Sensors and Actuators A 123–124 (2005) 258–266 Silicon resonant accelerometer with electronic compensation of input-output cross-talk V. Ferrari ∗ , A. Ghisla, D. Marioli, A. Taroni Dipartimento di Elettronica per l’Automazione and INFM, Universit` a di Brescia, Via Branze 38, 25123 Brescia, Italy Received 7 October 2004; received in revised form 17 March 2005; accepted 28 March 2005 Available online 31 May 2005 Abstract A resonant accelerometer manufactured in silicon bulk micromachining with electrothermal excitation and piezoresistive detection is presented. The structure is a seismic mass supported by two parallel flexure hinges as a doubly-sustained cantilever, with a resonating microbeam located between the hinges. The acceleration normal to the chip plane induces an axial stress in the microbeam and, in turn, a proportional change in the microbeam resonant frequency. Beam resonant frequency of around 70 kHz and acceleration sensitivity of 35 Hz/g over the range 0–3 kHz were measured on prototypes, in accordance with analytical calculations and simulations. The microbeam operates unsealed at atmospheric pressure, therefore a comparatively low quality factor results due to air damping. In this condition, the effect of the input-output cross-talk was found to be significant. The cross-talk is analyzed and modeled, and an electronic active compensation is proposed. The compensated sensor was inserted into a phase-locked loop oscillator and tested. Reported experimental results show that the sensor performs in excellent agreement with the theoretical predictions. © 2005 Elsevier B.V. All rights reserved. Keywords: Accelerometer; Resonant sensor; Cross-talk; Oscillator; MEMS 1. Introduction In resonant sensors the oscillation frequency at resonance of a mechanical microstructure is changed by a physical or chemical quantity to be measured, in such a way that the value of the measurand quantity can be derived by the shift in the resonant frequency of the microstructure [1–4]. The principle can be applied to several measurands, and resonance parameters other than the frequency, such as amplitude or phase, can also be used in the sensing process. Frequency-output resonant sensors typically offer high sensitivity and stability, potentially leading to good accuracy and resolution. In addition, the “quasi-digital” nature of the frequency signal eases interfacing to readout and processing circuitry and improves noise immunity. The fabrication of resonant sensors by means of silicon micromachining allows the use of the well-established ∗ Corresponding author. Tel.: +39 030 3715444; fax: +39 030 380014. E-mail address: vittorio.ferrari@unibs.it (V. Ferrari). silicon technology to obtain microdevices with excellent mechanical and elastic properties and a very precise control of the geometry and dimensions of the microstructure [5–7]. Moreover, silicon sensors can be more easily integrated with microelectronic or optical-fibre systems. Several methods for the actuation of the microresonator and detection of the oscillations are reported in the literature [8–13]. For the actuation, the electrostatic, magnetic, piezoelectric, acoustic, electrothermal and optothermal methods can be used. The sensing is typically accomplished by means of piezoresistive, capacitive, optical or piezoelectric methods. As a particular case of resonant sensors, resonant microaccelerometers have been reported in the literature [14–18] in response to the demand for high-performance all-silicon accelerometers, for instance in the automotive industry. Several examples use the electrothermal excitation and piezoresistive detection, which are straightforward to realize on silicon by means of implanted or deposited resistors [19–20]. As with other operating methods, the electrical nature of the input and output signals allows the 0924-4247/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2005.03.067