Inertial sensor with self-calibration function and preparation method thereof
By integrating a miniature vacuum gauge into the inertial sensor package cavity for in-situ measurement and self-calibration, the challenge of vacuum calibration in the wafer-level manufacturing process is solved, thereby improving sensor performance and reducing costs.
Patent Information
- Application Number
- CN202511150158.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-15
- Publication Date
- 2025-11-21
AI Technical Summary
Existing technologies cannot effectively achieve vacuum calibration of MEMS inertial sensors in wafer-level manufacturing processes, resulting in affected sensor performance and high costs.
A miniature vacuum gauge is integrated into the wafer-level bonded packaging cavity of the inertial sensor. The vacuum level is measured in situ and self-calibrated by a thermal or resonant vacuum gauge, thereby realizing the calibration and compensation of the sensor.
This improves the stability and reliability of the sensor, reduces manufacturing costs, and allows it to adapt to dynamic environmental changes.
Smart Images
Figure CN120991907A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of semiconductor, and particularly relates to an inertial sensor with a self-calibration function and a preparation method thereof. BACKGROUND
[0002] The performance of a MEMS inertial sensor (such as a MEMS gyroscope) is highly dependent on the dynamic characteristics of the internal micro-mechanical structure, and vacuum packaging is the key to ensuring high precision and low noise. Since the motion damping of the micro-mechanical structure is significantly affected by air pressure, changes in vacuum degree will change the quality factor (Q value) of the sensor, thereby affecting the zero bias stability and the accuracy of the scale factor, in addition, air pressure fluctuations will also cause changes in the motion characteristics of the resonant mass, introducing additional errors, and changes in gas thermal conductivity may cause temperature gradient drift of the structure, further coupling thermal mechanical errors.
[0003] Currently, high-performance MEMS inertial sensors mostly use device-level vacuum packaging, which relies on processes such as dicing, interconnection, welding, and getter to achieve, but this method is high in cost and susceptible to contamination. Wafer-level vacuum packaging technology has been rapidly developed and applied due to its many advantages, such as: 1) avoiding sticking and particle contamination during chip cutting, improving chip yield; 2) batch production, reducing chip cost, and improving device consistency; 3) device miniaturization and integration, expanding the application of the device, but its vacuum degree calibration faces challenges. The current calibration method for the influence of vacuum degree on MEMS inertial sensors mainly uses Q value calibration and vacuum degree mapping method, which relies on high-precision calibration equipment to calibrate the correlation between Q value and vacuum degree before device tube packaging, and measures the Q value after tube packaging, thereby mapping and deducing the vacuum degree, but this method cannot adapt to the wafer-level manufacturing process.
[0004] Based on the above problems, there is an urgent need for an inertial sensor with a self-calibration function and a preparation method thereof to realize the calibration and compensation of wafer-level MEMS inertial sensors, improve sensor performance, and reduce manufacturing cost. SUMMARY
[0005] The application is to solve all or part of the problems of the prior art, and provides an inertial sensor with a self-calibration function and a preparation method thereof, which integrates a miniature vacuum gauge in the packaging cavity of the inertial sensor wafer-level bonding, measures the vacuum degree in the packaging cavity in situ, and realizes the calibration and compensation of the wafer-level inertial sensor.
[0006] The application provides an inertial sensor with self-calibration function, comprising a device wafer and an upper cover wafer which are bonded, the device wafer comprises a device layer, a buried oxygen layer and a substrate layer, a cavity structure is formed in the upper cover wafer, and a vacuum chamber is formed in the device wafer and the upper cover wafer; an inertial sensor and a vacuum gauge are formed in the device layer, and the inertial sensor and the vacuum gauge are both located in the vacuum chamber; the device layer comprises an electrode layer and a structure layer, the electrode layer is located above the structure layer, an inertial device of the inertial sensor and a functional part of the vacuum gauge are formed in the structure layer, and electrodes of the inertial sensor and the vacuum gauge are formed in the electrode layer. In-situ monitoring and self-calibration of vacuum degree are realized, the use stability and reliability of the sensor are improved, and the manufacturing cost is reduced.
