Mechanically excited MEMS torsional fatigue fracture test structure and test method

Abstract

The invention discloses a mechanical excitation MEMS torsional fatigue fracture test structure and a test method. The test structure comprises three different structural forms, namely an MEMS process cantilever structure, an MEMS process dual-solid structure and an MEMS process dual-solid thermal stress structure. The measuring structure comprises a substrate, an isolating layer, an anchor area, a supporting beam and a mass block, wherein the supporting beam plays a role in supporting a spring. During testing, the MEMS technology cantilever structure and the MEMS technology double-fixed structure work through the vibration table, and the vibration table is used for applying stress to detect the fatigue condition of the supporting beam. According to the MEMS process dual-solid thermal stress structure, current is applied, and thermal stress is applied through the current to detect the fatigue condition of the supporting beam. The test structure provided by the invention is simple, the measurement method is easy, and low-cost and large-scale test can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of MEMS (micro-mechanical electronic systems) processing and manufacturing, process reliability testing, and device reliability testing, and in particular to a torsional fatigue characteristic and fracture strength test structure and test method for a structure in a MEMS device. Background Art

[0002] MEMS devices have the advantages of small size, light weight, low power consumption, low cost, and suitability for mass production. MEMS devices include two major branches: sensors and actuators.

[0003] Torsion structures are common in MEMS devices. For example, in MEMS accelerometers, Z-axis acceleration measurement often uses a torsion structure. Torsion structures are also commonly used for mirror steering in MEMS devices such as MEMS VOAs (optical attenuators), MEMS micromirrors in wavelength selective switches, and MEMS galvanometers in LiDAR (laser radar).

[0004] The torsional structure in MEMS devices will fatigue during long-term operation. For actuators such as MEMS galvanometers, due to the requirements of device specifications, the torsional angle is often large and the torsional execution needs to be performed at a high frequency, resulting in large alternating stress loads on the spring structure. Fatigue can cause device performance to drift and even break, and for such devices, fatigue issues become the key to device reliability. For devices with different designs, different processes, different foundry lines, and even different batches, the fatigue characteristics of their spring structures need to be evaluated to ensure that the designed service life of the device is met. In actual devices, multiple factors affect the torsional fatigue of MEMS devices, including: damage caused by the etching process, residual stress in the thin film, residual stress in the bonding process, packaging stress, the design of the device torsional structure and its related structures, the driving mode when the device is working, and the materials used in the device. There are several issues with fatigue testing using finished devices. First, the structural torsion angle of the finished device is limited during design, making it impossible to torsion at a larger angle for accelerated testing. Second, the drive structure (electrostatic, piezoelectric, electromagnetic, etc.) and drive circuit of the finished device are designed to match the designed torsion angle. Redesigning the drive structure and supporting drive circuit for a larger torsion angle is costly. Considering that torsional fatigue fracture of MEMS devices exhibits different characteristics under different device designs and process flows, designing a test structure that does not require a drive structure and drive circuit to conduct torsional fatigue testing and obtain fatigue characteristic parameters to assist in determining the lifespan of the device's torsional fatigue fracture is a feasible and low-cost solution. Summary of the Invention

[0005] Purpose of the invention: In order to solve the problem of unclear torsional fatigue fracture parameters of existing MEMS devices with different processes and types, this patent provides a mechanically excited MEMS torsional fatigue fracture test structure and method thereof, which are used to measure the torsional fatigue fracture parameters of the torsional structure in the MEMS device.

