Kivanc Azgin

High-Performance SOI-MEMS Gyroscope with Decoupled Oscillation Modes

This paper presents a new, high-performance SOI-MEMS gyroscope with decoupled oscillation modes. The gyroscope structure allows to achieve matched-resonance-frequencies, large drive-mode oscillation amplitude, high sense-mode quality factor, and low mechanical crosstalk, demonstrating a measured noise-equivalent rate of 90 (deg/hr)/Hz1/2even at atmospheric pressure. The angular rate sensitivity of the gyroscope is 100 µ V/(deg/sec) at atmospheric pressure. This value improves to 2.4mV/(deg/sec) at vacuum, for which the measured noise-equivalent rate of the gyroscope reaches to 35 (deg/hr)/Hz1/2. The R2-nonlinearity of the gyroscope is measured to be better than 0.02%. The gyroscope has a low quadrature signal of 70deg/sec and a short-term bias stability of 1.5deg/sec.

An SOI-MEMS tuning fork gyroscope with linearly coupled drive mechanism

This paper presents a new tuning fork gyroscope structure with a highly linear coupling mechanism that keeps the phases of the drive mode oscillating masses exactly opposite with the help of a symmetrically anchored ring-shaped spring. This structure eliminates the risk of drive mode instability due to any lower frequency structural modes and provides very linear drive mode oscillations together with very low g-sensitivity. The gyroscope is fabricated with the SOI-MUMPS process of MEMSCAP. The fabricated gyroscope has bias instability and angle random walk of 200 deg/hr and 5.47 deg/Vhr, respectively, according to Allan Variance curve. The g-sensitivy and scale factor are measured as 9.3 (deg/hr)/g and 12 mV/(deg/sec) with an R2 nonlinearity of 0.05%.

Simultaneous detection of linear and coriolis accelerations on a mode-matched MEMS gyroscope

This paper presents a novel “in operation acceleration sensing and compensation method” for a single-mass mode-matched MEMS gyroscope. In this method, the amplitudes of the sustained residual quadrature signals on the differential sense-mode electrodes are compared to measure the linear acceleration acting on the sense-axis of the gyroscope. By measuring the acceleration acting along the sense-axis, the g-sensitivity of the gyroscope output to these accelerations is mitigated without using a dedicated accelerometer. It has been experimentally demonstrated that the g-sensitivity of the studied gyroscope is substantially reduced from 1.08°/s/g to 0.04°/s/g, and the effect of the linear acceleration on the gyroscope output is highly-suppressed (by 96%) with the use of the compensation method proposed in this work.

A capacitive MEMS accelerometer readout with concurrent detection and feedback using discrete components

This paper presents an analog readout method for capacitive MEMS accelerometers in which the feedback actuation and capacitive detection are achieved simultaneously on the same electrode set. The presented circuit operates in closed-loop for improved linearity, and it is constructed in a hybrid platform package in which off-the-shelf discrete components are used together with the silicon-on-glass micro-accelerometer. The system is developed as a practical solution to reduce the complexity of the readout circuit and the accelerometer without degrading the overall system performance. Experimental results demonstrate 17.5 micro-g per square-root hertz velocity random walk, and 28 micro-g bias instability. Considering the estimated full scale range of 20 g, the dynamic range of the sensor is calculated to be close to 124 dB.

The effects of tine coupling and geometrical imperfections on the response of DETF resonators

This paper presents a two-degree-of-freedom analytical model for the electromechanical response of double ended tuning fork (DETF) force sensors. The model describes the mechanical interaction between the tines and allows investigation of the effect of a number of asymmetries, in tine stiffness, mass, electromechanical parameters and load sharing between the tines. These asymmetries are introduced during fabrication (e.g., as a result of undercut) and are impossible to completely eliminate in a practical design. The mechanical coupling between the tines induces a frequency separation between the in-phase and the out-of-phase resonant modes. The magnitude of this separation and the relative intensity of the two modes are affected by all the asymmetries mentioned above. Two key conclusions emerge: (i) as the external axial compressive load is increased, the in-phase mode reaches zero frequency (buckling) much faster than the out-of-phase (i.e., operational) mode, resulting in a device with a decreased load range. (ii) During the operation, balanced excitation is essential to guarantee that the out-of-phase mode remain significantly stronger than the in-phase mode, thus allowing sharp phase locked loop locking and hence robust performance. The proposed model can be used to assess the magnitude of asymmetries introduced by a given manufacturing process and accurately predict the performance of DETF force sensors. For the specific sensor characterized in this study, the proposed model can capture the full dynamic response of the DETF and accurately predict its maximum axial compressive load; by contrast, the conventional single-DOF model does not capture peak splitting and overpredicts the maximum load by ?18%. The proposed model fits the measured frequency response of the electromechanical system and its load-frequency data with coefficient of determination (R2) of 95.4% (0.954) and 99.2% (0.992), respectively.

