Sub-lithographic Diffractive MEMS Actuators
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Solution Overview
Problem
Conventional diffractive MEMS have limited angular light scattering capability and low fill factor due to minimum feature size limitations in lithographic techniques, restricting the ability to focus a larger solid angle of light without degrading contrast.
Innovation Solution
The method involves depositing a sacrificial layer and structural layers to form sub-lithographic diffractive MEMS with actuators having dimensions and pitches smaller than conventional lithographic limits, using a conformal sacrificial film to create sub-lithographic gaps, enabling higher scattering angles and fill factors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If cell pitch is reduced to increase scattering angle, then scattering angle increases, but fill factor drops below 50%
Solution Approach 1:
The patent introduces a temporal dimension to the fabrication process by using sacrificial layers that are removed after structural layer deposition. This allows the cell pitch to be defined by the sacrificial layer thickness rather than lithographic limits, enabling sub-lithographic pitch dimensions while maintaining adequate fill factor through precise control of the sacrificial layer thickness.
Solution Approach 2:
The sacrificial layer is deposited and patterned beforehand to define the cell pitch dimensions before the structural layers are formed. This preliminary action establishes the sub-lithographic pitch geometry that constrains subsequent structural layer deposition, allowing the final device to achieve pitch dimensions smaller than conventional lithography can directly pattern.
2Quantity of substance
If minimum feature size is reduced to increase fill factor, then fill factor improves, but manufacturing precision deteriorates due to lithography limits
Solution Approach 1:
The sacrificial layer acts as an intermediary element that mediates between the lithographic patterning process and the final structural geometry. By patterning the sacrificial layer at relaxed lithographic dimensions and then using it to define sub-lithographic features through conformal deposition, the method achieves high precision feature dimensions without being constrained by lithography resolution limits.
Solution Approach 2:
The patent changes the controlling parameter for feature size from lithographic resolution to sacrificial layer thickness. Since the sacrificial layer thickness can be controlled with high precision through deposition processes rather than lithography, this parameter change enables manufacturing precision at dimensions below the lithographic resolution limit while maintaining high fill factor.
3Ease of manufacture
If conventional lithography is used to pattern actuators, then manufacturing ease is maintained, but device complexity increases due to inability to achieve sub-lithographic dimensions
Solution Approach 1:
The fabrication process is segmented into distinct stages: sacrificial layer patterning at relaxed dimensions, conformal structural layer deposition, and sacrificial layer removal. This segmentation allows each stage to be optimized independently - the patterning stage uses conventional lithography for ease of manufacture, while the deposition and release stages create the sub-lithographic final structure, thereby reducing device complexity constraints.
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 approach allows for increased scattering angles and high fill factors, enabling a larger solid angle of light to be focused without degrading contrast, while maintaining high diffraction efficiency.
Implementation Method 1
conformably depositing a sacrificial film on the patterned structural layer
Implementation Method 2
removing the sacrificial layer and sacrificial film to release the plurality of actuators
Implementation Method 3
Diffractive MicroElectroMechanical Systems or MEMs use electrical signals to move micromechanical structures to control or modulate light incident thereon
Data Source
AI summary
A diffractive MicroElectroMechanical systems and a method of fabricating the same are provided. In one embodiment, the method comprises: depositing a sacrificial layer onto a substrate; depositing a first structural layer on the sacrificial layer and patterning the structural layer to form a patterned structural layer including plurality of actuators; conformably depositing a sacrificial film on the patterned structural layer; depositing a second structural layer on the sacrificial film; planarizing the second structural layer to expose the sacrificial film and the plurality of actuators; and removing the sacrificial layer and sacrificial film to release the plurality of actuators, each of the plurality of actuators separated from the second structural layer by a thickness of the conformal sacrificial film. Other embodiments are also provided.