Grounded LCoS Mirror Structure for Voltage Latchup Reduction
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Solution Overview
Problem
Advanced liquid crystal on silicon (LCoS) devices face challenges with voltage latchup due to charge accumulation in multilayer structures, particularly in distributed Bragg reflector (DBR) layers, which can lead to unresponsive pixels and impaired optical performance during high-frequency switching.
Innovation Solution
A grounded mirror structure is formed by creating a conductive contact between the mirror layer and the metal contact layer, using a dry etch process to form a sloped trench and depositing a conformal metal layer, followed by an oxide inclusion to reduce shielding effects and voltage latchup without affecting the DBR or pixel performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a floating conductive mirror interposed between metal contact layer and DBR is used, then the LCoS structure can be formed, but charge accumulation occurs causing shielding effect and voltage latchup
Solution Approach 1:
The patent extracts the harmful floating charge accumulation by introducing a grounded mirror structure. The mirror layer is electrically connected to the metal contact layer through a via structure, removing the floating condition that causes charge buildup and shielding effects during high-frequency switching operations.
Solution Approach 2:
The patent introduces an intermediary via structure filled with conductive material that mediates the electrical connection between the mirror layer and the metal contact layer. This intermediary pathway provides a controlled ground connection that prevents charge accumulation while maintaining the mirror's reflective function.
2Reliability
If the mirror layer is grounded to prevent charge accumulation, then voltage latchup is reduced, but the optical performance may be affected
Solution Approach 1:
The patent applies local quality by grounding the mirror layer only in specific localized regions through via structures, rather than making the entire mirror layer conductive. This localized grounding approach prevents charge accumulation at critical points while preserving the optical reflective properties of the mirror layer in the display regions.
Solution Approach 2:
The patent segments the grounding function from the reflective function by using discrete via structures to create ground connections at specific locations, separating the electrical grounding requirement from the optical performance requirements of different mirror regions.
3Reliability
If a via structure is formed through the mirror layer to create ground contact, then electrical connection is achieved, but the mirror layer continuity is disrupted
Solution Approach 1:
The patent performs preliminary action by forming the via structure through the mirror layer before completing the mirror layer deposition. The via is created in the spacer layer first, then the mirror layer is deposited conformally over the via, allowing the mirror to bridge over the via opening and maintain continuity while still providing ground connection through the via fill material.
Solution Approach 2:
The patent uses nesting by placing the via structure within the mirror layer deposition sequence, where the via is formed first and then the mirror layer is deposited around and over it, creating a nested configuration where the ground connection is embedded within the continuous mirror structure.
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 solution effectively reduces shielding effects and improves performance by grounding the mirror layer, minimizing voltage latchup and maintaining optical performance in LCoS displays.
Implementation Method 1
The metal layer may be revealed by a dry etch process
Implementation Method 2
forming the mirror layer may include depositing a conformal coating of a metal overlying the spacer layer and the trench
Implementation Method 3
forming the oxide inclusion may include forming an oxide layer. The oxide layer may be conformal with the mirror layer
Implementation Method 4
The lithographic mask may include a window. Revealing the metal layer may also include etching a trench through the window
Data Source
AI summary
Processing methods may be performed to form a grounded mirror structure on a semiconductor substrate. The methods may include revealing a metal layer. The metal layer may underlie a spacer layer. The metal layer may be revealed by a dry etch process. The method may include forming a mirror layer overlying the spacer layer and the metal layer. The mirror layer may contact the metal layer. The method may also include forming an oxide inclusion overlying a portion of the mirror layer. The portion of the mirror layer may be external to the spacer layer.