B. Wacogne et al., EFFECTIVE PIEZOELECTRIC ACTIVITY OF ZINC-OXIDE FILMS GROWN BY RADIOFREQUENCY PLANAR MAGNETRON SPUTTERING, Applied physics letters, 67(12), 1995, pp. 1674-1676
We present a study of the effective piezoelectric activity of;thin ZnO
films produced by radio-frequency (rf) planar magnetron sputtering. T
he 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 gr
owth. As a result, a precursor layer is formed which consists of small
randomly oriented crystallites, exhibiting poor piezoelectric activit
y. 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 incr
ease in the resonant frequency of the film. For example, a film design
ed 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 losse
s, scanning electron microscope imaging, and if electrical behavior ar
e presented in this letter. (C) 1995 American Institute of Physics.