Biomedical Engineering Reference
In-Depth Information
8
Longitudinal mode
Shear mode
7
6
5
4
3
2
1
0
0
10
20
30
40
50
60
70
80
θ
(deg)
FIGURE 8.16
Calculated electromechanical coupling for both shear and longitudinal modes at different AlN crystal tilt,
θ
.
For
c
-axis-inclined AlN films, inclined angle could have dramatic effect on acoustic velocity and coupling coef-
ficient for both Rayleigh wave and shear wave. (From Chen, Q.M., and Wang, Q.M.,
Appl. Phys. Lett.
, 86, 022904,
2005.)
are plotted as a function of the film thickness ratio
h
/
λ
. The phase velocity of each mode
decreases as the film thickness ratio increases. For mode 0, the value of phase velocity is
determined by the SAW velocity of (111) diamond, that is, 10.9 km/s at
h
/
λ
= 0. As the film
thickness ratio
h
/
λ
increases, the phase velocity curve rapidly decreases. At
h
/
λ
= 3, the
velocity of the (002) AlN/diamond is about 5.4 km/s. It can be observed that the harmonic
peaks of modes 1, 2, 3, and 4 cutoff at the critical point where the phase velocity is equal
to the shear bulk wave velocity in (111) diamond 12.3 km/s. For example, cutoff of mode 1
occurs at
h
/
λ
= 0.172, mode 2 at
h
/
λ
= 0.295, mode 3 at
h
/
λ
= 0.594, and mode 4 at
h
/
λ
= 0.693
(Wu et al., 2008).
13,000
12,000
11,000
10,000
9000
8000
7000
6000
5000
IDT/(002)AlN/(111)diamond
Mode 0
Mode 1
Mode 2
Mode 3
Mode 4
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Films thickness ratio (
h
/
λ
)
FIGURE 8.17
Phase velocities dispersion curves of first five Rayleigh SAW modes propagation in the IDT/_002_ AlN/_111_
diamond. The phase velocity dispersion curves of first five.
