Pyroelectric Skin Print Sensor Third Electrode Capacitance
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Solution Overview
Problem
Existing pyroelectric sensors face challenges in accurately discriminating between skin ridges and valleys, leading to difficulties in acquiring high-quality images due to similar output values from cells topped with ridges and valleys.
Innovation Solution
The introduction of a third electrode coated with a dielectric layer, arranged to form a capacitor with the user's skin, enhances the capacitance difference between cells topped with ridges and valleys, amplifying the voltage level difference and improving image discrimination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a standard pyroelectric sensor structure is used, then the device complexity is low, but the measurement precision for discriminating skin ridges and valleys is insufficient
Solution Approach 1:
The sensor structure is segmented into distinct functional components: a pyroelectric conversion element with first and second electrodes, and a separate third electrode forming a capacitor with the skin. This segmentation allows each component to contribute specifically to the overall measurement precision without excessive complexity
Solution Approach 2:
A third electrode coated with a dielectric layer is introduced as an intermediary element between the pyroelectric sensor and the skin. This intermediary forms a capacitor that enhances the voltage level difference between ridges and valleys, improving measurement precision while maintaining manageable device complexity
2Measurement precision
If the dielectric layer thickness is reduced, then the capacitance difference between ridges and valleys is enhanced, but the manufacturing precision requirements increase
Solution Approach 1:
The dielectric layer thickness is optimized within a specific range (0.5 μm to 50 μm) to achieve the desired capacitance difference. By defining this parameter range, the patent balances the need for enhanced measurement precision against the practical constraints of manufacturing 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 configuration allows for better differentiation between skin ridges and valleys, resulting in improved image quality by varying the capacitance and charge generation based on skin topography.
Implementation Method 1
each cell comprising a pyroelectric conversion element comprising first and second electrodes separated by a layer of a pyroelectric material
Implementation Method 2
a third electrode connected to the sense node and coated with a dielectric layer, the third electrode being intended to form a capacitor with a user's skin
Data Source
AI summary
The invention relates to a skin print sensor (120) comprising a plurality of elementary acquisition cells (121) which are arranged in and/or on a substrate and each of which includes: a pyroelectric conversion element (PYR) comprising first and second electrodes that are separated by a layer of pyroelectric material, the first electrode being connected to a node (GND) applying a reference potential of the sensor, and the second electrode being connected to a reading node (SN) of the cell; and a third electrode (EL) which is connected to the reading node (SN), is coated with a dielectric layer and is designed to form a capacitance along with the skin of a user.