MEMS Grating Upwards-Buckling Deformation Adhesion Prevention
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Solution Overview
Problem
Existing MEMS grating fabrication methods often result in adhesion between the movable grating structure and the substrate due to capillary attraction and hydrogen bonding, leading to permanent device failure.
Innovation Solution
A MEMS grating design featuring a deformable layer with compressive pre-stress, arranged above an insulation layer on a substrate, where the deformable layer includes movable and fixed grating bars with through holes that adjust compressive pre-stress and induce upwards-buckling deformation, increasing the initial gap and preventing adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If surface micromachining technology is used to fabricate MEMS grating, then the fabrication process is simple, but the movable grating structure adheres to the substrate due to capillary attraction and hydrogen bonding causing device failure
Solution Approach 1:
The patent applies preliminary action by introducing a releasing layer between the movable grating structure and substrate before the adhesion problem occurs. This releasing layer is deposited in advance to prevent capillary attraction and hydrogen bonding adhesion during the subsequent fabrication and releasing processes, thereby maintaining device reliability while keeping the surface micromachining process simple
2Object-affected harmful factors
If the thickness of the sacrificial layer is increased to reduce adhesion, then the initial gap between movable structure and substrate increases reducing capillary attraction, but the effective electrostatic force decreases and actuation voltage increases
Solution Approach 1:
The patent introduces a releasing layer as an intermediary substance between the movable grating structure and the substrate. This releasing layer mediates the interaction by preventing direct adhesion through capillary attraction and hydrogen bonding, allowing the use of thinner sacrificial layers without increasing power consumption or reducing electrostatic force effectiveness
3Object-affected harmful factors
If contact surface modification is used to reduce adhesive energy, then adhesion force is reduced, but the technology shows poor on-chip consistency and is greatly affected by environment humidity
Solution Approach 1:
The patent changes the material parameter of the interface between movable structure and substrate by introducing a releasing layer with specific material properties. This releasing layer provides consistent adhesion prevention across different chips without being significantly affected by environmental humidity, thereby improving on-chip consistency compared to surface modification techniques
4Reliability
If dry release or critical point drying is used to eliminate adhesion, then adhesion is eliminated remarkably, but the equipment cost is high and it is not suitable for large-batch production
Solution Approach 1:
The patent uses a releasing layer that can be deposited using standard thin-film deposition techniques available in conventional fabrication facilities. This approach replaces expensive specialized equipment like critical point drying devices with standard, cost-effective deposition processes, making the technology suitable for large-batch production while still effectively preventing adhesion
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 upwards-buckling deformation of the movable grating bars increases the initial gap between the grating bars and the substrate, reducing adhesion and preventing short circuits, while also enhancing the elastic restoring force and reliability of the device without increasing power consumption.
Implementation Method 1
the deformable layer includes movable grating bars and fixed grating bars, the fixed grating bars are fixedly connected with the insulation layer, the movable grating bars correspond to the cavities, included angles between the movable grating bars and the side wall of the insulation layer is smaller than or equal to 90°, and the movable grating bars are upwards-buckling camber surfaces
Implementation Method 2
after a sacrificial layer structure is released, a grating structure layer is prone to having a downward sunken deformation, so the movable grating structure is attached to the substrate due to an action of capillary attraction and a hydrogen bond of a liquid
Implementation Method 3
after a sacrificial layer structure is released, a grating structure layer is prone to having a downward sunken deformation, so the movable grating structure is attached to the substrate due to an action of capillary attraction and a hydrogen bond of a liquid
Implementation Method 4
a plurality of through holes are formed in the movable grating bars and used for adjusting a compressive pre-stress of the movable grating bars and changing a displacement amount of upwards-buckling of the movable grating bars
Data Source
AI summary
The present disclosure discloses a MEMS grating and a fabrication method. The MEMS grating includes a substrate layer, an insulation layer and a deformable layer. The deformable layer is made of a continuous conductive material, the insulation layer is distributed along transverse intervals on the substrate layer, and a cavity is formed between every two adjacent insulation layers. The deformable layer includes movable grating bars and fixed grating bars. The fixed grating bars are fixedly connected with the insulation layer, and the movable grating bars correspond to the cavities. A plurality of through holes are formed in the movable grating bars. During wet etching, the movable grating bars generate upwards buckling deformation, which increase an initial gap between the movable grating bars and a substrate. An adhesion effect caused by the wet etching is eliminated, which reduces permanent failures caused by the adhesion effect.