonators. This work is a prosecution of the research on resonant accelerometers published in [1,2].