Method for constructing cavity vacuum degradation model and evaluation method of vacuum-packaged MEMS device considering multiple failure mechanisms

Abstract

The present invention discloses a method for constructing a vacuum degradation model and an evaluation method for the cavity vacuum of a vacuum-packaged MEMS device considering multiple failure mechanisms. The model construction method includes: (1) Vacuum degree characterization: Characterize the vacuum degree of the cavity using the quality factor; (2) Modeling of the vacuum degradation mathematical model: a. Calculate the number of gas molecules released in the cavity to obtain the first vacuum degradation mathematical model caused by outgassing inside the cavity; b. Calculate the number of gas molecules leaking into the cavity from the outside to obtain the second vacuum degradation mathematical model caused by external leakage in the cavity; c. Based on the relationship between the total number of gas molecules in the cavity and the cavity air pressure in the first and second vacuum degradation mathematical models, obtain the vacuum degree degradation model inside the cavity. Based on the constructed vacuum degree degradation model, the present invention also provides a method for reliability evaluation of the vacuum degradation of a vacuum-packaged MEMS device, and can realize the reliability prediction of the vacuum degree degradation of a vacuum-packaged MEMS device.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-electromechanical systems (MEMS), and in particular relates to a method for constructing and evaluating a vacuum degradation model of a vacuum-packaged MEMS device cavity taking into account multiple failure mechanisms. Background Art

[0002] MEMS devices are widely used in military, consumer electronics, industry and medical fields due to their compact size, low weight, low energy consumption and high reliability. With the continuous expansion of MEMS technology and its application fields, the requirements for the performance of MEMS devices are also increasing. For example, the microstructures of devices such as MEMS gyroscopes, resonant accelerometers and pressure sensors usually need to work in a resonant state, and vacuum packaging can significantly improve the performance of these devices.

[0003] For MEMS gyroscopes, vacuum packaging can reduce air damping, improve the quality factor (Q value), and reduce the electrostatic drive voltage, thereby effectively suppressing mechanical thermal noise, reducing voltage and damping coupling, and improving the signal-to-noise ratio and overall performance of the device. Therefore, vacuum packaging is regarded as one of the key technologies to improve the performance of MEMS devices. However, changes in air pressure in the vacuum packaging cavity can affect the performance stability of MEMS devices and may even cause device failure. Maintaining the vacuum degree is essential to ensure the long-term reliable operation of MEMS devices. At present, research on vacuum packaged MEMS devices mainly focuses on the degradation mechanism of vacuum degree reduction caused by the gradual release of gas from internal materials over time. This model is usually based on the premise that the packaging cavity has a low leakage rate and can meet the product performance requirements. However, the existing model does not fully consider the two main vacuum degradation mechanisms: internal outgassing: the internal material of the cavity releases gas over time; external leakage: there is a small leak in the seal of the airtight shell, causing external gas to enter the cavity. Although the amount of external leakage may be small in some cases, the impact of external leakage cannot be ignored during long-term use (such as 15 years or more), because the total amount of gas introduced by external leakage is theoretically unlimited. In addition, in the accelerated life test, the main degradation mechanism in the early stage is internal outgassing, while in the later stage it is mainly external leakage.

[0004] Therefore, how to improve a reliability model so as to more accurately predict the performance degradation trend of vacuum packaged MEMS devices is one of the technical problems to be solved urgently in this field. Summary of the invention

[0005] The main objective of the present invention is to overcome the drawbacks and deficiencies of the prior art, and provide a method for constructing a vacuum degradation model and an evaluation method for the cavity of a vacuum-packaged MEMS device considering multiple failure mechanisms. By comprehensively considering two failure mechanisms, namely internal outgassing and external leakage, a corresponding mathematical model for reliability evaluation is established, providing a more accurate evaluation of the long-term reliability of vacuum-packaged MEMS devices and predicting the change of their vacuum degree.

[0006] To achieve the above objective, the present invention adopts the following technical solutions:

[0007] First, the present invention provides a method for constructing a vacuum degradation model for the cavity of a vacuum-packaged MEMS device considering multiple failure mechanisms, including the following steps:

[0008] Use the quality factor to measure the vacuum degree level in the vacuum cavity, and then determine the first relationship between the internal air pressure and the number of free gas molecules in the vacuum cavity, and the second relationship between the number of free gas molecules in the vacuum cavity and the quality factor.

[0009] Based on the total number of gas molecules and the diffusion coefficient when the internal outgassing of the vacuum cavity is constant, calculate the number of gas molecules released in the vacuum cavity to obtain the first mathematical model of vacuum degradation caused by internal outgassing in the cavity.

