Piezoelectric MEMS fan, stress optimization design method, preparation method and chip thereof

Abstract

This invention relates to piezoelectric MEMS fans and their stress optimization design, fabrication, and chip in the field of MEMS actuators. The piezoelectric MEMS fan includes a support frame and at least one piezoelectric motion arm extending from the support frame. The piezoelectric motion arm has multiple stress-dispersing openings, and the distribution pattern of these openings is configured to disperse stress concentration within the piezoelectric motion arm during vibration. This invention designs a specific stress-dispersing opening pattern on the piezoelectric motion arm, which is optimized based on vibration stress field analysis. This pattern effectively disperses and releases the alternating stress borne by the motion arm during long-term high-frequency vibration, especially alleviating stress concentration in critical areas such as the root, thereby greatly suppressing the initiation and propagation of fatigue cracks and reducing performance degradation and the probability of fracture failure.

Description

Technical Field

[0001] This invention relates to the field of MEMS actuator technology, and in particular to a fatigue-resistant piezoelectric MEMS fan and its stress optimization design method, fabrication method and chip. Background Technology

[0002] Piezoelectric MEMS fans utilize the inverse piezoelectric effect of piezoelectric materials to drive high-frequency bending vibrations of cantilever beams or diaphragms, thereby driving airflow for heat dissipation. Compared with traditional fans, they have advantages such as small size, no electromagnetic interference, and easy integration, and have broad application prospects in portable electronic devices and localized chip heat dissipation. However, the core component of piezoelectric MEMS fans—the piezoelectric moving arm (usually a cantilever beam or fixed beam)—is subjected to alternating mechanical stress under long-term high-frequency vibration, making it highly susceptible to fatigue cracks in stress concentration areas, leading to performance degradation or even fracture failure. Existing research shows that the root fixed end of the piezoelectric cantilever beam is the area with the highest stress concentration, where cracks typically initiate and propagate, ultimately causing device failure. Traditional designs often use homogeneous solid structures, which, while increasing thickness or using tough materials to improve strength, sacrifice driving efficiency, reduce resonant frequency, and fail to fundamentally solve the stress concentration problem. Summary of the Invention

[0003] To address the technical problem that existing piezoelectric MEMS fans, under long-term high-frequency vibration and alternating mechanical stress, are prone to fatigue cracks in stress concentration areas, leading to performance degradation or even fracture failure, this invention provides a fatigue-resistant piezoelectric MEMS fan and its stress optimization design and fabrication method.

[0004] In a first aspect, the present invention proposes a fatigue-resistant piezoelectric MEMS fan, which includes a support frame and at least one piezoelectric moving arm extending from the support frame. The piezoelectric moving arm has a plurality of stress-dispersing openings, and the distribution pattern of the plurality of stress-dispersing openings is configured to disperse the stress concentration inside the piezoelectric moving arm during vibration.

[0005] As a preferred example, the stress dispersion openings are distributed in the vibration strain neutral axis region of the piezoelectric moving arm.

[0006] As a preferred example, the stress-dispersing openings are distributed in the high-stress region at the root of the connection between the piezoelectric moving arm and the support frame.

[0007] As a preferred example, the stress dispersion openings are distributed in the vibration strain neutral axis region of the piezoelectric motion arm and the high-stress region at the root where the piezoelectric motion arm connects to the support frame.

[0008] As a preferred example, the distribution pattern of the multiple stress dispersion openings is an array extending along the strain neutral axis of the piezoelectric moving arm, or an arc-shaped outward expansion array around the root of the piezoelectric moving arm, or an array uniformly distributed on the plane of the piezoelectric moving arm.

[0009] As a preferred example, the piezoelectric moving arm has a multilayer thin film structure, which, from bottom to top, consists of: a support layer, a lower electrode, a piezoelectric thin film, an upper electrode, and a passivation layer. The stress dispersion opening penetrates through the support layer, the lower electrode, the piezoelectric thin film, the upper electrode, and the passivation layer.

[0010] As a preferred example, the piezoelectric moving arm has a multilayer thin film structure, which, from bottom to top, consists of: a support layer, a lower electrode, a piezoelectric thin film, an upper electrode, and a passivation layer. The stress dispersion opening penetrates through the lower electrode, the piezoelectric thin film, and the upper electrode.

