A dual-mode self-calibrating MEMS accelerometer and its calibration method

Abstract

This invention discloses a dual-mode self-calibrating MEMS accelerometer and its calibration method, belonging to the field of microelectromechanical system (MEMS) sensor technology. It includes a substrate, a mass block, a differential capacitance detection unit, an electrothermal driving unit, a tunneling current generation unit, and a data processing unit. The differential capacitance detection unit is located on both sides of the mass block along the sensitive axis and is used to detect the differential capacitance caused by the movement of the mass block. The differential capacitance detection unit includes a movable electrode fixed to one side of the mass block and a fixed electrode mounted on the substrate. The electrothermal driving unit is connected to the fixed electrode and is used to drive the fixed electrode to move closer to or away from the movable electrode. The tunneling current generation unit is located opposite each other at both ends of the mass block and is used to calibrate a specified position. When the mass block moves to the specified position, it generates a tunneling current and a capacitance value corresponding to the tunneling current. This invention achieves high-precision online self-calibration under all operating conditions.

Description

Technical Field

[0001] This invention belongs to the field of microelectromechanical systems (MEMS) sensor technology, specifically relating to a dual-mode self-calibrating MEMS accelerometer and its calibration method. Background Technology

[0002] Capacitive MEMS accelerometers are widely used in consumer electronics, automotive, and industrial fields due to their advantages such as simple structure, low power consumption, and ease of integration. However, their measurement accuracy is significantly affected by factors such as temperature drift, mechanical stress, circuit noise, and long-term aging. Traditional calibration methods are mostly one-time calibrations at the factory, which cannot compensate for time-varying errors during use, resulting in a decrease in accuracy over time.

[0003] In the existing technology, self-calibration methods are mainly divided into two categories: one is to provide a calibration benchmark by integrating additional calibration structures inside the sensor, such as a reference mass block, but this increases the chip area and process complexity; the other is to use the sensor's own structure for dynamic calibration, such as correcting sensitivity and offset by detecting the response of the mass block at a specific position, but this type of method usually relies on complex electrostatic control or resonant structures, and its stability and reliability need to be improved. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a dual-mode self-calibrating MEMS accelerometer and its calibration method. Through an electrothermal drive unit, the sensitivity can be continuously adjusted and physically disconnected, and a position reference with atomic precision can be provided by a tunneling current electrode, thereby achieving high-precision online self-calibration under all working conditions.

[0005] This invention provides the following technical solution:

[0006] A dual-mode self-calibrating MEMS accelerometer includes a substrate, a mass block, a differential capacitance detection unit, an electrothermal driving unit, a tunneling current generation unit, and a data processing unit. The mass block is movably connected above the substrate and moves along the sensitive axis after an acceleration is applied to it. The differential capacitance detection unit is located on both sides of the mass block along the sensitive axis and is used to detect the differential capacitance caused by the movement of the mass block. The differential capacitance detection unit includes a first movable electrode fixed to one side of the mass block and a first fixed electrode mounted on the substrate. The electrothermal driving unit is connected to the first fixed electrode and is used to drive the first fixed electrode to move closer to or away from the first movable electrode. The tunneling current generation unit is located opposite each other at both ends of the mass block and is used to calibrate a specified position. When the mass block moves to the specified position, it generates a tunneling current and a capacitance value corresponding to the tunneling current. The data processing unit is connected to the differential capacitance detection unit and the tunneling current generation unit and is used to calculate the calibrated actual acceleration value based on the capacitance values ​​output by the differential capacitance detection unit and the tunneling current generation unit.

[0007] As an optional technical solution of the present invention, the first fixed electrode plate is connected to the substrate through an electrothermal drive unit; the mass block is suspended on the substrate through a folding beam.

[0008] As an optional technical solution of the present invention, the electrothermal drive unit is V-shaped and made of polycrystalline silicon; when a driving voltage is applied to the electrothermal drive unit, the electrothermal drive unit drives the first fixed electrode plate to approach the first movable electrode plate.

[0009] As an optional technical solution of the present invention, the tunneling current generating unit includes a tunneling current electrode pair and a variable-pitch capacitor plate pair; the tunneling current electrode pair is located on one side of either end of the mass block, and the variable-pitch capacitor plate pair is located on the other side of either end of the mass block.

[0010] As an optional technical solution of the present invention, the tunneling current electrode includes a movable tip electrode and three fixed tip electrodes arranged in sequence; the fixed tip electrode is fixed on the substrate, and the movable tip electrode is fixed on the mass block; the fixed tip electrodes located on both sides are used to mark a designated position respectively, and when the mass block drives the movable tip electrode to move to any designated position, and the tips of the fixed tip electrode and the movable tip electrode are aligned, the fixed tip electrode and the movable tip electrode generate a tunneling current.