[0007] The vacuum gauge adopts a thermal vacuum gauge or a resonant vacuum gauge, which is compatible with the inertial sensor manufacturing process and is convenient for synchronous manufacturing with the inertial sensor in wafer-level packaging.
[0008] The thermal vacuum gauge comprises a release groove and a thermal vacuum gauge electrode, the release groove is formed on the surface of the structure layer, and the thermal vacuum gauge electrode is located above the release groove. The sensitivity and response speed of the thermal vacuum gauge test are ensured.
[0009] The resonant vacuum gauge comprises a comb structure and a resonant vacuum gauge electrode, the buried oxygen layer under the comb structure is selectively released to form a second suspended cavity, and the comb structure can move freely. The detection sensitivity is ensured, the vacuum degree monitoring with low power consumption and high stability is realized, and the resonant vacuum gauge is completely compatible with the inertial sensor process.
[0010] Further comprising an external electrode, the external electrode is arranged outside the vacuum chamber for external signal connection, and the sensor signal is led out.
[0011] The application further provides a preparation method of the inertial sensor with self-calibration function, which is used for preparing the above inertial sensor and comprises the following steps: providing an SOI wafer, the SOI wafer comprises a top layer of silicon, a buried oxygen layer and a substrate layer; forming a release groove in the top layer of silicon, the release groove is filled with an insulating medium; forming an electrode layer on the surface of the top layer of silicon, the electrode layer comprises a passivation layer and an internal electrode covered in the passivation layer; etching the electrode layer and the top layer of silicon in sequence to form an inertial device; releasing the insulating medium and the buried oxygen layer under the inertial device to form an inertial sensor and a vacuum gauge, and obtaining a device wafer; providing a second wafer, forming a cavity structure in the second wafer to obtain an upper cover wafer; bonding the device wafer and the upper cover wafer to form a vacuum chamber in the device wafer and the upper cover wafer, and locating the inertial sensor and the vacuum gauge in the vacuum chamber. The inertial sensor and the thermal vacuum gauge are integrated with high precision, and are suitable for wafer-level manufacturing process.
[0012] The insulating medium material is silicon oxide, which is convenient to release simultaneously with the buried oxygen layer.
[0013] The VHF process or the wet etching process is used to release the insulating medium and the buried oxygen layer, so that the insulating medium and part of the buried oxygen layer are removed simultaneously, with high selectivity, so as to avoid damage to other structures.
[0014] The application further provides another preparation method of the inertial sensor with the self-calibration function, which is used to prepare the inertial sensor and comprises the following steps: providing an SOI wafer, wherein the SOI wafer comprises a top layer of silicon, a buried oxygen layer and a substrate layer; forming an electrode layer on the surface of the top layer of silicon, wherein the electrode layer comprises a passivation layer and an inner electrode covered in the passivation layer; etching the electrode layer and the top layer of silicon in sequence to form an inertial device and a comb structure; releasing the buried oxygen layer under the inertial device and the comb structure to form a suspended cavity, thereby forming an inertial sensor and a vacuum gauge, and obtaining a device wafer; providing a second wafer, forming a cavity structure in the second wafer, and obtaining an upper cover wafer; bonding the device wafer and the upper cover wafer to form a vacuum cavity in the device wafer and the upper cover wafer, so that the inertial sensor and the vacuum gauge are both located in the vacuum cavity. The inertial sensor is highly compatible with the preparation process of the resonant sensor, and the preparation process is simplified.
[0015] The VHF process or the wet etching process is used to release the buried oxygen layer, with high selectivity, so as to avoid damage to other structures.
[0016] Compared with the prior art, the inertial sensor with the self-calibration function has the following beneficial effects: the micro vacuum gauge is integrated in the packaging cavity of the inertial sensor wafer, the vacuum degree in the cavity can be directly measured in situ in advance or during use, and the calibration parameters can be dynamically adjusted, so that the wafer-level inertial sensor is calibrated and compensated, the dynamic environmental adaptability is improved, and the manufacturing cost is reduced. BRIEF DESCRIPTION OF DRAWINGS
[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.
