With the development of science and technology, more and more portable electronic devices such as mobile phones, digital cameras, tablet computers, laptop computers and the like have become indispensable in people's life. Since the portable electronic devices are generally used by individuals and store some private data, the data stored in the electronic device, such as address books, pictures, personal information and the like, is privately owned. If an electronic device is lost, the data therein may be used by others, which may cause unnecessary losses. An electronic device may be prevented from being used by others by means of password protection. However, a password is easily leaked or cracked. Therefore, data security is low. In addition, users may use an electronic device only when inputting a correct password. If the password is forgotten, much inconvenience may be caused to the users. Therefore, a personal fingerprint identification system has been currently developed for identity authentication to improve data security.
In the prior art, a capacitive fingerprint identification system is an extremely popular fingerprint identification means, which employs a contact layer to receive a contact from a user finger, and senses a capacitance change of the contact layer so as to determine finger ridges or finger valleys of a fingerprint of the user. In order to avoid that the contact layer receives interference from other circuits, a shield layer is usually laid out below the contact layer in a circuit layout of the prior art so as to generate a shielding effect, thereby avoiding interference generated by a circuit below the shield layer to the contact layer. However, a parasitic capacitance may be generated between the contact layer and the shield layer, and a capacitance value of the parasitic capacitance is often greater than a capacitance value of a contact capacitance generated from a contact, which influences determination of the capacitance value of the contact capacitance by a capacitive sensing circuit or a capacitive fingerprint identification system, thereby reducing precision of fingerprint identification.