Black Color Stack for Capacitive Sensor
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Solution Overview
Problem
Conductive carbon pigments in black inks used for opaque regions in electronic devices interfere with capacitive sensors, and thick ink layers can affect sensor sensitivity and performance due to increased distance and potential contamination.
Innovation Solution
A thin, non-conductive black color stack is developed, comprising a light-absorbing tin layer and dielectric layers like silicon nitride or silicon oxide, with a pigment stack that adjusts refractive indices to maintain optical opacity while minimizing conductivity, allowing capacitive sensors to function effectively underneath.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If carbon pigments are used to achieve optical opacity, then the black ink becomes optically opaque, but the ink becomes conductive which interferes with capacitive sensor operation
Solution Approach 1:
The patent changes the material parameters by replacing carbon pigments with tin oxide (SnO2) pigment particles that have appropriate optical absorption properties but non-conductive electrical characteristics. This parameter change in material composition resolves the contradiction between achieving optical opacity and maintaining sensor functionality.
Solution Approach 2:
The patent creates a composite ink formulation combining tin oxide pigment particles with binder materials and optional conductive polymer分散 agents. This composite approach achieves both optical opacity through tin oxide and controlled electrical properties, preventing interference with capacitive sensors while maintaining black color appearance.
2Illumination intensity
If the ink layer thickness is increased to improve optical opacity, then the black coloring becomes more opaque, but the distance between the sensor and sensed object increases reducing sensor sensitivity
Solution Approach 1:
The patent changes the optical properties parameter by using tin oxide pigment particles with high refractive index and strong light absorption in the visible spectrum. This allows achieving adequate optical opacity with a thinner ink layer (maintained below 2 micrometers), thereby preserving capacitive sensor sensitivity while still providing sufficient black coloring and concealment.
3Illumination intensity
If the ink layer thickness is increased to improve optical opacity, then the black coloring becomes more opaque, but particles, voids, and contamination in the thicker ink layer affect sensor performance
Solution Approach 1:
The patent changes the ink layer thickness parameter to be maintained below 2 micrometers, which is sufficient for optical opacity when using tin oxide pigments with appropriate particle size and concentration. This reduced thickness parameter minimizes the presence of particles, voids, and contamination that would otherwise interfere with capacitive sensor readings.
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 provides a highly sensitive capacitive sensor operation with improved performance by maintaining sensor sensitivity and optical opacity, reducing the impact of ink layer thickness on sensor functionality.
Implementation Method 1
a relatively thin layer of a light absorbing material, such as tin
Implementation Method 2
The first dielectric layer has a first refractive index. The second dielectric layer has a second refractive index different from the first refractive index.
Data Source
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AI summary
An opaque cover for a capacitive sensor is provided. The cover includes a transparent substrate (202) and a black color stack disposed adjacent the transparent substrate. The black color stack includes a pigment stack having a first dielectric layer (204A), a second dielectric layer (204C), and a first light absorbing layer (204B positioned between the first and second dielectric layers. The light absorbing layer is one of tin, copper oxide or zinc oxide. The first dielectric layer (204A) has a first refractive index, is one of silicon oxide, silicon nitride or niobium oxide. The second dielectric layer, is one of silicon oxide, silicon nitride or niobium oxide, has a second refractive index different from the first refractive index. The black color stack also includes a plurality of second light absorption layers (204B) interleaved with a plurality of third dielectric layers (204A).