A reconstructed double-spoke MEMS multi-ring gyroscope with low thermoelastic damping

Abstract

This invention discloses a low thermoelastic damping reconstructed double-spoke MEMS multi-ring gyroscope, belonging to the field of microelectromechanical systems (MEMS). This MEMS multi-ring gyroscope has a fully symmetrical structure in a plane, consisting of a central fixed anchor point, multiple concentric rings, spokes, and electrodes. The central fixed anchor point is circular, fixed by an external structure, and shares the same center with the multiple concentric rings. The innermost concentric ring is connected to the anchor point via spokes. The multiple concentric rings are connected by spokes, and the width of the concentric rings can be adjusted as needed, with varying spacing between the rings. The spoke structure includes single straight spokes, double straight spokes, and reconstructed double straight spokes. Spokes of the same ring are evenly distributed circumferentially, with the axes of adjacent rings differing by 22.5°. The outermost ring is connected to the first ring from the outside in by a single straight spoke, the innermost ring is connected to the anchor point by double straight spokes, and the remaining rings are connected by reconstructed double straight spokes. This gyroscope features a unique reconfigured double spoke design that extends the heat transfer path to reduce heat transfer at the spokes, thereby altering the internal temperature and heat flux distribution of the gyroscope; reducing the thermoelastic damping of the device; improving the gyroscope's sensitivity; and reducing zero-bias instability.

Description

Technical Field

[0001] This invention relates to a reconstructed double-spoke MEMS multi-ring gyroscope with low thermoelastic damping, belonging to the field of micro-electro-mechanical systems (MEMS). Background Technology

[0002] MEMS gyroscopes are inertial sensors that utilize microelectromechanical systems (MEMS) fabrication technology combined with gyroscope technology requirements. They can sensitively detect the angular velocity or absolute angle of a carrier's rotation relative to inertial space. The core of a high-precision inertial navigation system lies in a high-precision gyroscope. MEMS-based gyroscopes, with their lightweight, small size, low power consumption, and suitability for mass production, have received significant attention and rapid development in recent years. MEMS multi-ring gyroscopes belong to the MEMS ring resonant gyroscope category and are among the most promising micro-mechanical gyroscopes currently available. Compared to hemispherical gyroscopes, multi-ring resonant gyroscopes do not have complex three-dimensional structures, making their fabrication process simpler and more suitable for mass production. Compared to single-ring resonant gyroscopes, multi-ring resonant gyroscopes possess a multi-concentric nested structure with embedded electrodes, resulting in higher sensitivity capacitance, modal quality, and energy density. They also retain the characteristic of identical operating modal frequencies found in both hemispherical and single-ring resonant gyroscopes, theoretically enabling extremely high sensitivity.

[0003] In its operating mode, the temperature fluctuations generated during the motion of a MEMS multi-ring gyroscope are negligible compared to the external environment. The structure primarily exchanges heat with the outside world through thermal convection and thermal radiation. Under high-vacuum packaging, energy loss due to thermal radiation is negligible, and thermal conduction is considered the only heat transfer mechanism. During operation, the resonant structure of the MEMS multi-ring gyroscope resonates under a periodic driving force. During deformation, the temperature of the structure subjected to compressive stress rises, while the temperature of the structure subjected to tensile stress decreases, creating a temperature difference within the resonant structure. During temperature equilibrium, heat flux is generated, and resonant mechanical energy is converted into thermal energy, resulting in irreversible energy loss. This type of energy loss can be represented by thermoelastic damping. Thermoelastic damping is highly correlated with key gyroscope parameters such as gyroscope sensitivity, Brownian thermal noise, and zero-bias instability. Reducing thermoelastic damping can effectively improve gyroscope performance.

