Novel silicon resonance accelerometer structure based on lever difference

Abstract

The invention belongs to the technical field of precision sensors, and discloses a novel silicon resonance accelerometer structure based on lever difference. The structure comprises an upper layer, a middle layer and a lower layer, the middle layer is a monocrystalline silicon micro-mechanical structure and comprises a mass block, an amplification lever structure, a double-end fixed tuning fork type resonator and the like; through a central anchor point and two amplification lever structures with opposite force transmission directions, the stress difference of the two resonators is realized, the number of supporting anchor points is reduced, the resonators are in a thermal expansion free state under a temperature change working condition, the thermal stress influence is reduced, and the temperature performance is improved; meanwhile, the area of the stress isolation frame is reduced, the difficulty of the processing technology is reduced, and the engineering application of the silicon resonance accelerometer to an ultra-precise system is promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of precision sensors, and in particular relates to a novel silicon resonant accelerometer structure based on lever differential designed for navigation-level engineering application requirements. Background Art

[0002] Silicon resonant accelerometer is a micromechanical inertial device based on the resonance principle. It outputs acceleration signals by measuring the change in the resonant frequency of the resonator caused by acceleration. Compared with traditional capacitive accelerometers, silicon resonant accelerometers have higher zero bias stability and scale factor stability, and are small in size, low in price, easy to integrate, and have strong anti-interference capabilities. Therefore, they have broad application prospects in high-precision inertial navigation systems, especially in the defense and military fields.

[0003] The micromechanical structure of a silicon resonant accelerometer is usually composed of a sensitive mass block, an amplifying lever structure, a resonator, a supporting mechanism, a driving mechanism, and a detecting mechanism. Its working principle is that the driving mechanism drives the resonator to resonate. When there is an acceleration input from the outside, the sensitive mass block senses the acceleration and converts it into an inertial force. The inertial force is transmitted to the resonator through the amplifying lever structure, causing the resonator to be pulled or compressed, thereby changing its resonant frequency. The detecting mechanism determines the magnitude of the input acceleration by detecting the change in the resonant frequency.

[0004] However, a major challenge facing silicon resonant accelerometers in practical applications is environmental adaptability, especially performance stability under extreme temperature changes. Changes in ambient temperature can cause mismatched thermal expansion of support anchors, resulting in thermal stress, which affects the performance stability and measurement accuracy of the accelerometer. In order to reduce the impact of thermal stress, there are currently two main methods: one is to achieve structural compensation by reasonably distributing multiple support anchors and designing detour beams, but this method is difficult to accurately adjust the position of the support anchors, and the thermal stress elimination effect is not completely controllable; the second is to use a single anchor support structure based on a stress isolation frame. Although it can effectively suppress thermal stress, the stress isolation frame requires a larger support stiffness, resulting in a limited layout area of ​​the resonator, which increases the difficulty of the process and limits its engineering application.

[0005] Therefore, it is particularly important to design a silicon resonant accelerometer structure that can effectively suppress the influence of thermal stress and has simple process, compact structure, and easy engineering application. In response to this demand, the present invention proposes a new silicon resonant accelerometer structure based on lever differential. Through an innovative design scheme, the problems existing in the prior art are solved, and the performance stability and engineering application capability of the silicon resonant accelerometer are improved. Summary of the invention

[0006] In response to the above problems, the present invention will provide a new silicon resonant accelerometer structure based on lever differential designed for navigation-level engineering application requirements. This structure is particularly suitable for high-precision inertial navigation systems. It aims to improve the performance stability of the accelerometer under extreme temperature changes through innovative mechanical structure design, reduce the impact of thermal stress on the resonator, and improve the zero bias stability and scale factor of the accelerometer, thereby meeting the urgent needs of the defense and military fields for high-performance and high-reliability sensors.

