Micromirror Arrays with Back-Side Etched Mirror Plates
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Solution Overview
Problem
Existing high-fill-factor micromirror arrays face challenges in achieving large optical apertures due to complex and costly fabrication processes, particularly with bulk silicon mirror plates, which require dedicated bonding steps and lack mechanical protection, limiting their suitability for applications like optical imaging.
Innovation Solution
The method involves forming silicon walls around the mirror plate during the back-side etch process to provide mechanical protection and using electrothermal bimorph actuation, allowing for flip-chip bonding or surface mounting without additional packaging, thereby simplifying the fabrication and integration process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If bulk silicon mirror plates are used to achieve large optical apertures, then the optical aperture size is improved, but the fabrication process complexity and cost increase due to dedicated bonding steps
Solution Approach 1:
The patent merges the mirror plate fabrication with the substrate processing by forming the mirror plate as part of the bulk silicon substrate through back-side etching. This integration eliminates the need for separate bonding steps to attach mirror plates, as the mirror plate is directly formed from the substrate material itself, thereby reducing fabrication complexity while maintaining large optical aperture capability
Solution Approach 2:
The patent inverts the conventional approach by forming the mirror plate on the back side of the substrate rather than on the front side. The substrate is first processed with actuators and bonding pads on the front, then the mirror plate is formed by etching through the substrate from the back side. This inversion allows the mirror plate to be integrated during substrate processing rather than requiring post-fabrication bonding
2Area of moving object
If bulk silicon mirror plates are used to achieve large optical apertures, then the optical aperture size is improved, but the device footprint increases
Solution Approach 1:
The patent moves the mirror plate formation to the back side of the substrate, utilizing the third dimension (depth/thickness of substrate) to accommodate the mirror plate. This allows the optical aperture to be formed without increasing the front-side footprint, as the mirror plate is positioned on the back side where space is available from the substrate thickness
3Area of moving object
If electrostatic or electrothermal actuation is used to achieve high fill factor, then the fill factor is improved, but the mirror plates lack mechanical protection
Solution Approach 1:
The patent provides mechanical protection for the mirror plate beforehand by forming protective structures during the substrate processing. The mirror plate is supported by the substrate structure and protective layers are applied during fabrication, preventing mechanical damage before the device is assembled and put into service
4Reliability
If dedicated bonding steps are added for mirror plate transfer, then the mirror plate can be attached, but the fabrication process becomes more complicated and expensive
Solution Approach 1:
The patent combines the mirror plate formation with the substrate processing steps. The mirror plate is formed by back-side etching of the substrate, integrating it into the existing fabrication process flow. This eliminates separate bonding steps and reduces the number of process stages while maintaining reliable mirror plate attachment
5Reliability
If flip-chip bonding is used for mirror plate transfer, then the mirror plate can be attached, but additional packaging steps are required
Solution Approach 1:
The patent merges the mirror plate formation with the substrate processing, eliminating the need for separate flip-chip bonding steps. The mirror plate is directly formed as part of the substrate structure through back-side etching, integrating the attachment function into the fabrication process itself and removing the need for additional packaging 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
This approach enables the creation of high-fill-factor micromirrors with large optical apertures, reduced device footprint, and enhanced mechanical protection, facilitating their use in applications such as endoscopic imaging and optical phased arrays with improved miniaturization and ease of integration.
Implementation Method 1
Certain implementations of the present invention utilize electrothermal bimorph actuation.
Implementation Method 2
electrothermal bimorph actuation
Data Source
AI summary
Embodiments of the subject invention relate to micromirror devices and methods of fabricating a micromirror/micromirror array. According to an embodiment, micromirrors can be fabricated from a semiconductor substrate where after forming actuators and bonding pads on a front side of the semiconductor substrate, the device is flipped over to have a portion of the back side of the substrate removed and formed to become the mirror plate surface. The subject micromirrors can allow further miniaturization of endoscopes and other optical applications without sacrificing the optical aperture through their surface mounting capabilities.