Biometric Sensor Stack With Dielectric Cap For Charge Isolation
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Solution Overview
Problem
Capacitive fingerprint recognition sensors face limitations in design flexibility due to the need for close proximity to the user's finger, potential for noticeable electric charge effects, and challenges in integrating with small devices, leading to fragility and unwanted design constraints.
Innovation Solution
The integration of a biometric sensor stack with a cap, trim, and switch, where the sensor is positioned beneath the cap, and the switch generates an electrical signal, allowing for capacitive data capture while providing tactile feedback and improved coupling with the user's finger, using techniques such as bonding wires through silicon wafers, trenches, or encapsulation in plastic molding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the fingerprint sensor is positioned close to the user's finger to improve measurement sensitivity, then capacitance measurement precision is improved, but the user may feel noticeable electric charge effects
Solution Approach 1:
The patent introduces a dielectric layer as an intermediary between the capacitive sensor and the user's finger. This dielectric layer enables effective capacitive coupling for precise measurements while preventing direct electrical contact that would cause noticeable charge effects on the user's skin.
Solution Approach 2:
The patent modifies the electrical parameters of the sensing system by introducing materials with specific dielectric properties. By changing the dielectric constant and electrical conductivity parameters of the intermediate layer, the system achieves optimal capacitance coupling while limiting charge transfer to the user's finger.
2Adaptability or versatility
If the fingerprint sensor is integrated into small devices to improve adaptability, then device miniaturization is achieved, but the sensor becomes more fragile and design flexibility is limited
Solution Approach 1:
The patent merges the fingerprint sensor with existing device components such as buttons, displays, or housing structures. By combining the sensor function with structural elements already present in the device, the system achieves miniaturization without compromising sensor strength or adding separate fragile components.
Solution Approach 2:
The patent employs composite material structures that combine rigid and flexible properties. The sensor assembly uses layered composites including dielectric materials, conductive layers, and flexible substrates that provide both structural integrity and adaptability for integration into compact devices.
3Measurement precision
If the sensor is positioned close to the capacitive plates to improve measurement accuracy, then capacitance differentiation is improved, but design flexibility for sensor size and position is limited
Solution Approach 1:
The patent resolves the spatial conflict by utilizing the vertical dimension (depth/thickness) rather than only horizontal positioning. The dielectric layer extends vertically between the sensor and finger, allowing the sensor to be positioned at optimal distances from the capacitive plates while maintaining measurement precision through vertical capacitive coupling.
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 enhances design flexibility, reduces noticeable charge effects, and enables effective fingerprint recognition in various device forms, including small devices, by positioning the sensor close to the user's finger while maintaining tactile feedback and improved capacitive coupling.
Implementation Method 1
Capacitive sensing of biometric data provides for collection of biometric information, such as fingerprint information, in response to distinct measures of capacitance. such measures of capacitance can be between, on the one hand, one or more capacitive plates in a fingerprint recognition sensor, and on the other hand, ridges and valleys of a user's finger
Implementation Method 2
use of anisotropic materials like sapphire for improved capacitive coupling
Data Source
AI summary
Various structures and methods are disclosed for packaging a biometric sensor, such as a capacitive biometric sensor. Embodiments incorporate various placements of the biometric sensor, structure surrounding a biometric sensor, connection structures (electrical, physical, or both), and techniques for enhanced sensor imaging, sensor retention, and guiding a user's finger to a proper location above a biometric sensor. For example, A biometric sensor assembly can include an aperture formed in a trim with a cap disposed in the aperture. A biometric sensor may be positioned below the cap and a switch positioned below the biometric sensor.