Temperature compensation of a capacitive MEMS accelerometer by using a MEMS oscillator

This study reports a temperature compensation method for a capacitive MEMS accelerometer by using a MEMS double-ended-tuning-fork (DETF) resonator integrated with the accelerometer structure on the same die. The proposed method utilizes the frequency information of the clamped-clamped DETF resonator which is oscillating in a closed-loop operation. In order to compensate the temperature dependence of the accelerometer output, frequency drift of the DETF resonator against changing temperature is used, i.e., the resonator frequency is used as the temperature data for compensation purposes. On-chip integration of two sensors allows precise temperature sensing abilities by removing the thermal lag between the DETF resonator and the accelerometer. Tests are held in the -20 °C and 60 °C range by operating both sensors simultaneously in a temperature-controlled oven. The measurement results indicate temperature coefficient of frequency (TCf) of 480 ppm/K for the integrated resonator and temperature dependence of 1,164 μg/K for the accelerometer output, which is decreased to 1.4 μg /K after temperature compensation. Improved noise performances indicate the bias instability of 30 μg and the velocity random walk of 24 μg/sqrt(Hz) with the removal of the temperature ramp (after 30 seconds) in Allan-deviation plot.

The Development and Performance Characterization of Turbine Prototypes for a MEMS Spirometer

The design, optimization, and performance characterization of turbine prototypes for the development of a Microelectromechanical Systems spirometer is reported. Four different turbines were designed based on large-scale Savonius turbine architecture. The number of turbine blades was optimized through finite-element simulations to maximize the induced moment and rotational speed at normal breathing flow rates. The turbines were manufactured and tested for their speed performance with respect to input flow rate, pressure difference, and actuation power, showing good agreement with the simulation results. The highest rotational speed was achieved with involute-bladed turbine design with eight blades, and was measured to be 10.56 kr/min at the peak 25-lpm flow rate. Real-life testing with this design was carried out on healthy subjects to demonstrate its capability of performing respiration flow rate measurements. The turbine prototypes presented in this paper allow for the development of low-cost and portable MEMS spirometers for remote- and self-monitoring of lung malfunctions in chronic obstructive pulmonary disease and asthma diseases.

A single mass two-axis capacitive MEMS accelerometer with force rebalance

This paper presents a single mass 2-axis MEMS capacitive accelerometer with a unique force rebalance method achieved with the readout circuit developed for the simultaneous 2-axis acceleration sensing. Using a single mass structure with extra fingers for reading multiple axes allows better sensor performances when compared to multi-axis accelerometers with individual proof masses occupying the same die area. Test results show 274 mV/g scale factor for x-axis, and 280 mV/g scale factor for y-axis, while the cross-axis sensitivity for x-axis is calculated as 3.4 mV/g (% 1.26), and the cross-axis sensitivity for y-axis is -3.9 mV/g (% 1.4). Additionally, the bias instability values are measured as 22 μg and 23 μg, and the velocity random walk values are determined as 9.8μg/ √Hz and 9.9 μg/ √Hz for x and y axes, respectively. This sensing and readout approach can easily be adapted to achieve a high performance single mass 3-axis accelerometer in a small die area.

A Novel In-Operation High g-Survivable MEMS Gyroscope

This paper presents a new SOI-MEMS gyroscope with very high in-operation shock survivability together with very low R nonlinearity and scale factor g-sensitivity, owing to its optimized mechanical structure and durable readout electronics. Maximum stress induced on the gyro structure under a shock loading of 10,000 g is determined to be below 860 MPa. The new gyroscope also allows keeping the proof mass voltage within the supply voltages of readout electronics, preventing the possibility of electronic failure in case of pull in. The scale factor at the atmospheric pressure is measured as 10.4 mV/(deg/sec) with an R2 nonlinearity of 0.03% and scale-factor g sensitivity of 1.89 (mV/deg/sec)/g. At the atmospheric pressure, the bias instability and angle random walk of the gyroscope are measured as 391deg/hr and 5.27degradichr, respectively. The gyroscope gives even better performance characteristics at vacuum ambient with a bias instability and angle random walk of 105deg/hr and 5.29degradichr, respectively.

Thermal sensitivity of the fundamental natural frequency of a resonant MEMS IR detector pixel

This paper presents the effect of temperature on the natural frequency of (1,1) mode shape of a Resonant MEMS IR bolometer pixel in the range of 295-340 K. The detector pixel has a square plate geometry having side length of 1400μm and thickness of 35μm. The resonating plate is supported at its geometric center, enabling more robust pixels with fill factor greater than 90% and less complicated fabrication process. The sensor is fabricated using a Silicon-On-Glass (SOG) process. For the first time in the literature, the closed form equation to calculate the natural frequency of the fundamental mode shape of a MEMS square plate as a function of temperature change is derived for the single crystal silicon as the structural material. FEM simulations and experiments are conducted to verify the analytical model. For the electromechanical response characterization of the pixel structure, frequency response and system level temperature tests are conducted. Fundamental natural frequency shift is also tested during the frequency response tests for the same temperature range and the scale factor of the fabricated sensor is measured to be 1.90Hz/K for mode shape (1,1).