Structure and preparation method of MEMS acceleration sensor chip

Abstract

The application relates to the technical field of micro electro mechanical system (MEMS) accelerometer. Specifically, it relates to a structure and a preparation method of a MEMS acceleration sensor chip. The structure of the MEMS acceleration sensor chip comprises a sensitive structure layer, which comprises a sensitive mass block unit, a main longitudinal beam, a sensitive mass block and a plurality of movable electrodes located on the two sides of the sensitive mass block; the sensitive mass block is elastically connected with the main longitudinal beam; the sensitive structure layer further comprises a fixed electrode unit located on the two sides of the sensitive mass block; the fixed electrode unit comprises at least a plurality of fixed electrodes; the movable electrodes and the fixed electrodes form a differential capacitor structure; wherein the main longitudinal beam is connected and fixed with a base layer through a main anchor point; a main auxiliary anchor point is further arranged on the opposite sides of the main anchor point along the extension direction of the main longitudinal beam; the main longitudinal beam is further connected and fixed with the base layer through the main auxiliary anchor points; the connection structure of the main auxiliary anchor point and the main longitudinal beam has a rigidity smaller in the sensitive direction of the sensitive mass block unit than in the non-sensitive direction.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of micro-electro-mechanical system (MEMS) accelerometer. Specifically, it relates to a structure of a MEMS acceleration sensor chip and a preparation method thereof. BACKGROUND

[0002] Micro-Electro-Mechanical Systems (MEMS) devices are micro devices or systems that highly integrate micro mechanical structures, micro sensors, micro actuators, and control circuits on a single or multiple chips. MEMS micro acceleration sensor chips are micro sensors specially used to measure acceleration, and play an important role in many fields such as automobiles, aerospace, biomedicine, communications, and consumer electronics. Common inertial acceleration sensor chips are based on Newton's second law, and can be simplified as a second-order system containing a sensitive mass block and a spring structure. The acceleration is first converted into displacement, and then the displacement is converted into an electrical signal through a conversion element, which is commonly based on piezoelectric, capacitive, and piezoresistive types. Among them, the capacitive comb tooth variable gap type is considered to be the best configuration for making high-sensitivity and high-temperature-range acceleration sensor chips due to its high sensitivity and temperature stability.

[0003] The movable structure part (sensitive mass block, moving electrode, spring) and the fixed electrode of the MEMS acceleration sensor chip are connected to the substrate through anchor structures, and these anchors are the only connection points between the sensitive structure of the acceleration sensor chip and the substrate. Residual stress and thermal stress introduced by manufacturing processes, packaging patches, and thermal stress caused by changes in external environmental temperature will be transmitted to the acceleration sensor chip structure through the anchors, causing structural deformation and detection capacitance changes, affecting the output stability of the sensor. There are several solutions in the prior art to improve the thermal stability of capacitive MEMS acceleration sensor chips, but the effect is still difficult to meet the requirements of extreme high-temperature environment acceleration detection and high-precision measurement. Therefore, a solution is needed to further improve the thermal stability of capacitive MEMS acceleration sensor chips (thermal stability refers to the ability of the MEMS acceleration sensor chip to maintain constant performance with changes in external temperature, more specifically, whether it can maintain relatively stable sensitivity under changes in external temperature), reduce the structural deformation of the movable structure part caused by thermal stress and the resulting detection capacitance changes, so that the capacitive MEMS acceleration sensor chip can meet the requirements of extreme high-temperature environment acceleration detection and high-precision measurement. SUMMARY

[0004] Therefore, the application provides a structure and a preparation method of a MEMS acceleration sensor chip, so as to improve the thermal stability of the capacitive MEMS acceleration sensor chip, reduce the structural deformation of the movable structure part caused by the thermal stress and the change of the detection capacitance caused thereby, and enable the capacitive MEMS acceleration sensor chip to meet the requirements of the detection of the acceleration in an extreme high-temperature environment and high-precision measurement.

[0005] The application provides a structure of a MEMS acceleration sensor chip, comprising: a sensor substrate, the sensor substrate comprising: a substrate layer, a functional layer and a sensitive structure layer which are stacked; the sensitive structure layer comprising a sensitive mass block unit, the sensitive mass block unit comprising a main longitudinal beam, a sensitive mass block and a plurality of movable electrodes located on both sides of the sensitive mass block; the sensitive mass block is arranged around the main longitudinal beam and is elastically connected with the main longitudinal beam; the movable electrodes are fixedly connected with the sensitive mass block; the sensitive structure layer further comprises a fixed electrode unit located on both sides of the sensitive mass block; the fixed electrode unit at least comprises a plurality of fixed electrodes extending towards the main longitudinal beam; the fixed electrode unit is fixedly connected with the substrate layer; the functional layer has a hollow area and an edge area surrounding the hollow area, the projection of the hollow area on the sensitive structure layer at least covers the sensitive mass block unit and the fixed electrode unit; the edge area is fixedly connected with the substrate layer and the sensitive structure layer; the movable electrodes and the fixed electrodes form a differential capacitance structure; the sensitive mass block is adapted to displace along the extension direction of the main longitudinal beam under the external applied acceleration, and drive the movable electrodes to displace; wherein the main longitudinal beam is connected and fixed with the substrate layer through a main anchor point; a main auxiliary anchor point is further arranged on the opposite sides of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is further connected and fixed with the substrate layer through the main auxiliary anchor points; the connection structure of the main auxiliary anchor point and the main longitudinal beam has a rigidity in the sensitive direction of the sensitive mass block unit which is smaller than that in the non-sensitive direction.

[0006] Optionally, the main auxiliary anchor point and the main longitudinal beam are connected through a main beam decoupling beam; the width of the main auxiliary anchor point is greater than that of the main longitudinal beam; the main body part of the main auxiliary anchor point is perpendicular to the extension direction of the main longitudinal beam; the two ends of the main body part of the main auxiliary anchor point extend out a length of the connecting part along the extension direction of the main longitudinal beam, and the connecting part connects the end part of the main longitudinal beam through the main beam decoupling beam; the main body part of the main auxiliary anchor point is fixedly connected with the substrate layer, and the connecting part of the main auxiliary anchor point and the main beam decoupling beam are suspended on the substrate layer; the main beam decoupling beam is adapted to deform along the extension direction of the main longitudinal beam, so that the distance between the position where the main beam decoupling beam connects the main longitudinal beam and the main body part of the main auxiliary anchor point changes in the sensitive direction when subjected to thermal stress.

[0007] Optionally, the sensitive mass block is provided with an elastic member accommodating groove on the side part facing the extension direction of the main longitudinal beam, and an elastic member is arranged in the elastic member accommodating groove, and the two ends of the elastic member are connected with the main longitudinal beam and the sensitive mass block respectively, so that the sensitive mass block is adapted to displace along the extension direction of the main longitudinal beam under the external applied acceleration.

[0008] Optionally, the elastic member is a folded beam spring; the folded beam spring is a serpentine folded structure, extending in a serpentine shape along the extension direction of the main longitudinal beam, one end being connected to the side of the main longitudinal beam, and the other end being connected to the side of the sensitive mass block.

[0009] Optionally, the sensitive mass block, the folded beam spring and the movable electrode jointly constitute a center-symmetric figure, and the center of symmetry of the center-symmetric figure coincides with the main anchor point; the fixed electrode unit is multiple, and is distributed in a center-symmetric manner with the main anchor point as the center of symmetry; taking the extension direction of the main longitudinal beam as the y-axis and the direction perpendicular to the y-axis and passing through the center of the main anchor point as the x-axis, the sensitive mass block, the folded beam spring, the movable electrode and the fixed electrode unit are symmetrically distributed along the y-axis and symmetrically distributed along the x-axis; adjacent movable electrodes and fixed electrodes constitute a capacitor; the capacitors located on the same side of the x-axis are connected in parallel; the capacitors located on both sides of the x-axis have opposite capacitor change conditions under the external applied acceleration.

[0010] Optionally, the sensitive mass block and the main longitudinal beam are provided with a plurality of process release holes penetrating through themselves in the thickness direction; the process release holes are arranged in an array, and the process release holes of adjacent rows are arranged in a staggered manner.

[0011] Optionally, the fixed electrode unit further comprises a secondary longitudinal beam; the secondary longitudinal beam is parallel to the main longitudinal beam and is connected and fixed to the base layer through a secondary anchor point; the fixed electrode unit is provided with a secondary auxiliary anchor point on one side in the extension direction of the secondary longitudinal beam; the secondary longitudinal beam is further connected and fixed to the base layer through the secondary auxiliary anchor point; the connection structure of the secondary auxiliary anchor point and the secondary longitudinal beam has a rigidity in a sensitive direction of the sensitive mass block unit smaller than a rigidity in a non-sensitive direction.

[0012] Optionally, the secondary auxiliary anchor point and the secondary longitudinal beam are connected through a secondary beam decoupling beam; the width of the secondary auxiliary anchor point is greater than the width of the secondary longitudinal beam; the main body part of the secondary auxiliary anchor point is perpendicular to the extension direction of the secondary longitudinal beam; the two ends of the main body part of the secondary auxiliary anchor point extend out a length of the connecting part in the extension direction of the secondary longitudinal beam, and the connecting part connects the end part of the main longitudinal beam through the secondary beam decoupling beam; the main body part of the secondary auxiliary anchor point is connected and fixed to the base layer, and the connecting part of the secondary auxiliary anchor point and the secondary beam decoupling beam are suspended on the base layer; the secondary beam decoupling beam is adapted to deform in the extension direction of the secondary longitudinal beam, so that the distance between the position where the secondary beam decoupling beam connects the secondary longitudinal beam and the main body part of the secondary auxiliary anchor point changes in the sensitive direction when subjected to thermal stress.

[0013] Optionally, the fixed electrode unit is multiple, and is distributed in a center-symmetric manner with the main anchor point as the center of symmetry; wherein, the secondary anchor points of each fixed electrode unit are distributed in a center-symmetric manner with the main anchor point as the center of symmetry, and simultaneously, the secondary auxiliary anchor points of each fixed electrode unit are also distributed in a center-symmetric manner with the main anchor point as the center of symmetry.

[0014] Optionally, the auxiliary longitudinal beam is provided with a plurality of process release holes penetrating through the auxiliary longitudinal beam in the thickness direction; the process release holes are arranged in an array, and the process release holes in adjacent rows are arranged in a staggered manner.

[0015] Optionally, the sensitive structure layer further comprises a bonding outer frame; the bonding outer frame surrounds a main body activity space, and the sensitive mass block unit and the fixed electrode unit are arranged in the main body activity space; the structure of the MEMS acceleration sensor chip further comprises: an upper cover; the upper cover comprises a cover plate and a frame protruding from a side surface of the cover plate; the frame and the cover plate jointly surround a cover plate activity space; the frame is adapted to be connected with the bonding outer frame, and the cover plate activity space corresponds to the main body activity space and jointly accommodates the sensitive mass block unit and the fixed electrode unit with the hollow space of the functional layer.

[0016] Optionally, the sensitive structure layer is provided with a conductive medium layer on a side facing the upper cover, and the conductive medium layer at least covers the sensitive structure unit and the fixed electrode unit; the cover plate is provided with a plurality of through holes exposing the conductive medium layer, the through holes are filled with conductive electrodes, the conductive electrodes are connected with the conductive medium layer and are exposed on a side surface of the cover plate away from the substrate layer; the positions of the through holes correspond to the main anchor points and the auxiliary anchor points.

