Cantilever beam type capacitance MEMS acceleration sensor

Abstract

The invention relates to a cantilever beam type capacitance MEMS acceleration sensor. The cantilever beam type capacitance MEMS acceleration sensor comprises an upper wafer layer, a middle wafer layer and a lower wafer layer which are arranged in sequence, the middle wafer layer is used for forming a movable mass block, a fixed electrode and an anchor point; the number of the anchor point is one, the anchor point is located at the first end of the movable mass block, and the anchor point is connected with the first end of the movable mass block through an elastic beam; a differential capacitor group is formed between the movable mass block and the fixed electrode along one or more directions, so that the acceleration in one or more directions can be measured; the upper wafer layer and the lower wafer layer are respectively connected with the middle wafer layer from two sides, and the fixed electrode and the anchor point are connected with the upper wafer layer and / or the lower wafer layer. According to the invention, the requirement of multi-axis detection is met, and the area utilization rate and the working reliability of the movable mass block are improved at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of capacitive MEMS sensors, in particular to a cantilever beam capacitive MEMS acceleration sensor. Background Art

[0002] MEMS (micro-electro-mechanical system) accelerometers can be used for vibration measurement, inclination measurement, and track calculation. They have the advantages of small size, high integration, and high precision. They are used in inertial navigation, drones, industrial robots and other fields. Capacitive MEMS sensors detect the capacitance change of the MEMS capacitor group to infer the change of the physical quantity to be detected. The capacitor group consists of a fixed electrode and a movable electrode. The fixed capacitor group does not produce displacement changes with changes in acceleration. The variable electrode is often composed of a movable mass block, which is displaced with the input of external acceleration, resulting in relative displacement between the fixed electrode and the movable electrode, thereby causing a change in capacitance.

[0003] From the detection principle, MEMS accelerometers mostly use capacitive and piezoresistive types. From the design structure, they include seesaw and cantilever beam types. Among them, capacitive types mostly use seesaw structures, and piezoresistive types mostly use cantilever beam structures. Among them, the sensitivity of the cantilever beam piezoresistive structure is low, the temperature characteristics are not good, and the multi-axis design is difficult to achieve. The fixed electrode and variable electrode of the capacitive seesaw structure accelerometer are usually composed of different wafer layers. In order to achieve high sensitivity, the spacing between the two wafer layers is very small, which makes it easy to produce adhesion, reliability problems, and the implementation process is complicated. At the same time, in order to increase the sensitivity of the seesaw structure and make it produce more obvious vibration or displacement when it is input by external acceleration, a counterweight is usually set on the movable mass block. The existence of the counterweight will lead to area waste, which is not conducive to the miniaturization design of the sensor chip. Reliability, cost price and performance are the core competitiveness of the product. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a cantilever beam capacitive MEMS acceleration sensor, the purpose of which is to meet the needs of multi-axis detection while improving chip reliability and reducing chip cost.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A cantilever beam capacitive MEMS acceleration sensor comprises an upper wafer layer, a middle wafer layer and a lower wafer layer which are arranged in sequence;

[0007] The intermediate wafer layer is used to form a detection part, and the detection part includes a movable mass block, a fixed electrode and an anchor point;

[0008] The anchor point is provided at a first end of the movable mass block, and the anchor point is connected to the first end of the movable mass block via an elastic beam;

[0009] A differential capacitor group is formed between the movable mass block and the fixed electrode along one or more directions to achieve the measurement of acceleration in one or more directions;

[0010] The upper wafer layer and the lower wafer layer are connected to the middle wafer layer from two sides respectively, and the fixed electrodes and anchor points are connected to the upper wafer layer and / or the lower wafer layer.