[0004] To address the thermoelastic damping, a key parameter in MEMS multi-ring gyroscopes, this paper proposes a reconstructed double-spoke MEMS multi-ring gyroscope with low thermoelastic damping. The traditional single straight spoke is replaced with a double spoke, and a connecting block is used to reconstruct the ring structure on both sides of the double spoke, effectively reducing the thermoelastic damping of the gyroscope and thus improving its performance. Summary of the Invention

[0005] The technical problem to be solved by this invention is: based on existing processing technology solutions, and addressing the key problems commonly found in current gyroscopes, this invention proposes a reconstituted double-spoke MEMS multi-ring gyroscope with low thermoelastic damping.

[0006] The magnitude of thermoelastic damping can be measured by the reciprocal of thermoelastic damping, the thermoelastic quality factor. By definition, if the total energy of a gyroscope resonant structure in one cycle of operation is W, then the thermoelastic quality factor is the ratio ΔW of the total energy and energy loss in one cycle. TED If related, the thermoelasticity quality factor can be calculated as follows:

[0007]

[0008]

[0009] Where k represents the thermal conductivity of the resonator material, p is the localized heat flux of the structure, and V represents the volume of the resonant structure. In the gyroscope structure, there are areas with high thermoelastic damping, corresponding to high-density heat flux distributions. The heat flux can be calculated as:

[0010]

[0011] Heat flux and temperature gradient in the region Proportional to heat transfer, reducing the temperature difference between the two sides of the heat transfer path or blocking heat transfer through the structure can effectively reduce heat loss caused by heat flux. During structural optimization, the heat flux distribution inside the gyroscope can be analyzed to precisely optimize areas with dense heat flow, thereby changing the structure to reduce the internal heat flux and lower thermoelastic damping.

[0012] In the heat flux analysis of existing MEMS multi-ring gyroscopes, the heat flux distribution is most concentrated around the spokes during the operating mode. Therefore, if a reduction in thermoelastic damping is required, the spoke structure needs to be redesigned. In the MEMS multi-ring gyroscope structure, the heat transfer capability satisfies:

[0013]

[0014] Where A represents the cross-sectional area of ​​the prismatic solid through which heat passes, and L represents the length of the heat-conducting part of the prismatic solid. The material of the MEMS multi-ring gyroscope resonant structure is single-crystal silicon, with a uniformly distributed thermal conductivity k, and a value of 130 W / (m·K). In the optimization design process, the material itself cannot be changed. Reducing the cross-sectional area at the spokes or extending the heat-conducting length can effectively reduce the heat transfer capacity of the structure.

[0015] To achieve the above objectives, the present invention adopts the following technical solution:

[0016] This invention proposes a recombinant dual-spoke MEMS multi-ring gyroscope with low thermoelastic damping. The MEMS multi-ring gyroscope has a fully symmetrical structure in the plane and consists of a central fixed anchor point, multiple concentric ring structures, spoke structures, and electrodes.

[0017] The central anchor point is circular and fixed by an external structure. It shares the same center with the multi-ring concentric structure, and the innermost concentric ring is connected to the anchor point by spokes.

[0018] The multiple concentric rings are connected by spokes, and the width of the concentric rings can be adjusted according to requirements. The spacing between the concentric rings is not equal.

[0019] The spoke structure includes single straight spokes, double straight spokes, and reconstituted double straight spokes. Spokes of the same ring are evenly distributed along the circumference of the ring, and the axes of the spokes of adjacent rings differ by 22.5°. The outermost ring is connected to the first ring from the outside in by single straight spokes, the innermost ring and the anchor point are connected by double straight spokes, and the remaining rings are connected by reconstituted double straight spokes.

[0020] The single straight spoke consists of a single rectangular spoke, the double straight spoke consists of two rectangular spokes, and the reconstituted double straight spoke consists of two rectangular spokes and a single rectangular reconstituted block between the spokes. In the reconstituted double straight spoke, the ring structures on both sides of the spokes are divided by the spoke spacing, and the two sides are reconnected using a connecting block, forming an H-shape. The length of the connecting block is determined by the spoke spacing, while the width and connection position can be adjusted as needed.

