Stress-Bent 3D Microstructures With Controlled Sacrificial Release
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Solution Overview
Problem
Existing methods for fabricating 3D microstructures, particularly microlenses, face challenges in reproducibility and predictability of shape, with techniques like grayscale lithography being costly and 3D pattern printing facing difficulties in creating molds for small dimensions, while microdisks deform unpredictably upon release due to stress relaxation.
Innovation Solution
A manufacturing process involving a stack of layers with controlled residual stress, including a supporting substrate, sacrificial layer, and tensor layer, where selective removal of the sacrificial layer induces controlled deformation of the layer of interest, allowing precise shaping through the tensor layer's residual stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If microdisks are released from substrate to enable deformation, then three-dimensional shape is achieved, but deformation direction and magnitude become uncontrollable
Solution Approach 1:
A sacrificial layer is introduced as an intermediary element between the microdisk and substrate. This layer enables controlled deformation by being selectively removed in specific patterns, allowing the microdisk to deform in predetermined directions and magnitudes while maintaining manufacturing precision
Solution Approach 2:
The sacrificial layer is deposited and patterned before the microdisk is released. This preliminary action creates a pre-planned deformation pathway, ensuring that when the microdisk is released, it deforms in the desired direction and magnitude rather than randomly
2Shape
If grayscale lithography is used to fabricate microlens arrays, then three-dimensional structures are obtained, but manufacturing cost increases significantly
Solution Approach 1:
Instead of using complex grayscale lithography, the invention uses a simple binary mask to define the sacrificial layer pattern. This copying approach replicates the desired microlens shape through the deformation process itself, avoiding the need for expensive grayscale lithography equipment and multiple exposure steps
Solution Approach 2:
The invention changes the approach from directly writing the 3D shape through lithography exposure parameters to creating the shape through mechanical deformation controlled by the sacrificial layer removal pattern. This parameter change simplifies the manufacturing process and reduces costs
3Shape
If 3D pattern printing is used to create microlens molds, then microlens structures are formed, but mold fabrication becomes challenging at small dimensions
Solution Approach 1:
The invention creates the microlens shape by copying the pattern of the sacrificial layer removal rather than requiring a physical 3D mold. The sacrificial layer pattern acts as a negative template, and its selective removal copies the desired microlens shape through deformation, eliminating the need for complex small-dimension mold fabrication
Solution Approach 2:
The microdisk acts as a flexible thin film that can be deformed into the desired 3D shape. This flexibility eliminates the need for rigid 3D molds, particularly simplifying the process at small dimensions where mold fabrication would be challenging
4Shape
If thermal creep is used to fabricate microlenses, then three-dimensional shapes are obtained, but shape reproducibility and predictability deteriorate
Solution Approach 1:
The invention replaces the thermal creep process with a mechanically controlled deformation process. By using the sacrificial layer removal to induce stress and cause bending, the process becomes more predictable and reproducible compared to thermal creep, which relies on complex thermomechanical behavior
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
Enables reproducible, controlled deformation of microstructures with limited budget, achieving desired shapes and rotational symmetry, particularly for microlenses, with precise direction and magnitude of deformation defined by numerical simulations.
Implementation Method 1
microdisks used in photonics as two-dimensional whispering-gallery resonators can deform upon release from the substrate due to stress relaxation
Data Source
Figure 1
Figure 2A~2B
Figure 2C~2D
AI summary
The invention relates to a method for manufacturing a three-dimensional structure comprising supplying a stack (1) consisting of, stacked along a so-called vertical direction (Z), a support substrate (400), a sacrificial layer (300), a layer of interest (200) having a flank (203), and a tensor layer (100) having a flank (103), the tensor layer having a residual stress σ100. The method also includes removing a shrinkage portion (350) of the sacrificial layer, while retaining a remaining portion (360) of the sacrificial layer underlying the layer of interest. The shrinkage portion is located at the edge of a lateral portion (250) of the layer of interest extending from the entire flank of the layer of interest. The residual stress σ100 of the tensor layer is configured to cause bending of the layer of interest during the shrinkage step of the shrinkage portion.