Improvement of the Sensitivity of a Passive RFID Magnetic SAW Sensor Based on Love Waves

In this paper we study and fabricate surface acoustic wave devices that combine magnetic field and temperature measurements and that integrate a radio-frequency identification functionality (RFID). The use of a Transmissive-Reflective Delay Line (TR-DL) design enables to control the amplitude of the RFID signal peaks while maximizing the sensitivity of the sensor. The latter is based on a double layer of magnetoelastic CoFeB film used as sensitive layer to the magnetic field and deposited on top of a ZnO-covered LiNbO
3
Y-X substrate. This structure is used to generate a Love wave which enhances the sensitivity to the magnetic field. The achieved device demonstrates a high sensitivity to the magnetic field, a temperature compensation and reflected signal levels of -20 dB in a wired connection. The obtained sensitivity of 3630 ppm/mT (or 1.482 Hz/nT), is among the highest reported in the literature on magnetic SAW sensors.