Biomedical Engineering Reference
In-Depth Information
in mobility. Because of strain generated in the semi-conducting i lm, energy
spacing decreases, which in turn helps to decrease the ef ective mass of the
charge carriers. Ef ective mass of the charge carriers is inversely propor-
tional to mobility. h e change in mobility therefore will give rise to a change
in the current with mechanical del ection. Also the piezoelectric property of
AZO can af ect the sensitivity. When the cantilever gets bent by an applied
force, because of the piezoelectric ef ect, a potential gets generated which
will help to reduce the surface potential barrier allowing additional carrier
injection into the channel, thereby increasing the drain current sensitivity.
9.5
Piezoelectric Nanocomposite (SU-8/ZNO)
h in Films Studies and h eir Integration with
Piezoelectric MEMS Devices
h e i eld of nanocomposite materials has been attracting researchers due to
the l exibility in their design, low cost, ease of fabrication and tunable physi-
cal and chemical properties [27, 51-54]. h e key drive for development of
nanocomposites is the need for combining desirable properties of dif erent
materials. For example, one may wish to enhance the piezoelectric sensitivity
of nanocomposite thin i lm but simultaneously also want to integrate these
thin i lms with micro scale fabrication technology. h us, for many applica-
tions, one might need two conl icting desirable properties and such require-
ments can only be achieved with combinations of useful properties of two or
more materials. Based on the concept of nanocomposite formulation, there
has been signii cant interest in research of lithographically patterned nano-
composite polymer such as SU-8 [25-27, 35, 56]. It is commonly known as
a negative photoresist, which is used as a structural material for realizing the
MEMS structures. h e advantage of SU-8 is its low Young's modulus and
photo patterning properties which makes it an obvious candidate to be used
as a polymer matrix for nanocomposite realization [27, 55]. Over the last few
decades, people have demonstrated SU-8 based nanocomposite with dif erent
physical and chemical properties by incorporating various inorganic i llers
such as carbon black nanoparticles, silver nano particles, carbon nanotubes
and magnetic nanoparticles [25-27, 30-32]. Concept of piezoelectric com-
posite was i rst proposed by Newman who presented various models of con-
nectivity of ceramics in polymer matrix for explaining piezoelectricity origin
in such type of systems [51-52]. h ere have been attempts in the past to real-
ize the piezoelectric composite materials by utilizing a polymer matrix with
piezoelectric ceramics inclusion [53]. Recently, piezoelectric nanocomposite