[0018] Figure 1 It is a structure schematic diagram of the inertial sensor with the self-calibration function of embodiment 1.
[0019] Figure 2 It is a process flow chart of the preparation method of the inertial sensor with the self-calibration function of embodiment 2.
[0020] Figure 3 Structure diagram of the inertial sensor with self-calibration function of Example 3.
[0021] Figure 4 Process flow chart of the preparation method of the inertial sensor with self-calibration function of Example 4. DETAILED DESCRIPTION
[0022] The following description and drawings are illustrative of specific embodiments of the present application and are not intended to limit the generality of the application. Other embodiments can include structural, logical, electrical, process, and other changes. The examples are representative of possible variations. Individual components and functions are optional unless explicitly required, and the order of operations can be varied. Portions and features of some embodiments can be included in or substituted for portions and features of other embodiments.
[0023] Example 1 This embodiment provides an inertial sensor with self-calibration function, as shown in Figure 1 which comprises a device wafer and an upper cover wafer, a cavity structure is formed in the upper cover wafer, and the device wafer and the upper cover wafer are connected by a bonding ring 6 to form a vacuum chamber; the device wafer comprises, from top to bottom, a device layer 5, a buried oxygen layer 2, and a substrate layer 1; the device layer 5 in the vacuum chamber is provided with an inertial sensor and a thermal vacuum gauge adjacent to each other.
[0024] The device layer 5 comprises a structure layer 51 and an electrode layer 52 on the structure layer 51. The inertial sensor comprises an inertial device 71 formed in the structure layer 51 and an inertial device electrode 72 formed in the electrode layer 52. The buried oxygen layer 2 under the inertial device 71 selectively releases a first suspended cavity, which, in combination with the above-mentioned vacuum chamber, allows the inertial device 71 to move freely; the thermal vacuum gauge comprises a functional part formed in the structure layer 51, the functional part comprises a release groove 8a on the surface of the structure layer 51, and a thermal vacuum gauge electrode 8b is formed above the release groove 8a. The inertial device electrode 72 and the thermal vacuum gauge electrode 8b are covered in a silicon nitride passivation layer of the electrode layer 52; further comprising an external electrode 9 arranged outside the vacuum chamber, a window is formed in the silicon nitride passivation layer above the external electrode 9 to expose the external electrode 9 for electrical connection.
[0025] Example 2 This embodiment provides a preparation method of an inertial sensor with self-calibration function, which is used to prepare the sensor described in Example 1, as shown in Figure 2 which comprises the following steps: An SOI wafer is provided, which comprises a top layer of silicon 3, a buried oxide layer 2 and a substrate layer 1; a release groove is etched on the top layer of silicon 3, the release groove is filled with an insulating medium 4 and the surface is planarized by chemical mechanical grinding, in the embodiment, the insulating medium 4 is silicon oxide. An electrode layer 52 is formed on the surface of the top layer of silicon 3, the inner electrode in the electrode layer 52 adopts a passivation layer-inner electrode-passivation layer structure, the inner electrode is covered in the passivation layer, wherein the inner electrode comprises an inertial sensor electrode and a vacuum gauge electrode, the above structure can be formed by a metal patterning method: a silicon nitride passivation layer is deposited on the surface of the top layer of silicon, a metal layer is deposited on the surface of the silicon nitride passivation layer, and the metal is patterned to form the inner electrode and the outer electrode, then a silicon nitride passivation layer is deposited, and then the surface is polished by chemical mechanical grinding (CMP), so that the surface of the passivation layer is flat, thereby providing a flat surface for subsequent bonding process; or a groove filling method can also be used to form: a silicon nitride passivation layer is deposited and patterned to form an electrode groove; an electrode metal is deposited and CMP is performed, so that the inner electrode and the outer electrode are formed in the electrode groove, and a silicon nitride is continuously deposited to cover the inner electrode and the outer electrode 9, in the embodiment, the inner electrode is an inertial device electrode 72 and a thermal vacuum gauge electrode 8b. Then, the outer electrode 9 is windowed in the outer electrode region to be partially covered in the passivation layer, which is used for connecting with an external signal, thereby forming the electrode layer 52; a bonding material is deposited on the electrode layer 52, and a first bonding ring 61 is formed on the electrode layer by exposure, development, etching and other steps, in the embodiment, the bonding material can be polycrystalline silicon or Ge material.