[0007] The technical solution adopted by the present invention is: a new silicon resonant accelerometer structure based on lever differential, the new silicon resonant accelerometer structure consists of three layers of structure: upper, middle and lower. The middle layer is the micromechanical structure of the accelerometer, and its material is single crystal silicon; the upper layer is a glass cover plate, which is bonded to the support anchor point, outer frame and electrode of the middle layer, and there are metal wires inside for leading out frequency signals; the lower glass cover plate is bonded to the silicon outer frame of the middle layer to realize vacuum packaging; the middle micromechanical structure includes a mass block, an amplifying lever structure, a double-ended fixed tuning fork resonator, a central stress isolation frame, drive detection comb teeth, a central anchor point, a mass block support anchor point, a mass block support beam and an outer frame.

[0008] There are two double-ended fixed tuning fork resonators with the same structural dimensions, symmetrically distributed along the non-acceleration sensitive direction, and centrally distributed along the acceleration sensitive direction; the two ends of each double-ended fixed tuning fork resonator are respectively connected to the output beam of the amplifying lever structure; the fulcrum beam of the amplifying lever structure is connected to the central stress isolation frame, and the geometric center of the central stress isolation frame is connected to the central anchor point.

[0009] The amplifying lever structure includes two forms with different force transmission directions. The first form has a fulcrum beam located between the input beam and the output beam, and the second form has a fulcrum beam located at the very end of the lever body. When the accelerometer is subjected to external acceleration, the differential effect of the force on the resonator is achieved through the two forms of amplifying lever structures.

[0010] The mass block is connected to the mass block support anchor point through a mass block support beam, and the interior of the mass block is connected to the input beam of the amplifying lever structure; the mass block support beam is designed as a U-shaped beam to reduce the stiffness along the acceleration sensitive direction.

[0011] The central anchor point and the mass block support anchor point are bonded to the upper glass cover plate to provide support for the double-ended fixed tuning fork resonator, the amplifying lever structure and the mass block; the outer frame is bonded to the upper glass cover plate and the lower glass cover plate respectively to ensure that the middle micromechanical structure layer is suspended above the lower glass, and the lower glass cover plate is coated with a getter to provide a sealed vacuum cavity for the structure layer.

[0012] The mass block support anchor points are symmetrically distributed at the upper left, lower left, upper right and lower right centers, and the central anchor point is distributed at the geometric center of the accelerometer; when the ambient temperature changes, the influence of thermal stress on the double-ended fixed tuning fork resonator is reduced through two forms of amplification lever structures and a central stress isolation frame design.

[0013] The drive detection comb teeth, the double-ended fixed tuning fork resonator, the central stress isolation frame and the central anchor point are located inside the mass block. The drive detection comb teeth are located on both sides of the double-ended fixed tuning fork resonator and are symmetrically distributed with the resonator as the central axis, and are used to drive the resonator to resonate and detect the resonant frequency.

[0014] The driving detection comb teeth include fixed comb teeth and movable comb teeth. The movable comb teeth are connected to the middle of the resonant beam, and the fixed comb teeth are bonded to the upper glass cover plate through electrodes to form driving capacitors and detection capacitors to achieve driving and frequency detection of the resonator.

[0015] The double-ended fixed tuning fork resonator includes two resonance beams distributed along the acceleration sensitive direction, and both ends of each resonance beam are respectively connected to the output beam of the amplifying lever structure. The magnitude of acceleration is characterized by detecting the frequency change of the resonance beam.

[0016] The two double-ended fixed tuning fork resonators produce differential changes when subjected to force, one resonator is subjected to pressure and the other is subjected to tension, and the scale factor and stability of the silicon resonant accelerometer are improved by detecting the frequency differential changes of the two resonators.

[0017] The beneficial effects of the present invention and the prior art are:

[0018] (1) The present invention designs a novel silicon resonant accelerometer structure based on lever differential, distributes the supporting anchor points at the geometric center and four corners of the accelerometer, and uses a central stress isolation frame to support the amplified lever structure. Based on the small thermal stress of the central anchor point and the buffering effect of the mass block support beam, the thermal stress transmitted from each anchor point to the double-ended fixed tuning fork resonator along the acceleration sensitive direction is minimized.