[0010] Based on the leakage coefficient, calculate the number of gas molecules leaking into the vacuum cavity from the outside to obtain the second mathematical model of vacuum degradation caused by external leakage in the vacuum cavity.

[0011] Based on the first mathematical model of vacuum degradation and the second mathematical model of vacuum degradation, obtain the total number of gas molecules in the vacuum cavity.

[0012] Based on the first relationship between the total number of gas molecules in the vacuum cavity and the internal air pressure of the cavity, obtain the relationship between the air pressure and the number of gas molecules in the degraded vacuum cavity.

[0013] Based on the relationship between the air pressure and the number of gas molecules in the degraded vacuum cavity, considering that the vacuum degradation caused by internal outgassing in the cavity decays exponentially with time and the vacuum degradation caused by external leakage decays linearly with time, obtain the vacuum degree degradation model inside the cavity of the vacuum-packaged MEMS device.

[0014] As a preferred technical solution, the first relationship and the second relationship are:

[0015] The internal air pressure p of the vacuum cavity is proportional to the fraction N of free gas molecules inside, and the number N of free gas molecules inside the vacuum cavity is inversely proportional to the reciprocal of the quality factor Q.

[0016] As a preferred technical solution, the number of gas molecules N in (t) released in the vacuum cavity is as follows:

[0017]

[0018] Among them, N tot is the total number of gas molecules when internal outgassing is constant, and D T is the diffusion coefficient; the diffusion coefficient is correlated with temperature, and t represents a certain time point.

[0019] As a preferred technical solution, the number of gas molecules N out leaked into the vacuum chamber from the outside is as follows:

[0020] N out (t) = L T ×t

[0021] Among them, L T is the leakage coefficient, and the leakage coefficient is related to temperature T, and t represents a certain time point.

[0022] As a preferred technical solution, the total number of gas molecules N(t) in the vacuum chamber is as follows:

[0023]

[0024] Among them, N 0 is the initial number of gas molecules inside the cavity, N tot is the total number of gas molecules when internal outgassing is constant, D T is the diffusion coefficient, the diffusion coefficient is related to temperature T, L T is the leakage coefficient, the leakage coefficient is related to temperature T, and t represents a certain time point.

[0025] As a preferred technical solution, the relationship between the air pressure and the number of gas molecules in the vacuum chamber after degradation is as follows:

[0026]

[0027] Among them, p(t) represents the air pressure in the vacuum chamber, Q(t) represents the quality factor, N tot is the total number of gas molecules when internal outgassing is constant, D T is the diffusion coefficient, the diffusion coefficient is related to temperature T, L T is the leakage coefficient, the leakage coefficient is related to temperature T, t represents a certain time point, Q 0 represents the quality factor at room temperature, and A is an empirical constant.

[0028] As a preferred technical solution, the vacuum degree degradation model inside the cavity of the vacuum-packaged MEMS device is as follows:

[0029] p(t) ∝ 1 / Q t ∝ N(t) = a + b × exp(c t) + d t

[0030] a = 1 / Q 0 +A×N tot

[0031] b = -A×N tot

[0032] c = D T

[0033] d = L T

[0034] Wherein, p(t) is the internal air pressure of the cavity, Q t is the number of gas molecules in the cavity, N(t) is the quality factor, and N tot is the total number of gas molecules when the internal outgassing is constant, and D T is the diffusion coefficient, which is related to the temperature T, and L T is the leakage coefficient, which is related to the temperature T, and Q 0 represents the quality factor at room temperature, A is an empirical constant, t represents a certain time point, a represents the total number of internal cavity gases in the sample caused by initial gas and internal release, and b represents the total number of released gases in the sample, which determines the amplitude of vacuum degradation caused by internal outgassing of the sample.

[0035] As a preferred technical solution, it further includes the steps of verifying the vacuum degree degradation model of the internal cavity of the vacuum-packaged MEMS device, specifically:

[0036] In a high-temperature environment, both internal outgassing and external leakage in the vacuum cavity will accelerate. Then, the vacuum degree degradation model of the internal cavity is specifically:

[0037]

[0038] Wherein, t m is the time point when the main failure mechanism of vacuum degradation of the vacuum-packaged MEMS device changes from internal outgassing to external leakage.