[0011] As a preferred example, the materials of the support layer and the passivation layer are SiO2 or SiN. x The thickness of the upper electrode is 0.5–2 μm. The material of the lower electrode is Ti / Pt composite material or Au, and its thickness is 0.1–0.3 μm. The material of the piezoelectric film is ScAlN, PZT, or AlN, and its thickness is 0.5–3 μm. The material of the upper electrode is Al or Pt, and its thickness is 0.1–0.3 μm.

[0012] As a preferred example, the minimum size of the stress-dispersing opening is 1μm to 20μm. The minimum spacing between adjacent stress-dispersing openings is not less than 1.5 times the thickness of the piezoelectric moving arm.

[0013] As a preferred example, the piezoelectric moving arm is a cantilever beam structure or a double-end fixed beam structure.

[0014] Secondly, the present invention also proposes a stress optimization design method for a fatigue-resistant piezoelectric MEMS fan, which is used to determine the stress dispersion aperture pattern on the fatigue-resistant piezoelectric MEMS fan mentioned in the first aspect. The stress optimization design method includes: A three-dimensional finite element model of the piezoelectric motion arm is established. Piezoelectric driving excitation is applied to the three-dimensional finite element model, and the vibration modes and stress distribution of the piezoelectric motion arm at the target operating frequency are solved to obtain a stress distribution cloud map. Based on the distribution cloud map, with the goal of maximizing the fatigue safety factor or minimizing the peak stress, and using the material distribution within the plane of the piezoelectric motion arm as the design variable, topology optimization is performed under given volume constraints to generate preliminary opening layout suggestions. The preliminary opening layout suggestions are transformed into specific opening patterns; harmonic response analysis and fatigue life prediction are performed on the three-dimensional finite element model with the opening patterns, and the reduction in peak stress and the improvement in fatigue life are evaluated; if the evaluation results do not meet expectations, the opening pattern, size, or distribution is adjusted. The topology optimization and opening pattern adjustment process is repeated until the design requirements are met to determine the final stress dispersion opening pattern.

[0015] Thirdly, this invention also proposes a method for fabricating a fatigue-resistant piezoelectric MEMS fan, which fabricates the fatigue-resistant piezoelectric MEMS fan described in the first aspect. The fabrication method includes: The stress-dispersing opening is etched in the same or consecutive process steps as the piezoelectric moving arm is released using a deep etching process to form its outer contour.

[0016] Fourthly, the present invention also proposes a chip that integrates the fatigue-resistant piezoelectric MEMS fan from the first aspect for heat dissipation.

[0017] The beneficial effects of this invention are as follows: 1. This invention designs a specific stress-dispersing perforation pattern on the piezoelectric motion arm. This pattern is optimized based on vibration stress field analysis, effectively dispersing and releasing the alternating stress borne by the motion arm during long-term high-frequency vibration, especially alleviating stress concentration in critical areas such as the root, thereby greatly inhibiting the initiation and propagation of fatigue cracks and reducing the probability of performance degradation and fracture failure. This invention can significantly improve the mechanical reliability and service life of MEMS fans without sacrificing aerodynamic performance, and is suitable for harsh environments requiring long-term stable operation.

[0018] 2. This invention, through optimized opening design, reduces the peak stress of the piezoelectric moving arm in the fan by 30%-50% and increases fatigue life by more than 10 times (from 10). 8 The next upgrade to 10 9 (Even higher), meeting the requirements of long-term continuous operation in industrial applications. In addition, the multi-path force transmission mechanism generated by the opening design makes the piezoelectric motion arm more tolerant to manufacturing defects (such as small edge notches) and local damage. Even if microcracks are generated locally, the crack propagation will be blunted or terminated by the opening, which enhances the robustness of the piezoelectric motion arm.

