Sloped Electrode for Torsional Spatial Light Modulator
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Solution Overview
Problem
The electrostatic efficiency of torsional spatial light modulators is limited by elevated address electrodes that are sensitive to edge variations and field gradients, leading to potential failure due to species migration and shorting issues, especially as structure sizes shrink.
Innovation Solution
The introduction of sloped electrodes formed using a sub-wavelength grey-scale lithographic process, which maintains a uniform energy density and reduces edge sensitivity by positioning the image member substantially parallel to the control electrode when tilted, thereby enhancing electrostatic torque delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the address electrode is elevated and parallel to the micromirror when horizontal, then the electrostatic torque can be generated, but the electrostatic efficiency is limited due to field gradients and edge variations when the micromirror is tilted
Solution Approach 1:
The address electrode is transformed from a parallel configuration to a sloped configuration, introducing a spatial dimension change. The electrode surface is angled relative to the substrate, creating a non-uniform height profile that maintains optimal spacing and field uniformity across the electrode-micromirror interface during tilting operation.
Solution Approach 2:
Different portions of the address electrode are given different orientations. The electrode surface is divided into regions with varying slopes, where each local region is optimized to maintain uniform field distribution with the micromirror at its operating tilt angles, rather than using a single uniform parallel orientation.
2Force
If a higher bias operation is provided to increase torque generation, then the torque generation improves, but field gradient induced migration of species occurs causing failure
Solution Approach 1:
The geometric parameters of the address electrode are changed by introducing a slope angle. This structural parameter modification allows the system to achieve the required electrostatic torque through optimized geometry rather than increasing the electrical bias parameters, thereby avoiding field gradient induced species migration and maintaining device stability.
3Productivity
If the structure size is shrunk, then the device density increases, but the design becomes more sensitive to electrostatic torque delivery variations from edge effects
Solution Approach 1:
By sloping the address electrode surface, the effective interaction area between the electrode and micromirror is optimized in three-dimensional space. This dimensional change compensates for the reduced feature sizes, maintaining sufficient electrostatic coupling and reducing edge effect sensitivity even as overall structure dimensions are shrunk to increase device density.
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 configuration improves electrostatic torque generation and maintains a uniform electric field and field gradient, reducing the risk of failure and increasing the operational margin of the spatial light modulator.
Implementation Method 1
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 2
exposing the spacer layer to a grey-scale lithographic mask to shape an upper surface of the spacer layer
Implementation Method 3
The image member is substantially parallel to the control electrode when tilted over and towards the control electrode to establish a substantially uniform energy density
Data Source
AI summary
A method of forming a micro-electromechanical systems (MEMS) pixel, such as a DMD-type pixel, by depositing a photoresist spacer layer upon a substrate. The photoresist spacer layer is exposed to a grey-scale lithographic mask to shape an upper surface of the photoresist spacer layer. A control member is formed upon the shaped spacer layer, and has a sloped portion configured to maximize energy density. An image member is configured to be positioned as a function of the control member to form a spatial light modulator (SLM).