Fingerprint Sensor in Display Stack for Accurate Biometric Capture
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Solution Overview
Problem
Existing fingerprint sensors integrated into touch screen displays face challenges such as image quality degradation and ineffective fingerprint reading due to the electrical shielding effect of liquid crystal display (LCD) or light-emitting diode (LED) layers, and the distance through these layers can be too great for accurate fingerprint capture.
Innovation Solution
Incorporating fingerprint sensors into the display stack with blind or through vias and conductive plates to minimize signal degradation, allowing for accurate fingerprint capture by shaping the electric field and providing a conductive interface, while also using full panel fingerprint sensors that function as touch sensing devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If fingerprint sensing functionality is added by inserting several layers of circuitry above the display structures, then fingerprint sensing capability is achieved, but image quality is degraded
Solution Approach 1:
The patent merges the fingerprint sensor and display into a single integrated structure where the fingerprint sensor is incorporated within the display stack itself. The sensor is positioned between the cover sheet and display layer, eliminating the need for separate circuitry layers above the display. This integration maintains image quality while achieving fingerprint sensing capability through shared structural elements and optimized layer arrangement.
2Device complexity
If the fingerprint sensor is located entirely beneath an LCD layer or LED layer, then the structure is simplified, but the electrical shield effect prevents accurate fingerprint reading
Solution Approach 1:
The patent applies local quality by creating localized openings (vias) in the cover sheet directly above the fingerprint sensor. These vias provide electrically conductive pathways that penetrate through the cover sheet to the sensor, establishing local electrical connections without requiring the entire cover sheet to be conductive. This localized approach maintains structural simplicity while enabling accurate fingerprint reading through targeted electrical access points.
Solution Approach 2:
The patent introduces conductive plates as intermediary elements positioned between the cover sheet and the fingerprint sensor. These conductive plates serve as mediators that transfer electrical signals through the cover sheet to the sensor, overcoming the electrical shielding effect. The intermediaries enable accurate fingerprint reading while maintaining the integrity and simplicity of the overall display structure.
3Measurement precision
If the distance through the LCD and LED layer is reduced to improve fingerprint reading, then fingerprint accuracy improves, but the structural integrity and shielding effect are compromised
Solution Approach 1:
The patent transitions from a planar arrangement to a three-dimensional integrated structure by incorporating the fingerprint sensor within the display stack's depth. The sensor is positioned between the cover sheet and display layer, with conductive plates and vias extending vertically through multiple layers. This dimensional integration allows the sensor to be close enough to the cover sheet surface for accurate fingerprint reading while maintaining structural integrity through the layered construction and preserved shielding effects of the display layers.
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
Enables effective fingerprint capture with minimal image quality degradation and improved sensitivity, allowing for accurate fingerprint imaging and touch sensing functionality within the display stack.
Implementation Method 1
Systems that capture a fingerprint by sensing electric fields may not function well when located entirely beneath a liquid crystal display (LCD) layer or a light-emitting diode (LED) layer of a display panel
Implementation Method 2
One or more conductive plates can be positioned between a top surface of the fingerprint sensor and a bottom surface of the cover sheet
Implementation Method 3
The structure of the LCD layer and the LED layer can act as an electrical shield, which prevents the system from reading the fingerprint
Data Source
AI summary
A fingerprint sensor is incorporated in a display stack in an electronic device. A single fingerprint can be captured at one time at a single pre-defined fixed location on a display. Alternatively, a single fingerprint can be acquired at one time at any location on a display. Alternatively, multiple touches on the display can be acquired substantially simultaneously where only one fingerprint is captured at a time or where all of the fingerprints are acquired at the same time. The fingerprint sensor can be implemented as an integrated circuit connected to a bottom surface of a cover sheet, near the bottom surface of the cover sheet, or connected to a top surface of a display. Alternatively, the fingerprint sensor can be implemented as a full panel fingerprint sensor.