[0039] In a second aspect, the present invention provides a system for constructing a vacuum degradation model of a cavity of a vacuum-packaged MEMS device considering multiple failure mechanisms, including a vacuum degree characterization module, a first vacuum degradation mathematical model construction module, a second vacuum degradation mathematical model construction module, a total gas molecule number calculation module in the vacuum cavity, a determination module for the relationship between the degraded air pressure and gas molecules, and a degradation model determination module;

[0040] The vacuum degree characterization module is used to measure the vacuum degree level in the vacuum cavity by using the quality factor, and further determine a first relationship between the internal air pressure and the number of free gas molecules in the vacuum cavity, and a second relationship between the number of free gas molecules and the quality factor in the vacuum cavity;

[0041] The first vacuum degradation mathematical model construction module is configured to calculate the number of gas molecules released in the vacuum chamber based on the total number of gas molecules and the diffusion coefficient when the outgassing in the vacuum chamber is constant, so as to obtain the first vacuum degradation mathematical model caused by the outgassing inside the chamber;

[0042] The second vacuum degradation mathematical model construction module is configured to calculate the number of gas molecules leaking into the vacuum chamber from the outside based on the leakage coefficient, so as to obtain the second vacuum degradation mathematical model caused by the external leakage in the vacuum chamber;

[0043] The total gas molecule number calculation module in the vacuum chamber is configured to obtain the total number of gas molecules in the vacuum chamber based on the first vacuum degradation mathematical model and the second vacuum degradation mathematical model;

[0044] The relationship determination module between the degraded air pressure and gas molecules is configured to obtain the relationship between the air pressure and the number of gas molecules in the degraded vacuum chamber based on the total number of gas molecules in the vacuum chamber and the first relational expression;

[0045] The degradation model determination module is configured to obtain the vacuum degree degradation model inside the cavity of the vacuum-packaged MEMS device based on the relationship between the air pressure and the number of gas molecules in the degraded vacuum chamber, considering that the vacuum degradation caused by the outgassing inside the chamber decays exponentially with time and the vacuum degradation caused by the external leakage decays linearly with time.

[0046] Thirdly, the present invention provides a method for evaluating the vacuum degradation model of the cavity of a vacuum-packaged MEMS device, including the following steps:

[0047] Build a test system and test the quality factor Q of the vacuum-packaged MEMS device at room temperature 0 value;

[0048] With the sample powered off, place the sample under the use conditions, storage conditions or reliability acceleration conditions;

[0049] After a certain time t 1 passes, based on the built test system, test the Q(t 1 ) value of the sample at room temperature;

[0050] Continue to place the sample in the above environment. After a certain time t 2 passes, based on the built test system, test the Q(t 2 ) value of the sample at room temperature;

[0051] Repeat the step of testing the Q value of the sample at room temperature until the test ends, and obtain the quality factor Q at a series of time points;

[0052] Process the acquired data, fit the quality factor Q values at different time points, and obtain various coefficients; the fitting of the quality factor Q values at different time points is processed by using the vacuum degree degradation model obtained by the method for constructing a vacuum encapsulation MEMS device cavity vacuum degradation model considering multiple failure mechanisms according to any one of claims 1-8;

[0053] Conduct analysis and evaluation on the obtained various coefficients; the analysis and evaluation include: obtaining whether the main failure source is internal leakage or internal outgassing through the various coefficients; obtaining the degradation mode at different times and the vacuum degree in the cavity through the various coefficients;

[0054] Based on the obtained cavity internal vacuum degree degradation model and its various coefficients, conduct reliability prediction on the vacuum degree degradation of the vacuum encapsulation MEMS device.

[0055] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0056] (1) By considering two failure mechanisms of internal outgassing and external leakage in the cavity, the present invention establishes a mathematical model for the vacuum degree degradation of the cavity of the vacuum encapsulation MEMS device, making up for the defect that the existing model only considers a single mechanism of internal outgassing in the cavity, and can more accurately evaluate the vacuum degree degradation of the vacuum encapsulation MEMS device.

[0057] (2) Based on the constructed mathematical model, the present invention provides a process and method for reliability evaluation of the vacuum degradation of the vacuum encapsulation MEMS device, and can realize the reliability prediction of the vacuum degree degradation of the vacuum encapsulation MEMS device.

[0058] (3) The present invention determines the cavity internal vacuum degree degradation model and model parameters according to the degradation data of the Q value of the vacuum encapsulation MEMS device, and obtains the time trend of the quality factor degradation of the vacuum encapsulation MEMS device according to the model. Thus, it provides an important theoretical basis and reference basis for the reliability design, reliability identification and reliability life prediction of the vacuum encapsulation MEMS device, and helps to develop highly reliable vacuum encapsulation MEMS devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0060] Figure 1 It is a flowchart of the method for constructing a vacuum encapsulation MEMS device cavity vacuum degradation model considering multiple failure mechanisms according to an embodiment of the present invention;

[0061] Figure 2 Schematic diagram of the method for evaluating the vacuum degradation model of the cavity of a vacuum-packaged MEMS device according to an embodiment of the present invention;

[0062] Figure 3 Sample data curve in a specific embodiment of the present invention;

[0063] Figure 4 Structural diagram of the system for constructing a vacuum degradation model of the cavity of a vacuum-packaged MEMS device considering multiple failure mechanisms according to an embodiment of the present invention. Detailed implementation manners

[0064] In order to enable those skilled in the art of the present technology to better understand the solutions of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part 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 efforts fall within the protection scope of the present application.

