A method for designing a high-reliability, low-cost layered composite material for a MEMS device

Abstract

The application discloses a design method of a high-service-reliability and cheap layered composite material for MEMS devices. The method designs a composite layered material which is composed of metal nickel layers and nickel-tungsten alloy layers which are alternately stacked, fatigue cracks generated in the material during long-term service can be reduced in crack propagation rate through passivation, deflection and interface debonding, so that the service life of the material is improved; the grain size matching between the heterogeneous layers of the material can be regulated through heat treatment, and the strength of the material is further improved. The application has the following characteristics: (1) the material has low cost, reliable mechanical properties and long service life; (2) the designed layered metal composite material can inhibit the initiation and propagation of fatigue cracks during the service of the device, and reduce local stress concentration; (3) the grain sizes of adjacent layers can be flexibly regulated in space, so that the grain sizes are matched with each other, and the material obtains higher strength.

Description

Technical Field

[0001] This invention relates to the field of MEMS device technology, and more specifically to a design method for high-reliability, low-cost layered composite materials for MEMS devices. Background Technology

[0002] MEMS devices are miniature, movable components fabricated using microelectromechanical systems (MEMS) technology. These include sensors, actuators, and MEMS switches, and offer advantages such as low cost and functional integration. They are currently widely used in military security systems, the automotive industry, and wireless communications. For contact-type MEMS devices, mechanical service reliability is a critical performance indicator in the design. Materials are required to withstand conditions exceeding 10... 7 The effects of cyclic loading. Traditional MEMS devices, such as gold-gold contact switches, are widely used in MEMS switching due to their high chemical stability and low resistivity. However, the low hardness and strength of gold cause surface deformation and adhesive wear after multiple on-off cycles, ultimately leading to MEMS switch failure. How to select inexpensive alloy materials that can impart high performance and long service life has been a persistent focus and challenge in the research and development of microscale MEMS devices. Summary of the Invention

[0003] The purpose of this invention is to provide a design method for high-reliability, low-cost layered composite materials for MEMS devices. Compared with existing methods, this invention has the advantages of low material cost, high strength and long service life, providing new ideas for the design and manufacturing of MEMS devices.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A design method for a high-reliability, low-cost layered composite material for MEMS devices, wherein the layered composite material is composed of alternating layers of metallic nickel and nickel-tungsten alloy; wherein the metallic nickel layer is elemental nickel with a purity of 99.0% or higher, and the nickel-tungsten alloy layer is a nickel-tungsten alloy with a tungsten content of 9.0 to 18.0 at.%.

[0006] The thickness of a single nickel layer is 0.10–20.00 μm, the thickness of a single nickel-tungsten alloy layer is 0.02–5.00 μm, and the total thickness of the layered composite material is 100–200 μm.

[0007] In this layered composite material, the ratio of the grain size of the nickel-tungsten alloy layer to the grain size of the metallic nickel layer is 1:2 to 1:10, and the strength of the layered composite material is 1000 to 2200 MPa.

[0008] The layered composite material can be annealed at 100-250℃. After annealing, the ratio of the grain size of the nickel-tungsten alloy layer to the grain size of the metallic nickel layer in the composite material is 1:2 to 1:40, and the strength of the composite material can be increased by nearly 100MPa compared with that before annealing.

[0009] Compared with existing technologies, this invention provides a design and processing method for inexpensive layered metal materials that meet the material requirements of MEMS devices, exhibiting high mechanical stability and long service life, and has the following characteristics:

[0010] 1. Using layered materials of inexpensive metals such as nickel and nickel-tungsten alloys as materials for MEMS devices can replace precious metals and their alloys such as gold, platinum, rhodium and ruthenium currently used in MEMS switches, greatly reducing production costs;

[0011] 2. The designed layered metal composite material can reduce local stress concentration and suppress crack initiation and propagation caused by fatigue loads during device service;

[0012] 3. The designed heterogeneous stacked structure can improve material strength by flexibly adjusting the grain size matching degree of adjacent layers, and enable the material to suppress the initiation and propagation of fatigue cracks, thereby improving the reliability and service life of the material.

[0013] 4. The strength of this layered material before and after annealing is much higher than that of pure gold (350MPa) and precious metal alloys such as platinum-rhodium alloys (~1000MPa) used in MEMS switches; and its tensile fatigue service life can be increased by 1 to 3 times compared with pure nickel materials used in various MEMS sensors and actuators. Attached Figure Description

[0014] Figure 1 Scanning electron microscope image of a composite material formed by laminating a metallic nickel layer and a nickel-tungsten alloy layer.