[0021] The electrode structure includes inter-ring island electrodes, inter-ring working electrodes, and outer-ring electrodes, which are connected to electrical signals via an external structure. The inter-ring island electrodes are inserted on both sides of the double-straight spokes and partially reconstructed double-straight spokes, while the inter-ring working electrodes are inserted on both sides of the partially reconstructed double-straight spokes, evenly distributed along the circumference of the rings and maintaining a fixed distance from the concentric rings and spoke structure. The outer-ring electrodes are distributed outside the outermost ring and evenly distributed along the circumference of the ring.

[0022] Furthermore, COMSOL multiphysics coupling simulation confirmed that the reconstituted double-spoke structure can reduce thermoelastic damping and achieve a high thermoelastic quality factor without reducing the effective capacitance area.

[0023] Furthermore, COMSOL multiphysics coupling simulation confirmed that the reconstituted double-spoke structure can optimize the gyroscope's vibration mode, resulting in a lower stiffness axis offset angle and less frequency fragmentation in the gyroscope's working mode.

[0024] The beneficial effects of this invention are:

[0025] The reconstructed double-spoke MEMS multi-ring gyroscope with low thermoelastic damping proposed in this invention has the following advantages:

[0026] 1. The MEMS multi-ring gyroscope designed in this invention will have a unique recombined double spokes, which extends the heat transfer path to reduce heat transfer at the spokes, thereby changing the internal temperature and heat flux distribution of the gyroscope;

[0027] 2. The MEMS multi-ring gyroscope designed in this invention reduces the overall temperature difference within the structure under equal driving displacement, and the temperature on both sides of the spokes decreases significantly;

[0028] 3. In the MEMS multi-ring gyroscope designed in this invention, the heat flux distribution within the short spokes at a 45° offset of the antinode axis is no longer obvious, and the heat transfer within the ring is blocked at a 22.5° offset of the antinode axis. The narrow H-shaped structure effectively extends the heat transfer path, reduces the heat flux density, and lowers the thermoelastic damping of the device.

[0029] 4. The MEMS multi-ring gyroscope designed in this invention has low thermoelastic damping after multiphysics simulation, which can effectively improve the quality factor of the gyroscope. Under modal matching, it can improve the driving modal displacement, improve the sensitivity of the gyroscope, and reduce zero-bias instability.

[0030] 5. The reconstituted double-spoke structure enables the gyroscope to have regular operating mode shape, lower stiffness axis offset angle, and less frequency fragmentation, which helps to improve the gyroscope's sensitivity and reduce zero-bias instability.

[0031] Ultimately, based on existing processing technologies and technical solutions, the overall performance of the gyroscope was improved and optimized, achieving the desired effect. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of a reconstructed double-spoke MEMS multi-ring gyroscope resonant structure.

[0033] Figure 2 This is a three-dimensional schematic diagram of the reconstructed double-spoke MEMS multi-ring gyroscope resonant structure;

[0034] Figure 3 This is a schematic diagram of the reconstructed double-spoke structure;

[0035] Figure 4(a) is a schematic diagram of the reconstructed double-spoke MEMS multi-ring gyroscope electrode structure in plan view;

[0036] Figure 4(b) is a schematic planar view of the inter-ring working electrode structure;

[0037] Figure 5(a) shows the operating mode shape of the reconstructed double-spoke MEMS multi-ring gyroscope;

[0038] Figure 5(b) shows the temperature distribution under the working mode of the reconstituted double-spoke MEMS multi-ring gyroscope;

[0039] Figure 5(c) shows the temperature distribution of the short spokes at a 45° offset from the anti-axis of the reconstructed double-spoke MEMS multi-ring gyroscope.

[0040] Figure 5(d) shows the heat flux distribution of the short spokes at a 45° offset from the anti-axis of the reconstructed double-spoke MEMS multi-ring gyroscope.

[0041] Figure 5(e) shows the temperature distribution of the long spokes at a 22.5° offset from the antiaxial axis of the reconstructed double-spoke MEMS multi-ring gyroscope.

