Online proceedings - EDA Publishing Association

11-13
May 2011, Aix-en-Provence, France
Design, Fabrication, and Integration of
Piezoelectric MEMS Devices for Applications in
Wireless Sensor Network
Jian Lu*, Yi Zhang, Toshihiro Itoh, Ryutaro Maeda
Research Center for Ubiquitous MEMS and Micro Engineering (UMEMSME),
National Institute of Advanced Industrial Science and Technology (AIST), Namiki 1-2-1, Tsukuba, Ibaraki, 305-8564, Japan
Abstract- One of the competitive solutions to expand the
function of microelectromechanical system (MEMS) is the
integration of piezoelectric lead zirconate titanate (PZT) thin
films for device self-actuation at low driving voltage, device
self-sensing with low power consumption, as well as for energy
harvesting. However, up-to-date, difficulties still exist not only
in PZT film preparation but also in PZT film integration with
other MEMS components and ICs. This paper therefore
presents our recent progress on large area deposition, fine
pattern etching, and low temperature bonding of PZT thin
films for wafer scale PZT film integration and piezoelectric
MEMS application. The energy dissipation mechanism in
piezoelectric MEMS devices was also discussed to optimize the
device structure for the pursuit of better performance.
Ultra-sensitive micro cantilever and disk resonator with
on-chip piezoelectric PZT transducers were presented herein as
an exploratory application of piezoelectric MEMS devices in
distributed wireless sensor network.
I. BACKGROUND
To deal with population aging, environmental pollution,
global warming, and other modern society problems,
microelectromechanical system (MEMS) is significantly
important because various applications, such as human
healthcare, food safety, environmental monitoring, animal
watching, green manufacturing, mechanical structure
monitoring, and smart living, can be realized by MEMS and
distributed wireless sensor network (WSN) technology with
high sensitivity, low cost, and low power consumption
[1]-[4].
To expand the function of MEMS for applications in
WSN, the integration of various materials or components for
device actuation and sensing is essential. One of the most
competitive materials is the piezoelectric lead zirconate
titanate (Pb(Zr x ,Ti 1-x )O 3 , PZT) thin film because PZT is a
high energy density material which scales very favorably
upon miniaturization [5]. The piezoelectric coefficient d 33
and dielectric constant ɛ of the PZT film was reported as
high as 143 pC/N and 1310 respectively, which is one order
higher than that of zinc oxide (ZnO) film (d 33 =11 pC/N,
ɛ =11) and aluminum nitride (AlN) film (d 33 =3.4 pC/N,
ɛ =10.4). Besides, the well-integrated PZT film on MEMS
devices can be used not only for device self-actuation at low
driving voltage and device self-sensing with low power
consumption, but also can be used for energy harvesting.
However, up-to-date, difficulties still exist in PZT
preparation and PZT integration with other MEMS
components and ICs. It is mostly due to the high temperature
annealing process and the residual stress of the film, as well
as the energy dissipation of the piezoelectric MEMS devices
[6]-[8]. Moreover, the high volume mass production and
commercialization of MEMS have been expected for many
years since IC industry went to the well-developed stage. The
bottlenecks, which discourage MEMS industry to advanced
steps, are the difficulties in integration of MEMS
components with ICs, the yields, and the cost. Especially to
piezoelectric MEMS, the fabrication, integration of the
piezoelectric PZT thin film, and the design, optimization of
the device structure need great efforts not only from the
technical point of view but also through innovative academic
research.
We have engaged in large-area deposition, fine pattern
etching, low temperature bonding of PZT thin films for
MEMS application, and energy dissipation mechanism of the
piezoelectric MEMS devices for the pursuit of better device
performance for many years. This paper thus presents our
recent progress of above work. Moreover, the design,
fabrication and evaluation of ultra-sensitive micro
cantilevers and disk resonators, which has on-chip
PZT-electrode stacks as the transducer, were presented in
this paper as an exploratory application of piezoelectric
MEMS devices in distributed wireless sensor network for
human healthcare, environmental monitoring, and other
applications.
II.
RESULTS AND DISCUSSION
2.1 Large area PZT film deposition by sol-gel process
For PZT preparation in large area, residual stress
frequently leads to wafer-warpage, PZT film delaminating,
217