[0011] As an optional technical solution of the present invention, the variable-pitch capacitor plate pair includes a second movable plate and a second fixed plate; the second fixed plate is fixed on the substrate, and the second movable plate is fixed on the mass block; the mass block drives the second movable plate to move relative to the two ends of the second fixed plate, and the second movable plate and the second fixed plate generate a capacitance value corresponding to the tunneling current.

[0012] In a second aspect, a calibration method for a dual-mode self-calibrating MEMS accelerometer as described in the first aspect is provided, comprising: after a power-on system applies a driving voltage to the electrothermal driving unit, such that a preset measurement distance is reached between the first movable electrode and the first fixed electrode, an initial capacitance generated by the first movable electrode and the first fixed electrode is obtained.

[0013] After the acceleration application system applies a standard acceleration to the dual-mode self-calibrating MEMS accelerometer to generate a tunneling current, the differential capacitance corresponding to the tunneling current is obtained.

[0014] Based on the initial capacitance and differential capacitance, the update offset and update sensitivity of the dual-mode self-calibrating MEMS accelerometer are calculated.

[0015] The zero-point capacitance is obtained when the power supply system does not apply a driving voltage to the electrothermal drive unit and the acceleration application system does not apply a standard acceleration to the dual-mode self-calibrating MEMS accelerometer.

[0016] After applying actual acceleration to the dual-mode self-calibrating MEMS accelerometer, the differential capacitance under the actual acceleration is obtained. Based on the updated offset, updated sensitivity, and zero-point capacitance, the calibrated actual acceleration is calculated.

[0017] As an optional technical solution of the present invention, the calculation of the update offset and update sensitivity of the dual-mode self-calibrating MEMS accelerometer based on the initial capacitance and differential capacitance includes:

[0018] The initial sensitivity is calculated based on the initial capacitance. and initial offset , respectively represented as:

[0019] ;

[0020] ;

[0021] in, , This represents the initial capacitance measured under two different standard accelerations. , Representing different standard accelerations;

[0022] The first corrected sensitivity is calculated based on the differential capacitance. and the first correction offset , respectively represented as:

[0023] ;

[0024] ;

[0025] in, , This represents the differential capacitance under two different standard accelerations.

[0026] The update sensitivity and update offset are calculated and expressed as follows:

[0027] ;

[0028] ;

[0029] in, Indicates an update to sensitivity. This indicates that the offset is being updated.

[0030] As an optional technical solution of the present invention, the step of calculating the calibrated actual acceleration based on the updated offset, updated sensitivity, and zero-point capacitance includes:

[0031] The second corrected sensitivity is calculated based on the zero-point capacitance. Second correction offset , respectively represented as:

[0032] ;

[0033] ;

[0034] in, , This represents the zero-point capacitance under two different standard accelerations. , Representing different standard accelerations;

[0035] Calculate the calibrated offset and calibrated sensitivity , represented as:

[0036] ;

[0037] ;

[0038] in, Indicates an update to sensitivity. This indicates that the offset is being updated;

[0039] Based on the calibrated offset and calibrated sensitivity The actual acceleration after calibration is derived and expressed as:

[0040] ;

[0041] in, This indicates the actual acceleration after calibration. This represents the differential capacitance under actual acceleration.

[0042] Compared with the prior art, the beneficial effects of the present invention are:

[0043] The dual-mode self-calibrating MEMS accelerometer provided by this invention achieves continuous sensitivity adjustment and physical disconnection through an electrothermal drive unit, and provides an atomically accurate position reference using a tunneling current generation unit, thereby realizing high-precision online self-calibration under all working conditions. It has a simple structure and is easy to implement. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the structure of the dual-mode self-calibrating MEMS accelerometer in an embodiment of the present invention;

[0045] Figure 2 This is a schematic diagram of the structure of the electrothermal drive unit in an embodiment of the present invention;

[0046] Figure 3 This is a schematic diagram of the tunneling current generating unit in an embodiment of the present invention.

[0047] The following are labeled in the figure: mass block 1, first movable electrode 2a, first fixed electrode 2b, electrothermal drive unit 3, movable tip electrode 4a, fixed tip electrode 4b, second movable electrode 5a, and second fixed electrode 5b. Detailed Implementation

[0048] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0049] Example 1

[0050] This embodiment provides a dual-mode self-calibrating MEMS accelerometer, such as Figure 1 As shown, it includes a substrate, a mass block 1, a differential capacitance detection unit, an electrothermal drive unit 3, a tunneling current generation unit, and a data processing unit.