[0042] Figure 5(f) shows the heat flux distribution of the long spokes at a 22.5° offset from the antiaxial axis of the reconstructed double-spoke MEMS multi-ring gyroscope.

[0043] Figure 6(a) shows the relationship between the spoke spacing x1 and frequency of the reconstructed double-spoke MEMS multi-ring gyroscope;

[0044] Figure 6(b) shows the relationship between the spoke spacing x1 and the thermoelastic quality factor of the reconstituted double-spoke MEMS multi-ring gyroscope;

[0045] Figure 6(c) shows the relationship between the distance x2 from the reconstructed double-spoke MEMS multi-ring gyroscope connector block to the inner ring, the width x3, and the frequency;

[0046] Figure 6(d) shows the relationship between the distance x2, width x3, and thermoelastic quality factor of the reconstituted double-spoke MEMS multi-ring gyroscope connector block to the inner ring;

[0047] Figure 7 It is the final optimized and reconstructed double-spoke MEMS multi-ring gyroscope structure Detailed Implementation Plan

[0048] The following description, in conjunction with the accompanying drawings and specific examples, provides a detailed account of the proposed solutions. However, it should be noted that the present invention protects not only the proposed embodiments, but also any improvements made based on them, which fall within the scope of protection of the present invention.

[0049] This invention proposes a reconstructed double-spoke MEMS multi-ring gyroscope with low thermoelastic damping. The gyroscope is resonantly fabricated under the (111) crystal plane of single-crystal silicon, and the device thickness varies from 30um to 250um. It can be fabricated through a variety of processing techniques.

[0050] This MEMS multi-ring gyroscope has a fully symmetrical structure in the plane. The gyroscope's resonant structure, such as... Figure 1-3 As shown, it consists of a central fixed anchor point 1, concentric ring structures 2 to 4 with a total number of rings N, and spoke structures 5 to 9 connecting the anchor point and each ring.

[0051] The central anchor point 1 is circular, sharing the same center with all the concentric rings. The first ring from the inside out is connected to the central anchor point via spokes. The central anchor point is fixed by an external structure, while the remaining resonant structures are suspended and can vibrate at a certain frequency under the excitation of an electrical signal.

[0052] The main resonant structure of the double-spoke MEMS multi-ring gyroscope consists of N sets of concentric rings with varying numbers and widths. The spacing between the rings is not fixed and is not equal. From the inside out, all rings except the first ring 2 and the second ring 3 are grouped in pairs, called grouped rings 4. The grouped rings 4 form short spacings, while the non-grouped rings form long spacings. The anchor point to the first ring 2 and the first ring 2 to the second ring 3 form independent spacings.

[0053] The spoke structure exists within each gap, connecting the anchor point and each ring. It includes single straight spokes 6, double straight spokes 5, and reconstituted double straight spokes 7-9. There are 8 spokes in each ring, and the spokes are evenly distributed along the circumference of the ring. The axes of the spokes between adjacent rings differ by 22.5°. Only the short gap between the Nth ring and the (N-1)th ring contains single straight spokes 6, and the independent gap between the anchor point and the first ring 2 contains double straight spokes 5. The remaining spokes are reconstituted double straight spokes.

[0054] The single straight spoke is a single rectangular spoke; the double straight spoke is two parallel rectangular spokes of the same size; and the reconstituted double straight spoke, such as... Figure 3 As shown, it consists of two rectangular spokes of the same size and a single rectangular reassembly block between the spokes. In the reassembly type double straight spoke, the ring structure on both sides of the spokes is divided by the double straight spokes 11 and the spoke spacing 10, and the two sides are reconnected using a connecting block 12, forming an H shape. The length of the connecting block is determined by the spoke spacing, while the width and connection position can be adjusted as needed.