[0019] 3. The opening structure and the piezoelectric moving arm shape in this invention can be formed simultaneously in the same deep etching step without the need for additional photomasks or process steps, which has good industrialization prospects. Furthermore, the design process based on finite element and topology optimization can be customized for different sizes, materials and working conditions, making it highly versatile. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a top view of a cantilever beam fan with openings at the root region of the piezoelectric moving arm. Figure 2 This is a top view of a fan with an arc-shaped outward-expanding array of openings surrounding the root of the piezoelectric moving arm. Figure 3 This is a top view of a fan structure in which the aperture distribution pattern is uniformly distributed in an array on the plane of the piezoelectric moving arm. Figure 4 This is a top view of a fan with elongated openings and a pattern extending along the strain neutral axis of the piezoelectric moving arm. Figure 5 This is a top view of a fan structure with circular openings and a distribution pattern extending along the strain neutral axis of the piezoelectric moving arm. Figure 6 yes Figure 1 A schematic diagram of the AA-direction cross section, with the opening being a through hole; Figure 7 yes Figure 1 A schematic diagram of the AA-direction cross section, where the opening is a blind hole; Figure 8 This is a stress diagram of an unperforated cantilever beam fan; Figure 9 This is a stress diagram of a cantilever beam fan with openings; Figure 10 This is a flowchart of a stress optimization design method for fatigue-resistant piezoelectric MEMS fans.

[0022] In the figure: support frame 1, piezoelectric moving arm 2, stress dispersion opening 3, support layer 21, lower electrode 22, piezoelectric film 23, upper electrode 24, passivation layer 25. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] It should be noted that when a component is said to be "installed on" another component, it can be directly on the other component or it may be in a component that is centered on it. When a component is said to be "set on" another component, it can be directly set on the other component or it may also be in a component that is centered on it. When a component is said to be "fixed to" another component, it can be directly fixed to the other component or it may also be in a component that is centered on it.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "or / and" as used herein includes any and all combinations of one or more of the associated listed items.

[0026] The fatigue-resistant piezoelectric MEMS fan provided by this invention introduces a through-hole pattern designed through finite element analysis and topology optimization into the plane of the piezoelectric moving arm. These openings actively change the local stiffness distribution, redistributing peak stress originally concentrated in a narrow area to a wider area and forming a multi-path load transfer network, thereby significantly extending fatigue life. In this embodiment, the piezoelectric MEMS fan includes a support frame and at least one piezoelectric moving arm. The support frame can be made of silicon or SOI material, serving as the base of the entire fan to provide mechanical support. The piezoelectric moving arm can be a cantilever beam structure or a double-ended fixed beam structure. In the case of a cantilever beam structure, one end of the piezoelectric moving arm is fixedly connected to the support frame, and the other end is a free end. Due to the structural characteristics of the piezoelectric moving arm, the free end can bend and vibrate under the drive of an electrical signal. Specifically, the piezoelectric moving arm is a multilayer thin film structure, which, from bottom to top, consists of: a support layer, a lower electrode, a piezoelectric thin film, an upper electrode, and a passivation layer. The materials of the support layer and the passivation layer are SiO2 or SiN. x The thickness of the upper electrode can be set to 0.5–2 μm. The material of the lower electrode is Ti / Pt composite material or Au, and its thickness can be set to 0.1–0.3 μm. The material of the piezoelectric thin film is ScAlN, PZT, or AlN, and its thickness can be set to 0.5–3 μm. The material of the upper electrode is Al or Pt, and its thickness can be set to 0.1–0.3 μm.

[0027] One of the key design focuses of this invention is the design of stress-dispersing openings and their patterns on the piezoelectric motion arm. These stress-dispersing openings need to be distributed in critical areas of the piezoelectric motion arm, including the high-stress region at the root and near the strain neutral axis along the length direction. The pattern, size, and distribution of the openings are based on stress field optimization design, with the design principle aiming to achieve the following functions: 1. Reduce peak stress: Opening the hole interrupts the continuous transmission of stress flow, causing stress redistribution and reducing the local maximum value.

[0028] 2. Dispersing stress distribution: The opening divides the originally concentrated stress area into multiple smaller areas, making the stress distribution more uniform.

