Laser Scribing Transparent Conductive Layer for Touch Sensors
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Solution Overview
Problem
The existing methods for forming capacitive touch sensor electrodes on LCDs are complex and prone to defects, especially when using lithographic processes after the LCD assembly, and laser ablation risks damaging the underlying color filter, black matrix, or organic planarizing layers.
Innovation Solution
A method using pulsed laser ablation with a 'top hat' beam profile to pattern transparent conductive layers on top of organic and color filter layers, ensuring minimal damage to underlying layers by controlling energy density and pulse length, allowing for direct formation of electrode structures within a single step.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If standard laser ablation is used to form electrode patterns in the TC layer, then the patterning process is simplified and can be performed after LCD assembly, but there is a significant risk that the CF, BM or OP layers below the TC will be damaged
Solution Approach 1:
The patent applies parameter changes by modifying the laser beam characteristics - specifically using a pulsed laser with controlled pulse duration (nanosecond to picosecond range) and energy density parameters. This allows the laser to ablate the TC layer while limiting thermal diffusion to underlying layers, thus simplifying the patterning process while preventing damage to CF, BM, or OP layers
Solution Approach 2:
The patent employs periodic action through pulsed laser irradiation instead of continuous laser exposure. The pulsed regime allows brief intervals between energy deliveries, preventing cumulative thermal damage to sensitive underlying layers while effectively removing TC material. The pulse duration is specifically controlled to be in the nanosecond to picosecond range to achieve this effect
2Manufacturing precision
If multi-step lithographic processes are used to form electrode structures, then the electrode patterns can be formed with good precision, but the process becomes complex and is prone to defects especially when carried out after LCD assembly
Solution Approach 1:
The patent replaces the mechanical/chemical lithographic system with a direct laser ablation system. Instead of using photoresist coating, exposure, development, and etching steps, the laser directly removes TC material wherever the beam is directed. This substitution maintains manufacturing precision through computer-controlled beam positioning while dramatically reducing process complexity and eliminating defects associated with multi-step lithography
Solution Approach 2:
The patent extracts and removes the complex lithographic process steps, keeping only the essential patterning function. By using laser ablation, the method extracts the core functionality of pattern formation while eliminating the cumbersome intermediate steps of lithography (resist application, exposure, development, etching), thus reducing device complexity while maintaining precision
3Weight of moving object
If the touch sensor is integrated directly into the LCD, then the device thickness and weight are reduced, but the risk of damaging underlying layers during electrode formation increases
Solution Approach 1:
The patent uses parameter changes in laser processing - specifically controlling pulse duration (nanosecond to picosecond), energy density, and beam wavelength - to enable direct integration of touch sensors into LCDs. These parameter adjustments allow selective removal of the TC electrode layer while preserving the underlying CF, BM, and OP layers, thus reducing device weight without increasing damage risk
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 approach enables efficient and defect-free formation of capacitive touch sensor electrodes, reducing the thickness and weight of devices by integrating the touch sensor directly into the LCD, offering a more efficient and reliable alternative to traditional lithographic methods.
Implementation Method 1
A method using pulsed laser ablation with a 'top hat' beam profile to pattern transparent conductive layers
Data Source
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AI summary
A method of forming an electrode structure for a capacitive touch sensor in a transparent conductive layer located on a transparent non-conductive layer which is located on a colour filter layer by a direct write laser scribing process using a pulsed solid state laser, the laser wavelength, pulse length and beam profile at the substrate being selected to have a wavelength in the range 257nm to 266nm, a pulse length in the range 50fs to 50ns, and a top hat beam profile having a uniformity of power or energy density between a value (Emax) and a minimum value (Emin) of less than 10%, where uniformity is defined as (Emax - Emin)/(Emax + Emin). 1 Grooves can thus be formed in the transparent conductive layer to electrically isolate areas of the transparent conductive layer on opposite sides of each groove with substantially no damage to the transparent non-conductive layer or the colour filter layer beneath the transparent conductive layer.