Capacitive Fingerprint Sensor With Through-Chip Vias
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Solution Overview
Problem
Capacitive fingerprint sensors face reduced sensitivity and accuracy due to the need for a cover plate that increases the distance between the sensor plates and the finger, making it difficult to discriminate between ridges and valleys.
Innovation Solution
The implementation of electrically conductive through-chip vias extending from connection points on a capacitive sensor array chip to the back side, allowing a cover plate to be attached at a spacing of less than 25 μm, reducing the distance between the cover plate and the sensor chip, thereby enhancing sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cover plate is placed over the sensor array to protect it from damage, then the sensor durability is improved, but the distance between the sensor plates and the finger increases, reducing sensitivity and measurement precision
Solution Approach 1:
The patent introduces an intermediary structure (recessed mounting configuration) between the cover plate and sensor array that allows the cover plate to be positioned closer to the sensor elements. This intermediary mechanism enables the cover plate to provide protection while minimizing its impact on the capacitive measurement distance, thereby resolving the contradiction between durability and measurement precision.
2Measurement precision
If the distance between the cover plate and sensor is reduced to improve sensitivity, then measurement precision is improved, but the protection capability of the cover plate is reduced
Solution Approach 1:
The patent employs a nested structure where the sensor array is recessed into the substrate, and the cover plate is positioned to overlie the recessed sensor array. This nesting configuration allows the cover plate to be in close proximity to the sensor elements (improving sensitivity) while still providing adequate protection through its positioning over the recessed area, thus resolving the contradiction between measurement precision and protection capability.
3Measurement precision
If the cover plate is positioned closer to the sensor array, then sensitivity is improved, but the risk of damage to the sensor from pressure or foreign substances increases
Solution Approach 1:
The patent segments the sensor assembly into distinct functional zones: a recessed area housing the sensor array and a raised area providing protection. This segmentation allows the sensor elements to be positioned close to the cover plate for high sensitivity while the raised protective structure around the recessed area shields the sensors from direct exposure to pressure and foreign substances, thereby resolving the contradiction between sensitivity and vulnerability to harmful factors.
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 approach improves the sensitivity and accuracy of fingerprint capture by reducing the distance between the cover plate and the sensor, allowing for better discrimination between ridges and valleys while maintaining the durability of the cover plate.
Implementation Method 1
each cell 102a, 102b corresponds to a pixel and includes two conductor plates 104a, 104b, covered with an insulating layer 106 which acts as a capacitor dielectric
Implementation Method 2
the insulating layer 106 which acts as a capacitor dielectric
Data Source
AI summary
A method of creating an improved sensitivity capacitive fingerprint sensor involves forming vias from a first side of a sensor chip having an array of capacitive sensors, making the vias electrically conductive, and attaching a cover plate over the first side of the sensor chip spaced from the sensor chip by a distance of less than 25 μm. An improved sensitivity capacitive fingerprint sensor has a capacitive sensor array including multiple sensor cells and electrically conductive, through-chip vias extending from connection points for sensor cell circuitry to a back side of the capacitive sensor array, a chip including active detection circuitry and electrical connection points, the electrical connection points being respectively connected to corresponding ones of the sensor cell circuitry connection points, and a cover plate, disposed above the sensor cells at a spacing of less than 25 μm.