[0011] Further technical solutions are:

[0012] The structure of the movable mass block comprises a first body, one end of the first body along the X-axis direction is connected to the second body, and the other end along the X-direction is connected to the anchor point through the elastic beam;

[0013] Y-axis fixed electrodes are provided on both sides of the first body along the Y-axis direction, and the two Y-axis fixed electrodes and the first body form a Y-axis differential capacitor group;

[0014] The second body is provided with two sets of movable teeth at intervals along the X-axis direction;

[0015] The first group of moving teeth comprises first moving teeth respectively located on both sides of the Y-axis direction, and X-axis fixed electrodes are respectively arranged on both sides of the first group of moving teeth in the Y-axis direction, and first fixed teeth are arranged on both X-axis fixed electrodes, which are used to form an X-axis comb-tooth differential capacitor group corresponding to the first moving teeth on both sides;

[0016] The second group of moving teeth comprises second moving teeth respectively located on both sides of the Y-axis direction, and Z-axis fixed electrodes are respectively arranged on both sides of the second group of moving teeth in the Y-axis direction, and second fixed teeth are arranged on both Z-axis fixed electrodes, which are used to form a Z-axis comb-tooth differential capacitor group corresponding to the second moving teeth on both sides;

[0017] The Y-axis differential capacitor group detects the acceleration in the Y-axis direction through variable gap capacitor detection;

[0018] The X-axis comb-tooth differential capacitor group detects the acceleration in the X-axis direction through variable gap capacitor detection;

[0019] The Z-axis comb-tooth differential capacitor group detects acceleration along the Z-axis direction through variable positive area capacitor detection.

[0020] The first body, the second body and the elastic beam of the movable mass block are all symmetrically arranged with the X-axis as a symmetry axis, and the anchor point is located on the symmetry axis.

[0021] The length direction of the elastic beam extends along the Y axis.

[0022] The first fixed teeth and the first movable teeth located on the same side are matched one by one.

[0023] The second fixed teeth and the second movable teeth located on the same side intersect in sequence.

[0024] An upper groove is provided at the bottom of the upper wafer layer, and a lower groove is provided at the bottom of the lower wafer layer. The upper groove and the lower groove correspond to the movable mass block respectively, and the spacing between the bottom of the upper groove and the lower groove and the movable mass block is 5-50um.

[0025] The detection part, the upper groove and the lower groove are all formed by etching.

[0026] The upper wafer layer and the lower wafer layer are bonded to the middle wafer layer respectively.

[0027] The elastic beam is in a hollow ring structure, and the ring is a long rectangular strip.

[0028] The beneficial effects of the present invention are as follows:

[0029] The present invention can be provided with one or more differential capacitor groups to realize single-axis or multi-axis acceleration detection. Regardless of single-axis or multi-axis detection, the entire movable mass block is arranged on one side of the anchor point, forming a cantilever beam with the fulcrum at the end, which greatly improves the area utilization of the movable mass block and meets the miniaturization design and application requirements of the sensor chip.

[0030] The detection part of the present invention, i.e., the fixed electrode and the movable mass block are formed by processing the same wafer, i.e., the middle wafer layer. The electrical detection part only occurs in the middle layer. In the overall assembly structure, the upper and lower wafer layers do not participate in the electrical detection. Therefore, the distance between the movable structure of the upper and lower wafer layers and the middle wafer layer can be set farther, that is, the depth of the upper and lower grooves can be set larger, thereby avoiding problems such as contact and adhesion, and improving the reliability of the device.

[0031] The single anchor point design of the present invention has good stress characteristics.

[0032] The differential capacitance detection structure of the present invention has good temperature characteristics.

[0033] Other features and advantages of the present invention will be set forth in the following description or may be learned by practicing the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 FIG. 1 is an XY plane schematic diagram of a structure formed on an intermediate wafer layer according to an embodiment of the present invention.

[0035] Figure 2 Schematic diagram of the arrangement principle between the movable mass block and the Z-axis fixed electrode according to an embodiment of the present invention.

[0036] Figure 3 It is a schematic diagram of the overall structure of an embodiment of the present invention.

[0037] In the figure: 1, anchor point; 2, elastic beam; 7, first movable tooth; 8, second movable tooth; 41, first Y-axis fixed electrode; 42, second Y-axis fixed electrode; 51, first X-axis fixed electrode; 52, second X-axis fixed electrode; 61, first Z-axis fixed electrode; 62, second Z-axis fixed electrode; 100, middle wafer layer; 200, upper wafer layer; 201, upper groove; 300, lower wafer layer; 301, first body; 302, second body; 310, lower groove; 511, first fixed tooth A; 521, first fixed tooth B; 611, second fixed tooth A; 621, second fixed tooth B. DETAILED DESCRIPTION

[0038] The specific implementation of the present invention is described below with reference to the accompanying drawings.

