Shield Layer Reduces Parasitic Capacitance in Optical Sensors
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Solution Overview
Problem
Optical sensors used for detecting fingerprint and vein patterns face errors due to increased parasitic capacitance between signal lines or between signal lines and lower electrodes, leading to variations in potential and detection signal inaccuracies.
Innovation Solution
A detection device is designed with a substrate, photodiodes, signal lines, and a shield layer disposed between the signal lines or lower electrodes to reduce parasitic capacitance, improving signal accuracy by minimizing potential variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If signal lines are arranged closely to increase detection density, then productivity is improved, but parasitic capacitance increases causing detection accuracy to deteriorate
Solution Approach 1:
A shield layer is introduced as an intermediary component between adjacent signal lines and between signal lines and lower electrodes. This shield layer acts as a mediator that reduces parasitic capacitance coupling while allowing the signal lines to maintain close spacing for high detection density. The shield layer is electrically connected to a reference potential, creating a protective barrier that eliminates harmful capacitive interference.
2Measurement precision
If shield layer is added to reduce parasitic capacitance, then detection accuracy is improved, but device complexity increases
Solution Approach 1:
The shield layer serves multiple functions simultaneously: it reduces parasitic capacitance between adjacent signal lines, reduces parasitic capacitance between signal lines and lower electrodes, and provides electromagnetic shielding. By consolidating these protective functions into a single layer structure, the design achieves high detection accuracy without proportionally increasing device complexity.
Solution Approach 2:
The shield layer's electrical parameter (potential) is changed to match the reference potential, creating a stable electromagnetic environment. This parameter adjustment allows the shield layer to effectively reduce parasitic capacitance while maintaining compatibility with the existing photodiode and signal line structure, thereby improving accuracy without significant complexity increase.
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 introduction of a shield layer effectively reduces parasitic capacitance, enhancing the accuracy of detection signals and improving the overall detection process in optical sensors.
Implementation Method 1
If parasitic capacitance generated between the signal lines or between the signal line and the lower electrode that are adjacent to each other increases, variations in potential (also called crosstalk) may occur between the signal lines or between the signal line and the lower electrode that are adjacent to each other.
Data Source
AI summary
According to an aspect, a detection device includes: a substrate; a plurality of photodiodes that are arranged on the substrate and each include a lower electrode, a lower buffer layer, an active layer, an upper buffer layer, and an upper electrode that are stacked on the substrate in the order as listed; a plurality of signal lines electrically coupled to the respective lower electrodes of the photodiodes; a detection circuit electrically coupled to the photodiodes through the signal lines; and a shield layer disposed between the signal lines in plan view.