MEMS Switch Beam Plating to Prevent NiO Stress Deflection
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Solution Overview
Problem
Nickel-containing alloys in MEMS devices are prone to stress and thermal expansion mismatch, leading to beam deflection and oxidation issues during high-temperature processes, which affect actuation performance and stability.
Innovation Solution
A two-layer structure is employed, comprising a nickel alloy first layer and a second layer of gold, platinum, or palladium, acting as a barrier to prevent nickel oxidation and minimize stress/thermal expansion mismatch, with the second layer being thinner and having similar thermal expansion to the first layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a nickel alloy layer is used in MEMS devices, then the beam can be formed with appropriate mechanical properties, but nickel oxidizes at high temperature to form high stress NiO layer causing beam deflection
Solution Approach 1:
A thin second layer (0.05-1.0 microns) of oxidation-resistant material (gold, platinum, or palladium) is deposited on the nickel alloy first layer. This intermediate layer acts as a barrier preventing nickel diffusion to the surface and subsequent oxidation, while being thin enough to minimize stress and thermal expansion mismatch effects on beam performance
Solution Approach 2:
The beam structure uses a composite layered approach with a nickel alloy first layer providing mechanical strength and a thin noble metal second layer providing oxidation protection. This composite structure combines the advantages of nickel alloy mechanical properties with the oxidation resistance of noble metals while minimizing the disadvantages of stress mismatch
2Reliability
If a thick second layer is used to prevent nickel oxidation, then oxidation protection is improved, but stress and thermal expansion mismatch cause increased beam deflection
Solution Approach 1:
The thickness of the second layer is precisely controlled within the range of 0.05-1.0 microns. This parameter optimization ensures sufficient oxidation protection while minimizing the layer's contribution to stress and thermal expansion mismatch, thereby reducing beam deflection
Solution Approach 2:
The second layer is applied locally only where needed for oxidation protection on the nickel alloy surface, rather than using a thick uniform coating throughout. This localized approach provides adequate protection while minimizing overall stress effects
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents nickel oxidation and reduces beam deflection, maintaining actuation performance and stability by using a thinner, low-stress, and thermally compatible second layer.
Implementation Method 1
The second layer may provide a barrier between the first layer and oxygen within the device chamber. This barrier may prevent nickel at the surface of the first layer from oxidizing at elevated temperature processing steps
Implementation Method 2
the second layer is deposited by electroplating
Implementation Method 3
the second layer is deposited by electroless deposition
Implementation Method 4
nickel within a nickel alloy can diffuse to the surface of the beam. If this high temperature process is performed in the presence of O2, this surface nickel can oxidize, forming a high stress NiO layer on the beam surface. As the nickel is oxidized, and the free nickel is consumed, more nickel continues to diffuse to the surface to replace it
Data Source
AI summary
A beam for a microelectromechanical system (MEMS) switch may include a first layer including a nickel alloy and a second layer on at least a portion of the first layer.