InFO Fingerprint Sensor Electrode Layout to Reduce Circuit Interference
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Solution Overview
Problem
Conventional fingerprint sensors face interference issues due to the close proximity of sensing electrodes to the circuits in the sensor die, limiting the accuracy and sensitivity of fingerprint image capture.
Innovation Solution
The formation of sensing electrodes in Redistribution Layers (RDLs) rather than on the surface of the sensor die, which increases the distance between the electrodes and the circuits, reducing interference and allowing for a larger sensing area without sacrificing sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If sensing electrodes are placed on the surface of the sensor die, then the sensing area can be maximized, but the proximity to circuits causes interference that reduces measurement precision
Solution Approach 1:
The sensing electrodes are moved from the surface plane to the backside of the sensor die, utilizing the third dimension (depth) to separate the sensing function from the circuit function. This vertical separation eliminates electromagnetic interference while preserving the full sensing area on the front surface.
Solution Approach 2:
The sensor die is divided into functionally separate regions: the front surface dedicated to sensing electrodes and the backside dedicated to circuits. This segmentation allows each component to perform its function optimally without mutual interference.
2Device complexity
If sensing electrodes are placed close to circuits for compact design, then device complexity is reduced, but circuit interference degrades sensitivity
Solution Approach 1:
By utilizing the backside of the sensor die for circuit placement, the design achieves spatial separation in the vertical dimension while maintaining a compact overall footprint. This resolves the conflict between compactness and sensitivity.
3Ease of manufacture
If wire bonding is used to connect bond pads to external circuits, then manufacturing is simplified, but the bonding process adds complexity and potential failure points
Solution Approach 1:
The bond pads are directly integrated with the circuit traces on the backside of the sensor die, eliminating the need for separate wire bonding structures. This merging of functions reduces the number of interconnection components and potential failure points.
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 enhances the sensitivity and durability of fingerprint sensor packages by reducing circuit interference and enabling a larger sensing area, improving the accuracy and quality of fingerprint image capture.
Implementation Method 1
capacitance sensors use principles associated with capacitance in order to form fingerprint images. Each of the sensing electrodes in a sensor array acts as one plate of a parallel-plate capacitor. The dermal layer (which is electrically conductive) of the finger to be sensed acts as the other plate, and the non-conductive epidermal layer of the finger acts as a dielectric layer.
Data Source
AI summary
A package includes a sensor die, and an encapsulating material encapsulating the sensor die therein. A top surface of the encapsulating material is substantially coplanar with or higher than a top surface of the sensor die. A plurality of sensing electrodes is higher than the sensor die and the encapsulating material. The plurality of sensing electrodes is arranged as a plurality of rows and columns, and the plurality of sensing electrodes is electrically coupled to the sensor die. A dielectric layer covers the plurality of sensing electrodes.