Capacitive Fingerprint Sensor Array for Low-Cost Integration
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Solution Overview
Problem
Conventional optical fingerprint acquisition apparatuses are structurally complex and costly, making them unsuitable for integration into portable devices like mobile phones, and existing MEMS-based systems are expensive.
Innovation Solution
A fingerprint acquisition apparatus using a plurality of sensing units with built-in capacitors that detect the difference in capacitance between fingerprint ridges and valleys, employing a simple circuit structure to differentiate between ridge and valley portions, allowing for fingerprint pattern generation on a single chip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical fingerprint acquisition apparatus is used, then measurement precision is acceptable, but device complexity increases and integration into portable devices becomes difficult
Solution Approach 1:
The patent replaces the conventional optical mechanical system with a capacitive sensing system. Instead of using lenses, light sources, and mechanical scanning components, the invention uses an array of capacitive sensing units that directly detect fingerprint features through capacitance changes, thereby eliminating mechanical complexity while maintaining detection capability
Solution Approach 2:
The patent changes the detection parameter from optical properties (light reflection, transmission) to electrical properties (capacitance). By measuring capacitance changes at each sensing unit when touched by fingerprint ridges or valleys, the system achieves fingerprint acquisition without complex optical-mechanical subsystems
2Device complexity
If MEMS system is used for single chip integration, then device complexity is reduced, but manufacturing cost becomes too high
Solution Approach 1:
The patent divides the fingerprint sensing function into multiple independent sensing units, each with its own capacitor and transistor switch. This modular segmentation allows the system to be implemented using standard semiconductor fabrication processes rather than complex MEMS techniques, reducing manufacturing cost while achieving single-chip integration
Solution Approach 2:
The patent uses simple, inexpensive components (capacitors and transistor switches) that can be easily fabricated using standard CMOS processes, replacing expensive MEMS structures. These simple components are sufficient for the application and can be manufactured cost-effectively at scale
3Ease of manufacture
If simple capacitor and transistor switch structures are used, then manufacturing cost is reduced and single chip integration is enabled, but the ability to distinguish fingerprint features must be maintained
Solution Approach 1:
The patent segments the sensing array into multiple units, each capable of independently detecting capacitance changes. This segmentation allows the system to build up fingerprint information from multiple simple measurements, achieving feature differentiation through spatial distribution of simple sensing elements rather than through complex individual sensors
Solution Approach 2:
The patent employs feedback mechanisms where the output of each sensing unit is processed to determine whether a ridge or valley was detected. By comparing capacitance changes against threshold values and processing signals from multiple units, the system achieves accurate fingerprint feature identification despite using simple individual components
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 solution reduces system complexity and cost, enabling fingerprint acquisition on a single chip by effectively distinguishing between ridge and valley portions through capacitance detection, thus simplifying the apparatus and making it suitable for portable devices.
Implementation Method 1
A inducing capacitor is formed when each of the sensing units is touched by the fingerprint. The built-in capacitor of the sensing unit and the inducing capacitor together form a first potential when the sensing unit is touched by the ridge portion of the fingerprint. The built-in capacitor of the sensing unit and the inducing capacitor together form a second potential when the sensing unit is touched by the valley portion of the fingerprint.
Data Source
AI summary
A fingerprint acquisition apparatus including a plurality of sensing units is provided. The fingerprint acquisition apparatus is used for sensing the ridge portion and the valley portion of a fingerprint. Each sensing unit includes a built-in capacitor. There is an inducing capacitance generated between each of the sensing units and the fingerprint while the fingerprint touches each of the sensing units. The fingerprint acquisition apparatus of the invention generates a fingerprint pattern by detecting the difference of inducing capacitances between the ridge portion of the fingerprint and the valley portion of the fingerprint.