[0006] Technical solution: In order to achieve the above-mentioned purpose of the invention, the technical solution adopted by the present invention is:

[0007] The present invention discloses a mechanically stimulated MEMS torsional fatigue fracture test structure and method thereof. The test structure includes three different structural forms: a MEMS process cantilever structure, a MEMS process dual-solid structure, and a MEMS process dual-solid thermal stress structure. The measurement structure mainly includes a substrate, an isolation layer, an anchor area, a support beam and a mass block, wherein the support beam acts as a supporting spring. The MEMS process cantilever structure includes an isolation layer provided on the substrate, a support beam anchor area provided on the isolation layer, the support beam is fixed above the substrate through the support beam anchor area position, the mass block is connected to the anchor area through the support beam, and the mass block is eccentrically installed between the support beam; the MEMS process dual-solid structure includes two isolation layers symmetrically provided on the substrate, a support beam anchor area provided on the isolation layer, the support beam is fixed above the substrate through the support beam anchor area position, the mass block is connected to the anchor area through the support beam, and the mass block is eccentrically installed between the support beam; the MEMS process dual-solid thermal stress structure includes an isolation layer and four small isolation layers on the substrate, a support beam anchor area and a thermal actuator anchor area provided on the isolation layer, the support beam and the thermal actuator anchor area are fixed above the substrate through the support beam anchor area and the thermal actuator anchor area position, the mass block is connected to the anchor area through the support beam, and the mass block is eccentrically installed between the support beam; based on the MEMS process cantilever structure, MEMS process dual-solid structure and MEMS process dual-solid thermal stress structure, a cavity is etched in the substrate to provide a torsional space for the mass block.

[0008] The mass block 5 and the support beam 4 are eccentrically installed. The greater the eccentricity, the greater the energy coupled input by the vertical mechanical vibration.

[0009] A cavity 9 is etched on the substrate 1 to provide space for the torsion of the mass block, so as to obtain a larger torsion angle.

[0010] The present invention also provides a test method for a mechanically excited MEMS torsional fatigue fracture test structure, the test method being as follows:

[0011] Step 1: The device is excited using a piezoelectric ceramic or crystal oscillator, and the excitation signal is a periodic chirp signal or a white noise signal. (For the dual-solid thermal stress structure of the MEMS process, it is necessary to apply a current between the thermal actuator anchor area (7) and the ground terminal (8) to generate thermal stress.) The vibration spectrum is measured using the LDV system to obtain the approximate location of its multi-order resonant frequency. The test structure is then excited using a DC+AC sinusoidal signal, and the resonant frequency point is found by measuring the amplitude in the target first-order resonant frequency region.

[0012] Step 2: The device is assembled on a vibration table using a tool (a vacuum environment can be used to reduce damping and increase amplitude). (For MEMS process dual-solid thermal stress structures, it is necessary to apply current between the thermal actuator anchor area (7) and the ground terminal (8) to generate thermal stress.) The vibration frequency is set and the vibration table is started to perform fatigue testing. During the test, the frequency and amplitude can be monitored using a high-speed camera or the capacitance between the substrate and the anchor area.

[0013] Step 3: According to the technical requirements, after a fixed interval (one week), take out the sample, return to step 1, and repeat the test until it breaks.

[0014] Beneficial effects: The present invention provides a mechanically excited MEMS torsional fatigue fracture test structure and method thereof, which performs torsional fatigue testing in the absence of a test structure that does not require a driving structure and a driving circuit, and obtains fatigue characteristic parameters to assist in determining the life of the device's torsional fatigue fracture. Electrostatic driving may result in insufficient driving force. Even if the voltage is increased, it is easy to cause breakdown. The test frequency setting for thermal execution is insufficient, and the test cycle is uncontrollable, which may cause the test time to be too long. Electromagnetic driving requires adding a coil to the original structure, which will destroy the original structure of the device and may affect the accuracy of the test results. Piezoelectric driving requires adding piezoelectric materials, which will also destroy the original structure and may affect the accuracy of the test results. In addition, commonly used piezoelectric ceramic materials are prone to depolarization and are not suitable for long-term testing; and the piezoelectric coefficient of aluminum nitride materials is low, which easily causes insufficient driving force. Therefore, the present invention adopts mechanical stress driving. The test structure provided by the present invention is simple, the measurement method is easy, and low-cost, large-scale testing can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the MEMS process cantilever structure of the present invention;

[0016] Figure 2 Schematic diagram of the dual-solid structure of the MEMS process of the present invention;

[0017] Figure 3 Schematic diagram of the dual-solid thermal stress structure of the MEMS process of the present invention;

[0018] Figure 4 This is a schematic diagram of the cantilever structure cavity of the MEMS process of the present invention;

[0019] Figure 5 Schematic diagram of the dual-solid structure cavity of the MEMS process of the present invention;

[0020] Figure 6 This is a schematic diagram of the dual-solid thermal stress structure cavity of the MEMS process of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to the accompanying drawings.

