Impedance Fingerprint Sensor Using Flexible PCB Electrodes

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Solution Overview

Problem

Conventional two-dimensional fingerprint sensors are costly due to the need for large silicon areas and complex interconnects, and swipe sensors face challenges with accuracy and ergonomics, particularly in mobile devices where space is limited and user interaction is cumbersome.

Innovation Solution

A two-dimensional sensor configuration using a flexible substrate with drive and pickup lines that form impedance sensing electrode pairs at crossover locations, eliminating the need for distinct electrode structures and allowing for a high-density pixel array with reduced alignment requirements, enabling low-cost manufacturing and improved accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional two-dimensional fingerprint sensors use silicon sensor surfaces, then sensing accuracy and reliability are improved, but manufacturing cost increases significantly

Engineering Contradiction:

Improvesensing accuracyVSAvoidmanufacturing cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent replaces expensive silicon sensor surfaces with inexpensive plastic films containing printed circuit boards. This substitution uses low-cost materials (plastic instead of silicon) while maintaining the essential sensing function, directly addressing the cost-accuracy contradiction by achieving acceptable sensing performance through cheaper alternatives.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The patent replaces the traditional silicon-based capacitive sensing mechanism with an impedance sensing system using printed circuit board traces. This substitution uses standard PCB manufacturing techniques instead of specialized silicon fabrication, significantly reducing manufacturing cost while maintaining sensing capability through electrical impedance measurements.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If conventional two-dimensional fingerprint sensors maintain full fingerprint scanning size, then authentication accuracy is improved, but device size and cost increase

Engineering Contradiction:

Improveauthentication accuracyVSAvoidsensor area

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

The patent uses flexible plastic films as the sensor substrate instead of rigid silicon. This flexibility allows the sensor to be made compact and adaptable to various device form factors while maintaining full fingerprint scanning capability, resolving the contradiction between sensing area and device size.

Inventive Principle:

Principle #30Flexible shells and thin films

3Ease of manufacture

If swipe sensors are used to reduce cost and size, then manufacturing cost and device size are reduced, but authentication accuracy and user ergonomics deteriorate

Engineering Contradiction:

Improvemanufacturing costVSAvoidauthentication accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent creates a placement sensor that can function as both a fingerprint authentication device and a touch-sensitive control interface. This multi-functionality eliminates the need for separate swipe sensors, maintaining authentication accuracy while reducing overall device complexity and cost.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 the creation of a low-cost, high-resolution two-dimensional fingerprint sensor that is compact and user-friendly, addressing the limitations of existing technologies by reducing silicon usage and enhancing sensor accuracy and ergonomics in mobile devices.

Implementation Method 1

the crossover locations of different sensor lines create impedance sensing locations for sensing features and/or characteristics of an object

Methodology Applied

Scientific EffectImpedance sensing: Electrical Impedance Tomography

Implementation Method 2

drive lines located on or about an insulating dielectric substrate and configured to transmit a signal onto a surface of an object being sensed. Pickup lines are located near or about the drive lines and configured to receive the transmitted signal from the surface of an object

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentEP2524339B1Fingerprint sensing system with a switch underlying a fingerprint sensor array or embedded within layers of the fingerprint sensor array

Publication Date: 2020.10.14 IDEX ASA

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AI summary

An novel impedance sensor for use together with a switch is provided having a plurality of substantially parallel drive lines configured to transmit a signal into a surface of a proximally located object, and also a plurality of substantially parallel pickup lines oriented substantially perpendicular to the drive lines and separated from the pickup lines by a dielectric to form intrinsic electrode pairs that are impedance sensitive at each of the drive and pickup crossover locations.