[0051] The mass block 1 is movably connected above the substrate and suspended on the substrate by a folded beam. After an acceleration is applied to the sensitive axis direction of the accelerometer, the mass block 1 moves along the sensitive axis direction.

[0052] The differential capacitance detection unit is located on both sides of the mass block 1 along the sensitive axis and is used to detect the differential capacitance caused by the movement of the mass block 1. The differential capacitance detection unit includes a first movable electrode plate 2a fixed to one side of the mass block 1 and a first fixed electrode plate 2b mounted on the substrate.

[0053] The electrothermal drive unit 3 is connected to the first fixed electrode plate 2b and is used to drive the first fixed electrode plate 2b closer to or further away from the first movable electrode plate 2a. For example... Figure 2 As shown, the first fixed electrode 2b is connected to the substrate via an electrothermal driving unit 3. The electrothermal driving unit 3 is V-shaped and made of polycrystalline silicon. When current flows through it, the two arms of the V-shaped beam bend due to the difference in their coefficients of thermal expansion, thereby causing the first fixed electrode 2b connected to it to move closer to or away from the first movable electrode 2a. When a driving current is applied to the electrothermal driving unit 3, the electrothermal driving unit 3 moves the first fixed electrode 2b closer to the first movable electrode 2a, thereby precisely controlling the distance between the first fixed electrode 2b and the first movable electrode 2a. By controlling the driving current of the electrothermal driving unit, the distance between the capacitor plates is adjusted, thereby adjusting the sensor's sensitivity or cutting off capacitive coupling. When the driving current is zero, the distance between the first fixed electrode and the first movable electrode is at its maximum, and the capacitive coupling is at its weakest; when a driving current is applied, the distance between the first fixed electrode and the first movable electrode decreases, and the capacitive sensitivity increases.

[0054] The tunneling current generating unit is positioned opposite each other at both ends of the mass block 1, and is used to calibrate a designated position and detect whether the mass block 1 has reached at least one designated position. When the mass block 1 moves to a designated position, a tunneling current is generated, along with a capacitance value corresponding to the tunneling current. When the tunneling current generating unit detects that the mass block has reached a preset calibration position, it immediately records the output value of the differential capacitance detection unit at that moment, and updates the sensor's transfer function parameters, including offset and sensitivity, based on this output value and the known inertial input value corresponding to the preset calibration position.

[0055] like Figure 3As shown, the tunneling current generating unit includes a tunneling current electrode pair and a variable-pitch capacitor plate pair; the tunneling current electrode pair is located on one side of either end of the mass block 1, and the variable-pitch capacitor plate pair is located on the other side of either end of the mass block 1. The tunneling current electrode includes a movable tip electrode 4a and three fixed tip electrodes 4b arranged in sequence; the fixed tip electrode 4b is fixed on the substrate, and the movable tip electrode 4a is fixed on the mass block 1; the fixed tip electrodes 4b on both sides are used to mark a designated position, corresponding to +50% and -50% of the acceleration range, respectively. When the mass block 1 moves the movable tip electrode 4a to either designated position, and the tips of the fixed tip electrode 4b and the movable tip electrode 4a are aligned, the fixed tip electrode 4b and the movable tip electrode 4a generate a tunneling current. When the tunneling current reaches its peak value, a sharp trigger pulse is generated. The variable-pitch capacitor plate pair includes a second movable plate 5a and a second fixed plate 5b; the second fixed plate 5b is fixed on the substrate, and the second movable plate 5a is fixed on the mass block 1; the mass block 1 drives the second movable plate 5a to move relative to the two ends of the second fixed plate 5b, and the second movable plate 5a and the second fixed plate 5b generate a capacitance value corresponding to the tunneling current. After the mass block 1 moves, the capacitance value generated by the second movable plate 5a and the second fixed plate 5b corresponding to the tunneling current is the same as the differential capacitance generated by the differential capacitance detection unit.

[0056] The data processing unit is connected to the differential capacitance detection unit and the tunneling current generation unit, and is used to calculate the calibrated actual acceleration value based on the capacitance value output by the differential capacitance detection unit and the tunneling current generation unit.

[0057] Example 2

[0058] This embodiment provides a calibration method for the dual-mode self-calibrating MEMS accelerometer described in Embodiment 1, comprising:

[0059] Step 1: Apply a driving voltage to the electrothermal drive unit 3 in the power supply system so that the first movable plate 2a and the first fixed plate 2b reach a preset measurement distance, and obtain the initial capacitance generated by the first movable plate 2a and the first fixed plate 2b.