[0019] (2) The present invention designs a novel silicon resonant accelerometer structure based on lever differential, and adopts two amplifying lever structures with different force transmission directions to realize differential force on the resonator, and enables the resonator to be symmetrically distributed along the non-acceleration and non-sensitive directions, thereby ensuring the support stiffness of the central stress isolation frame, reducing the support area, increasing the mass block area, and thus improving the scale factor of the accelerometer.

[0020] (3) The present invention designs a new silicon resonant accelerometer structure based on lever differential, which has fewer supporting anchor points, reduces the bonding area between glass and silicon, and reduces the thermal stress introduced by the processing technology. In addition, the area of ​​the central stress isolation frame is greatly reduced, which reduces the difficulty of the processing technology and improves the survival rate of the accelerometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the intermediate structure layer of the novel silicon resonant accelerometer in the present invention;

[0022] Figure 2 It is a schematic diagram of the mass block support beam structure in the present invention;

[0023] Figure 3 It is a schematic diagram of the amplified lever structure with the fulcrum beam in the middle in the present invention;

[0024] Figure 4 It is a schematic diagram of the amplified lever structure of the fulcrum beam at the end of the present invention;

[0025] Figure 5 It is a schematic diagram of the force of the resonator in the present invention;

[0026] Figure 6 It is a schematic diagram of the structure of a double-ended fixed tuning fork resonator in the present invention;

[0027] Figure 7 It is a schematic diagram of the drive detection comb structure in the present invention. DETAILED DESCRIPTION

[0028] In order to more clearly understand the purpose, technical solutions and advantages of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and simulation data.

[0029] Combination Figure 1 The present invention is a novel silicon resonant accelerometer structure based on lever differential, which is composed of an upper, middle and lower three-layer structure. The middle layer is a micromechanical structure of the accelerometer, and its material is single crystal silicon; the upper layer is a glass cover plate, which is bonded to the support anchor point, outer frame and electrode of the middle layer, and has a metal wire inside for extracting the frequency signal; the lower glass cover plate is bonded to the silicon outer frame of the middle layer to achieve vacuum packaging. The middle micromechanical structure includes a mass block (1), an amplifying lever structure (2a, 2b, 2c, 2d), a double-ended fixed tuning fork resonator (3a, 3b), a central stress isolation frame (4), drive detection comb teeth (5a, 5b, 5c, 5d), a central anchor point (6), a mass block support anchor point (7a, 7b, 7c, 7d), a mass block support beam (8a, 8b, 8c, 8d) and an outer frame (9).

[0030] The two double-ended fixed tuning fork resonators (3a, 3b) are acceleration sensitive structures with consistent structural dimensions, symmetrical distribution along the Y direction, and central distribution along the X acceleration sensitive direction. The two ends (13a, 13b, 14a, 14b) of each double-ended fixed tuning fork resonator (3a, 3b) are respectively connected to the output beams (11a, 11b, 11c, 11d) of the amplifying lever structure (2a, 2b, 2c, 2d). The fulcrum beams (12a, 12b, 12c, 12d) of the amplifying lever structure (2a, 2b, 2c, 2d) are connected to the central stress isolation frame (4), and the geometric center of the central stress isolation frame (4) is connected to the central anchor point (6). The central anchor point and the central stress isolation frame can not only ensure the fixation of the resonator and reduce the number of supporting anchor points, but also make the structural layout of the resonator simpler.

