Low Profile Optical Fingerprint Sensor Using Collimator Filter
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Solution Overview
Problem
Conventional optical fingerprint sensors are too bulky for integration in mobile devices, and capacitive sensors face challenges in detecting fingerprints through thick cover glass, requiring cutouts and mechanical buttons which detract from device aesthetics and functionality.
Innovation Solution
An optical fingerprint sensor design featuring a collimator filter layer between a light illumination layer and an image sensor array, allowing reflected light to be filtered and focused onto specific optical sensing elements, enabling detection through thick cover layers without blurring and improving sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional optical fingerprint sensors are used, then fingerprint detection capability is achieved, but sensor size becomes too bulky for mobile devices
Solution Approach 1:
The optical sensor is divided into multiple functional layers including a cover glass layer, illumination layer, collimator layer, and image sensor layer. This segmentation allows each layer to perform its specific function efficiently while reducing the overall sensor volume and enabling integration into mobile devices.
Solution Approach 2:
The patent transitions from a conventional bulk optical sensor design to a planar layered structure. By arranging components in separate layers along the vertical dimension, the sensor achieves compact footprint suitable for mobile devices while maintaining detection capability through the cover glass.
2Volume of moving object
If capacitive fingerprint sensors are used to reduce size, then sensor compactness is improved, but ability to sense through thick cover glass deteriorates
Solution Approach 1:
The patent introduces a collimator layer with aperture structures as an intermediary between the illumination layer and image sensor. This collimator acts as a optical mediator that directs light rays through the thick cover glass at controlled angles, enabling precise fingerprint detection despite the presence of thick protective glass in mobile devices.
3Reliability
If cutouts are formed in cover glass for capacitive sensors, then fingerprint detection is enabled, but device aesthetics and flush surface are compromised
Solution Approach 1:
The cover glass layer serves multiple functions: it provides mechanical protection for the display, maintains the aesthetic flush surface appearance, and simultaneously acts as the sensing surface for fingerprint detection. This multi-functionality eliminates the need for separate cutout areas while achieving both protective and biometric authentication goals.
4Reliability
If mechanical buttons are added for discrete fingerprint sensors, then fingerprint authentication is enabled, but device real estate and aesthetics are reduced
Solution Approach 1:
The patent merges the fingerprint authentication function with the existing display cover glass structure. By integrating the optical sensor layers beneath the cover glass, the system combines the protective glass function with biometric authentication capability, eliminating the need for separate mechanical buttons and optimizing device real estate.
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 a lower-profile fingerprint sensor capable of detecting fingerprints through thick cover layers, enhancing user experience by eliminating the need for cutouts and mechanical buttons, while maintaining high sensitivity and resolution.
Implementation Method 1
an organic light emitting diode (OLED) layer positioned below the transparent electrode layer, wherein the OLED layer is configured to emit an illumination light beam towards the top surface of the cover glass
Implementation Method 2
the collimator filter comprises an aperture extending from the top surface of the collimator filter to the bottom surface of the collimator filter, wherein the aperture is configured to transmit the reflected light beam after the reflected light beam is transmitted through the opening of the metal electrode layer
Implementation Method 3
wherein the intermediate surface of the collimator filter is configured to block a stray light beam that is reflected from the top surface of the cover glass
Data Source
AI summary
An optical fingerprint sensor includes: cover glass for receiving a finger; a transparent electrode layer below a bottom surface of the cover glass; an organic light emitting diode layer (OLED) below the transparent electrode layer; and a metal electrode layer below the OLED layer. Multiple openings extend through each of the transparent electrode layer, OLED layer, and metal electrode layer, and transmit reflected light reflected from a top surface of the cover glass when a finger is positioned over the top surface of the cover glass. A collimator or pinhole filter is below the metal electrode layer, and includes multiple apertures for transmitting the reflected light after the reflected light is transmitted through the multiple openings. An imager is below the bottom surface of the collimator or pinhole filter, and includes an array of pixels that detects the reflected light after the reflected light is transmitted through the multiple apertures.