Optical Fingerprint Sensor Under LCD Backlight Module

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Solution Overview

Problem

Optical fingerprint sensors (OFPS) cannot be integrated under LCD displays due to backlight module reflection and protection anomalies, which block light and reduce the aspect ratio of the display.

Innovation Solution

An OFPS is designed with a light source, reflector, infrared pass filter coating, and wafer-level optic layer, including lenses, to be positioned beneath the LCD screen by forming a hole through the backlight module's reflective coating and metal shield, allowing light transfer and using an infrared light source to capture fingerprint images without obstructing the backlight.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If OFPS is integrated under LCD display, then fingerprint sensing capability is improved, but backlight module reflection and metal shield block light from reaching the sensor

Engineering Contradiction:

Improvefingerprint sensing capabilityVSAvoidbacklight module reflection and metal shield blocking light

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent divides the backlight module into segments by creating a first aperture in the reflective coating and a second aperture in the metal shield, allowing light to pass through specific pathways to the OFPS while maintaining the overall structure's light-diffusing function for the display

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces an infrared pass filter (IRPF) coating as an intermediary layer that selectively transmits infrared light from the light source to the OFPS while blocking visible light from the backlight module, effectively mediating between the conflicting light sources

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If OFPS is located under non-display area, then backlight module interference is avoided, but display aspect ratio is reduced

Engineering Contradiction:

Improvebacklight module interferenceVSAvoiddisplay aspect ratio

Core Design Contradiction:

Object-affected harmful factorsVSArea of stationary object

Solution Approach 1:

The patent applies local quality by creating specific apertures at precise locations in the reflective coating and metal shield, allowing the OFPS to be positioned under the display area where it can capture fingerprints without being interfered with by the backlight module, while the rest of the backlight module continues to function normally

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent converts the harmful backlight module structure into a beneficial element by using its existing reflective coating and metal shield layers, modifying them with apertures that allow fingerprint sensing while maintaining their original light-diffusing function for the display, thus eliminating the need to sacrifice display area

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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

Enables the placement of OFPS under LCD displays without blocking light, maintaining display performance and aspect ratio, and captures high-resolution fingerprint images using infrared light and wafer-level optics.

Implementation Method 1

an infrared pass filter (IRPF) coating formed on a substantially flat top surface of the wafer-level optic layer

Methodology Applied

Scientific EffectInfrared pass filter: Filter (optical)

Implementation Method 2

The IRPF coating having properties that reflect visible light and allow infrared light to pass through

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 3

a wafer-level optic layer bonded to the sensor layer, wherein the wafer-level optic layer includes one or more lenses

Methodology Applied

Scientific EffectLens focusing: Lens

Implementation Method 4

the wafer-level optic layer includes one or more lenses to direct light generated by a light source

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 5

an optical fingerprint sensor (OFPS) is made with a light source... an infrared light source for projecting infrared light towards the fingerprint sensing area

Methodology Applied

Scientific EffectInfrared light emission: Light Emitting Diode

Data Source

PatentUS11538269B2Optical fingerprint sensor for LCD panel

Publication Date: 2022.12.27 OMNIVISION TECHNOLOGIES INC

AI summary

An optical fingerprint sensor (OFPS) for use with a liquid-crystal display (LCD) panel having a backlight module is positioned under the backlight module and captures an image of a fingerprint sensing area on the LCD panel through an aperture in both a reflector and a metal shield of the backlight module. The OFPS includes a sensor layer, a wafer-level optic layer bonded to the sensor layer and an infrared pass filter (IRPF) coating formed on a substantially flat top surface of the wafer-level optic layer. An OFPS may be formed with a flat top and may include a wafer-level optic layer having one or more lenses to direct light generated by a light source beneath the wafer-level optic layer. The wafer-level lenses may be bonded with the fingerprint scanner. The flat top of the OFPS may be made with an IRPF coating.