What's New

In recent years, although face recognition locks and video locks have seen rapid growth, data released by authoritative institutions shows that fingerprint recognition modules are still the standard biometric solution in both existing market stock and newly launched products by brands.

As the most widely used biometric method in smart locks, some observant users may have noticed that some smart locks come with larger fingerprint sensors, while others are smaller in size.

Compared to smaller modules, larger fingerprint modules cover a greater area of the skin. So, does this mean they perform better in terms of recognition accuracy and security?

Currently, most fingerprint sensors in smart locks are capacitive sensors. These sensors are made up of a capacitive array, typically containing around 10,000 miniaturized capacitors. When a user places their finger on the sensor, the skin forms one plate of the capacitor array, with the insulated substrate on the back forming the other. Since the ridges and valleys of fingerprints vary in distance across different regions, the capacitance of each unit changes accordingly, producing a fingerprint image.

Industry-standard fingerprint sensors typically come in sizes such as 160×160, 112×88, and 80×64, with 160×160 and 112×88 being the most common. Among these, the AA area (active area) is the most important — a larger AA area allows for capturing more fingerprint data at once, which can significantly improve FRR (False Rejection Rate) and FAR (False Acceptance Rate). If the AA area is too small, even a large fingerprint module may frequently “miss” the correct fingerprint area.

However, it’s important to note that the visible size of a fingerprint sensor does not always equate to its AA area. In other words, a large fingerprint sensor only determines the upper limit of recognition performance — it does not guarantee a better baseline performance.

So, a larger fingerprint module does not necessarily mean better recognition performance. In fact, if the internal chip’s AA area remains unchanged in a larger module, the chances of “off-target” fingerprint presses may even increase.

From a manufacturing perspective, there are currently two common processes for capacitive fingerprint modules: Coating and glass cover plate. These mainly differ in surface treatment:

Coating process: Ink is directly sprayed onto the fingerprint chip surface, usually in three layers — primer, intermediate coat, and top coat.

Glass cover plate process: The surface of the fingerprint chip is coated or glued, and a glass plate is applied and then defoamed.

Regarding small-area fingerprint modules, in recent years, as capacitive fingerprint technology has become more mature — coupled with intense industry competition and cost control — the AA areas of fingerprint modules have been shrinking, which places higher demands on the performance of the MCU (microcontroller unit).

In summary:

❶ What affects the fingerprint module's recognition performance is not the visible size, but the AA area (active sensing area). The larger the AA area, the more fingerprint data can be captured in one scan, significantly impacting FRR and FAR.
❷ Do not blindly pursue large-sized fingerprint modules — if the AA area is small, the recognition performance will still be poor. The module size only determines the potential ceiling of fingerprint performance, not the baseline.
❸ Smaller fingerprint modules require more powerful MCUs, and as fingerprint recognition algorithms continue to improve, it's likely that fingerprint module AA areas will continue to decrease in size.