Capacitive acceleration sensor for a vehicle body suspension system and method of manufacture
By employing a capacitive accelerometer with a dual-row comb structure and differential detection design, the problems of low sensitivity and insufficient shock resistance in existing technologies have been solved, achieving acceleration detection with high sensitivity and good linearity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HEFEI UNIV OF TECH
- Filing Date
- 2024-01-05
- Publication Date
- 2026-07-07
AI Technical Summary
Existing small-range capacitive accelerometers suffer from low sensitivity, poor linearity, and insufficient shock resistance.
The capacitive accelerometer design employs a dual-row comb tooth structure, including unequal-height comb tooth electrodes and a differential detection structure. Combined with an SOI substrate and damping hole design, it enhances the sensor's sensitivity and overload resistance.
It improves the sensor's sensitivity and linearity, enhances its ability to detect Z-axis acceleration, and protects the sensor from damage in high-impact environments.
Smart Images
Figure CN117849392B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of acceleration sensor technology, and in particular to a capacitive acceleration sensor for vehicle suspension systems and its fabrication method. Background Technology
[0002] Micromechanical accelerometers (MEMS) are widely used in inertial navigation, electronic devices, and control systems due to their advantages such as small size, light weight, and simple manufacturing process. Among them, small-range MEMS accelerometers are one of the most important inertial devices in automotive sensors, widely used in systems such as airbags, suspensions, and navigation. Currently, capacitive accelerometers are widely used in the automotive industry, medical equipment, and motion detection fields due to their advantages such as high sensitivity, fast response speed, low zero drift, low power consumption, simple design, and good stability.
[0003] Measurement range, sensitivity, linearity, and shock resistance are important specifications for capacitive accelerometers. However, current small-range capacitive accelerometers suffer from low sensitivity, poor linearity, and insufficient shock resistance. To address these issues, it is necessary to develop a sensor with high sensitivity, good linearity, and excellent overload resistance. Summary of the Invention
[0004] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one objective of this invention is to provide a capacitive acceleration sensor for vehicle suspension systems and its fabrication method, with a measurement range of -16g to 16g, possessing advantages such as small size, high sensitivity, good linearity, and good overload resistance.
[0005] According to the present invention, a capacitive acceleration sensor for a vehicle suspension system includes an isolation frame layer, a sensitive layer, a buried oxygen layer, a cavity layer, and a glass substrate. The isolation frame layer is disposed on one side of the sensitive layer, the buried oxygen layer is disposed on the other side of the sensitive layer, the cavity layer is disposed on the side of the buried oxygen layer away from the sensitive layer, and the glass substrate is disposed on the side of the cavity layer away from the buried oxygen layer.
[0006] Preferably, the sensitive layer includes a sensitive mass block and a fixed frame. A connecting groove is provided in the middle of both sides of the sensitive mass block. The fixed frame is connected to the sensitive mass block through a cantilever beam. The cantilever beam is disposed inside the connecting groove. Four sets of limiting grooves are provided near the four corners of the sensitive mass block. Limiting blocks are embedded in the limiting grooves. The limiting blocks are connected to the fixed frame through auxiliary beams.
[0007] Preferably, the sensitive mass block includes two sets of H-shaped mass blocks, which are symmetrical about the cantilever beam. The sensitive layer is provided with eight sets of comb-tooth structures of unequal height for detecting Z-axis acceleration, which are correspondingly arranged at the four corners of the H-shaped mass block.
[0008] Preferably, the unequal height comb tooth structure includes low comb tooth electrodes and high comb tooth electrodes, which are arranged alternately. The low comb tooth electrodes in the upper left and lower right groups of the unequal height comb tooth structure are connected to the sensitive mass block, the low comb tooth electrodes in the lower left and upper right groups of the unequal height comb tooth structure are connected to the fixed frame, the high comb tooth electrodes in the upper left and lower right groups of the unequal height comb tooth structure are connected to the fixed frame, and the high comb tooth electrodes in the lower left and upper right groups of the unequal height comb tooth structure are connected to the sensitive mass block.
