With the rapid development of the display technology, the semiconductor element technology as a core of display devices also gets great and rapid progress accordingly. For existing display devices, the organic light emitting diode (OLED) as a current-type light emitting device, has been more and more applied in the field of high performance display by right of its characteristics of self-luminous, quick response, wide view angle and manufacturably on a flexible substrate.
The OLED can be divided into passive matrix driving OLED (PMOLED) and active matrix driving OLED (AMOLED) according to the driving modes. Because the AMOLED display has the advantages of low manufacture cost, high response speed, power saving, DC driving available for a portable device, wide range of operating temperature etc., it is desirable to become the next generation of new flat panel displays in place of the liquid crystal display (LCD). In the existing AMOLED display panel, each OLED includes a plurality of thin film transistor (TFT) switch circuits. The amorphous silicon TFT is taken as an important electronic device because it has excellent static electricity characteristics, and has been widely used in liquid crystal displays and matrix image sensors etc.
However, in the prior art, the instability of the amorphous silicon TFT has always been an unsolved problem. A main instability of the amorphous silicon TFT is that shifts of the TFT threshold voltage may occur when it is applied with a DC gate bias for a long time. Specifically, in a high voltage area (generally greater than 25V), the threshold voltage shift is caused by shielding of the gate electric field after the trap in the insulating layer captures charges. In a low voltage area (generally the working voltage of the amorphous silicon TFT), the threshold voltage shift is caused by generation or elimination of dangling bond states due to bias in the active layer. The threshold voltage shift as above may result in decrease of the luminance of the AMOLED display, thereby influencing brightness constancy of the display. In addition, because the TFT in the AMOLED under the working state may be in a bias state for a long time, it accelerates attenuation of the TFT, thereby reducing the lifetime of the display device.
In addition, the fingerprint identification function is one of the commonly used functions of the electronic devices at present. It is important in enhancing security of the electronic device and expanding its application scope etc. However, most of current AMOLED displays do not have the fingerprint identification function, or they have to add an independent fingerprint identification circuit to achieve the purpose of fingerprint identification. In this way, however, the structure will be complex and the cost will be increased.