[0065] Referring to "embodiment" in the present application means that the specific features, structures or characteristics described in combination with the embodiment can be included in at least one embodiment of the present application. The phrase appears in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described in the present application can be combined with other embodiments.

[0066] MEMS refers to a Micro-Electro-Mechanical System, a micro-system integrating micro-mechanical structures, sensors, actuators, and electronic control units. These systems usually have very small sizes and can operate on scales from microns to millimeters.

[0067] Please refer to Figure 1 , this embodiment provides a method for a vacuum degradation model of the cavity of a vacuum-packaged MEMS device considering multiple failure mechanisms, including the following steps:

[0068] S11. Vacuum degree characterization method;

[0069] To conduct a reliability assessment of the vacuum degradation of vacuum-packaged MEMS devices, it is necessary to accurately monitor the vacuum degree within their vacuum cavities. Since the vacuum cavities of MEMS devices are extremely tiny, it is difficult for existing detection equipment to perform non-destructive detection on them. Additionally, vacuum-packaged MEMS devices usually contain movable resonant structures, and their motion characteristics are directly affected by the vacuum degree of the surrounding environment. Therefore, considering these characteristics of MEMS devices, we choose the Q value of vacuum-packaged MEMS devices as an indicator to characterize their internal vacuum degree.

[0070] Specifically, the quality factor of the MEMS resonant structure is inversely proportional to the damping, and the damping is directly proportional to the internal air pressure of the cavity. The relationships among the internal air pressure of the cavity of the vacuum-packaged MEMS device, the number of gas molecules in the cavity, and the quality factor are as follows: The internal air pressure p of the sealed cavity is directly proportional to the fraction N of free gas molecules inside and inversely proportional to the reciprocal of the quality factor Q.

[0071] p t∝N(t∝1 / Q t(1)

[0072] S12. Construct a model for the degradation of the internal vacuum degree of the cavity;

[0073] The total number of gas molecules N(t) in the cavity of the vacuum-packaged MEMS device is as follows:

[0074] N(t)=N 0 +N in (t)+N out (t(2)

[0075] Among them, N 0 is the initial number of gas molecules inside the cavity, N in (t) is the number of gas molecules released inside the cavity, and N out (t) is the number of gas molecules leaking from outside the cavity.

[0076] a. The first mathematical model of vacuum degradation caused by outgassing inside the cavity. The first mathematical model of vacuum degradation is obtained by calculating the number of gas molecules released in the vacuum cavity based on the total number of gas molecules and the diffusion coefficient when the outgassing inside the vacuum cavity is constant;

[0077] The number of gas molecules N in (t) released in the cavity of the vacuum-packaged MEMS device is as follows:

[0078]

[0079] Among them, N tot is the total number of gas molecules when the outgassing inside is constant, and D T is the diffusion coefficient (related to temperature).

[0080] b. Mathematical model of the second vacuum degradation caused by external leakage in the cavity; the second vacuum degradation mathematical model is obtained by calculating the number of gas molecules leaking into the vacuum cavity from the outside based on the leakage coefficient;

[0081] The number of gas molecules N out (t) leaking into the vacuum encapsulated MEMS device cavity from the outside is as follows:

[0082] N out (t) = L T ×t(4)

[0083] where L T is the leakage coefficient, and the leakage coefficient is related to the temperature T.

[0084] Taking into account both the internal outgassing and external leakage failure mechanisms, based on the first vacuum degradation mathematical model and the second vacuum degradation mathematical model, the total number of gas molecules in the vacuum cavity is obtained. That is, substituting equations (3) and (4) into equation (2), the total number of gas molecules N(t) in the vacuum encapsulated MEMS device cavity is as follows:

[0085]

[0086] Based on the total number of gas molecules in the vacuum cavity and the first relationship, the relationship between the degraded vacuum cavity pressure and the number of gas molecules is obtained. That is, based on the relationship between the cavity pressure and the number of gas molecules in equation (1), it can be obtained:

[0087]

[0088] It can be seen from equation (6) that considering the vacuum degradation caused by internal outgassing in the cavity decays exponentially with time; considering the vacuum degradation caused by external leakage decays linearly with time.

