Light-Absorbing Conductive Nano-Material Electrode for Optical Fingerprint Sensors
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Solution Overview
Problem
Traditional optical fingerprint sensors using metal conductive materials for the lower electrode suffer from incomplete light absorption and conversion, leading to inaccurate current signals due to reflected light.
Innovation Solution
The use of a light-absorbing conductive nano-material, such as iron oxide doped with conductive metals, for the first electrode of the photodiode, combined with a curved side surface and a second electrode that fully surrounds it, increases light absorption and contact area, enhancing conductivity and signal accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal conductive material is used for the lower electrode of the photodiode to ensure conductivity, then the electrical conductivity is improved, but the light absorption is insufficient causing light to be emitted by the diode and resulting in inaccurate current signals
Solution Approach 1:
The patent applies composite materials by combining light-absorbing materials (such as ITO, IZO, or other transparent conductive oxides) with conductive materials to create a lower electrode that simultaneously achieves both light absorption and electrical conductivity. This composite structure resolves the contradiction by integrating multiple material properties into a single functional layer, allowing the electrode to absorb stray light while maintaining the necessary conductivity for signal readout.
2Reliability
If the lower electrode is made of metal conductive material to ensure conductivity, then the electrical connection is improved, but optical signals cannot be completely absorbed and converted into current signals leading to signal inaccuracy
Solution Approach 1:
The patent converts the harmful effect of stray light that would otherwise be lost or cause interference into a beneficial contribution to the current signal. By using light-absorbing conductive materials for the lower electrode, the stray light that passes through the photodiode is absorbed and converted into additional current signal, thereby improving the overall signal strength and accuracy while maintaining electrical connectivity.
3Measurement precision
If a light-absorbing conductive nano-material is used for the first electrode, then light absorption rate is improved, but the contact area with the second electrode needs to be increased to maintain conductivity
Solution Approach 1:
The patent applies curvature by forming the side surface of the first electrode with a curved portion instead of a flat surface. This curved geometry increases the surface area available for contact with the second electrode, thereby maintaining adequate electrical conductivity while allowing the use of light-absorbing conductive nano-materials that provide superior light absorption characteristics.
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 configuration improves light absorption rates and electrical conductivity, resulting in more accurate fingerprint recognition by effectively converting incident light into electrical signals.
Implementation Method 1
The traditional optical fingerprint sensor usually uses a Si:H diode as the photosensitive unit for photoelectric conversion
Implementation Method 2
there is an optical signal transmitted to the diode that cannot be completely absorbed and converted into a current signal, and thus a part of the light will be emitted by the diode
Data Source
AI summary
The present disclosure provides an optical fingerprint sensor and a display module. The optical fingerprint sensor includes a photodiode and a switching thin film transistor connected to the photodiode, in which the photodiode includes a first electrode made of a light-absorbing conductive nano-material; the first electrode is located in a same layer as a second electrode of the switching thin film transistor, and the first electrode includes a light-entering end surface facing a light-entering side and a side surface connected to the light-entering end surface, the side surface includes a curved portion, and the second electrode is at least connected to the curved portion.