Electronic Design

Aluminum Nitride In The Offing For Acoustic Sensing

The laser micromachining of aluminum-nitride (AlN) holds promise as a piezoelectric material for acoustic sensing, as demonstrated by experiments at Wayne State University, Detroit, Mich. Researchers Feng Zhong, Changhe Huang, and Gregory W. Auner have shown the material to have good performance characteristics for both surface transwave (STW) and surface acoustic-wave (SAW) detection. They used a dual-mode AlN sensor to demonstrate both detection methods.

The material has high acoustic velocity, a linear thermal coefficient, and a large electromechanical coupling coefficient. These properties make it well-suited for biochemical applications such as liquid sensing, where conventional SAW sensors suffer excess attenuation when exposed to liquids.

AlN can be used in high-frequency (up to 2.4 GHz) bandpass filters for wireless and mobile communications. It's also highly selective for detecting gases and organic compounds when it serves as the frequency-determining element of an oscillator.

AlN thin films were grown on <1000> C-plane sapphire using a molecular-beam epitaxy (MBE) hollow-cathode source lined with MBE-grade aluminum. A two-port resonator was used, one port with central gratings and the other without. The sapphire can be switched between SAW and STW modes.

The results show phase velocities of 5566 m/s and 6568 m/s for SAW and STW propagation, respectively, in nonliquid environments. In liquids, SAW propagation (see the figure) was expectedly attenuated by nearly 80%, but not STW. Both modes functioned well in air.

Contact the researchers at (313) 577-2424 or www.wayne.edu.

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