Fingerprint Sensor With Through-Wafer Leads and Flush Mounting
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Solution Overview
Problem
Current fingerprint sensors are either too large and expensive for widespread use, or they require complex production methods and are impractical in design due to their recessed positioning, which can lead to dirt accumulation and reduced image quality.
Innovation Solution
A fingerprint sensor with sensor elements on one side of a silicon substrate and a processing unit on the other, utilizing through-wafer conducting leads and a dielectric protecting layer, allowing for flexible production and flush mounting, enabling impedance measurements with a second conductor lead for improved functionality and aesthetics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fingerprint sensors are made large for immigration control applications, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The sensor is divided into two separate substrates: a sensor substrate containing sensor elements and a processing substrate containing the processing unit. This segmentation allows each substrate to be optimized independently and manufactured using standard processes, reducing overall complexity while maintaining measurement precision.
Solution Approach 2:
A through-substrate conductor structure acts as an intermediary, providing electrical connection between the sensor elements on the sensor substrate and the processing unit on the processing substrate. This mediator enables signal transmission while allowing the substrates to be manufactured separately and assembled later.
2Ease of manufacture
If sensor elements are positioned in a recess in the product shell, then ease of manufacture is improved, but object-affected harmful factors worsen due to dirt accumulation
Solution Approach 1:
The sensor surface is positioned in the same plane as the product surface rather than being recessed below it. This dimensional change eliminates the recess that causes dirt accumulation while maintaining ease of manufacture through standardized mounting structures.
3Device complexity
If through substrate via conductors are used in insulating substrates, then device complexity is reduced, but manufacturing precision worsens due to insulation requirements
Solution Approach 1:
The substrate material is changed from insulating materials (glass, ceramics) to semiconducting material (silicon). This parameter change in material properties eliminates the need for complex insulation structures in via conductors, as the silicon substrate itself provides the necessary electrical characteristics.
4Device complexity
If single chip solutions with circuitry in substrate are used, then device complexity is reduced, but ease of manufacture worsens due to complex production methods
Solution Approach 1:
The integrated circuitry is segmented into the processing unit on a separate processing substrate, which can be manufactured using standard semiconductor fabrication processes. This segmentation allows the sensor substrate and processing substrate to be manufactured independently and assembled together, improving ease of manufacture.
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 enables a cost-effective, high-volume production of fingerprint sensors that can be mounted flush with the surface, reducing dirt accumulation and improving image quality while allowing for flexible production and efficient impedance measurements.
Implementation Method 1
The substrate also comprises a dielectric layer insulating the sensor elements from the substrate
Implementation Method 2
The processing unit is adapted to measure an impedance at the finger surface
Data Source
Figure 1~2
AI summary
The invention relates to a sensor for measuring structures in a surface, e.g. a fingerprint sensor comprising a chosen number of sensor elements at chosen positions for coupling to a finger surface having a size less or comparable to the size of the structures in the finger surface, and a processing unit including interrogation electrodes coupled to said sensor elements for providing impedance measurements at said finger surface, the processing unit being mounted on one side of a substrate and the sensor elements being positioned on the opposite side of said substrate, the substrate including through going first conducting leads between said sensor elements and said interrogation electrodes. The substrate is made from a semiconductor material such as silicon and said first conducting leads are constituted by through going substrate sections of a chosen size surrounded byan insulating dielectric separating them from the substrate.