Navigation Grade Performance Research Articles

Temperature compensation of MEMS resonant accelerometers with an on-chip platinum film thermometer

Temperature-dominated drift is generally the main error source for high-performance micromachined resonant accelerometers (MRAs) due to inherent thermal stress effect of resonator structure and die-attach process. This paper describes the design and experimental evaluation of a temperature compensation scheme for MEMS resonant accelerometers that demonstrates excellent bias and scale factor stability against temperature variation. An on-chip temperature sensor fabricated by sputtering platinum film on glass substrate is proposed to accurately sense the temperature-induced frequency change of the resonator. A polynomial fitting-based post-compensation model is firstly used to suppress the temperature sensitivity of the MRA over dynamic temperature environment. The temperature drift test and compensation of four accelerometer prototypes in a range from −40 ∘C to 60 ∘C show that the stability of bias and scale factor has been improved greatly with navigation-grade performance. Temperature compensation results with three improved drift models based on polynomial fitting, convolutional neural network and support vector regression respectively are presented and compared to suppress the temperature drift hysteresis in consecutive temperature-varying tests. These experimental results indicate that this resonant accelerometer exhibits excellent temperature stability after compensation, which offers the promise for high-performance inertial navigation applications.

Bias Thermal Stability Improvement of Mode-Matching MEMS Gyroscope Using Mode Deflection

This letter presents a novel strategy to eliminate the bias drift by using mode deflection. The bias of a mode-match gyroscope is mainly caused by the asymmetrical damping and its azimuth. Mode deflection is a method to deflect the drive mode to the direction of damping axis through the circuit configuration, thereby nulling the damping azimuth. After deflection, the bias is not sensitive to the drift of damping and its stability will be greatly improved. Experiments performed on a honeycomb disk resonator gyroscope have demonstrated the effect of this method. The compensation method yields a navigation-grade performance with the bias instability of 0.014°/h. The bias variation overall temperature range from −40°C to 60°C is improved from 73.6°/h to 1.15°/h and the RMS of the bias is 0.26°/h. [2022-0167]

0.02 °/h, 0.004°/√h, 6.3-mA NEMS Gyroscope With Integrated Circuit

This work introduces a system formed by an integrated circuit and a micro-machined piezoresistive gyroscope, with navigation grade performance. After discussing the specifications in terms of maximum allowed electronic noise, so not to worsen the thermo-mechanical noise limits, three different front-end topologies are analysed, and the current-feedback instrumentation amplifier is chosen as the optimal solution in terms of noise and current consumption. After coupling to a gyroscope based on nano-gauges, the system demonstrates 200 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dps</i> full-scale, 0.02 °/h stability and 0.004 °/ √ h angle random walk, confirming navigation-grade performance at a current consumption well below 10 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mA</i> and an overall power consumption below 40 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mW</i> .

1.3 mm2 Nav-Grade NEMS-Based Gyroscope

The research reports the design and experimental results of novel gyroscopes based on nano-resistive sensing, capable to meet navigation grade specifications within a sensor footprint of 1.3 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a total silicon structural volume of 0.026 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> only. A significant increase of the scale-factor is obtained through a combination of (i) optimization of the Coriolis force transduction into a stress on the resistive gauges, (ii) increase of the drive motion amplitude and (iii) increase of the current through the sensing gauges. Combined with low-pressure eutectic packaging, this enables approaching the thermomechanical noise limits of the sensor at about 0.004 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> /√ hr. At the same time, electronics is developed with minimum demodulation phase errors, thus enabling optimized closed-loop quadrature compensation and minimization of drift effects. Thanks to the inherent rejection of parasitic couplings and associated drifts of the used technology, the overall stability reaches 0.02 °/hr on average on 6 samples. These performances are demonstrated for a 30-Hz system bandwidth and few hundred dps input range over several samples. Navigation grade performance are confirmed by additional in-operation experiments like gyrocompassing and in-run 9-minute long angle measurements from rate integration. [2021-0073]

