Sculpted Raised Address Electrode for MEMS Pixel Torque
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Solution Overview
Problem
The monolithic design of semiconductor spatial light modulators (SLMs) faces challenges in shrinking structures while maintaining electrostatic torque delivery, which becomes sensitive to edge variations due to quasi-planar topography coupling, leading to non-uniformity in electrostatic torque delivery and reduced operational margin.
Innovation Solution
The use of sub-wavelength grey-scale lithography masking to planarize the photoresist spacer layer, removing thickness variations and curling in elevated address electrodes and spring tips, thereby improving electrostatic torque delivery and operational space by sculpting a raised address electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the DMD structure is shrunk to reduce pixel size, then the pixel density and resolution are improved, but the electrostatic torque delivery becomes more sensitive to edge variations and topography non-uniformity
Solution Approach 1:
The patent applies local quality by selectively modifying the topography of specific components (address electrodes, hinges, spring tips) through grey-scale lithography. Instead of uniformly planarizing the entire structure, the invention locally adjusts the height and shape of critical elements to compensate for edge effects and topography variations, thereby maintaining uniform electrostatic torque delivery even in shrunk pixel structures.
2Manufacturing precision
If multiple photomask layers are used to form the superstructure, then the fabrication precision and structural accuracy are improved, but the manufacturing complexity and process steps increase
Solution Approach 1:
The patent merges multiple photomask functions into a single grey-scale lithography mask. Instead of using separate photomask layers for different structural elements, the invention combines the patterning of address electrodes, hinges, and spring tips into one mask layer that directly defines the three-dimensional topography of all these components simultaneously, reducing fabrication steps while maintaining precision.
3Ease of manufacture
If quasi-planar topography is maintained throughout the structure, then the fabrication process is simplified, but the electrostatic torque delivery becomes non-uniform due to topography coupling
Solution Approach 1:
The patent applies preliminary action by pre-shaping the photoresist spacer layer topography before depositing metal layers. The grey-scale lithography mask creates the desired height variations in the spacer layer in advance, so that when subsequent metal layers are deposited, they naturally conform to the pre-established topography, eliminating the need for complex post-processing and ensuring uniform electrostatic torque delivery.
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 enhances electrostatic torque delivery and operational margin by reducing topography variations, improving the sensitivity and efficiency of the spatial light modulator's pixel elements, leading to more reliable and efficient light modulation.
Implementation Method 1
exposing the spacer layer to a grey-scale lithographic mask to planarize an upper surface of the spacer layer
Implementation Method 2
The addressing electrodes are selectively energized by a control circuit with a voltage potential to create an electrostatic attraction force causing the respective micromirrors to tilt towards the respective address electrode
Implementation Method 3
The image member has a light reflective upper surface configured to modulate incident light and form an image
Data Source
AI summary
A method of forming a micro-electromechanical systems (MEMS) pixel, such as a DMD type pixel, by forming a substrate having a non-planar upper surface, and depositing a photoresist spacer layer upon the substrate. The spacer layer is exposed to a grey-scale lithographic mask to shape an upper surface of the spacer layer. A control member is formed upon the planarized spacer layer, and an image member is formed over the control member. The image member is configured to be positioned as a function of the control member to form a spatial light modulator (SLM). The spacer layer is planarized by masking a selected portion of the spacer layer with a grey-scale lithographic mask to remove binge in the selected portion.