MEMS Mirror Array Planarization for Uniform Tilt and Height
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Solution Overview
Problem
Poor uniformity of MEMS elements, such as mirrors on a PLM or a DMD, limits the optical performance due to issues like inefficient diffraction patterns, low contrast, and ghost images, which are caused by uneven etching and incomplete filling of gap-filling substances in via structures.
Innovation Solution
A two-layer deposition and etching process using a non-photoactive organic polymer to uniformly fill and planarize via structures, ensuring a flat top surface for MEMS elements, thereby improving uniformity and optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional single-layer deposition and etching processes are used to fill via structures, then the manufacturing process is simpler and faster, but the top surface remains uneven and MEMS element uniformity deteriorates
Solution Approach 1:
The deposition process is segmented into multiple layers (first layer and second layer of non-photoactive organic polymer) with different functions. The first layer fills the via structure while the second layer planarizes the top surface, allowing each layer to optimize for its specific purpose rather than requiring a single thick layer to accomplish both tasks.
Solution Approach 2:
The first layer of non-photoactive organic polymer is deposited and cured before the second layer to preliminarily fill the via structure and provide a base for subsequent planarization. This preliminary filling action enables the second layer to focus solely on creating a flat top surface without worrying about via filling completeness.
2Manufacturing precision
If gap-filling substances are used to fill via structures, then via filling is improved, but uneven etching occurs causing non-uniform MEMS element heights and tilt angles
Solution Approach 1:
The patent uses the same non-photoactive organic polymer material for both the first and second layers, ensuring homogeneous material composition throughout. This homogeneity guarantees uniform etching rates across all layers during the etching process, eliminating the non-uniform etching that occurs when different materials with different etch rates are used.
Solution Approach 2:
The solution creates a composite structure using two layers of the same non-photoactive organic polymer material, where the first layer serves as the gap-filling substance and the second layer serves as the planarization layer. This composite approach maintains material consistency while achieving both via filling and surface planarization.
3Ease of manufacture
If photoactive organic polymer is used as gap-filling substance, then via filling is achieved, but the material requires additional photochemical processing steps increasing process complexity
Solution Approach 1:
The patent extracts the photoactive property from the organic polymer material, using only the non-photoactive version. This eliminates the need for photochemical processing steps while retaining the material's effectiveness as a gap-filling substance that can be cured through alternative methods such as thermal curing or UV curing without requiring photolithographic patterning.
Solution Approach 2:
The non-photoactive organic polymer serves as a temporary sacrificial material that is deposited, cured, and then completely removed after serving its purpose of defining the via structure and supporting the MEMS elements during fabrication. This disposable approach simplifies the process by eliminating the need for complex photochemical patterning steps.
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 process results in flatter and more uniform MEMS elements with improved optical performance, reducing ghost images and enhancing efficiency and contrast by ensuring consistent tilt angles and heights across an array of mirrors.
Implementation Method 1
A two-layer deposition and etching process using a non-photoactive organic polymer to uniformly fill and planarize via structures
Implementation Method 2
The first layer is cured to form a first cured layer. The second layer is cured to form a second cured layer
Data Source
AI summary
In an example, a MEMS device includes MEMS elements supported on a substrate. The MEMS elements satisfy one or more uniformity metrics. Various uniformity metrics may be used, include tilt angle of each MEMS element, height of each MEMS element, and shape of each MEMS element. To maintain uniformity among the MEMS elements are constructed such that the tilt angles, heights, and/or shapes of the MEMS elements are within acceptable range(s). In other examples, the MEMS elements may be on a wafer, in which case the uniformity metric(s) may be enforced across the wafer. The uniformity metric(s) may also be enforced across multiple wafers.