Micro Hemispherical Resonator Gyroscope With Teeth-Like Tines

Micro hemispherical resonator shows great potential for applications in high-performance gyroscopes. This paper introduces micro hemispherical resonator with teeth-like tines along the edge, aiming at improving mechanical sensitivity of the gyroscope and simplifying the mechanical trimming. The optimized glassblowing resonators with substrate thickness of 200 μm and height near 4.5 mm shows high quality factor, large sensitivity, and balanced electrode gaps. The n = 2 wineglass modes operate at 4.3 kHz, achieving quality factor of 1.18 million and as-fabricated frequency split of 17.8 Hz. After mechanical trimming, the frequency split is reduced below 70 mHz. The vacuum-packaged micro hemispherical resonator gyroscope (mHRG) operating in force-rebalance mode exhibits full-scale range of ±200 deg/sec and bias instability of 0.133 deg/h at room temperature without compensation, indicating that the performance of the gyroscope is limited by the readout electronics. Further improvement is in progress to achieve navigation-grade performance with rate-integrating operation.

Frequency tracking out-of-lock control in a resonator fiber-optic gyro.

A resonator fiber-optic gyro (RFOG) is being pursued because of its theoretical potential to meet navigation-grade performance with small size, high precision, and lower cost. The stability of the RFOG operation is based on the synchronization of laser frequency to the fiber ring resonator (FRR) resonance frequency. Frequency tracking out-of-lock will lead to peak pulse and zero-bias change at the output of the RFOG, which seriously degrades the performance. First, the influence mechanism of frequency tracking out-of-lock is analyzed. The change of current and temperature in frequency tracking and the symmetry change caused by backscatter and polarization are the main reasons for the peak pulse and zero-bias error. Second, a scheme of out-of-lock control of the RFOG based on temperature closed-loop operation using digital signal processing is proposed. The improved scheme, signal processing, and implementation method are investigated in detail. Finally, a RFOG prototype is assembled and tested, and 10 min tracking of the laser frequency to the FRR's single-resonance frequency is realized by temperature closed-loop operation. The static performance of the RFOG over 1 h shows that the RFOG output errors caused by frequency tracking out-of-lock are successfully eliminated. The output peak pulse is reduced from 3000 to 200 deg/h, the zero bias is eliminated from 50 to 600 deg/h to 0, and the bias stability of the RFOG is improved from 15.2 to 1.85 deg/h, which indicates a remarkable advance in the performance of the RFOG to satisfy civil navigation application requirements.

0.04 degree-per-hour MEMS disk resonator gyroscope with high-quality factor (510\u2009k) and long decaying time constant (74.9\u2009s)

The disk resonator gyroscope is an attractive candidate for high-performance MEMS gyroscopes. This gyroscope consists of a sensor and readout electronics, and the characteristics of the sensor directly determine the performance. For the sensor, a high-quality factor and long decaying time constant are the most important characteristics required to achieve high performance. We report a disk resonator gyroscope with a measured quality factor of 510 k and decaying time constant of 74.9 s, which is a record for MEMS silicon disk resonator gyroscopes, to the best of our knowledge. To improve the quality factor of the DRG, the quality factor improvement mechanism is first analyzed, and based on this mechanism two stiffness-mass decoupled methods, i.e., spoke length distribution optimization and lumped mass configuration design, are proposed and demonstrated. A disk resonator gyroscope prototype is fabricated based on these design strategies, and the sensor itself shows an angle random walk as low as 0.001°/√h, demonstrating true potential to achieve navigation-grade performance. The gyroscope with readout electronics shows an angle random walk of 0.01°/√h and a bias instability of 0.04°/h at room temperature without compensation, revealing that the performance of the gyroscope is severely limited by the readout electronics, which should be further improved. We expect that the quality factor improvement methods can be used in the design of other MEMS gyroscopes and that the newly designed DRG can be further improved to achieve navigation-grade performances for high-end industrial, transportation, aerospace, and automotive applications.

MEMS and FOG Technologies for Tactical and Navigation Grade Inertial Sensors-Recent Improvements and Comparison.

