Flexible Fingerprint Sensor Ledge Contact Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current fingerprint sensors are either too large and expensive for widespread use, particularly in applications like airports and immigration control, or they are silicon-based and lack robustness and optimal electronic interconnections, making them unsuitable for thin and flexible applications such as smartcards.
Innovation Solution
A flexible fingerprint sensor is developed using additive or semi-additive build-up processes to create a substrate with embedded sensor electrodes for coupling to the finger surface, allowing for high accuracy and minimal feature and alignment tolerances, and can be manufactured using liquid or dry film dielectrics with conductive materials deposited through sputter or plating technology, enabling a flush mount design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional silicon production techniques are used for fingerprint sensors, then electrical interconnection features can be achieved, but the sensor size and rigid properties significantly limit integration in thin and flexible applications
Solution Approach 1:
The patent changes the fundamental material parameter from rigid silicon to flexible polymer substrates (polyimide, PET, PC). This material substitution enables the sensor to be thin and flexible while maintaining electrical interconnection capabilities through conductive traces deposited on the flexible substrate. The polymer-based approach resolves the contradiction by allowing both electrical functionality and mechanical flexibility simultaneously.
Solution Approach 2:
The patent employs composite material structures combining polymer substrates with conductive materials (metal traces, conductive inks) and dielectric layers. This composite approach creates a flexible sensor assembly that integrates electrical interconnection features without the rigidity of traditional silicon, enabling both ease of manufacture and adaptability to thin/flexible applications.
2Reliability
If recessed mounting is implemented to improve robustness and protection, then sensor protection is enhanced, but esthetical design is compromised and protection from dirt and moisture is insufficient
Solution Approach 1:
The patent transitions from recessed (3D) mounting to flush mounting (2D plane alignment). The sensor surface is positioned flush with the device surface, eliminating the recessed cavity while maintaining protection through integrated sealing structures. This dimensional change resolves the contradiction by providing both esthetical design (flush appearance) and functional protection (sealing against dirt and moisture).
Solution Approach 2:
The patent introduces sealing structures (gaskets, adhesive layers, or integrated seals) as intermediary elements between the sensor and the device housing. These intermediaries provide the necessary protection against dirt and moisture while allowing flush mounting, thus resolving the contradiction between esthetical design and environmental protection.
3Ease of manufacture
If subtractive PCB process with etching is used for substrate manufacturing, then through-substrate-via conductors can be achieved, but resolution is low and dimensional accuracy is insufficient for small sensor features
Solution Approach 1:
The patent inverts the manufacturing approach from subtractive (etching away material) to additive (depositing material layers). Instead of etching through the substrate to create vias, the patent uses sequential deposition of conductive and dielectric layers to build up the sensor structure. This inversion enables high-resolution features and precise dimensional control while maintaining ease of manufacture through established deposition techniques.
Solution Approach 2:
The patent performs preliminary actions by pre-defining conductor trace patterns and via locations through photolithography masks before material deposition. This preliminary patterning ensures high dimensional accuracy for small sensor features, as the conductor paths are precisely defined before the actual deposition process, avoiding the resolution limitations of post-manufacturing etching.
4Ease of manufacture
If layer thickness is not sufficiently accurate in substrate manufacturing, then manufacturing is easier, but measurement accuracy and sensor unit precision are reduced
Solution Approach 1:
The patent implements feedback control in the layer deposition process by using real-time monitoring and adjustment mechanisms during sputtering, spray, or plating operations. This feedback ensures that each deposited layer achieves the precise thickness required for accurate sensor measurements, resolving the contradiction between ease of manufacture and measurement precision through automated process control.
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 a thin, flexible, and cost-effective fingerprint sensor with improved accuracy and robustness, suitable for various applications, including smartcards, while maintaining high measurement precision and aesthetic design considerations.
Implementation Method 1
The substrate may be manufactured using liquid or dry film dielectrics alternated with layers of conductive materials deposited through sputter, spray or other plating technology
Implementation Method 2
layers of conductive materials deposited through sputter, spray or other plating technology
Implementation Method 3
Subsequent layers of conductive material and dielectrics are added using photo lithography and corresponding mask sets to define required section features
Data Source
AI summary
A fingerprint sensor for incorporation into a smart card includes sensor electrodes for detecting fingerprint features of a finger placed on a contact surface, the sensor electrodes being disposed above a substrate layer that comprises a first portion, a second portion, and a ledge where an edge of the first portion extends beyond an edge of the second portion. Contact points disposed on the ledge connect the fingerprint sensor to electrical conductors of an intermediate layer of a multi-layer smartcard. The fingerprint sensor is disposed within a cavity formed in a body of the smartcard, and the contact points disposed on the ledge are set at a depth corresponding to the thickness of an outer layer covering the electrical conductors of the intermediate layer of the smartcard.