[0055] The electrode structure includes inter-ring island electrodes 13-14, inter-ring working electrodes 15, and external electrodes 16, which are connected to electrical signals via an external structure. Inter-ring island electrodes 13-14 are inserted between the anchor point and the first ring, and between the first ring and the second ring. Inter-ring working electrodes 15 are inserted on both sides of the long spoke in the reconstructed double straight spoke structure. Both types of electrodes are evenly distributed along the circumference of the ring, with eight sets of electrodes inserted in each spacing, maintaining a fixed distance from the concentric rings and spoke structure. External electrodes 16 are distributed outside the Nth ring, evenly distributed along the circumference of the ring, and maintain a fixed distance from the Nth ring, for a total of 16 electrodes.

[0056] The inter-ring working electrode consists of an inner ring working electrode 17, an isolation electrode 18, and an outer ring working electrode 19. The inner ring working electrode 17 and the inner ring form a capacitor, and the outer ring working electrode 19 and the outer ring form a capacitor. Different signals are introduced into the two types of electrodes. To reduce parasitic capacitance, an isolation electrode 18 is inserted between the two types of electrodes.

[0057] To further illustrate the advantages of the reconstituted dual-straight-spoke MEMS multi-ring gyroscope, the following examples will provide further explanation:

[0058] A dual-straight-spoke MEMS multi-ring gyroscope with a device thickness of 100µm is designed. The gyroscope has 10 rings, all of which are 15µm wide. The distance from the anchor point to the first ring and from the first ring to the second ring is 200µm. The distance between two adjacent groups of rings and between the second and third rings is 260µm. The distance between rings in the same group is 10µm. The width of a single straight spoke is 15µm. The width of the double straight spokes and the recombined double straight spokes is 15µm. The spoke spacing is 10µm. The distance from the connecting block to the inner ring is 130µm. The width of the connecting block is 20µm. Each electrode is 10µm away from the resonant structure.

[0059] To illustrate the heat flux distribution inside the resonant structure under operating modes, this invention uses COMSOL Multiphysics 5.6 multiphysics coupling analysis software to simulate the frequency, thermoelastic quality factor, mode shape distribution, temperature distribution, and heat flux distribution of the gyroscope under operating modes.

[0060] To ensure standardized and clear simulation results, all thermodynamic simulations in this invention control the maximum displacement to 2.5 μm. The simulation results are highly correlated with mesh quality. Under appropriate mesh density and complete centrosymmetry, the frequency difference and thermoelastic quality factor difference between the driving mode and the sensitive mode are minimized, and the internal temperature distribution and heat flux distribution of the resonator are completely identical, requiring analysis of only one mode.

[0061] Furthermore, the reconstructed MEMS multi-ring gyroscope structure was simulated, and the results are shown in Figure 5. Figure 5(a) shows the mode shape of the reconstructed double-spoke MEMS gyroscope, Figure 5(b) shows the temperature distribution under the working mode of the reconstructed double-spoke MEMS gyroscope, Figure 5(c) shows the temperature distribution of the short spokes at a 45° offset from the antinode axis of the reconstructed double-spoke MEMS gyroscope, Figure 5(d) shows the heat flux distribution of the short spokes at a 45° offset from the antinode axis of the reconstructed double-spoke MEMS gyroscope, Figure 5(e) shows the temperature distribution of the long spokes at a 22.5° offset from the antinode axis of the reconstructed double-spoke MEMS gyroscope, and Figure 5(f) shows the heat flux distribution of the long spokes at a 22.5° offset from the antinode axis of the reconstructed double-spoke MEMS gyroscope. Based on the above analysis of the temperature and heat flux distribution within the structure under the working modes, it can be concluded that the working mode frequency of this structure is 11596Hz, and the thermoelastic quality factor is 229260, showing a significant improvement. Under the same driving displacement, compared with the prototype gyroscope, this structure significantly reduces the overall temperature difference within the structure, and the temperature on both sides of the spokes decreases significantly. The heat flux distribution within the short spokes at a 45° offset of the antinode axis is no longer obvious, and the heat transfer within the ring is blocked at a 22.5° offset of the antinode axis, resulting in a reduction in heat flux density. The narrow H-shaped structure effectively extends the heat transfer path, and the thermoelastic quality factor of the device is improved.

