Browsing by Author "Tatar, Erdinc"

Now showing 1 - 2 of 2

Embargo
Analytical and experimental study of stress effects in a MEMS ring gyroscope
(Elsevier, 2023-09-09) Hosseini-Pishrobat, Mehran; Erkan, Derin; Tatar, Erdinc
External stress affects the stiffness distribution of a MEMS gyroscope and, along with temperature, is affiliated with long-term drift. Although the detrimental effects of stress on MEMS gyroscopes are well-documented, modeling of such effects is still lacking in the literature. For the first time, we present an analytical model that mathematically describes the stress effects in a ring gyroscope. Our model revolves around the key observation that stress-induced anchor displacements result in variations of electrostatic gaps and nonhomogeneous boundary conditions at the interface between the gyroscope’s suspension system and the anchored internal structure. Our gyroscope is equipped with 16 capacitive stress sensors distributed with 45° symmetry on the inside and outside of the main ring. We use these stress sensors’ measurements to interpolate the strain field across the substrate and deduce the anchor displacements. To capture the stress effects, we show that two fundamental assumptions in the existing literature should be amended: (1) Linearity: the linear engineering strain should be upgraded to the nonlinear Green–Lagrange strain to reveal the stress-induced stiffness through geometric nonlinearity; (2) Inextensibility: for a ring, this stress stiffness is determined by the extensional stress arising from centerline extensibility. We analyze variations of frequencies and mode shapes’ orientation along with the resultant quadrature and in-phase errors. Moreover, we present a fairly general formulation incorporating fabrication-induced imperfections and elastic anisotropy. We validate our model experimentally using extensive bending tests performed on our 59 kHz, 3.2 mm diameter gyroscope.
Open Access
Characterization of packaging stress with a capacitive stress sensor array
(Institute of Electrical and Electronics Engineers Inc., 2023-01) Veske, Tolga; Erkan, Derin; Tatar, Erdinc
This paper presents a high-resolution capacitive stress sensor array to precisely characterize the distributed MEMS packaging stress, for the first time. The unit stress measurement cell utilizes a bridge-type mechanical amplifier that converts the substrate strain into capacitance variations. We have measured and compared the MEMS die stress over temperature for different die attaches with a custom designed PCB housing an on-chip heater. The proposed approach significantly simplifies the evaluation and selection of packaging materials. Comparing the temperature responses of a soft silicone-based and stiffer silver-filled epoxy reveals difficult to predict results.