[0017] The application further provides a preparation method of the structure of the MEMS acceleration sensor chip, comprising the following steps: forming a sensor substrate, comprising: providing a substrate layer; forming an initial functional layer on the substrate layer; forming an initial sensitive structure layer on a side of the initial functional layer away from the substrate layer; etching the initial sensitive structure layer to form a sensitive structure layer, comprising: forming a sensitive mass block unit, the sensitive mass block unit comprising a main longitudinal beam, a sensitive mass block and a plurality of movable electrodes located on both sides of the sensitive mass block; the sensitive mass block is arranged around the main longitudinal beam and is elastically connected with the main longitudinal beam; the movable electrodes are fixedly connected with the sensitive mass block; simultaneously forming a fixed electrode unit located on both sides of the sensitive mass block; the fixed electrode unit at least comprises a plurality of fixed electrodes extending towards the main longitudinal beam; etching the functional layer through the sensitive structure layer to form a hollow region and an edge region surrounding the hollow region, the projection of the hollow region on the sensitive structure layer at least covering the sensitive mass block unit and the fixed electrode unit; the edge region is fixedly connected with the substrate layer and the sensitive structure layer; wherein the step of etching the initial sensitive structure layer to form the sensitive structure layer further comprises: forming a main anchor point for fixing the main longitudinal beam with the substrate layer; forming a main auxiliary anchor point on each of the opposite sides of the main anchor point along the extension direction of the main longitudinal beam; the main longitudinal beam is further fixedly connected with the substrate layer through the main auxiliary anchor points; the connection structure of the main auxiliary anchor point and the main longitudinal beam has a rigidity in a sensitive direction of the sensitive mass block unit smaller than a rigidity in a non-sensitive direction.

[0018] Optionally, in the step of etching the initial sensitive structure layer to form the sensitive structure layer, the method comprises: forming a sensitive layer mask on the side of the sensitive structure layer away from the base layer; using the sensitive layer mask as a mask to pattern and etch the initial sensitive structure layer to form the sensitive mass block unit and the fixed electrode unit; and removing the sensitive layer mask.

[0019] Optionally, in the step of forming the sensitive mass block unit, the method comprises: forming a main beam decoupling beam connecting the main auxiliary anchor point and the main longitudinal beam; the width of the main auxiliary anchor point is greater than the width of the main longitudinal beam; the main body part of the main auxiliary anchor point is perpendicular to the extension direction of the main longitudinal beam; the two ends of the main body part of the main auxiliary anchor point extend out a length of the connecting part along the extension direction of the main longitudinal beam, and the connecting part connects the end part of the main longitudinal beam through the main beam decoupling beam; the main beam decoupling beam is adapted to deform along the extension direction of the main longitudinal beam, so that the distance between the position where the main beam decoupling beam connects the main longitudinal beam and the main body part of the main auxiliary anchor point changes in the sensitive direction when subjected to thermal stress.

[0020] Optionally, in the step of forming the sensitive mass block unit, the method comprises: forming an elastic member accommodating groove on the side of the sensitive mass block facing the extension direction of the main longitudinal beam, and arranging an elastic member in the elastic member accommodating groove, the two ends of the elastic member being connected to the main longitudinal beam and the sensitive mass block respectively, so that the sensitive mass block is adapted to displace along the extension direction of the main longitudinal beam under the action of an external acceleration; the elastic member is a folded beam spring; the folded beam spring is a serpentine folded structure, and extends in a serpentine shape along the extension direction of the main longitudinal beam, one end of the folded beam spring being connected to the side of the main longitudinal beam, and the other end of the folded beam spring being connected to the side of the sensitive mass block.

[0021] Optionally, the sensitive mass block, the folded beam spring and the movable electrode together form a central symmetric pattern, and the center of symmetry of the central symmetric pattern coincides with the main anchor point; the formed fixed electrode unit is a plurality of fixed electrode units, which are centrally symmetrically distributed with the main anchor point as the center of symmetry; the extension direction of the main longitudinal beam is the y-axis, and the direction perpendicular to the y-axis and passing through the center of the main anchor point is the x-axis, the sensitive mass block, the folded beam spring, the movable electrode and the fixed electrode unit are symmetrically distributed along the y-axis and symmetrically distributed along the x-axis; adjacent movable electrodes and fixed electrodes form a capacitor; the capacitors on the same side of the x-axis are connected in parallel; the capacitors on the two sides of the x-axis have opposite changes under the action of an external acceleration.

[0022] Optionally, in the step of forming the fixed electrode unit on the two sides of the sensitive mass block, the method further comprises: simultaneously forming a secondary longitudinal beam; the secondary longitudinal beam is parallel to the main longitudinal beam and is fixedly connected to the base layer through a secondary anchor point; a secondary auxiliary anchor point is formed on the side of the fixed electrode unit along the extension direction of the secondary longitudinal beam, and the secondary longitudinal beam is further fixedly connected to the base layer through the secondary auxiliary anchor point; the secondary auxiliary anchor point is an axisymmetric structure with the central axis of the secondary longitudinal beam as the axis of symmetry; the secondary auxiliary anchor point is an axisymmetric structure with the central axis of the secondary longitudinal beam as the axis of symmetry; the connection structure of the secondary auxiliary anchor point and the secondary longitudinal beam has a smaller stiffness in the sensitive direction of the sensitive mass block unit than in the non-sensitive direction.

[0023] Optionally, the step of forming the fixed electrode unit on both sides of the sensitive mass block further comprises: simultaneously forming a sub-beam decoupling beam connecting the sub-assistant anchor point and the sub-beam; the width of the sub-assistant anchor point is greater than the width of the sub-beam; the main body part of the sub-assistant anchor point is perpendicular to the extension direction of the sub-beam; the two ends of the main body part of the sub-assistant anchor point extend out a length of the connecting part along the extension direction of the sub-beam, and the connecting part connects the end part of the main beam through the sub-beam decoupling beam; the main body part of the sub-assistant anchor point is connected and fixed with the substrate layer, and the connecting part of the sub-assistant anchor point and the sub-beam decoupling beam are suspended on the substrate layer; the sub-beam decoupling beam is adapted to deform along the extension direction of the sub-beam, so that the distance between the position of the sub-beam decoupling beam connected with the sub-beam and the main body part of the sub-assistant anchor point changes in the sensitive direction when subjected to thermal stress.

[0024] Optionally, a plurality of fixed electrode units are formed, which are centrally symmetrically distributed with the main anchor point as the center of symmetry; wherein the sub-anchor points of each fixed electrode unit are centrally symmetrically distributed with the main anchor point as the center of symmetry, and the sub-assistant anchor points of each fixed electrode unit are also centrally symmetrically distributed with the main anchor point as the center of symmetry.

[0025] Optionally, the step of etching the functional layer through the sensitive structure layer comprises: forming a release hole mask on the side of the sensitive structure layer away from the substrate layer; etching a process release hole in the sensitive structure layer using the release hole mask as a mask, the process release hole exposing the initial functional layer at the corresponding position; etching the initial functional layer through the process release hole to form a hollow area in the initial functional layer; the projection of the hollow area on the sensitive structure layer covers at least the sensitive structure unit and the fixed electrode unit; and removing the release hole mask.

[0026] Optionally, the minimum line width of the process release hole is greater than 3 μm; and the length of the long side of the process release hole is 2-3 times greater than the length of the short side.

[0027] Optionally, before the step of forming the sensitive mass block unit and simultaneously forming the fixed electrode unit, the step further comprises: forming a patterned conductive medium layer and a first bonding medium layer on the side of the initial sensitive structure layer away from the substrate layer; the conductive medium layer covers at least the positions where the sensitive mass block unit and the fixed electrode unit are to be formed; and the first bonding medium layer covers the positions of the corresponding edge regions; in the step of forming the sensitive mass block unit and simultaneously forming the fixed electrode unit, the corresponding part of the conductive medium layer removed when forming the sensitive mass block unit is removed together, and the corresponding part of the conductive medium layer removed when forming the fixed electrode unit is removed together; and in the step of forming the process release hole, the conductive medium layer at the position corresponding to the process release hole to be formed is removed together.

[0028] Optionally, the method for preparing the structure of the MEMS acceleration sensor chip further comprises the following steps: forming the upper cover, including: providing a cover plate base; etching the cover plate base to form a cover plate and a frame protruding from one side surface of the cover plate; the frame and the cover plate jointly define a cover plate active space; in the process of forming the sensitive structure layer, further comprising: forming a bonding frame, the bonding frame surrounds and defines a main active space, and the sensitive mass block unit and the fixed electrode unit are arranged in the main active space; the frame is adapted to be connected with the bonding frame, and the active space corresponds to the main active space and jointly accommodates the sensitive mass block unit and the fixed electrode unit.

[0029] Optionally, a blind hole is formed at a preset position of the cover plate, and the blind hole is filled with electroplated metal to form a conductive electrode; the preset position corresponds to the positions of the main anchor point and the auxiliary anchor point in the sensor base; after the conductive electrode is formed, a patterned second bonding medium layer is formed on the side of the cover plate that exposes the conductive electrode; the second bonding medium layer is connected with the conductive electrode.

[0030] Optionally, the sensor base and the upper cover are bonded and connected through the first bonding medium layer and the second bonding medium layer; after bonding, the conductive electrode corresponds to the main anchor point and the auxiliary anchor point and is connected with the conductive medium layer through the second bonding medium layer; the frame of the upper cover and the bonding frame of the sensor base are bonded and connected through the first bonding medium layer and the second bonding medium layer; the active space corresponds to the main active space and jointly accommodates the sensitive mass block unit and the fixed electrode unit with the hollow space of the functional layer.

[0031] The technical scheme of the present application has the following beneficial effects:

[0032] The MEMS acceleration sensor chip provided by the application has the following structure: a sensitive structure layer includes a sensitive mass unit and a fixed electrode unit; the fixed electrode unit is fixedly connected with a substrate layer; two sides of the sensitive mass are provided with movable electrodes, and the fixed electrode unit is provided with fixed electrodes; the movable electrodes and the fixed electrodes form a differential capacitor structure; the sensitive mass is elastically connected with a main longitudinal beam through an elastic component; and the main longitudinal beam is fixedly connected with the substrate layer through a main anchor point. In this way, the sensitive mass is suitable for displacement along the extension direction of the main longitudinal beam under the action of external acceleration, and the movable electrodes are driven to displace, so that differential capacitor type acceleration sensing measurement can be realized. Compared with single capacitor type acceleration sensing measurement, the differential capacitor type acceleration sensing measurement has doubled capacitance change amount, doubled sensitivity and better non-linearity error performance for the same electrode plate displacement. On this basis, a main auxiliary anchor point is arranged on both sides of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is further connected and fixed with the substrate layer through the main auxiliary anchor points. The main auxiliary anchor point is an axisymmetric structure with the central axis of the main longitudinal beam as the axis of symmetry; the connection structure of the main auxiliary anchor point and the main longitudinal beam has smaller rigidity in the sensitive direction of the sensitive mass unit than in the non-sensitive direction. In this way, the main auxiliary anchor point is arranged in an axisymmetric manner, and because the rigidity in the sensitive direction of the sensitive mass unit is smaller than the rigidity in the non-sensitive direction, the main longitudinal beam is supported in the non-sensitive direction (such as a direction other than the extension direction of the main longitudinal beam), so that the main longitudinal beam is not prone to deformation displacement in the non-sensitive direction when receiving interference in the non-sensitive direction, and the sensitive mass is not prone to deformation displacement in the non-sensitive direction. In the sensitive direction, the connection structure of the main auxiliary anchor point and the main longitudinal beam can also eliminate the deformation caused by thermal stress, so that the main longitudinal beam itself is not prone to deformation under the influence of thermal stress, and the displacement of the movable electrodes caused by acceleration is not prone to the influence of thermal stress, so that the measurement of acceleration is not prone to the interference of thermal stress, thereby improving the thermal stability of the MEMS acceleration sensor chip.

