Fingerprint Sensor Dielectric Layout for Higher Capacitance Sensitivity

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Solution Overview

Problem

Fingerprint sensors with active self-capacitive technology face challenges in achieving optimal sensing sensitivity due to the larger window sensing distance required, which can lead to defective sensing operations when ridges and valleys of fingerprints are not accurately detected.

Innovation Solution

A fingerprint sensor design incorporating a sensor protective layer with distinct regions of varying permittivity, where a high permittivity region is disposed over the sensor electrode and a low permittivity region is placed between sensor electrodes, enhancing capacitance ratio and sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a uniform sensor protective layer is used, then the manufacturing process is simple, but the sensing sensitivity is insufficient due to larger window sensing distance

Engineering Contradiction:

Improvesensing sensitivityVSAvoidsensor protective layer structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The sensor protective layer is divided into a first region with higher permittivity positioned over the sensor electrode and a second region with lower permittivity positioned over the pixel electrode. This local differentiation of material properties enhances the capacitance ratio between adjacent capacitors, thereby improving sensing sensitivity without requiring complex multi-layer structures.

Inventive Principle:

Principle #3Local quality

2Reliability

If the window sensing distance is reduced, then the sensing sensitivity improves, but the distance between sensor electrode and user hand becomes insufficient

Engineering Contradiction:

Improvesensing sensitivityVSAvoidwindow sensing distance

Core Design Contradiction:

ReliabilityVSLength of moving object

Solution Approach 1:

The permittivity parameter of the sensor protective layer is changed spatially, with the first region having a higher permittivity than the second region. This parameter modification enhances the electric field concentration between the sensor electrode and the user's finger, improving sensing sensitivity while maintaining an adequate window sensing distance for comfortable user interaction.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If adjacent capacitors have similar capacitance values, then the sensor structure is simple, but the capacitance ratio is low leading to defective sensing

Engineering Contradiction:

Improvecapacitance ratioVSAvoidsensor protective layer configuration

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

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 design improves sensing sensitivity by increasing the capacitance of the sensor when ridges or valleys are detected, reducing the impact of adjacent capacitors and enhancing overall fingerprint recognition accuracy.

Implementation Method 1

A sensor protective layer is formed by hardening the first resin and the second resin

Methodology Applied

Scientific EffectPhotopolymerization: Photopolymerisation

Implementation Method 2

The sensor protective layer is hardened

Methodology Applied

Scientific EffectThermal curing:

Implementation Method 3

the minimum distance required between a sensor electrode of the fingerprint sensor and the hand of the user is larger than is typical for mutual-capacitive fingerprint sensors. This distance is known as the 'window sensing distance.'

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 4

an active self-capacitive fingerprint sensor senses a fingerprint based on a change in capacitance of a capacitor formed between it and the hand of a user

Methodology Applied

Scientific EffectElectrostatic induction: Electrostatic Induction

Data Source

PatentUS10565421B2Fingerprint sensor and method of manufacturing the same

Publication Date: 2020.02.18 SAMSUNG DISPLAY CO LTD

AI summary

A fingerprint sensor includes a sensor substrate. A plurality of sensor pixels is configured to sense a change in capacitance corresponding to a touch of a user. Each of the plurality of sensor pixels includes a sensor electrode. A sensor protective layer is configured to protect the sensor substrate and the plurality of sensor pixels. The sensor protective layer includes a first region disposed over the sensor electrode, and a second region. The first region has a first permittivity. The second region has a second permittivity lower than the first permittivity.