[0031] The mass block (1) occupies the largest area of ​​the accelerometer, and its upper left, lower left, upper right and lower right corners are connected to the mass block support anchor points (7a, 7b, 7c, 7d) through mass block support beams (8a, 8b, 8c, 8d), and combined with Figure 2 In order to ensure that the mass block support beam (8a, 8b, 8c, 8d) has a buffering effect along the acceleration sensitive direction, its structure is designed as a U-shaped beam to reduce its stiffness along the acceleration sensitive direction. The mass block (1) is internally connected to the input beams (10a, 10b, 10c, 10d) of the amplifying lever structures (2a, 2b, 2c, 2d) distributed symmetrically at the upper left, lower left, upper right, and lower right. In order to achieve force differential, the amplifying lever structures (2a, 2b, 2c, 2d) are designed as two force transmission forms, combined with Figure 3 The fulcrum beams (12a, 12c) of the amplified lever structures (2a, 2c) are located between the input beams (10a, 10c) and the output beams (11a, 11c); Figure 4 The fulcrum beams (12b, 12d) of the amplified lever structures (2b, 2d) are located at the end of the lever body. Figure 5 When the accelerometer is subjected to external acceleration in the positive X direction, the mass block (1) generates an inertial force F in the positive X direction. m, the mass block support beam (8a, 8b, 8c, 8d) supports and buffers the mass block (1), and the input beam (10a, 10b, 10c, 10d) transmits the force to the amplifying lever structure (2a, 2b, 2c, 2d). Since the positions of the fulcrum beams of the two forms of amplifying lever structures are different, the directions of the lever force transmission are different. Therefore, the two ends (13a, 14a) of the resonator (3a) are subjected to pressure, and the two ends (13b, 14b) of the resonator (3b) are subjected to tension. Similarly, when there is an acceleration in the opposite direction of X, the two ends (13a, 14a) of the resonator (3a) are subjected to tension, and the two ends (13b, 14b) of the resonator (3b) are subjected to pressure. The differential effect of the force on the resonant beams (3a, 3b) is achieved by using the two forms of levers. Combination Figure 6 When the resonator is under pressure, the force-frequency characteristic is expressed as follows:

[0032]

[0033] In the formula, f F is the resonant frequency of the resonant beam (15a, 15b, 16a, 16b) after being subjected to force, E is the Young's modulus of single crystal silicon, w is the width of the resonant beam (15a, 15b, 16a, 16b), L f is the length of the resonant beam (15a, 15b, 16a, 16b), h is the thickness of the intermediate layer, F is the pressure on a single resonant beam (15a, 15b, 16a, 16b), ρ is the density of single crystal silicon, and m is the mass of the movable comb teeth (17a, 17b, 17c, 17d) connected to the resonant beam (15a, 15b, 16a, 16b). Therefore, when the resonant beams of the two double-ended fixed tuning fork resonators (3a, 3b) are subjected to inertial force, the resonant frequency of the resonator can be obtained by Taylor expansion by eliminating high-order terms:

[0034]

[0035] In the formula, f n is the resonant frequency of the resonant beams (15a, 16a) and the resonant beams (15b, 16b) when they are not subjected to tensile or compressive stress, f Fa is the resonant frequency of the resonant beam (15a, 16a) of the double-ended fixed tuning fork resonator (3a) after being subjected to pressure, f Fb It is the resonant frequency of the resonant beam (15b, 16b) of the double-ended fixed tuning fork resonator (3b) after being subjected to tension. It can be seen from the above formula that the two resonators have a differential effect when subjected to force. By differentiating the output frequencies of the two resonators, the scale factor of the silicon resonant accelerometer can be increased, the common mode error can be eliminated, and the stability of the accelerometer can be improved.

[0036] The central anchor point (6) and the mass block support anchor points (7a, 7b, 7c, 7d) are bonded to the upper glass cover plate to provide support for the double-ended fixed tuning fork resonator (3a, 3b), the amplifying lever structure (2a, 2b, 2c, 2d) and the mass block (1). The outer frame (9) is bonded to the upper glass cover plate and the lower glass cover plate respectively to ensure that the middle micromechanical structure layer is suspended above the lower glass. The lower glass cover plate is coated with a getter to provide a sealed vacuum cavity for the structure layer, thereby improving the Q value of the resonant mode of the resonator.

