VELOCITY SURFACE MEASUREMENTS FOR ZNO FILMS OVER (001)-CUT GAAS

A potential application for a piezoelectric film deposited on a GaAs s ubstrate is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the filmed structure is critical for the optimum design of such devices. I n this article, the measurements of the velocity surface, which direct ly affects the SAW diffraction, on the bare and metallized ZnO/SiO2 or Si3N4/GaAs {001}-cut samples are reported using two different techniq ues: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope. Comparisons, such as measurement accuracy and tradeoffs, between the former (dry) and the latter (wet) method are given. It is found that near the [110] propagation direction the autocollimating SA W property of the bare GaAs changes into a noncollimating one for the layered structure, but a reversed phenomenon exists near the [100] dir ection. The passivation layer Of SiO2 or Si3N4 (<0.2 mum thick) and th e metallization layer change the relative velocity but do not signific antly affect the velocity surface. On the other hand, the passivation layer reduces the propagation loss by 0.5-1.3 dB/mus at 240 MHz depend ing upon the ZnO film thickness. Our SAW propagation measurements agre e well with theoretical calculations. We have also obtained the anisot ropy factors for samples with ZnO films of 1.6, 2.8, and 4.0 mum thick ness. Comparisons concerning the piezoelectric coupling and acoustic l oss between dc triode and rf magnetron sputtered ZnO films are provide d.