[0033] The application provides a preparation method of the structure of the MEMS acceleration sensor chip, and the structure of the MEMS acceleration sensor chip can be manufactured. The formed structure of the MEMS acceleration sensor chip comprises a sensitive structure layer, a fixed electrode unit and a base layer. The sensitive structure layer comprises a sensitive mass unit and the fixed electrode unit. The fixed electrode unit is fixedly connected with the base layer. The sensitive mass is provided with movable electrodes on two sides, and the fixed electrode unit is provided with a fixed electrode. The movable electrode and the fixed electrode form a differential capacitor structure. The sensitive mass is elastically connected with a main longitudinal beam through an elastic component, and the main longitudinal beam is fixedly connected with the base layer through a main anchor point. In this way, the sensitive mass is adapted to displace along the extension direction of the main longitudinal beam under the action of an external acceleration. In this way, the sensitive mass is adapted to displace along the extension direction of the main longitudinal beam under the action of an external acceleration, and the movable electrode is driven to displace, so that the acceleration sensor measurement in the differential capacitor mode can be realized. The acceleration sensor measurement in the differential capacitor mode has a doubled capacitance change amount, a doubled sensitivity and a better nonlinear error performance for the same electrode plate displacement amount, as compared with the acceleration sensor measurement in the single capacitor mode. On this basis, a main auxiliary anchor point is arranged on each side of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is further connected and fixed with the base layer through the main auxiliary anchor points. The main auxiliary anchor point is an axisymmetric structure with the central axis of the main longitudinal beam as the axis of symmetry. The connection structure of the main auxiliary anchor point and the main longitudinal beam has a rigidity in a sensitive direction of the sensitive mass unit smaller than a rigidity in a non-sensitive direction. In this way, the main auxiliary anchor points are arranged in an axisymmetric mode. Since the rigidity in the sensitive direction of the sensitive mass unit is smaller than the rigidity in the non-sensitive direction, the main auxiliary anchor points provide support to the main longitudinal beam in the non-sensitive direction (such as a direction other than the extension direction of the main longitudinal beam), so that the main longitudinal beam is not prone to deformation displacement in the non-sensitive direction when receiving interference in the non-sensitive direction, and further so that the sensitive mass is not prone to deformation displacement in the non-sensitive direction. In the sensitive direction, the connection structure of the main auxiliary anchor point and the main longitudinal beam can also eliminate the deformation caused by thermal stress, so that the main longitudinal beam itself is not prone to deformation under the influence of thermal stress, and further so that the displacement of the movable electrode caused by the acceleration is not prone to being affected by the thermal stress, so that the measurement of the acceleration is not prone to being disturbed by the thermal stress, and thus the thermal stability of the MEMS acceleration sensor chip is improved. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the specific embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or prior art description. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative effort.

[0035] Figure 1 It is a simple schematic diagram of acceleration converted into displacement when the capacitive acceleration sensor chip measures acceleration.

[0036] Figure 2a Conversion diagram of displacement and capacitance when measuring acceleration for a single-capacitance acceleration sensor chip;

[0037] Figure 2b Conversion diagram of displacement and capacitance when measuring acceleration for a differential-capacitance acceleration sensor chip;

[0038] Figure 3 Structure diagram of a MEMS acceleration sensor chip according to an embodiment of the present application;

[0039] Figure 4 Top view diagram of a sensitive structure layer of a MEMS acceleration sensor chip according to an embodiment of the present application;

[0040] Figure 5 Structure diagram of a decoupling beam portion of a MEMS acceleration sensor chip according to an embodiment of the present application;

[0041] Figure 6 Arrangement diagram of process release holes of a MEMS acceleration sensor chip according to an embodiment of the present application;

[0042] Figure 7 Flow diagram of a preparation method of a MEMS acceleration sensor chip according to an embodiment of the present application;

[0043] Figure 8a-8i Diagram of each state in a flow of forming a sensor chip substrate in a preparation method of a MEMS acceleration sensor chip according to an embodiment of the present application;

[0044] Figure 9a-9e Diagram of each state in a flow of forming an upper cover in a preparation method of a MEMS acceleration sensor chip according to an embodiment of the present application;

[0045] Figure 10a-Figure 10c Diagram of each state in a flow of bonding a sensor substrate and an upper cover in a preparation method of a MEMS acceleration sensor chip according to an embodiment of the present application;

[0046] Figure 11a Optical imaging diagram of a functional layer remaining after etching the functional layer when the process release holes are misarranged;

[0047] Figure 11b Optical imaging diagram of a functional layer remaining after etching the functional layer when the process release holes are not misarranged;

[0048] Figure 11c Etching condition diagram of etching a functional layer when the process release holes are not misarranged;

[0049] Figure 12 The full-differential capacitance change of the MEMS acceleration sensor chip of an embodiment of the present application at 20°C and 100°C under different accelerations is shown in the following table. DETAILED DESCRIPTION

[0050] Reference Figure 1 Since acceleration itself is difficult to measure directly, it needs to be converted into other physical quantities for measurement. The most commonly used way is to convert acceleration into the displacement change of a mass block, and then convert the displacement change into other quantities for measurement. The principle is simply explained as Figure 1 As shown in the figure, a second-order inertial system composed of a mass block m, a spring k and a system damping b is used to convert the accelerometer input a into a displacement x, and then the displacement x is converted into an electrical signal output through a piezoresistive, piezoelectric or capacitive displacement detection element, etc. By detecting the electrical signal, the acceleration can be calculated.

[0051] When the accelerometer input tends to be stable, the displacement of the mass block also tends to be stable, and at this time the relationship between the displacement x of the system and the acceleration a can be expressed as:

[0052]

[0053] Displacement sensitivity S x is:

[0054]

[0055] where ω0 is the natural frequency of the second-order system, which is determined by the mass m of the system mass block m and the stiffness k of the spring k, and the definition is It can be seen that for the second-order mechanical system of the inertial accelerometer, the displacement sensitivity is affected by the natural frequency of the system. The greater the frequency, the smaller the displacement sensitivity. At the same time, the greater the mass of the system, the smaller the stiffness of the spring, the lower the natural frequency, and the greater the displacement sensitivity, but the smaller the quality factor.

[0056] The working principle of the capacitive accelerometer is to change the displacement to change the parameters in the capacitor, and then realize the conversion of mechanical physical quantities to electrical quantities, and realize the output of the signal. The basic working principle of the capacitive sensitive part can be explained by using a plate capacitor. Ignoring the edge effect, the capacitance of the capacitive sensitive part can be expressed as:

[0057]

[0058] where C is the capacitance, ε is the dielectric constant of the medium between the plates, A is the opposite area between the plates, and d is the distance between the plates. It can be seen that the change of the dielectric constant, the change of the plate area and the scaling of the plate distance will cause the change of the capacitance, and form an exact functional relationship with it.

[0059] For example, Figure 2a and Figure 2b As shown, the displacement change of the electrode plate causes the initial gap d0 to change by Δd, and then the acceleration a is measured by the change of the capacitance value C.

[0060] The thermal stability of MEMS acceleration sensor chips is related to their manufacturing materials, sensor body structure, and measurement circuits. Since MEMS are typically silicon-based devices, the silicon material will expand thermally with changes in temperature, which can generate stress and strain within the sensitive structure of the accelerometer chip. If stress is concentrated on the spring beam, the system stiffness, i.e., the spring stiffness k, will change. If the strain accumulates and cannot be properly released, the initial gap d0 of the capacitor comb pair will change, thereby affecting the output ΔC of the capacitance signal. Limited by the above problems, the sensitive structure of existing technologies cannot meet the requirements of acceleration detection and high-precision measurement in extremely high-temperature environments.

[0061] To address the problem that capacitive MEMS accelerometer chips are unable to meet the requirements for acceleration detection and high-precision measurement in extremely high-temperature environments, the inventors of this application, after careful research, have proposed a structure and preparation method for a MEMS accelerometer chip to improve the thermal stability of the capacitive MEMS accelerometer chip, reduce the structural deformation of the movable structure caused by thermal stress and the resulting changes in detection capacitance, so that the capacitive MEMS accelerometer chip can meet the requirements for acceleration detection and high-precision measurement in extremely high-temperature environments.

[0062] The application provides a structure of a MEMS acceleration sensor chip, comprising: a sensor substrate, the sensor substrate comprising: a substrate layer, a functional layer and a sensitive structure layer which are stacked; the sensitive structure layer comprising a sensitive mass unit, the sensitive mass unit comprising a main longitudinal beam, a sensitive mass and a plurality of movable electrodes located on both sides of the sensitive mass; the sensitive mass is arranged around the main longitudinal beam and is elastically connected to the main longitudinal beam; the movable electrodes are fixedly connected to the sensitive mass; the sensitive structure layer further comprises a fixed electrode unit located on both sides of the sensitive mass; the fixed electrode unit comprises at least a plurality of fixed electrodes extending to the main longitudinal beam; the fixed electrode unit is fixedly connected to the substrate layer; the functional layer has a hollow area and an edge area surrounding the hollow area, a projection of the sensitive structure layer on the hollow area at least covers the sensitive mass unit and the fixed electrode unit; the edge area fixedly connects the substrate layer and the sensitive structure layer; the movable electrodes and the fixed electrodes form a differential capacitor structure; the sensitive mass is adapted to displace along the extension direction of the main longitudinal beam under an external applied acceleration, and drive the movable electrodes to displace; wherein the main longitudinal beam is connected and fixed to the substrate layer through a main anchor point; a main auxiliary anchor point is further arranged on the opposite sides of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is further connected and fixed to the substrate layer through the main auxiliary anchor points; the connection structure of the main auxiliary anchor point and the main longitudinal beam has a rigidity in a sensitive direction of the sensitive mass unit which is smaller than a rigidity in a non-sensitive direction.

[0063] The application further provides a preparation method of the structure of the MEMS acceleration sensor chip, comprising the following steps: forming a sensor substrate, comprising: providing a substrate layer; forming an initial functional layer on the substrate layer; forming an initial sensitive structure layer on the side of the initial functional layer away from the substrate layer; etching the initial sensitive structure layer to form a sensitive structure layer, comprising: forming a sensitive mass unit, the sensitive mass unit comprising a main longitudinal beam, a sensitive mass and a plurality of movable electrodes located on both sides of the sensitive mass; the sensitive mass is arranged around the main longitudinal beam and is elastically connected to the main longitudinal beam; the movable electrodes are fixedly connected to the sensitive mass; simultaneously forming a fixed electrode unit located on both sides of the sensitive mass; the fixed electrode unit comprises at least a plurality of fixed electrodes extending to the main longitudinal beam; etching the functional layer through the sensitive structure layer to form a hollow area and an edge area surrounding the hollow area, a projection of the sensitive structure layer on the hollow area at least covers the sensitive mass unit and the fixed electrode unit; the edge area fixedly connects the substrate layer and the sensitive structure layer; wherein the step of etching the initial sensitive structure layer to form the sensitive structure layer further comprises: forming a main anchor point for connecting and fixing the main longitudinal beam to the substrate layer; forming a main auxiliary anchor point on the opposite sides of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is further connected and fixed to the substrate layer through the main auxiliary anchor points; the connection structure of the main auxiliary anchor point and the main longitudinal beam has a rigidity in a sensitive direction of the sensitive mass unit which is smaller than a rigidity in a non-sensitive direction.

