Anti-Static Layer Sheet Resistance for Touch Sensing in LCD
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Solution Overview
Problem
Touch sensing in IPS mode and FFS mode LCD devices is hindered by anti-static layers made of transparent conductive materials like ITO and IZO, which discharge capacitance generated by user touch, preventing effective detection of touch input due to their high sheet resistance similar to metallic materials.
Innovation Solution
A touch sensing type LCD device with an anti-static layer on the outer side of the second substrate, featuring a sheet resistance of 107 to 109 ohms per square, allowing for static electricity dissipation without obstructing touch sensing, achieved by using zinc-tin-oxide (ZTO) with a thickness of 100 to 1000 angstroms, enabling the formation of a capacitor between the user's finger and the common electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an anti-static layer made of transparent conductive materials (ITO, IZO) is used, then static electricity protection is provided, but touch sensing capability is blocked due to high sheet resistance
Solution Approach 1:
The patent changes the sheet resistance parameter of the anti-static layer from conventional values (similar to metallic materials) to a specific range of 10^7 to 10^9 ohms per square. This parameter change allows the layer to differentiate between static electricity discharge (handled by the lower resistance path) and touch sensing signals (detected through the high impedance capacitive coupling), thereby resolving the contradiction between static protection and touch sensitivity.
Solution Approach 2:
The patent uses zinc-tin-oxide (ZTO) as a composite transparent conductive material to form the anti-static layer. ZTO provides optimized electrical properties with可调 sheet resistance in the 10^7 to 10^9 ohms per square range, combining both static electricity dissipation capability and touch sensing transparency, thus resolving the contradiction between these two functions.
2Object-generated harmful factors
If a conventional anti-static layer with sheet resistance similar to metallic materials is used, then effective static electricity discharge is achieved, but touch capacitance detection becomes impossible
Solution Approach 1:
The anti-static layer with sheet resistance of 10^7 to 10^9 ohms per square acts as an intermediary between the touch surface and the underlying electrode structure. It provides a controlled electrical pathway that allows capacitive coupling for touch sensing while still offering protection against static electricity discharge, mediating between these two conflicting requirements.
Solution Approach 2:
By changing the sheet resistance parameter to the specific range of 10^7 to 10^9 ohms per square, the anti-static layer creates an electrical impedance that is high enough to maintain capacitive coupling for touch detection but low enough to provide static electricity protection, thereby resolving the contradiction between these two functions.
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 anti-static layer with a sheet resistance of 107 to 109 ohms per square effectively serves as a conductive path for static electricity while allowing touch detection by forming a capacitor with the common electrode, preventing device damage from static and enabling accurate touch sensing.
Implementation Method 1
an anti-static layer on an outer side of the second substrate 271, the anti-static layer having a sheet resistance of about 10^7 to 10^9 ohms per square (Ω/sq)
Implementation Method 2
allowing for static electricity dissipation without obstructing touch sensing, achieved by using zinc-tin-oxide (ZTO) with a thickness of 100 to 1000 angstroms, enabling the formation of a capacitor between the user's finger and the common electrode
Data Source
AI summary
A touch sensing type liquid crystal display device includes an array substrate including a first substrate, a common electrode, a pixel electrode, and a touch sensing unit; a color filter substrate including a second substrate and facing the array substrate; an anti-static layer on an outer side of the second substrate, the anti-static layer having a sheet resistance of about 107 to 109 ohms per square (Ω/sq); and a liquid crystal layer between the first substrate and an inner side of the second substrate.