EFFECTIVE PIEZOELECTRIC ACTIVITY OF ZINC-OXIDE FILMS GROWN BY RADIOFREQUENCY PLANAR MAGNETRON SPUTTERING

We present a study of the effective piezoelectric activity of;thin ZnO films produced by radio-frequency (rf) planar magnetron sputtering. The energetic plasma particles which bombard the substrate in the above deposition system increase the substrate temperature, thus causing a gradual variation in film structure during the beginning of the him growth. As a result, a precursor layer is formed which consists of small randomly oriented crystallites, exhibiting poor piezoelectric activity. Hence, the film thickness responsible for piezoelectric activity is generally less than the physical thickness of the him and is adjacent to a layer having different acoustic impedance. This leads to an increase in the resonant frequency of the film. For example, a film designed to have a half-wave resonance at 288 MHz, was found to be resonant at 332 MHz. The poorly structured initial layer meant in this typical case that only 87% of this him volume exhibited piezoelectric activity. Investigations based on the substrate temperature, the optical losses, scanning electron microscope imaging, and if electrical behavior are presented in this letter. (C) 1995 American Institute of Physics.