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EP-4388279-B1 - ANGULAR RATE SENSORS

EP4388279B1EP 4388279 B1EP4388279 B1EP 4388279B1EP-4388279-B1

Inventors

  • LAPADATU, DANIEL
  • Kvisterøy, Terje

Dates

Publication Date
20260506
Application Date
20220526

Claims (15)

  1. A micro-electromechanical sensor, MEMS, device for measuring z-axis angular rate, the device comprising: a substrate (129, 2000) defining a substrate plane and a z-axis perpendicular to the substrate plane; a first vibratory structure comprising a first proof mass (21, 22, 101, 102, 201, 202) and a second proof mass (21, 22, 101, 102, 201, 202); a second vibratory structure comprising a first sense mass and a second sense mass (31, 32, 109, 110, 209, 210), the first and second proof masses (21, 22, 101, 102, 201, 202) each respectively having first and second drive structures (11, 12, 104, 105, 105, 203, 204, 205, 206) comprising first and second drive masses, respectively, said drive structures for generating drive-mode movements of said proof masses (21, 22, 101, 102, 201, 202) in drive-mode direction (x), the drive mode corresponding to the anti-phase movement of said proof masses (21, 22, 101, 102, 201, 202); wherein the first and second vibratory structures being elastically coupled to each other, characterised by the device further comprising a mechanical structure (111) for amplifying a Coriolis-induced movement in the sense mode direction (y) of said proof masses (21, 22, 101, 102, 201, 202) and for converting said amplified Coriolis induced movement into movement of the sense masses (31, 32, 109, 110, 209, 210) in the drive-mode direction (x), wherein the in-phase sense movement of said proof masses (21, 22, 101, 102, 201, 202) is suppressed, the mechanical structure (111) comprising two pivots (118), two pairs of mechanical converter springs (119) and a lever pivotable about the z-axis, wherein each pair of mechanical converter springs (119) is respectively rigidly connected to one of said pivots (118), the mechanical converter springs (119) in each pair being rigidly connected at an angle from each other, the mechanical structure further comprising a mechanical decoupler for decoupling the drive and sense modes.
  2. A MEMS device according to claim 1, wherein the mechanical structure comprises at least one in-phase suppressing element (107, 108).
  3. A MEMS device according to claim 2, wherein said suppressing element comprises the lever (107, 108).
  4. A MEMS device according to claim 3, wherein said suppressing element further comprises a spring (43, 45, 46).
  5. A MEMS device according to any one of the preceding claims, wherein the mechanical decoupler (117) is pronged.
  6. A MEMS device according to claim 5, wherein the mechanical decoupler (117) is three-pronged.
  7. A MEMS device according to any one of the preceding claims, wherein the mechanical decoupler (117) comprises a decoupling spring (44).
  8. A MEMS device according to claim 7, wherein the decoupling spring (44) is Psishaped spring (126).
  9. A MEMS device according to any one of the preceding claims, wherein the drive and sense modes occur respectively parallel to the substrate plane (129, 2000).
  10. A MEMS device according to any one of the preceding claims, wherein the first vibratory structure comprises electrodes (123) for quadrature error compensation.
  11. A MEMS device according to any one of the preceding claims, wherein the second vibratory structure comprises a first plurality of electrodes for sense detection and a second plurality of electrodes for sense actuation.
  12. A MEMS device according to any one of claims 1 to 10, wherein the second vibratory structure comprises a plurality of electrodes (121, 122, 123, 124) arranged to operate for a first time period as actuation electrodes, the same plurality of electrodes (121, 122, 123, 124) being arranged to operate for a second time period, shorter than the first time period, as detection electrodes.
  13. A MEMS device according to any one of the preceding claims, wherein at least one of the drive structures comprises at least one spring (42, 43) for suppressing the movement of the at least one drive structure in sense mode direction (y).
  14. A MEMS device according to any one of the preceding claims, wherein at least one of the drive structures comprises an anchor structure (72, 112), the anchor structure (72, 112) comprising at least one anchor (72, 112) for supressing the-in phase movement of the at least one drive structure.
  15. A MEMS device according to claim 14, wherein the anchor structure (72) further comprises at least one anchor (71, 81) for suppressing the movement of the sense masses in the sense mode direction (y).