[0037] The mass block support anchor points (7a, 7b, 7c, 7d) are symmetrically distributed at the upper left, lower left, upper right and lower right centers, and the central anchor point (6) is distributed at the geometric center of the accelerometer. When the ambient temperature changes, the intermediate structure layer undergoes thermal expansion. Based on the design of the two forms of amplifying lever structures (2a, 2b, 2c, 2d) and the central stress isolation frame (4), the connection between the double-ended fixed tuning fork resonator (3a, 3b) and the mass block (1) is only the middle anchor point (1) and the mass block support anchor points (7a, 7b, 7c, 7d) at the four corners. The thermal stress generated by the middle anchor point (1) in the X and Y directions is very small and is transmitted to the double-ended fixed tuning fork resonator through the central stress isolation frame (4). The thermal stress of the resonator (3a, 3b) is very small; the thermal stress of the mass block support anchor points (7a, 7b, 7c, 7d) along the X-acceleration sensitive direction is buffered and released through the mass block support beams (8a, 8b, 8c, 8d), so the thermal stress transmitted to the resonator through the amplifying lever structure (2a, 2b, 2c, 2d) along the X-acceleration sensitive direction is very small; the acceleration sensitive structure of the entire middle layer approaches a free thermal expansion state, and the thermal stress has a very small effect on the double-end fixed tuning fork resonator (3a, 3b).

[0038] Combination Figure 7The drive detection comb teeth (5a, 5b, 5c, 5d), the double-ended fixed tuning fork resonator (3a, 3b) and the central stress isolation frame (4) are located inside the mass block (1), and the drive detection comb teeth (5a, 5b, 5c, 5d) are located on both sides of the double-ended fixed tuning fork resonator (3a, 3b) and are symmetrically distributed with the resonator as the central axis. Among them, the movable comb teeth (17a, 17b, 17c, 17d) are respectively connected to the middle of the resonant beam (15a, 15b, 16a, 16b), and the fixed comb teeth (18a, 19a, 20a) are bonded to the upper glass cover plate through electrodes (21a, 22a, 23a) to achieve electrode fixation. The fixed comb teeth (19a) and the movable comb teeth (17a) form a driving capacitor, and the fixed comb teeth (19a) apply an electrostatic force on the movable comb teeth (17a) to drive the movable comb teeth (17a) to move, thereby causing the resonance beam (15a) to resonate; at the same time, the fixed comb teeth (18a, 20a) and the movable comb teeth (17a) form a detection capacitor, and the fixed comb teeth (18a, 20a) detect the capacitance change, thereby measuring the resonance frequency of the resonance beam (15a). Similarly, the driving detection methods of the other three resonance beams (15b, 16a, 16b) are consistent. Since the four resonance beams (15a, 15b, 16a, 16b) have the same size, the resonance frequency changes of the resonance beams (15a, 16a) are consistent, and the resonance frequency changes of the resonance beams (15b, 16b) are consistent. Finally, the frequency of the double-ended fixed tuning fork resonator (3a) and the double-ended fixed tuning fork resonator (3b) are differentiated to characterize the magnitude of acceleration.

[0039] The above is only the design structure of the present invention and does not constitute any limitation to the protection scope of the present invention; any technical solutions formed by equivalent transformation or equivalent replacement shall fall within the protection scope of the present invention; the parts not elaborated in detail in the present invention belong to the known technologies of those skilled in the art.

Claims

1. A novel silicon resonant accelerometer structure based on lever differential, characterized in that: The novel silicon resonant accelerometer structure is composed of three layers: upper, middle and lower. The middle layer is the micromechanical structure of the accelerometer, and its material is single crystal silicon. The upper layer is a glass cover plate, which is bonded to the support anchor points, outer frame and electrodes of the middle layer. There are metal wires inside to lead out the frequency signal. The lower glass cover plate is bonded to the middle silicon outer frame to achieve vacuum packaging.