[0026] The electrode layer 52 and the top layer of silicon 3 are etched to form an inertial device 71; specifically, the silicon nitride passivation layer is etched by reactive ion etching to expose part of the top layer of silicon 3 and part of the insulating medium 4, and then the exposed top layer of silicon 3 is etched by deep reactive ion etching to form the inertial device 71; the insulating medium 4 and part of the buried oxide layer 2 under the inertial device 71 are released, which can be released by VHF process or released by wet etching with a mixed solution of ammonium fluoride and hydrofluoric acid (BOE) as an etching solution, thereby forming a first suspended cavity and obtaining a structure layer 51 containing a suspended inertial device 71; in the etching process, the first bonding ring 61 is protected by photoresist, thereby obtaining a device wafer.
[0027] A second wafer is provided, in the embodiment, the second wafer is a silicon wafer, after a bonding material is deposited on the surface of the silicon wafer and a second bonding ring 62 is formed correspondingly, a cavity structure is etched, in the etching process, the second bonding ring 62 is protected by photoresist, thereby obtaining a cover wafer; the bonding ring 6 is formed by corresponding bonding of the first bonding ring 61 and the second bonding ring 62, thereby encapsulating the device wafer and the cover wafer.
[0028] Embodiment 3 The embodiment provides an inertial sensor with a self-calibration function, and different from the embodiment 1, in the embodiment, a resonant vacuum gauge is used. As shown in Figure 3 Fig. 1, a device wafer and an upper cover wafer are included, a cavity structure is formed in the upper cover wafer, the device wafer and the upper cover wafer are connected by a bonding ring 6 to form a vacuum chamber, the device wafer includes, from top to bottom, a device layer 5, a buried oxygen layer 2 and a substrate layer 1, the inertial sensor and the resonant vacuum gauge are formed in the device layer 5, and the inertial sensor and the resonant vacuum gauge are located in the vacuum chamber.
[0029] The device layer 5 includes a structure layer 51 and an electrode layer 52 on the structure layer 51. The inertial sensor includes an inertial device 71 formed in the structure layer 51 and an inertial device electrode 72 formed in the electrode layer 52, and the resonant vacuum gauge includes a functional part formed in the structure layer 51 and a resonant vacuum gauge electrode 8d formed in the electrode layer 52, the functional part includes a comb structure 8c, the buried oxygen layer 2 below the inertial device 51 and the comb structure 8c is selectively released to form a second suspended cavity, and the inertial device 51 and the comb structure 8c can move freely in cooperation with the vacuum chamber. The inertial device electrode 72 and the resonant vacuum gauge electrode 8d are covered in a silicon nitride passivation layer of the electrode layer 52, and an outer electrode 9 arranged outside the vacuum chamber is further included, a window is formed in the silicon nitride passivation layer above the outer electrode 9, so that the outer electrode 9 is exposed to facilitate electrical connection.
