Establishment method and evaluation method of vacuum degradation model of vacuum packaging MEMS device cavity considering multiple failure mechanisms

Abstract

The invention discloses a construction method and an evaluation method for a vacuum degradation model of a vacuum packaging MEMS device cavity considering various failure mechanisms. The model construction method comprises the following steps: (1) vacuum degree characterization: characterizing the vacuum degree of the cavity by using a quality factor; (2) vacuum degeneration mathematical model modeling: a, calculating the number of gas molecules released in the cavity, and obtaining a first vacuum degeneration mathematical model caused by gas release in the cavity; b, the number of gas molecules leaked from the outside in the cavity is calculated, and a second vacuum degradation mathematical model caused by external leakage in the cavity is obtained; and c, the first vacuum degeneration mathematical model and the second vacuum degeneration mathematical model are used for obtaining a vacuum degree degeneration model in the cavity based on the relationship between the total number of gas molecules in the cavity and the air pressure of the cavity. On the basis of the constructed vacuum degree degradation model, the invention also provides a method for evaluating the reliability of the vacuum degradation of the vacuum packaging MEMS device, and the reliability prediction of the vacuum degree degradation of the vacuum packaging MEMS device can be realized.

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 purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method for constructing and evaluating a vacuum degradation model for a vacuum-packaged MEMS device cavity that takes into account a variety of failure mechanisms. By comprehensively considering the two failure mechanisms of internal outgassing and external leakage, a corresponding reliability evaluation mathematical model is established, which provides a more accurate evaluation of the long-term reliability of vacuum-packaged MEMS devices and the prediction of changes in their vacuum degree.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] First, the present invention provides a method for constructing a vacuum degradation model of a vacuum packaged MEMS device cavity taking into account multiple failure mechanisms, comprising the following steps:

[0008] 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;

[0009] 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;

[0010] 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;

[0011] 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;

[0012] Based on the first relationship between the total number of gas molecules in the vacuum chamber and the gas pressure inside the chamber, a relationship between the gas pressure of the vacuum chamber after degradation and the number of gas molecules is obtained;

[0013] 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.

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

[0015] 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.

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

[0017]

[0018] 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.

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

[0020] N out (t) = L T ×t

[0021] Among them, L T is the leakage coefficient, which is related to the 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, 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.

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

[0026]

[0027] 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.

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

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

[0030] a=1 / Q0+A×N tot

[0031] b=-A×N tot

[0032] c=D T

[0033] d=L T

[0034] Where p(t) is the pressure inside the cavity, Qt is the number of gas molecules in the cavity, N(t) is the quality factor, 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.

[0035] As a preferred technical solution, the method further includes the step of verifying the vacuum degradation model inside the vacuum packaged MEMS device cavity, specifically:

[0036] 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:

[0037]

[0038] 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.

[0039] In a second aspect, the present invention provides a vacuum degradation model construction system for a vacuum-packaged MEMS device cavity that takes into account a variety of 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 post-degradation gas pressure and gas molecule relationship determination module, and a degradation model determination module;

[0040] 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;

[0041] 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;

[0042] 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;

[0043] 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;

[0044] 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;

[0045] 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.

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

[0047] Build a test system to test the quality factor Q0 value of vacuum packaged MEMS devices at room temperature;

[0048] When the sample is not powered, place the sample under usage conditions, storage conditions or reliability acceleration conditions;

[0049] After a certain time t1, the Q(t1) value of the sample is tested at room temperature based on the constructed test system;

[0050] The sample is placed in the above environment for a certain period of time t2, and the Q(t2) value of the sample is tested at room temperature based on the constructed test system;

[0051] 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;

[0052] 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 8;

[0053] 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;

[0054] 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.

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

[0056] (1) The present invention establishes a mathematical model for the degradation of the vacuum degree inside the cavity of a vacuum-packaged MEMS device by considering two failure mechanisms, namely, internal gas release and external leakage. This makes up for the defect that the existing model only considers the single mechanism of internal gas release, and can more accurately evaluate the degradation of the vacuum degree of vacuum-packaged MEMS devices.

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

[0058] (3) The present invention determines the vacuum degree degradation model and model parameters inside the cavity based on the degradation data of the Q value of the vacuum-encapsulated MEMS device, and obtains the time trend of the quality factor degradation of the vacuum-encapsulated MEMS device based on the model. This provides an important theoretical basis and reference basis for the reliability design, reliability evaluation and reliability life prediction of the vacuum-encapsulated MEMS device, and is helpful for the development of highly reliable vacuum-encapsulated 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 drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0060] Figure 1 A flow chart of a method for constructing a vacuum degradation model of a vacuum packaged MEMS device cavity considering multiple failure mechanisms according to an embodiment of the present invention;

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

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

[0063] Figure 4 A structural diagram of a system for constructing a vacuum degradation model for a vacuum-packaged MEMS device cavity taking into account multiple failure mechanisms according to an embodiment of the present invention. DETAILED DESCRIPTION

[0064] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present application.

