MEMS inertial sensor micromechanical structure based on inner and outer double-layer staggered cantilever beams

Abstract

The invention belongs to the field of inertial instruments, and particularly relates to an MEMS inertial sensor micromechanical structure based on inner and outer double-layer staggered cantilever beams, which comprises a sensing unit, a cantilever beam assembly and a fixed frame, the cantilever beam assembly comprises a connecting ring sleeving the periphery of the sensing unit, n inner cantilever beams which are radially connected between the connecting ring and the sensing unit and are uniformly distributed along the circumference of the connecting ring, and m outer cantilever beams which are radially connected between the connecting ring and the fixed frame and are uniformly distributed along the circumference of the connecting ring; the n inner cantilever beams form an inner layer cantilever beam, the m outer cantilever beams form an outer layer cantilever beam, the n inner cantilever beams and the m outer cantilever beams are arranged in a staggered mode, and the cantilever beam assembly is symmetrical about the central axis of a micro-mechanical structure through the staggered arrangement mode. According to the invention, the cross axis suppression ratio of the MEMS inertial sensor can be improved.

Description

Technical Field

[0001] The invention belongs to the field of inertial instruments, and more specifically, relates to a MEMS inertial sensor micromechanical structure based on inner and outer double-layer staggered cantilever beams. Background Art

[0002] An inertial sensor is a sensor that uses Newton's second law and the law of conservation of angular momentum to detect acceleration, posture, angular velocity and other data of the monitored object. MEMS technology integrates microsensors, microactuators, signal processing and control circuits, providing a technical basis for the miniaturization of inertial sensors. With the continuous maturity of MEMS technology, the resolution and stability of MEMS inertial sensors are constantly improving. They have important applications in mechanical equipment, automobiles, missiles, aircraft, mobile phones and other fields, mainly used in posture recognition, motion tracking, high-speed motion control, safety monitoring and health detection.

[0003] The cross-axis suppression ratio is the ratio of the sensor's response to an input signal on its non-sensitive axis to its response to the same input signal on its sensitive axis. In actual application scenarios, inertial sensors often face complex environmental conditions, and the ability of the vibration system in the sensor to suppress movement in the non-sensitive axis direction must be considered. If the characteristic frequency in the non-sensitive axis direction is close to the characteristic frequency in the sensitive axis direction, interference displacement signals will also be generated in the non-sensitive axis direction during actual application, causing errors in displacement detection. A higher cross-axis suppression ratio can reduce this interference, which is particularly important for high-precision dynamic measurement applications. Summary of the invention

[0004] In view of the defects and improvement needs of the prior art, the present invention provides a MEMS inertial sensor micromechanical structure based on inner and outer double-layer staggered cantilever beams, which aims to improve the cross-axis suppression ratio of the MEMS inertial sensor.

[0005] To achieve the above object, according to one aspect of the present invention, a MEMS inertial sensor micromechanical structure based on inner and outer double-layer staggered cantilever beams is provided, comprising: a sensitive unit, a cantilever beam assembly, and a fixed frame;

[0006] The cantilever beam assembly comprises: a connecting ring sleeved on the outer circumference of the sensitive unit, n inner cantilever beams radially connected between the connecting ring and the sensitive unit and evenly distributed along the circumference of the connecting ring, and m outer cantilever beams radially connected between the connecting ring and the fixed frame and evenly distributed along the circumference of the connecting ring;

[0007] The n inner cantilever beams constitute an inner layer of cantilever beams, the m outer cantilever beams constitute an outer layer of cantilever beams, the n inner cantilever beams and the m outer cantilever beams are arranged in a staggered manner, and the staggered arrangement makes the cantilever beam assembly symmetrical about the central axis of the micromechanical structure.

[0008] Furthermore, the n inner cantilever beams have the same structural dimensions, the m outer cantilever beams have the same structural dimensions, and the length and width structural dimension relationship between the inner cantilever beams and the outer cantilever beams satisfies that the stiffness difference between the inner cantilever beams and the outer cantilever beams enables the sensor to achieve the required cross-axis suppression ratio.

[0009] Furthermore, the staggered angle between two adjacent inner cantilever beams and the outer cantilever beam is selected from 30° to 45°, wherein the staggered angle is the angle between the two cantilever beams on the horizontal plane.

[0010] Furthermore, the staggered angle between two adjacent inner cantilever beams and the outer cantilever beam is 45°.

[0011] Furthermore, it is prepared by using an SOI silicon wafer, wherein the cantilever beam component is composed only of a thin silicon layer portion of the SOI silicon wafer after photolithography, development and etching of the SOI silicon wafer.