[0089] Furthermore, the internal vacuum degree degradation model of the vacuum encapsulated MEMS device cavity is obtained as:

[0090] p(t) ∝ 1 / Q t ∝ N(t) = a + b×exp(c t) + d t (7)

[0091] In the formula, a, b, c, and d are empirical constants, a = 1 / Q 0 + A×N tot 、b = -A×N tot 、c = D T 、d = L T , and the experimental data can be fitted based on the above formula to obtain each coefficient.

[0092] The physical meanings of the parameters in equation (7) are as follows:

[0093] Parameter a characterizes the total number of internal cavity gases caused by initial gas and internal release within the sample;

[0094] Parameter b characterizes the total number of gases released within the sample, determining the amplitude of vacuum degradation caused by internal outgassing of the sample;

[0095] Parameter c characterizes the rate of outgassing degradation within the sample, and this parameter is related to temperature;

[0096] Parameter d characterizes the rate of external leakage of the sample, and this parameter is related to temperature;

[0097] 1 / (a + b) is the initial value of the Q value that can be obtained for the sample.

[0098] Optionally, during the high-temperature and other environmental stress acceleration tests on vacuum-packaged MEMS devices, both internal outgassing and external leakage will accelerate. However, in the initial stage of the test, internal outgassing dominates. After a period of time, when most of the gases inside the cavity have been released, external leakage dominates in the middle and late stages of the test. Therefore, for the high-temperature acceleration and other reliability tests of vacuum-packaged MEMS devices, Equation (6) can be changed to

[0099]

[0100] where tm is the time point at which the main failure mechanism of vacuum degradation of the vacuum-packaged MEMS device changes from internal outgassing to external leakage.

[0101] Correspondingly, Equation (7) becomes:

[0102]

[0103] Please refer to Figure 2 , this embodiment provides a method for evaluating the cavity vacuum degradation model of a vacuum-packaged MEMS device, including the following steps:

[0104] S21. Before the test, through the built test system, measure the quality factor Q 0 value of the vacuum-packaged MEMS device at room temperature;

[0105] S22. With the sample in a non-powered state, place the sample under operating conditions or storage conditions or reliability acceleration conditions;

[0106] S23. After a certain time t 1 , based on the built test system, measure the Q(t 1 ) value of the sample at room temperature;

[0107] S24. Continue to place the sample in the above environment. After a certain time t 2 , based on the built test system, measure the Q(t of the sample at room temperature2 ) value;

[0108] S25. Repeat steps S23 and S24 until the end of the test to obtain a series of Q values Q0, Q(t1), Q(t2), Q(t3), Q(t4), Q(t5), Q(t6),... of the samples at time points t = 0, t1, t2, t3, t4, t5, t6,...; 1 , t 2 , t 3 , t 4 , t 5 , …… time points; 0 , Q(t 1 ), Q(t 2 ), Q(t 3 ), Q(t 4 ), Q(t 5 ),...;

[0109] S26. Process the obtained data. Fit the measured Q values of the quality factor at different time points according to the formula 1 / Qt = a + b×exp(ct) + dt to obtain each coefficient;

[0110] S27. Conduct analysis and evaluation on each obtained coefficient;

[0111] S28. Based on the obtained model and parameters, conduct reliability prediction on the degradation of the vacuum degree of the vacuum-packaged MEMS device.

[0112] In a more specific embodiment, a further description is made on the method for modeling and analyzing the degradation of the vacuum-packaged MEMS device:

[0113] S31. Design a device-level vacuum-packaged MEMS gyroscope;

[0114] S32. Before the test, through the built Q value test system of the quality factor, test the Q value of the driving axis of the sample at t = 0h at room temperature; 0 value;

[0115] S33. Conduct a high-temperature test on the sample: heat the incubator to 85°C, and after the temperature reaches the specified temperature, put the sample into the incubator;

[0116] S34. Conduct high-temperature baking on the sample. Take out the sample from the incubator after 16.5h, 66.75h, 189.25h, 248.75h, and 752.75h respectively;

[0117] S35. After placing it at room temperature for 2 hours, test and record the Q value of the driving axis of the sample, as shown in Table 1;

[0118] S36. As shown in the sample data curve, fit the measured data according to formula (9) to obtain each coefficient. Figure 3 shown, fit the measured data according to formula (9) to obtain each coefficient.

[0119] Table 1

[0120]

[0121]

[0122] S36. The sample data curve is as Figure 3 shown. According to formula (9), the measured data is fitted to obtain various coefficients.

