Accepted abstracts by author > Bologna Alles Aldo

G. Sánchez(1, 2), P. Tristant(1), C. Dublanche-Tixier(1), F. Tétard(3), A. Bologna Alles(2)

(1) SPCTS, UMR CNRS 6638, Université de Limoges, 12 rue Atlantis, 87068 Limoges, France

(2) Departamento de Ingeniería de Materiales, Facultad de Ingeniería, Universidad de la República,

Julio Herrera y Reissig 565, 11300 Montevideo, Uruguay

 (3) LPMTM, CNRS UPR 9001, Université de Paris XIII, Av. J.B. Clément, 93430, Villetaneuse, France

Aluminum nitride is one of the most investigated piezoelectric materials for the manufacture of acoustic wave devices due to its high acoustic velocity and fairly large piezoelectric coupling coefficient. Single crystal properly oriented films would be the ideal choice for these applications; however, high quality polycrystalline preferentially oriented films can be used with good success. Minimal film surface roughness is required to reduce acoustic losses in surface acoustic wave devices. The reduction of residual stresses is important in order to assure film integrity as well as to avoid non desired deformations in Micro-Electromechanical Systems (MEMS) applications.

We have previously informed the deposition of polycrystalline oriented AlN films by a Microwave – Plasma Enhanced Chemical Vapor Deposition (PECVD) technique, using no RF bias, with the substrate holder at the floating potential. The resulting films showed tensile residual stresses, which were partly associated to thermal residual stresses derived from the process substrate temperature at the optimal deposition conditions (700°C). With this setting, thicknesses thinner than 1 µm could be deposited with adequate microstructure, but, for higher thicknesses, cracked films were obtained.

In this study, AlN films were prepared with a Microwave Plasma Enhanced Chemical Vapor Deposition reactor at 1 Pa and 700°C using different radiofrequency bias , i.e. different energy ion bombardment, in order to obtain polycrystalline oriented films with minimal residual stresses for piezoelectric applications. The films developed were characterized in term of microstructure, composition and mechanical properties. Crystalline development, exclusive orientation and high tensile residual stresses were observed when the substrate-holder was at the floating potential. A progressive degradation of the crystalline structure was observed with the increase of the negative bias potential together with the evolution to compressive residual stresses. Simultaneously, significant changes in the microstructure of the surface were observed by atomic force microscopy, as well as in the preferential orientation from to <1010>. The adequate selection of bias potential allowed optimizing film properties for piezoelectric applications.