[0039] See also Figure 1 and Figure 3 The cantilever beam capacitive MEMS acceleration sensor of this embodiment includes an upper wafer layer 200, a middle wafer layer 100 and a lower wafer layer 300 which are arranged in sequence;

[0040] The middle wafer layer 100 is used to form a detection part, and the structure of the detection part includes a movable mass block, a fixed electrode and an anchor point 1;

[0041] An anchor point 1 is provided, which is located at the first end of the movable mass block, and the anchor point 1 is connected to the first end of the movable mass block through an elastic beam 2;

[0042] A differential capacitor group is formed between the movable mass block and the fixed electrode along one or more directions to achieve the measurement of acceleration in one or more directions;

[0043] Among them, the upper wafer layer 200 and the lower wafer layer 300 play a supporting and fixing role. The upper wafer layer 200 and the lower wafer layer 300 are bonded to the middle wafer layer 100 from both sides respectively, and the fixed electrode and anchor point 1 are connected to the upper wafer layer 200 and / or the lower wafer layer 300.

[0044] The first body 301, the second body 302 and the elastic beam 2 of the movable mass block are all symmetrically arranged with the X axis as the symmetry axis, and the anchor point 1 is located on the symmetry axis. Figure 2 The fulcrum (i.e., anchor point 1) shown is in the form of a "cantilever beam" at the very end. In this form, the entire movable mass block is located on one side of the anchor point, and any out-of-plane acceleration will cause the movable mass block to move out of the plane as a whole. There is no need to set up an additional counterweight block. The area utilization rate of the movable mass block is high, which is conducive to reducing the chip size.

[0045] As a preferred embodiment, the length direction of the elastic beam 2 extends along the Y axis.

[0046] As a preferred embodiment, the elastic beam 2 is a hollow ring structure, and the ring is a long rectangular strip.

[0047] As a specific implementation, the structure of the movable mass block includes a first body 301, one end of the first body 301 along the X-axis direction is connected to the second body 302, and the other end along the X-axis direction is connected to the anchor point 1 through the elastic beam 2;

[0048] Y-axis fixed electrodes are disposed on both sides of the first body 301 along the Y-axis direction, namely a first Y-axis fixed electrode 41 and a second Y-axis fixed electrode 42 . The two Y-axis fixed electrodes and the first body 301 form a Y-axis differential capacitor group.

[0049] When acceleration occurs in the Y direction, the entire movable mass block twists up and down along the Y axis with the anchor point 1 as the center, and the gap between the first Y-axis fixed electrode 41 and the second Y-axis fixed electrode 42 changes, with one side of the gap becoming smaller while the other side of the gap becomes larger, resulting in a differential output signal from the first Y-axis fixed electrode 41 and the second Y-axis fixed electrode 42, that is, variable gap capacitance detection is realized, thereby detecting the acceleration in the Y-axis direction.

[0050] Two groups of moving teeth are arranged on the two Y-axis fixed electrode second bodies 302 at intervals along the X-axis direction, namely, a first group of moving teeth and a second group of moving teeth.

[0051] Among them, the first group of moving teeth includes first moving teeth 7 located on both sides of the Y-axis direction, and X-axis fixed electrodes are respectively provided on both sides of the first group of moving teeth in the Y-axis direction, namely, a first X-axis fixed electrode 51 and a second X-axis fixed electrode 52. First fixed teeth are provided on the two X-axis fixed electrodes, namely, a first fixed tooth A511 and a first fixed tooth B521. The first fixed tooth A511 and the first fixed tooth B521 correspond to the first moving teeth 7 on both sides to form an X-axis comb-tooth differential capacitor group.

[0052] When acceleration in the X direction occurs, the entire movable mass block moves (extends or compresses) in the X direction with the anchor point 1 as the fulcrum, and the gaps between the first movable tooth 7 and the first fixed tooth A 511 and the first fixed tooth B 521 on both sides change, with one side gap becoming smaller while the other side gap becoming larger, resulting in differential output signals of the first X-axis fixed electrode 51 and the second X-axis fixed electrode 52, that is, variable gap capacitance detection is realized, thereby detecting the acceleration in the X-axis direction.

