MEMS Mirror Drive Coil Diffusion Barrier
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Solution Overview
Problem
Mirror drive devices using MEMS technology face issues with short-circuiting due to diffusion of metallic materials like Cu into insulating layers, leading to conduction faults, especially when employing materials with low electrical resistance.
Innovation Solution
A mirror drive device design featuring a substrate with a spiral groove containing a drive coil made of a first metallic material, covered by a second metallic material layer that suppresses diffusion, and an insulating layer to prevent short-circuiting, allowing for a higher density coil and increased Lorentz force, thereby enhancing the mirror's range of movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Cu is used as the metallic material for the drive coil to achieve low electrical resistance, then electrical resistance is reduced, but diffusion into the insulating layer occurs causing short-circuiting
Solution Approach 1:
A covering layer made of W (tungsten) or Mo (molybdenum) is introduced as an intermediary between the Cu drive coil and the insulating layer. This covering layer acts as a diffusion barrier that prevents Cu atoms from migrating into the insulating layer, thereby eliminating short-circuiting while allowing the Cu coil to maintain its low electrical resistance property.
Solution Approach 2:
The patent employs a composite structure consisting of multiple material layers: the Cu drive coil embedded in a groove, covered by a W or Mo covering layer, and then covered by an insulating layer. This composite material structure combines the electrical conductivity benefits of Cu with the diffusion barrier properties of W or Mo, resolving the contradiction between low resistance and diffusion prevention.
2Force
If the drive coil is wound in spiral fashion to increase Lorentz force, then the range of mirror movement is increased, but the complexity of external connection increases
Solution Approach 1:
The patent resolves the external connection complexity by transitioning from a planar two-dimensional connection approach to a three-dimensional approach. The external connection conductor is positioned to pass through the insulating layer at a location where it does not intersect with the spiral drive coil, utilizing the vertical dimension to achieve clean separation between the coil structure and connection paths.
3Manufacturing precision
If the metallic material is embedded by damascene process to achieve fine etching, then manufacturing precision is improved, but diffusion into insulating layer occurs causing short-circuiting
Solution Approach 1:
The covering layer is formed on the metallic material before the insulating layer is deposited. This preliminary action of adding the diffusion barrier layer prevents the harmful diffusion effect from occurring in subsequent processing steps, while allowing the damascene process to achieve its fine etching precision benefits.
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 short-circuiting, allowing for a larger range of mirror movement and maintaining low electrical resistance, even with materials prone to diffusion like Cu or Au, by using a covering layer to suppress diffusion into the insulating layer.
Implementation Method 1
a covering layer constituted by a second metallic material that suppresses diffusion of the first metallic material and extends as far as the main face so as to cover the aperture of the groove
Implementation Method 2
When current flows in the drive coil, a Lorentz force is generated in the drive coil by interaction with the magnetic field generated between the pair of permanent magnets, causing the movable frame to rotate with respect to the fixed frame
Implementation Method 3
a magnet that forms a magnetic field around the movable section
Data Source
AI summary
A mirror drive device is provided whereby conduction faults due to short-circuiting can be eliminated.A mirror drive device 1A is provided with a fixed frame, a movable frame 14, a mirror, and a permanent magnet 10. The movable frame 14 has a substrate 100, a drive coil 18, covering layer 102 and an insulating layer 104. The substrate 100 includes a groove 100a extending in spiral fashion and located at the side of the main face S4. A drive coil 18 is constituted by metallic material arranged within the groove 100a. The covering layer 102 extends to above the main face S4 so as to cover the aperture of the groove 100a and is constituted by metallic material that suppresses diffusion of the metallic material constituting the drive coil 18. The insulating layer 104 is arranged on the main face S4 and the covering layer 102. An external-connection conductor 28b that is electrically connected with the inside terminal of the drive coil 18 three-dimensionally intersects the drive coil 18, through the insulating layer 104.