[0009] Preferably, an H-shaped groove is formed on the outer surface of the H-shaped mass block located on one side, and multiple sets of damping holes are uniformly formed at the bottom of the H-shaped groove.
[0010] Preferably, the isolation frame layer includes an isolation frame body, and the isolation frame body is provided with ten sets of ohmic contact metal patterns corresponding to the installation positions of the unequal height comb tooth structure and the cantilever beam installation positions. Two sets of ohmic contact metal patterns at the four corners of the isolation frame body in the same length direction are connected by metal wires.
[0011] Preferably, the glass substrate includes borosilicate glass and limiting posts, a cavity is formed in the middle of the cavity layer, and four sets of limiting posts are installed at the four corners of the borosilicate glass, with the limiting posts disposed inside the cavity of the cavity layer.
[0012] Preferably, the fabrication method of a capacitive acceleration sensor for a vehicle suspension system includes the following steps:
[0013] S1: Select an n-type SOI wafer as the substrate and perform a standard cleaning process on the wafer to remove natural oxidation and other impurities from the surface;
[0014] S2: Silicon dioxide is deposited by chemical vapor deposition, and after photolithography, an ohmic contact window for making an ohmic contact is etched on the silicon dioxide by a RIE etching machine.
[0015] S3: Metal Al is sputtered by sputtering, and the desired ohmic contact metal pattern is obtained after peeling. Based on this, metal electrodes and metal interconnects are formed by photolithography mask patterning, metal sputtering, and peeling processes.
[0016] S4: Apply a layer of silicon dioxide film based on step S3;
[0017] S5: Photolithography and etching are performed on the surface of the silicon dioxide film to retain the high comb teeth on the left and right sides, the sensitive mass blocks except for the H-shaped grooves, and the silicon dioxide on the fixed frame.
[0018] S6: A silicon nitride film is added on top of S5;
[0019] S7: Photolithography and etching are performed on the surface of the silicon nitride film to retain the silicon nitride on both sides of the low comb teeth, high comb teeth, sensitive mass block, cantilever beam and fixed frame;
[0020] S8: The first etching is performed using reactive plasma etching technology. The etching depth is controlled by controlling the reaction time, and the etching depth is 30μm.
[0021] S9: After removing the silicon nitride film, a second etching is performed using reactive ion etching, stopping at the buried oxide layer in the middle of SOI, with an etching depth of 20μm, to release the sensitive structure;
[0022] S10: Remove the first layer of silicon oxide, grow a silicon dioxide film on the bottom silicon surface, etch the fixed frame back cavity through deep reactive ion etching process, stop after etching away the middle buried oxide layer, and remove excess silicon dioxide.
[0023] S11: The borosilicate glass is anodized to the back cavity connected to the silicon fixed frame through an anodizing process.
[0024] The beneficial effects of this invention are:
[0025] (1) The double-row comb structure increases the number of comb electrodes, which effectively improves the sensitivity of capacitive accelerometers compared to other single-row comb sensor structures.
[0026] (2) The fixed comb tooth electrode and the movable comb tooth electrode form a comb tooth structure with different heights. The eight sets of comb tooth structures with different heights are symmetrically arranged around the center point to form a differential detection structure for detecting the acceleration of the Z-axis. The capacitance changes caused by the changes of the X-axis and Y-axis in the plane will cancel each other out. The capacitance changes are all generated by the displacement along the Z-axis, thereby canceling the interference of the non-sensitive axis direction on the Z-sensitive axis.
[0027] (3) The structure of single-sided groove and single-sided damping hole is adopted to reduce damping and shift the position of the center of mass of the sensitive mass block, thereby increasing the angle of comb deflection and improving the sensitivity of the sensor.
