A novel photo sensor by LTPS TFT backplane technology is developed, which amorphous silicon (a‐Si) layer stacks on poly silicon (p‐Si) layer to form a vertical hybrid poly and amorphous silicon PIN photo diode (HPAS‐PIN). This photo diode shows good photosensitivity as traditional a‐Si photo sensor. An optical fingerprint sensor array is realized based on the novel HPAS‐PIN photo diode and successfully capturing fingerprint image.
LTPS image sensor (LIS) driven by active pixel senor (APS) circuit based on LTPS backplane technology is demonstrated. Optical solution for LCD with in-cell optical fingerprint scanning function is discussed. A 400PPI LTPS-TFT LCD with in-cell touch and in-cell screen fingerprint scanning function is designed to realize fingerprint image capture when finger is 1.0mm height over the LIS array.
A method of FTDI (Fingerprint Touch Display Integration), namely LTPS TDDI with full‐screen optical multi‐points fingerprint recognition function, is proposed. Display driven circuit, touch function and fingerprint image sensor are designed in the same LTPS TFT glass substrate. Partitions image collection design combined with skip‐frame driving are adopted to realize multi‐points fingerprint image collection. Photoconversion characteristics together with noise characteristics of fingerprint system are also presented. By improving sensitivity of APS circuit and decreasing readout noise, the FTDI can get a false rejection ratio <1.0% when single point fingerprint recognition mode is used.
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