Fingerprint Sensor Optical Stack for Parasitic Noise Isolation
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Solution Overview
Problem
The reduction in thickness of the optical layer in fingerprint sensors leads to signal interference between the display panel and the light sensing layer, causing noise reflection in the sensing signals due to parasitic capacitance.
Innovation Solution
Incorporating a light-blocking conductive layer and a light guide unit with lenses, collimators, or pinholes to minimize noise interference by separating the signal lines of the display panel and the fingerprint sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the thickness of the optical layer is reduced to prevent interference with other components, then the space for component arrangement is improved, but signal interference between display panel signal lines and light sensing layer signal lines increases
Solution Approach 1:
A light-blocking layer is introduced as an intermediary component between the display panel and the light sensing layer. This layer selectively blocks light paths that would cause parasitic capacitance coupling between scan lines and sensing lines, while allowing necessary light to reach the sensor. The light-blocking layer acts as a mediator that prevents harmful optical interference without compromising the thin-profile design.
Solution Approach 2:
The optical path is segmented by dividing it into blocked regions and transmitted regions. The light-blocking layer creates distinct zones where light is either blocked or allowed to pass through, enabling selective control over light propagation. This segmentation prevents parasitic capacitance coupling in specific areas while maintaining optical functionality in other areas.
2Volume of moving object
If the optical layer thickness is reduced, then the device profile is improved, but noise reflection in sensing signals increases due to parasitic capacitance
Solution Approach 1:
The light-blocking layer serves as a mediator that eliminates the source of noise reflection by blocking stray light paths. This prevents parasitic capacitance from coupling scan line noise into sensing lines, thereby improving sensing signal accuracy while maintaining the reduced thickness design.
Solution Approach 2:
The invention converts the harmful effect of thin optical layers (which cause parasitic capacitance and noise) into a benefit by using the same thin-profile advantage while adding a light-blocking layer that eliminates the noise source. The light-blocking layer transforms the problematic direct coupling into a controlled optical path that benefits from the thin design without suffering from its drawbacks.
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 effectively reduces noise reflection by isolating the scan and sensing signals, enhancing the accuracy of fingerprint recognition.
Implementation Method 1
a light-blocking conductive layer LCSL disposed on the common electrode CE and including light transmitting holes LTH
Implementation Method 2
a light guide unit 420 disposed on the light-blocking conductive layer LCSL
Implementation Method 3
a light sensing element PD that includes a sensing electrode RE disposed on the substrate FSUB, a semiconductor layer PSEM disposed on the sensing electrode RE, and a common electrode CE disposed on the semiconductor layer PSEM
Data Source
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AI summary
A fingerprint sensor including: a substrate; a light sensing element that includes a sensing electrode disposed on the substrate, a semiconductor layer disposed on the sensing electrode, and a common electrode disposed on the semiconductor layer; a light-blocking conductive layer disposed on the common electrode and including light transmitting holes; and a light guide unit disposed on the light-blocking conductive layer.