[0123] Table 2

[0124] Model parameters Fitted value (internal outgassing) Fitted value (external leakage) a 2.381e-4 2.382e-4 b -1.675e-4 / c -6.053e-2 / d / 6.175e-8

[0125] As shown in Table 2, the fitting values of the vacuum degradation model parameters of the vacuum-packaged MEMS gyroscope at a high temperature of 85°C can be obtained. The model of the internal air pressure of the vacuum-packaged MEMS gyroscope at a high temperature of 85°C is as follows:

[0126]

[0127] According to the above model, the quality factor of the sample at different time points can be calculated, and the degradation of the internal vacuum degree of the sample cavity can be predicted.

[0128] It should be noted that for the foregoing method embodiments, for the sake of simplicity of description, they are all expressed as a series of action combinations. However, those skilled in the art should know that the present invention is not limited by the described action sequence, because according to the present invention, certain steps can be performed in other sequences or simultaneously.

[0129] Based on the same idea as the method for constructing a vacuum degradation model of the cavity of a vacuum-packaged MEMS device considering multiple failure mechanisms in the above embodiments, the present invention also provides a system for constructing a vacuum degradation model of the cavity of a vacuum-packaged MEMS device considering multiple failure mechanisms. This system can be used to execute the method for constructing a vacuum degradation model of the cavity of a vacuum-packaged MEMS device considering multiple failure mechanisms. For the sake of convenience of description, in the structural schematic diagram of the embodiment of the system for constructing a vacuum degradation model of the cavity of a vacuum-packaged MEMS device considering multiple failure mechanisms, only the part related to the embodiment of the present invention is shown. Those skilled in the art can understand that the illustrated structure does not constitute a limitation on the device, and it may include more or fewer components than those illustrated, or combine some components, or arrange different components.

[0130] Please refer to Figure 4, in another embodiment of the present application, a system 100 for constructing a vacuum degradation model of a cavity of a vacuum-packaged MEMS device considering multiple failure mechanisms is provided. The system includes a vacuum degree characterization module 101, a first vacuum degradation mathematical model construction module 102, a second vacuum degradation mathematical model construction module 103, a total gas molecule number calculation module 104 in the vacuum cavity, a relationship determination module 105 between the degraded air pressure and gas molecules, and a degradation model determination module 106;

[0131] The vacuum degree characterization module 101 is configured to measure the vacuum degree level in the vacuum cavity by using a quality factor, and further determine a first relationship between the internal air pressure of the vacuum cavity and the number of free gas molecules, and a second relationship between the number of free gas molecules inside the vacuum cavity and the quality factor;

[0132] The first vacuum degradation mathematical model construction module 102 is configured to calculate the number of gas molecules released in the vacuum cavity based on the total number of gas molecules and the diffusion coefficient when the outgassing inside the vacuum cavity is constant, and obtain a first vacuum degradation mathematical model caused by outgassing inside the cavity;

[0133] The second vacuum degradation mathematical model construction module 103 is configured to calculate the number of gas molecules leaked into the vacuum cavity from the outside based on the leakage coefficient, and obtain a second vacuum degradation mathematical model caused by external leakage in the vacuum cavity;

[0134] The total gas molecule number calculation module 104 in the vacuum cavity is configured to obtain the total number of gas molecules in the vacuum cavity based on the first vacuum degradation mathematical model and the second vacuum degradation mathematical model;

[0135] The relationship determination module 105 between the degraded air pressure and gas molecules is configured to obtain a relationship between the air pressure and the number of gas molecules in the degraded vacuum cavity based on the total number of gas molecules in the vacuum cavity and the first relationship;

[0136] The degradation model determination module 106 is configured to obtain a vacuum degree degradation model inside the cavity of the vacuum-packaged MEMS device based on the relationship between the air pressure and the number of gas molecules in the degraded vacuum cavity, considering that the vacuum degradation caused by outgassing inside the cavity decays exponentially with time and the vacuum degradation caused by external leakage decays linearly with time.

[0137] It should be noted that the system for constructing a vacuum degradation model for a vacuum-packaged MEMS device cavity considering multiple failure mechanisms of the present invention corresponds one-to-one to the method for constructing a vacuum degradation model for a vacuum-packaged MEMS device cavity considering multiple failure mechanisms of the present invention. The technical features and beneficial effects described in the embodiment of the method for constructing a vacuum degradation model for a vacuum-packaged MEMS device cavity considering multiple failure mechanisms are all applicable to the embodiment of constructing a vacuum degradation model for a vacuum-packaged MEMS device cavity considering multiple failure mechanisms. For specific contents, please refer to the description in the embodiment of the method of the present invention, which will not be repeated here. This is hereby declared.

