A Method for Enhancing the Sensing Distance of a Fingerprint Sensor

Area of Science:

• Electrical Engineering
• Biometrics
• Materials Science

Background:

• Capacitive fingerprint sensors can suffer from reduced image quality at longer sensing distances due to fringe capacitance.
• Edge capacitance between sensor pixels and fingerprint patterns degrades the signal-to-noise ratio.

Purpose of the Study:

• To develop a method for improving fingerprint image quality at extended sensing distances.
• To reduce fringe capacitance in capacitive fingerprint sensors.

Main Methods:

• Air-walls were integrated onto the glass surface of a capacitive fingerprint sensor.
• Three-dimensional capacitance analysis was used to model fingerprint and air-wall structures.
• A prototype sensor with stacked glass layers and air-walls (50 μm depth, 50 μm pitch) was fabricated.

Main Results:

• The air-wall structure effectively reduced edge capacitance.
• Simulations and experiments confirmed high resolution, distinguishing 2.5 line pairs/mm at sensing distances of 300 μm and beyond.
• Image contrast improved substantially from 0.59 to 0.98.

Conclusions:

• The proposed air-wall structure is an effective solution for enhancing fingerprint image quality in capacitive sensors.
• This method enables reliable fingerprint pattern recognition at longer sensing distances.
• The technology offers improved performance for biometric security applications.