Superposed Pyroelectric Sensor Pixel for Fingerprint Contrast
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Solution Overview
Problem
Existing thermal pattern sensors, such as fingerprint sensors, face challenges in maintaining image contrast over time due to thermal equilibrium between the sensor and the object being imaged, leading to unsatisfactory image quality.
Innovation Solution
A thermal patterns sensor design featuring a matrix of pixels with both a calibration and measurement portion, each containing pyroelectric material, where the calibration portion is heated independently to generate calibration charges, allowing for the subtraction of unwanted signals and enhancing image contrast by measuring the difference between calibration and measurement charges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If heating means are added to maintain temperature difference, then image contrast is improved over time, but device complexity and energy consumption increase
Solution Approach 1:
The sensor divides each pixel into two separate pyroelectric portions: a first portion for calibration that is thermally isolated from the object, and a second portion for measurement that contacts the object. This segmentation allows independent thermal management of calibration and measurement functions, enabling contrast stability without requiring complex external heating means.
Solution Approach 2:
The invention changes the thermal parameter configuration by creating different thermal coupling conditions for the two pyroelectric portions. The first portion is thermally decoupled from the object to maintain stable calibration charges, while the second portion remains thermally coupled to detect object temperature variations. This parameter differentiation resolves the contradiction between contrast stability and device simplicity.
2Stability of the object's composition
If heating means are used to prevent thermal equilibrium, then image contrast is maintained, but energy consumption increases
Solution Approach 1:
The sensor performs preliminary calibration by measuring the response of the first pyroelectric portion to initial temperature conditions before actual measurement begins. This preliminary action establishes a baseline that accounts for thermal equilibrium effects, allowing subsequent measurements to maintain contrast without continuous energy input from heating means.
Solution Approach 2:
The differential measurement between the two pyroelectric portions enables the sensor to self-correct for thermal equilibrium effects. The system uses its own internal reference (the first portion) to compensate for environmental thermal changes, eliminating the need for external heating means and reducing energy consumption.
3Device complexity
If single pyroelectric portion is used, then device simplicity is maintained, but image contrast deteriorates over time due to thermal equilibrium
Solution Approach 1:
Each pixel is segmented into two pyroelectric portions with different thermal coupling configurations. The first portion serves as a thermal reference that is isolated from the object, while the second portion measures the object's thermal signature. This simple segmentation maintains device simplicity while preventing contrast deterioration through differential measurement.
Solution Approach 2:
The invention applies different local thermal qualities to the two portions within each pixel: the first portion has low thermal coupling to the object (for stable calibration), while the second portion has high thermal coupling (for sensitive measurement). This local differentiation resolves the contradiction between structural simplicity and contrast stability.
4Strength
If thicker protection layers are added to protect pyroelectric material, then sensor durability is improved, but thermal sensitivity decreases
Solution Approach 1:
The invention changes the thermal parameter configuration by creating a differential measurement system where the protection layer's thermal effect is subtracted out. The first pyroelectric portion measures the protection layer's thermal response, which is then used to compensate for the same layer's effect on the second portion's measurement, maintaining sensitivity despite thicker protection.
Solution Approach 2:
The first pyroelectric portion acts as an intermediary that measures the thermal effect of the protection layer. This intermediary measurement allows the system to mathematically remove the protection layer's thermal influence from the final measurement, enabling the use of thicker protection layers without sacrificing measurement 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
This design improves image contrast by eliminating unnecessary signal portions, increasing sensor sensitivity, reducing energy consumption, and allowing for thicker protection layers, while maintaining high precision and simplifying fabrication by eliminating the need for complex calculations and precise heating control.
Implementation Method 1
Each pyroelectric capacitor comprises a portion made of a pyroelectric material located between a lower electrode and an upper electrode. One electrode is set at a constant potential, and forms a reference electrode. The other electrode collects pyroelectric charges, generated by the pyroelectric material in response to a temperature variation.
Implementation Method 2
A heat transfer between the skin and the contact surface of the sensor takes place by conduction, which leads to a first variation of the temperature with time.
Data Source
AI summary
A pyroelectric sensor includes several pixels distributed above a substrate and each pixel includes a first portion made of a pyroelectric material, in direct physical contact with a charge collection electrode, a second portion made of a pyroelectric material, in direct physical contact with a charge collection electrode, the first portion, the second portion and the at least one charge collection electrode being superposed above the substrate, at least one heating element to heat the first and second portions including a pyroelectric material, and an electronic device to measure a difference between charges generated by the first portion including a pyroelectric material and charges generated by the second portion including a pyroelectric material. The pyroelectric sensor makes it possible to suppress a useless part of a measurement signal. It is particularly advantageous for taking an image of a papillary print.