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In MEMS technology development, it is always exciting to see the next technology frontier, the border of the known and the unknown. Talent and hard work (along with ingenuity) can move this frontier and enrich all of us. We respect the efforts of MEMS innovators, who have developed original and creative ideas by building upon past knowledge and wisdom and have integrated this knowledge across multiple disciplines. We believe that MEMS gyroscopes are poised to advance to this next technology frontier, addressing the challenges of temperature stability and wider bandwidth that limit existing gyroscope designs.
A MEMS gyroscope is a micro-machined device that can measure rotational motion (the angular rate of rotation or the angle of orientation). MEMS gyroscopes are small, inexpensive and have been incorporated in many consumer electronic devices (such as cell phones and drones). MEMS gyroscopes typically use a microfabricated suspended structure that measures the change in Coriolis forces (a force that acts upon an object as the mass experiences a rotation relative to its frame of reference).
Conventional Coriolis vibratory gyroscopes use amplitude modulation (AM), where intentionally mode-mismatched, closed-loop phase control and automatic gain control by synchronous detection are employed. AM gyroscopes have a trade-off between the sensitivity and bandwidth of the device. From a practical viewpoint, AM gyroscopes have quadrature error (out-of-phase error) and in-phase error. Dissipation through the substrate (anchor loss) and thermoelastic dissipation (TED) of the MEMS gyroscope can also degrade the quality factor (Q-factor) and performance of the device.
Frequency modulation (FM) gyroscopes are a promising new architecture in gyroscope design. These gyroscopes measure a frequency difference of the degenerated resonator. The measured frequency difference is proportional to the angular rate of motion. Moreover, a rate integrating gyroscope (RIG) using whole angle mode can measure rotation angle directly. The main challenge of these devices is asymmetry of frequency and Q-factor mismatch caused by fabrication imperfections. Coventor recently had the opportunity to model some RIG resonators developed at Tohoku University1. A CoventorMP® model of the resonators is shown below.
Courtesy of Tohoku University, Professor Tanaka laboratory.
MEMS FM/RIG will bring us to the next technology frontier in gyroscope architecture. The upcoming IEEE INERTIAL conference will feature discussions about these devices. We look forward to seeing the next technology frontier in MEMS gyroscope and inertial sensor design at the IEEE INERTIAL conference and hope to meet you there.
Reference:
- Shihe Wang, Muhammad Salman Al Farisi, Takashiro Tsukamoto and Shuji Tanaka, “Dynamically Balanced Out-of-Plane Resonator for Roll/Pitch Rate Integrating Gyroscope,” in Proc. Sensor Symposium, Nov. 2019, 20am2-LN2-77.
