Abstract
In this paper, we introduce a transparent fingerprint sensing system using a thin film transistor (TFT) sensor panel, based on a self-capacitive sensing scheme. An armorphousindium gallium zinc oxide (a-IGZO) TFT sensor array and associated custom Read-Out IC (ROIC) are implemented for the system. The sensor panel has a 200 × 200 pixel array and each pixel size is as small as 50 μm × 50 μm. The ROIC uses only eight analog front-end (AFE) amplifier stages along with a successive approximation analog-to-digital converter (SAR ADC). To get the fingerprint image data from the sensor array, the ROIC senses a capacitance, which is formed by a cover glass material between a human finger and an electrode of each pixel of the sensor array. Three methods are reviewed for estimating the self-capacitance. The measurement result demonstrates that the transparent fingerprint sensor system has an ability to differentiate a human finger’s ridges and valleys through the fingerprint sensor array.
Highlights
Fingerprint sensors have become a popular biometric identification solution for mobile devices, such as the smart phone [1,2]
A sensor relies on self-capacitance, which is formed between a human finger and sensing electrodes
The transmittance of the fabricated transparent fingerprint sensor array can be attached to a conventional display panel to detect identity, thin film transistor (TFT)
Summary
Fingerprint sensors have become a popular biometric identification solution for mobile devices, such as the smart phone [1,2]. There is an effort to adopt the entire display area of a smart phone as a fingerprint sensor. In such cases, a transparent fingerprint sensor should be embedded under the cover glass on top of an existing display panel area, in order to realize a front-panel fingerprint system. A sensor panel’s pixel dimension must be less than 50 μm × 50 μm to realize a high-resolution fingerprint sensor array. In order to realize large panel sensor systems, there are a few technical challenges to overcome In this case, a sensor relies on self-capacitance, which is formed between a human finger and sensing electrodes. A given cover unrealistically small, since mobile phones often require a thicker cover glass for safety.
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