A silicon-based MEMS three-axis acceleration sensor and a manufacturing method thereof

Abstract

The application relates to the technical field of semiconductor chip manufacturing, in particular to a silicon-based MEMS three-axis acceleration sensor and a manufacturing method thereof, which comprises a first sensitive unit, a second sensitive unit, a third sensitive unit, a device layer, an anchor point, a lower cover plate and an upper cover plate; the first sensitive unit, the second sensitive unit and the third sensitive unit are arranged in the device layer, the second-axis sensitive unit and the third-axis sensitive unit are inlaid into the first sensitive unit, and the three sensitive units share the same anchor point; the first sensitive unit is used for detecting Z-axis acceleration, the second sensitive unit is used for detecting X-axis acceleration, and the third sensitive unit is used for detecting Y-axis acceleration; the device layer is packaged by adopting the upper cover plate and the lower cover plate; the application adopts three sensing units to share one anchor point, effectively reduces the stress of the device, and effectively reduces the complexity of electrical wiring.

Description

Technical Field

[0001] This invention relates to the field of semiconductor chip manufacturing technology, specifically to a silicon-based MEMS triaxial accelerometer and its fabrication method. Background Technology

[0002] MEMS accelerometers are miniature accelerometers manufactured using micro-nano technology. They measure the acceleration of an object in a sensitive direction and convert it into an electrical signal output. MEMS accelerometers can be classified into capacitive, piezoresistive, and resonant types. MEMS capacitive accelerometers, based on their detection method, can be further divided into comb-type and planar-plate type. Planar-plate type accelerometers are generally used for measuring the Z-axis torsional oscillator structure. The detection principle of MEMS capacitive accelerometers is primarily based on the capacitance effect. Its core components include a movable sensing mass and two symmetrical fixed electrodes, maintained at a small distance. When the sensing mass is subjected to a force, it displaces, changing the distance between the mass and the fixed electrodes, thus causing a change in capacitance. This change allows for accurate derivation of the object's acceleration.

[0003] Existing triaxial accelerometers typically consist of three accelerometers along three axes, each with an independent structure and anchor points distributed on the mass block. These anchor points introduce significant stress into the device. Furthermore, the wiring and electrical connections of the three axial components are complex during manufacturing. Generally, the three accelerometers are arranged side-by-side, resulting in a larger chip area. Z-axis accelerometers are mostly implemented using a torsional accelerometer, which typically measures acceleration directly by measuring changes in capacitance, resulting in relatively low sensitivity. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention proposes a silicon-based MEMS triaxial accelerometer. The device includes: a first sensing unit, a second sensing unit, a third sensing unit, a device layer, an anchor point, a lower cover plate, and an upper cover plate. The first, second, and third sensing units are all disposed in the device layer. The second and third sensing units are embedded within the first sensing unit, and all three units share the same anchor point. The first sensing unit detects Z-axis acceleration, the second sensing unit detects X-axis acceleration, and the third sensing unit detects Y-axis acceleration. The upper and lower cover plates encapsulate the device layer.

[0005] A method for fabricating a silicon-based MEMS triaxial accelerometer, the method comprising:

[0006] Step 1: Obtain a glass disc and etch the anchor point structure and cavity into the glass disc;

[0007] Step 2: Anodicly bond the silicon wafer to the glass disc;

[0008] Step 3: Perform DRIE on the silicon wafer to etch out the device layer sensitive structure;

[0009] Step 4: Deposit metal at the device layer anchor points;

[0010] Step 5: Take another glass disc and perform cavity etching;

[0011] Step 6: Deposit metal on the surface of the glass disc;

[0012] Step 7: Etch through holes in the glass disc;

[0013] Step 8: Anodicly bond the glass disc to the sensitive structure to obtain the accelerometer.

[0014] The beneficial effects of this invention are:

[0015] (1) The present invention uses three sensing units to share one anchor point, which effectively reduces the stress on the device;

[0016] (2) The present invention conducts electricity directly through the device layer and sets pad points in the anchor area for external electrical connection, which effectively reduces the complexity of electrical wiring.

[0017] (3) All three sensitive units of the present invention use differential acceleration measurement, which can effectively reduce measurement error and maintain good linearity and sensitivity.

[0018] (4) The present invention embeds the second and third sensitive units in the first sensitive unit, effectively reducing space and chip area.