[0064] The technical solutions of the present application will be described clearly and completely below in conjunction with the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application. In the description of the present application, it should be noted that the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0065] Embodiment 1

[0066] Reference Figure 3-Figure 5 The present application provides a structure of a MEMS acceleration sensor chip, comprising:

[0067] A sensor substrate 1, which comprises a substrate layer 11, a functional layer 12 and a sensitive structure layer 13 arranged in layers.

[0068] The sensitive structure layer 13 comprises a sensitive mass unit, which comprises a main longitudinal beam 132, a sensitive mass 131 and a plurality of movable electrodes (including 133a, 133b, 133c and 133d) located on both sides of the sensitive mass; the sensitive mass 131 is arranged around the main longitudinal beam 132 and is elastically connected to the main longitudinal beam 132; the movable electrodes are fixedly connected to the sensitive mass 131.

[0069] The sensitive structure layer 13 further comprises a fixed electrode unit located on both sides of the sensitive mass; the fixed electrode unit comprises at least a plurality of fixed electrodes (including 134a, 134b, 134c and 134d) extending towards the main longitudinal beam 132; the fixed electrode unit is fixedly connected to the substrate layer 11;

[0070] The functional layer 12 has a hollow area and an edge area around the hollow area, and the projection of the sensitive structure layer 13 on the hollow area covers at least the sensitive mass unit and the fixed electrode unit; the edge area is fixedly connected to the substrate layer 11 and the sensitive structure layer 13;

[0071] The movable electrodes and the fixed electrodes form a differential capacitance structure; the sensitive mass 131 is adapted to displace along the extension direction of the main longitudinal beam 132 under the action of an external acceleration, thereby driving the movable electrodes to displace.

[0072] The main longitudinal beam 132 is connected and fixed to the substrate layer 11 through a main anchor point 135; a main auxiliary anchor point (including 1351a and 1351b) is further arranged on the opposite side of the main anchor point 135 along the extension direction of the main longitudinal beam 132, and the main longitudinal beam 132 is further connected and fixed to the functional layer 12 and the substrate layer 11 through the main auxiliary anchor points; the connection structure of the main auxiliary anchor point and the main longitudinal beam 132 (including Figure 4In the structure at the position indicated by 1352a and 1352b in FIG, in the sensitive direction of the sensitive mass block unit (i.e., the direction in which the sensitive mass block is displaced, in this embodiment, Figure 4 The rigidity of the middle main longitudinal beam 132 in the extension direction is smaller than that in the non-sensitive direction (i.e. Figure 4 The rigidity in the direction other than the extension direction of the main longitudinal beam 132).

[0073] The structure of the MEMS acceleration sensor chip provided in this embodiment comprises a sensitive structural layer 13 comprising a sensitive mass unit and a fixed electrode unit; the fixed electrode unit is fixedly connected to the base layer; movable electrodes are provided on either side of the sensitive mass 131, and the fixed electrode unit is provided with fixed electrodes, forming a differential capacitance structure. The sensitive mass 131 is elastically connected to the main longitudinal beam 132 via an elastic member, and the main longitudinal beam 132 is fixedly connected to the base layer 11 via a main anchor point 135. This allows the sensitive mass to displace along the extension direction of the main longitudinal beam under external acceleration, driving the movable electrodes to displace as well, thereby enabling differential capacitance acceleration sensing. Compared to single capacitance acceleration sensing, differential capacitance acceleration sensing doubles the capacitance change for the same plate displacement, doubles the sensitivity, and exhibits better nonlinear error performance. Furthermore, primary auxiliary anchor points are provided on either side of the main anchor point 135 along the extension direction of the main longitudinal beam. The main longitudinal beam 132 is also fixedly connected to the functional layer 12 and the base layer 11 via the primary auxiliary anchor points. The main auxiliary anchor points are axisymmetric, with the central axis of the main longitudinal beam 132 as the axis of symmetry. The connection structure between the main auxiliary anchor points and the main longitudinal beam 132 has a lower stiffness in the sensitive direction of the sensitive mass unit than in the non-sensitive direction. This axisymmetric arrangement of the main auxiliary anchor points, due to their lower stiffness in the sensitive direction of the sensitive mass unit than in the non-sensitive direction, provides support for the main longitudinal beam in non-sensitive directions (e.g., directions outside the extension direction of the main longitudinal beam). This prevents the main longitudinal beam from deforming or displacing in non-sensitive directions even when subjected to interference from non-sensitive directions, thereby minimizing deformation and displacement of the sensitive mass. Furthermore, in the sensitive direction, the connection structure between the main auxiliary anchor points and the main longitudinal beam 132 can mitigate deformation caused by thermal stress, making the main longitudinal beam 132 less susceptible to deformation under the influence of thermal stress. This, in turn, reduces the impact of thermal stress on the displacement of the movable electrode caused by acceleration, thereby reducing the impact of thermal stress on acceleration measurement and improving the thermal stability of the MEMS acceleration sensor chip.

[0074] refer to Figure 2a and 2b , Figure 2a It is a capacitance diagram of a single capacitive acceleration sensor chip; Figure 2bThe figure is a schematic diagram of the capacitance of a differential capacitive acceleration sensor chip; the working modes of the two are compared in the following table 1.

[0075] Table 1: Comparison of single-capacitance mode and differential mode

[0076]

[0077] Comparing the data in the table, it can be found that compared with the single-capacitance mode, the capacitance change of the same plate displacement is doubled, the sensitivity is doubled, and the non-linearity error is better. Therefore, the differential capacitive sensor has better effect.

[0078] Further, the main auxiliary anchor point is connected with the main longitudinal beam 132 through the main beam decoupling beam; that is, the connection structure of the main auxiliary anchor point and the main longitudinal beam 132 is the main beam decoupling beam (including 1352a and 1352b in the figure). The width of the main auxiliary anchor point (1351a, 1351b) is greater than the width of the main longitudinal beam 132; the main body part of the main auxiliary anchor point (1351a, 1351b) is perpendicular to the extension direction of the main longitudinal beam 132; the two ends of the main body part of the main auxiliary anchor point (1351a, 1351b) extend a length of the connection part along the extension direction of the main longitudinal beam 132, and the connection part connects the end part of the main longitudinal beam 132 through the main beam decoupling beam (1352a, 1352b); the main body part of the main auxiliary anchor point (1351a, 1351b) is connected and fixed with the base layer 11, and the connection part of the main auxiliary anchor point (1351a, 1351b) and the main beam decoupling beam are suspended on the base layer 11; the main beam decoupling beam (1352a, 1352b) is suitable for deforming along the extension direction of the main longitudinal beam, so that the distance between the position where the main beam decoupling beam (1352a, 1352b) connects the main longitudinal beam 132 and the main body part of the main auxiliary anchor point (1351a, 1351b) changes in the sensitive direction when subjected to thermal stress.

[0079] Reference Figure 5 In the embodiment, the two ends of the main body part of the main auxiliary anchor point 1351a extend a length of the connection part along the extension direction of the main longitudinal beam 132, and the connection part connects the end part of the main longitudinal beam 132 through the main beam decoupling beam 1352a; the main beam decoupling beam 1352a is suitable for deforming along the extension direction of the main longitudinal beam 132, so that the distance between the position where the main beam decoupling beam 1352a connects the main longitudinal beam 132 and the main body part of the main auxiliary anchor point 1351a changes in the sensitive direction when subjected to thermal stress; in other words, the main beam decoupling beam 1352a can deform in the sensitive direction when the structure is affected by thermal stress. In this way, in the sensitive direction of the sensitive mass block 131, that is, in the extension direction of the main longitudinal beam 132, the main beam decoupling beam (1352a, 1352b) can deform as shown in Figure 5 Fig. 4 when thermal expansion occurs. Figure 4 In the sensitive direction, i.e. the direction along the extension direction of the main longitudinal beam 132, the force direction is consistent with the length direction of the main-beam-decoupling beam 1352a, and the deformation is not prone to occur, and thus the main-beam-decoupling beam 1352a has better rigidity in this direction and is not prone to be interfered. The case of the main-beam-decoupling beam 1352b on the other side is the same as the above, and thus is not described herein.

[0080] In this way, by arranging the main-beam-decoupling beam, the connection stability of the main longitudinal beam is improved, and the deformation or strain caused by the thermal stress is reduced, thereby improving the thermal stability of the MEMS acceleration sensor.

[0081] Further, referring to Figure 4 The sensitive mass 131 is provided with an elastic member accommodating groove on the side facing the extension direction of the main longitudinal beam 132, and the elastic member 136 is arranged in the elastic member accommodating groove, and the two ends of the elastic member 136 are connected with the main longitudinal beam 132 and the sensitive mass 131 respectively, so that the sensitive mass 131 is adapted to displace along the extension direction of the main longitudinal beam 132 under the external applied acceleration.

[0082] By arranging the elastic member accommodating groove, the elastic member 136 is accommodated in the structural range of the elastic member 136, which simplifies the overall structure, and avoids the influence of the reduced sensitivity caused by the fact that the main longitudinal beam 132 and the sensitive mass 131 are too far away due to the need to arrange the elastic member.

[0083] Specifically, in the embodiment, the elastic member 136 is a folded beam spring; the folded beam spring is a serpentine folded structure, and extends in a serpentine shape along the extension direction of the main longitudinal beam, and one end is connected with the side of the main longitudinal beam, and the other end is connected with the side of the sensitive mass. In this way, by the folded beam spring with the serpentine folded structure, the elastic connection of the sensitive mass 131 and the main longitudinal beam 132 is realized on the side of the main longitudinal beam 132, and the displacement along the extension direction of the main longitudinal beam 132 is realized. In some embodiments, the corner of the folded beam spring is a circular arc shape. The corner of the circular arc shape has better transverse rigidity interference ability than the corner of the fold line.

[0084] Further, in the embodiment, the sensitive mass 131, the folded beam spring and the movable electrodes (including 133a, 133b, 133c and 133d) jointly constitute a central symmetric pattern, and the symmetry center of the central symmetric pattern coincides with the main anchor point; the fixed electrode unit is multiple, and is centrally symmetrically distributed with the main anchor point as the symmetry center; taking the main longitudinal beam extension direction as the y axis and the direction perpendicular to the y axis and passing through the center of the main anchor point as the x axis, the sensitive mass, the folded beam spring, the movable electrode and the fixed electrode unit are symmetrically distributed along the y axis and symmetrically distributed along the x axis; adjacent movable electrodes and fixed electrodes constitute a capacitor; the capacitors on the same side of the x axis are connected in parallel; and the capacitors on the two sides of the x axis have opposite capacitor change conditions under the external applied acceleration.

[0085] Specifically, referring to Figure 4 , the movable electrodes are divided into four groups of 133a, 133b, 133c and 133d by the x axis and the y axis, the fixed electrodes are divided into four groups of 134a, 134b, 134c and 134d by the x axis and the y axis, adjacent movable electrodes and fixed electrodes constitute a capacitor, such as 133a and 134a, 133b and 134b, each constituting a capacitor. The capacitors on the same side of the x axis are connected in parallel. At the same time, the capacitors on the two sides of the x axis, such as the capacitors composed of 133a and 134a and the capacitors composed of 133c and 134c, have opposite capacitor changes under the external applied acceleration. As shown in the figure, on one side of the x axis in the figure, the movable electrode 133a is the lower plate and the fixed electrode 134a is the upper plate; while on the other side of the x axis, the movable electrode 133a is the upper plate and the fixed electrode 134a is the lower plate; therefore, when the sensitive mass 131 moves along the extension direction of the main longitudinal beam 132, the movable electrodes on the two sides of the x axis have the same displacement direction, but the generated capacitor changes are opposite: for example, when the sensitive mass 131 moves upwards in the figure, the upper and lower plates on the side of 133a and 134a approach, while the upper and lower plates on the side of 133c and 134c approach. However, the change conditions of 133a and 134a group and 133b and 134b group on the same side of the x axis are the same. In this way, a differential capacitor is formed.

