Thermal fingerprint sensing
Capture thermique d'empreintes digitales

Thermal fingerprint sensors are taking advantage of the large physical parameter differences between the skin and the air, namely thermal resistivity and thermal capacitance. Like other types of sensors, thermal sensing can be

  • passive: this is the temperature difference between the sensor and the skin which produces the heat exchange. static acquisition is a problem as the thermal equilibrium is quickly reached (less than one second).
  • active: injecting some heat in the pixel produces a temperature change. If it is the skin (ridge), the heat is pumped and the final temperature is lower than in the air (valley) situation.

The first commercial thermal fingerprint sensor was the FingerChip from Atmel (formerly Thomson-CSF), using PVDF-TrFE (a pyro-electric material able to convert changes of temperature into charges) as sensing layer over a silicon chip. This technology was coming from an uncooled IR camera. It was also the first swipe sensor in 1997: swiping enabled to use a passive sensor.

Other thermal fingerprint sensors are based on microthermistances, with or without heating, with or without a cavity (bolometers) to increase the thermal isolation so the sensitivity.

Thermal sensing

Products

Thomson-CSF > 2000 > Atmel

  • Atmel FingerChip , the best sensor ;-)
  • sweep thermal sensing
  • AT77C101 DIL COB color AT77C104 COB

    Next Biometrics

  • (2013 Dec) Next Biometrics unveils a new active thermal sensor, composed of an area sensor (LTPS -Low Temperature Poly Silicon- TFT -Thin Film Transistors- and Devices) on glass + a silicon companion chip to drive and read the sensor.

  • Reseach & Development

    Hunno Technologies

  • Hunno Technologies [www.hunno.com] & Hyung-Kew Lee (Korea, KAIST) have studied a thermal fingerprint sensor in 1999, probably using bolometers.

  • INO Institut National d'Optique

  • (1998) INO (Institut National d'Optique / Canada) has used bolometers to make a 160x120 pixel fingerprint sensor (US patent 6,633,656). Bolometric FPA for fingerprint recording
  • Papers:


    Nagoya University, then Wakayama University

  • Nagoya University has studied a thermal sensor based on MEMS, using a resistor to heat a sensor above a cavity.
    L'université de Nagoya a étudié un capteur thermique basé sur des éléments micro-usinés, utilisant une résistance pour chauffer un capteur situé au-dessus d'une cavité.
  • (2008) Hirobumi Han from the Wakayama university proposes a thermal sensor using micro-heaters on a polyimide substrate. Characteristics of thermal-type fingerprint sensor.
  • (2016 Apr) Survey of Biometric Authentication and Proposal of and Proposal of New Sensing Mechanism / Hirofumi Miki, Shigeki Tsuchitani (Department of Systems Engineering, Wakayama University).
    New? seems to be active sensing using polyimide, like the previous paper.

  • Papers:


    IMTEK

  • (2005) IMTEK & Schippers propose a thermal fingerprint sensor based on a similar technique than Nagoya Univ., adapted for a smart card.
  • Papers:

    • P. Schippers et al. (2005) "Thermal flexible foil-fingerprint sensor," Digest of Technical Papers. TRANSDUCERS '05, pp. 579-580 Vol. 1. doi: 10.1109/SENSOR.2005.1496483
    Imtek