[0065] Reference to "embodiments" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0066] MEMS refers to Micro-Electro-Mechanical System, a micro system that integrates micro-mechanical structures, sensors, actuators and electronic control units. These systems are usually very small in size and can work on a scale of microns to millimeters.

[0067] See also Figure 1 This embodiment provides a vacuum degradation model method for a vacuum packaged MEMS device cavity taking into account multiple failure mechanisms, including the following steps:

[0068] S11, vacuum degree characterization method;

[0069] In order to conduct reliability assessment on vacuum degradation of vacuum-encapsulated MEMS devices, it is necessary to accurately monitor the vacuum degree in their vacuum cavity. Since the vacuum encapsulated cavity of MEMS devices is very small, it is difficult for existing testing equipment to perform non-destructive testing on them. In addition, vacuum-encapsulated MEMS devices usually contain movable resonant structures, and their motion characteristics are directly affected by the vacuum degree of the environment. Therefore, in view of these characteristics of MEMS devices, we choose the Q value of vacuum-encapsulated 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, while the damping is proportional to the air pressure inside the cavity. The relationship between the air pressure inside the cavity of a vacuum-packaged MEMS device and the number of gas molecules inside the cavity and the quality factor is as follows: The air pressure p inside the sealed cavity is proportional to the fraction of free gas molecules N inside, and inversely proportional to the inverse of the quality factor Q.

[0071] pt∝N(t∝1 / Q t(1)

[0072] S12, constructing a vacuum degradation model inside the cavity;

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

[0074] N(t)=N0+N in (t)+N out (t(2)

[0075] Among them, N0 is the initial number of gas molecules inside the cavity, N in (t) is the number of gas molecules released inside the cavity, N out (t) is the number of gas molecules leaking outside the cavity.

[0076] a. a first vacuum degradation mathematical model caused by outgassing inside the cavity, wherein the first vacuum degradation mathematical model is obtained by calculating 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 inside the vacuum cavity is constant;

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

[0078]

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

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

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

[0082] N out (t) = L T ×t(4)

[0083] Among them, L T is the leakage coefficient, which is related to temperature T.

[0084] Taking into account the two failure mechanisms of internal outgassing and external leakage, 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. That is, by substituting equations (3) and (4) into equation (2), the total number of gas molecules N(t) in the cavity of the vacuum packaged MEMS device is obtained as follows:

[0085]

[0086] Based on the total number of gas molecules in the vacuum chamber and the first relational expression, the relational expression between the vacuum chamber pressure and the number of gas molecules after degradation is obtained. That is, based on the relation between the chamber pressure and the number of gas molecules in equation (1), it can be obtained that:

[0087]

[0088] From formula (6), it can be seen that the vacuum degradation caused by the outgassing inside the cavity decays exponentially with time; the vacuum degradation caused by the external leakage decays linearly with time.

[0089] Then the vacuum degradation model inside the vacuum packaged MEMS device cavity is obtained as follows:

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

[0091] In the formula, a, b, c, d are empirical constants, a = 1 / Q0 + A × N tot , b=-A×N tot 、c=D T d=L T , the test data can be fitted based on the above formula to obtain various coefficients.

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

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

[0094] The parameter b characterizes the total amount of gas released from the sample and determines the amplitude of vacuum degradation caused by internal outgassing.

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

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

[0097] 1 / (a+b) is the initial value of the sample Q value.

[0098] Alternatively, during the high temperature and other environmental stress accelerated tests on vacuum packaged MEMS devices, both internal outgassing and external leakage will be accelerated, but in the early stage of the test, internal outgassing will dominate. After a period of time, when most of the gas inside the cavity is released, external leakage will dominate in the middle and late stages of the test. Therefore, for reliability tests such as high temperature acceleration of vacuum packaged MEMS devices, formula (6) can be changed to

[0099]

[0100] Here, tm is the time point when the main failure mechanism of vacuum degradation of vacuum-packaged MEMS devices changes from internal outgassing to external leakage.

[0101] Accordingly, formula (7) becomes:

[0102]

[0103] See also Figure 2 This embodiment provides a method for evaluating a vacuum degradation model of a vacuum packaged MEMS device cavity, comprising the following steps:

[0104] S21. Before the test, the quality factor Q0 value of the vacuum packaged MEMS device is tested at room temperature using the built test system;

[0105] S22. When the sample is not powered on, place the sample under usage conditions, storage conditions or reliability acceleration conditions;

[0106] S23, after a certain time t1, the Q(t1) value of the sample is tested at room temperature based on the constructed test system;

[0107] S24, continue to place the sample in the above environment, and after a certain time t2, test the Q(t2) value of the sample at room temperature based on the constructed test system;

[0108] S25, repeat steps S23 and S24 until the test is finished, and obtain a series of Q values ​​Q0, Q(t1), Q(t2), Q(t3), Q(t4), Q(t5), ... of the samples at time points t=0, t1, t2, t3, t4, t5, ...;

