Thick aluminium nitride films deposited by room-temperature sputtering for ultrasonic applications

Lee, C.K., Cochran, S. , Abrar, A., Kirk, K.J. and Placido, F. (2004) Thick aluminium nitride films deposited by room-temperature sputtering for ultrasonic applications. Ultrasonics, 42(1-9), pp. 485-490. (doi: 10.1016/j.ultras.2004.02.007) (PMID:15047333)

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Abstract

Materials in film form for electromechanical transduction have a number of potential applications in ultrasound. They are presently under investigation in flexural transducers for air-coupled ultrasound and underwater sonar operating at frequencies up to a few megahertz. At higher frequencies, they have the potential to be integrated with electronics for applications of ultrasound requiring high spatial resolution. However, a number of fabrication difficulties have arisen in studies of such films. These include the high temperatures required in many thick and thin film deposition processes, making them incompatible with other stages in transducer fabrication, and difficulties maintaining film quality when thin film––typically sub-1 μm––processes are extended to higher thicknesses. In this paper, we first outline a process which has allowed us to deposit aluminium nitride (AlN) films capable of electromechanical transduction at thicknesses up to more than 5 μm without substrate heating. As an ultrasonic transduction material, AlN has functional disadvantages, particularly a high acoustic velocity and weak electromechanical transduction. However, it also has a number of advantages relating to practicality of fabrication and functionality. These include the ability to be deposited on a variety of amorphous substrates, a very high Curie temperature, low permittivity, and low electrical and mechanical losses. Here, we present experimental results highlighting the transduction capabilities of AlN deposited on aluminium electrodes on glass and lithium niobate. We compare the results with those from standard simulation processes, highlighting the reasons for discrepancies and discussing the implications for incorporation of AlN into standard ultrasonic transducer design processes.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Cochran, Professor Sandy
Authors: Lee, C.K., Cochran, S., Abrar, A., Kirk, K.J., and Placido, F.
College/School:College of Science and Engineering > School of Engineering > Systems Power and Energy
Journal Name:Ultrasonics
Publisher:Elsevier
ISSN:0041-624X
Published Online:13 February 2004

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