Online proceedings - EDA Publishing Association

deposition and PZT fine pattern dry-etching techniques. Fig.
6 shows SEM images of the fabricated cantilever (Fig. 6 (a))
and the disk resonator (Fig. 6 (b)).
In cantilever as shown in Fig. 6 (a), two PZT actuators
were arranged symmetrically on both sides of the silicon
cantilever and connected to the cantilever via thin beams
near to substrate for cantilever excitation. Then the
piezoelectric PZT actuator could be separated from the
resonant structure to compress the energy dissipation from
PZT film and the multi-layered structure. To compress
negative effects from residual stress, support beams were
designed at the front end of the actuator to reduce actuator’s
initial bending. Another purpose of the support beam is to
limit actuator’s vibration amplitude at the resonant frequency
to suppress energy dissipation. A piezoresistive
Wheatstone-bridge-gauge was integrated at the fixed end of
the cantilever to detect its vibration.
(a)
11-13
May 2011, Aix-en-Provence, France
The PZT-electrode stacks were kept far from support beams
to avoid clamped energy loss. To reduce the effects of
support beam on disk vibration as well as to compress
clamped energy loss, support beams were designed as thin as
possible (7 μm×15 μm) after finite element analysis (FEA)
using ANSYS ® . An Au/Cr layer with the thickness of
200/50 nm was deposited on both cantilever and disk surface
as the mass adsorption area to demonstrate its application as
a mass sensor.
2.5 Device evaluation and application
After fabrication, the devices were wire-bonded and
then packaged for evaluation. The results demonstrated that
the cantilever (length: 100 μm; width: 30 μm) has excellent
Q-factor of 1113 in air, which is several times higher than
latest reported Q-factor of other integrated micro cantilevers
[20][21]. Under reduced pressure of about 30 Pa, Q-factor of
the cantilever was as high as 7279. Fig. 7 shows measured
equivalent capacitance Cs values of the PZT film on disk
resonator (Fig. 6 (b)). Clearly, the Cs variation was 0.2~0.3%
at the resonant frequency owing to its vibration-induced
piezoelectric charge. The disk shows great signal to noise
ratio besides its high Q-factor (~1300 in air). It is also
noteworthy that an electric voltage of 0.2~1 volt was proved
sufficient for cantilever and disk actuation, which improves
its integration capability from the viewpoints of power
supplies and power consumption.
(b)
PZT-electrode
stack
Silicon Disk
Fig. 7 Piezoelectric induced output (equivalent capacitance Cs) of a
fabricated piezoelectric disk resonator.
Fig. 6 SEM images of the fabricated (a) micro cantilevers actuated by PZT
thin film and (b) disk resonator transduced by PZT thin film.
In disk as shown in Fig. 6 (b), PZT-electrode stacks with
limited size to reduce its energy dissipation were integrated
on surface of the disk for both disk actuation and sensing.
Various piezoelectric MEMS devices are expected to be
integrated in sensor network for ubiquitous applications due
to its self-actuation at low driving voltage, device
self-sensing with low power consumption, as well as its
energy harvesting capabilities. Fig. 8 explains concept of a
human healthcare system by wireless sensor network
technology. Although lots of work must be done, we believe
it will come to reality soon.
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