[0019] (5) The present invention achieves the process by anodic bonding, which is less difficult. Since the thermal expansion coefficients of silicon wafer and Pyrex7740 are basically the same when the temperature is below 300℃, this method can effectively reduce the stress problem caused by the material. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A schematic diagram of a silicon-based MEMS triaxial accelerometer provided in an embodiment of the present invention;

[0022] Figure 2This is a schematic diagram of the structure of a silicon-based MEMS triaxial accelerometer provided in an embodiment of the present invention;

[0023] Figure 3 An exploded view of a silicon-based MEMS triaxial accelerometer provided in an embodiment of the present invention;

[0024] Figure 4 The three sensing units of a silicon-based MEMS triaxial accelerometer provided in this embodiment of the invention share a common anchor point;

[0025] Figure 5 A schematic diagram of the first sensing unit of a silicon-based MEMS triaxial accelerometer provided in an embodiment of the present invention;

[0026] Figure 6 A schematic diagram of the second sensing unit of a silicon-based MEMS triaxial accelerometer provided in an embodiment of the present invention;

[0027] Figure 7 A schematic diagram of the third sensing unit of a silicon-based MEMS triaxial accelerometer provided in an embodiment of the present invention;

[0028] Figure 8 A process flow chart for fabrication of a silicon-based MEMS triaxial accelerometer is provided for embodiments of the present invention.

[0029] In the diagram, 1. First sensitive unit; 2. Second sensitive unit; 3. Third sensitive unit; 4. Device layer; 5. Anchor point; 6. Lower cover plate; 7. Upper cover plate; 101. Spring beam of the first sensitive unit; 102. Mass frame of the first sensitive unit; 103. Anchor point of the triaxial sensitive unit; 104. Detection electrode of the first sensitive unit. 201. Mass frame of the second sensitive unit; 202. Spring beam of the second sensitive unit; 203. Moving comb tooth of the detection electrode of the second sensitive unit; 204. Anchor point of the fixed comb tooth of the second sensitive unit; 205. Fixed comb tooth of the detection electrode of the second sensitive unit. 301. Mass frame of the third sensitive unit; 302. Spring beam of the third sensitive unit; 303. Moving comb tooth of the detection electrode of the third sensitive unit; 304. Fixed comb tooth of the detection electrode of the third sensitive unit; 305. Anchor point of the fixed comb tooth of the detection electrode of the third sensitive unit. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0032] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature; in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0033] A silicon-based MEMS triaxial accelerometer, such as Figures 1-7 As shown, the device includes: a first sensitive unit, a second sensitive unit, a third sensitive unit, a device layer, an anchor point, a lower cover plate, and an upper cover plate; the first sensitive unit, the second sensitive unit, and the third sensitive unit are all disposed on the device layer, the second axis sensitive unit and the third axis sensitive unit are embedded in the first sensitive unit, and the three sensitive units share the same anchor point; the first sensitive unit is used to detect Z-axis acceleration, the second sensitive unit is used to detect X-axis acceleration, and the third sensitive unit is used to detect Y-axis acceleration; the upper cover plate and the lower cover plate are used to encapsulate the device layer.

[0034] As one implementation, the acceleration sensor consists of three axial accelerometers, which move through their respective spring beams and mass frames and are connected by the same anchor point.

[0035] As one implementation method, the first axis sensing unit includes a first axis mass frame, a first axis torsion beam, a first axis detection electrode, and an anchor point. When subjected to acceleration in the Z direction, the first axis torsion beam drives the mass frame to torsion. At this time, the gap between the first axis mass frame and the detection capacitor above changes, causing the capacitance value to change with the acceleration, thereby detecting the acceleration of the Z axis.

[0036] As one embodiment, the second axis sensing unit includes a second axis mass frame, an anchor point shared with the first and third axis sensing units, a second axis spring beam, and second axis comb-tooth detection capacitors. When subjected to X-axis acceleration, the second axis spring beam drives the second axis mass frame to move along the X-axis. At this time, the spacing between the second axis comb-tooth capacitors changes, thereby detecting the X-axis acceleration.

[0037] As one implementation, the third-axis sensing unit includes a third-axis mass frame, an anchor point shared with the first-axis and second-axis sensing units, a third-axis spring beam, and third-axis comb-tooth detection capacitors. When subjected to Y-axis acceleration, the third-axis spring beam drives the third-axis mass frame to move towards the Y-axis. At this time, the spacing between the third-axis comb-tooth capacitors changes, thereby detecting the Y-axis acceleration.

[0038] As one implementation method, the first axis sensitive unit capacitor comb is divided into a first electrode plate and a second electrode plate, which are fixed on the lower cover plate. The first electrode plate and the second electrode plate can be differentially applied when subjected to acceleration, which effectively increases the sensitivity of the device.

[0039] As one implementation method, the second axis sensitive unit capacitor comb teeth are divided into upper and lower parts, and the structure is arranged in a centrally symmetrical manner. The detection comb teeth are fixed to the lower cover plate by anchor points. The upper and lower parts of the capacitor comb teeth can perform differential acceleration, which effectively increases the sensitivity of the device.

