Fingerprint Sensor Shielding Electrode Noise Reduction

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Solution Overview

Problem

Conventional fingerprint sensors require the user's finger to be in close proximity to the sensing array, making mechanical packaging and integration into electronic devices difficult, costly, and prone to moisture and dust ingress, while also limiting the use of protective coatings and increasing power consumption due to the need for thicker dielectric materials and higher drive voltages.

Innovation Solution

An electronic device with an array of biometric finger sensing pixel electrodes and an array shielding electrode, along with a finger coupling electrode and drive circuitry that generates compensating drive signals to reduce noise and allow imaging through thicker materials, including a semiconductor substrate and dielectric cap, enabling operation at a larger distance from the sensing pixels.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the user's finger is placed in close proximity to the sensing array, then the sensing precision is improved, but the mechanical packaging complexity and susceptibility to moisture/dust ingress increase

Engineering Contradiction:

Improvefingerprint sensing precisionVSAvoidmechanical packaging complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent introduces a vertical stacking dimension by placing the finger coupling electrode, array shielding electrode, and sensing array in different vertical layers separated by dielectric materials. This three-dimensional arrangement allows the finger to be sensed through thicker materials without requiring close horizontal proximity, thereby reducing mechanical packaging complexity while maintaining sensing precision.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The array shielding electrode acts as an intermediary element between the finger coupling electrode and the sensing array. It enables the system to sense fingerprints through thicker dielectric materials by providing a controlled electrical field path, allowing operation at larger distances without compromising sensing quality.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If thicker dielectric materials are used to increase operating distance, then the device durability is improved, but the power consumption increases due to higher drive voltages

Engineering Contradiction:

Improvedevice durabilityVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent modifies the electrical parameters by introducing the array shielding electrode with specific voltage relationships to the finger coupling electrode. This configuration optimizes the electrical field distribution through thicker dielectric materials, enabling operation at larger distances without requiring proportionally higher drive voltages, thus maintaining power efficiency while improving durability.

Inventive Principle:

Principle #35Parameter changes

3Object-generated harmful factors

If the finger coupling electrode is coupled to device ground, then the noise reduction is improved, but the electrical field distribution may be affected

Engineering Contradiction:

Improvenoise in finger imagesVSAvoidelectrical field distribution

Core Design Contradiction:

Object-generated harmful factorsVSStability of the object's composition

Solution Approach 1:

The array shielding electrode serves as an intermediary that mediates between the grounded finger coupling electrode and the sensing array. It maintains proper electrical field distribution while allowing the finger coupling electrode to be grounded for noise reduction, effectively decoupling the noise reduction benefit from potential electrical field disruption.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 reduces noise in finger images and allows for more robust and cost-effective integration of fingerprint sensors into electronic devices, improving durability and reducing power consumption by enabling operation through thicker materials without compromising authentication quality.

Implementation Method 1

a finger coupling electrode outside the array shielding electrode and coupled to the device ground... drive circuitry capable of generating a drive signal for the array of biometric finger sensing pixel electrodes

Methodology Applied

Scientific EffectCapacitive coupling: Capacitance

Implementation Method 2

The finger sensing IC includes a layer of piezoelectric or pyroelectric material placed between upper and lower electrodes to provide electric signals representative of an image of the ridges and valleys of the fingerprint

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 3

Methodology Applied

Scientific EffectPyroelectric effect: Pyroelectric Effect

Data Source

PatentUS9581628B2Electronic device including device ground coupled finger coupling electrode and array shielding electrode and related methods

Publication Date: 2017.02.28 APPLE INC

AI summary

An electronic device may include a housing and circuitry carried by the housing and having a device ground associated therewith. The electronic device may also include an array of biometric finger sensing pixel electrodes and an array shielding electrode outside the array of biometric finger sensing pixels. A finger coupling electrode may be outside the array shielding electrode and coupled to the device ground. The electronic device may also include drive circuitry capable of generating a drive signal for the array of biometric finger sensing pixel electrodes and a compensating drive signal for the array shielding electrode.