Fingerprint Sensor Types
There are many types of Fingerprint Sensor Types, but most commonly used are Optical Fingerprint sensors and Capacitive fingerprint sensors.
Capacitive sensors use an array capacitor plates to image the fingerprint. Skin is conductive enough to provide a capacitive coupling with an individual capacitive element on the array.
Ridges, being closer to the detector, have a higher capacitance and valleys have a lower capacitance.
Capacitive sensors can be sensitive to electrostatic discharge (shock) but they are insensitive to ambient lighting and are more resist contamination issues than some optical designs.
Capacitive sensors use a difference between skin-sensor and air-sensor contact in terms of capacitive values.
When a finger is placed on the sensor, an array of pixels measures the variation in capacity between the valleys and the ridges in the fingerprint.
Optical sensors use arrays of photodiode or phototransistor detectors to convert the energy in light incident on the detector into electrical charge.
The sensor package usually includes a light-emitting-diode (LED) to illuminate the finger.
With optical sensors, the finger is placed on a plate and illuminated by LED light sources. Through a prism and a system of lenses, the image is projected on a CMOS image sensor. Using frame grabber techniques, the image is stored and ready for analysis.
- Greater miniaturization
- Newer technology
- Can be embedded into small devices
- Prone to dirt etc since finger touches silicon
- Relatively cheap
- Larger sensing area since manufacturing large pure silicon chips is expensive
- More robust. Longer life
- More expensive
- Better image quality and higher resolution
Fingerprint Sensor Types
|A Comparison : Optical vs. Capacitive (Semiconductor) Fingerprint Sensors|
(Semiconductor or chip)
|Sensor Surface||No special treatments or maintenance required||Usually needs surface treatments, including ESD and other protective coatingsCoatings may be uneven, wear out over time, degrade performance, and shorten product lifetime|
|Overall Durability||Scratch-proof, unbreakable glass platen made of material as hard as quartz. Resistant to shock, ESD, and extreme weather||Corrodes easily from repeated handling and everyday exposureSusceptible to damage by electrostatic discharge
Thin silicon chips are inherently fragile and susceptible to damage by hard external impact and scratches
|Imaging Area, Resolution, and Size||Large imaging area (0.5 inch x 0.6 inch)High resolution (500 dpi)
Large image size (78,000 pixels)
|Usually smaller imaging area, image size, and resolution due to greater cost of manufacturing larger, high-quality chips|
|Cost-Effectiveness||Low manufacturing cost, long life, no maintenance required||Consistent quality surface coatings may be expensive to produceReplacement, maintenance, and downtime costs can add up|
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