[0012] The present invention also provides a MEMS inertial sensor, comprising a micromechanical structure part and a microelectronic structure part, wherein the micromechanical structure part adopts the above-mentioned MEMS inertial sensor micromechanical structure based on inner and outer double-layer staggered cantilever beams.

[0013] Furthermore, the sensor is a MEMS acceleration inertial sensor.

[0014] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0015] (1) The sensor micromechanical structure design proposed in the present invention enhances the symmetry of the structure and reduces the sensitivity to the non-sensitive axis direction. At the same time, the design of the inner and outer staggered cantilever beams is to arrange different cantilever beams in a staggered manner. This arrangement can effectively disperse the load and reduce the local stiffness in a certain direction; at the same time, in the inner and outer staggered beam structure, the arrangement of the cantilever beams causes the inner and outer staggered beams to be regarded as a series connection between the stiffness of the inner and outer beams, thereby reducing the stiffness of the cantilever beams in the sensitive axis direction, thereby improving the sensitivity to the target sensing parameter. In addition, when the geometric parameters of the inner and outer beams are optimized, their deformation behaviors when subjected to external loads will be different, thereby reducing the degree of mutual influence, thereby minimizing the mechanical coupling between the inner and outer beams and improving the measurement accuracy. Therefore, the MEMS acceleration inertial sensor of the present invention adopts the inner and outer staggered beam structure design, mainly by enhancing the symmetry of the structure, the stiffness in the non-sensitive axis direction and the mechanical decoupling, thereby reducing the response of the sensor to the acceleration of the non-sensitive axis, thereby improving the cross-axis suppression ratio.

[0016] (2) The present invention further proposes that the structural dimensions of the n inner cantilever beams are the same, the structural dimensions of the m outer cantilever beams are the same, and the length and width structural dimension relationship between the inner cantilever beams and the outer cantilever beams satisfies that the stiffness difference between the inner cantilever beams and the outer cantilever beams can enable the sensor to achieve the required cross-axis suppression ratio. Therefore, the stiffness difference caused by the size difference between the inner and outer cantilever beams can be optimized according to specific indicators.

[0017] (3) Through a suitable staggered arrangement, they can also be made more independent when subjected to external forces, thereby reducing the coupling between them and ensuring that the sensor only responds to the acceleration of the sensitive axis, while minimizing the acceleration response in the direction of the non-sensitive axis, thereby improving the cross-axis suppression ratio of the overall structure. The present invention further proposes that the staggered angle between the internal and external staggered cantilever beams of the MEMS is generally between 30° and 45°. A moderate staggered angle can effectively improve the sensitivity of the sensor to the sensitive axis, optimize the layout of the cantilever beam, while maintaining good structural rigidity and avoiding nonlinear response caused by excessive softness. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic plan view of a micromechanical structure of a MEMS inertial sensor based on inner and outer double-layer staggered cantilever beams provided in an embodiment of the present invention;

[0019] Figure 2 A structural diagram of a cantilever beam assembly provided in an embodiment of the present invention;

[0020] Figure 3 A three-dimensional diagram of the micromechanical structure of a MEMS inertial sensor based on inner and outer double-layer staggered cantilever beams provided in an embodiment of the present invention;

[0021] Figure 4 A diagram showing the working state changes of the micromechanical structure of a MEMS inertial sensor based on inner and outer double-layer staggered cantilever beams provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] Embodiment 1

[0024] A MEMS inertial sensor micromechanical structure based on inner and outer double-layer staggered cantilever beams, such as Figure 1 As shown, it includes: a sensitive unit, a cantilever beam assembly, and a fixed frame;

[0025] Among them, Figure 2 As shown, the cantilever beam assembly includes: a connecting ring sleeved on the outer circumference of the sensitive unit, n inner cantilever beams radially connected between the connecting ring and the sensitive unit and evenly distributed along the circumference of the connecting ring, and m outer cantilever beams radially connected between the connecting ring and the fixed frame and evenly distributed along the circumference of the connecting ring;

[0026] The n inner cantilever beams constitute an inner layer of cantilever beams, and the m outer cantilever beams constitute an outer layer of cantilever beams. The n inner cantilever beams and the m outer cantilever beams are arranged in a staggered manner, and the staggered arrangement makes the cantilever beam assembly symmetrical about the central axis of the micromechanical structure.

