Optical Fingerprint Sensor Structure for Low Leakage Current
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Solution Overview
Problem
Fingerprint sensors integrated into display devices, such as smartphones, face issues with noise generation due to small sensing currents from PIN diodes, which affect the accuracy of fingerprint detection.
Innovation Solution
An optical sensor design featuring a substrate with a circuit element layer, a photoelectric element layer including a PIN diode structure with a self-assembled monolayer and bias electrode, and a protective layer to minimize leakage current, along with a method of manufacturing that includes oxygen plasma treatment to prevent etching of the insulating layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a PIN diode is used as the photoelectric element in the optical sensor, then the sensor can detect light for fingerprint sensing, but leakage current is generated which creates noise and reduces sensing accuracy
Solution Approach 1:
An insulating layer is introduced as an intermediary between the anode and the I-type layer in the PIN diode structure. This insulating layer acts as a mediator that blocks leakage current paths while maintaining the photoelectric functionality of the PIN diode, thereby reducing noise without compromising fingerprint sensing accuracy.
Solution Approach 2:
The patent modifies the electrical parameters of the PIN diode by introducing the insulating layer, which changes the current flow characteristics. This parameter change effectively reduces the leakage current magnitude, transforming the electrical behavior to minimize noise generation while preserving the light detection capability.
2Measurement precision
If external light sources are used for fingerprint sensing, then adequate lighting for detection is provided, but manufacturing costs increase
Solution Approach 1:
The display device's display elements serve a dual function: they act as both the display interface and the light source for fingerprint sensing. By utilizing the existing display structure as the illumination source, the patent eliminates the need for separate external light sources, thereby reducing manufacturing costs while maintaining adequate lighting for accurate fingerprint detection.
Solution Approach 2:
The patent merges the display function and the light source function into a single integrated structure. The display elements are combined with the fingerprint sensing system, allowing the same components to serve multiple purposes: displaying information and providing illumination for fingerprint capture, thus simplifying the overall system and reducing component count.
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 reduces leakage current noise, enhancing the accuracy of fingerprint sensing and reducing manufacturing costs by eliminating the need for external light sources, thus improving the overall performance of fingerprint detection systems.
Implementation Method 1
a self-assembled monolayer disposed on the photoelectric element
Implementation Method 2
reduces leakage current noise
Implementation Method 3
a photoelectric element layer including a photoelectric element... a P-Intrinsic-N (PIN) layer disposed on the lower electrode
Implementation Method 4
performing oxygen plasma treatment of the substrate after the bias electrode is formed
Data Source
AI summary
An optical sensor including: a substrate; a circuit element layer disposed on the substrate and including a circuit element; and a photoelectric element layer including a photoelectric element, a self-assembled monolayer, and a bias electrode connected to the photoelectric element, wherein the photoelectric element is connected to the circuit element, and wherein the self-assembled monolayer is disposed on the photoelectric element.