Fingerprint Sensor Light Direction Switching Layer
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Solution Overview
Problem
Conventional fingerprint recognition sensors face challenges in achieving high image definition and uniformity due to light loss through cover glass, leading to increased thickness and volume, and difficulty in coupling with other devices like display panels.
Innovation Solution
A fingerprint recognition sensor design featuring a light source and a light direction switching layer with a right-angled triangular cross-section, along with a cover layer, which enhances light reflection and reduces thickness by using photo sensors to detect total-reflected light from the cover layer, facilitating integration with display devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate lens and detector are used for fingerprint recognition, then the recognition function is achieved, but the total thickness and volume of the system increase
Solution Approach 1:
The patent combines the lens and detector functions into an integrated sensor pixel structure. The sensor pixel directly senses light reflected from the fingerprint without requiring a separate lens, merging multiple optical components into a single integrated element that reduces overall system thickness while maintaining recognition functionality.
Solution Approach 2:
The sensor pixel is designed to perform multiple functions: it acts as both the light-sensing element and the detection component, eliminating the need for separate dedicated lens and detector components. This multi-functional design reduces the number of parts and overall system volume.
2Ease of operation
If a separate driving transistor is provided externally for the fingerprint recognition system, then the system can be driven, but the volume increases
Solution Approach 1:
The driving transistor is integrated within the sensor pixel structure rather than being provided externally. This integration merges the control function with the sensing function, eliminating the need for separate external driving components and reducing overall system volume.
3Device complexity
If light is irradiated vertically to the substrate through cover glass, then the structure is simple, but light loss occurs and fingerprint image definition deteriorates
Solution Approach 1:
The patent changes the light irradiation direction from vertical to oblique incidence. By irradiating light at an oblique angle rather than vertically, the system achieves better fingerprint image definition and reduces light loss, trading structural simplicity for improved measurement precision.
Solution Approach 2:
The patent changes the optical parameter of light incidence angle from vertical (90 degrees) to oblique. This parameter change improves light reflection characteristics and fingerprint image quality while reducing light loss through the cover glass.
4Ease of manufacture
If the thickness of cover glass is much larger than sensor pixel, then coupling is facilitated, but light loss increases and recognition accuracy decreases
Solution Approach 1:
The patent changes the light incidence angle parameter to oblique, which compensates for the light loss caused by thicker cover glass. The oblique incidence improves light reflection and reduces absorption, maintaining recognition accuracy even when cover glass thickness exceeds sensor pixel thickness.
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 design improves fingerprint image definition and uniformity, reduces sensor thickness and volume, and enables easier integration with other devices by minimizing light loss and enhancing light reflection.
Implementation Method 1
having a thickness-direction cross-section having a right-angled triangular shape, and including multiple protrusions constituted by a first surface in which the light irradiated from the light source is incident and refracted
Implementation Method 2
sensing the light transmitted from the light direction switching layer toward the substrate and total-reflected on a surface contacting a fingerprint of a user on the cover layer
Data Source
AI summary
Disclosed are a fingerprint recognition sensor including: a light source positioned while being spaced apart on one surface of the substrate and irradiating light toward the substrate; and a light direction switching layer positioned between the substrate and the light source, having a thickness-direction cross-section having a right-angled triangular shape, and including multiple protrusions constituted by a first surface in which the light irradiated from the light source is incident and refracted, a second surface contacting the one surface of the substrate, in which the refracted light is transmitted toward the substrate, and a third surface vertical to the one surface of the substrate, and a mobile display device having the same.