[0027] The present embodiment proposes a novel structure of a MEMS inertial sensor micromechanical structure, the three-dimensional structure is as follows Figure 3 As shown, it has the following characteristics:

[0028] (1) Compared with the existing structure, the micromechanical structure design of the sensor in this embodiment enhances the symmetry of the structure and reduces the sensitivity to the non-sensitive axis direction. The reason is that this inner and outer staggered beam structure makes the sensor highly symmetrical in all directions. The symmetrical structural design can make the stress and deformation caused by acceleration in the non-sensitive axis direction offset each other as a whole. When the sensor is subjected to acceleration in the non-sensitive axis direction, the stress directions on the inner and outer beams are opposite, resulting in a reduction in the overall stress response. This stress offset effect reduces the sensitivity of the sensor to acceleration in the non-sensitive axis direction, thereby improving the cross-axis suppression ratio;

[0029] (2) Compared with the existing structure, the micromechanical structure design of the sensor in this embodiment reduces the stiffness of the overall structure in the sensitive axis direction and improves the sensitivity to the target sensing parameter. For example, when the sensing parameter is acceleration, the design of the inner and outer staggered cantilever beams is to arrange different cantilever beams in a staggered manner. This arrangement can effectively disperse the load and reduce the local stiffness in a certain direction; at the same time, in the inner and outer staggered beam structure, the arrangement of the cantilever beams causes the inner and outer staggered beams to be regarded as a series connection between the stiffness of the inner and outer beams, thereby reducing the stiffness of the cantilever beam in the sensitive axis direction. When the sensor is affected by acceleration, the relative movement between the inner and outer cantilever beams will increase. This movement amplifies the displacement of the sensitive unit and reduces the stiffness of the cantilever beam. On the contrary, because the internal and external staggered structural layout makes the geometric shape of the cantilever beam in the non-sensitive axis direction more stable. This arrangement can effectively constrain the degree of freedom of the cantilever beam, making it less likely to deform too much when subjected to external force, thereby improving its stiffness in the non-sensitive axis direction and reducing the response to acceleration in the non-target direction, thereby improving the cross-axis suppression ratio.

[0030] (3) Compared with the existing structure, the micromechanical structure design of the sensor in this embodiment reduces the mechanical coupling between the inner and outer cantilever beams. The internal and external staggered cantilever beam structure can minimize the mechanical coupling between the inner and outer beams. By selecting the appropriate beam width and length, the stiffness difference between the inner and outer beams can be effectively controlled. When the geometric parameters of the inner and outer beams are optimized, their deformation behaviors when subjected to external loads will be different, thereby reducing the degree of mutual influence. At the same time, when the staggered arrangement method satisfies the condition that the cantilever beam assembly is symmetrical about the central axis of the micromechanical structure, the appropriate specific staggered arrangement method can make them more independent when subjected to external forces, thereby reducing the coupling between them, ensuring that the sensor only responds to the acceleration of the sensitive axis, and the acceleration response to the non-sensitive axis direction is minimized, thereby also improving the cross-axis suppression ratio of the overall structure.

[0031] In general, the MEMS acceleration inertial sensor of this embodiment adopts the inner and outer staggered beam structure design, which mainly reduces the response of the sensor to the acceleration of the non-sensitive axis by enhancing the symmetry of the structure, the stiffness in the non-sensitive axis direction and the mechanical decoupling, thereby improving the cross-axis suppression ratio. This design effectively improves the axial selectivity and measurement accuracy of the MEMS acceleration inertial sensor, and meets the requirements for high precision and high reliability.

[0032] As a preferred implementation, the n inner cantilever beams have the same structural dimensions, the m outer cantilever beams have the same structural dimensions, and the length and width structural dimension relationship between the inner cantilever beams and the outer cantilever beams satisfies that the stiffness difference between the inner cantilever beams and the outer cantilever beams can enable the sensor to achieve the required cross-axis suppression ratio.

[0033] Through optimization simulation, it is found that the greater the difference in stiffness between the inner and outer beams, the higher the sensitivity of the sensor to the sensitive axis, making its response to the target acceleration more obvious. At the same time, increasing the stiffness in the direction of the non-sensitive axis helps to suppress cross-axis interference and improve the cross-axis suppression ratio. However, if the stiffness difference is too large, it may lead to increased nonlinear behavior and affect the accuracy and stability of the signal. If the stiffness difference is smaller, it may also cause the sensor to be less sensitive to the target acceleration, affecting the measurement accuracy.

[0034] Therefore, the stiffness difference caused by the size difference between the inner and outer cantilever beams should be optimized according to specific indicators. Generally speaking, a moderate stiffness difference can effectively improve the sensitivity and cross-axis suppression ratio while maintaining good linear response.

