Photodiode Detection Device With Segmented Lower Electrode
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Solution Overview
Problem
Optical sensors used for detecting fingerprint and vein patterns face a trade-off between increasing capacitance and reducing the time required to read photocarriers, and maintaining sensitivity, as the area of the lower electrode affects both parameters.
Innovation Solution
A detection device with a substrate and photodiodes having a lower electrode with multiple openings, a lower buffer layer, an active layer, and an upper electrode, which reduces the time constant while minimizing the decrease in detection sensitivity by optimizing the resistance of the lower buffer layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the area of the lower electrode is increased to increase capacitance, then the detection sensitivity is improved, but the time required to read photocarriers increases
Solution Approach 1:
The lower electrode is divided into multiple segments by forming openings (through-holes or recesses) in the electrode structure. This segmentation reduces the effective capacitance between the lower and upper electrodes, thereby decreasing the time constant and enabling faster photocarrier readout while maintaining sufficient detection sensitivity through the remaining electrode area
Solution Approach 2:
The lower electrode is designed with a porous structure containing multiple openings distributed throughout the electrode area. This porous configuration reduces the effective capacitance by creating air gaps or voids between the lower and upper electrodes, thus reducing the time constant while preserving enough conductive material to maintain detection sensitivity
2Loss of time
If the area of the lower electrode is reduced to decrease the time required to read photocarriers, then the reading speed is improved, but the detection sensitivity is reduced
Solution Approach 1:
The lower electrode structure is optimized with non-uniform distribution of openings - denser in regions where fast readout is critical and sparser in regions where sensitivity is paramount. This local variation in electrode structure allows different areas to be optimized for their specific functional requirements, achieving both fast readout and high sensitivity simultaneously
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 allows for faster detection without compromising sensitivity, as the openings in the lower electrode reduce the time required for reading while maintaining effective capacitance.
Implementation Method 1
Optical sensors capable of detecting fingerprint patterns and vein patterns are known
Data Source
AI summary
According to an aspect, a detection device includes a substrate and a plurality of photodiodes arranged on the substrate. Each of the photodiodes includes 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 the lower electrodes are each provided with a plurality of openings.