[0086] Taking 133a and 133b as the capacitor C1, 133b and 134b as the capacitor C2, 133c and 133b as the capacitor C3, and 133d and 134d as the capacitor C4, the differential capacitor output ΔC = C1 + C2 - C3 - C4, since C1, C2, C3 and C4 are completely centrally symmetrically arranged structures, assuming that the initial state is ΔC = C 1初始 + 2初始 - 3初始 - 4初始 , if a transverse cross-axis acceleration disturbance is introduced, the capacitors will change due to the position change of the plates, and the change amounts of the capacitors are ΔC1, ΔC2, ΔC3 and ΔC4 respectively, then at this time C1 = C1初始 + ΔC1, C2 = C 2初始 + ΔC2, C3 = C 3初始 - ΔC3, C4 = C 4初始 - ΔC4; the differential capacitance output is substituted into the above formula to obtain ΔC = C 1初始 + C 2初始 - C 3初始 - C 4初始 + ΔC1 + ΔC2 - ΔC3 - ΔC4, since the structure is completely symmetrical, ΔC1 = ΔC3, ΔC2 = ΔC4; therefore, the differential capacitance output is still ΔC = C when subjected to lateral interference 1初始 + C 2初始 - C 3初始 - C 4初始 ; therefore, the completely symmetrical distribution can enhance stability; similarly, when the external environment temperature of the accelerometer changes, the acceleration sensor chip will expand thermally from the anchor center to the surrounding, driving the electrodes to move by a micro displacement, at this time, the capacitance change ΔC1 = ΔC2 = ΔC3 = ΔC4 caused by the micro displacement can be eliminated in the differential working mode. Therefore, the completely symmetrical structure can play a common mode rejection role.

[0087] Further, the sensitive mass block 131 and the main longitudinal beam 132 are provided with a plurality of process release holes h penetrating the thickness direction thereof; the process release holes h are arranged in an array, and adjacent columns of the process release holes are staggered, as shown in Figure 6 . The process release holes h can also be arranged without staggering, as shown in Figure 4 . The process release holes h are used to process the functional layer 12 below the process release holes during preparation, so as to realize the suspended state of the main longitudinal beam 132, the sensitive mass block 131 and the fixed electrode, so that the sensitive mass block 131 can be displaced. For the distribution of the process release holes h, reference can be made to Figure 11a , Figure 11b and Figure 11c . The release hole shape and the gap are the same, and only the arrangement manner is different, wherein Figure 11b is non-staggered arrangement, Figure 11a is staggered arrangement, and it can be seen that the acceleration chip with staggered arrangement has less residual sacrificial layer, which indicates that the etching of the gas-phase hydrofluoric acid is faster. In addition, reference can be made to Figure 11c , according to the etching condition shown in the figure, it can be seen that when the non-staggered arrangement is used, the etching of the sacrificial layer is gradually diffused from the center of the release hole to the surrounding. Taking four adjacent release holes as a repeating unit for explanation, it can be seen from the figure that the center region of the four release holes forms a region where etching is most difficult to occur, leaving a diamond-shaped sacrificial layer residue as shown in the figure, and the staggered arrangement can improve this phenomenon.

[0088] Further, reference can be made to Figure 4, the fixed electrode unit further comprises a sub-beam (including 137a, 137b, 137c and 137d); the sub-beam is parallel to the main beam 132 and is connected and fixed with the base layer through a sub-anchor point (including 139a, 139b, 139c and 139d); the fixed electrode unit is provided with a sub-assistant anchor point (including 1391a, 1391b, 1391c and 1391d) on one side along the extension direction of the sub-beam, and the sub-beam is further connected and fixed with the base layer 11 through the sub-assistant anchor point; the sub-assistant anchor point is an axisymmetric structure with the central axis of the sub-beam as the axis of symmetry; the connection structure (including 1392a, 1392b, 1392c, 1392d) of the sub-assistant anchor point and the sub-beam is smaller in stiffness in the sensitive direction of the sensitive mass unit than in the non-sensitive direction.

[0089] Similar to the structure of the main beam 132 and the main assistant anchor point, the sub-assistant anchor point is arranged in axis symmetry through the sub-assistant anchor point, and because the stiffness in the sensitive direction of the sensitive mass unit is smaller than the stiffness in the non-sensitive direction, it provides support to the sub-beam in the non-sensitive direction (such as the direction other than the extension direction of the main beam), so that the sub-beam is not easy to deform and displace in the non-sensitive direction when receiving interference in the non-sensitive direction, and further so that the fixed electrode is not easy to deform and displace in the non-sensitive direction. In the sensitive direction, the connection structure of the sub-assistant anchor point and the sub-beam can also eliminate the deformation caused by thermal stress, so that the sub-beam itself is not easy to deform under the influence of thermal stress, and further so that the fixed electrode is not easy to deform or displace under the influence of acceleration, so that the measurement of acceleration is not easy to be disturbed by the influence of thermal stress, thereby improving the thermal stability of the MEMS acceleration sensor chip.

[0090] Specifically, similar to the main assistant anchor point, the sub-assistant anchor point is connected with the sub-beam through a sub-beam decoupling beam; the width of the sub-assistant anchor point is greater than the width of the sub-beam; the main body part of the sub-assistant anchor point is perpendicular to the extension direction of the sub-beam; the two ends of the main body part of the sub-assistant anchor point extend a length of the connection part in the extension direction of the sub-beam, and the connection part connects the end part of the main beam through the sub-beam decoupling beam; the main body part of the sub-assistant anchor point is connected and fixed with the base layer, and the connection part of the sub-assistant anchor point and the sub-beam decoupling beam are suspended on the base layer; the sub-beam decoupling beam is adapted to deform along the extension direction of the sub-beam, so that the distance between the position where the sub-beam decoupling beam connects the sub-beam and the main body part of the sub-assistant anchor point changes in the sensitive direction when subjected to thermal stress. Therefore, the sub-beam decoupling beam can provide support to the sub-beam in the non-sensitive direction and eliminate thermal stress and strain in the sensitive direction, thereby improving the thermal stability of the MEMS acceleration sensor chip.

[0091] Further, the fixed electrode units are multiple, and are symmetrically distributed with the main anchor point as the center of symmetry; wherein the secondary anchor points of each fixed electrode unit are symmetrically distributed with the main anchor point as the center of symmetry, and meanwhile, the secondary auxiliary anchor points of each fixed electrode unit are also symmetrically distributed with the main anchor point as the center of symmetry.

[0092] Similar to the aforementioned sensitive mass block 131 and the movable electrode, the fixed electrode units are also multiple, and are symmetrically distributed accordingly to achieve complete symmetry, thereby achieving the common mode rejection of the differential capacitive MEMS acceleration sensor.

[0093] Further, the secondary longitudinal beam is provided with a plurality of process release holes h penetrating through the secondary longitudinal beam in the thickness direction; the process release holes are arranged in an array, and the process release holes in adjacent rows are arranged in a staggered manner. Similar to the process release holes h of the aforementioned sensitive mass block 131 and the main longitudinal beam 132, the process release holes are used to process the functional layer thereunder to form a hollow area, thereby achieving the suspension of the secondary longitudinal beam and the fixed electrode.

[0094] Further, the sensitive structure layer 13 further comprises a bonding outer frame 1300; the bonding outer frame 1300 surrounds a main movable space, and the sensitive mass block unit and the fixed electrode unit are arranged in the main movable space; the structure of the MEMS acceleration sensor chip further comprises: an upper cover 2; the upper cover 2 comprises a cover plate and a frame protruding from a side surface of the cover plate; the frame and the cover plate jointly surround a cover plate movable space; the frame is suitable for being connected with the bonding outer frame 1300, and the cover plate movable space corresponds to the main movable space and jointly accommodates the sensitive mass block unit and the fixed electrode unit with the hollow space of the functional layer. In a specific embodiment, the frame is connected with the bonding outer frame 1300 through a bonding medium layer.

[0095] Further, the sensitive structure layer 13 is provided with a conductive medium layer on a side facing the upper cover 2, and the conductive medium layer at least covers the sensitive structure unit and the fixed electrode unit; the conductive medium layer is used to guide the capacitive change of the sensitive structure layer to the conductive medium layer; the cover plate is provided with a plurality of through holes exposing the conductive medium layer, and the through holes are filled with conductive electrodes connected with the conductive medium layer and exposed on a side surface of the cover plate away from the substrate layer; the positions of the through holes correspond to the main anchor points and the secondary anchor points. Through the conductive electrodes, the electric signal in the conductive medium layer can be led out, so that the external monitoring device can measure the acceleration according to the change of the electric signal in the MEMS acceleration sensor chip.

[0096] In order to reflect the actual working effect of the structure of the MEMS acceleration sensor chip provided in the embodiment, the MEMS acceleration sensor chip is tested under different temperatures with the same acceleration, and the data is collected and plotted. Referring to Figure 12At 20 DEG C (normal temperature) and 100 DEG C (non-normal high temperature), the full-differential capacitance and the change amount remain basically consistent under the same acceleration amount input, thereby indicating that the temperature stability of the structure of the MEMS acceleration sensor chip provided in the embodiment is good.

[0097] Embodiment 2

[0098] The embodiment provides a preparation method of a structure of a MEMS acceleration sensor chip, and is used for preparing the MEMS acceleration sensor chip in Embodiment 1. Figure 7 , and comprises the following steps:

[0099] The sensor substrate is formed, and comprises:

[0100] Referring to Figure 8a , a substrate layer 11 is provided; an initial functional layer 120 is formed on the substrate layer 11; and an initial sensitive structure layer 130 is formed on a side of the initial functional layer 120, which is away from the substrate layer 11;

[0101] The initial sensitive structure layer 130 is etched to form a sensitive structure layer 13, and the step comprises:

[0102] Referring to Figure 8b-8f , and Figure 4 , the sensitive mass block unit is formed, and the sensitive mass block unit comprises a main longitudinal beam, a sensitive mass block and a plurality of movable electrodes located on two sides of the sensitive mass block; the sensitive mass block is arranged around the main longitudinal beam and elastically connected with the main longitudinal beam; and the movable electrodes are fixedly connected with the sensitive mass block.

[0103] Also referring to Figure 8b-8f , and Figure 4 , the fixed electrode unit located on the two sides of the sensitive mass block is formed simultaneously; the fixed electrode unit at least comprises a plurality of fixed electrodes extending towards the main longitudinal beam.

[0104] Referring to Figure 8h-8i , the initial functional layer 120 is etched through the sensitive structure layer to form a functional layer 12, and a hollow area and an edge area surrounding the hollow area are formed; the projection of the sensitive structure layer 13 at least covers the sensitive mass block unit and the fixed electrode unit; and the edge area is fixedly connected with the substrate layer 11 and the sensitive structure layer 13.