[0029] 3. Formation of multi-path load transfer: The ligaments between the openings form multiple parallel force transmission paths. Even if a microcrack appears in one ligament, the load can be redistributed through adjacent paths, avoiding catastrophic failure. Therefore, the minimum size of the stress-dispersing openings can be set to 1μm to 20μm. The minimum spacing between adjacent stress-dispersing openings is not less than 1.5 times the thickness of the piezoelectric moving arm to facilitate load redistribution in the event of a crack.

[0030] The specific design of the perforation pattern can be differentiated according to different areas of the piezoelectric motion arm. The design concept includes: 1. High-stress area at the root of the piezoelectric motion arm (near the fixed end): The stress is greatest here. The openings should be densely distributed, mainly in circular or elliptical shapes, with the long axis perpendicular to the principal stress direction (i.e., perpendicular to the longitudinal direction of the piezoelectric motion arm) to effectively block stress flow. The openings can be arranged in an alternating pattern to avoid forming a linear weakening zone.

[0031] 2. Near the strain neutral axis of the piezoelectric moving arm: Along the longitudinal direction of the piezoelectric moving arm, there exists a neutral axis where the strain is zero during bending. Long, narrow openings can be arranged in this region, with the long side parallel to the longitudinal direction of the piezoelectric moving arm. This can reduce mass, increase the resonant frequency, and guide smoother deformation without significantly affecting the bending stiffness.

[0032] 3. Near the free end: The stress is relatively small, so no holes need to be made or only a few circular holes need to be arranged to further reduce weight.

[0033] The following description, in conjunction with the accompanying drawings, illustrates the various types of feasible opening patterns: (1) Please refer to Figure 1 The stress dispersion openings are set to be circular and are distributed in the high-stress area at the root of the piezoelectric moving arm and the support frame.

[0034] (2) Please refer to Figure 2 The stress dispersion opening is set to be circular, and its distribution pattern is an arc-shaped outward array around the root of the piezoelectric moving arm.

[0035] (3) Please refer to Figure 3 The stress dispersion openings are set to be circular, and their distribution pattern is an array uniformly distributed on the plane of the piezoelectric moving arm.

[0036] (4) Please refer to Figure 4 The stress dispersion opening is set as a long strip, with the long side parallel to the longitudinal direction of the piezoelectric moving arm, and its distribution pattern is an array extending along the strain neutral axis of the piezoelectric moving arm.

[0037] (5) Please refer to Figure 5 The stress dispersion openings are set to be circular, and their distribution pattern is an array extending along the strain neutral axis of the piezoelectric moving arm.

[0038] (6) Please refer to Figure 6 , Figure 7 The stress dispersion orifice can be configured as a through-hole or a blind hole. When the stress dispersion orifice is a through-hole, it penetrates the support layer, the lower electrode, the piezoelectric film, the upper electrode, and the passivation layer. When the stress dispersion orifice is a blind hole, it penetrates the lower electrode, the piezoelectric film, and the upper electrode.

[0039] To verify the fatigue resistance of the piezoelectric MEMS fan in this invention, stress tests were performed on a fan without openings and the fan in this invention for comparison. For example... Figure 8 As shown, in an unperforated fan, the stress is significantly concentrated at the root of the piezoelectric moving arm. Under long-term high-frequency vibration, this stress-concentrated root region is prone to fatigue cracks. Figure 9 As shown, the stress dispersion openings are circular and through holes, and their array is distributed in the high-stress area at the root of the piezoelectric moving arm connected to the support frame. It can be seen that the stress that was originally concentrated in the root area of ​​the piezoelectric moving arm is dispersed and interrupted by the openings, thereby effectively reducing the generation of fatigue cracks.

[0040] In another embodiment, a stress optimization design method for a fatigue-resistant piezoelectric MEMS fan is also provided, which is used to design the stress dispersion aperture pattern on the aforementioned fatigue-resistant piezoelectric MEMS fan. For example... Figure 10 As shown, the stress optimization design method includes: S1. Establish a three-dimensional finite element model of the piezoelectric motion arm. Based on the geometry, material parameters, and boundary conditions of the MEMS fan, establish a three-dimensional finite element model of the piezoelectric motion arm. The three-dimensional finite element model includes various material layers such as the support layer, upper / lower electrodes, and piezoelectric thin film, and assigns corresponding elastic constants, densities, and piezoelectric constants.

