Fingerprint Sensor Coupling Electrode ESD Protection
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Solution Overview
Problem
Fingerprint sensing devices, such as capacitive fingerprint sensors, face challenges in achieving adequate capacitive coupling and electrostatic discharge (ESD) protection in resource-constrained devices like smart cards and IoT devices, where cost-sensitive and low-performing computing platforms require miniaturization without compromising sensitivity or ESD protection.
Innovation Solution
A fingerprint sensing device is designed with a substrate having a fingerprint sensor on one side and a coupling electrode on the other, providing capacitive coupling between the finger and the sensor's circuit ground, while also acting as an ESD path, with the coupling electrode being larger in area than the sensor and positioned to surround it, ensuring effective capacitive coupling and ESD protection without overlapping the sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the sensor size is reduced to minimize device area, then the device area is reduced, but the sensor sensitivity deteriorates
Solution Approach 1:
The coupling electrode is positioned on the backside of the substrate, creating a three-dimensional arrangement where the coupling electrode and sensor do not overlap in the planar projection. This spatial separation in the vertical dimension allows the coupling electrode area to be enlarged without occupying sensor area, thereby improving capacitive coupling while maintaining small sensor footprint and sensitivity.
Solution Approach 2:
The coupling electrode is designed to surround the projection of the sensor, creating a nested geometric relationship where the coupling electrode forms an outer boundary that encloses the sensor area. This nesting arrangement maximizes the coupling electrode area relative to the sensor while maintaining compact overall device dimensions.
2Reliability
If the coupling electrode area is increased to improve capacitive coupling, then the capacitive coupling is improved, but the device area increases
Solution Approach 1:
By moving the coupling electrode to the backside of the substrate and utilizing the vertical dimension for spatial arrangement, the design achieves large coupling electrode area for improved capacitive coupling without increasing the planar device footprint. The coupling electrode surrounds the sensor projection without overlapping, enabling enhanced coupling in a compact form factor.
3Reliability
If the coupling electrode overlaps with the sensor, then the capacitive coupling is improved, but the ESD protection is compromised
Solution Approach 1:
The device structure is segmented into two separate layers: the sensor is positioned on the front side of the substrate while the coupling electrode is positioned on the backside. This spatial segmentation eliminates overlap between the coupling electrode and sensor, preventing ESD interference while maintaining effective capacitive coupling through the substrate.
Solution Approach 2:
The coupling electrode is relocated to the backside of the substrate, creating vertical separation from the sensor. This three-dimensional arrangement allows the coupling electrode to provide both capacitive coupling and ESD protection simultaneously, as the non-overlapping configuration prevents ESD interference while the close proximity through the thin substrate maintains coupling effectiveness.
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 achieves enhanced capacitive coupling and ESD protection, maintaining sensor sensitivity while minimizing the sensor's size, thus addressing the conflict between area reduction and sensitivity, and facilitating integration into resource-constrained devices.
Implementation Method 1
a coupling electrode placed on another side of the substrate, wherein the coupling electrode is arranged to provide a coupling capacitance between a surface of a finger and a circuit ground of the fingerprint sensor
Implementation Method 2
the coupling electrode is further arranged to provide an electrostatic discharge path
Data Source
AI summary
In accordance with a first aspect of the present disclosure, a fingerprint sensing device is provided, comprising: a substrate; a fingerprint sensor placed on one side of the substrate; a coupling electrode placed on another side of the substrate, wherein said coupling electrode is arranged to provide a coupling capacitance between a surface of a finger and a circuit ground of said fingerprint sensor. In accordance with a second aspect of the present disclosure, a corresponding method of producing a fingerprint sensing device is conceived.