Capacitive Fingerprint Sensing with Integrated OLED Display
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Solution Overview
Problem
Conventional TFT-based display panels face challenges in integrating high-resolution capacitive fingerprint sensing due to the limited number of transistors per pixel and reduced sensitivity when sensing under glass, which requires additional circuitry and increased sensitivity.
Innovation Solution
A capacitive fingerprint sensing device with a protective dielectric top layer, optically transparent electrodes, an organic light emitting layer, and integrated display element control circuitry, allowing switching between fingerprint sensing and display modes using a diode-based switching mechanism to minimize current flow during fingerprint sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If TFT technology is used for display panel, then display properties and visual quality are improved, but the number of transistors per pixel is limited making high-resolution fingerprint sensing difficult
Solution Approach 1:
The patent combines display pixel structure with fingerprint sensing elements into a single integrated structure. The same transparent electrode serves both as a display pixel electrode and as a capacitive sensing electrode, eliminating the need for separate transistor circuits for fingerprint sensing while maintaining display functionality.
Solution Approach 2:
The transparent electrode in the display pixel is given dual functionality: it acts as both the pixel electrode for display purposes and as the sensing electrode for capacitive fingerprint detection. This multi-functionality resolves the transistor count limitation by using existing display structures for sensing.
2Reliability
If sensing is performed under glass, then protective coverage is improved, but sensitivity is reduced due to increased distance between finger and sensor
Solution Approach 1:
The patent changes the electrical parameters of the transparent electrode (increasing its capacitance and optimizing its electrical characteristics) to compensate for the reduced sensitivity caused by the glass layer. By adjusting the electrode's electrical properties rather than its physical position, the system maintains sensing capability while preserving protective coverage.
3Measurement precision
If additional circuitry is added to sensing elements, then fingerprint sensing capability is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent merges the display pixel circuitry with the fingerprint sensing circuitry into a shared structure. The same transparent electrode and control circuits serve both display and sensing functions, eliminating the need for additional dedicated sensing circuitry and reducing overall device complexity.
Solution Approach 2:
The display pixel's existing circuit components are made multi-functional to handle both display control and fingerprint sensing operations. This approach avoids adding separate circuitry while achieving enhanced sensing capability through intelligent use of existing structures.
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 high-resolution fingerprint sensing with integrated display functionality, maintaining sensitivity and visual performance without the need for additional circuitry, by controlling the bias of the diode to optimize current flow for both modes.
Implementation Method 1
an organic light emitting layer arranged between said first and second electrodes
Implementation Method 2
capacitive fingerprint sensing device comprising a plurality of sensing elements
Data Source
Figure 1~2
Figure 3A
Figure 3B
AI summary
There is provided a capacitive fingerprint sensing device (20) for sensing a fingerprint pattern of a finger, the capacitive fingerprint sensing device comprising a plurality of sensing elements (22). Each sensing element comprises a protective dielectric top layer (30) to be touched by the finger; a first electrode (34) comprising an optically transparent electrically conductive sensing structure arranged underneath the top layer; fingerprint sensing circuitry connected to the first electrode and configured to provide an analog sensing signal indicative of a distance between the finger and the sensing structure, a second electrode (36) arranged underneath the first electrode; an organic light emitting layer (38) arranged between the first and second electrodes; display element control circuitry (42) connected to the second electrode and configured to control a display element comprising the first and second electrodes and the organic light emitting layer; and a switching mechanism configured to switch the sensing element between a fingerprint sensing mode and a display mode.