Development of aluminum nitride-based acoustic wave sensors

One of the most important applications of acoustic wave sensor systems is to detect chemical or biological agents because of their great potential for realtime and highly sensitive detection at low cost. We report preliminary experimental results on developing novel acoustic wave sensors for biomedical applications using aluminum nitride (AlN) thin films. Compared to conventional piezoelectric materials such as quartz, AlN is advantageous in terms of higher acoustic velocity, higher electromechanical coupling coefficient, and higher stability in harsh environment, translating to better sensor performance. We have designed, prototyped, and tested an AlN-based. sensor. The center frequency is measured 174 MHz for its surface acoustic wave mode and 206 MHz for its surface transverse wave mode. The phase velocities are 5569 m/s and 6608 m/s, respectively. As expected, the frequency response of the surface transverse wave mode changed little when under water load. Immobilization was investigated using chemical compounds or magnetic microbeads. The result showed good affinity to AlN film. Finally, we found an almost linear relationship between the resonant frequency of the sensor and temperature, with the temperature coefficient being about 90 PPM/°C.