[0041] S2. Perform modal analysis and harmonic response analysis. Apply piezoelectric driving excitation to the three-dimensional finite element model, solve the vibration modes and stress distribution of the piezoelectric motion arm at the target operating frequency (usually the first-order bending resonant frequency), obtain the distribution cloud map of the first principal stress (tensile stress) of the piezoelectric motion arm, and identify high stress risk areas (usually located on both sides of the fixed end at the root of the piezoelectric motion arm and near the strain neutral axis).

[0042] S3. Preliminary Topology Optimization Design. Based on the distribution cloud map, with the goal of maximizing the fatigue safety factor or minimizing the peak stress, and using the material distribution within the plane of the piezoelectric motion arm as the design variable, topology optimization is performed under given volume constraints to generate preliminary opening layout suggestions. Topology optimization can employ either the variable density method or the progressive structural optimization method.

[0043] S4. Patterning and Parametricization. The continuous material distribution obtained from topology optimization, i.e., the preliminary aperture layout suggestion, is transformed into specific aperture patterns, such as circles, ellipses, strips, or combinations thereof. The aperture size needs to take into account the minimum linewidth limit of the process (usually ≥2μm), and the minimum spacing between adjacent apertures (ligament width) should not be less than 1.5 times the total thickness of the piezoelectric motion arm to ensure structural rigidity.

[0044] S5. Iterative Verification and Optimization. Perform harmonic response analysis and fatigue life prediction on the 3D finite element model with the opening pattern (e.g., using SN curves and Miner's linear cumulative damage theory), and evaluate the reduction in peak stress and the improvement factor in fatigue life. If the evaluation results do not meet expectations, adjust the opening pattern, size, or distribution, and repeat steps S3-S5 until the design requirements are met.

[0045] S6. Output the final design. If the evaluation results meet expectations, determine the corresponding final aperture pattern for mask fabrication and tape-out.

[0046] In another embodiment, a method for fabricating a fatigue-resistant piezoelectric MEMS fan is also proposed, which fabricates the aforementioned fatigue-resistant piezoelectric MEMS fan. The fabrication method includes etching stress-dispersing openings in the same or consecutive process steps where a deep etching process is used to release the piezoelectric moving arm to form its outer contour. This fabrication method can achieve both fan structure release and stress management design in a single etching step, solving the reliability bottleneck of fatigue fracture caused by high-frequency vibration in piezoelectric MEMS fans from the source without increasing process complexity. This achieves the advantages of low cost, high precision, and long lifespan for mass production of the fan.

[0047] In another embodiment, a single cantilever beam piezoelectric MEMS fan is used as an example, and the MEMS fan structure, stress optimization design method, and fabrication method described in the above embodiments are explained. This embodiment provides a small piezoelectric MEMS fan suitable for mobile phone heat dissipation. In this piezoelectric MEMS fan, the dimensions of the piezoelectric moving arm are: length 1500μm, width 300μm, and total thickness 10μm (wherein, the support layer is made of SiO2 with a thickness of 2μm. The lower electrode is made of Ti / Pt composite material with a thickness of 0.2μm. The piezoelectric thin film is made of ScAlN with a thickness of 2μm. The upper electrode is made of Al with a thickness of 0.3μm. The passivation layer is made of SiO2 with a thickness of 0.5μm). In the initial design, a cantilever beam model is established using the finite element software ANSYS. The material parameters are: silicon Young's modulus 170GPa, Poisson's ratio 0.28; ScAlN Young's modulus 320GPa, Poisson's ratio 0.3; piezoelectric constant d 31 =-2.5pm / V. Boundary conditions: The fixed end of the piezoelectric motion arm is fully constrained, and the free end is free. Harmonic response analysis was performed with a unit voltage applied, extracting the first-order bending mode frequency of 23.5kHz. The stress cloud diagram shows that the maximum tensile stress is located on both sides of the root, reaching 45MPa. The stress near the neutral axis is relatively small. In topology optimization, minimizing the peak stress is the objective. The volume of the piezoelectric motion arm is constrained to 80% of its original volume. Topology optimization yields the following material distribution suggestions: material should be removed from the root region to form holes, and strip-shaped material can be removed near the neutral axis. In the final hole pattern design, holes are designed on the piezoelectric motion arm based on the optimization results. Root region: Design two rows of staggered elliptical holes with a major axis of 10μm (perpendicular to the length of the piezoelectric moving arm), a minor axis of 6μm, a hole spacing (center distance) of 15μm, and a row spacing of 12μm. The opening area extends 200μm backward from the fixed end.