[0138] In addition, in the implementation of the vacuum degradation model system for a vacuum-packaged MEMS device cavity considering multiple failure mechanisms in the above-mentioned embodiment, the logical division of each program module is only an example. In actual applications, the above-mentioned functions can be assigned to different program modules as needed, for example, for the convenience of corresponding hardware configuration requirements or software implementation. That is, the internal structure of the vacuum degradation model system for a vacuum-packaged MEMS device cavity considering multiple failure mechanisms is divided into different program modules to complete all or part of the functions described above.

[0139] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the program can be stored in a non-volatile computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0140] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0141] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for constructing a vacuum degradation model of a vacuum packaged MEMS device cavity considering multiple failure mechanisms, characterized in that: The steps include: The quality factor is used to measure the vacuum level in the vacuum chamber, thereby determining a first relationship between the gas pressure inside the vacuum chamber and the number of free gas molecules, and a second relationship between the number of free gas molecules inside the vacuum chamber and the quality factor; The number of gas molecules released in the vacuum cavity is calculated based on the total number of gas molecules and the expansion coefficient when the outgassing in the vacuum cavity is constant, and the first vacuum degradation mathematical model caused by the outgassing in the cavity is obtained; The number of gas molecules leaking from the outside into the vacuum chamber is calculated based on the leakage coefficient, and a mathematical model of the second vacuum degradation caused by the external leakage in the vacuum chamber is obtained; The total number of gas molecules in the vacuum cavity is obtained based on the first vacuum degradation mathematical model and the second vacuum degradation mathematical model; the total number of gas molecules N(t) in the vacuum cavity is as follows: Among them, N0 is the initial number of gas molecules inside the cavity, N tot is the total number of gas molecules when the internal outgassing is constant, D T is the diffusion coefficient, which is related to the temperature T, L T is the leakage coefficient, which is related to the temperature T, and t represents a certain time point; Based on the first relationship between the total number of gas molecules in the vacuum cavity and the gas pressure inside the cavity, the relationship between the gas pressure of the vacuum cavity after degradation and the number of gas molecules is obtained; the relationship between the gas pressure of the vacuum cavity after degradation and the number of gas molecules is as follows: Where p(t) represents the pressure in the vacuum chamber, Q(t) represents the quality factor, and N tot is the total number of gas molecules when the internal outgassing is constant, D T is the diffusion coefficient, which is related to the temperature T, L T is the leakage coefficient, which is related to the temperature T, t represents a certain time point, Q0 represents the quality factor at room temperature, and A is an empirical constant; Based on the relationship between the vacuum cavity pressure and the number of gas molecules after degradation, the vacuum degradation model inside the cavity of vacuum packaged MEMS devices is obtained by considering that the vacuum degradation caused by the outgassing inside the cavity decays exponentially with time and the vacuum degradation caused by the external leakage decays linearly with time.

2. The method for constructing a vacuum degradation model of a vacuum packaged MEMS device cavity considering multiple failure mechanisms according to claim 1, characterized in that: The first relational expression and the second relational expression are: The gas pressure p inside the vacuum chamber is proportional to the fraction N of free gas molecules inside, and the number N of free gas molecules inside the vacuum chamber is inversely proportional to the inverse of the quality factor Q.

3. The method for constructing a vacuum degradation model of a vacuum packaged MEMS device cavity considering multiple failure mechanisms according to claim 1, characterized in that: The number of gas molecules released in the vacuum chamber is N in (t), as follows: Among them, N tot is the total number of gas molecules when the internal outgassing is constant, D T is the diffusion coefficient; the diffusion coefficient is correlated with temperature, and t represents a certain time point.

4. The method for constructing a vacuum degradation model of a vacuum packaged MEMS device cavity considering multiple failure mechanisms according to claim 1, characterized in that: The number of gas molecules N leaking from the outside into the vacuum chamber out (t) is as follows: N out (t)=L T ×t Among them, L T is the leakage coefficient, which is related to the temperature T, and t represents a certain time point.