[0105] In the step of etching the initial sensitive structure layer 130 to form the sensitive structure layer 13, the step further comprises: forming a main anchor point for fixing the main longitudinal beam and the substrate layer; and forming a main auxiliary anchor point on each of opposite sides of the main anchor point along the extension direction of the main longitudinal beam, so that the main longitudinal beam is further fixedly connected with the substrate layer through the main auxiliary anchor points; and the connection structure of the main auxiliary anchor point and the main longitudinal beam has a rigidity in a sensitive direction of the sensitive mass block unit smaller than a rigidity in a non-sensitive direction.

[0106] The method for preparing the structure of the MEMS acceleration sensor chip provided in this embodiment can manufacture the structure of the MEMS acceleration sensor chip provided in the above-mentioned embodiment 1. The structure of the resulting MEMS acceleration sensor chip comprises a sensitive structural layer including a sensitive mass block unit and a fixed electrode unit; the fixed electrode unit is fixedly connected to the base layer; movable electrodes are provided on both sides of the sensitive mass block, and the fixed electrode unit is provided with fixed electrodes, and the movable electrodes and the fixed electrodes form a differential capacitance structure. The sensitive mass block is elastically connected to the main longitudinal beam via an elastic member, and the main longitudinal beam is fixedly connected to the base layer via a main anchor point. This allows the sensitive mass block to be adapted to displace along the extension direction of the main longitudinal beam under external acceleration. This allows the sensitive mass block to be adapted to displace along the extension direction of the main longitudinal beam under external acceleration, driving the movable electrode to displace, thereby enabling differential capacitance acceleration sensing measurement. Compared to single capacitance acceleration sensing measurement, differential capacitance acceleration sensing doubles the capacitance change for the same plate displacement, doubles the sensitivity, and exhibits better nonlinear error performance. On this basis, main auxiliary anchor points are respectively provided on both sides of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is also connected and fixed to the base layer via the main auxiliary anchor points. The main auxiliary anchor points are axisymmetric structures with the central axis of the main longitudinal beam as the axis of symmetry; the connection structure between the main auxiliary anchor points and the main longitudinal beam has a stiffness in the sensitive direction of the sensitive mass block unit that is less than that in the non-sensitive direction. In this way, through the axisymmetric arrangement of the main auxiliary anchor points, since the stiffness in the sensitive direction of the sensitive mass block unit is less than that in the non-sensitive direction, it provides support for the main longitudinal beam in the non-sensitive direction (such as the direction other than the extension direction of the main longitudinal beam). When the main longitudinal beam is disturbed in the non-sensitive direction, it is less likely to deform or displace in the non-sensitive direction, thereby making it less likely for the sensitive mass block to deform or displace in the non-sensitive direction. In the sensitive direction, the connection structure between the main auxiliary anchor point and the main longitudinal beam can also eliminate the deformation caused by thermal stress, so that the main longitudinal beam itself is not easily deformed under the influence of thermal stress, and the displacement of the movable electrode caused by acceleration is not easily affected by thermal stress, so that the acceleration measurement is not easily disturbed by the influence of thermal stress, thereby improving the thermal stability of the MEMS acceleration sensor chip.

[0107] Furthermore, the step of etching the initial sensitive structure layer to form the sensitive structure layer includes:

[0108] refer to Figure 8f , forming a sensitive layer mask M3 on the side of the initial sensitive structure layer 130 facing away from the base layer 11;

[0109] refer to Figure 8g , using the sensitive layer mask M3 as a mask, pattern-etching the initial sensitive structure layer 130 to form a sensitive mass block unit and a fixed electrode unit;

[0110] refer to Figure 8h , removing the sensitive layer mask.

[0111] Further, in the step of forming the sensitive mass unit, the step comprises: forming a main beam decoupling beam connecting the main auxiliary anchor point and the main longitudinal beam; the width of the main auxiliary anchor point is greater than the width of the main longitudinal beam; the main body part of the main auxiliary anchor point is perpendicular to the extension direction of the main longitudinal beam; the two ends of the main body part of the main auxiliary anchor point extend out a length of the connecting part along the extension direction of the main longitudinal beam, and the connecting part connects the end of the main longitudinal beam through the main beam decoupling beam; the main beam decoupling beam is adapted to deform along the extension direction of the main longitudinal beam, so that the distance between the position where the main beam decoupling beam connects the main longitudinal beam and the main body part of the main auxiliary anchor point changes in the sensitive direction when subjected to thermal stress.

[0112] Further, in the step of forming the sensitive mass unit, the step comprises: forming an elastic member accommodating groove on the side of the sensitive mass towards the extension direction of the main longitudinal beam, and arranging an elastic member in the elastic member accommodating groove; the two ends of the elastic member are connected to the main longitudinal beam and the sensitive mass respectively, so that the sensitive mass is adapted to displace along the extension direction of the main longitudinal beam under the action of external acceleration; the elastic member is a folded beam spring; the folded beam spring is a serpentine folded structure, and extends in a serpentine shape along the extension direction of the main longitudinal beam, with one end connected to the side of the main longitudinal beam and the other end connected to the side of the sensitive mass.

[0113] Further, the sensitive mass, the folded beam spring, and the movable electrode together form a center-symmetric figure, and the center of symmetry of the center-symmetric figure coincides with the main anchor point; the formed fixed electrode unit is multiple, and is distributed in a center-symmetric manner with the main anchor point as the center of symmetry; taking the extension direction of the main longitudinal beam as the y-axis and the direction perpendicular to the y-axis and passing through the center of the main anchor point as the x-axis, the sensitive mass, the folded beam spring, the movable electrode, and the fixed electrode unit are symmetrically distributed along the y-axis and symmetrically distributed along the x-axis; adjacent movable electrodes and fixed electrodes form a capacitor; the capacitors on the same side of the x-axis are connected in parallel; the capacitors on the two sides of the x-axis have opposite changes under the action of external acceleration.

[0114] Further, in the step of forming the fixed electrode unit on both sides of the sensitive mass, the step further comprises: simultaneously forming a secondary longitudinal beam; the secondary longitudinal beam is parallel to the main longitudinal beam and is connected and fixed to the substrate layer through a secondary anchor point; a secondary auxiliary anchor point is formed on one side of the fixed electrode unit along the extension direction of the secondary longitudinal beam, and the secondary longitudinal beam is further connected and fixed to the substrate layer through the secondary auxiliary anchor point; the secondary auxiliary anchor point is an axis-symmetric structure with the central axis of the secondary longitudinal beam as the axis of symmetry; the connection structure of the secondary auxiliary anchor point and the secondary longitudinal beam has a rigidity in the sensitive direction of the sensitive mass unit that is smaller than a rigidity in a non-sensitive direction.

[0115] Further, the step of forming the fixed electrode unit on both sides of the sensitive mass further comprises: simultaneously forming a secondary beam decoupling beam connecting the secondary auxiliary anchor point and the secondary longitudinal beam; the width of the secondary auxiliary anchor point is greater than the width of the secondary longitudinal beam; the main body part of the secondary auxiliary anchor point is perpendicular to the extension direction of the secondary longitudinal beam; the two ends of the main body part of the secondary auxiliary anchor point extend out a length of the connecting part along the extension direction of the secondary longitudinal beam, and the connecting part connects the end of the main longitudinal beam through the secondary beam decoupling beam; the main body part of the secondary auxiliary anchor point is fixedly connected with the substrate layer, and the connecting part of the secondary auxiliary anchor point and the secondary beam decoupling beam are suspended on the substrate layer; the secondary beam decoupling beam is adapted to deform along the extension direction of the secondary longitudinal beam, so that the distance between the position where the secondary beam decoupling beam connects the secondary longitudinal beam and the main body part of the secondary auxiliary anchor point changes in the sensitive direction when subjected to thermal stress.

[0116] Further, the fixed electrode unit is formed in multiple, with the main anchor point as the center of symmetry, and is centrally symmetrically distributed; wherein the secondary anchor points of each fixed electrode unit are centrally symmetrically distributed with the main anchor point as the center of symmetry, and the secondary auxiliary anchor points of each fixed electrode unit are also centrally symmetrically distributed with the main anchor point as the center of symmetry.

[0117] Further, the step of etching the functional layer through the sensitive structure layer comprises: forming a release hole mask on the side of the sensitive structure layer away from the substrate layer; etching a process release hole in the sensitive structure layer using the release hole mask as a mask, the process release hole exposing the initial functional layer at the corresponding position; etching the initial functional layer through the process release hole to form a hollow area in the initial functional layer; the projection of the hollow area on the sensitive structure layer covers at least the sensitive structure unit and the fixed electrode unit; and removing the release hole mask.

[0118] Further, the minimum line width of the process release hole is greater than 3μm. The process release hole is not a functional structure of the sensor and does not serve the acceleration sensing function, but is a non-functional structure added for the preparation of the sensor. For example, the capacitor and the folded beam spring in the sensitive structure layer of the sensor are structures set for the sensing function of the sensor, which are functional structures. The minimum gap of the capacitor is 3μm, and the length, width, and gap of other functional structures are not less than 3μm, so the minimum line width of the functional structure can be referred to as 3μm.

[0119] In the etching process in the semiconductor process, the minimum line width affects the etching rate. With the same processing parameters, the smaller the minimum line width of the processed pattern, the slower the material removal rate of the etching process, so a minimum line width needs to be limited.

[0120] Therefore, the minimum line width of the process release hole is greater than 3μm (for example, either the length or the width must be greater than the minimum line width in the original structure layer, which is greater than 3μm according to the above distance). This is to avoid the introduction of the release process hole, which will lead to a longer overall etching time.

[0121] Furthermore, the long side of the process release hole is 2-3 times greater than the short side. When the long side of the process release hole is 2-3 times greater than the short side, the etching rate at the process release hole can be further improved. However, the spacing between the long sides should not be too long. Too long will not only increase the area of ​​a single opening, but also lead to an excessively large overall opening ratio of the entire structure, which will reduce the mass of the mass block and reduce the sensitivity and stability of the sensor. At the same time, an excessive opening ratio will also lead to a decrease in structural strength. Therefore, it is preferred that the long side is 2-3 times the short side.

[0122] For further reference, Figure 8b-8d , before the steps of forming the sensitive mass unit and simultaneously forming the fixed electrode unit, the method further includes:

[0123] A patterned conductive dielectric layer 31 and a first bonding dielectric layer 32 are formed on the side of the initial sensitive structure layer facing away from the base layer; the conductive dielectric layer 31 at least covers the positions where the sensitive mass unit and the fixed electrode unit are to be formed; and the first bonding dielectric layer 32 covers the position corresponding to the edge area.

[0124] Specifically include:

[0125] refer to Figure 8b , forming a patterned first mask M1 on the side of the initial sensitive structure layer facing away from the base layer;

[0126] refer to Figure 8c , forming a first initial dielectric layer 3, filling the portion not covered by the first mask M1;

[0127] refer to Figure 8d , the first initial dielectric layer 3 is thinned to expose the first mask M1 , and then the first mask M1 is removed, and the remaining first initial dielectric layer 3 forms a patterned conductive dielectric layer 31 and a first bonding dielectric layer 32 .

[0128] The steps of forming the sensitive mass block unit and simultaneously forming the fixed electrode unit also include: removing the conductive medium layer 31 corresponding to the portion removed when forming the sensitive mass block unit, and removing the conductive medium layer 31 corresponding to the portion removed when forming the fixed electrode unit; and when forming the process release hole, removing the conductive medium layer 31 at the position corresponding to the predetermined process release hole.