[0022] Example: Figure 1 The figure shows a MEMS process cantilever structure in a mechanically excited MEMS torsional fatigue fracture test structure. The test structure shown includes a substrate 1, an isolation layer 2, a support beam anchor area 3, a support beam 4 and a mass block 5; the substrate 1 is provided with an isolation layer 2, the isolation layer 2 is provided with an anchor area 3, the support beam 4 is fixed above the substrate 1 through the anchor area 3, the mass block 5 is connected to the anchor area 3 through the support beam 4, and the mass block 5 is eccentrically installed between the support beam 4.

[0023] like Figure 2 As shown, a MEMS process dual-solid structure in a mechanically excited MEMS torsional fatigue fracture test structure includes a substrate 1, an isolation layer 2, an anchor area 3, a support beam 4 and a mass block 5; two isolation layers 2 are symmetrically provided on the substrate 1, and an anchor area 3 is provided on the isolation layer 2. The support beam 4 is fixed above the substrate 1 through the anchor area 3, and the mass block 5 is connected to the anchor area 3 through the support beam 4. The mass block 5 is eccentrically installed between the support beam 4 and the support beam 4.

[0024] like Figure 3 As shown, a MEMS process dual-solid thermal stress structure in a mechanically stimulated MEMS torsional fatigue fracture test structure, the test structure shown includes a substrate 1, an isolation layer 2, a support beam anchor area 3, a support beam 4, a mass block 5, a thermal execution beam 6, a thermal actuator anchor area 7 and a grounding terminal 8; an isolation layer 2 and four small isolation layers 2 are provided on the substrate 1, and a support beam anchor area 3, a thermal actuator anchor area 7 and a grounding terminal 8 are provided on the isolation layer 2. The support beam 4 and the thermal execution beam 6 are fixed above the substrate through the support beam anchor area 3 and the thermal actuator anchor area 7, and the mass block 5 is connected to the anchor area 3 and the thermal actuator anchor area 7 through the support beam 4 and the thermal execution beam 6, and the mass block 5 is eccentrically installed between the support beam 4.

[0025] like Figure 4 A MEMS process cantilever structure cavity in a mechanically excited MEMS torsional fatigue fracture test structure, wherein the test structure shown is based on the MEMS process cantilever structure, and a cavity 9 is etched on a substrate 1 to provide space for the torsion of the mass block.

[0026] like Figure 5 A MEMS process dual-solid structure cavity in a mechanically excited MEMS torsional fatigue fracture test structure. The test structure shown is based on the MEMS process dual-solid structure, and a cavity 9 is etched on the substrate 1 to provide space for the torsion of the mass block.

[0027] like Figure 6 A MEMS process dual-solid thermal stress structure cavity in a mechanically stimulated MEMS torsional fatigue fracture test structure is disclosed. The test structure is based on the MEMS process dual-solid thermal stress structure, and a cavity (9) is etched on a substrate 1 to provide space for the torsion of a mass block.

[0028] The specific test steps are as follows:

[0029] Step 1: The device is excited using a piezoelectric ceramic or crystal oscillator, and the excitation signal is a periodic chirp signal or a white noise signal. (For the dual-solid thermal stress structure of the MEMS process, it is necessary to apply a current between the thermal actuator anchor area (7) and the ground terminal (8) to generate thermal stress.) The vibration spectrum is measured using the LDV system to obtain the approximate location of its multi-order resonant frequency. The test structure is then excited using a DC+AC sinusoidal signal, and the resonant frequency point is found by measuring the amplitude in the target first-order resonant frequency region.

