Capacitive Touch Screen Using Plastic Sheet and Ground Plane
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Solution Overview
Problem
The development of cost-effective large format capacitive touch screens is hindered by the limitations of transparent conducting oxides (TCO) in achieving high frame rates and signal-to-noise ratios, and the high cost and interference issues associated with glass touch surfaces in large format devices.
Innovation Solution
A capacitive touch screen design utilizing a plastic optically clear touch sheet with a matrix of metallic electrodes and optically clear adhesive layers, configured to minimize electric interference from the LCD stack and reduce manufacturing costs by eliminating the need for rigid glass.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If glass touch surface is used in large format displays, then high dielectric constant and structural stability are achieved, but manufacturing cost increases, weight increases, and rigid-to-rigid bonding requires thick adhesive layers
Solution Approach 1:
The patent changes the material parameter from glass to plastic touch surface, which fundamentally alters the dielectric properties and mechanical characteristics. This parameter change enables flexible-to-rigid bonding that eliminates the need for thick adhesive layers while reducing manufacturing cost and weight.
Solution Approach 2:
The patent employs a plastic touch surface that can be bonded directly to the rigid LCD substrate without requiring a thick flexible adhesive layer. The plastic material itself provides the necessary flexibility and dielectric properties, eliminating the intermediate thick adhesive layer required in glass constructions.
2Reliability
If glass touch surface is used in large format displays, then high dielectric constant is achieved, but weight increases and rigid-to-rigid bonding requires thick flexible adhesive layers to absorb lamination strain
Solution Approach 1:
The patent changes the material from glass to plastic, which maintains sufficient dielectric constant for capacitive touch sensing while dramatically reducing weight. The plastic material provides the necessary electrical properties without the weight penalty of glass.
Solution Approach 2:
The patent uses plastic touch surfaces that are lighter and less expensive than glass, making large format displays more accessible to consumers. The plastic material achieves the required functional performance without the weight and cost burden of glass.
3Ease of manufacture
If plastic touch sheet is used instead of glass, then manufacturing cost decreases, but electric interference from LCD stack increases and touch sensing performance degrades
Solution Approach 1:
The patent introduces a ground plane as an intermediary layer between the LCD stack and the touch sensor electrodes. This ground plane shields the electrodes from electric interference generated by the LCD, enabling the use of plastic touch surfaces without sacrificing touch sensing performance.
Solution Approach 2:
The patent converts the potentially harmful electric interference from the LCD stack into a controllable parameter by introducing the ground plane. The ground plane captures and redirects the interference, transforming it from a degradation factor into a manageable aspect of the design that enables cost-effective plastic touch surfaces.
4Illumination intensity
If TCO touch sensor is used in large format displays, then transparency is achieved, but resistance increases and RC time constant becomes too slow for desired frame rate
Solution Approach 1:
The patent replaces expensive TCO materials with more economical metallic electrode alternatives that provide sufficient transparency and electrical performance for large format displays. This substitution reduces material cost while maintaining the required frame rate performance.
Solution Approach 2:
The patent changes the electrode material from TCO to metal-based alternatives, which fundamentally alters the electrical resistance and optical transparency parameters. The metallic electrodes provide lower resistance that enables the desired frame rate while maintaining acceptable transparency for large format displays.
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 design enables accurate multi-touch sensing in large format displays with reduced manufacturing costs and improved signal-to-noise ratios, while avoiding the interference and structural issues associated with glass surfaces.
Implementation Method 1
Capacitive touch screens measure changes in capacitance in a touch sensor having a matrix of rows and columns of electrodes
Implementation Method 2
an optically clear adhesive layer between the touch sensor and the display stack
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A display device with a capacitive touch screen display having a touch surface in close proximity to a display stack is provided. The display may include a touch sheet with a top surface, a touch sensor having a matrix of capacitors formed of electrodes positioned below the touch sheet and configured to exhibit a change in capacitance of at least one of the capacitors in response to a touch on the top surface by a digit or stylus of a user, a display stack positioned below the matrix of capacitors and configured to emit light through a top surface of the display stack to travel in a light emitting direction through the matrix of capacitors and the touch sheet. A distance between the top surface of the touch sheet and the top surface of the display stack is between about 225 and 1500 micrometers.