Fixed-wing MAV attitude stability in atmospheric turbulence, part 1: Suitability of conventional sensors

This paper presents a closed-loop accelerometer interface based on a force-feedback ΔΣ loop. The interface reduces the offset, and its drift, arising from asymmetry in the parasitic capacitances of the bondwires connecting the CMOS interface IC and the MEMS sensor element. This is achieved by modulating the spring constant of the sensor electrostatically and continuously measuring and nulling the offset via an offset cancellation loop. In a bondwire deformation experiment, we show that the offset cancellation loop reduces an induced offset of 350 mg by 54 dB down to 0.7 mg. The interface was fabricated in a 0.18-μm CMOS technology. The active circuit area is 1.35 mm2 and the interface consumes 3.1 mW from a 3-V supply, while achieving a noise floor of 220 μg/√Hz over a 1-kHz bandwidth. When the offset cancellation loop is turned on the bandwidth available for the signal is 200 Hz.

A $\Delta \Sigma$ Interface for MEMS Accelerometers Using Electrostatic Spring Constant Modulation for Cancellation of Bondwire Capacitance Drift

This paper proposes and verifies a structure for the isolation of packaging stress in silicon-on-insulator-based microelectromechanical systems devices. The packaging-stress isolation structure resides on the handle layer and consists of a circular disk, eight elastic beams, and a support frame. The disk is located in the center of the die and occupies less than 5% of the handle-layer area; this can reduce packaging stress and avoid uneven stress distribution. The elastic beams are L-shaped and symmetrically distributed to decouple the deformation from the disk to the frame and suppress the stress evenly. The in-plane and out-of-plane deformation induced by packaging stress was modeled and experimentally measured. The comparison results demonstrate that the packaging stress was successfully isolated.

Design and Verification of a Structure for Isolating Packaging Stress in SOI MEMS Devices

Moire interferometry has been a valuable experimental technique for the understanding of the mechanical behavior of materials and structures. Over the last decade less emphasis has been placed on the development of the technique and more towards applications. This paper is a review article on recent applications using moire interferometry in the fields of microelectronics devices, material characterization, micromechanics, residual stress, composite materials, fracture mechanics, and biomechanics. The general principles of moire interferometry and advancement of techniques will not be discussed in this text, but references will be provided.

Recent Applications of Moiré Interferometry

Long-term gyroscope drift can be effectively removed by employing simultaneous on-chip stress and temperature compensation. Stress effects are significant and their inclusion augments the commonly applied temperature compensation. A silicon-on-insulator matched-mode z-axis vibratory-rate gyroscope, as a prototype testbed to study these effects, includes released silicon resistors connected in a Wheatstone bridge as on-chip stress sensors. The gyroscope is ovenized within 300 K ± 20 mK using an external heater and an on-chip temperature sensor to suppress the temperature effects. The gyroscope is in-house vacuum packaged and operated at matched closed-loop drive and sense modes. Stress compensation significantly suppresses long-term drift resulting in 9°/h/√Hz angle random walk and 1°/h bias instability at 10000 s (around 3 h) averaging time, which is seven times improvement over the uncompensated gyroscope output. The sensitivity of zero-rate offset to stress is -0.22°/day/Pa and -0.045°/day/Pa for the tests with and without externally applied stress, respectively.

https://ieeexplore.ieee.org/ielaam/84/7936684/7887664-aam.pdf

Stress Effects and Compensation of Bias Drift in a MEMS Vibratory-Rate Gyroscope

In microelectromechanical system (MEMS) devices, the deformation of MEMS structure caused by packaging induced stress is of great concern since it directly affects the performance of the device. In this paper, deformation behavior of the MEMS gyroscope package subjected to temperature change is investigated using a high-sensitivity moire interferometry. Temperature dependent analyses of warpage and extension/contraction of the package are presented. Analysis of the package reveals that global bending deformation occurs due to the mismatch of the coefficient of thermal expansion between the chip, the molding compound, and the printed circuit board. Detailed global and local deformations of the package by temperature change are investigated, and their effect on the frequency shift of the MEMS gyroscope is studied. It is found that package deformation or package induced stress results in the frequency shift of the MEMS gyroscope structure. In order to increase robustness of the structure against deformation, a "crab-leg" type spring is replaced with a semi-folded spring. The results show that the frequency shift is greatly reduced after applying the semi-folded spring. This frequency shift is within the tolerance limit of the gyroscope sensor in this work

Jin-Won Joo

Papers

Deformation Behavior of MEMS Gyroscope Sensor Package Subjected to Temperature Change