Passive Pyroelectric Pixel Array With Row Heating for Thermal Sensing
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Solution Overview
Problem
Existing thermal fingerprint sensors face issues with signal loss when the finger and sensor are at the same temperature and varying contrast in captured images, particularly in static acquisition, and the presence of transistors within the pixel matrix increases manufacturing complexity and cost.
Innovation Solution
A thermal pattern sensor with a passive pixel matrix that uses pyroelectric capacitors and heating elements, eliminating the need for transistors within the pixels, allowing for fabrication on semiconductor or flexible substrates using printed electronics, and employing conductive inks for cost-effective production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If passive thermal sensors are used to detect temperature differences, then the sensor structure is simple, but the signal level becomes zero when finger and sensor are at the same temperature
Solution Approach 1:
The patent applies preliminary action by heating the pixels before fingerprint detection to create a temperature difference. The heating elements pre-heat the sensor pixels, and then the finger is placed on the sensor during an integration period. This preliminary heating ensures that even if the finger and sensor were initially at the same temperature, a temperature difference is created for detection, resolving the signal loss problem of passive sensors.
Solution Approach 2:
The patent implements periodic action through the heating cycle: heating elements are activated for a specific duration, followed by an integration period where temperature differences are measured. This periodic heating and measurement cycle allows the sensor to generate reliable thermal signals consistently, overcoming the limitation of passive sensors that fail when no temperature difference exists.
2Reliability
If active thermal sensors with heating elements are used to eliminate signal loss, then the signal level is maintained, but transistors are required in each pixel increasing device complexity
Solution Approach 1:
The patent merges the heating element with the pixel structure by integrating the heating function into the pixel's conductive layers. Instead of adding separate heating components to each pixel, the invention utilizes existing conductive layers (such as ITO or metal traces) to serve dual purposes: as electrical interconnects and as heating elements. This merging eliminates the need for additional transistors in each pixel while maintaining active thermal sensing capabilities.
Solution Approach 2:
The patent applies multi-functionality by making the conductive layers serve multiple functions: they act as both electrical interconnects for the pixel circuitry and as heating elements for thermal activation. This universal use of conductive materials eliminates the need for dedicated heating components and transistors in each pixel, reducing device complexity while maintaining signal level reliability.
3Measurement precision
If transistors are included in each pixel for active sensing, then thermal detection accuracy is improved, but manufacturing cost and complexity increase
Solution Approach 1:
The patent extracts the transistor component from the pixel structure, eliminating the need for individual transistors in each pixel. By removing this complex and costly component while retaining the essential heating and detection functions through simplified conductive layer integration, the invention maintains thermal detection accuracy while significantly reducing manufacturing complexity and cost.
Solution Approach 2:
The patent replaces expensive transistor-based active pixels with simpler, cheaper conductive layer structures that perform heating and sensing functions. The conductive layers (such as ITO or thin metal traces) are inexpensive materials that can be deposited using standard thin-film fabrication techniques, making the sensor much more cost-effective to manufacture while maintaining adequate thermal detection precision.
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 sensor simplifies manufacturing, reduces costs, and enhances signal control by heating pixels row-by-row, providing accurate thermal detection without transistors and capacitive sensing, while being insensitive to parasitic capacitances.
Implementation Method 1
the sensor's pixels are coupled to heating elements that typically utilize the Joule effect, which dissipates heat from a resistive element carrying a current
Implementation Method 2
each pixel has a pyroelectric capacitor formed by two conductive electrodes with a portion of pyroelectric material between them... converts a temperature change into a change in potential or electrical current
Data Source
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AI summary
Thermal pattern sensor (100) comprising a matrix of several rows and columns of pixels (102), each pixel comprising: - a pyroelectric capacitance comprising a pyroelectric portion disposed between lower (112) and upper (130) electrodes, in which a first of these electrodes forms a reading electrode, and - a heating element (130) capable of heating the pyroelectric portion of said pixel, and in which: - for each row of pixels, the heating elements are capable of heating the pyroelectric portion of the pixels of said row independently of the heating elements of the pixels of other rows, and - for each column of pixels, the reading electrodes of each pixel are electrically connected to each other and formed by a first electrically conductive portion (112) in contact with the pyroelectric portions of the pixels of said column and distinct from the first portions of the other columns.