[0028] (4) Four limit blocks are set in the plane to limit the displacement of the X and Y axes, and a glass substrate with protrusions is bonded outside the plane to limit the displacement of the Z axis, so as to prevent the sensor from being damaged when the vehicle is hit.
[0029] (5) Using a customized SOI substrate as the substrate can effectively control the thickness of the sensitive structure, prevent PN junction leakage, and improve the stability of the sensor. Attached Figure Description
[0030] In the attached diagram:
[0031] Figure 1 This is a schematic diagram of a capacitive acceleration sensor structure for a vehicle suspension system proposed in this invention;
[0032] Figure 2 An exploded view of the capacitive acceleration sensor for vehicle suspension systems proposed in this invention;
[0033] Figure 3 This is a schematic diagram of the structure of the isolation frame proposed in this invention;
[0034] Figure 4 This is a schematic diagram of the structure of the sensitive layer proposed in this invention;
[0035] Figure 5 The present invention proposes Figure 4 A magnified view of a section at point I;
[0036] Figure 6 The present invention proposes Figure 4 Enlarged view of a section at point II;
[0037] Figure 7 This is a schematic diagram of the structure of the glass substrate proposed in this invention;
[0038] Figure 8 This is a schematic diagram of the structure of step 1 of the preparation method proposed in this invention;
[0039] Figure 9 This is a schematic diagram of step 2 of the preparation method proposed in this invention;
[0040] Figure 10 This is a schematic diagram of the structure of step 3 in the preparation method proposed in this invention;
[0041] Figure 11 This is a schematic diagram of step 4 of the preparation method proposed in this invention;
[0042] Figure 12 This is a schematic diagram of step 5 of the preparation method proposed in this invention;
[0043] Figure 13 This is a schematic diagram of step 6 of the preparation method proposed in this invention;
[0044] Figure 14 This is a schematic diagram of step 7 of the preparation method proposed in this invention;
[0045] Figure 15 This is a schematic diagram of step 8 of the preparation method proposed in this invention;
[0046] Figure 16 This is a schematic diagram of step 9 of the preparation method proposed in this invention;
[0047] Figure 17 This is a schematic diagram of the structure of step 10 in the preparation method proposed in this invention;
[0048] Figure 18 This is a schematic diagram of the structure of step 11 of the preparation method proposed in this invention;
[0049] Figure 19 This is a comparison diagram of the effects of acceleration proposed in this invention on the sensitive axis and the cross axis.
[0050] In the diagram: 1-isolation frame layer, 2-sensitive layer, 3-buried oxide layer, 4-cavity layer, 5-glass substrate;
[0051] 11-Ohmic contact window, 12-Ohmic contact metal pattern, 13-Metal interconnect, 14-Silicon dioxide film, 15-Silicon nitride film, 16-Isolation frame body;
[0052] 21-Sensitive mass block, 22-Cantilever beam, 23-Fixed frame, 24-Limiting block, 25-Damping hole, 26-Auxiliary beam, 27-Low comb tooth electrode, 28-High comb tooth electrode, 29-H-shaped groove;
[0053] 51-Borosilicate glass, 52-Limiting post;
[0054] 100 - Top layer silicon, 101 - Middle buried oxide layer, 102 - Bottom layer silicon. Detailed Implementation
[0055] Reference Figure 1 , Figure 2 A capacitive acceleration sensor for a vehicle suspension system includes an isolation frame layer 1, a sensitive layer 2, a buried oxide layer 3, a cavity layer 4, and a glass substrate 5. The isolation frame layer 1 is disposed on one side of the sensitive layer 2, and the buried oxide layer 3 is disposed on the other side of the sensitive layer 2. The buried oxide layer 3 is made of silicon dioxide and is used to isolate the sensitive structure and the substrate, prevent PN junction leakage, and serve as an etching stop layer for the sensitive structure, enabling accurate control of the thickness of the sensitive structure. The cavity layer 4 is disposed on the side of the buried oxide layer 3 away from the sensitive layer 2, and the glass substrate 5 is disposed on the side of the cavity layer 4 away from the buried oxide layer 3. The cavity layer 4 is connected to the upper silicon fixed frame, providing sufficient space for the movable comb teeth. The other side is bonded to the glass substrate 5 through an anodic bonding process. The glass substrate 5 contains a limiting post structure to limit out-of-plane acceleration and protect the sensor under overload conditions.
