Capacitive micromachined ultrasonic transducer (cMUT) for biometric applications Thesis for the Degree of Erasmus Mundus Master of Nanoscience and Nanotechnology

Biometric devices (such as fingerprint sensors, iris scanners, face recognition systems etc.) are becoming more and more popular in areas where personal identification is required migration control, physical access, online banking etc. Nowadays the most used biometric sensor is a fingerprint scanner which provides a good combination of accuracy, size and price. However, fingerprint recognition is not always successful in case of sweaty/dirty fingers and the accuracy rate can fall down to 80-90% which is not enough for high-security applications. The solution of this problem can be found in combining fingerprint pattern with other biometric data inside the finger (vein pattern or bone geometry). It can be achieved using ultrasound imaging technique and capacitive micromachined ultrasonic transducer (cMUT) is a good choice to perform these measurements. The main advantage of cMUT is ideal design compatibility with the fingerprint sensor based on capacitive method a product of Fingerprint Cards AB (FPC) which participates as an industrial partner in this project. Modeling and fabrication of a cMUT array was done using the top interconnect layers of the CMOS technology which can be integrated in the process line of the FPC fingerprint capacitive sensor. Thus, it will be possible to create a multi-modal biometric device with an ability to acquire both fingerprint pattern and additional biometric features (vein pattern, bone geometry).