On-Chip Tests for the Characterization of the Mechanical Strength of Polysilicon †

Microelectromechanical systems (MEMS) are nowadays widespread in the sensor market, with several different applications. New production techniques and ever smaller device geometries require a continuous investigation of potential failure mechanisms in such devices. This work presents an experimental on-chip setup to assess the geometry- and material-dependent strength of stoppers adopted to limit the deformation of movable parts, using an electrostatically actuated device. A series of comb-finger and parallel plate capacitors are used to provide a rather large stroke to a shuttle, connected to the anchors through flexible springs. Upon application of a varying voltage, failure of stoppers of variable size is observed and confirmed by post-mortem DC–V curves. The results of the experimental campaign are collected to infer the stochastic property of the strength of polycrystalline, columnar silicon films

Direct Phase Measurement and Compensation to Enhance MEMS Gyroscopes ZRO Stability

This research introduces a closed-loop method to improve the zero-rate output (ZRO) stability of amplitude-modulated (AM) capacitive MEMS gyroscopes, even in absence of quadrature compensation electrodes. The method relies on the direct measurement and closed-loop compensation of the variation of the relative phase between the quadrature output, modulated by the drive carrier frequency, and the demodulation reference. The closed loop includes a phase meter, whose output regulates the phase of the lock-in amplifier inside the sense-mode, open-loop, demodulation chain. The proposed technique, tested on the pitch axis of a consumer-grade commercial monolithic 3-axis gyroscope, brings up to 300-fold stability improvements over temperature transients, without affecting noise and scale-factor performance. Stability limits depend on the phase meter resolution and on the lock-in granularity in regulating the phase. Overall, a mdps/K stability is obtained with a one-time calibration at ambient temperature and no post-acquisition processing. [2021-0049

Chipping and wearing in MEMS inertial sensors: Effects on stability and predictive analysis through test structures

Impacts between fixed and moving parts in capacitive MEMS inertial sensors can generate debris and wear that undermine the device stability. This work investigates the effects of impacts and friction between rotors and stoppers through dedicated test structures. After modeling the scenario, considering the impact kinetic energy and the tensile/ compressive nominal strength of silicon, different stopper topologies and collision angles are studied. Results show how impact kinetic energies, up to 40 nJ (velocities in the 1-3 m/s range for typical inertial sensor masses), correlate with silicon rupture and provide first guidelines for robust sensors design

Mems gyroscope with improved rejection of a quadrature error

A MEMS gyroscope is equipped with: at least a first mobile mass suspended from the top of a substrate by means of elastic suspension elements coupled to anchor points rigidly fixed to the substrate, in such a manner as to be actuated in an actuating movement along a first axis of a horizontal plane and to carry out a measurement movement along a vertical axis, transverse to the horizontal plane, in response to a first angular velocity acting about a second axis of the horizontal plane, transverse to the first axis. The elastic suspension elements are configured in such a manner as to internally compensate unwanted displacements out of the horizontal plane along the vertical axis originating from the actuating movement, such that the mobile mass remains in the horizontal plane during the actuating movement

A comprehensive model of beams' anisoelasticity in MEMS gyroscopes, with focus on the effect of axial non-vertical etching

This paper describes a comprehensive approach to model and efficiently simulate the behavior of MEMS gyroscopes in presence of beams' anisoelasticity, that causes out-of-plane mechanical quadrature. Special focus is given to the effects of non-vertical etching along the axial direction of flexural beams, which have been poorly investigated in the literature. A device-level numerical simulation tool to evaluate the effects of beams' anisoelasticity on quadrature is developed and validated through the comparison with 3D FEM simulations

Trattato dei Diritti Reali. 1, Propriet\ue0 e possesso

A comprehensive view on property rights in italian law. Volume I, deals with property and possession in all relevant aspects