[0056] ReferenceFigures 4-6 The sensitive layer 2 includes a sensitive mass block 21 and a fixed frame 23. The sensitive mass block 21 has a connecting groove in the middle of both sides. The fixed frame 23 is connected to the sensitive mass block 21 through a cantilever beam 22. The cantilever beam 22 is set inside the connecting groove. The sensitive mass block 21 has four sets of limiting grooves near the four corners. Limiting blocks 24 are embedded in the limiting grooves. The limiting blocks 24 are connected to the fixed frame 23 through an auxiliary beam 26.
[0057] The sensitive mass block 21 includes two sets of H-shaped mass blocks, which are symmetrical along the cantilever beam 22. The sensitive layer 2 is provided with eight sets of comb-tooth structures of unequal height for detecting Z-axis acceleration, which are correspondingly set at the four corners of the H-shaped mass blocks.
[0058] The unequal height comb tooth structure includes low comb tooth electrodes 27 and high comb tooth electrodes 28, which are arranged alternately. The low comb tooth electrodes 27 in the two sets of unequal height comb tooth structures on the upper left and the two sets on the lower right are connected to the sensitive mass block 21. The low comb tooth electrodes 27 in the two sets of unequal height comb tooth structures on the lower left and the two sets on the upper right are connected to the fixed frame 23. The high comb tooth electrodes 28 in the two sets of unequal height comb tooth structures on the upper left and the two sets on the lower right are connected to the fixed frame 23. The high comb tooth electrodes 28 in the two sets of unequal height comb tooth structures on the lower left and the two sets on the upper right are connected to the sensitive mass block 21.
[0059] An H-shaped groove 29 is provided on the outer surface of the H-shaped mass block located on one side, and multiple sets of damping holes 25 are evenly provided at the bottom of the H-shaped groove.
[0060] Sensitive layer 2 is equipped with eight sets of evenly spaced, unequal-height comb-tooth structures forming a differential detection capacitor. This eliminates interference from other non-sensitive axis directions on the Z-sensitive axis. The multiple sets of comb-tooth structures increase the number of comb-tooth electrodes, further improving sensitivity. Four planar limiting blocks are also provided to prevent damage to the accelerometer under high impact.
[0061] Reference Figure 2 The isolation frame layer 1 includes an isolation frame body 16. The isolation frame body 16 is provided with ten sets of ohmic contact metal patterns 12 corresponding to the installation positions of the unequal height comb tooth structure and the cantilever beam 22. Two sets of ohmic contact metal patterns 12 at the four corners of the isolation frame body 16 along the same length direction are connected by metal connecting wires 13.
[0062] The isolation frame layer 1 uses Al metal as the conductive layer with a thickness of 2μm. It has low resistivity and a relatively simple process. Below the ohmic contact metal pattern 12 and the metal connection 13 is the isolation frame body 16. The empty space of the isolation frame body 16 matches the ohmic contact metal pattern 12 and the metal connection 13 to avoid short circuits when input electrical signals occur. The isolation frame body 16 is made of silicon dioxide and is used to isolate the sensitive layer 2 and the metal region. Ohmic contact windows 11 are etched above the ion implantation area.
[0063] Reference Figure 7 The glass substrate 5 includes borosilicate glass 51 and limiting posts 52. A cavity is opened in the middle of the cavity layer 4. Four sets of limiting posts 52 are installed at the four corners of the borosilicate glass 51. The limiting posts 52 are set in the cavity of the cavity layer 4.
