Browsing by Subject "Temperature effects"
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Item Open Access Analytical and experimental study of imperfections, stress, and temperature effects in circular MEMS gyroscopes(2024-02) Hosseini-Pishrobat, MehranInspired by the outstanding performance of the hemispherical resonator gyroscopes (HRG), MEMS gyroscopes with circularly symmetric structures are a promising candidate for the next generation of high-performance, cost-effective gyroscopes. However, scaling down to MEMS poses certain performance-limiting challenges: increased sensitivity to inevitable fabrication imperfections and environmental variations, chiefly stress and temperature, that perturb the gyroscope’s ideal modal space and result in quadrature/in-phase errors and, more importantly, long-term drift. Understanding these limiting factors is imperative for harnessing the full potential of circular MEMS gyroscopes. This thesis approaches this objective through an analytical modeling viewpoint. Here, “analytical” is meant to connote an approach based on the physics underlying the gyroscopes’ operation as described by the variational principles of solid mechanics. For the experimental evaluations, we use our fabricated double-ring vibrating ring gyroscope (VRG) (3.2 mm-diameter, 57-59 kHz) and 10-ring disk resonator gyroscope (DRG) (3.4 mm-diameter, 41 kHz). We start by calculating the mode shapes of the entire structure of multi-ring gyroscopes in the presence of structural imperfections and elastic anisotropy. By deriving the gyroscope’s nonideal drive-sense transfer function matrix, we provide rigorous definitions for the quadrature and in-phase outputs, highlighting the role of angular gain, frequency split, mode shape rotations, and quadrature leakage into the in-phase due to the sense mode’s phase error. Next, we present a model for the effects of mechanical stresses leading to the concept of stress stiffness, an additional stiffness induced by such stresses through geometric nonlinearity. We carry out an eigenvalue perturbation analysis to obtain the frequency shifts, mode shape rotations, and quadrature/in-phase errors generated by the stress stiffness. Taking advantage of the circular geometry, we have equipped our ring gyroscopes with 16 capacitive stress sensors located 45◦-apart (eight inside and eight outside the main ring), which pick up the local stress at the substrate level. We present an interpolation scheme to reconstruct the substrate’s stress field using the outputs of the stress sensors, providing us with the mechanical stresses responsible for the stress stiffness in the silicon layer. We validate the model based on PCB bending tests. We finally set out a modeling framework for temperature effects in ring gyroscopes. Our temperature experiments gave temperature coefficient of frequencies (TCFs), such as -10 ppm/◦C and -14 ppm/◦C, that are considerably different than the TCF value ~-30 ppm/◦C expected from the ~-60 ppm/◦C temperature dependency of Young’s modulus of silicon. The model revolves around the engendered stiffness and opposing interaction of two fundamental mechanisms of temperature effects: changes in material properties and thermal stresses. The model demonstrates remarkable efficacy in accurately predicting the TCF and sheds light on residual stresses’ role in forming frequency-temperature hysteresis loops. Considering the great potential of integrating stress with temperature for the long-term performance improvement of MEMS gyroscopes, the results of this thesis serve as a building block toward physics-informed drift compensation algorithms.Item Open Access Modeling temperature effects in a MEMS ring gyroscope: toward physics-aware drift compensation(Institute of Electrical and Electronics Engineers, 2025-01-15) Hosseini-Pishrobat, Mehran; Tatar, ErdinçTemperature plays an indispensable role in the long-term performance of MEMS gyroscopes, and despite extensive studies in the literature, analytical treatment of temperature effects is still an open problem. This paper, to the best of our knowledge, is the first attempt to address this gap for ring gyroscopes. We start with a superposition principle that disentangles thermal displacement fields from the gyroscope's nominal vibration. We set forth a geometrically nonlinear variational formulation to obtain the temperature-induced stiffness matrix. We conduct temperature tests on our 3.2 mm-diameter, 58 kHz ring gyroscopes equipped with 16 capacitive stress sensors. The experimental data validate our analytical modeling in the following key aspects: 1) The model accounts for not only changes in material properties but also a less explored factor, thermal stresses. Thanks to a strain interpolation module that leverages the measured stresses, the model predicts frequency variations consistently and captures hysteresis loops arising from residual stresses. Notably, we accurately estimate the deviation of the temperature coefficient of frequency (TCF) from the expected value -30 ppm/C-degrees (based on the widely known -60 ppm/C-degrees dependency of Young's modulus of silicon). 2) The model is able to capture stiffness couplings in the orders of less than 0.1 N/m (in a 7 kN/m device) and closely predicts the quadrature error and its leakage into the in-phase channel. Additionally, the model incorporates temperature variations of mechanical scale factor, drive mode's amplitude, damping coupling, and sense mode's phase in terms of their contribution to the in-phase error. Based on these merits, our model serves as a building block toward drift compensation algorithms encompassing the underlying physics of the temperature effects.Item Open Access Quantum conductance and temperature effects in titanium oxide-based memristive devices(IEEE, 2024-03) Köymen, Itır; De Carlo, Ivan; Fretto, Matteo; Milano, GianlucaA thorough investigation of quantum conductance properties and the effects of temperature on $\text {Cr/Au/TiO}_{{2}}/\text {TiO}_{x}\text {/Cr/Au}$ memristive devices is presented. Besides fabrication and resistive switching characteristics, two different programming strategies have been explored to observe quantum conductance effects. The first strategy was based on device stimulation with slow current sweeps to observe quantum levels in the SET region, while the second aimed to achieve quantum steps during RESET using slow sweep stimulation. The effects of the two different programming strategies are compared. It is also shown that these devices can be programed to achieve stable quantum levels, as revealed by retention measurements performed after programming the device to $1~{G}_{{0}}$. Furthermore, the temperature-dependent electronic conduction mechanism of the device after being programed to different internal resistance states has been analyzed, revealing a semiconductor behavior with an increase in resistance by lowering the temperature in either a pristine state, low-resistance state, or resistance states close to the quantum conduction regime.