[0048] Neutral axis region: A row of long strip holes is designed along the center line of the piezoelectric moving arm. The holes are 80μm long, 8μm wide, and 40μm apart, extending from 300μm from the root to 200μm from the free end.

[0049] Free end area: No openings.

[0050] The designed piezoelectric MEMS fan was validated: The piezoelectric MEMS fan with the opening was re-simulated, and the first-order resonant frequency increased to 24.2kHz, while the maximum tensile stress decreased to 28MPa (a 38% reduction). The fatigue life (10) was estimated using the SN curve of the Copper alloy. 7 The corresponding stress amplitude is 40 MPa, 10 9 (corresponding to 25MPa), the lifespan of the solid piezoelectric motion arm is approximately 3×10⁻⁵ MPa. 7 The lifespan of the perforated piezoelectric motion arm is >10. 9This represents an improvement of over 30 times. On the other hand, in terms of fabrication process, SOI wafers (15μm silicon device layer) are used, with each thin film layer deposited sequentially. Finally, deep reactive ion etching is used to simultaneously etch the cantilever beam shape and internal openings. After releasing the structure, testing showed an actual resonant frequency of 23.8kHz, consistent with simulation results.

[0051] In another embodiment, taking a double-ended fixed-beam piezoelectric MEMS fan as an example, a double-ended fixed-beam piezoelectric MEMS fan suitable for high-flow-rate heat dissipation is provided. The dimensions of the piezoelectric moving arm of this piezoelectric MEMS fan are: length 2000μm, width 400μm, and total thickness 12μm (the support layer is made of SiN). x The piezoelectric MEMS fan has a thickness of 1.5 μm, a lower electrode made of Pt with a thickness of 0.2 μm, a piezoelectric film made of PZT with a thickness of 3 μm, and an upper electrode made of Pt with a thickness of 0.2 μm. First, stress analysis was performed on the piezoelectric MEMS fan. Its first-order bending mode frequency was 18.7 kHz, and the maximum tensile stress, reaching 52 MPa, was located at the fixed ends of the piezoelectric moving arm. The stress in the central region of the piezoelectric moving arm was relatively low. In the opening design of this piezoelectric MEMS fan, a set of radial short slits, 30 μm long and 5 μm wide, were designed at each of the fixed ends of the piezoelectric moving arm, arranged radially at 45°, for a total of 8 slits, covering a 200 μm range at the ends. In the middle of the piezoelectric moving arm, a row of elongated holes, 100 μm long and 10 μm wide, with a spacing of 50 μm, was designed along its neutral axis. Finally, simulation showed that the peak stress decreased to 32 MPa (a reduction of 38%), the frequency increased to 19.2 kHz, and the fatigue life increased from 2 × 10⁻⁶. 7 The next upgrade is >10 9 Second-rate.

[0052] In another embodiment, a chip integrating the fatigue-resistant piezoelectric MEMS fan described in the above embodiments is proposed for heat dissipation of the chip body. This chip includes, but is not limited to: edge AI computing chips, thin and light SoCs, image ISP chips, SSD controller chips, NAND flash memory chips, cache chips, DSP digital signal processing chips, silicon photonics driver chips, high-speed transceiver ICs, integrated SoCs (CPU / GPU / NPU), fast-charging power management chips, image ISP chips, low-voltage CPUs, lightweight discrete / integrated GPUs, onboard power supply chips, and internally attached SSD controllers. The MEMS fan achieves localized heat dissipation at specific points on the chip, adapting to low-to-medium power consumption heat-generating chips in compact devices. Furthermore, this chip with integrated MEMS fan can be applied to AI glasses / XR wearable devices, SSD solid-state drives, high-speed optical modules, mobile phones / tablets, or thin and light laptops.

[0053] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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.