[0064] The fabrication method of a capacitive acceleration sensor for a vehicle suspension system includes the following steps:
[0065] S1: Reference Figure 8 We selected an n-type SOI wafer as the substrate and performed a standard cleaning process on the wafer to remove natural oxidation and other impurities from the surface.
[0066] S2: Reference Figure 9 Silicon dioxide is deposited by chemical vapor deposition, and after photolithography, an ohmic contact window 11 for making an ohmic contact is etched on the silicon dioxide by a RIE etching machine.
[0067] S3: Reference Figure 10 Metal Al is sputtered by sputtering, and after stripping, the desired ohmic contact metal pattern 12 is obtained. Based on this, metal electrodes and metal interconnects 13 are formed by photolithography mask patterning, metal sputtering, and stripping processes.
[0068] S4: Reference Figure 11 A silicon dioxide film 14 is then applied on top of step S3;
[0069] S5: Reference Figure 12 The surface of the silicon dioxide film 14 is photolithographically and etched to retain the high comb teeth on the left and right sides, the sensitive mass block 21 except for the H-shaped groove 29, and the silicon dioxide on the fixed frame 23.
[0070] S6: Reference Figure 13 On top of S5, a silicon nitride thin film 15 is coated;
[0071] S7: Reference Figure 14 Photolithography and etching are performed on the surface of silicon nitride film 15 to retain silicon nitride on both sides of low comb teeth, high comb teeth, sensitive mass block 21, cantilever beam 22 and fixed frame 23.
[0072] S8: Reference Figure 15 The first etching was performed using reactive plasma etching (RIE) technology. The etching depth was controlled by adjusting the reaction time, and the etching depth was 30 μm.
[0073] S9: Reference Figure 16 In addition to the silicon nitride thin film 15, a second etching is performed using reactive ion etching (RIE) until the SOI buried oxide layer 101 is reached, with an etching depth of 20 μm, to release the sensitive structure.
[0074] S10: Reference Figure 17 Remove the first layer of silicon oxide, grow a silicon dioxide film 14 on the bottom silicon substrate, etch the back cavity of the fixed frame 23 by deep reactive ion etching process (DIRE), stop after etching away the middle buried oxide layer 101, and remove excess silicon dioxide.
[0075] S11: Reference Figure 18 The borosilicate glass 51 is anodized to the back cavity connected to the silicon fixed frame 23 via an anodizing process.
[0076] Reference Figure 19 , Figure 19 The diagram comparing the effects of acceleration on the sensitive axis and the cross axis shows that the cantilever beam 32 in this embodiment has very good linearity and displacement sensitivity in the sensitive axis direction, while it has very small displacement in the cross axis direction. The X-axis cross axis displacement is 1.42% of the sensitive axis displacement, and the Y-axis cross axis displacement is 0.002% of the sensitive axis displacement, which can be ignored, thus reducing measurement error.