[0035] For reference only, the staggered angle between two adjacent inner cantilever beams and outer cantilever beams is 45°. The width of the inner cantilever beam is 0.01-0.05 mm and the length is 0.1-1.5 mm, while the width of the outer cantilever beam is 0.01-0.05 mm and the length is 0.1-1.5 mm.

[0036] As a preferred embodiment, the staggered angle between two adjacent inner cantilever beams and the outer cantilever beam is selected from 30° to 45°, wherein the staggered angle is the angle between the two cantilever beams on the horizontal plane.

[0037] As mentioned above, through a suitable staggered arrangement, they can also be made more independent when subjected to external forces, thereby reducing the coupling between them, ensuring that the sensor only responds to the acceleration of the sensitive axis, and the acceleration response to the non-sensitive axis direction is minimal, thereby also improving the cross-axis suppression ratio of the overall structure. As a preferred option, the staggered angle between the inner and outer staggered cantilever beams of MEMS is usually considered to be an ideal choice between 30° and 45°. A moderate staggered angle can effectively improve the sensitivity of the sensor to the sensitive axis, optimize the layout of the cantilever beam, while maintaining good structural stiffness and avoiding nonlinear response caused by excessive softness. Through simulation and experiment, the staggered angle that best suits the performance of a specific sensor can be found. For reference only, the staggered angle between two adjacent inner and outer cantilever beams is 45°.

[0038] It should be noted that both SOI silicon wafers (three layers, including: a thin silicon layer, a silicon dioxide layer and a thick silicon layer) and ordinary silicon wafers (single-layer silicon) can be used to prepare the micromechanical structure proposed in this embodiment, without limitation, except that the material is limited to silicon. As a preferred implementation, it can be prepared by using an SOI silicon wafer, wherein the cantilever beam assembly is composed of only the thin silicon layer of the SOI silicon wafer after photolithography, development and etching of the SOI silicon wafer.

[0039] The sensor usually uses a thin silicon layer in an SOI silicon wafer to make a cantilever beam assembly located between the sensitive unit and the fixed frame. The thin silicon layer and the thick silicon layer together make the sensitive unit (i.e., the test mass) and the fixed frame. When stimulated by an acceleration signal outside the installation plane, the test mass vibrates up and down in the out-of-plane direction under the action of the cantilever beam to achieve sensing. The main principle is to realize signal acquisition through the deformation and capacitance change of the micromechanical structure. Taking the acceleration signal acquisition as an example, the working principle is generally explained to help readers understand how the micromechanical structure proposed in this embodiment plays a role in the work of the MEMS inertial sensor, as follows:

[0040] (1) Regarding structural design, the inner and outer staggered beam structure mainly consists of the following parts:

[0041] Sensing cell: The movable part located in the center of the sensor that moves when subjected to acceleration.

[0042] Internal and external staggered cantilever beam: It is an elastic beam connecting the sensitive unit and the fixed frame. The internal cantilever beam and the external cantilever beam are staggered to provide elastic support.

[0043] Interdigitated capacitor electrodes: Finger-shaped electrodes extending from the mass block and the fixed frame are nested together to form capacitor plates.

[0044] (2) Mechanical deformation caused by acceleration

[0045] When the sensor is subjected to external acceleration, according to Newton's second law, the mass block will generate an inertial force in the opposite direction of the acceleration. The inertial force causes the mass block to move slightly along the sensitive axis. In this process, the internal and external staggered beams undergo elastic deformation, providing a restoring force to hinder the displacement of the mass block and enable the system to reach a new equilibrium position. Figure 3 As shown, the initial position of the cantilever beam assembly is the position without color filling, and the position after movement is the position with blue filling.

[0046] (3) Generation of Capacitance Change

[0047] The finger electrodes on the mass block and the fixed frame are interlaced to form multiple parallel plate capacitors. When the mass block moves, the overlapping area of ​​the interdigitated electrodes changes, resulting in a change in capacitance. The elastic deformation of the beam may also cause a slight change in the spacing between the electrodes, further affecting the capacitance. This design makes the capacitance change proportional to the acceleration, with a good linear relationship.

[0048] (4) Signal acquisition and processing

[0049] Using a capacitance-to-voltage converter or oscillation circuit, tiny capacitance changes are converted into measurable electrical signals such as voltage or frequency. The signal is amplified, filtered, and converted from analog to digital to obtain accurate acceleration data, thereby realizing the acquisition of acceleration signals.