2. According to claim 1, a novel silicon resonant accelerometer structure based on lever differential is characterized in that: The intermediate micromechanical structure includes a mass block, an amplifying lever structure, a double-ended fixed tuning fork resonator, a central stress isolation frame, drive detection comb teeth, a central anchor point, a mass block support anchor point, a mass block support beam and an outer frame.

3. The novel silicon resonant accelerometer structure based on lever differential according to claim 2, characterized in that: There are two double-ended fixed tuning fork resonators with the same structural dimensions, symmetrically distributed along the non-acceleration sensitive direction, and centrally distributed along the acceleration sensitive direction; the two ends of each double-ended fixed tuning fork resonator are respectively connected to the output beam of the amplifying lever structure; the fulcrum beam of the amplifying lever structure is connected to the central stress isolation frame, and the geometric center of the central stress isolation frame is connected to the central anchor point.

4. The novel silicon resonant accelerometer structure based on lever differential according to claim 3 is characterized in that: The amplifying lever structure includes two forms with different force transmission directions. The first form has a fulcrum beam located between the input beam and the output beam, and the second form has a fulcrum beam located at the very end of the lever body. When the accelerometer is subjected to external acceleration, the differential effect of the force on the resonator is achieved through the two forms of amplifying lever structures.

5. The novel silicon resonant accelerometer structure based on lever differential according to claim 2, characterized in that: The mass block is connected to the mass block support anchor point through a mass block support beam, and the interior of the mass block is connected to the input beam of the amplifying lever structure; the mass block support beam is designed as a U-shaped beam to reduce the stiffness along the acceleration sensitive direction.

6. The novel silicon resonant accelerometer structure based on lever differential according to claim 2, characterized in that: The central anchor point and the mass block support anchor point are bonded to the upper glass cover plate to provide support for the double-ended fixed tuning fork resonator, the amplifying lever structure and the mass block; the outer frame is bonded to the upper glass cover plate and the lower glass cover plate respectively to ensure that the middle micromechanical structure layer is suspended above the lower glass, and the lower glass cover plate is coated with a getter to provide a sealed vacuum cavity for the structure layer.

7. The novel silicon resonant accelerometer structure based on lever differential according to claim 2 is characterized in that: The mass block support anchor points are symmetrically distributed at the upper left, lower left, upper right and lower right centers, and the central anchor point is distributed at the geometric center of the accelerometer; when the ambient temperature changes, the influence of thermal stress on the double-ended fixed tuning fork resonator is reduced through two forms of amplification lever structures and a central stress isolation frame design.

8. The novel silicon resonant accelerometer structure based on lever differential according to claim 2 is characterized in that: The drive detection comb teeth, the double-ended fixed tuning fork resonator, the central stress isolation frame and the central anchor point are located inside the mass block. The drive detection comb teeth are located on both sides of the double-ended fixed tuning fork resonator and are symmetrically distributed with the resonator as the central axis, and are used to drive the resonator to resonate and detect the resonant frequency.

9. The novel silicon resonant accelerometer structure based on lever differential according to claim 8, characterized in that: The driving detection comb teeth include fixed comb teeth and movable comb teeth. The movable comb teeth are connected to the middle of the resonant beam, and the fixed comb teeth are bonded to the upper glass cover plate through electrodes to form driving capacitors and detection capacitors to achieve driving and frequency detection of the resonator.

10. The novel silicon resonant accelerometer structure based on lever differential according to claim 2, characterized in that: The double-ended fixed tuning fork resonator includes two resonance beams distributed along the acceleration sensitive direction, and both ends of each resonance beam are respectively connected to the output beam of the amplifying lever structure. The magnitude of acceleration is characterized by detecting the frequency change of the resonance beam.

11. The novel silicon resonant accelerometer structure based on lever differential according to claim 10, characterized in that: Two double-ended fixed tuning fork resonators produce differential changes when subjected to force, one resonator is subjected to pressure and the other is subjected to tension. The scale factor and stability of the silicon resonant accelerometer are improved by detecting the frequency differential changes of the two resonators.

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