[0060] Step 2: After applying a standard acceleration to the dual-mode self-calibrating MEMS accelerometer to generate tunneling current using the acceleration application system, obtain the differential capacitance corresponding to the tunneling current.

[0061] The differential capacitance corresponding to the tunneling current is generated by the second movable plate 5a and the second fixed plate 5b.

[0062] Step 3: Based on the initial capacitance and differential capacitance, calculate the update offset and update sensitivity of the dual-mode self-calibrating MEMS accelerometer.

[0063] The initial sensitivity is calculated based on the initial capacitance. and initial offset , respectively represented as:

[0064] ;

[0065] ;

[0066] in, , This represents the initial capacitance measured under two different standard accelerations. , These represent different standard accelerations.

[0067] The first corrected sensitivity is calculated based on the differential capacitance. and the first correction offset , respectively represented as:

[0068] ;

[0069] ;

[0070] in, , This represents the differential capacitance under two different standard accelerations.

[0071] The update sensitivity and update offset are calculated and expressed as follows:

[0072] ;

[0073] ;

[0074] in, Indicates an update to sensitivity. This indicates that the offset is being updated.

[0075] Step 4: Obtain the zero-point capacitance when the power supply system does not apply a driving voltage to the electrothermal drive unit 3 and the acceleration application system does not apply a standard acceleration to the dual-mode self-calibrating MEMS accelerometer.

[0076] The control of the electrothermal drive unit maximizes the distance between the first movable plate and the first fixed plate, i.e., the coupling is broken. At this time, the zero-point capacitor mainly reflects the zero-point drift of the system and is used for real-time zero-point calibration.

[0077] Zero-point capacitance primarily reflects the zero-point drift of the circuit itself.

[0078] Step 5: After applying the actual acceleration to the dual-mode self-calibrating MEMS accelerometer, obtain the differential capacitance under the actual acceleration. Based on the updated offset, updated sensitivity, and zero-point capacitance, calculate the calibrated actual acceleration.

[0079] The second corrected sensitivity is calculated based on the zero-point capacitance. Second correction offset , respectively represented as:

[0080] ;

[0081] ;

[0082] in, , This represents the zero-point capacitance under two different standard accelerations. , These represent different standard accelerations.

[0083] Calculate the calibrated offset and calibrated sensitivity , represented as:

[0084] ;

[0085] ;

[0086] in, Indicates an update to sensitivity. This indicates that the offset is being updated.

[0087] Based on the calibrated offset and calibrated sensitivity The actual acceleration after calibration is derived and expressed as:

[0088] ;

[0089] in, This indicates the actual acceleration after calibration. This represents the differential capacitance under actual acceleration.

[0090] If the error between the calibrated acceleration and the actual input acceleration value is greater than the preset error threshold, the calibration should be repeated.

[0091] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are used only for the convenience of describing the 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, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., 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.

[0092] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0093] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A dual mode self-calibrating MEMS accelerometer characterized by: Includes a substrate, a mass block (1), a differential capacitance detection unit, an electrothermal drive unit (3), a tunneling current generation unit, and a data processing unit; The mass block (1) is movably connected above the substrate. After an acceleration is applied to the sensitive axis direction of the accelerometer, the mass block (1) moves along the sensitive axis direction. The differential capacitance detection unit is located on both sides of the mass block (1) along the sensitive axis and is used to detect the differential capacitance caused by the movement of the mass block (1). The differential capacitance detection unit includes a first movable electrode plate (2a) fixed on one side of the mass block (1) and a first fixed electrode plate (2b) mounted on the substrate. The electrothermal drive unit (3) is connected to the first fixed electrode plate (2b) and is used to drive the first fixed electrode plate (2b) to move closer to or away from the first movable electrode plate (2a). The tunneling current generating unit is positioned opposite to both ends of the mass block (1) to calibrate a specified position. When the mass block (1) moves to the specified position, it generates a tunneling current and generates a capacitance value corresponding to the tunneling current. The data processing unit is connected to the differential capacitance detection unit and the tunneling current generation unit, and is used to calculate the calibrated actual acceleration value based on the capacitance value output by the differential capacitance detection unit and the tunneling current generation unit.

2. The dual-mode self-calibrating MEMS accelerometer of claim 1, wherein: The first fixed electrode plate (2b) is connected to the substrate via an electrothermal drive unit (3); the mass block (1) is suspended on the substrate via a folding beam.