[0053] In order to realize variable gap differential detection, the number of the first moving teeth 7 on both sides of the Y-axis direction is the same, and the number of the first fixed teeth on the two X-axis fixed electrodes is the same, and the first fixed teeth are matched with the first moving teeth 7 one by one.

[0054] Among them, the second group of moving teeth includes second moving teeth 8 located on both sides of the Y-axis direction, and Z-axis fixed electrodes are respectively provided on both sides of the second group of moving teeth in the Y-axis direction, which are respectively the first Z-axis fixed electrode 61 and the second Z-axis fixed electrode 62. Second fixed teeth are provided on the two Z-axis fixed electrodes, which are respectively the second fixed tooth A 611 and the second fixed tooth B 621. The second fixed tooth A 611 and the second fixed tooth B 621 correspond to the second moving teeth 8 on both sides to form a Z-axis comb-tooth differential capacitor group.

[0055] See also Figure 1 and Figure 2 When acceleration in the Z direction occurs, the entire movable mass block moves along the Z axis with the anchor point 1 as the fulcrum (generating out-of-plane motion), and the facing areas between the second movable teeth 8 and the second fixed teeth A611 and the second fixed teeth B 621 on both sides change, with the facing area on one side increasing while the facing area on the other side decreases, resulting in differential output signals from the first Z-axis fixed electrode 61 and the second Z-axis fixed electrode 62, that is, variable facing area capacitance detection is realized, thereby detecting acceleration in the Z-axis direction.

[0056] In order to realize the variable positive area differential detection, the second moving teeth 8 located on both sides of the Y-axis direction have the same height along the Z-axis direction, and the second fixed teeth of the Z-axis fixed electrode located on both sides of the Y-axis direction of the second group of moving teeth have different heights along the Z-axis direction. Figure 2 The second fixed teeth and the second movable teeth 8 intersect in sequence.

[0057] Figure 2 In (a) and (b), respectively Figure 1 A schematic diagram of the matching structure of the initial state between the second movable tooth 8 on the upper side in the middle Y-axis direction and the second fixed tooth A611 of the first Z-axis fixed electrode 61, and Figure 1 Schematic diagram of the matching structure of the initial state between the lower second movable tooth 8 in the middle Y-axis direction and the second fixed tooth B 621 of the second Z-axis fixed electrode 62. As can be seen from the figure, the upper second movable tooth 8 is flush with the bottom of the second fixed tooth A 611 and the top is misaligned, while the lower second movable tooth 8 is flush with the bottom of the second fixed tooth B 621 and the top is misaligned. When the second movable tooth 8 moves upward in the direction of the arrow in the figure, the area directly facing the second fixed tooth A 611 becomes smaller, while the area directly facing the second fixed tooth B 621 becomes larger, and vice versa.

[0058] It can be understood that in this embodiment, the differential capacitor group can be set in only one direction to realize single-axis acceleration detection, or three groups of differential capacitor groups can be set as shown in the drawings of the specification to perform three-axis acceleration detection. Regardless of single-axis or multi-axis detection, the entire movable part is set on one side of the anchor point, which greatly improves the area utilization of the movable mass block and can meet the miniaturization design and application requirements of the detection chip.

[0059] As a specific implementation method, Figure 3 As shown, an upper groove 201 is provided at the bottom of the upper wafer layer 200, and a lower groove 310 is provided at the bottom of the lower wafer layer 300. The upper groove 201 and the lower groove 310 correspond to the positions of the movable mass block on the middle wafer layer 100 in upper and lower directions respectively, and the spacing between the bottom of the upper groove 201 and the lower groove 310 and the movable mass block is 5 to 50 um to avoid contact between the movable mass block and the upper and lower wafers, thereby increasing reliability.

[0060] Specifically, the detection portion, the upper groove 201 and the lower groove 310 are all formed by etching.

[0061] In this embodiment, the fixed electrode and the movable mass block are formed by processing the same wafer, i.e., the middle wafer layer. In the overall assembly structure, the upper and lower wafer layers do not participate in electrical detection. Therefore, the distance between the movable structures of the upper and lower wafer layers and the middle wafer layer can be set farther, which is less likely to cause problems such as contact and adhesion, thereby improving reliability.

