Biomedical Engineering Reference
In-Depth Information
200
150
100
50
0
0
2
4 6 8
Voltage RMS (V)
10
12
Figure 9.19
Piezoelectric measurements of SU8/ZnO nanocomposite thin i lms on the
surface showing almost linear relation between the PR amplitude and drive amplitude [32].
the piezoelectric activity of embedded ZnO particles in nanocomposite thin
i lms. A linear relationship was observed between the PR amplitude and
applied PR drive which varied between 2 to 10 V. For recording the PFM
images the alternate current voltage with modulated frequency 14.2 KhZ
was applied to PtIr
5
coated cantilever tip. Resonance ef ect [63] was mini-
mized by keeping the modulated frequency lower than the cantilever reso-
nance frequency (66.67 kHz). h e ef ective piezoelectric coei cient d33 was
observed in range of 15-23 pm/V which is higher as compared to bulk [32,
64-65]. h e high piezoelectricity of the nanocomposite thin i lms could be
due to small size and shape of ZnO nanoparticles [64-67]. Recently, some
studies showed that as the size goes down in nanoscle dimension the surface
to volume ratio goes high which signii cantly impacts the atomic polariza-
tions of surface atoms [65]. h e other contribution in enhancement of piezo-
electric properties is the shape anisotropic nature of nanoparticles [66-67].
9.5.1.3
Mechanical Properties of Nanocomposite h in Films:
h e advantage of SU-8 for realization of MEMS structures over the Silicon
material is its low young modulus and low temperature processing [27, 54,
68]. It was observed that the mechanical properties of SU-8 changes with
incorporation of inorganic i ller such as CB and ZnO [27, 32]. For real-
ization of piezoelectric cantilever MEMS devices with SU-8/ZnO nano-
composite, stif ness is a very important parameter; hence the mechanical
properties of SU-8/ZnO thin i lms were studied. h e young modulus of
SU-8 and SU-8/ZnO thin i lms was calculated with the formula repre-
sented in Equation 9.3[27, 69-70]:
