Biomedical Engineering Reference
In-Depth Information
Figure 4.6 ii, iii). Appropriate corner compensation was given to the edges of the structure
so that the undercutting of the anisotropic etchant did not affect the tooth-like pattern due
to the long etch duration of this step. The cross section of the final silicon part is shown
in Figure 4.6 iv.
4.1.2.2 Patterning the PVDF Film
A25
μ
m uniaxially drawn, metalized (aluminum) and poled PVDF film was cut as a
20
14 mm section. This dimension was 5 mm larger on each side than the footprint of
the silicon piece. The piezoelectric coefficients of the PVDF film,
d
31
,
d
32
,and
d
33
were
20, 2, and
×
20 pC N
-1
, respectively. The PVDF sample was carefully taped onto a clean
silicon wafer (dummy wafer) such that the film was stretched uniformly over the wafer,
and the tape covered all sides, overlapping by at least 2 mm. Using a spinner, photoresist
was spun onto the PVDF film. In order to ensure a uniform coating, the spin speed was
slowly increased from 0 to 500 RPM. The resultant film was then soft baked at 50
◦
C
for 40 minutes. This process was repeated for the second side of the PVDF film. The
masks containing the patterns for the two sides of the PVDF film were aligned and held
on top of each other. The photoresist-coated PVDF film was then inserted between the
pre-aligned masked plates. Using a UV source for the mask alignment, both sides of the
photoresist-coated PVDF film were exposed consecutively. The exposed film was then
developed, rinsed, and baked at 50
◦
C for 60 minutes.
The electrodes were patterned using a commercial aluminum etchant. Acetone was used
to remove the photoresistive material. The PVDF film was rinsed in de-ionized (DI) water
and later dried. Figure 4.7 illustrates the steps for the PVDF electrode pattern process.
−
4.1.2.3 Sensor Assembly
A thin layer of nonconductive epoxy was applied to the underside of the silicon wafer as
shown in Figure 4.7. Using a stereo microscope, the PVDF film was aligned using the
four alignment marks, and attached to the silicon. This assembly was uniformly pressed
Figure 4.7
Fabrication steps of the PVDF film