Claims
1. A capacitive acceleration sensor for a vehicle suspension system, characterized in that: The system includes an isolation frame layer (1), a sensitive layer (2), a buried oxide layer (3), a cavity layer (4), and a glass substrate (5). The isolation frame layer (1) is disposed on one side of the sensitive layer (2), the buried oxide layer (3) is disposed on the other side of the sensitive layer (2), the cavity layer (4) is disposed on the side of the buried oxide layer (3) away from the sensitive layer (2), and the glass substrate (5) is disposed on the side of the cavity layer (4) away from the buried oxide layer (3). The sensitive layer (2) includes a sensitive mass block (21) and a fixed frame (23). The sensitive mass block (21) has a connecting groove in the middle of both sides. The fixed frame (23) is connected to the sensitive mass block (21) through a cantilever beam (22). The cantilever beam (22) is set inside the connecting groove. The sensitive mass block (21) has four sets of limiting grooves near the four corners. Limiting blocks (24) are embedded in the limiting grooves. The limiting blocks (24) are connected to the fixed frame (23) through an auxiliary beam (26). The sensitive mass block (21) includes two sets of H-shaped mass blocks. The two sets of H-shaped mass blocks are symmetrical along the cantilever beam (22). The sensitive layer (2) is provided with eight sets of comb tooth structures of unequal height for detecting Z-axis acceleration. The eight sets of comb tooth structures of unequal height are correspondingly arranged at the four corners of the H-shaped mass block. The unequal height comb structure includes a low comb electrode (27) and a high comb electrode (28). The low comb electrode (27) and the high comb electrode (28) are arranged alternately. The low comb electrodes (27) in the upper left and lower right groups of the unequal height comb structure are connected to the sensitive mass block (21). The low comb electrodes (27) in the lower left and upper right groups of the unequal height comb structure are connected to the fixed frame (23). The high comb electrodes (28) in the upper left and lower right groups of the unequal height comb structure are connected to the fixed frame (23). The high comb electrodes (28) in the lower left and upper right groups of the unequal height comb structure are connected to the sensitive mass block (21). An H-shaped groove (29) is provided on the outer surface of the H-shaped mass block located on one side, and multiple sets of damping holes (25) are uniformly provided at the bottom of the H-shaped groove. The isolation frame layer (1) includes an isolation frame body (16). The isolation frame body (16) is provided with ten sets of ohmic contact metal patterns (12) corresponding to the installation positions of the unequal height comb structure and the cantilever beam (22). Two sets of ohmic contact metal patterns (12) at the four corners of the isolation frame body (16) along the same length direction are connected by metal connecting lines (13). The glass substrate (5) includes borosilicate glass (51) and limiting posts (52). A cavity is provided in the middle of the cavity layer (4). Four sets of limiting posts (52) are installed at the four corners of the borosilicate glass (51). The limiting posts (52) are located in the cavity of the cavity layer (4).
2. The method for fabricating a capacitive acceleration sensor for a vehicle suspension system according to claim 1, characterized in that, The method steps are as follows: S1: Select an n-type SOI wafer as the substrate and perform a standard cleaning process on the wafer to remove natural oxidation and other impurities from the surface; S2: Silicon dioxide is deposited by chemical vapor deposition, and after photolithography, an ohmic contact window for making an ohmic contact is etched on the silicon dioxide by a RIE etching machine (11). S3: Sputter metal Al by sputtering, and obtain the required ohmic contact metal pattern after stripping (12). On this basis, form metal electrodes and metal interconnects through photolithography mask patterning, metal sputtering, and stripping processes (13). S4: Based on step S3, a layer of silicon dioxide film is coated (14). S5: Photolithography and etching are performed on the surface of the silicon dioxide film (14) to retain the high comb teeth on the left and right sides, the sensitive mass block (21) except for the H-shaped groove (29), and the silicon dioxide on the fixed frame (23); S6: On the basis of S5, another layer of silicon nitride film (15) is coated. S7: Photolithography and etching are performed on the surface of the silicon nitride film (15) to retain the silicon nitride on both sides of the low comb teeth, high comb teeth, sensitive mass block (21), cantilever beam (22) and fixed frame (23); S8: The first etching is performed using reactive plasma etching technology. The etching depth is controlled by controlling the reaction time, and the etching depth is 30μm. S9: Remove the silicon nitride thin film (15), perform a second etching using reactive ion etching, stop etching at the intermediate buried oxide layer (101) of SOI, with an etching depth of 20 μm, and release the sensitive structure; S10: Remove the first layer of silicon oxide, grow a silicon dioxide film (14) on the bottom surface of the bottom silicon, etch the back cavity of the fixed frame (23) by deep reactive ion etching process, etch away the middle buried oxide layer (101) and stop, remove the excess silicon dioxide. S11: The borosilicate glass (51) is anodized to the back cavity connected to the silicon fixed frame (23) by anodizing process.