[0015] Figure 2 Transmission electron microscopy (TEM) images of the nickel and nickel-tungsten layers of the composite material before and after annealing heat treatment; where: (a) before annealing heat treatment; (b) after annealing heat treatment.

[0016] Figure 3 The stress-strain curves of the composite material before and after annealing heat treatment are shown in the room temperature tensile engineering curves.

[0017] Figure 4 The room temperature high-cycle fatigue SN curves for nickel and nickel-tungsten layered materials. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0019] Example 1

[0020] like Figure 1 As shown, the layered composite material in this embodiment is formed by alternating layers of metallic nickel and nickel-tungsten alloy; wherein the metallic nickel layer is elemental nickel with a purity of 99.0%, and the nickel-tungsten alloy layer is a nickel-tungsten alloy with a tungsten content of 11 at.%. The thickness of a single layer of metallic nickel is 1.50 μm, and the thickness of a single layer of nickel-tungsten alloy is 0.15 μm.

[0021] A layered composite material with the aforementioned layer-to-thickness ratio and a total thickness of 100.00 μm was prepared by electrodeposition. The interface between the nickel-tungsten layer and the nickel layer was straight, and the grain size ratio was 1:2 to 1:10. After annealing the material for 1 hour, the grain size distribution of the nickel layer ranged from 20 nm to 150 nm, and the grain size of the nickel-tungsten layer was 7 nm. Figure 2 As shown, the ratio of the grain size of two adjacent nickel-tungsten layers to the grain size of the nickel layer is 1:3 to 1:22.

[0022] Figure 3 Typical room temperature tensile stress-strain curves of the materials before and after heat treatment are shown. It can be seen that the yield strength of nickel and nickel-tungsten layered materials can reach 1485 MPa, and the tensile strength can reach 1858 MPa, far exceeding the tensile strength of pure gold (~350 MPa) and platinum-rhodium alloy (1000±200 MPa). After annealing, the yield strength of the materials can reach 1721 MPa, and the tensile strength increases to 1898 MPa. High-cycle fatigue performance tests were conducted on nickel and nickel-tungsten layered materials. The fatigue loading stress amplitude was converted to an R=-1 stress ratio mode according to the Gerber relation to obtain... Figure 4 As shown by the SN curve, the fatigue life of this material can reach 10. 7 It did not fracture after 10 cycles, and its fatigue strength was 341 MPa, which is 1.2 to 2 times higher than the tensile fatigue strength (160-290 MPa) of pure nickel materials used in mainstream MEMS sensors and actuators. For MEMS switches, the actual application involves loading at the end of a cantilever beam. It is known that the high-cycle fatigue strength (10 MPa) of pure nickel materials under cantilever beam loading is... 7 The high-cycle fatigue strength limit (without fracture after 10 cycles) is 334 MPa, while the high-cycle fatigue strength limit of pure gold cantilever beams used in mainstream MEMS switches is only 230 MPa. The stress level is far higher than the fatigue load stress level in actual MEMS switch applications. Therefore, this layered material can fully meet the mechanical performance requirements for actual MEMS switch applications. It is evident that this material achieves excellent performance in various application fields of MEMS devices under different loading methods.

Claims

1. A design method for high-reliability, low-cost layered composite materials for MEMS devices, characterized in that: The layered composite material is composed of alternating layers of metallic nickel and nickel-tungsten alloy; wherein the metallic nickel layer is elemental nickel with a purity of 99.0% or higher, and the nickel-tungsten alloy layer is a nickel-tungsten alloy with a tungsten content of 9.0 to 18.0 at.%.

2. The design method for high-reliability, low-cost layered composite materials for MEMS devices according to claim 1, characterized in that: The thickness of a single nickel layer is 0.10–20.00 μm, the thickness of a single nickel-tungsten alloy layer is 0.02–5.00 μm, and the total thickness of the layered composite material is 100–200 μm.

3. The design method for high-reliability, low-cost layered composite materials for MEMS devices according to claim 1, characterized in that: In this layered composite material, the ratio of the grain size of the nickel-tungsten alloy layer to the grain size of the metallic nickel layer is 1:2 to 1:10, and the strength of the layered composite material is 1000 to 2200 MPa.

4. The design method for high-reliability, low-cost layered composite materials for MEMS devices according to claim 1, characterized in that: After the layered composite material is annealed at 100-250℃, the ratio of the grain size of the nickel-tungsten alloy layer to the grain size of the metallic nickel layer in the composite material obtained after annealing is 1:2 to 1:40, and the strength of the composite material can be increased by nearly 100MPa compared with that before annealing.

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