Copper Circuit Trace on Silicon Spring for MEMS
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Solution Overview
Problem
Micromechanical springs in MEMS devices face challenges in maintaining purely elastic behavior while carrying high electric currents, as pure metals used for conductivity deform plastically under mechanical stress, leading to inaccurate position determination and material fatigue.
Innovation Solution
A micromechanical structure with a silicon spring and copper circuit traces having a layer structure of contiguous copper layers, deposited using a Damascene process with alternating high and low current densities, resulting in fine-grained copper with increased yield point and high electrical conductivity, allowing elastic deformation and stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pure copper is used as a conductive material on the silicon spring, then electrical conductivity is improved, but the material deforms plastically under mechanical stress
Solution Approach 1:
The patent applies composite materials by combining copper with a specific underlying layer structure (silicon nitride barrier layer and silicon oxide layer) to achieve both high electrical conductivity and increased yield point. The copper layer is deposited on top of these barrier layers, creating a composite structure where the copper provides conductivity while the underlying layers provide mechanical support and prevent plastic deformation.
Solution Approach 2:
The patent changes the physical parameters of the copper by controlling the deposition process (PVD or CVD) to achieve specific grain sizes and crystallographic orientations. By optimizing deposition parameters such as temperature, pressure, and deposition rate, the copper layer achieves a fine-grained structure with high yield point while maintaining excellent electrical conductivity.
2Stability of the object's composition
If the spring is designed to keep tension below the yield point of pure metal, then plastic deformation is prevented, but this is not possible for many applications requiring high current
Solution Approach 1:
The patent uses composite materials to resolve this contradiction by creating a copper conductor layer on top of a silicon nitride barrier layer and silicon oxide layer. This composite structure allows the spring to carry high currents through the copper layer while the underlying barrier layers provide mechanical support that prevents plastic deformation, maintaining purely elastic behavior even under high tension.
Solution Approach 2:
The silicon nitride barrier layer and silicon oxide layer act as intermediaries between the copper conductor and the silicon spring. These intermediary layers transfer and distribute the mechanical stress, preventing concentration of stress in the copper layer that would lead to plastic deformation, while still allowing high current flow through the copper.
3Strength
If alloys are used instead of pure copper to increase yield point, then mechanical strength is improved, but electrical conductivity is reduced
Solution Approach 1:
Instead of changing the material composition to alloys, the patent changes the physical parameters of pure copper by controlling the deposition process. By optimizing deposition conditions (temperature, pressure, rate) and creating specific microstructures (fine grains, specific crystal orientations), the patent achieves increased yield point in pure copper while maintaining its high electrical conductivity, avoiding the trade-off inherent in using alloys.
4Strength
If multilayer conductive materials separated by insulating layers are used, then yield point is increased, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent creates a composite material structure with copper conductor layer on silicon nitride barrier layer and silicon oxide layer, achieving increased yield point through material composition rather than complex multilayer construction. This integrated approach combines the conductive, barrier, and mechanical support functions in a streamlined structure that is easier to manufacture than separate multilayer assemblies.
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 structure achieves reversible and reproducible elastic behavior with high electrical conductivity and thermal stability, reducing material fatigue and enabling accurate position determination, while minimizing technological complexity and maintaining high conductivity.
Implementation Method 1
The function of the spring is to deform mechanically in order, thus, to allow movement of the island with respect to the mainland. This deformation must be purely elastic, in order to be reversible and reproducible.
Implementation Method 2
Osaka et al., 'Electrochemical Deposition Process for ULSI Interconnection Devices,' in 'Modern Electroplating,' edited by Mordechay Schlesinger and Milan Paunovic, Chapter 13, describes a method in which pure copper is used for a current-carrying conductor, the copper being deposited electrochemically and patterned to form circuit traces, using the Damascene process.
Data Source
AI summary
A micromechanical structure includes a fixing point, a silicon spring, and a movable part. The silicon spring is connected to the fixing point at a first end and to the movable part at a second end. At least one copper circuit trace is situated on the silicon spring and extends at least from the first end to the second end. The copper circuit trace has a layer structure including a plurality of contiguous copper layers.