[0040] As one implementation method, the third axis sensitive unit capacitor comb teeth are divided into four parts. The detection comb teeth are fixed to the lower cover plate by anchor points. The upper and lower parts of the capacitor comb teeth on the right side and the upper and lower parts of the capacitor output on the left side can be differentially divided when subjected to acceleration, which effectively increases the sensitivity of the device.

[0041] As one embodiment, both the second sensitive unit and the third sensitive unit include movable comb teeth and fixed comb teeth that cooperate with each other, wherein the movable comb teeth of the second sensitive unit and the movable comb teeth of the third sensitive unit are respectively fixed on the lower cover plate.

[0042] As one embodiment, the first sensitive unit includes a Z-axis detection structure, which is a parallel plate capacitor structure, including a first plate and a second plate respectively fixed on the upper cover plate.

[0043] As one implementation method, the sensor is fabricated using anodizing, which reduces the stress on the device. The electrical signal is directly extracted from the anchor point of the device layer, simplifying the wiring.

[0044] A silicon-based MEMS triaxial accelerometer, the overall structure of which is as follows: Figure 1 , 2 As shown in Figure 3, the device consists of a lower device layer 4, an anchor point 5, a lower cover plate 6, and an upper cover plate 7. This device is generally made of semiconductor silicon, with the device layer potentially being SOI. The device comprises a first sensitive unit 1, a second sensitive unit 2, and a third sensitive unit 3. The first sensitive unit has a hollow center, and the second and third sensitive units 2 and 3 are embedded within the hollow center of the first sensitive unit. The three sensitive units' moving mass frames are connected and fixed to the lower cover plate via an anchor point, and the electrical signals of the three sensitive units are output through the same anchor point.

[0045] Figure 4 It is an anchor point structure shared by three sensing units of a silicon-based MEMS triaxial accelerometer.

[0046] Figure 5 This is a schematic diagram of the first sensing unit structure of a silicon-based MEMS triaxial accelerometer. The sensing unit includes a spring beam 101, which is a double-ended fixed beam. 103 is an anchor point connecting the mass frame 102. When the mass frame 102 is subjected to a Z-axis impact, it undergoes torsion. The detection electrode 104 is attached to the upper cover plate. When the mass frame 102 torsional, the gap between it and the electrode 104 attached to the upper cover plate changes, with one section of the gap increasing and the other decreasing. The capacitance values ​​at both ends also change accordingly. By differentiating the capacitance values ​​at both ends, the relationship between acceleration and capacitance can be obtained, thereby detecting acceleration in the sensing direction.

[0047] Figure 6 This is a schematic diagram of the second sensing unit structure of a silicon-based MEMS triaxial accelerometer. The sensing unit includes a spring beam 202, which is a U-shaped beam. When subjected to a load in the X direction, the spring beam 202 causes the mass frame 201 to move. At this time, the detection comb electrode 203 attached to the mass frame moves, and the distance between it and the comb electrode 205 fixed on the anchor point 204 changes. The value of the comb capacitance of the device changes. The upper and lower comb electrodes of the second sensing unit can be differentially divided. At this time, by obtaining the relationship between acceleration and capacitance, the acceleration in the sensing direction can be detected.

[0048] Figure 7 This is a schematic diagram of the third sensing unit structure of a silicon-based MEMS triaxial accelerometer. The sensing unit includes a spring beam 302, which is a U-shaped beam. When subjected to a load in the Y direction, the spring beam 302 causes the mass frame 301 to move. At this time, the detection comb electrode 303 attached to the mass frame moves, and the distance between it and the comb electrode 304 fixed on the anchor point 305 changes. The value of the comb capacitance of the device changes. The upper and lower comb electrodes at the left and right ends of the mass frame of the third sensing unit can perform differential calculation. At this time, by obtaining the relationship between acceleration and capacitance change, the acceleration in the sensing direction can be detected.

[0049] A method for fabricating a silicon-based MEMS triaxial accelerometer, the method comprising:

[0050] Step 1: Obtain a glass disc and etch the anchor point structure and cavity into the glass disc;

[0051] Step 2: Anodicly bond the silicon wafer to the glass disc;

[0052] Step 3: Perform DRIE on the silicon wafer to etch out the device layer sensitive structure;

[0053] Step 4: Deposit metal at the device layer anchor points;

[0054] Step 5: Take another glass disc and perform cavity etching;

[0055] Step 6: Deposit metal on the surface of the glass disc;

[0056] Step 7: Etch through holes in the glass disc;

[0057] Step 8: Anodicly bond the glass disc to the sensitive structure to obtain the accelerometer.

[0058] In this embodiment, the silicon wafer thickness is 10–30 μm.