Description

Technical Field Aspects of the present invention generally relate to angular rate sensors. More specifically, aspects of the present invention are directed to micro-electromechanical systems (MEMS) vibratory gyroscopes for tactical and inertial grade applications. Background Angular rate sensors are known devices that directly measure angular rate, without integration in conditioning electronics. MEMS vibratory gyroscopes are a type of angular rate sensors that use a vibrating structure to determine the rate of rotation. The underlying physical principle is that a vibrating object tends to continue vibrating in the same plane even if its support rotates. The Coriolis effect causes the object to exert a force on its support, and, by measuring this force, the rate of rotation can be determined. Vibrating structure gyroscopes are simpler and cheaper than conventional rotating gyroscopes of similar accuracy. Inexpensive vibrating structure gyroscopes manufactured with MEMS technology are widely used in smartphones, gaming devices, cameras and many other applications. Mechanical gyroscopes usually include a continuously rotating or vibrating element mounted on a gyro frame, along with a separate sense element that monitors the motion of this rotating or vibrating element. Friction is inevitably produced by a rotating mechanical element becoming an increasing problem in smaller gyroscopes and ultimately can lead to operational problems. Therefore, for MEMS gyroscopes a vibrating mechanical element is preferred. The minimum detectable angular rate is not the only performance parameter for an angular rate sensor; there are a number of other criteria that determine the overall quality of the sensor. These parameters include: the rate noise density, bias stability, angle random walk (ARW), measurement range, scale-factor linearity, input bandwidth, power supply requirements, operation temperature range, and g-sensitivity. Out of the listed parameters, rate noise density, ARW and bias stability define the performance grade of the gyroscope. Performance grades of gyroscope can be classified into four main groups: rate grade, tactical grade, navigation grade and space grade. MEMS vibratory gyroscopes have been successfully employed for tactical grade applications, however, there are a number of challenges faced in these developments, including: efficient use of actuation energy, the requirement of a vacuum to achieve high mechanical quality factors, mechanical crosstalk between the drive and sense modes, symmetric design of the flexures for the drive and sense modes, minimising electronic dampening, noise, repeatability of the fabrication process, stress-free reliable packaging, assembly of sensor and readout chips, and shock-survival characteristics. Several MEMS vibratory gyroscopes use a tuning fork structure which has twin-mass architecture, where two masses oscillate in opposite directions along the drive axis. The tuning-fork configuration is robust against spurious responses due to external acceleration inputs, since the acceleration inputs cause a common deflection of the tines in the same direction, being rejected by differential readout. Some highperformance tactical-grade tuning-fork have been fabricated by micromachining of single-crystal quartz. However, micromachined quartz rate sensors require complicated electronics for temperature compensation of quartz materials and fabricating quartz sensors adds complexity. For these reasons, quartz rate sensors have been superseded by advances in silicon micromachining technologies and the integration of silicon rate sensors with readout electronics on the same chip. More recent MEMS vibrational gyroscope angular rate sensors still have a number of design flaws that limit the performance of instruments. These include, amongst others: sense masses that are not coupled and operate independently from one another, large numbers of undesired modes due to the shape and dimensions of designs, weak actuation, insufficient frequency adjust range and insufficient quadrature compensation. US 2010/0313657 A1 and US 11,118,907 B2 each disclose examples of prior art devices, which are very large in size and therefore present a challenge for fabrication and proper functionality. The masses and other elements that should otherwise be rigid are becoming flexible in the out of plane direction, thus compromising the functionality of the devices. Another disadvantage of these devices is that, from the presented drawings, the drive and sense modes are not entirely decoupled. Furthermore, these devices are prone to quadrature errors caused by residual orthogonal drive motion inherent to the illustrated mechanical couplings between the various masses and levers. In particular, US 11,118,907 B2 shows a U-shaped decoupling flexure that is not eliminating the residual orthogonal movement, contributing to quadrature errors. Aspects of the present invention address problems with the prior art