[0050] The staggered cantilever beam structure proposed in this embodiment optimizes the displacement of the sensitive unit. When the sensor is affected by acceleration, the relative movement between the inner and outer cantilever beams will increase. This movement amplifies the displacement of the sensitive unit, making the capacitance change more obvious and enhancing the acceleration response in the direction of the sensitive axis. At the same time, the symmetrical beam structure effectively suppresses the interference in the direction of the non-sensitive axis and improves the measurement accuracy. The design of the cantilever beam also meets the working requirements of the sensor that a good linear relationship is maintained between the capacitance change and the acceleration. This design makes full use of the characteristics of the micromechanical structure to achieve high-sensitivity and high-precision acceleration measurement.

[0051] The specific steps of micro-nano process processing of inertial sensor micromechanical structure are described as follows:

[0052] Step 1: Maintain cleanliness by performing organic washing and oxygen cleaning on the SOI silicon wafer, and complete the photolithography development of the cantilever beam structure, external frame and inspection quality shape on the thin silicon layer, so as to transfer the image of the thin silicon layer sensor structure to the silicon wafer, and etch out the sensor structure through deep reactive ion etching (DRIE).

[0053] Step 2: Soak the silicon wafer with the sensor pattern etched in acetone to remove the surface photoresist. Complete the photolithography development of the sensor structure and release hole on the thick silicon layer, and perform the stacking operation. Also, use deep reactive ion etching (DRIE) to etch the sensor structure and release hole structure on the thick silicon layer to prepare for the release of the structure.

[0054] Step 3: Use acetone to separate the support wafer (ordinary silicon wafer) and the SOI silicon wafer, and finally use HF vapor phase etching to release the sensing structure to obtain a discrete single out-of-plane acceleration sensor sample.

[0055] In one example, the final optimized design parameter values ​​of the manufactured MEMS acceleration inertial sensor are: inner beam width 0.03mm, length 0.2mm, outer beam width 0.03mm, length 1.4mm. By reasonably optimizing the length and width of the beam and the arrangement of the inner and outer beams, the final simulation results are: the first-order characteristic frequency in the sensitive axis direction is 713.49Hz, and the second-order characteristic frequency in the non-sensitive axis direction is 1140.9Hz. The cross-axis suppression ratio is the ratio of the characteristic frequency in the non-sensitive axis direction to the characteristic frequency in the sensitive axis direction, which is 1.6, which improves its cross-axis suppression ratio by 45% compared with the structure before optimization.

[0056] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A MEMS inertial sensor micromechanical structure based on inner and outer double-layer staggered cantilever beams, characterized in that: include: Sensitive unit, cantilever beam assembly, and fixed frame; The cantilever beam assembly comprises: a connecting ring sleeved on the outer circumference of the sensitive unit, n inner cantilever beams radially connected between the connecting ring and the sensitive unit and evenly distributed along the circumference of the connecting ring, and m outer cantilever beams radially connected between the connecting ring and the fixed frame and evenly distributed along the circumference of the connecting ring; The n inner cantilever beams constitute an inner layer of cantilever beams, the m outer cantilever beams constitute an outer layer of cantilever beams, the n inner cantilever beams and the m outer cantilever beams are arranged in a staggered manner, and the staggered arrangement makes the cantilever beam assembly symmetrical about the central axis of the micromechanical structure.

2. The MEMS inertial sensor micromechanical structure according to claim 1, characterized in that: The n inner cantilever beams have the same structural dimensions, the m outer cantilever beams have the same structural dimensions, and the length and width structural dimensions of the inner cantilever beams and the outer cantilever beams satisfy that the stiffness difference between the inner cantilever beams and the outer cantilever beams enables the sensor to achieve the required cross-axis suppression ratio.

3. The MEMS inertial sensor micromechanical structure according to claim 1, characterized in that: The staggered angle between two adjacent inner cantilever beams and outer cantilever beams is selected from 30° to 45°, wherein the staggered angle is the angle between the two cantilever beams on the horizontal plane.

4. The MEMS inertial sensor micromechanical structure according to claim 3, characterized in that: The staggered angle between two adjacent inner cantilever beams and the outer cantilever beam is 45°.

5. The MEMS inertial sensor micromechanical structure according to claim 1, characterized in that: It is prepared by using an SOI silicon wafer, wherein the cantilever beam component is only composed of a thin silicon layer portion of the SOI silicon wafer after photolithography, development and etching of the SOI silicon wafer.

6. A MEMS inertial sensor, comprising a micromechanical structure part and a microelectronic structure part, characterized in that: The micromechanical structure part thereof adopts a MEMS inertial sensor micromechanical structure based on inner and outer double-layer staggered cantilever beams as described in any one of claims 1 to 5.

7. A MEMS inertial sensor according to claim 6, characterized in that: The sensor is a MEMS acceleration inertial sensor.

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