CXA3621GE データシートの表示（PDF） - Sony Semiconductor

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CXA3621GE

Fingerprint Sensor

Sony Semiconductor 

CXA3621GE

Description of Operation

• Fingerprint sensor principle

The principle of this newly developed fingerprint sensor is described below (Fig. 1). The sensor block

contains an array of metal electrodes which are covered on top by an insulating film (overcoat). When a

finger (which is conductive matter) is placed directly against this surface, the three elements of the metal

electrode, the insulating film and the finger form a capacitor.

The difference between the fingerprint ridges and valleys is the difference in distance to the metal electrodes,

and becomes the difference in the capacitance values of the individually formed capacitors. (The ridge

capacitance values are determined by the dielectric constant of the insulating film, but the valleys contain air

in addition to this, making the difference between the ridge and valley capacitance values even greater than

the difference in distance.)

Using this principle, by applying a constant voltage to all metal electrodes, the charge level accumulated in

each electrode differs, making it possible to output the unevenness of the fingerprint as an electric signal by

transferring and converting these charges to voltages.

Ridge Valley

Si

Fig. 1

Fingerprint unevenness

Overcoat

Metal electrode

Inter-layer film

–8–

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