Performance improvement of high frequency aluminum nitride ultrasonic transducers

This paper presents three methods to improve the performance of a high frequency aluminum nitride (AlN) ultrasonic transducer. For a high frequency AlN ultrasonic transducer, its properties are related with its top electrode size, electrical impedance matching and layers of the piezoelectric plate. However, until now, no research has been published to analyze their influence on the performance of AlN ultrasonic transducers, especially in the frequency range above 200 MHz. First, two factors related with the top electrode size are proposed based on transmission coefficient and stored energy, and analysis is performed on an Al-AlN-Al on silicon wafers with different electrode sizes. The result proves when the electrode size is 1mm2, the transducer can provide the maximum output voltage and the maximal signal- to-noise ratio (SNR). Then, electrical impedance matching is conducted to improve the performance of transducers, and the experiment result shows that after matching , the resolution and sensitivity have been improved. Finally, a stacked AlN transducer is developed and its model is constructed to analyze its properties in time domain and frequency domain. The comparison between the simulation and the experiment shows the effectiveness of the proposed model, and a stacked structure can be used to improve the sensitivity of a high frequency AlN ultrasonic transducer.