5. The method for constructing a vacuum degradation model of a vacuum packaged MEMS device cavity considering multiple failure mechanisms according to claim 1, characterized in that: The vacuum degradation model of the vacuum packaged MEMS device cavity is as follows: p(t)∝1 / Q(t)∝N(t)=a+b×exp(c×t)+d×t a=1 / Q0+A×N tot b=-A×N tot c=D T d=L T Where p(t) is the pressure inside the cavity, Q(t) is the number of gas molecules in the cavity, N(t) is the quality factor, and N tot is the total number of gas molecules when the internal outgassing is constant, D T is the diffusion coefficient, which is related to the temperature T, L T is the leakage coefficient, which is related to the temperature T, Q0 represents the quality factor at room temperature, A is an empirical constant, t represents a certain point in time, a represents the total number of internal cavity gases caused by the initial gas and internal release inside the sample, and b represents the total number of gases released inside the sample, which determines the amplitude of vacuum degradation caused by internal outgassing of the sample.

6. The method for constructing a vacuum degradation model of a vacuum packaged MEMS device cavity considering multiple failure mechanisms according to claim 5, characterized in that: The method also includes the steps of verifying the vacuum degradation model inside the cavity of the vacuum packaged MEMS device, specifically: Under high temperature environment, the degassing inside the vacuum cavity and the external leakage will accelerate, so the vacuum degree degradation model inside the cavity is specifically as follows: Among them, t m It is the time point when the main failure mechanism of vacuum degradation of vacuum-packaged MEMS devices changes from internal outgassing to external leakage.

7. A system for constructing a vacuum degradation model of a vacuum-packaged MEMS device cavity considering multiple failure mechanisms, applied to the method for constructing a vacuum degradation model of a vacuum-packaged MEMS device cavity considering multiple failure mechanisms as described in any one of claims 1 to 6, characterized in that: It includes a vacuum degree characterization module, a first vacuum degradation mathematical model construction module, a second vacuum degradation mathematical model construction module, a total gas molecule number calculation module in the vacuum chamber, a post-degradation gas pressure and gas molecule relationship determination module, and a degradation model determination module; The vacuum characterization module is used to measure the vacuum level in the vacuum cavity by using the quality factor, and then determine the first relationship between the air pressure inside the vacuum cavity and the number of free gas molecules, and the second relationship between the number of free gas molecules inside the vacuum cavity and the quality factor; The first vacuum degradation mathematical model construction module is used to calculate the number of gas molecules released in the vacuum cavity based on the total number of gas molecules and the expansion coefficient when the outgassing in the vacuum cavity is constant, so as to obtain the first vacuum degradation mathematical model caused by the outgassing in the cavity; The second vacuum degradation mathematical model building module is used to calculate the number of gas molecules leaked from the outside into the vacuum cavity based on the leakage coefficient, and obtain a second vacuum degradation mathematical model caused by external leakage in the vacuum cavity; The total gas molecule number calculation module in the vacuum cavity is used to obtain the total gas molecule number in the vacuum cavity based on the first vacuum degradation mathematical model and the second vacuum degradation mathematical model; The module for determining the relationship between the degraded gas pressure and the gas molecules is used to obtain a relationship between the degraded gas pressure and the number of gas molecules in the vacuum cavity based on the total number of gas molecules in the vacuum cavity and the first relationship; The degradation model determination module is used to obtain a vacuum degree degradation model inside the cavity of a vacuum-packaged MEMS device based on a relationship between the vacuum cavity pressure and the number of gas molecules after degradation, taking into account that vacuum degradation caused by outgassing inside the cavity decays exponentially over time and vacuum degradation caused by external leakage decays linearly over time.

8. A method for evaluating the vacuum degradation model of a vacuum packaged MEMS device cavity, characterized in that: The following steps are involved: Build a test system to test the quality factor Q0 value of vacuum packaged MEMS devices at room temperature; When the sample is not powered, place the sample under usage conditions, storage conditions or reliability acceleration conditions; After a certain time t1, the Q(t1) value of the sample is tested at room temperature based on the constructed test system; Continue to place the sample in the same environment, and after a certain time t2, test the Q(t2) value of the sample at room temperature based on the constructed test system; Repeat the steps of testing the Q value of the sample at room temperature until the test is completed, and obtain the quality factor Q at a series of time points; The obtained data is processed, and the quality factor Q values ​​at different time points are fitted to obtain various coefficients; the fitting of the quality factor Q values ​​at different time points is processed by using the vacuum degradation model obtained by the method for constructing a vacuum degradation model of a vacuum packaged MEMS device cavity considering multiple failure mechanisms in any one of claims 1 to 6; Conduct analysis and evaluation on the obtained coefficients; the analysis and evaluation includes: obtaining whether the main failure is caused by internal leakage or internal outgassing through the various coefficients; obtaining the degradation mode and vacuum degree in the cavity at different times through the various coefficients; Based on the obtained vacuum degree degradation model inside the cavity and its various coefficients, the reliability prediction of the vacuum degree degradation of vacuum packaged MEMS devices is carried out.

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