[0030] Embodiment 4 The embodiment provides a preparation method of an inertial sensor with a self-calibration function, and is used for preparing the sensor described in the embodiment 3. As shown in Figure 4 Fig. 4, the method includes the following steps. An SOI wafer is provided, which comprises a top layer of silicon 3, a buried oxide layer 2 and a substrate layer 1; an electrode layer 52 is formed on the surface of the top layer of silicon 3, and the inner electrode in the electrode layer 52 adopts a passivation layer-inner electrode-passivation layer structure, and the inner electrode is covered inside the passivation layer, wherein the inner electrode comprises an inertial sensor electrode and a vacuum gauge electrode, and the above structure can be formed by a metal patterning method: a silicon nitride passivation layer is deposited on the surface of the top layer of silicon, a metal layer is deposited on the surface of the silicon nitride passivation layer, and the metal is patterned to form the inner electrode and the outer electrode, respectively, then a silicon nitride passivation layer is deposited, and then a CMP surface polishing is performed to realize the flatness of the surface of the passivation layer, thereby providing a flat surface for subsequent bonding process; or a groove filling method can be used to form: a silicon nitride passivation layer is deposited and patterned to form an electrode groove; an electrode metal is deposited and CMP is performed to form the inner electrode and the outer electrode in the electrode groove, and silicon nitride is continuously deposited to cover the inner electrode and the outer electrode 9, in this embodiment, the inner electrode is an inertial device electrode 72 and a resonant vacuum gauge electrode 8d. Then, the outer electrode 9 is windowed in the outer electrode region to form the electrode layer 52; a bonding material is deposited on the electrode layer 52, and a first bonding ring 61 is formed on the electrode layer 52 through exposure, development, etching and other steps, and in this embodiment, the bonding material can be polycrystalline silicon or Ge material.
[0031] The electrode layer 52 and the top layer of silicon 3 are etched to obtain the inertial device 71 and the comb structure 8c, specifically, first, the silicon nitride passivation layer is etched by reactive ion etching to expose part of the top layer of silicon 3; then, the exposed top layer of silicon 3 is etched by deep reactive ion etching to form the inertial device 71 and the comb structure 8c; the buried oxide layer under the inertial device 51 and the comb structure 8c is released, which can be released by VHF process or by wet etching with a mixed solution of ammonium fluoride and hydrofluoric acid (BOE) as the etching solution, to form a first suspended cavity and a second suspended cavity, respectively, to obtain a structure layer 51 comprising a suspended inertial device 71 and a suspended comb structure 8c, and in the etching process, the first bonding ring 61 is protected by photoresist covering to obtain a device wafer.
[0032] A second wafer is provided, and in this embodiment, the second wafer adopts a silicon wafer, after a bonding material is deposited on the surface of the silicon wafer and a second bonding ring 62 is formed correspondingly, a cavity structure is etched, and in the etching process, the second bonding ring 62 is protected by photoresist covering to obtain a cover wafer; the bonding ring 6 is formed by corresponding bonding of the first bonding ring 61 and the second bonding ring 62 to encapsulate the device wafer and the cover wafer.
[0033] For MEMS inertial devices, the higher the vacuum degree (the lower the cavity pressure), the smaller the collision damping of gas molecules on the vibrating structure, and the mechanical energy loss is reduced, so that the Q value is improved. Therefore, for gyroscope devices, low pressure (a few hundred Pa millibars to high vacuum) is required to maintain high Q value, to ensure high sensitivity and long decay time. The present application can be compensated by the following working modes: (1) Output signal adaptive adjustment: ① Calibrate the relationship between the MEMS inertial sensor output signal and the vacuum degree, which can be done with the help of an inertial test machine with a vacuum environment; ② Write the collected calibration data into the data processing system of the inertial device; ③ During the use of the sensor, according to the vacuum degree data obtained by the vacuum module, the relationship between the vacuum degree and the output signal calibrated in step ①, the actual output signal is adjusted accordingly to obtain the calibrated inertial sensor data.
[0034] (2) Closed-loop driving parameter adjustment: ① Calibrate the relationship between the MEMS inertial sensor output signal and the vacuum degree, which can be done with the help of an inertial test machine with a vacuum environment; ② Adjust the driving voltage of the inertial device under different vacuum degrees to compensate for the decrease in Q value caused by the change in vacuum degree, so as to restore to the reference state, and record the voltage compensation relationship under different vacuum degrees; ③ During the use of the sensor, according to the vacuum degree data obtained, the voltage compensation relationship under different vacuum degrees calibrated in step ②, when the Q value decreases to cause insufficient amplitude, the PI controller increases the driving voltage output, and enhances the electrostatic driving force to maintain the constant vibration amplitude. For example, by increasing the voltage between the comb electrodes, the Coulomb force is enhanced to overcome the increased damping loss caused by the decrease in vacuum degree.