[0059] Figure 8 This is a process flow diagram for fabricating a silicon-based MEMS triaxial accelerometer. Step 401 involves Pyrex 7740; step 402 involves etching a cavity structure from the Pyrex 7740; step 403 involves anodic bonding of the etched Pyrex 7740 to a silicon wafer; step 404 involves DRIE etching on the bonded wafer to create the sensitive structure of the device layer; step 405 involves metal deposition at the anchor points of the sensitive structure; step 406 involves taking another Pyrex 7740; step 407 involves etching the cavity of the Pyrex 7740; step 408 involves metal deposition on the surface of the Pyrex 7740; step 409 involves further etching the exposed metal pad points; and step 410 involves anodic bonding of the etched Pyrex 7740 to the sensitive structure to obtain the MEMS accelerometer.

[0060] The silicon-based MEMS triaxial accelerometer in this embodiment has a compact and independent detection structure in each direction, which is easy to detect, not easily affected by interference, and has higher detection accuracy.

[0061] The above-described embodiments further illustrate the purpose, technical solution, and advantages of the present invention. It should be understood that the above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A silicon-based MEMS triaxial accelerometer, characterized in that, include: The system comprises a first sensitive unit, a second sensitive unit, a third sensitive unit, a device layer, an anchor point, a lower cover plate, and an upper cover plate. The first, second, and third sensitive units are all disposed on the device layer. The second and third axis sensitive units are embedded within the first sensitive unit, and all three sensitive units share the same anchor point. The first sensitive unit is used to detect Z-axis acceleration, the second sensitive unit is used to detect X-axis acceleration, and the third sensitive unit is used to detect Y-axis acceleration. The device layer is encapsulated using an upper cover and a lower cover. The first sensing unit adopts a torsion accelerometer, including: a first-axis mass frame, a first-axis torsion beam, and a first-axis detection electrode; when the first sensing unit is subjected to acceleration in the Z direction, the first-axis torsion beam drives the mass frame to torsion, at which time the gap between the first-axis mass frame and the detection capacitor above changes, the capacitance value changes with the acceleration, and the acceleration in the Z axis is detected. The second sensing unit includes a second-axis mass frame, a second-axis spring beam, and a second-axis comb-tooth detection capacitor. When the sensor is subjected to X-axis acceleration, the second-axis spring beam drives the second-axis mass frame to move towards the X-axis. At this time, the spacing between the second-axis comb-tooth capacitors changes, and the X-axis acceleration is detected. The third sensing unit uses a comb-type capacitive accelerometer, which includes a third-axis mass frame, a third-axis spring beam, and third-axis comb-type detection capacitors. When the sensor is subjected to Y-axis acceleration, the third-axis spring beam drives the third-axis mass frame to move towards the Y-axis. At this time, the spacing between the third-axis comb-type capacitors changes, thus detecting the Y-axis acceleration.

2. The silicon-based MEMS triaxial accelerometer according to claim 1, characterized in that, The second-axis comb tooth detection capacitor is composed of the moving comb tooth of the second sensitive unit detection electrode and the fixed comb tooth of the second sensitive unit detection electrode. The moving comb tooth of the second sensitive unit detection electrode and the fixed comb tooth of the second sensitive unit detection electrode correspond to each other to form the second-axis comb tooth detection capacitor.

3. A silicon-based MEMS triaxial accelerometer according to claim 1, characterized in that, The moving comb teeth of the second sensitive unit detection electrode and the fixed comb teeth of the second sensitive unit detection electrode are both divided into upper and lower parts, and the structure is arranged in a centrally symmetrical manner. The upper and lower parts of the capacitive comb teeth perform differential acceleration.

4. A silicon-based MEMS triaxial accelerometer according to claim 1, characterized in that, The third-axis comb-tooth detection capacitor adopts a comb-tooth structure and is divided into four parts; the upper and lower parts of the right-side capacitor comb and the upper and lower parts of the left-side capacitor output are differentially divided when subjected to acceleration.

5. A method for fabricating a silicon-based MEMS triaxial accelerometer, the method being used to fabricate the silicon-based MEMS triaxial accelerometer as described in claim 1, characterized in that, include: Step 1: Obtain a glass disc and etch the anchor point structure and cavity into the glass disc; Step 2: Anodicly bond the silicon wafer to the glass disc; Step 3: Perform DRIE on the silicon wafer to etch out the device layer sensitive structure; Step 4: Deposit metal at the device layer anchor points; Step 5: Take another glass disc and perform cavity etching; Step 6: Deposit metal on the surface of the glass disc; Step 7: Etch through holes in the glass disc; Step 8: Anodicly bond the glass disc to the sensitive structure to obtain the accelerometer.

6. The method for fabricating a silicon-based MEMS triaxial accelerometer according to claim 5, characterized in that, The thickness of the silicon wafer is 10~30μm.

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