[0062] This invention further investigates the relationship between three dimensional parameters introduced in the reconstituted double-spoke design: x1 spoke spacing, x2 distance between the connecting block and the inner ring, and x3 connecting block width, and frequency and thermoelastic quality factor. The simulation results are shown in Figures 6(a) to (d). During the simulation, to ensure no unreasonable structures appear and to run the simulation in a reasonable order, the dimensions must meet the following conditions: all double-spoke spacings are equal and change with the spoke spacing; the ratio of the distance between the connecting block and the inner ring to the length of the short spoke is equal in all types of reconstituted double-spoke designs; the width of the connecting block at the short spoke is fixed at 15 μm; when the sum of the distance between the connecting block and the inner ring at the short spoke and the width of the connecting block is greater than 40 μm, the distance between the connecting block and the inner ring is set to 25 μm to ensure that the edge of the connecting block does not exceed the edge of the outer ring. All dimensions in the simulation results are represented by the dimensions of the connecting blocks at the long spokes.

[0063] Simulation results show that the thermoelastic quality factor is approximately negatively correlated with the spoke spacing. The thermoelastic quality factor reaches its maximum when the spoke spacing is at its minimum value. Due to manufacturing limitations, the minimum spoke spacing is set to 10 μm. When the distance from the connecting block to the inner ring is less than 200 μm, the thermoelastic quality factor increases as the distance decreases. Within the study range, the thermoelastic quality factor is negatively correlated with the connecting block width. Therefore, the thermoelastic quality factor reaches its maximum when both the distance from the connecting block to the inner ring and the connecting block width are minimized. For ease of manufacturing, the distance from the connecting block to the inner ring is set to 0 μm, and the connecting block width is set to 15 μm. Figure 7 As shown, at this time the connecting block and the inner ring are completely overlapped, the frequency is 9875, and the thermoelastic quality factor reaches 290200.

Claims

1. A reconstructed double-spoke MEMS multi-ring gyroscope with low thermoelastic damping, characterized in that, It has a fully symmetrical structure in the plane, consisting of a central fixed anchor point, multiple concentric ring structures, a spoke structure, and electrodes; The central anchor point is circular and fixed by an external structure. It shares the same center with the multi-ring concentric structure. The innermost concentric ring is connected to the anchor point by spokes. The multiple concentric rings are connected by spokes, and the width of the concentric rings can be adjusted as needed, with varying spacing between each concentric ring. The spoke structure includes single straight spokes, double straight spokes, and recombined double straight spokes. Spokes of the same ring are evenly distributed along the circumference of the ring, and the axes of the spokes of adjacent rings differ by 22.5°. The outermost ring is connected to the first ring from the outside to the inside by single straight spokes, the innermost ring and the anchor point are connected by double straight spokes, and the remaining rings are connected by recombined double straight spokes. The single straight spoke consists of a single rectangular spoke, the double straight spoke consists of two rectangular spokes, and the recombined double straight spoke consists of two rectangular spokes and a single rectangular recombined block between the spokes; In the reconstituted double straight spokes, the ring structures on both sides of the spokes are divided by the spoke spacing, and the two sides are reconnected using connecting blocks, forming an H shape; the length of the connecting block is determined by the double spoke spacing, and the width and connection position can be adjusted according to requirements. The electrode structure includes an inter-ring island electrode, an inter-ring working electrode, and an outer ring electrode, which are connected to electrical signals through an external structure. The inter-ring island electrodes are inserted on both sides of the double straight spokes and the partially reconstructed double straight spokes, while the inter-ring working electrodes are inserted on both sides of the partially reconstructed double straight spokes. They are evenly distributed along the circumference of the ring and maintain a fixed distance from the concentric rings and spoke structure. The outer ring electrodes are distributed outside the outermost ring and are evenly distributed along the circumference of the ring.

Images