[0109] S26, processing the obtained data, fitting the quality factor Q values ​​measured at different time points according to the formula 1 / Q t=a+b×exp(ct)+dt, and obtaining various coefficients;

[0110] S27. Analyze and evaluate the various coefficients obtained;

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

[0112] In a more specific embodiment, the degradation modeling and analysis and evaluation method of the vacuum packaged MEMS device is further described:

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

[0114] S32. Before the test, the Q0 value of the sample drive shaft is tested at room temperature at t = 0h by using the quality factor Q value test system built;

[0115] S33. Conduct high temperature test on the sample: raise the temperature of the incubator to 85°C, and when the temperature reaches the specified temperature, place the sample in the incubator;

[0116] S34, baking the samples at high temperature, and taking the samples out of the incubator after 16.5 h, 66.75 h, 189.25 h, 248.75 h, and 752.75 h, respectively;

[0117] S35. After being placed at room temperature for 2 hours, the Q value of the sample drive shaft is tested and recorded, as shown in Table 1;

[0118] S36, sample data curve is as follows Figure 3 As shown, the measured data is fitted according to formula (9) to obtain various coefficients.

[0119] Table 1

[0120]

[0121]

[0122] S36, sample data curve is as follows Figure 3 As shown, the measured data is fitted according to formula (9) 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 used to obtain the model of the internal air pressure of the vacuum packaged MEMS gyroscope at a high temperature of 85°C, as shown in the following formula:

[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 vacuum degree inside the sample cavity can be predicted.

[0128] It should be noted that, for the sake of convenience, the aforementioned method embodiments are all expressed as a series of action combinations, but those skilled in the art should know that the present invention is not limited to the described order of actions, because according to the present invention, certain steps can be performed in other orders or simultaneously.

[0129] Based on the same idea as the method for constructing a vacuum degradation model of a vacuum-encapsulated MEMS device cavity considering multiple failure mechanisms in the above-mentioned embodiment, the present invention also provides a system for constructing a vacuum degradation model of a vacuum-encapsulated MEMS device cavity considering multiple failure mechanisms, which can be used to execute the above-mentioned method for constructing a vacuum degradation model of a vacuum-encapsulated MEMS device cavity considering multiple failure mechanisms. For ease of explanation, the structural schematic diagram of the embodiment of the system for constructing a vacuum degradation model of a vacuum-encapsulated MEMS device cavity considering multiple failure mechanisms only shows the parts related to the embodiment of the present invention. Those skilled in the art can understand that the illustrated structure does not constitute a limitation on the device, and may include more or fewer components than shown in the diagram, or combine certain components, or arrange the components differently.

[0130] See also Figure 4 In another embodiment of the present application, a vacuum degradation model construction system 100 for a vacuum packaged MEMS device cavity considering multiple failure mechanisms is provided, the system comprising 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 post-degradation gas pressure and gas molecule relationship determination module 105, and a degradation model determination module 106;

[0131] The vacuum characterization module 101 is used to measure the vacuum level in the vacuum chamber by using the quality factor, and then determine the first relationship between the air pressure inside the vacuum chamber and the number of free gas molecules, and the second relationship between the number of free gas molecules inside the vacuum chamber and the quality factor;

[0132] The first vacuum degradation mathematical model building module 102 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 a first vacuum degradation mathematical model caused by the outgassing in the cavity;

[0133] The second vacuum degradation mathematical model building module 103 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;

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

[0135] The module 105 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 chamber based on the total number of gas molecules in the vacuum chamber and the first relationship.

[0136] The degradation model determination module 106 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.

[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 may be combined arbitrarily. To make the description concise, 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, they should be considered to be within the scope of this specification.

[0141] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are 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; Based on the first relationship between the total number of gas molecules in the vacuum chamber and the gas pressure inside the chamber, a relationship between the gas pressure of the vacuum chamber after degradation and the number of gas molecules is obtained; 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 vacuum degradation model method of vacuum packaged MEMS device cavity considering multiple failure mechanisms according to claim 1 is 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 vacuum degradation model method of vacuum packaged MEMS device cavity considering multiple failure mechanisms according to claim 1 is 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 vacuum degradation model method of vacuum packaged MEMS device cavity considering multiple failure mechanisms according to claim 1 is 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 vacuum degradation model method of vacuum packaged MEMS device cavity considering multiple failure mechanisms according to claim 1, characterized in that: The total number of gas molecules N(t) in the vacuum chamber 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.

6. The vacuum degradation model method of vacuum packaged MEMS device cavity considering multiple failure mechanisms according to claim 1, characterized in that: The relationship between the gas pressure of the vacuum chamber and the number of gas molecules after degradation 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.

7. The vacuum degradation model method of 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.

8. The vacuum degradation model method of vacuum packaged MEMS device cavity considering multiple failure mechanisms according to claim 7, 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.

9. A vacuum degradation model construction system for vacuum packaged MEMS device cavity considering multiple failure mechanisms, 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.

10. 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; The sample is placed in the above environment for a certain period of time t2, and the Q(t2) value of the sample is tested 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 8; 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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