Under-display Fingerprint Sensor with NFV Collimator
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Solution Overview
Problem
Optical fingerprint sensors face challenges in consistency over time due to unstable glass-air interfaces and are not cost-effective for large-area sensing, with long image capture times due to the need for multiple illumination patterns to separate reflection rays at various angles.
Innovation Solution
An under-display optical fingerprint sensor with a narrow field-of-view (NFV) collimator and a thin-film transistor (TFT)-based organic imager, where the collimator layer collimates reflected light to achieve a one-to-one imaging ratio between the finger surface and the image sensor, and a micro-lens layer separates angled illumination reflections, enhancing signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If glass-air interfaces are used in optical fingerprint sensors, then the sensor can be integrated into the display, but the performance consistency deteriorates over time due to interface instability
Solution Approach 1:
A collimator layer is introduced as an intermediary component between the display and the fingerprint sensor. This collimator layer stabilizes the optical path and compensates for the instability of glass-air interfaces, maintaining consistent performance over time while enabling display integration
2Measurement precision
If multiple illumination patterns are used to separate reflection rays, then the separation precision improves, but the image capture time increases to several seconds
Solution Approach 1:
The collimator layer is divided into multiple columns, each responsible for a specific angular range of reflection rays. This segmentation allows simultaneous processing of multiple illumination patterns through parallel optical paths, achieving precise ray separation without requiring sequential capture of multiple images
Solution Approach 2:
The system transitions from temporal multiplexing (sequential illumination patterns) to spatial multiplexing (parallel optical paths through collimator columns). By distributing different illumination patterns across spatial dimensions in the collimator structure, the system achieves ray separation in parallel, reducing capture time from seconds to milliseconds
3Area of stationary object
If large-area sensors using CMOS are used, then the sensing area increases, but the cost effectiveness deteriorates
Solution Approach 1:
The large-area sensing requirement is divided into multiple smaller sensor elements arranged in an array. Each element captures a specific portion of the fingerprint, and the results are combined to form the complete fingerprint image. This segmentation allows the use of smaller, more cost-effective sensor elements while achieving the required large sensing area
Solution Approach 2:
The system transitions from using a single large-area CMOS sensor to a multi-element sensor array. By organizing sensors in a two-dimensional array pattern, the system achieves large effective sensing area through spatial arrangement rather than requiring a single large sensor, improving cost effectiveness
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 provides consistent and rapid fingerprint sensing with improved signal-to-noise ratio, reducing image capture time and increasing cost-effectiveness by stabilizing the glass-air interface and optimizing the field-of-view for effective reflection separation.
Implementation Method 1
The collimator layer can collimate the reflected light
Implementation Method 2
a micro-lens layer separates angled illumination reflections
Implementation Method 3
a micro-lens layer separates angled illumination reflections
Data Source
AI summary
An apparatus for fingerprint sensing includes a touch-display layer covered by a transparent layer. The touch-display layer can emit light to illuminate a finger surface touching the transparent layer. The touch-display layer is transparent to reflected light from the surface to underlying layers. The underlying layers include a collimator layer and a pixelated image sensor. The collimator layer can collimate the reflected light, and the pixelated image sensor can sense the collimated reflected light. The collimator can collimate the reflected light to enable a one-to-one imaging ratio between an area of the finger surface touching the transparent layer and an area of a corresponding image formed on the pixelated image sensor.