[0030] Step 2: The device is assembled on a vibration table using a tool (a vacuum environment can be used to reduce damping and increase amplitude). (For MEMS process dual-solid thermal stress structures, it is necessary to apply current between the thermal actuator anchor area (7) and the ground terminal (8) to generate thermal stress.) The vibration frequency is set and the vibration table is started to perform fatigue testing. During the test, the frequency and amplitude can be monitored using a high-speed camera or the capacitance between the substrate and the anchor area.

[0031] Step 3: According to the technical requirements, after a fixed interval (one week), take out the sample, return to step 1, and repeat the test until it breaks.

[0032] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A mechanically excited MEMS torsional fatigue fracture test structure, characterized in that: The test structure includes three different structural forms: MEMS process cantilever structure, MEMS process dual-solid structure, and MEMS process dual-solid thermal stress structure; The MEMS process cantilever structure comprises a substrate (1), an isolation layer (2), a support beam anchor region (3), a support beam (4), and a mass block (5); the substrate (1) is provided with an isolation layer (2), the isolation layer (2) is provided with a support beam anchor region (3), the support beam (4) is fixed above the substrate (1) via the support beam anchor region (3), the mass block (5) is connected to the support beam anchor region (3) via the support beam (4), and the mass block (5) and the support beam (4) are eccentrically installed. The MEMS process dual-solid structure comprises a substrate (1), an isolation layer (2), a support beam anchor region (3), a support beam (4), and a mass block (5); two isolation layers (2) are symmetrically provided on the substrate (1); a support beam anchor region (3) is provided on the isolation layer (2); the support beam (4) is fixed above the substrate (1) via the support beam anchor region (3); the mass block (5) is connected to the support beam anchor region (3) via the support beam (4); the mass block (5) and the support beam (4) are eccentrically installed. The MEMS process dual-solid thermal stress structure comprises a substrate (1), an isolation layer (2), a support beam anchor area (3), a support beam (4), a mass block (5), a thermal actuator beam (6), a thermal actuator anchor area (7) and a grounding terminal (8); an isolation layer (2) and four small isolation layers (2) are provided on the substrate (1); a support beam anchor area (3), a thermal actuator anchor area (7) and a grounding terminal (8) are provided on the isolation layer (2); the support beam (4) and the thermal actuator beam (6) are fixed above the substrate via the support beam anchor area (3) and the thermal actuator anchor area (7); the mass block (5) is connected to the anchor area (3) and the thermal actuator anchor area (7) via the support beam (4) and the thermal actuator beam (6); and the mass block (5) is eccentrically installed with respect to the support beam (4).

2. A mechanically excited MEMS torsional fatigue fracture test structure according to claim 1, characterized in that: The mass block (5) is eccentrically installed with respect to the support beam (4).

3. The mechanically excited MEMS torsional fatigue fracture test structure according to claim 1, characterized in that: A cavity (9) is etched on a substrate (1).

4. A test method using the mechanically excited MEMS torsional fatigue fracture test structure according to any one of claims 1 to 3, characterized in that: The test method is as follows: Step 1: The device is excited by a piezoelectric ceramic or crystal oscillator. The excitation signal is a periodic chirp signal or a white noise signal. The vibration spectrum is measured by the LDV system to obtain the approximate position of its multi-order resonant frequency. Then, the test structure is excited by a DC+AC sinusoidal signal. The resonant frequency point is found by measuring the amplitude in the target first-order resonant frequency area. Step 2: The device is assembled on a vibration table through a tooling to set the vibration frequency, and the vibration table is started to perform fatigue testing. During the test, the frequency and amplitude can be monitored by high-speed camera observation or the capacitance between the substrate and the anchor area. Step 3: According to the technical requirements, after a fixed interval (one week), take out the sample, return to step 1, and repeat the test until it breaks.

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