Thin Films for Acoustoelectronics
The advantages to be gained by using thin films to realize new acoustoelectronic devices and enhance the properties of existing devices has long been understood but only applied in a limited way over the past 30 years. The most successful commercial applications have been the use of zinc oxide films for high frequency bulk acoustic wave (BAW) delay lines and for surface acoustic wave (SAW) TV filters and convolvers. Thin-film technology has benefited from theoretical and experimental work on the dynamics of film growth, a better understanding of the relationship of film structure to acoustic wave generation and propagation, and the steady progress made in new film deposition equipment and methods for semiconductor integrated circuit manufacturing. While film technology has not recently been applied on a large scale to improving existing acoustoelectronic devices, there has been a continuation of important work which could lead to significant device applications in the near future. The purpose of this special issue is to gather together work representative of thin-film research and development activities in the acoustic area at this time, which could provide the basis for such applications in the near future.
The papers represented in this issue extend from fundamental material research to very applied device developments. Wright and Gusev lead-off this special issue with a study of the acoustic properties of thin-film copper using ultrafast pulse laser generation and detection. This is followed by four papers on the application of zinc oxide (ZnO) films as BAW and SAW transducers for device applications. Yoshimoto and coauthors describe a multi-layer BAW transducer with air-gap structure which is aimed at developing miniaturized ultrasonic image transducers. Kadota and Minakata describe the properties of very high quality ZnO films on glass produced by an RF-magnetron ECR sputtering system. Kim and coworkers present information which is essential for the design of SAW devices using ZnO films on gallium arsenide. Nakahata and coauthors have theoretically studied the SAW characteristics of substrates with piezoelectric and diamond film layers and delineated some unique film-layer structures. The next three papers address measurement procedures and results of measurements for the elastic properties of thin-films and crystals. Lee and coworkers have measured the elastic constants of two oxide crystals and two oxide films on those crystals using line-focus acoustic microscopy. Yamanaka and coauthors have presented a novel noncontact method for measuring SAW velocity characteristics and have applied it to the measurement of silicon nitride and silicon dioxide films on silicon. Tsukahara and coworkers have measured the elastic properties of a flame hydrolysis deposited glass using an ultrasonic microspectrometer technique. The final four papers characterize the acoustic properties of nitride and oxide films by direct SAW measurements to determine their potential for enhancing traditional SAW devices on piezoelectric substrates and for consideration as active and passive films for the integration of BAW and SAW devices with semiconductor circuitry. Yamanouchi and coauthors have used sputtered glass on lithium niobate and lithium tantalate as a means of developing temperature stable GHz frequency SAW devices for use in mobile communication systems. Hines and coauthors have examined the deposition conditions and SAW characteristics for PECVD silicon nitride on lithium niobate for device applications. Liaw and Hickernell have characterized sputtered aluminum nitride on silicon using SAW measurement techniques to yield useful acoustic data for the development of integrated SAW and BAW devices. The final paper gives elastic constant data and SAW propagation loss data for PECVD nitride, carbide, and oxide films of silicon deposited on gallium arsenide, which should assist in the design of acoustic devices using these films as support layers for integration of BAW and SAW devices on semiconductor substrates.
The assembly and review of the papers was a cooperative international effort. Each paper was reviewed by one reviewer or more in Europe, Japan, and North America. The reviewers applied themselves to the task of critically examining the papers, the authors were responsive to their comments, and the editors moved the process along. Each did their job in a timely fashion. The guest editors are very grateful for the cooperation of the authors and reviewers in the bringing together of this special issue
It is the hope of the guest editors that this special issue will help raise the awareness of those involved in acoustoelectronic device development of the properties and device potential of thin films and the gains that can be made in device performance through the use of thin films.
NORIYOSHI CHUBACHI
FRED S. HICKERNELL
ADRIAN VENEMA
Guest Editors
© 1995, by The Institute of Electrical and Electronics Engineers, Inc. All rights reserved.