17 March 2008 Characteristics of thermal-type fingerprint sensor
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In this paper, a novel micro fingerprint sensor was proposed using densely arrayed micro heaters as the sensing elements. Because it senses the temperature differences between the touching ridges and non-touching valleys of fingerprint patterns, there is no electrical static discharge (ESD), and promising to realize robust sensing. By MEMS process, it could be fabricated portably small size. Silicon-based and poyimide (PI) film-based approach was tried. In the first case, due to its great thermal conductivity (λ-silicon: 150 W/m•K), special structure was necessary for the thermal isolation that make the fabrication process complex and expensive. In the latter case, with the thickness of 25μm PI film (λ: 0.12 W/m•K) as the substrate, other special structure was not necessary for further thermal isolation, and flexible enough to be easily attached to non-planar surface. The whole fabrication process was simple and achieved in a low temperature range (< 130°C). The arrayed sensing elements were micro resistors made from sputtered platinum. Because of its small thermal capacity (sensing element: 200nm thick /10μm wide) and effective thermal isolation, this sensor was very sensitive (at 5V input, ΔT: 270°C /0.1μs). Characteristics of the sensor (silicon and PI film-based) were introduced, and the sensing principle was demonstrated by experiments.
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Hiro Han, Hiro Han, Yasuhiro Koshimoto, Yasuhiro Koshimoto, } "Characteristics of thermal-type fingerprint sensor", Proc. SPIE 6944, Biometric Technology for Human Identification V, 69440P (17 March 2008); doi: 10.1117/12.777024; https://doi.org/10.1117/12.777024


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