[0035] It is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application. Any reference signs in the claims should not be regarded as limiting the claims involved.
Claims
1. An inertial sensor with self-calibration function, characterized in that, A device wafer and an upper cover wafer are bonded, the device wafer comprising a device layer, a buried oxide layer and a substrate layer, a cavity structure being formed in the upper cover wafer, a vacuum chamber being formed in the device wafer and the upper cover wafer; An inertial sensor and a vacuum gauge are formed in the device layer, the inertial sensor and the vacuum gauge being located in the vacuum chamber; The device layer comprises an electrode layer and a structure layer, the electrode layer being located above the structure layer, an inertial device of the inertial sensor and a functional part of the vacuum gauge being formed in the structure layer, electrodes of the inertial sensor and electrodes of the vacuum gauge being formed in the electrode layer.
2. The inertial sensor with self-calibration function according to claim 1, characterized in that, The vacuum gauge is a thermal vacuum gauge or a resonant vacuum gauge.
3. The inertial sensor with self-calibration function according to claim 2, characterized in that, The thermal vacuum gauge comprises a release groove formed on the surface of the structure layer and a thermal vacuum gauge electrode located above the release groove.
4. The inertial sensor with self-calibration function according to claim 2, characterized in that, The resonant vacuum gauge comprises a comb structure and a resonant vacuum gauge electrode, the buried oxide layer under the comb structure being selectively released to form a second suspended cavity, the comb structure being freely movable.
5. The inertial sensor with self-calibration function according to claim 1, characterized in that, An external electrode is further provided outside the vacuum chamber for external signal connection.
6. A method of manufacturing an inertial sensor having a self-calibration function, characterized by, The method comprises the following steps: An SOI wafer is provided, the SOI wafer comprising a top silicon layer, a buried oxide layer and a substrate layer; A release groove is formed in the top silicon layer, the release groove being filled with an insulating medium; An electrode layer is formed on the surface of the top silicon layer, the electrode layer comprising a passivation layer and an inner electrode covered in the passivation layer; The electrode layer and the top silicon layer are etched in sequence to form an inertial device; The insulating medium and the buried oxide layer under the inertial device are released to form an inertial sensor and a vacuum gauge, thereby obtaining a device wafer; A second wafer is provided, a cavity structure being formed in the second wafer, thereby obtaining an upper cover wafer; The device wafer and the upper cover wafer are bonded, a vacuum chamber being formed in the device wafer and the upper cover wafer, the inertial sensor and the vacuum gauge being located in the vacuum chamber.
7. The method of claim 6, wherein the method further comprises: The insulating medium is silicon oxide. 8. The method of claim 7, wherein the method further comprises: The release of the insulating medium and the buried oxide layer adopts a VHF process or a wet etching process.
9. A method of manufacturing an inertial sensor having a self-calibration function, characterized by, The method comprises the following steps: An SOI wafer is provided, the SOI wafer comprising a top silicon layer, a buried oxide layer and a substrate layer; An electrode layer is formed on the surface of the top silicon layer, the electrode layer comprising a passivation layer and an inner electrode covered in the passivation layer; The electrode layer and the top silicon layer are etched in sequence to form an inertial device and a comb structure; The buried oxide layer under the inertial device and the comb structure is released to form a suspended cavity, thereby forming an inertial sensor and a vacuum gauge, thereby obtaining a device wafer; A second wafer is provided, a cavity structure being formed in the second wafer, thereby obtaining an upper cover wafer; The device wafer and the upper cover wafer are bonded, a vacuum chamber being formed in the device wafer and the upper cover wafer, the inertial sensor and the vacuum gauge being located in the vacuum chamber.
10. The method of claim 9, wherein the method further comprises: The release of the buried oxide layer adopts a VHF process or a wet etching process.