[0054] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A fatigue resistant piezoelectric MEMS fan comprising a support frame and at least one piezoelectric motion arm extending from the support frame, characterized in that, The piezoelectric motion arm has multiple stress-dispersing openings, and the distribution pattern of the multiple stress-dispersing openings is configured to disperse the stress concentration inside the piezoelectric motion arm during vibration.

2. The fatigue resistant piezoelectric MEMS fan of claim 1, wherein, The stress dispersion openings are distributed in the vibration strain neutral axis region of the piezoelectric moving arm; And / or, the stress-dispersing openings are distributed in the high-stress region at the root of the piezoelectric motion arm where it connects to the support frame.

3. The fatigue resistant piezoelectric MEMS fan of claim 1, wherein, The distribution pattern of multiple stress dispersion openings can be an array extending along the strain neutral axis of the piezoelectric moving arm, an arc-shaped outward expansion array around the root of the piezoelectric moving arm, or an array uniformly distributed on the plane of the piezoelectric moving arm.

4. The fatigue resistant piezoelectric MEMS fan of claim 1, wherein, The piezoelectric motion arm has a multilayer thin film structure, which consists of, from bottom to top: a support layer, a lower electrode, a piezoelectric thin film, an upper electrode, and a passivation layer. The stress dispersion opening penetrates the support layer, the lower electrode, the piezoelectric film, the upper electrode, and the passivation layer. Alternatively, the stress-dispersing opening penetrates the lower electrode, the piezoelectric film, and the upper electrode.

5. The fatigue-resistant piezoelectric MEMS fan of claim 4, wherein, The material of the support layer and the passivation layer is SiO2 or SiN x with a thickness of 0.5-2 μm; The material of the lower electrode is a Ti / Pt composite material or Au, and its thickness is 0.1 to 0.3 μm; The piezoelectric thin film is made of ScAlN, PZT or AlN, and its thickness is 0.5 to 3 μm; The upper electrode is made of Al or Pt and has a thickness of 0.1–0.3 μm.

6. The fatigue resistant piezoelectric MEMS fan of claim 1, wherein, The minimum size of the stress dispersion opening is 1μm to 20μm; The minimum spacing between adjacent stress-dispersing openings shall not be less than 1.5 times the thickness of the piezoelectric moving arm.

7. The fatigue resistant piezoelectric MEMS fan of claim 1, wherein, The piezoelectric moving arm is a cantilever beam structure or a double-end fixed beam structure.

8. A stress-optimized design method for a fatigue-resistant piezoelectric MEMS fan, characterized by, It is used to determine the stress dispersion aperture pattern on the fatigue-resistant piezoelectric MEMS fan as described in any one of claims 1 to 7; Stress optimization design methods include: A three-dimensional finite element model of the piezoelectric motion arm is established; A piezoelectric drive excitation is applied to a three-dimensional finite element model to solve the vibration modes and stress distribution of the piezoelectric motion arm at the target operating frequency, and a stress distribution cloud map is obtained. Based on the distribution cloud map, with the goal of maximizing the fatigue safety factor or minimizing the peak stress, and taking the material distribution in the plane of the piezoelectric motion arm as the design variable, topology optimization is performed under the given volume constraints to generate preliminary opening layout suggestions. The initial opening layout suggestions are transformed into specific opening patterns; harmonic response analysis and fatigue life prediction are performed on the three-dimensional finite element model with opening patterns, and the reduction in peak stress and the improvement in fatigue life are evaluated; if the evaluation results do not meet expectations, the opening pattern, size or distribution is adjusted. Repeat the topology optimization and aperture pattern adjustment process until the design requirements are met to determine the final stress-dispersion aperture pattern.

9. A method of making a fatigue resistant piezoelectric MEMS fan, comprising: It fabricates the fatigue-resistant piezoelectric MEMS fan as described in any one of claims 1 to 7; the fabrication method includes: The stress-dispersing opening is etched in the same or consecutive process steps in which the piezoelectric moving arm is released using a deep etching process to form its outer contour.

10. A chip, characterized by It integrates a fatigue-resistant piezoelectric MEMS fan as described in any one of claims 1 to 7 for heat dissipation.

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