Finite Repeat Length Metal Mesh Electrodes for Touch Sensors
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Solution Overview
Problem
The design and fabrication of large format capacitive touch sensors with metal mesh electrodes are hindered by the complexity of creating unique electrode geometries, leading to computational limitations and high tooling costs, as well as the visibility of moiré effects when integrated with pixelated displays.
Innovation Solution
The solution involves a capacitive touch sensor design where the metal mesh electrodes and inter-electrode alleys are derived from a continuous mesh with a finite repeat length, using specific combinations of parameters to minimize moiré visibility and allow for step-and-repeat processes, reducing the complexity of tooling and fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If unique electrode geometries are designed for large format touch sensors, then sensing performance is improved, but computational complexity and tooling costs increase significantly
Solution Approach 1:
The electrode array is segmented into repeating units that can be independently designed and then replicated across the large format substrate. Each repeating unit contains a complete electrode geometry that can be tiled to form the full array, reducing computational complexity while maintaining sensing performance.
Solution Approach 2:
Instead of designing unique geometries for each electrode in large format sensors, the patent uses copying by creating a single repeating unit that is replicated across the entire array. This approach maintains the required sensing performance while dramatically reducing computational complexity and tooling costs.
2Ease of manufacture
If metal mesh electrodes are used in large format displays, then manufacturing feasibility is improved, but moiré effects become visible when integrated with pixelated displays
Solution Approach 1:
The patent introduces asymmetry by offsetting the repeating units in alternating rows or columns. This asymmetric arrangement disrupts the periodicity that causes moiré effects while maintaining the manufacturing feasibility of using standardized repeating units. The offset pattern prevents alignment between the mesh electrodes and display pixels that would otherwise create visible interference patterns.
3Ease of manufacture
If repeating units are used to reduce tooling complexity, then fabrication cost is reduced, but common edges of repeating units may become visible to users
Solution Approach 1:
The patent applies local quality by making the repeating units electrically discontinuous at their boundaries. This means that while the physical mesh continues across unit boundaries, the electrical connectivity is interrupted, preventing visible edge effects. Each repeating unit has differentiated edge properties that eliminate visual artifacts while maintaining the cost benefits of repetition.
Data Source
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Figure 3
Figure 4A
AI summary
An array of electrodes is comprised of a plurality of electrodes. Each electrode extends along a first direction X, and is periodically arrayed along a second direction Y perpendicular to X at a pitch pe. Each electrode further comprises a continuous periodic metal mesh having a square unit cell of edge length pm, the square unit cell having axes displaced by an oblique angle θ from X and Y. The array is configured such that θ = arctan (a/b) and pm = n*pe/(m*sqrt(a 2 + b 2 )), where a, b, m, and n are positive integers. In this way, the electrodes repeat with a finite repeat length, while rendering the common edges of the repeating units visually imperceptible by a user.