Acoustic wave sensing system based on aluminum nitride dual-mode sensors and digital phase detection approach

Recently, SAW sensors with high sensitivity, low cost and compact size attracted interests in various sensing fields, especially in the biosensing fields. This work focuses on the developments of AlN thin film based SAW sensor system, related digital phase detection system and the AlN SH-SAW sensor applications.;A complete process procedure has been developed to fabricate delay line devices using plasma source molecular beam epitaxy system and photolithography techniques. Critical parameters, such as insertion losses and operating frequencies of devices, have been measured to assist to reduce the influences of the second order effects, like electromagnetic feedthrough, edge reflections and triple transient interference. Sensor and circuit optimizations have led to high signal noise ratio for differential sensors.;A digital phase detection system based on the zero-crossing algorithm has been developed. Phase detection limits with and without AlN differential sensors have been measured. Our baseline experiments without a sensor indicate that the system has a level of phase noise with the standard deviation being about 0.005°. Experiments with the AlN differential sensors running in the SAW and SH-SAW modes illustrate that the system can reach a phase detection limit of 0.02° at operating frequencies of more than 200 MHz. Differential configuration exhibits excellent performance regarding impact of temperature variation on the two sensors.;Several kinds of coating methods and flow cells for liquid sensing experiments have been developed and compared. Conductivity and viscosity sensing experiments have been taken and the results exhibit the attractive features of the AlN SH-SAW mode in liquid applications. Biosensing procedures for detecting E. coli K99 have been undertaken and the results show responses and sensitivity of AlN sensors to the binding between bacteria and specific antibodies.