Capacitive Fingerprint Sensor Lens Design
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Solution Overview
Problem
Capacitive fingerprint sensors face limitations in design flexibility due to the need for precise finger positioning, potential electric charge sensation, and capacitive coupling with subdermal layers, which restricts their size, position, and integration with other device components, especially in small devices like smartphones.
Innovation Solution
The use of a fingerprint recognition sensor system with a capacitive grid or optical sensor integrated into a button assembly, featuring a sapphire lens and ground ring for capacitive isolation, and a silicon wafer with through-silicon vias for reduced vertical space, allowing for superior capacitive coupling with the epidermis while providing tactile feedback and enhanced imaging capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the user's finger is placed close to the capacitive plates to achieve small capacitance differences, then measurement precision is improved, but device design flexibility is limited
Solution Approach 1:
The patent transitions from planar capacitive plates to a three-dimensional lens structure that focuses electric field lines. The lens element creates a concentrated electric field region that extends vertically from the sensor surface, enabling precise fingerprint detection without requiring the finger to be in direct contact with the sensor plane. This dimensional transformation resolves the contradiction by maintaining measurement precision through field concentration while freeing the sensor from rigid positioning constraints.
Solution Approach 2:
The patent introduces a dielectric lens element as an intermediary between the capacitive plates and the user's finger. This lens serves as a field-shaping mediator that concentrates electric field lines toward the finger ridges, enhancing capacitance contrast without requiring the finger to be positioned directly over the capacitive plates. The intermediary lens enables precise measurement while providing design flexibility in sensor placement and device integration.
2Measurement precision
If electric charge is introduced on the epidermis for capacitance measurement, then fingerprint recognition is enabled, but the user may feel tingling or noticeable effects
Solution Approach 1:
The patent applies local quality by concentrating the electric field precisely at the finger-ridge locations using the lens structure. Instead of distributing charge across a broad area, the lens focuses the electric field lines to intersect only with the raised ridges of the fingerprint, creating localized capacitance variations. This localized field concentration enables fingerprint recognition while minimizing the total charge introduced to the skin, reducing the likelihood of user sensation.
Solution Approach 2:
The dielectric lens acts as an intermediary that shapes and directs the electric field to interact selectively with the fingerprint ridges. The lens modifies the field distribution so that charge introduction is confined to specific localized regions rather than being spread across the entire contact area. This intermediary function enables effective fingerprint sensing while minimizing the overall electric charge exposure to the user's skin.
3Measurement precision
If the fingerprint sensor is positioned within a conductive ring for capacitive coupling, then sensing capability is improved, but the size and position of the sensor are significantly limited
Solution Approach 1:
The patent moves the sensing function from a two-dimensional planar configuration within a conductive ring to a three-dimensional field-based approach using a lens element. The lens creates a vertical electric field component that extends beyond the sensor plane, allowing capacitive coupling to occur through the lens structure rather than requiring the sensor to be confined within a horizontal conductive ring. This dimensional change enables flexible sensor placement and device integration while maintaining sensing capability.
Solution Approach 2:
The lens element serves as an intermediary that enables capacitive coupling between the capacitive plates and the user's finger without requiring direct alignment within a conductive ring. The lens shapes the electric field to bridge the gap between the sensor and finger, providing coupling capability that is not constrained by the geometric limitations of a conductive ring structure. This intermediary function restores design flexibility while preserving sensing performance.
4Measurement precision
If capacitive coupling involves subdermal layers of the finger, then sensing depth is increased, but relatively greater electric charge must be introduced causing user sensation
Solution Approach 1:
The patent applies local quality by concentrating the electric field at the epidermal ridge locations using the lens structure. The lens focuses field lines to intersect primarily with the superficial fingerprint ridges rather than penetrating deeply into subdermal layers. This localized field interaction achieves effective fingerprint sensing at the epidermal level while minimizing the total charge introduced to the skin, thereby reducing user sensation. The local quality principle ensures that sensing occurs where the fingerprint features are most prominent without requiring deep tissue penetration.
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 enables effective fingerprint recognition with improved design flexibility, reduced vertical space requirements, and enhanced capacitive sensing, allowing for seamless integration into various devices without noticeable electric charge effects on the user.
Implementation Method 1
featuring a sapphire lens and ground ring for capacitive isolation, and a silicon wafer with through-silicon vias for reduced vertical space, allowing for superior capacitive coupling with the epidermis while providing tactile feedback and enhanced imaging capabilities
Implementation Method 2
Capacitive sensing of fingerprints provides for collection of fingerprint information in response to distinct measures of capacitance 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 3
featuring a sapphire lens and ground ring for capacitive isolation
Data Source
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AI summary
An assembly for an electronic device (100), comprising a device housing (106) including an opening (108), a fingerprint sensor (102), plastic molded above the fingerprint sensor, the plastic defining a button structure (104) disposed to fit in the opening, a switch (118) stacked vertically below the fingerprint sensor; and a support plate (122) positioned between the fingerprint sensor (102) and the switch (118).