In the following paper, we present an industry perspective of inertial sensors for navigation purposes driven by applications and customer needs. Microelectromechanical system (MEMS) inertial sensors have revolutionized consumer, automotive, and industrial applications and they have started to fulfill the high end tactical grade performance requirements of hybrid navigation systems on a series production scale. The Fiber Optic Gyroscope (FOG) technology, on the other hand, is further pushed into the near navigation grade performance region and beyond. Each technology has its special pros and cons making it more or less suitable for specific applications. In our overview paper, we present latest improvements at NG LITEF in tactical and navigation grade MEMS accelerometers, MEMS gyroscopes, and Fiber Optic Gyroscopes, based on our long-term experience in the field. We demonstrate how accelerometer performance has improved by switching from wet etching to deep reactive ion etching (DRIE) technology. For MEMS gyroscopes, we show that better than 1°/h series production devices are within reach, and for FOGs we present how limitations in noise performance were overcome by signal processing. The paper also intends a comparison of the different technologies, emphasizing suitability for different navigation applications, thus providing guidance to system engineers.

Optimal Design of a Center Support Quadruple Mass Gyroscope (CSQMG).

This paper reports a more complete description of the design process of the Center Support Quadruple Mass Gyroscope (CSQMG), a gyro expected to provide breakthrough performance for flat structures. The operation of the CSQMG is based on four lumped masses in a circumferential symmetric distribution, oscillating in anti-phase motion, and providing differential signal extraction. With its 4-fold symmetrical axes pattern, the CSQMG achieves a similar operation mode to Hemispherical Resonant Gyroscopes (HRGs). Compared to the conventional flat design, four Y-shaped coupling beams are used in this new pattern in order to adjust mode distribution and enhance the synchronization mechanism of operation modes. For the purpose of obtaining the optimal design of the CSQMG, a kind of applicative optimization flow is developed with a comprehensive derivation of the operation mode coordination, the pseudo mode inhibition, and the lumped mass twisting motion elimination. The experimental characterization of the CSQMG was performed at room temperature, and the center operation frequency is 6.8 kHz after tuning. Experiments show an Allan variance stability 0.12°/h (@100 s) and a white noise level about 0.72°/h/√Hz, which means that the CSQMG possesses great potential to achieve navigation grade performance.

Optical Cavity Interrogation for MEMS Accelerometers

MEMS accelerometers utilizing electrostatic, piezoelectric, and magnetic proof mass displacement readout approaches have achieved success in both commercial- and defense-related applications. However, there is a desire for improved acceleration resolution suitable for navigation-grade applications. Optical readout of mechanical displacements has demonstrated high levels of resolution in macro-scale applications including precision movement and placement systems. In addition, optical techniques are common in high performance inertial sensors such as fiber optic gyros and ring laser gyros. Incorporating optical readout approaches into MEMS acceleration devices may yield sufficient resolution to achieve navigation-grade performance. Therefore, the U.S. Army AMRDEC is developing MEMS accelerometers based on optical cavity resonance readout. In the device, an optical cavity is formed between a MEMS proof mass and a reference reflector. A tunable laser excites the cavity on the edge of its resonance peak. Small displacements of the cavity from its rest position are detected by frequency shifts of the resonance, leading to high-resolution proof mass displacement detection and therefore high acceleration resolutions. This paper will present modeling associated with the design concept, as well predictions of device geometries and performance with the goal of achieving less than 1 micro-g bias instability and a velocity random walk of better than 0.2 micro-g/rt.Hz.

High and Moderate-Level Vacuum Packaging of Vibratory MEMS

We report vacuum packaging procedures for low-stress die attachment and versatile hermetic sealing of resonant MEMS. The developed in-house infrastructure allows for both high and moderate-level vacuum packaging addressing the requirements of various applications. Prototypes of 100 μm silicon-on-insulator Quadruple Mass Gyroscopes (QMGs) were packaged using the developed process with and without getters. Characterization of stand-alone packaged devices with no getters resulted in stable quality factors (Q-factors) of 1000 (corresponding to 0.5 Torr vacuum level), while devices sealed with activated getters demonstrated Q-factors of 1.2 million (below 0.1 mTorr level inside the package). Due to the high Q-factors achieved in this work, we project that the QMG used in this work can potentially reach the navigation-grade performance, potentially bridging the gap between the inertial silicon MEMS and the state-of-the-art fused quartz hemispherical resonator gyroscopes.