3. The dual-mode self-calibrating MEMS accelerometer of claim 1, wherein: The electrothermal drive unit (3) is V-shaped and made of polycrystalline silicon; When a driving voltage is applied to the electrothermal drive unit (3), the electrothermal drive unit (3) drives the first fixed electrode plate (2b) to approach the first movable electrode plate (2a).

4. The dual-mode self-calibrating MEMS accelerometer of claim 1, wherein: The tunneling current generating unit includes a tunneling current electrode pair and a variable-pitch capacitor plate pair; The tunneling current electrode pair is located on one side of either end of the mass block (1), and the variable-pitch capacitor plate pair is located on the other side of either end of the mass block (1).

5. The dual mode self-calibrating MEMS accelerometer of claim 4, wherein: The tunneling current electrode includes a movable tip electrode (4a) and three fixed tip electrodes (4b) arranged in sequence. The fixed tip electrode (4b) is fixed on the substrate, and the movable tip electrode (4a) is fixed on the mass block (1); The fixed tip electrode (4b) located on both sides is used to mark a designated position respectively. When the mass block (1) moves the movable tip electrode (4a) to any designated position and the tip of the fixed tip electrode (4b) is aligned with the tip of the movable tip electrode (4a), the fixed tip electrode (4b) and the movable tip electrode (4a) generate tunneling current.

6. The dual mode self-calibrating MEMS accelerometer of claim 4, wherein: The variable-pitch capacitor plate pair includes a second movable plate (5a) and a second fixed plate (5b). The second fixed electrode plate (5b) is fixed on the substrate, and the second movable electrode plate (5a) is fixed on the mass block (1); The mass block (1) causes the second movable electrode plate (5a) to move relative to the two ends of the second fixed electrode plate (5b), and the second movable electrode plate (5a) and the second fixed electrode plate (5b) generate capacitance values ​​corresponding to the tunneling current.

7. A calibration method for the dual-mode self-calibrating MEMS accelerometer of any one of claims 1 to 6, characterized in that, include: After the power supply system applies a driving voltage to the electrothermal drive unit (3) so that the first movable electrode plate (2a) and the first fixed electrode plate (2b) reach a preset measurement distance, the initial capacitance generated by the first movable electrode plate (2a) and the first fixed electrode plate (2b) is obtained. After the acceleration application system applies a standard acceleration to the dual-mode self-calibrating MEMS accelerometer to generate a tunneling current, the differential capacitance corresponding to the tunneling current is obtained. Based on the initial capacitance and differential capacitance, the update offset and update sensitivity of the dual-mode self-calibrating MEMS accelerometer are calculated. When the power supply system does not apply a driving voltage to the electrothermal drive unit (3) and the acceleration application system does not apply a standard acceleration to the dual-mode self-calibrating MEMS accelerometer, the zero-point capacitance is obtained; After applying actual acceleration to the dual-mode self-calibrating MEMS accelerometer, the differential capacitance under the actual acceleration is obtained. Based on the updated offset, updated sensitivity, and zero-point capacitance, the calibrated actual acceleration is calculated.

8. The method of calibration of a dual mode self-calibrating MEMS accelerometer according to claim 7, characterized in that: The calculation of the update offset and update sensitivity of the dual-mode self-calibrating MEMS accelerometer based on the initial capacitance and differential capacitance includes: According to the initial capacitance, an initial sensitivity is calculated and an initial offset are calculated, respectively ； ； wherein , represents the initial capacitance measured at two different standard accelerations, , represents different standard accelerations; According to the differential capacitance, a first corrected sensitivity is calculated and a first corrected offset are calculated, respectively as ； ； wherein , represents the differential capacitance at two different standard accelerations; The update sensitivity and update offset are calculated and expressed as follows: ； ； wherein, represents an update sensitivity, represents an update offset.

9. The method of calibration of a dual mode self-calibrating MEMS accelerometer according to claim 7, characterized in that: The calculation of the calibrated actual acceleration based on the updated offset, updated sensitivity, and zero-point capacitance includes: The second modified sensitivity is calculated according to the zero point capacitance and the second modified offset are respectively represented as ； ； wherein , represents the zero-point capacitance at two different standard accelerations, , represents different standard accelerations; Calculate the calibrated offset and calibrated sensitivity , represented as: ； ； in, Indicates an update to sensitivity. This indicates that the offset is being updated; Based on the calibrated offset and calibrated sensitivity The actual acceleration after calibration is derived and expressed as: ； in, This indicates the actual acceleration after calibration. This represents the differential capacitance under actual acceleration.

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