Monolithic MEMS SLMs With SiGe Ribbons and Integrated Drivers
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Solution Overview
Problem
Existing MEMS-based spatial light modulators face issues with slower switching speeds, higher power consumption, and lower drive channel counts due to separate die fabrication, which is exacerbated by incompatibilities between driver and modulator materials and processes, leading to damage and layout restrictions.
Innovation Solution
A monolithic microelectromechanical systems (MEMS) based spatial light modulator with a driver integrated in a common substrate, utilizing a tensile amorphous silicon-germanium (SiGe) layer for structural support and ribbon electrodes, and a CMOS-compatible driver layer below the modulators, allowing for simultaneous fabrication without interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the driver and MEMS modulators are fabricated on separate dies, then the fabrication processes can be optimized independently, but the switching speed decreases and wire bond failures increase
Solution Approach 1:
The patent integrates the driver circuitry and MEMS modulator array onto a single substrate, eliminating the need for separate dies and wire bonds. This merging of previously separate components resolves the reliability issues associated with wire bond failures while managing the complexity through unified fabrication processes.
2Ease of manufacture
If the driver is fabricated on a common substrate laterally separated from the MEMS array, then integration is achieved, but the high temperature deposition processes damage the driver metal layers and vias
Solution Approach 1:
The patent positions the driver circuitry in the lateral dimension, separated from the MEMS modulator array on the same substrate. This spatial arrangement allows the driver to be fabricated using standard CMOS processes while the MEMS structures are formed subsequently, avoiding thermal damage to the driver's metal layers and vias during high-temperature MEMS fabrication steps.
Solution Approach 2:
The substrate is divided into distinct functional regions: one for the driver circuitry and another for the MEMS modulator array. This segmentation allows each region to be optimized for its specific fabrication requirements, with the driver using CMOS-compatible processes and the MEMS structures using specialized processes that do not damage the driver.
3Manufacturing precision
If the top light reflective surfaces of the MEMS modulators are polished by CMP, then the surface finish is improved, but the height above the substrate surface is reduced, limiting the number of CMOS layers
Solution Approach 1:
The patent applies chemical mechanical polishing (CMP) selectively to specific regions of the substrate where light reflective surfaces are required, while leaving other regions unaffected. This localized polishing approach achieves the necessary surface finish for optical performance without excessively reducing the height of CMOS structures in the driver region, thereby preserving the ability to integrate multiple CMOS layers.
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 faster switching speeds, increased drive channel counts, and reduced power consumption by integrating the driver and modulators on a single substrate, maintaining functionality and layout flexibility.
Implementation Method 1
The electrostatic force generated by a drive voltage from a drive-circuitry or driver coupled to the substrate-electrode and ribbon-electrodes
Implementation Method 2
a first, light reflective surface that may be moved or deflected relative to another ribbon or to a second, passive or static light reflective surface
Implementation Method 3
each including a layer of tensile, amorphous silicon-germanium (SiGe layer) that serves as a structural layer and as a ribbon electrode
Data Source
AI summary
Monolithic microelectromechanical systems (MEMS) based spatial light modulators (SLM) including ribbon-type modulators and drivers integrally fabricated in or on a common substrate are provided. Generally, the monolithic MEMS-based SLM includes a common electrode in or on a substrate, a number of electrostatically displaceable ribbons, each including a tensile, amorphous silicon-germanium layer (SiGe layer) that serves as a structural layer and as a ribbon electrode, and a light reflective surface on the SiGe layer facing away from the surface on the substrate. A driver including a plurality of drive channels monolithically integrated in the substrate below the surface, the driver electrically coupled to the common electrode and each ribbon electrode and operable to apply voltages thereto to drive the plurality of ribbons to modulate light reflected from the light reflective surfaces.