Integrated Fingerprint and Force Sensor on Flexible Circuit
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Solution Overview
Problem
Conventional methods for integrating fingerprint sensors with other input devices, such as buttons, result in increased thickness and design complexity, along with the need for mechanical switches that can affect other components in electronic devices.
Innovation Solution
A flexible circuit-based solution that combines a fingerprint sensor and a force sensor, where the flexible circuit serves as a common substrate for both sensors, with a compressible layer and force electrodes, allowing for integrated sensing and reduced thickness, and minimizing electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a discrete fingerprint sensor is stacked over a mechanical tactile switch, then fingerprint sensing functionality is integrated with button input, but the overall thickness increases and mechanical switch design constraints affect other components
Solution Approach 1:
The patent merges the fingerprint sensor and force sensor into a single integrated sensor package that combines both sensing functionalities. The fingerprint sensor electrodes and force sensor electrodes are integrated on the same substrate, allowing both fingerprint identification and force detection to occur through the same physical structure, thereby reducing overall thickness while maintaining dual functionality.
Solution Approach 2:
The integrated sensor package serves multiple functions simultaneously: it detects fingerprint patterns through capacitive coupling and measures applied force through the force sensor. This multi-functional design eliminates the need for separate discrete sensors, reducing thickness and design complexity while providing versatile input capabilities.
2Adaptability or versatility
If a discrete fingerprint sensor is stacked over a mechanical tactile switch, then button input functionality is achieved, but mechanical switches create design constraints that affect other device components
Solution Approach 1:
The patent replaces the mechanical tactile switch with a force sensor that uses capacitive or piezoresistive sensing mechanisms. This substitution eliminates moving parts, contact wear, and mechanical complexity while providing equivalent button press detection capability. The force sensor detects pressure through electrical property changes rather than mechanical contact, simplifying the overall device design.
Solution Approach 2:
The patent introduces a compressible layer as an intermediary between the fingerprint sensor and the force sensor. This layer transmits mechanical pressure from the user's finger to the force sensor while maintaining electrical isolation and enabling proper capacitive coupling for fingerprint detection. The compressible layer mediates the interaction between the two sensing mechanisms, allowing both to function optimally within the integrated structure.
3Productivity
If fingerprint sensor and force sensor are integrated on a flexible circuit, then manufacturing efficiency is improved and thickness is reduced, but electromagnetic interference between sensors must be minimized
Solution Approach 1:
The patent extracts and separates the electrode patterns for the fingerprint sensor and force sensor into distinct regions on the flexible circuit substrate. By spatially separating the electrode layouts and using dedicated trace routing, the design minimizes capacitive coupling and electromagnetic interference between the two sensing systems while maintaining their integrated structure for manufacturing efficiency.
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 simplifies the integration of fingerprint and force sensors, reducing design complexity and thickness, while enabling effective detection of both fingerprint and force information, enhancing usability and manufacturing efficiency.
Implementation Method 1
The force sensor comprises a compressible layer disposed between the second portion of first side and the first portion of the first side, and one or more force electrodes
Implementation Method 2
The fingerprint sensor is disposed on the first portion of the second side and comprises a sensor package. The sensor package includes an integrated circuit, and fingerprint sensor electrodes communicatively coupled to the integrated circuit
Data Source
AI summary
An integrated sensing device comprising a force sensor and fingerprint sensor disposed on different portions of a flexible circuit. The fingerprint sensor is disposed on a first side of a first portion of the flexible circuit and the force sensor is disposed on a second portion of the flexible circuit. The flexible circuit is configured such that the first portion is over the second portion. The fingerprint sensor includes fingerprint sensor electrodes disposed on the first side of the first portion. The force sensor comprises a compressible layer disposed between a second side of the first portion and a first side of the second portion, and one or more one force electrodes.