[0062] Those skilled in the art can understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions recorded in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A cantilever beam capacitive MEMS acceleration sensor, characterized in that: It comprises an upper wafer layer (200), a middle wafer layer (100) and a lower wafer layer (300) which are arranged in sequence; The intermediate wafer layer (100) is used to form a detection part, and the detection part comprises a movable mass block, a fixed electrode and an anchor point (1); The anchor point (1) is provided with one, which is located at the first end of the movable mass block, and the anchor point (1) is connected to the first end of the movable mass block via an elastic beam (2); A differential capacitor group is formed between the movable mass block and the fixed electrode along one or more directions to achieve the measurement of acceleration in one or more directions; The upper wafer layer and the lower wafer layer are connected to the middle wafer layer from both sides respectively, and the fixed electrodes and anchor points (1) are connected to the upper wafer layer and / or the lower wafer layer.

2. The cantilever beam capacitive MEMS acceleration sensor according to claim 1, characterized in that: The structure of the movable mass block comprises a first body (301), one end of the first body (301) along the X-axis direction is connected to a second body (302), and the other end along the X-direction is connected to an anchor point (1) via the elastic beam (2); The first body (301) is provided with Y-axis fixed electrodes on both sides along the Y-axis direction, and the two Y-axis fixed electrodes and the first body (301) form a Y-axis differential capacitor group; The second body (302) is provided with two sets of movable teeth at intervals along the X-axis direction; The first group of moving teeth comprises first moving teeth (7) respectively located on both sides of the Y-axis direction, and X-axis fixed electrodes are respectively arranged on both sides of the first group of moving teeth in the Y-axis direction, and first fixed teeth are arranged on both X-axis fixed electrodes, which are used to form an X-axis comb-tooth differential capacitor group corresponding to the first moving teeth (7) on both sides; The second group of moving teeth comprises second moving teeth (8) respectively located on both sides of the Y-axis direction, and Z-axis fixed electrodes are respectively provided on both sides of the second group of moving teeth in the Y-axis direction, and second fixed teeth are provided on both Z-axis fixed electrodes, which are used to form a Z-axis comb-tooth differential capacitor group corresponding to the second moving teeth (8) on both sides; The Y-axis differential capacitor group detects the acceleration in the Y-axis direction through variable gap capacitor detection; The X-axis comb-tooth differential capacitor group detects the acceleration in the X-axis direction through variable gap capacitor detection; The Z-axis comb-tooth differential capacitor group detects acceleration along the Z-axis direction through variable positive area capacitor detection.

3. The cantilever beam capacitive MEMS acceleration sensor according to claim 2, characterized in that: The first body (301), the second body (302) and the elastic beam (2) of the movable mass block are all symmetrically arranged with the X-axis as the symmetry axis, and the anchor point (1) is located on the symmetry axis.

4. The cantilever beam capacitive MEMS acceleration sensor according to claim 3, characterized in that: The length direction of the elastic beam (2) extends along the Y axis.

5. The cantilever beam capacitive MEMS acceleration sensor according to claim 2, characterized in that: The first fixed teeth and the first movable teeth (7) located on the same side are matched one by one.

6. The cantilever beam capacitive MEMS acceleration sensor according to claim 2, characterized in that: The second fixed teeth and the second movable teeth (8) located on the same side intersect in sequence.

7. The cantilever beam capacitive MEMS acceleration sensor according to claim 1, characterized in that: An upper groove (201) is provided at the bottom of the upper wafer layer (200), and a lower groove (310) is provided at the bottom of the lower wafer layer (300). The upper groove (201) and the lower groove (310) correspond to the movable mass block in upper and lower directions, respectively, and the spacing between the bottoms of the upper groove (201) and the lower groove (310) and the movable mass block is 5 to 50 μm.

8. The cantilever beam capacitive MEMS acceleration sensor according to claim 7, characterized in that: The detection portion, the upper groove (201) and the lower groove (310) are all formed by etching.

9. The cantilever beam capacitive MEMS acceleration sensor according to claim 1, characterized in that: The upper wafer layer (200) and the lower wafer layer (300) are respectively bonded to the middle wafer layer (100).

10. The cantilever beam capacitive MEMS acceleration sensor according to claim 1, characterized in that: The elastic beam (2) is in the form of a hollow ring structure, and the ring is a long rectangular shape.

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