[0129] Furthermore, the method for preparing the structure of the MEMS acceleration sensor chip further includes the following steps: forming an upper cover, including:

[0130] providing a cover substrate;

[0131] etching the cover substrate to form a cover plate and a frame protruding from one side surface of the cover plate;

[0132] Figure 9e comprising: forming a third cover mask M6 on one side of the cover substrate; etching the cover substrate to form the frame and the active space with the third cover mask M6 as a mask.

[0133] In the process of forming the sensitive structure layer, further comprising:

[0134] forming a bonding frame, the bonding frame surrounding the main active space, the sensitive mass unit and the fixed electrode unit being arranged in the main active space; the frame being adapted to be connected with the bonding frame, the active space corresponding to the main active space, and the active space and the main active space together accommodating the sensitive mass unit and the fixed electrode unit.

[0135] Further, a blind hole is formed at a predetermined position of the cover plate, and a conductive electrode is formed by filling the blind hole with electroplated metal; the predetermined position corresponding to the positions of the main anchor point and the auxiliary anchor point in the sensor substrate.

[0136] Specifically comprising:

[0137] Referring to Figure 9a forming a first cover mask M4 on one side surface of the cover substrate 20;

[0138] Referring to Figure 9b etching the cover substrate to form a blind hole with the first cover mask M4 as a mask;

[0139] Referring to Figure 9c forming an electroplated metal layer, the electroplated metal layer filling the blind hole and covering the surface of the cover plate. Then, the electroplated metal layer on the surface of the cover plate is removed, and the second initial dielectric layer remaining in the blind hole forms a conductive electrode 21.

[0140] After the conductive electrode is formed, a patterned second bonding dielectric layer 33 is formed on the side of the cover plate exposing the conductive electrode; the second bonding dielectric layer 33 being connected with the conductive electrode 21.

[0141] Specifically comprising:

[0142] Referring to Figure 9d forming a patterned second cover mask M5 on one side surface of the cover substrate 20; the patterned second cover mask M5 exposing at least the conductive electrode 21. Filling the part not covered by the second cover mask M5 to form a second bonding dielectric layer 33, the second bonding dielectric layer 33 being connected with the conductive electrode 21. Then, the second cover mask M5 is removed.

[0143] In addition, when the third cover plate mask M6 is subsequently formed, the third cover plate mask M6 is formed on the surface of the second bonding medium layer 33.

[0144] Further, in some embodiments, after the blind hole is formed, before the metal is electroplated to fill the blind hole, the method further comprises: forming a composite film layer of an insulating layer, a barrier layer and a seed layer on the sidewall of the blind hole (the step is not shown in the figure). Then the following steps are performed Figure 9e , etching the cover plate base to form a cover plate active space.

[0145] Further, referring to Figure 10a , the sensor base 1 and the upper cover 2 are bonded and connected through the first bonding medium layer 32 and the second bonding medium layer 33.

[0146] After bonding, the conductive electrode 21 corresponds to the main anchor point and the auxiliary anchor point, and is connected to the conductive medium layer 31 through the second bonding medium layer 33; the frame of the upper cover 2 is bonded and connected to the bonding frame of the sensor base 1 through the first bonding medium layer 32 and the second bonding medium layer 33.

[0147] The cover plate active space corresponds to the main body active space, and together with the hollow space of the functional layer, it accommodates the sensitive mass block unit and the fixed electrode unit.

[0148] In addition, in some embodiments, the method further comprises:

[0149] Referring to Figure 8e , on the side of the base layer 11 opposite to the sensitive structure layer 13, a base positioning hole is formed through the second mask M2. Then in Figure 9e , the step of etching the cover plate base 20 to form the cover plate active space, the cover plate positioning hole is formed synchronously. In Figure 10a , the bonding step, the positioning of the upper cover and the sensor base is realized through the cover plate positioning hole and the base positioning hole.

[0150] Referring to Figure 10b , the cover plate base 20 is thinned to expose the surface of the conductive electrode 21 on the side of the cover plate base 20 opposite to the sensor base 1.

[0151] Referring to Figure 10c , a metal electrode pad 22 is formed on the surface of the conductive electrode 21 exposed on the surface of the cover plate base 20 opposite to the sensor base 1, so that the conductive electrode 21 realizes the lead-out of the electrical signal outward. Among them, the metal electrode pad 22 can also be positioned and formed through the base positioning hole.

[0152] Obviously, the above embodiments are merely example for clearly illustrating but not limitation to the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, all the embodiments need not and can not be enumerated. The obvious changes or variations derived from the above description are still within the protection scope of the present application.

Claims

1. A structure of a MEMS acceleration sensor chip, characterized in that: include: A sensor substrate, comprising: a base layer, a functional layer, and a sensitive structural layer stacked in layers; The sensitive structural layer includes a sensitive mass block unit, which includes a main longitudinal beam, a sensitive mass block, and a plurality of movable electrodes located on both sides of the sensitive mass block; the sensitive mass block is arranged around the main longitudinal beam and elastically connected to the main longitudinal beam; the movable electrodes are fixedly connected to the sensitive mass block; The sensitive structural layer further comprises fixed electrode units located on both sides of the sensitive mass block; the fixed electrode units at least comprise a plurality of fixed electrodes extending toward the main longitudinal beam; the fixed electrode units are fixedly connected to the base layer; The functional layer has a hollow area and an edge area surrounding the hollow area, wherein the projection of the hollow area on the sensitive structure layer at least covers the sensitive mass block unit and the fixed electrode unit; the edge area is fixedly connected to the base layer and the sensitive structure layer; The movable electrode and the fixed electrode form a differential capacitor structure; the sensitive mass block is adapted to be displaced along the extension direction of the main longitudinal beam under external acceleration, thereby driving the movable electrode to be displaced; The main longitudinal beam is connected and fixed to the base layer via a main anchor point; main auxiliary anchor points are respectively provided on opposite sides of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is further connected and fixed to the base layer via the main auxiliary anchor points; the main auxiliary anchor points are axisymmetric structures with the central axis of the main longitudinal beam as the axis of symmetry; the stiffness of the connection structure between the main auxiliary anchor points and the main longitudinal beam in the sensitive direction of the sensitive mass unit is less than the stiffness in the non-sensitive direction; The main auxiliary anchor point is connected to the main longitudinal beam via a main beam decoupling beam; The width of the main auxiliary anchor point is greater than the width of the main longitudinal beam; the main body of the main auxiliary anchor point is perpendicular to the extension direction of the main longitudinal beam; both ends of the main body of the main auxiliary anchor point extend a portion of the length of the connecting portion along the extension direction of the main longitudinal beam, and the connecting portion is connected to the end of the main longitudinal beam through the main beam decoupling beam; the main body of the main auxiliary anchor point is connected and fixed to the base layer, and the connecting portion of the main auxiliary anchor point and the main beam decoupling beam are suspended above the base layer; The main beam decoupling beam is suitable for deforming along the extension direction of the main longitudinal beam, so that the distance between the position where the main beam decoupling beam connects the main longitudinal beam and the main body of the main auxiliary anchor point changes in a sensitive direction when subjected to thermal stress.

2. The structure of the MEMS acceleration sensor chip according to claim 1, characterized in that: The sensitive mass block is provided with an elastic component accommodating groove on the side facing the extension direction of the main longitudinal beam, and an elastic component is provided in the elastic component accommodating groove. The two ends of the elastic component are respectively connected to the main longitudinal beam and the sensitive mass block, so that the sensitive mass block is suitable for displacement along the extension direction of the main longitudinal beam under external acceleration.

3. The structure of the MEMS acceleration sensor chip according to claim 2, characterized in that: The elastic component is a folding beam spring; the folding beam spring is a serpentine folding structure, extending in a serpentine shape along the extension direction of the main longitudinal beam, with one end connected to the side of the main longitudinal beam and the other end connected to the side of the sensitive mass block.

4. The structure of the MEMS acceleration sensor chip according to claim 3, characterized in that: The sensitive mass, the folded beam spring and the movable electrode together form a central symmetrical figure, and the symmetry center of the central symmetrical figure coincides with the main anchor point; There are multiple fixed electrode units, which are symmetrically distributed with the main anchor point as the center of symmetry; The extending direction of the main longitudinal beam is defined as the y-axis, and the direction perpendicular to the y-axis and passing through the center of the main anchor point is defined as the x-axis. The sensitive mass, the folded beam spring, the movable electrode, and the fixed electrode unit are symmetrically distributed along the y-axis and symmetrically distributed along the x-axis. The adjacent movable electrodes and the fixed electrodes form a capacitor; The capacitors located on the same side of the x-axis are connected in parallel; The capacitance changes of the capacitors located on both sides of the x-axis are opposite to each other under external acceleration.

5. The structure of the MEMS acceleration sensor chip according to claim 1, characterized in that: The sensitive mass block and the main longitudinal beam are provided with a plurality of process release holes penetrating through the blocks in the thickness direction; the process release holes are arranged in an array, and the process release holes in adjacent rows are staggered.

6. The structure of the MEMS acceleration sensor chip according to claim 1, wherein: The fixed electrode unit further includes a secondary longitudinal beam; the secondary longitudinal beam is parallel to the main longitudinal beam and is connected and fixed to the base layer through a secondary anchor point; The fixed electrode unit is provided with a secondary auxiliary anchor point on one side along the extension direction of the secondary longitudinal beam, and the secondary longitudinal beam is also connected and fixed to the base layer through the secondary auxiliary anchor point; the secondary auxiliary anchor point is an axisymmetric structure with the central axis of the secondary longitudinal beam as the axis of symmetry; the connection structure between the secondary auxiliary anchor point and the secondary longitudinal beam has a stiffness in the sensitive direction of the sensitive mass block unit that is less than the stiffness in the non-sensitive direction.

7. The structure of the MEMS acceleration sensor chip according to claim 6, characterized in that: The secondary auxiliary anchor point is connected to the secondary longitudinal beam via a secondary beam decoupling beam; The width of the secondary auxiliary anchor point is greater than the width of the secondary longitudinal beam; the main body of the secondary auxiliary anchor point is perpendicular to the extension direction of the secondary longitudinal beam; Both ends of the main body of the secondary auxiliary anchor point extend partially along the extension direction of the secondary longitudinal beam, and the connecting portions are connected to the ends of the main longitudinal beam through the secondary beam decoupling beam; the main body of the secondary auxiliary anchor point is connected and fixed to the base layer, and the connecting portions of the secondary auxiliary anchor point and the secondary beam decoupling beam are suspended above the base layer; The auxiliary beam decoupling beam is suitable for deforming along the extension direction of the auxiliary longitudinal beam, so that the distance between the position where the auxiliary beam decoupling beam connects the auxiliary longitudinal beam and the main body of the secondary auxiliary anchor point changes in a sensitive direction when subjected to thermal stress.

8. The structure of the MEMS acceleration sensor chip according to claim 7, characterized in that: There are multiple fixed electrode units, which are symmetrically distributed with the main anchor point as the center of symmetry; The secondary anchor points of each fixed electrode unit are distributed symmetrically with the main anchor point as the center of symmetry. Meanwhile, the secondary auxiliary anchor points of each fixed electrode unit are also distributed symmetrically with the main anchor point as the center of symmetry.

9. The structure of the MEMS acceleration sensor chip according to claim 8, characterized in that: The secondary longitudinal beam is provided with a plurality of process release holes penetrating the secondary longitudinal beam in the thickness direction; the process release holes are arranged in an array, and the process release holes in adjacent rows are staggered.

