Semiconductor fingerprint sensorAlso known as single-chip integrated fingerprint sensor or CMOS solid-state fingerprint sensor, it was introduced in the late 1990s. Mainly including temperature difference sensing fingerprint sensors and capacitive sensing fingerprint sensors.

(1) Temperature sensitive fingerprint sensor

It is made based on the principle of temperature sensing, with each unitsensorIt represents one pixel, and the entire integrated fingerprint sensor is placed under constant temperature control (which is slightly lower than body temperature). When the finger is placed on the fingerprint sensor, the temperature of the fingerprint sensor is controlled below+33C, and the temperature of the ridge point on the fingerprint represents body temperature. The temperature of the valley point on the fingerprint is the ambient temperature. Therefore, the ridge point andsensorThe temperature difference between them is not equal to the temperature difference between the valley and the sensor, and fingerprint images can be obtained through scanning. The scanning rate of this sensor is very fast, and it is necessary to obtain fingerprint images in a very short time, generally less than 0.1 seconds. Because over time, the fingers and chips become at the same temperature.

(2) Capacitive sensing fingerprint sensor

It is composed of a capacitor array and contains approximately 10000 miniaturized components insidecapacitor. When the user places their finger on the front, the skin forms one electrode of the capacitor array, and the back of the capacitor array is an insulated electrode. Due to the unequal distance between the ridges and valleys of fingerprints in different regions, the capacitance of each unit varies accordingly, thus obtaining fingerprint images.

Semiconductor fingerprint sensorIt has the advantages of low price, small size, and high recognition rate, but its disadvantage is that its service life is not as long as optical imaging equipment, and the imaging quality is slightly worse than ultrasonic scanning. In addition, this fingerprint sensor is susceptible to interference from external electromagnetic fields, and the most dangerous situation is the occurrence of electrostatic discharge (ESD) that can damage the chip. To achieve this, the following measures can be taken: firstly, the protective film of the capacitive sensing fingerprint sensor should be as thin as possible (not exceeding a few millimeters) and have good insulation performance; Secondly, add electrostatic protection circuits that can withstand electrostatic voltages of several thousand volts or more; Thirdly, connect the device and fingers to the ground.