Wavelength-Tunable Interference Filter with Offset Bonding
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Solution Overview
Problem
Existing wavelength-tunable interference filters face challenges in miniaturization due to large planar size, which can compromise substrate bonding strength and reliability, as reducing the bonding area to minimize size may lead to substrate separation and decreased reliability.
Innovation Solution
The design incorporates a first substrate with a moving part, a diaphragm part, and an outer circumferential part of varying thickness, with the first electrode positioned over a range from the diaphragm to the outer circumferential part, and a bonding part that maintains sufficient bonding strength by offsetting membrane stress moments, allowing for reduced size without compromising reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the electrode is provided over a range from the moving part to outside the diaphragm, then the planar size becomes large, but narrowing the bonding area to reduce size may reduce substrate bonding strength and cause separation
Solution Approach 1:
The substrate is divided into three distinct parts with different thicknesses: a moving part, a diaphragm part, and an outer circumferential part. This segmentation allows the electrode to be positioned specifically on the diaphragm part without requiring extension to the outer circumferential part, thereby reducing the bonding area while maintaining sufficient bonding strength through the thicker outer circumferential part.
Solution Approach 2:
Different parts of the substrate are given different thicknesses to serve different functions: the moving part has sufficient thickness for structural integrity, the diaphragm part is thinner to allow electrostatic actuation, and the outer circumferential part has greater thickness for strong bonding. This local quality differentiation enables miniaturization while maintaining bonding strength.
2Volume of moving object
If the bonding area is narrowed to reduce planar size, then the device becomes more compact, but the substrate bonding strength is reduced and separation may occur
Solution Approach 1:
Instead of increasing bonding area in the planar dimension to strengthen bonding, the invention increases the thickness (z-dimension) of the outer circumferential part. This dimensional transition allows the bonding area to be narrowed in the planar view while maintaining or even enhancing bonding strength through increased thickness.
Solution Approach 2:
The substrate is designed as a composite structure with regions of different thicknesses, effectively creating a multi-layered composite where each layer serves a specific function. The thicker outer circumferential part provides strong bonding, while the thinner diaphragm part enables actuation, achieving both miniaturization and strength.
3Area of stationary object
If the substrate thickness is reduced to enable miniaturization, then the planar size is reduced, but temperature changes may have greater impact on gap dimensions
Solution Approach 1:
The substrate exhibits local quality variation in thickness: the diaphragm part is thinner for actuation while the outer circumferential part is thicker for thermal stability. The thicker outer region provides thermal mass and structural rigidity that reduces the impact of temperature changes on the gap dimensions, even though the overall device is miniaturized.
Solution Approach 2:
The thicker outer circumferential part acts as a thermal and structural counterweight that compensates for the thermal expansion and contraction effects on the thinner diaphragm part. This counterbalancing structure reduces the net impact of temperature changes on the gap dimensions.
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
This configuration enables a compact wavelength-tunable interference filter with maintained reliability by offsetting membrane stress moments and ensuring sufficient bonding strength, reducing the planar size while minimizing the impact of temperature changes on gap dimensions.
Implementation Method 1
a first electrode provided at the first substrate, and a second electrode provided at the second substrate and facing the first electrode via a second gap G2
Implementation Method 2
a wavelength-tunable interference filter (optical filter) having a pair of mirrors arranged facing each other via an air gap
Data Source
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AI summary
A wavelength-tunable interference filter includes: a first substrate where a first mirror and a first electrode are provided; a second substrate where a second mirror corresponding to the first mirror and a second electrode facing the first electrode are provided; and a bonding part bonding the first substrate and the second substrate together. The first substrate includes a moving part where the first mirror is arranged, a diaphragm part holding the moving part in such a way that the moving part is movable in the Z-direction, and an outer circumferential part provided outside of the diaphragm part. The diaphragm part includes a planar part having a uniform thickness, and a first slope part having a thickness in the Z-direction incrementing as it goes from the planar part toward the outer circumferential part. The first electrode is provided over a range from the planar part to the first slope part. An outer edge of the first electrode, which is an edge opposite to the first mirror, is located at the first slope part. The bonding part is provided over a range from a part of the first slope part to the outer circumferential part.