10. The structure of the MEMS acceleration sensor chip according to claim 6, characterized in that: The sensitive structural layer also includes a bonding outer frame; The bonding outer frame surrounds and defines a main body activity space, and the sensitive mass block unit and the fixed electrode unit are arranged in the main body activity space; The structure of the MEMS acceleration sensor chip also includes: Upper cover; The upper cover includes a cover plate and a frame protruding from one side surface of the cover plate; the frame and the cover plate together enclose a cover plate activity space; the frame is suitable for connection with the bonding outer frame, the cover plate activity space corresponds to the main body activity space, and together with the hollow space of the functional layer, accommodates the sensitive mass block unit and the fixed electrode unit.

11. The structure of the MEMS acceleration sensor chip according to claim 10, wherein: A conductive medium layer is provided on the side of the sensitive structure layer facing the upper cover, and the conductive medium layer at least covers the sensitive structure unit and the fixed electrode unit; The cover plate is provided with a plurality of through holes, wherein the through holes expose the conductive medium layer, and the through holes are filled with conductive electrodes, which are connected to the conductive medium layer and exposed on the surface of the cover plate facing away from the base layer; The positions of the through holes are arranged corresponding to the main anchor points and the secondary anchor points.

12. A method for preparing a structure of a MEMS acceleration sensor chip, characterized in that: The following steps are involved: A sensor substrate is formed, comprising: Providing a base layer; forming an initial functional layer on the base layer; and forming an initial sensitive structural layer on the side of the initial functional layer facing away from the base layer; Etching the initial sensitive structure layer to form a sensitive structure layer includes: A sensitive mass unit is formed, the sensitive mass unit comprising a main longitudinal beam, a sensitive mass, and a plurality of movable electrodes located on both sides of the sensitive mass; the sensitive mass is disposed around the main longitudinal beam and elastically connected to the main longitudinal beam; the movable electrodes are fixedly connected to the sensitive mass; At the same time, fixed electrode units are formed on both sides of the sensitive mass; the fixed electrode units at least include a plurality of fixed electrodes extending toward the main longitudinal beam; The initial functional layer is corroded to form a functional layer; the functional layer is corroded through the sensitive structural layer to form a hollow area and an edge area surrounding the hollow area, wherein the projection of the hollow area on the sensitive structural layer at least covers the sensitive mass unit and the fixed electrode unit; the edge area is fixedly connected to the base layer and the sensitive structural layer; The step of etching the initial sensitive structural layer to form the sensitive structural layer further includes: forming a main anchor point for connecting and fixing the main longitudinal beam to the base layer; forming main auxiliary anchor points on opposite sides of the main anchor point along the extension direction of the main longitudinal beam, the main longitudinal beam being further connected and fixed to the base layer via the main auxiliary anchor points; the main auxiliary anchor points being an axisymmetric structure with the central axis of the main longitudinal beam as the axis of symmetry; and the stiffness of the connection structure between the main auxiliary anchor points and the main longitudinal beam in the sensitive direction of the sensitive mass unit being less than the stiffness in the non-sensitive direction. The steps of forming the sensitive mass block unit include: forming a main beam decoupling beam connecting the main auxiliary anchor point and the main longitudinal beam; The width of the main auxiliary anchor point is greater than the width of the main longitudinal beam; the main body of the main auxiliary anchor point is perpendicular to the extension direction of the main longitudinal beam; both ends of the main body of the main auxiliary anchor point extend a portion of the length of the connecting portion along the extension direction of the main longitudinal beam, and the connecting portion is connected to the end of the main longitudinal beam through the main beam decoupling beam; The main beam decoupling beam is suitable for deforming along the extension direction of the main longitudinal beam, so that the distance between the position where the main beam decoupling beam connects the main longitudinal beam and the main body of the main auxiliary anchor point changes in a sensitive direction when subjected to thermal stress.

13. The method for preparing the structure of the MEMS acceleration sensor chip according to claim 12, characterized in that: The step of etching the initial sensitive structure layer to form a sensitive structure layer includes: forming a sensitive layer mask on the side of the sensitive structure layer facing away from the base layer; Using the sensitive layer mask as a mask, pattern-etching the initial sensitive structure layer to form the sensitive mass unit and the fixed electrode unit; The sensitive layer mask is removed.

14. The method for preparing the structure of a MEMS acceleration sensor chip according to claim 12, wherein: The steps of forming the sensitive mass block unit include: An elastic member receiving groove is formed on a side of the sensitive mass block in the extension direction of the main longitudinal beam, an elastic member is disposed in the elastic member receiving groove, and two ends of the elastic member are respectively connected to the main longitudinal beam and the sensitive mass block, so that the sensitive mass block is suitable for displacement along the extension direction of the main longitudinal beam under external acceleration; The elastic component is a folding beam spring; the folding beam spring is a serpentine folding structure, extending in a serpentine shape along the extension direction of the main longitudinal beam, with one end connected to the side of the main longitudinal beam and the other end connected to the side of the sensitive mass block.

15. The method for preparing the structure of the MEMS acceleration sensor chip according to claim 14, characterized in that: The formed sensitive mass, the folded beam spring and the movable electrode together form a central symmetrical figure, and the symmetry center of the central symmetrical figure coincides with the main anchor point; The fixed electrode units are formed in a plurality and are centrally symmetrically distributed with the main anchor point as the center of symmetry; The extending direction of the main longitudinal beam is defined as the y-axis, and the direction perpendicular to the y-axis and passing through the center of the main anchor point is defined as the x-axis. The sensitive mass, the folded beam spring, the movable electrode, and the fixed electrode unit are symmetrically distributed along the y-axis and symmetrically distributed along the x-axis. The adjacent movable electrodes and the fixed electrodes form a capacitor; The capacitors located on the same side of the x-axis are connected in parallel; The capacitance changes of the capacitors located on both sides of the x-axis are opposite to each other under external acceleration.

16. The method for preparing the structure of a MEMS acceleration sensor chip according to claim 13, wherein: The step of forming fixed electrode units located on both sides of the sensitive mass further includes: A secondary longitudinal beam is also formed at the same time; the secondary longitudinal beam is parallel to the main longitudinal beam and is connected and fixed to the base layer through a secondary anchor point; A secondary auxiliary anchor point is formed on one side of the fixed electrode unit along the extension direction of the secondary longitudinal beam, and the secondary longitudinal beam is also connected and fixed to the base layer through the secondary auxiliary anchor point; the secondary auxiliary anchor point is an axisymmetric structure with the central axis of the secondary longitudinal beam as the axis of symmetry; the connection structure between the secondary auxiliary anchor point and the secondary longitudinal beam has a stiffness in the sensitive direction of the sensitive mass block unit that is less than the stiffness in the non-sensitive direction.

17. The method for preparing the structure of a MEMS acceleration sensor chip according to claim 16, characterized in that: The step of forming fixed electrode units located on both sides of the sensitive mass further includes: A secondary beam decoupling beam is also formed simultaneously to connect the secondary auxiliary anchor point and the secondary longitudinal beam; The width of the secondary auxiliary anchor point is greater than the width of the secondary longitudinal beam; the main body of the secondary auxiliary anchor point is perpendicular to the extension direction of the secondary longitudinal beam; both ends of the main body of the secondary auxiliary anchor point extend a portion of the length of the connecting portion along the extension direction of the secondary longitudinal beam, and the connecting portion is connected to the end of the main longitudinal beam through the secondary beam decoupling beam; the main body of the secondary auxiliary anchor point is connected and fixed to the base layer, and the connecting portion of the secondary auxiliary anchor point and the secondary beam decoupling beam are suspended above the base layer; The auxiliary beam decoupling beam is suitable for deforming along the extension direction of the auxiliary longitudinal beam, so that the distance between the position where the auxiliary beam decoupling beam connects the auxiliary longitudinal beam and the main body of the secondary auxiliary anchor point changes in a sensitive direction when subjected to thermal stress.

18. The method for preparing the structure of a MEMS acceleration sensor chip according to claim 17, wherein: There are multiple fixed electrode units, which are symmetrically distributed with the main anchor point as the center of symmetry; wherein the secondary anchor points of each fixed electrode unit are symmetrically distributed with the main anchor point as the center of symmetry, and at the same time, the secondary auxiliary anchor points of each fixed electrode unit are also symmetrically distributed with the main anchor point as the center of symmetry.

19. The method for preparing the structure of a MEMS acceleration sensor chip according to claim 12, wherein: The step of corroding the functional layer through the sensitive structural layer includes: forming a release hole mask on the side of the sensitive structure layer facing away from the base layer; Using the release hole mask as a mask, etching a process release hole in the sensitive structure layer, wherein the process release hole exposes the initial functional layer at a corresponding position; The holes are released by the process, and the initial functional layer is corroded to form a hollow area in the initial functional layer; the projection of the hollow area on the sensitive structure layer at least covers the sensitive structure unit and the fixed electrode unit; The release hole mask is removed.

20. The method for preparing the structure of a MEMS acceleration sensor chip according to claim 19, characterized in that: The minimum line width of the process release hole is greater than 3μm; The long side of the process release hole is 2-3 times larger than the short side.

21. The method for preparing the structure of a MEMS acceleration sensor chip according to claim 19, wherein: Before the steps of forming the sensitive mass unit and simultaneously forming the fixed electrode unit, the method further includes: A patterned conductive dielectric layer and a first bonding dielectric layer are formed on the side of the initial sensitive structure layer facing away from the base layer; the conductive dielectric layer at least covers the positions where the sensitive mass unit and the fixed electrode unit are to be formed; and the first bonding dielectric layer covers the position corresponding to the edge area. The steps of forming the sensitive mass unit and the fixed electrode unit at the same time further include: removing together the conductive medium layer corresponding to the portion removed when forming the sensitive mass unit, and removing together the conductive medium layer corresponding to the portion removed when forming the fixed electrode unit; When forming the process release hole, the conductive medium layer at the position corresponding to the process release hole is removed together.

22. The method for preparing the structure of a MEMS acceleration sensor chip according to claim 21, characterized in that: The following steps are also included: Forming the upper cover, including: providing a cover plate substrate; Etching the cover plate substrate to form a cover plate and a frame protruding from a surface of one side of the cover plate; the frame and the cover plate together enclose a cover plate movable space; The process of forming the sensitive structural layer further includes: forming a bonding outer frame, wherein the bonding outer frame surrounds and defines a main body activity space, and the sensitive mass block unit and the fixed electrode unit are arranged in the main body activity space; The frame is suitable for connecting with the bonding outer frame, and the activity space corresponds to the main body activity space, and the sensitive mass block unit and the fixed electrode unit are jointly accommodated.

23. The method for preparing the structure of the MEMS acceleration sensor chip according to claim 22, characterized in that: forming a blind hole at a preset position of the cover plate, and filling the blind hole with electroplated metal to form a conductive electrode; The preset positions correspond to the positions of the main anchor point and the secondary anchor point in the sensor base; After forming the conductive electrode, forming a patterned second bonding dielectric layer on the side of the cover plate that exposes the conductive electrode; The second bonding medium layer is connected to the conductive electrode.

24. The method for preparing the structure of a MEMS acceleration sensor chip according to claim 23, wherein: Bonding the sensor base and the upper cover through the first bonding medium layer and the second bonding medium layer; After bonding, the conductive electrodes correspond to the main anchor point and the secondary anchor point, and are connected to the conductive dielectric layer through the second bonding dielectric layer; The frame of the upper cover and the bonding outer frame of the sensor base are bonded together through the first bonding medium layer and the second bonding medium layer; the activity space corresponds to the main body activity space, and together with the hollow space of the functional layer, accommodates the sensitive mass block unit and the fixed electrode unit.

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